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Sample records for crown pull-off test

  1. Retention Load of Telescopic Crowns with Different Taper Angles between Cobalt-Chromium and Polyetheretherketone Made with Three Different Manufacturing Processes Examined by Pull-Off Test.

    Science.gov (United States)

    Wagner, Christina; Stock, Veronika; Merk, Susanne; Schmidlin, Patrick R; Roos, Malgorzata; Eichberger, Marlis; Stawarczyk, Bogna

    2016-04-01

    To investigate the retention loads of differently fabricated secondary telescopic polyetheretherketone (PEEK) crowns on cobalt-chromium primary crowns with different tapers. Cobalt-chromium primary crowns with 0°, 1°, and 2° tapers were constructed, milled, and sintered. Corresponding secondary crowns were fabricated by milling, pressing from pellets, and pressing from granules. For these nine test groups, the pull-off tests of each crown combination were performed 20 times, and the retention loads were measured (Zwick 1445, 50 mm/min). Data were analyzed using linear regression, covariance analysis, mixed models, Kruskal-Wallis, and Mann-Whitney U-test, together with the Benferroni-Holm correction. The mixed models covariance analysis reinforced stable retention load values (p = 0.162) for each single test sequence. There was no interaction between the groups and the separation cycles (p = 0.179). Milled secondary crowns with 0° showed the lowest mean retention load values compared to all tested groups (p = 0.003) followed by those pressed form pellets with 1°. Regarding the different tapers, no effect of manufacturing method on the results was observed within 1° and 2° groups (p = 0.540; p = 0.052); however, among the 0° groups, the milled ones showed significantly the lowest retention load values (p = 0.002). Among the manufacturing methods, both pressed groups showed no impact of taper on the retention load values (p > 0.324 and p > 0.123, respectively), whereas among the milled secondary crowns, the 0° taper showed significantly lower retention load values than the 1° and 2° taper (p manufacturing of PEEK materials for telescopic crowns are warranted, especially for 0°. © 2016 by the American College of Prosthodontists.

  2. PEEK Primary Crowns with Cobalt-Chromium, Zirconia and Galvanic Secondary Crowns with Different Tapers—A Comparison of Retention Forces

    Directory of Open Access Journals (Sweden)

    Veronika Stock

    2016-03-01

    Full Text Available In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF between polyetheretherketone (PEEK primary and cobalt-chromium (CoCr, zirconia (ZrO2 and galvanic (GAL secondary crowns with three different tapers. Primary PEEK-crowns were milled with the tapers 0°, 1°, and 2° (n = 10/taper, respectively. Afterwards, 90 secondary crowns were fabricated: (i 30 CoCr-crowns milled from Ceramill Sintron (AmannGirrbach, Koblach, Austria (n = 10/taper, (ii 30 ZrO2-crowns milled from Ceramill ZI (AmannGirrbach, Koblach, Austria (n = 10/taper, and (iii 30 GAL-crowns made using electroforming (n = 10/taper. RF was measured in a pull-off test (20 pull-offs/specimen and data were analyzed using 2-/1-way Analysis of Variance (ANOVA followed by the Tukey-Honestly Significant Difference (HSD post hoc test and linear regression analyses (p < 0.05. The measured mean RF values ranged between 9.6 and 38.2 N. With regard to the 0°, 1°, and 2° tapered crowns, no statistically significant differences between CoCr and ZrO2 were observed (p > 0.141. At 0° taper, no differences in retention forces between GAL, CrCr, and ZrO2 crowns were found (p = 0.075. However, at 1° and 2° taper, lower RF for GAL-crowns were observed (p < 0.009, p < 0.001, respectively. According to this laboratory study, PEEK might be a suitable material for primary crowns, regardless of the taper and the material of secondary crown. Long-term results, however, are still necessary.

  3. In Vitro Analysis of the Tribological Behaviour of Different Material Combinations for Telescopic Crowns

    Directory of Open Access Journals (Sweden)

    Wigbert Linek

    2016-06-01

    Full Text Available Telescopic crowns are used to connect removable dental prostheses with the remaining dentition. Several material combinations are used for manufacturing primary and secondary crowns. The present experimental study analysed the influence of different material combinations on the long-term development of surface roughness and pull-off forces. Six different material combinations were tested. Secondary crowns were manufactured either by casting or electroforming. Each material combination was tested with n = 10 specimens. A material testing device with integrated power sensors was used for 10,000 cycles per test. Signs of wear were identified by surface roughness measurements, and visualized by a scanning electron microscope (SEM and X-ray spectroscopy (EDX technologies. Statistical significances were tested by using the U-Test with Bonferroni correction. The choice of materials and the manufacturing process were found to influence the long-term development of pull-off forces as well as wear-associated surface roughness. Combinations of different groups of materials for primary and secondary crowns showed favourable results. Worse results were found for the combination pure titanium and pure titanium and the combination high gold alloy and electroformed gold. Wear-associated surface roughness was higher for combinations of similar or identical groups of materials. For manufacturing telescopic crowns, combinations of different groups of materials are preferred. For secondary crown manufacturing, electroforming is superior to casting.

  4. T-Cap Pull-Off and Bending Behavior for Stitched Structure

    Science.gov (United States)

    Lovejoy, Andrew E.; Leone, Frank A., Jr.

    2016-01-01

    The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) is a structural concept that was developed by The Boeing Company to address the complex structural design aspects associated with a pressurized hybrid wing body aircraft configuration. An important design feature required for assembly is the integrally stitched T-cap, which provides connectivity of the corner (orthogonal) joint between adjacent panels. A series of tests were conducted on T-cap test articles, with and without a rod stiffener penetrating the T-cap web, under tension (pull-off) and bending loads. Three designs were tested, including the baseline design used in largescale test articles. The baseline had only the manufacturing stitch row adjacent to the fillet at the base of the T-cap web. Two new designs added stitching rows to the T-cap web at either 0.5- or 1.0-inch spacing along the height of the web. Testing was conducted at NASA Langley Research Center to determine the behavior of the T-cap region resulting from the applied loading. Results show that stitching arrests the initial delamination failures so that the maximum strength capability exceeds the load at which the initial delaminations develop. However, it was seen that the added web stitching had very little effect on the initial delamination failure load, but actually decreased the initial delamination failure load for tension loading of test articles without a stiffener passing through the web. Additionally, the added web stitching only increased the maximum load capability by between 1% and 12.5%. The presence of the stiffener, however, did increase the initial and maximum loads for both tension and bending loading as compared to the stringerless baseline design. Based on the results of the few samples tested, the additional stitching in the T-cap web showed little advantage over the baseline design in terms of structural failure at the T-cap web/skin junction for the current test articles.

  5. Measurement of pull-off force on imprinted nanopatterns in an inert liquid

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jae Kwan; Lee, Dong Eon; Lee, Woo Il; Suh, Kahp Y, E-mail: wilee@snu.ac.kr, E-mail: sky4u@snu.ac.kr [School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of)

    2010-07-23

    We report on the measurement of the pull-off force on nanoscale patterns that are formed by thermal nanoimprint lithography (t-NIL). Various patterns with feature sizes in the range of 50-900 nm were fabricated on silicon substrates using a rigiflex polymeric mold of ultraviolet curable polyurethane acrylate (PUA, Young's modulus {approx} 1 GPa) or perfluoropolyether (PFPE, Young's modulus {approx} 10.5 MPa) and a resist layer of polystyrene (PS) of three different molecular weights (M{sub w} = 18 100, 211 600 and 2043 000). The pull-off force was measured in non-polar, non-reactive perfluorodecalin (PFD) solvent between a sharp atomic force microscopy (AFM) tip and an imprinted pattern. Our experimental data demonstrated that the measured pull-off forces were in good agreement with a simple adhesion model based on Lifshitz theory. Also, the force on the pressed region (valley) is higher than that on the cavity region (hill), with the ratio (hill/valley) decreasing with the decrease of pattern size and the increase of molecular weight. The confinement effects were more pronounced for smaller patterns (<300 nm) and higher molecular weights (M{sub w} = 211 600 and 2043 000) presumably due to sluggish movement of polymer chains into nano-cavities. Finally, the experimental observations were compared with molecular dynamic simulations based on a simplified amorphous polyethylene model.

  6. Evaluation of fracture resistance of indirect composite resin crowns by cyclic impact test: influence of crown and abutment materials.

    Science.gov (United States)

    Sakoguchi, Kenji; Minami, Hiroyuki; Suzuki, Shiro; Tanaka, Takuo

    2013-01-01

    This study evaluated the effect of abutment materials on the fracture resistance of composite crowns for premolars. Composite crowns were fabricated using two different indirect composite resin materials (Meta Color Prime Art or Estenia C&B) and cemented onto either a metal (Castwell M.C. 12) or composite resin (Build-It FR and FibreKor) abutment with resin cement (Panavia F2.0). Twenty-four specimens were fabricated for four groups (n=6 each) and subjected to 280-N cyclic impact loading at 1.0 Hz. The number of cycles which caused the composite crown to fracture was defined as its fracture resistance. All data were statistically analyzed using ANOVA and the Bonferroni test (α=0.05). Composite crowns cemented onto resin abutments showed higher fracture resistance than those cemented onto metal abutments.

  7. Suitability of Secondary PEEK Telescopic Crowns on Zirconia Primary Crowns: The Influence of Fabrication Method and Taper

    Directory of Open Access Journals (Sweden)

    Susanne Merk

    2016-11-01

    Full Text Available This study investigates the retention load (RL between ZrO2 primary crowns and secondary polyetheretherketone (PEEK crowns made by different fabrication methods with three different tapers. Standardized primary ZrO2 crowns were fabricated with three different tapers: 0°, 1°, and 2° (n = 10/group. Ten secondary crowns were fabricated (i milled from breCam BioHPP blanks (PM; (ii pressed from industrially fabricated PEEK pellets (PP (BioHPP Pellet; or (iii pressed from granular PEEK (PG (BioHPP Granulat. One calibrated operator adjusted all crowns. In total, the RL of 90 secondary crowns were measured in pull-off tests at 50 mm/min, and each specimen was tested 20 times. Two- and one-way ANOVAs followed by a Scheffé’s post-hoc test were used for data analysis (p < 0.05. Within crowns with a 0° taper, the PP group showed significantly higher retention load values compared with the other groups. Among the 1° taper, the PM group presented significantly lower retention loads than the PP group. However, the pressing type had no impact on the results. Within the 2° taper, the fabrication method had no influence on the RL. Within the PM group, the 2° taper showed significantly higher retention load compared with the 1° taper. The taper with 0° was in the same range value as the 1° and 2° tapers. No impact of the taper on the retention value was observed between the PP groups. Within the PG groups, the 0° taper presented significantly lower RL than the 1° taper, whereas the 2° taper showed no differences. The fabrication method of the secondary PEEK crowns and taper angles showed no consistent effect within all tested groups.

  8. Pull-off characteristics of double-shanked compared to single-shanked ligation clips: an animal study

    Directory of Open Access Journals (Sweden)

    Schenk Martin

    2016-09-01

    Full Text Available The use of surgical ligation clips is considered as the gold standard for the closure of vessels, particularly in laparoscopic surgery. The safety of clips is mainly achieved by the deep indentation of the metal bar with a high retention force. A novel double-shanked (DS titanium clip was compared to two single-shanked clips with respect to axial and radial pull-off forces.

  9. 纤维水泥砂浆与混凝土界面黏结性能钻芯拉拔试验研究%Core drilling and pull-off tests of interfacial bond behaviors between fiber cement mortar and concrete

    Institute of Scientific and Technical Information of China (English)

    卜良桃; 周云鹏

    2016-01-01

    To investigate the interfacial bond behaviors between fiber cement mortar and concrete with core drilling and pull⁃off tests, medium⁃sized columnar concrete samples enclosed with different strengths of polyvinyl alcohol fiber cement mortar, polypropylene fiber cement mortar, and steel fiber cement mortar were prepared. Core drilling and pull⁃off tests were conducted on the samples to obtain the pulling force with failure occurring at the interface, and the results of different kinds of samples from pull⁃off tests were compared with the axial tensile strength of concrete and compressive strength of fiber cement mortar. The results show that the interfacial bond strength between synthetic fiber cement mortar and concrete is higher than that between steel fiber cement mortar and concrete, and that the interfacial bond strength is positively correlated with the axial tensile strength of concrete and compressive strength of fiber cement mortar. There is also a linear correlation between the interfacial bond strength and compressive strength of fiber cement mortar.%为研究纤维水泥砂浆与混凝土界面黏结性能,采用钻芯拉拔法试验制作模拟中型柱混凝土构件,并分别外包不同强度的聚乙烯醇纤维水泥砂浆、聚丙烯纤维水泥砂浆、钢纤维水泥砂浆。对制作的试验构件进行钻芯拉拔试验,得出界面破坏时的拉拔力,将得到的不同类型的纤维水泥砂浆构件拉拔力数据与构件混凝土轴心抗拉强度、纤维水泥砂浆抗压强度进行比较分析。结果表明,在该试验中合成纤维水泥砂浆的界面黏结强度比钢纤维水泥砂浆的界面黏结强度高;界面黏结强度与构件混凝土轴心抗拉强度呈正相关关系,与纤维水泥砂浆抗压强度呈正相关关系,界面黏结力与砂浆抗压强度呈线性相关关系。

  10. Dental ceramics and the molar crown testing ground

    Directory of Open Access Journals (Sweden)

    Van P. Thompson

    2004-01-01

    Full Text Available All ceramic crowns are highly esthetic restorations and their popularity has risen with the demand for life-like and cosmetic dentistry. Recent ceramic research has concentrated on developing a fundamental understanding of ceramic damage modes as influenced by microstructure. Dental investigations have elucidated three damage modes for ceramic layers in the 0.5-2 mm thickness using point contacts that duplicate tooth cuspal radii; classic Hertzian cone cracking, yield (pseudo-plastic behavior, and flexural cracking. Constitutive equations based upon materials properties have been developed that predict the damage modes operational for a given ceramic and thickness. Ceramic thickness or thickness of the stiff supporting core in layer crowns is critical in flexural cracking as well as the flaw state of the inner aspect of the crown. The elastic module of the supporting structure and of the luting cement and its thickness play a role in flexural fracture. Clinical studies of ceramics extending over 16 years are compared to the above relationships and predictions. Recommendations for clinical practice are made based upon the above.

  11. Influence of splints and temporary crowns upon electric and thermal pulp-testing procedures.

    Science.gov (United States)

    Fulling, H J; Andreasen, J O

    1976-09-01

    The influence of different splints and temporary crowns upon the reliability of electric and thermal pulp-testing procedures was examined in 10 patients with vital maxillary central incisors and 10 patients with vital maxillary central incisors and 10 patients with unilateral pulp necrosis of a central incisor. The pulp-testing procedures were: (1) Bofors Pulp Tester, (2) Siemens Sirotest, (3) heated guttapercha, (4) ice, and (5) carbon dioxide snow (Odontotest). The splints or temporary crowns were: (1) silver cap splint, (2) acrylic cap splint, (3) Hawley orthodontic plate, (4) Saur's arch bar, (5) orthodontic bands, (6) stainless steel crown, and (7) stainless steel crown with labial surface removed. A reliable electrometric pulp response could only be elicited if the pulp tester was applied directly upon enamel and preferably upon the incisal edge. In this instance metal splints or partial steel crowns applied to the tooth had no effect on the pain threshold. A false positive reaction in case of pulp necrosis was only elicited when the electrode was placed directly upon metal which contacted neighboring vital teeth. The use of ice and heated guttapercha appeared to be of limited value, due to inconsistent pulp responses. Carbon dioxide snow gave a reliable response, unless applied on the incisal edge.

  12. Survival and testing parameters of zirconia-based crowns under cyclic loading in an aqueous environment: A systematic review.

    Science.gov (United States)

    Elshiyab, Shareen Hayel; Nawafleh, Noor; George, Roy

    2017-03-19

    To study the hypothesis that in vitro fatigue testing variables in an aqueous environment affect the survival results of zirconia-based restorations, and evaluate the level of agreement between in vitro and previous in vivo data. An electronic search of literature was conducted in PubMed and Scopus to identify in vitro studies testing zirconia-based crowns using cyclic loading in an aqueous environment. Only studies that complied with the inclusion criteria were included. Data extracted were used for survival analysis and assessment of in vitro parameters for fatigue testing of implant and tooth-supported crowns. Using "Assessing the Methodological Quality of Systematic Reviews" (AMSTAR), recent in vivo systematic review studies were assessed prior to consideration for comparison with the current in vitro data. After applying the inclusion criteria only 25 articles were included. Five-year cumulative survival rate of zirconia-based implant-supported crowns was lower than tooth-supported crowns (84% and 88.8% respectively). Tooth-supported crowns subjected to wet fatigue showed a lower 5-year cumulative survival rate compared to thermocycling (62.8% and 92.6% respectively). Monolithic crowns showed higher fracture resistance compared to bi-layered structure (pressed or hand-layered). Only in vivo systematic reviews, which complied with AMSTAR assessment criteria, were used for comparison to the in vitro data. As for fatigue testing parameters, differences in the experimental setting were evident and affected the outcomes. Crown survivals depend on type of support, type of fatigue test conducted, crown structure, and veneering method. In vitro fatigue testing protocols are highly variable, which introduces a need for international standardization to allow for more valid comparability of data. © 2017 John Wiley & Sons Australia, Ltd.

  13. Crown Zellerbach Well No. 2, Livingston Parish, Louisiana. Volume I. Completion and testing. Final report

    Energy Technology Data Exchange (ETDEWEB)

    1981-01-01

    The Crown Zellerbach Well No. 2, approximately 23 miles east of Baton Rouge, Louisiana, is the eighth successful test of a geopressured-geothermal aquifer under the DOE Wells of Opportunity program. The well was tested through the annulus between 7-inch casing and 2-3/8 inch tubing. Two flow tests and one reservoir pressure buildup test were conducted on the lower zone during a 13-day period. A total of 12,489 barrels of water was produced. The highest flow rate achieved was about 3887 BWPD. One flow test followed by a buildup period was conducted on the combined upper and lower zones during a 3-day period. A total of 4739 barrels of water was produced. The highest flow rate achieved was about 3000 BWPD. The gas/water ratio measured during testing was about 32.0 SCF/BBL for the lower zone. The extrapolated latoratory data indicates that the solubility of the gas is 55.7 SCF/BBL. It appears that the reservoir brine is considerably undersaturated. The methane content of the flare line gas averaged 71.0 mole percent. Crown Zellerbach Company carefully studied the commercial feasibility of using the well to produce energy for a wood-drying facility and decided against the project.

  14. 挠性电路板焊盘拉脱失效原因分析及控制%The study of failure mechanism of Flexible Printed Circuit Board pad pull-off and its control

    Institute of Scientific and Technical Information of China (English)

    易小龙; 莫欣满; 陈蓓

    2016-01-01

    As an important media of electronic components mounting, pads are vitally important to the life and reliability of the final products. In this paper, a universal tensile testing machine was employed to comprehensively survey the impact of the type of material, copper thickness, pad size, welding temperature and welding times on the pads’ pull-off strength from three suppliers’ lfexible substrates; a metallurgical microscope and TGA were further used to discuss the pads’ pull-off failure mechanism; orthogonal analysis method was then employed to obtain that the main factors during the welding process are welding temperature and welding times, and on the basis of above, the range of parameters were ifnally given to optimize the process design.%焊盘作为线路板与电子元器件焊接装联的必要媒介,其焊接的可靠性是影响最终产品的寿命和可靠性的重要因素。本文以三家供应商的无胶挠性板材为例,运用万能实验拉力机在不同条件下对焊盘进行拉脱,从材料种类、铜厚、焊盘尺寸、焊接温度、焊接次数五个方面考察了其对焊盘拉脱强度的影响;通过金相显微镜和热重分析讨论了挠性板材在焊接过程中焊盘脱落的机制;最后运用正交分析法得出了焊接过程中的主要影响因素是焊接温度及焊接次数,在此基础上给出了参数范围,优化了工艺设计。

  15. Dental crowns

    Science.gov (United States)

    ... you. The different types of crowns include: Stainless steel crowns: Are pre-made Work well as temporary crowns, especially for young children. The crown falls off when the child loses the baby tooth. Metal crowns: Hold up to chewing and teeth ...

  16. Effect of production method on surface roughness, marginal and internal fit, and retention of cobalt-chromium single crowns.

    Science.gov (United States)

    Lövgren, Nils; Roxner, Rikard; Klemendz, Susanne; Larsson, Christel

    2017-07-01

    New production methods have been developed for metal-ceramic restorations. Different production methods may show different surface roughness and fit, which may affect retention and long-term success. The purpose of this in vitro study was to examine 3 different production methods with regard to surface roughness, marginal and internal fit, and retention of cobalt-chromium alloy single-crown copings. A master abutment of a premolar mandibular tooth preparation with 4-mm height and a 0.6-mm deep 120-degree chamfer finish line with a 12-degree angle of convergence was replicated in die stone and scanned. Thirty-six cobalt-chromium alloy copings were produced using 3 different production techniques. Twelve copings were produced by laser-sintering, 12 by milling, and 12 by milled wax/lost wax. The surface microstructure of 2 copings in each group was analyzed using interferometry. The remaining 10 copings in each group were used to evaluate marginal and internal fit by using an impression material replica method, and retention was evaluated by using a uniaxial tensile force pull-off test. The copings from each test group were cemented with zinc phosphate cement onto resin abutments. Statistical analyses of differences in marginal and internal fit were performed using 1-way ANOVA and the Mann-Whitney U test. Differences in surface topography were analyzed with the Kruskal-Wallis and Mann-Whitney U tests for nonparametric data. Differences in retentive values were analyzed using the Mann-Whitney U test for nonparametric data (all α=.05). Differences in surface microstructure were seen. The laser-sintered copings showed increased surface roughness compared with milled and milled wax/lost wax copings. Differences in marginal and internal fit were noted. Laser-sintered showed significantly smaller spaces between coping and abutment than milled wax/lost wax copings (P=.003). At the margins, laser-sintered copings showed significantly smaller spaces than either the milled

  17. Biomechanical influence of crown-to-implant ratio on stress distribution over internal hexagon short implant: 3-D finite element analysis with statistical test.

    Science.gov (United States)

    Ramos Verri, Fellippo; Santiago Junior, Joel Ferreira; de Faria Almeida, Daniel Augusto; de Oliveira, Guilherme Bérgamo Brandão; de Souza Batista, Victor Eduardo; Marques Honório, Heitor; Noritomi, Pedro Yoshito; Pellizzer, Eduardo Piza

    2015-01-02

    The study of short implants is relevant to the biomechanics of dental implants, and research on crown increase has implications for the daily clinic. The aim of this study was to analyze the biomechanical interactions of a singular implant-supported prosthesis of different crown heights under vertical and oblique force, using the 3-D finite element method. Six 3-D models were designed with Invesalius 3.0, Rhinoceros 3D 4.0, and Solidworks 2010 software. Each model was constructed with a mandibular segment of bone block, including an implant supporting a screwed metal-ceramic crown. The crown height was set at 10, 12.5, and 15 mm. The applied force was 200 N (axial) and 100 N (oblique). We performed an ANOVA statistical test and Tukey tests; p0.05) under axial load. However, crown heights of 12.5 and 15 mm caused statistically significant damage to the stress distribution of screws and to the cortical bone (p<0.001) under oblique load. High crown to implant (C/I) ratio harmed microstrain distribution on bone tissue under axial and oblique loads (p<0.001). Crown increase was a possible deleterious factor to the screws and to the different regions of bone tissue.

  18. CROWN LENGTHENING

    OpenAIRE

    2014-01-01

    2014 Latar Belakang: Penampilan jaringan gingiva disekitar gigi memegang peranan penting secara estetis. Abnormalitas dalam simetris dan kontur akan memiliki efek harmonisasi penampilan gigi-geligi. Prosedur yang dapat memberikan solusi untuk masalah estetik, periodontal dan restoratif ini adalah crown lengthening. Crown lengthening adalah prosedur bedah yang bertujuan dalam pengambilan dari jaringan periodontal untuk peningkatan panjang klinis ma...

  19. A study on affecting factors by using dolly in coating adhesion test

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Yun-Ho; Son, Seong-Mo; Park, Chung-Seo [Industrial Technology Institute, Hyundai Heavy Industries, Ulsan (Korea, Republic of)

    2014-10-15

    Establishment of adhesion strength measurement procedure for marine epoxy coatings was conducted in order to ensure reliability of the test results. It was found that (1) the increase in thickness of the substrates would induce increase of pull-off strength. Especially, the increase in adhesion strength with the substrate thickness increment was attributed to the transition of stress mode to the pure tensile mode excluding bending effect. (2) The longer curing time, the higher pull-off strength. It may be due to higher cross-linking density of the coating (3) The pull-off strength increases as coating thickness increases due to the diminishment of bending effect (4) The longer drying time after water immersion, the higher pull-off strength. It may be due to the evaporation of water molecule at the coating-substrate interface.

  20. Crown Zellerbach Well No. 2, Livingston Parish, Louisiana. Volume II. Well test data. Final report

    Energy Technology Data Exchange (ETDEWEB)

    1981-01-01

    The following well test data are included: final report of field test data, IGT compiled data, ERMI raw data, Gas Producer's Associated tentative method of testing for hydrogen sulfide in natural gas using length of stain tubes, IGT combined sample log, report on reservoir fluids, well test analysis, sampling and chemical analysis procedures, and scale and corrosion evaluation. (MHR)

  1. 基于霍夫曼树和逆云模型的雷达拖引干扰识别%Identification of Radar Pull-off Jamming Based on Huffman Tree and Backward Cloud Model

    Institute of Scientific and Technical Information of China (English)

    李芳; 熊英; 唐斌

    2013-01-01

    A new method is presented to improve the identification rate of radar jamming for the identification of radar pull-off jamming based on Huffman tree and backward cloud model.Firstly,a parameter library is built according to the jamming library,then an identification model based on Huffman tree can be established.Finally the degree of membership is used to identify jamming on each node of the tree.Compared with traditional method,the presented method deals well with the randomness and fuzziness of jamming caused by noise,and identifies jamming effectively when parameters overlap partially.%针对噪声环境中雷达干扰正确识别率较低的问题,提出了一种新的基于霍夫曼树和逆云模型联合的雷达欺骗干扰识别方法.该方法首先利用干扰数据库,提取有效的识别特征参数库,然后基于霍夫曼树建立识别模型.在每个节点,利用基于逆云模型的隶属度分类,实现待测干扰的识别.仿真结果表明,与传统的干扰识别方法相比,该识别方法能很好地应对雷达干扰的随机性和模糊性,能在干扰参数数值区间有重叠时有效识别雷达干扰.

  2. Influence of fatigue testing and cementation mode on the load-bearing capability of bovine incisors restored with crowns and FRC posts.

    Science.gov (United States)

    Nothdurft, Frank P; Schmitt, Thomas; Rupf, Stefan; Pospiech, Peter R

    2011-01-01

    The aim of the study was to evaluate the influence of fatigue and cementation mode on the fracture behaviour of endodontically treated bovine incisors restored with fiber-reinforced-composite (FRC) posts and crowns. Forty-eight endodontically treated incisors were restored with FRC posts, composite build-ups, and cast crowns. In 16 teeth, each of the posts were cemented conventionally with KetacCem (3M Espe) or adhesively with Panavia F (Kuraray) or RelyXUniCem (3M Espe). One-half of the specimens in each group were subjected to thermal cycling with 10,000 cycles at 5-55°C and mechanical aging, loading the specimens in 1,200,000 cycles with 50 N. Fracture resistance was determined by loading the specimens until fracture at an angle of 45°. The loading test showed that cementation mode and fatigue testing had an influence on the load bearing capability. Before fatigue testing no statistically significant differences between the different cementation modes could be detected. After fatigue testing, conventionally cemented FRC posts lead to statistically significant higher fracture loads compared to adhesively luted posts. Most specimens fractured in a favourable way, independent from the type of cementation.

  3. Orthodontic crown lengthening.

    Science.gov (United States)

    Hohlt, W F

    1992-01-01

    As comprehensive dentistry becomes more complex, procedures must be developed to save teeth once considered unsuitable for crown restoration due to inaccessible finishing lines. Orthodontic crown lengthening is less invasive than a flap procedure and does not result in crestal bone reduction. The crown lengthening procedure is a simple and time-saving remedy for a difficult restorative problem.

  4. Marginal Strength of Collarless Metal Ceramic Crown

    Directory of Open Access Journals (Sweden)

    Sikka Swati

    2010-01-01

    fracture strength at margins of metal ceramic crowns cemented to metal tooth analogs. Crowns evaluated with different marginal configurations, shoulder and shoulder bevel with 0 mm, 0.5 mm, 1 mm, and 1.5 mm, were selected. Methods. Maxillary right canine typhodont tooth was prepared to receive a metal ceramic crown with shoulder margin. This was duplicated to get 20 metal teeth analogs. Then the same tooth was reprepared to get shoulder bevel configuration. These crowns were then cemented onmetal teeth analogs and tested for fracture strength atmargin on an Instron testing machine. A progressive compressive load was applied using 6.3 mm diameter rod with crosshead speed of 2.5 mm per minute. Statisticaly analysis was performed with ANOVA, Student's “t” test and “f” test. Results. The fracture strength of collarless metal ceramic crowns under study exceeded the normal biting force. Therefore it can be suggested that collarless metal ceramic crowns with shoulder or shoulder bevel margins up to 1.5 mm framework reduction may be indicated for anteriormetal ceramic restorations. Significance. k Collarless metal ceramic crowns have proved to be successful for anterior fixed restorations. Hence, it may be subjected to more clinical trials.

  5. Elliptic Fourier analysis of crown shapes in Quercus petraea trees

    Directory of Open Access Journals (Sweden)

    Ovidiu Hâruţa

    2011-06-01

    Full Text Available Shape is a fundamental morphological descriptor, significant in taxonomic research as well as in ecomorphology, one method of estimation being from digitally processed images. In the present study, were analysed shapes of Q. petraea crowns, pertaining to five different stem diameter classes, from three similar stands. Based on measurements on terrestrial digital vertical photos, crown size analysis was performed and correlations between crown and stem variables were tested. Linear regression equations between crown volumes and dbh, and crown volumes and stem volumes were derived, explaining more than half of data variability. Employment of elliptic Fourier analysis (EFA, a powerful analysis tool, permitted the extraction of the mean shape from crowns, characterized by high morphological variability. The extracted, most important, coefficients were used to reconstruct the average shape of the crowns, using Inverse Fourier Transform. A mean shape of the crown, corresponding to stand conditions in which competition is added as influential shaping factor, aside genetic program of the species, is described for each stem diameter class. Crown regions with highest shape variability, from the perspective of stage development of the trees, were determined. Accordingly, the main crown shape characteristics are: crown elongation, centroid position, asymmetry with regard to the main axis, lateral regions symmetrical and asymmetrical variations. 

  6. Elliptic Fourier analysis of crown shapes in Quercus petraea trees

    Directory of Open Access Journals (Sweden)

    Ovidiu Hâruţa

    2011-02-01

    Full Text Available Shape is a fundamental morphological descriptor, significant in taxonomic research as well as in ecomorphology, one method of estimation being from digitally processed images. In the present study, were analysed shapes of Q. petraea crowns, pertaining to five different stem diameter classes, from three similar stands. Based on measurements on terrestrial digital vertical photos, crown size analysis was performed and correlations between crown and stem variables were tested. Linear regression equations between crown volumes and dbh, and crown volumes and stem volumes were derived, explaining more than half of data variability. Employment of elliptic Fourier analysis (EFA, a powerful analysis tool, permitted the extraction of the mean shape from crowns, characterized by high morphological variability. The extracted, most important, coefficients were used to reconstruct the average shape of the crowns, using Inverse Fourier Transform. A mean shape of the crown, corresponding to stand conditions in which competition is added as influential shaping factor, aside genetic program of the species, is described for each stem diameter class. Crown regions with highest shape variability, from the perspective of stage developmentof the trees, were determined. Accordingly, the main crown shape characteristics are: crown elongation, mass center, asymmetry with regard to the main axis, lateral regions symmetrical and asymmetrical variations.

  7. Crown Fire Potential

    Data.gov (United States)

    Earth Data Analysis Center, University of New Mexico — Crown fire potential was modeled using FlamMap, an interagency fire behavior mapping and analysis program that computes potential fire behavior characteristics. The...

  8. Crown lengthening revisited.

    Science.gov (United States)

    Rosenberg, E S; Cho, S C; Garber, D A

    1999-06-01

    Over the last 37 years, crown-lengthening procedures have been used predictably to restore teeth broken down from caries, trauma, and extensive wear. With crown lengthening, the dentogingival junction is "re-created" at a more apical level on the root to accommodate the junctional epithelium and the connective tissue attachment. Forced eruption can be used in addition, or as an alternative, to tooth lengthening. The authors discuss the indications for tooth lengthening, forced eruption, and orthodontic extrusion, as well as the treatment planning for these procedures.

  9. Fatigue resistance of CAD/CAM resin composite molar crowns.

    Science.gov (United States)

    Shembish, Fatma A; Tong, Hui; Kaizer, Marina; Janal, Malvin N; Thompson, Van P; Opdam, Niek J; Zhang, Yu

    2016-04-01

    To demonstrate the fatigue behavior of CAD/CAM resin composite molar crowns using a mouth-motion step-stress fatigue test. Monolithic leucite-reinforced glass-ceramic crowns were used as a reference. Fully anatomically shaped monolithic resin composite molar crowns (Lava Ultimate, n=24) and leucite reinforced glass-ceramic crowns (IPS Empress CAD, n=24) were fabricated using CAD/CAM systems. Crowns were cemented on aged dentin-like resin composite tooth replicas (Filtek Z100) with resin-based cements (RelyX Ultimate for Lava Ultimate or Multilink Automix for IPS Empress). Three step-stress profiles (aggressive, moderate and mild) were employed for the accelerated sliding-contact mouth-motion fatigue test. Twenty one crowns from each group were randomly distributed among these three profiles (1:2:4). Failure was designated as chip-off or bulk fracture. Optical and electron microscopes were used to examine the occlusal surface and subsurface damages, as well as the material microstructures. The resin composite crowns showed only minor occlusal damage during mouth-motion step-stress fatigue loading up to 1700N. Cross-sectional views revealed contact-induced cone cracks in all specimens, and flexural radial cracks in 2 crowns. Both cone and radial cracks were relatively small compared to the crown thickness. Extending these cracks to the threshold for catastrophic failure would require much higher indentation loads or more loading cycles. In contrast, all of the glass-ceramic crowns fractured, starting at loads of approximately 450N. Monolithic CAD/CAM resin composite crowns endure, with only superficial damage, fatigue loads 3-4 times higher than those causing catastrophic failure in glass-ceramic CAD crowns. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  10. Aesthetic Surgical Crown Lengthening Procedure.

    Science.gov (United States)

    de Oliveira, Pablo Santos; Chiarelli, Fabio; Rodrigues, José A; Shibli, Jamil A; Zizzari, Vincenzo Luca; Piattelli, Adriano; Iezzi, Giovanna; Perrotti, Vittoria

    2015-01-01

    The aim of this case report was to describe the surgical sequence of crown lengthening to apically reposition the dentogingival complex, in addition to an esthetic restorative procedure. Many different causes can be responsible for short clinical crown. In these cases, the correct execution of a restorative or prosthetic rehabilitation requires an increasing of the crown length. According to the 2003 American Academy of Periodontology (Practice Profile Survey), crown lengthening is the most habitual surgical periodontal treatment.

  11. Aesthetic Surgical Crown Lengthening Procedure

    OpenAIRE

    2015-01-01

    The aim of this case report was to describe the surgical sequence of crown lengthening to apically reposition the dentogingival complex, in addition to an esthetic restorative procedure. Many different causes can be responsible for short clinical crown. In these cases, the correct execution of a restorative or prosthetic rehabilitation requires an increasing of the crown length. According to the 2003 American Academy of Periodontology (Practice Profile Survey), crown lengthening is the most h...

  12. Aesthetic Surgical Crown Lengthening Procedure

    Science.gov (United States)

    de Oliveira, Pablo Santos; Chiarelli, Fabio; Rodrigues, José A.; Shibli, Jamil A.; Zizzari, Vincenzo Luca; Piattelli, Adriano; Iezzi, Giovanna; Perrotti, Vittoria

    2015-01-01

    The aim of this case report was to describe the surgical sequence of crown lengthening to apically reposition the dentogingival complex, in addition to an esthetic restorative procedure. Many different causes can be responsible for short clinical crown. In these cases, the correct execution of a restorative or prosthetic rehabilitation requires an increasing of the crown length. According to the 2003 American Academy of Periodontology (Practice Profile Survey), crown lengthening is the most habitual surgical periodontal treatment. PMID:26609452

  13. Aesthetic Surgical Crown Lengthening Procedure

    Directory of Open Access Journals (Sweden)

    Pablo Santos de Oliveira

    2015-01-01

    Full Text Available The aim of this case report was to describe the surgical sequence of crown lengthening to apically reposition the dentogingival complex, in addition to an esthetic restorative procedure. Many different causes can be responsible for short clinical crown. In these cases, the correct execution of a restorative or prosthetic rehabilitation requires an increasing of the crown length. According to the 2003 American Academy of Periodontology (Practice Profile Survey, crown lengthening is the most habitual surgical periodontal treatment.

  14. Crown lengthening procedures

    Directory of Open Access Journals (Sweden)

    AA. Khoshkhonejad

    1994-06-01

    Full Text Available Nowadays, due to recent developments and researches in dental science, it is possible to preserve and restore previously extracted cases such as teeth with extensive caries, fractured or less appropriate cases for crown coverage as well as teeth with external perforation caused by restorative pins. In order to restore the teeth with preservation of periodontium, we should know thoroughly physiological aspects of periodontium and protection of Biologic Width which is formed by epithelial and supracrestal connective tissue connections. Considering biologic width is one of the principal rules of teeth restoration, otherwise we may destruct periodontal tissues. Several factors are involved in placing a restoration and one of the most important ones is where the restoration margin is terminated. Many studies have been conducted on the possible effects of restoration margin on the gingiva and due to the results of these studies it was concluded that restoration margin should be finished supragingivally. However, when we have to end the restoration under Gingival Crest, First a healthy gingival sulcus is required. Also, we should not invade the biological width. Since a normal biologic with is reported 2 mm and sound tooth tissue should be placed at least 2 mm coronal to the epithelial tissue, the distance between sound tooth tissue and crown margin should be at least 4mm. Thus, performing crown lengthening is essential to increase the clinical crown length. Basically, two objectives are considered: 1 restorative 2 esthetic (gummy smile Surgical procedure includes gingivectomy and flap procedure. Orthodontic procedure involves orthodontic extrusion or force eruption technique which is controlled vertical movements of teeth into occlusion. Besides, this procedure can also used to extrude teeth defects from the gingival tissue. By crown lengthening, tooth extraction is not required and furthermore, adjacent teeth preparation for placing a fixed

  15. Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core-veneer all-ceramic layered crown design.

    Science.gov (United States)

    Bonfante, Estevam A; Rafferty, Brian; Zavanelli, Ricardo A; Silva, Nelson R F A; Rekow, Elizabeth D; Thompson, Van P; Coelho, Paulo G

    2010-04-01

    This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth-motion fatigue. The dimensions of a mandibular first molar were imported into computer-aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900 degrees C to 25 degrees C. Crowns were fabricated and mouth-motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue.

  16. Engineering properties and performance of dental crowns.

    Science.gov (United States)

    Mitchell, C A; Orr, J F

    2005-07-01

    Dental crowns are used to replace damaged natural crowns of teeth and are fixed to prepared teeth with luting cements, which should provide an adhesive bond to the tooth structure giving reliable retention and minimal microleakage. Mechanical testing of crowns in vitro gives failure load distributions that are well described by Weibull models, comparing probabilities of survival and reliability. Fatigue testing of crowns is time consuming, but regression analysis to interpolate functions through data points quoting probability limits or applying Weibull analysis is achievable. A complementary approach is to conduct materials tests with appropriate interfacial geometries. Luting cements are used in thin layers of 40-150 microm. Contraction during polymerization is restrained by adhesion to substrates, allowing little relaxation of stresses. Conventional and resin-modified glass ionomer cements create thin zones of interaction with dentine and fail cohesively. The chevron notch short rod technique has been used to measure fracture toughness and rank cements. A development of this method, using chevron notch short bar specimens, permitted fracture toughness to be determined for luting cement--dentine substrate interfaces. Representative fracture experiments need to be developed to apply mixed mode conditions. The basic challenge to predict long-term performance from short-term laboratory tests remains.

  17. Evaluation of marginal fit of 2 CAD-CAM anatomic contour zirconia crown systems and lithium disilicate glass-ceramic crown.

    Science.gov (United States)

    Ji, Min-Kyung; Park, Ji-Hee; Park, Sang-Won; Yun, Kwi-Dug; Oh, Gye-Jeong; Lim, Hyun-Pil

    2015-08-01

    This study was to evaluate the marginal fit of two CAD-CAM anatomic contour zirconia crown systems compared to lithium disilicate glass-ceramic crowns. Shoulder and deep chamfer margin were formed on each acrylic resin tooth model of a maxillary first premolar. Two CAD-CAM systems (Prettau®Zirconia and ZENOSTAR®ZR translucent) and lithium disilicate glass ceramic (IPS e.max®press) crowns were made (n=16). Each crown was bonded to stone dies with resin cement (Rely X Unicem). Marginal gap and absolute marginal discrepancy of crowns were measured using a light microscope equipped with a digital camera (Leica DFC295) magnified by a factor of 100. Two-way analysis of variance (ANOVA) and post-hoc Tukey's HSD test were conducted to analyze the significance of crown marginal fit regarding the finish line configuration and the fabrication system. The mean marginal gap of lithium disilicate glass ceramic crowns (IPS e.max®press) was significantly lower than that of the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) (PCAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia). In terms of absolute marginal discrepancy, the CAD-CAM anatomic contour zirconia crown system (ZENOSTAR®ZR translucent) had under-extended margin, whereas the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) and lithium disilicate glass ceramic crowns (IPS e.max®press) had overextended margins.

  18. In vitro fracture resistance of three commercially available zirconia crowns for primary molars.

    Science.gov (United States)

    Townsend, Janice A; Knoell, Patrick; Yu, Qingzhao; Zhang, Jian-Feng; Wang, Yapin; Zhu, Han; Beattie, Sean; Xu, Xiaoming

    2014-01-01

    The purpose of this study was to measure the fracture resistance of primary mandibular first molar zirconia crowns from three different manufacturers-EZ Pedo (EZP), NuSmile (NSZ), and Kinder Krowns (KK)-and compare it with the thickness of the zirconia crowns and the measured fracture resistance of preveneered stainless steel crowns (SSCs). The thickness of 20 zirconia crowns from three manufacturers were measured. The mean force required to fracture the crowns was determined. Preveneered NuSmile (NSW) SSCs were tested as a control. EZP crowns were significantly thicker in three of the six measured locations. The force required to fracture the EZP crown was significantly higher than that required for NSZ and KK. There was a positive correlation between fracture resistance and crown thickness in the mesial, distal, mesioocclusal, and distoocclusal dimensions. None of the zirconia crowns proved to be as resistant to fracture as the preveneered SSCs. Statistically significant differences were found among the forces required to fracture zirconia crowns by three different manufacturers. The increase in force correlated with crown thickness. The forces required to fracture the preveneered stainless steel crowns were greater than the forces required to fracture all manufacturers' zirconia crowns.

  19. [Clinical evaluation of gingival tissue restored with stainless steel crown].

    Science.gov (United States)

    Chao, D D; Tsai, T P; Chen, T C

    1992-12-01

    The use of stainless steel crown for the restoration of primary molars is widely accepted in pediatric dentistry. There has been a concern regarding their effect on the health of the gingival tissue. It is a possibility that the preformed crown may be a contributing cause of gingivitis. This study evaluated one hundred and thirty-seven crowns in forty-five patients who had received pedodontic treatment at Chang Gung Memorial Hospital. The results indicated that the majority of stainless steel crowns had one or more defects, with crown crimping being the most common error. According to what the paired t-test showed, non-ideal crowns indicated that the gingival index was significantly higher than the entire mouth and control teeth. However the supragingival plaque accumulation of these teeth was significant lower than the entire mouth and control teeth. There was only a moderate positive correlation between supragingival plaque and gingivitis. The operator is necessary to adapt the stainless steel crown margin as closely as possible to the tooth and to avoid the mechanical defect of a crown. It minimizes the irritation of gingival tissue and diminishes the bacterial adherence of subgingival plaque, therefore preserving the health of gingival tissue.

  20. Crown lengthening: a clinical review.

    Science.gov (United States)

    Talbot, T R; Briggs, P F; Gibson, M T

    1993-09-01

    The use of crown lengthening surgery as an adjunct to restorative therapy was first suggested by Rosen and Gitnick. This technique is designed to increase the clinical crown heights of teeth requiring restoration following extensive wear through attrition, abrasion and erosion. This loss of tooth tissue and resulting clinical crown height may be localized to a few teeth or affect the entire dentition. This clinical problem is reflected by the increasing number of reports of treatment of the worn dentition.

  1. Fracture Strength of Aged Monolithic and Bilayer Zirconia-Based Crowns.

    Science.gov (United States)

    Lameira, Deborah Pacheco; Buarque e Silva, Wilkens Aurélio; Andrade e Silva, Frederico; De Souza, Grace M

    2015-01-01

    The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP) crowns in monolithic (1.5 mm thickness) and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer) configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n = 10): Polished monolithic zirconia crowns (PM); Glazed monolithic zirconia crowns (GM); Bi-layer crowns (BL). Crowns were cemented with resin cement, submitted to artificial aging in a chewing simulator (2.5 million cycles/80 N/artificial saliva/37 °C), and tested for fracture strength. Two remaining crowns referring to PM and GM groups were submitted to a chemical composition analysis to measure the level of yttrium after aging. One-way ANOVA and Tukey's test (P = .05) indicated that monolithic zirconia crowns presented similar fracture strength (PM = 3476.2 N ± 791.7; GM = 3561.5 N ± 991.6), which was higher than bilayer crowns (2060.4 N ± 810.6). There was no difference in the yttrium content among the three surfaces evaluated in the monolithic crowns. Thus, monolithic zirconia crowns present higher fracture strength than bilayer veneered zirconia after artificial aging and surface finishing does not affect their fracture strength.

  2. [Restoration of composite on etched stainless steel crowns. (1)].

    Science.gov (United States)

    Goto, G; Zang, Y; Hosoya, Y

    1990-01-01

    Object of investigation The retention of composite resin to etched stainless steel crowns was tested as a possible method for restoring primary anterior teeth. Method employed 1) SEM observation Stainless steel crowns (Sankin Manufacture Co.) were etched with an aqua resia to create surface roughness and undercut to retain the composite resin to the crowns. Etching times were 1, 2, 3, 5, 8, 10 and 20 minutes, then washed in a 70% alcohol solution using an ultrasonic washer and dried. A total of 96 etched samples and non etched control samples were observed through the scanning electron microscope (Hitachi 520). 2) Shear bond strength test Stainless steel crowns were etched in an aqua resia from 1 to 20 minutes, then washed and dried. Composite resin (Photo Clearfil A, Kuraray Co.) with the bonding agent was placed on the crowns and the shear bond strength was tested in 56 samples using an Autograph (DCS-500, Shimazu). Results 1) SEM observation showed that the etching surface of stainless steel crowns created surface roughness and undercut. The most desirable surface was obtained in the 3 to 5 minute etching time specimens. 2) The highest bond strength was obtained in a 3 minute etching specimen. It was 42.12 MPa, although 29.26 MPa in mean value. Conclusion Etching with an aqua resia increased the adherence of composite resin to the surface of stainless steel crowns.

  3. Chromatographic zinc isotope separation by phenol formaldehyde benzo crown resin.

    Science.gov (United States)

    Ding, Xingcheng; Nomura, Masao; Suzuki, Tatsuya; Sugiyama, Yuichi; Kaneshiki, Toshitaka; Fujii, Yasuhiko

    2006-04-28

    New types of phenol formaldehyde resin having benzo crown as a functional group were synthesized and applied to zinc isotope chromatographic operation. Zinc adsorption and isotope separation capacities were dramatically improved by using phenol formaldehyde benzo-15-crown-5 resin. Zinc batch adsorption tests were performed by various dehydrated organic solvents. Separation coefficient, epsilon 8.1 x 10(-4) and height equivalent to a theoretical plate (HETP) 0.105 cm for the isotopic pair of 68Zn/64Zn in phenol formaldehyde benzo-15-crown-5 resin were obtained in the case of acetone as the solvent at 298+/-1K.

  4. Preformed posterior stainless steel crowns: an update.

    Science.gov (United States)

    Croll, T P

    1999-02-01

    For almost 50 years, dentists have used stainless steel crowns for primary and permanent posterior teeth. No other type of restoration offers the convenience, low cost, durability, and reliability of such crowns when interim full-coronal coverage is required. Preformed stainless steel crowns have improved over the years. Better luting cements have been developed and different methods of crown manipulation have evolved. This article reviews stainless steel crown procedures for primary and permanent posterior teeth. Step-by-step placement of a primary molar stainless steel crown is documented and permanent molar stainless steel crown restoration is described. A method for repairing a worn-through crown also is reviewed.

  5. Internal adaptation of cast titanium crowns

    Directory of Open Access Journals (Sweden)

    Sicknan Soares da Rocha

    2007-08-01

    Full Text Available As the adaptation of titanium crowns obtained by Rematitan Plus investment, specific for titanium, is not recognized to be suitable, this study evaluated the effect of the concentration of the specific liquid and the temperature of the mold of investments on the internal misfit of crowns cast on commercially pure titanium. Individual dies of epoxy resin were obtained, representing teeth prepared for full-crown restoration with a 6-degree axial surface convergence angle and shoulder (1.0 mm. For the waxing of each crown, a ring-shaped stainless steel matrix (8.0mm internal diameter; 7.5 mm height was adapted above the individual dies of epoxy resin. The Rematian Plus investment was mixed according to the manufacturer's instructions using two different concentrations of the specific liquid: 100%, 75%. Casting was performed in a Discovery Plasma Ar-arc vacuum-pressure casting machine with molds at temperatures of 430ºC, 515ºC and 600ºC. The crowns were cleaned individually in a solution (1% HF + 13% HNO3 for 10 min using a ultrasonic cleaner, with no internal adaptations, and luted with zinc phosphate cement under a 5 kg static load. The crown and die assemblies were embedded in resin and sectioned longitudinally. The area occupied by cement was observed using stereoscopic lens (10X and measured by the Leica Qwin image analysis system (mm². The data for each experimental condition (n=8 were analyzed by Kruskal-Wallis non-parametric test (á=0.05. The results showed that liquid dilution and the increase in mold temperature did not significantly influence the levels of internal fit of the cast titanium crowns. The lowest means (±SD of internal misfit were obtained for the 430ºC/100%: (7.25 mm² ±1.59 and 600ºC/100% (8.8 mm² ±2.25 groups, which presented statistically similar levels of internal misfit.

  6. Ready to crown

    LENUS (Irish Health Repository)

    McReynolds, David

    2017-04-01

    When multiple teeth or localised segments of the mouth require crowns, the restorative interventions involved can be psychologically and physically demanding for the operator, patient and dental technician alike.1,2 It is important that all parties involved in restorations of this nature hold a shared understanding of the expected outcome of treatment, with a realistic, common end goal in mind right from the very beginning. Such clarity of thought and communication is key to avoiding biological, mechanical and aesthetic failures in the planning and execution of advanced restorative treatments. Biomechanically stable and aesthetically pleasing provisional restorations are an essential aspect of treatment, which allow teeth to be prepared and provisionalised over multiple appointments within the comfort zone of the operator and patient.3

  7. Randomized, controlled clinical trial of bilayer ceramic and metal-ceramic crown performance.

    Science.gov (United States)

    Esquivel-Upshaw, Josephine; Rose, William; Oliveira, Erica; Yang, Mark; Clark, Arthur E; Anusavice, Kenneth

    2013-04-01

    Analyzing the clinical performance of restorative materials is important, as there is an expectation that these materials and procedures will restore teeth and do no harm. The objective of this research study was to characterize the clinical performance of metal-ceramic crowns, core ceramic crowns, and core ceramic/veneer ceramic crowns based on 11 clinical criteria. An IRB-approved, randomized, controlled clinical trial was conducted as a single-blind pilot study. The following three types of full crowns were fabricated: (1) metal-ceramic crown (MC) made from a Pd-Au-Ag-Sn-In alloy (Argedent 62) and a glass-ceramic veneer (IPS d.SIGN veneer); (2) non-veneered (glazed) lithium disilicate glass-ceramic crown (LDC) (IPS e.max Press core and e.max Ceram Glaze); and (3) veneered lithia disilicate glass-ceramic crown (LDC/V) with glass-ceramic veneer (IPS Empress 2 core and IPS Eris). Single-unit crowns were randomly assigned. Patients were recalled for each of 3 years and were evaluated by two calibrated clinicians. Thirty-six crowns were placed in 31 patients. A total of 12 crowns of each of the three crown types were studied. Eleven criteria were evaluated: tissue health, marginal integrity, secondary caries, proximal contact, anatomic contour, occlusion, surface texture, cracks/chips (fractures), color match, tooth sensitivity, and wear (of crowns and opposing enamel). Numerical rankings ranged from 1 to 4, with 4 being excellent, and 1 indicating a need for immediate replacement. Statistical analysis of the numerical rankings was performed using a Fisher's exact test. There was no statistically significant difference between performance of the core ceramic crowns and the two veneered crowns at year 1 and year 2 (p > 0.05). All crowns were rated either as excellent or good for each of the clinical criteria; however, between years 2 and 3, gradual roughening of the occlusal surface occurred in some of the ceramic-ceramic crowns, possibly caused by dissolution and

  8. Randomized, Controlled Clinical Trial of Bilayer Ceramic and Metal-Ceramic Crown Performance

    Science.gov (United States)

    Esquivel-Upshaw, Josephine; Rose, William; Oliveira, Erica; Yang, Mark; Clark, Arthur E.; Anusavice, Kenneth

    2013-01-01

    Purpose Analyzing the clinical performance of restorative materials is important, as there is an expectation that these materials and procedures will restore teeth and do no harm. The objective of this research study was to characterize the clinical performance of metal-ceramic crowns, core ceramic crowns, and core ceramic/veneer ceramic crowns based on 11 clinical criteria. Materials and Methods An IRB-approved, randomized, controlled clinical trial was conducted as a single-blind pilot study. The following three types of full crowns were fabricated: (1) metal-ceramic crown (MC) made from a Pd-Au-Ag-Sn-In alloy (Argedent 62) and a glass-ceramic veneer (IPS d.SIGN veneer); (2) non-veneered (glazed) lithium disilicate glass-ceramic crown (LDC) (IPS e.max Press core and e.max Ceram Glaze); and (3) veneered lithia disilicate glass-ceramic crown (LDC/V) with glass-ceramic veneer (IPS Empress 2 core and IPS Eris). Single-unit crowns were randomly assigned. Patients were recalled for each of 3 years and were evaluated by two calibrated clinicians. Thirty-six crowns were placed in 31 patients. A total of 12 crowns of each of the three crown types were studied. Eleven criteria were evaluated: tissue health, marginal integrity, secondary caries, proximal contact, anatomic contour, occlusion, surface texture, cracks/chips (fractures), color match, tooth sensitivity, and wear (of crowns and opposing enamel). Numerical rankings ranged from 1 to 4, with 4 being excellent, and 1 indicating a need for immediate replacement. Statistical analysis of the numerical rankings was performed using a Fisher’s exact test. Results There was no statistically significant difference between performance of the core ceramic crowns and the two veneered crowns at year 1 and year 2 (p > 0.05). All crowns were rated either as excellent or good for each of the clinical criteria; however, between years 2 and 3, gradual roughening of the occlusal surface occurred in some of the ceramic-ceramic crowns

  9. Fracture toughness of zirconia ceramic crowns made by feather-edge tooth preparation design

    Directory of Open Access Journals (Sweden)

    Mirković Nemanja

    2012-01-01

    Full Text Available Background/Aim. Fracture toughness determines functional crown strenght and prevents damages on ceramics during mastication. There is a lack of relevant literature data about fracture toughness of crowns made by feather-edge preparation. Mechanical testing of ceramic samples is supposed to show if feather-edge tooth preparation is a successful method for making ceramic crowns without any risk of reduction of their mechanical properties. This research was done to establish effects of feather-edge tooth preparation on fracture toughness of single zirconia ceramic crowns. Methods. The research was performed as an experimental study. Sixty (60 ceramic crowns were made on non-carious extracted human premolars. Thirty (30 crowns were made on the basis of feather-edge preparation (experimental group I. The group II included 30 crowns made on 1 mm rounded shoulder. Crowns fabrication was executed on a copy mill production system “Zirkonzahn” (Zirkonzahn GMBH, Gais, Germany. The spherical compression test was used to determine fracture toughness, using 6 mm diameter ceramic ball. Fracture load for damaging ceramic crown was recorded on a universal testing machine - Zwick, type 1464, with the speed of 0.05 mm/min. Results. The results of this research introduced significant differences between fracture toughness of ceramic samples in every examined group. However, fracture toughness of crowns from both group was above 2 000 N, what was double beyond a recommended value. The mean value of fracture toughness in the feather-edge group was 2 090 N, and in shoulder group it was 2 214 N. Conclusion. This research showed a high fracture toughness of zirconia crowns made on feather-edge preparation. The examined crowns showed a fracture resistance at a sufficient distance in relation to the minimum values of functional loads. Further research of functional loads of these crown is necessary, as well as research of marginal adaptation of cemented crowns and

  10. Clinical assessment of enamel wear caused by monolithic zirconia crowns.

    Science.gov (United States)

    Stober, T; Bermejo, J L; Schwindling, F S; Schmitter, M

    2016-08-01

    The purpose of this study was to measure enamel wear caused by antagonistic monolithic zirconia crowns and to compare this with enamel wear caused by contralateral natural antagonists. Twenty monolithic zirconia full molar crowns were placed in 20 patients. Patients with high activity of the masseter muscle at night (bruxism) were excluded. For analysis of wear, vinylpolysiloxane impressions were prepared after crown incorporation and at 6-, 12-, and 24-month follow-up. Wear of the occlusal contact areas of the crowns, of their natural antagonists, and of two contralateral natural antagonists (control teeth) was measured by use of plaster replicas and a 3D laser-scanning device. Differences of wear between the zirconia crown antagonists and the control teeth were investigated by means of two-sided paired Student's t-tests and linear regression analysis. After 2 years, mean vertical loss was 46 μm for enamel opposed to zirconia, 19-26 μm for contralateral control teeth and 14 μm for zirconia crowns. Maximum vertical loss was 151 μm for enamel opposed to zirconia, 75-115 μm for control teeth and 60 μm for zirconia crowns. Statistical analysis revealed significant differences between wear of enamel by zirconia-opposed teeth and by control teeth. Gender, which significantly affected wear, was identified as a possible confounder. Monolithic zirconia crowns generated more wear of opposed enamel than did natural teeth. Because of the greater wear caused by other dental ceramics, the use of monolithic zirconia crowns may be justified.

  11. Failure Probability of Three Designs of Zirconia Crowns.

    Science.gov (United States)

    Ramos, Gabriela Freitas; Monteiro, Evelyn Barbosa; Bottino, Marco Antonio; Zhang, Yu; Marques de Melo, Renata

    2015-01-01

    This study used a two-parameter Weibull analysis for evaluation of the lifespan of fully or partially porcelain-/glaze-veneered zirconia crowns after fatigue test. A sample of 60 first molars were selected and prepared for full-coverage crowns with three different designs (n = 20): traditional (crowns with zirconia framework covered with feldspathic porcelain), modified (crowns partially covered with veneering porcelain), and monolithic (full-contour zirconia crowns). All specimens were treated with a glaze layer. Specimens were subjected to mechanical cycling (100 N, 3 Hz) with a piston with a hemispherical tip (Ø = 6 mm) until the specimens failed or up to 2 × 10⁶ cycles. Every 500,000 cycles, the fatigue tests were interrupted and stereomicroscopy (10×) was used to inspect the specimens for damage. The authors performed Weibull analysis of interval data to calculate the number of failures in each interval. The types and numbers of failures according to the groups were: cracking (13 traditional, 6 modified) and chipping (4 traditional) of the feldspathic porcelain, followed by delamination (1 traditional) at the veneer/core interface and debonding (2 monolithic) at the cementation interface. Weibull parameters (β, scale; η, shape), with a two-sided confidence interval of 95%, were: traditional-1.25 and 0.9 × 10⁶ cycles; modified-0.58 and 11.7 × 10⁶ cycles; and monolithic-1.05 and 16.5 × 10⁶ cycles. Traditional crowns showed greater susceptibility to fatigue, the modified group presented higher propensity to early failures, and the monolithic group showed no susceptibility to fatigue. The modified and monolithic groups presented the highest number of crowns with no failures after the fatigue test. The three crown designs presented significantly different behaviors under fatigue. The modified and monolithic groups presented less probability of failure after 2 × 10⁶ cycles.

  12. Shear bond strength of self-ligating orthodontic brackets on different types of porcelain crowns

    Directory of Open Access Journals (Sweden)

    Karamdeep Singh Ahluwalia

    2013-01-01

    Full Text Available Aim: The aim of this study is to compare shear bond strength (SBS and adhesive remnant index (ARI of self-ligating orthodontic brackets bonded to different porcelain crowns. Materials and Methods: Three groups of different types of porcelain crowns, each containing 12 crowns were fabricated by the same technician and allocated to one of the study groups as follows: Group I - IPS porcelain crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein, Group II - Porcelain fused to zirconia crowns (Zirkonzahn GmbH, Gais, Italy, Noritake Co., Tokyo, Japan and Group III - Conventional porcelain fused to metal crowns (Ceramco3, Densply, PA, USA. The orthodontic brackets were bonded to these crowns using hydrofluoric acid (HFA + silane etching protocol. After bonding, the SBS of the brackets were tested with a universal testing machine under standard test conditions. Results: Statistical evaluation using analysis of variance showed a significant difference between the groups (P 0.05. Chi-square comparison revealed no significant difference in ARI scores between groups (P > 0.05. Conclusions: When HFA + silane etching protocol were used, IPS crowns showed the greatest SBS of orthodontic brackets. The ARI score was non-significant. Therefore, if there is a need to place crowns over teeth then these crowns can be used for restoration of teeth before orthodontic treatment.

  13. Simulation of clinical fractures for three different all-ceramic crowns.

    Science.gov (United States)

    Oilo, Marit; Kvam, Ketil; Gjerdet, Nils R

    2014-06-01

    Comparison of fracture strength and fracture modes of different all-ceramic crown systems is not straightforward. Established methods for reliable testing of all-ceramic crowns are not currently available. Published in-vitro tests rarely simulate clinical failure modes and are therefore unsuited to distinguish between the materials. The in-vivo trials usually lack assessment of failure modes. Fractographic analyses show that clinical crowns usually fail from cracks initiating in the cervical margins, whereas in-vitro specimens fail from contact damage at the occlusal loading point. The aim of this study was to compare three all-ceramic systems using a clinically relevant test method that is able to simulate clinical failure modes. Ten incisor crowns of three types of all-ceramic systems were exposed to soft loading until fracture. The initiation and propagation of cracks in these crowns were compared with those of a reference group of crowns that failed during clinical use. All crowns fractured in a manner similar to fracture of the clinical reference crowns. The zirconia crowns fractured at statistically significantly higher loads than alumina and glass-ceramic crowns. Fracture initiation was in the core material, cervically in the approximal areas. © 2014 Eur J Oral Sci.

  14. Overdenture dengan Pegangan Telescopic Crown

    Directory of Open Access Journals (Sweden)

    Pambudi Santoso

    2014-06-01

    Full Text Available Kaitan presisi merupakan alat retensi mekanis yang menghubungkan antara satu atau lebih pegangan gigi tiruan, yang bertujuan untuk menambah retensi dan/atau stabilisasi. Kaitan presisi dapat digunakan secara luas pada gigi tiruan cekat, gigi tiruan sebagian lepasan, overdenture, implant untuk retensi overdenture, dan protesa maksilo fasial. Overdenture dengan kaitan presisi dapat membantu dalam pembagian beban kunyah, meminimalkan trauma pada gigi pegangan dan jaringan lunak, meminimalkan resorbsi tulang, dan meningkatkan estetik dan pengucapan suara. Salah satu jenis dari kaitan presisi adalah telescopic crown, terdiri dari 2 macam mahkota, yaitu mahkota primer yang melekat secara permanen pada gigi penyangga, dan mahkota sekunder yang melekat pada gigi tiruan. Tujuan pemaparan kasus ini adalah untuk memberikan informasi tentang rehabilitasi pasien edentulous sebagian rahang atas dengan telescopic crown..  Pasien wanita berusia 45 tahun datang ke klinik prostodonsia RSGM Prof.Soedomo dengan keluhan ingin dibuatkan gigi tiruan. Pasien kehilangan gigi 11 12 15 16 17 21 22 24 25 26 dan 27 yang diindikasikan untuk pembuatan overdenture gigi tiruan sebagian lepasan (GTS kerangka logam dengan pegangan telescopic crown pada gigi 13 dan 14 dengan sistem parallel-sided crown. Tahap-tahap pembuatan telescopic crown yaitu mencetak model study dengan catatan gigit pendahuluan. Perawatan saluran dilakukan pada akar gigi 13, dilanjutkan pemasangan pasak fiber serta rewalling dinding bukal. Gigi 13 dan 14 dilakukan preparasi mahkota penuh, dilanjutkan dengan pencetakan model kerja untuk coping primer dan kerangka logam dengan metode double impression. Coping primer disementasi pada gigi penyangga, dilanjutkan pasang coba coping sekunder beserta kerangka logam. Selanjutnya dilakukan pencatatan gigit, pencetakan model kerja, penyusunan gigi dan pasang coba penyusunan gigi pada pasien. Prosedur dilanjutkan dengan proses di laboratorium, serta insersi pada

  15. Raspberry Crown Borer [Pennisetia marginata

    OpenAIRE

    Alston, Diane

    2015-01-01

    This fact sheet described raspberry crown borer, a pest that attacks raspberry plants in northern Utah, causing cane-wilt and death. It includes life history, host injury, monitoring and thresholds, and management techniques.

  16. Horizontal Roll Vortices and Crown Fires.

    Science.gov (United States)

    Haines, Donald A.

    1982-06-01

    Observational evidence from nine crown fires suggests that horizontal roll vortices are a major mechanism in crown-fire spread. Post-burn aerial photography indicates that unburned tree-crown streets are common with crown fire. Investigation of the understory of these crown streets after two fires showed uncharred tree trunks along a center line. This evidence supports a hypothesis of vortex action causing strong downward motion of air along the streets. Additionally, photographs of two ongoing crown fires show apparent horizontal roll vortices. Discussion also includes laboratory and numerical studies in fluid dynamics that may apply to crown fires.

  17. Evaluation of marginal circumference and marginal thickness changes in precrimped stainless steel crowns, after recrimping

    Directory of Open Access Journals (Sweden)

    Afshar H

    2006-07-01

    Full Text Available Background and Aim: The need for recrimping precrimped stainless steel crowns by the dentist in clinic is controversial. This study aimed to evaluate the rate of marginal circumference and marginal thickness change of precrimped stainless steel crowns after recrimping. Materials and Methods: In this experimental study, 30 primary photos were taken from margins of 30 S.S.Cs (3M, Ni-Cr related to tooth 85 with a digital camera fixed at a determined distance. Margins of crowns were crimped by 114 and 137 pliers with a controlled force (0.2 N and then 30 secondary photos were taken in the same conditions. The circumference of crown margins in primary (group A and secondary (group B photos were assessed by a digitizer system. Comparing the circumferences of crown margins in primary and secondary photos showed a significant decrease after crimping. Thickness of 30 random points on the crown margins of a crown similar to mentioned cases was measured by SEM (×150. Then similar procedures including taking a primary photo, crimping and taking a secondary photo was done for the sample crown. After significant reduction in margin circumference, thickness of 30 other random points on the crown margin were measured by SEM. Data were analyzed by paired sample t-test with p<0.05 as the limit of significance. Results: The mean marginal circumference of precrimped stainless steel crowns was reduced by 7.3% which was significant (P<0.001. On the other hand the mean marginal thickness of sample stainless steel crown showed 18µ increase. Conclusion: According to the results of this study, marginal circumference of precrimped stainless steel crowns (3M, Ni-Cr showed a significant decrease after crimping. It is concluded that crimping the stainless steel crowns even for precrimped ones seems necessary.

  18. Crown color match of implant-supported zirconia and Porcelain-Fused-to-Metal restorations:

    DEFF Research Database (Denmark)

    Peng, Min; Fei, Wei; Hosseini, Mandana

    2014-01-01

    Objectives: The aim of the present study was to compare the crown color match of implant supported zirconia restorations and Porcelain-Fused-to-Metal (PFM) restorations in anterior maxillary region by spectrophotometric evaluation. Materials and Methods: Eighteen patients with 29 implant......-supported single crowns in anterior maxillary area were recruited, 11 of the implant crowns were zirconia restorations and 18 were PFM restorations. Color match of the implant crown with contra-lateral/neighboring tooth at the position of body 1/3 of the crown were assessed using spectrophotometer (Spectro......ShadeTM, Micro Dental) in CIEL¿a¿b¿ coordinates. Subjective crown color match scores were evaluated. Independent sample t test of SPSS17.0 was used to compare the difference between zirconia restoration and PFM restoration. Spearman correlation was used to analyze the relationship between the spectrophotometric...

  19. Crown color match of implant-supported zirconia and Porcelain-Fused-to-Metal restorations:

    DEFF Research Database (Denmark)

    Peng, Min; Fei, Wei; Hosseini, Mandana

    2014-01-01

    Objectives: The aim of the present study was to compare the crown color match of implant supported zirconia restorations and Porcelain-Fused-to-Metal (PFM) restorations in anterior maxillary region by spectrophotometric evaluation. Materials and Methods: Eighteen patients with 29 implant......-supported single crowns in anterior maxillary area were recruited, 11 of the implant crowns were zirconia restorations and 18 were PFM restorations. Color match of the implant crown with contra-lateral/neighboring tooth at the position of body 1/3 of the crown were assessed using spectrophotometer (Spectro......ShadeTM, Micro Dental) in CIEL¿a¿b¿ coordinates. Subjective crown color match scores were evaluated. Independent sample t test of SPSS17.0 was used to compare the difference between zirconia restoration and PFM restoration. Spearman correlation was used to analyze the relationship between the spectrophotometric...

  20. Forest Crown Cover Estimation in Northern Boreal and Temperate European Forest

    Science.gov (United States)

    Sirro, Laura; Hame, Tuomas; Ahola, Heikki; Lonnqvist, Anne

    2012-04-01

    A method for forest crown cover estimation using high resolution optical earth observation data was developed and tested at four study sites in Europe. Crown cover was estimated using the probability estimation method of VTT and Image2006 data. The accuracy of the crown cover predictions was assessed using reference data that were collected by visual interpretation of very high resolution aerial and space borne imagery. The average crown cover values in the reference data varied from 17 % to 86 % and in the predictions from 18 % to 80 %. The absolute root mean square error of the crown cover predictions varied between 14 % and 33 %. The results of the study showed that it is possible to map forest crown cover with twenty to thirty meter spatial resolution optical earth observation data using the single pixel values. However, understanding the variable results at different sites requires further investigation.

  1. Fracture resistance of computer-aided design/computer-aided manufacturing-generated composite resin-based molar crowns.

    Science.gov (United States)

    Harada, Akio; Nakamura, Keisuke; Kanno, Taro; Inagaki, Ryoichi; Örtengren, Ulf; Niwano, Yoshimi; Sasaki, Keiichi; Egusa, Hiroshi

    2015-04-01

    The aim of this study was to investigate whether different fabrication processes, such as the computer-aided design/computer-aided manufacturing (CAD/CAM) system or the manual build-up technique, affect the fracture resistance of composite resin-based crowns. Lava Ultimate (LU), Estenia C&B (EC&B), and lithium disilicate glass-ceramic IPS e.max press (EMP) were used. Four types of molar crowns were fabricated: CAD/CAM-generated composite resin-based crowns (LU crowns); manually built-up monolayer composite resin-based crowns (EC&B-monolayer crowns); manually built-up layered composite resin-based crowns (EC&B-layered crowns); and EMP crowns. Each type of crown was cemented to dies and the fracture resistance was tested. EC&B-layered crowns showed significantly lower fracture resistance compared with LU and EMP crowns, although there was no significant difference in flexural strength or fracture toughness between LU and EC&B materials. Micro-computed tomography and fractographic analysis showed that decreased strength probably resulted from internal voids in the EC&B-layered crowns introduced by the layering process. There was no significant difference in fracture resistance among LU, EC&B-monolayer, and EMP crowns. Both types of composite resin-based crowns showed fracture loads of >2000 N, which is higher than the molar bite force. Therefore, CAD/CAM-generated crowns, without internal defects, may be applied to molar regions with sufficient fracture resistance. © 2015 Eur J Oral Sci.

  2. Tests for ultrasonic vibration assisted grinding of sintered zirconia ceramics crowns%超声振动辅助磨削完全烧结氧化锆陶瓷牙冠的实验研究

    Institute of Scientific and Technical Information of China (English)

    郑侃; 肖行志; 廖文和

    2014-01-01

    针对现有全锆牙在制作过程中存在二次烧结、收缩精度难以控制等问题,提出了采用超声振动辅助磨削完全烧结氧化锆陶瓷牙冠的方法。从理论分析的角度对其运动学特性进行了研究,并通过超声振动辅助磨削和普通金刚石磨削实验,对该方法的可行性进行了分析。结合牙冠的加工特点,重点研究了主轴转速对材料去除率、表面粗糙度以及最大边缘碎裂的影响规律。实验结果表明,超声振动辅助磨削不仅能提升材料的去除率,有效抑制出口边缘碎裂,同时降低了工件表面的粗糙度,是实现完全烧结氧化锆陶瓷牙冠高效低损伤加工的新方法。%Aiming at machining problems of zirconia ceramics dental prosthesis,such as,complexly processing, difficult to control shrinkage and so on,a new method using ultrasonic vibration assisted grinding presintered zirconia ceramics crowns was proposed.Firstly,its macro kinematic characteristics were investigated with theoretical analysis. Then,tests for machining presintered zirconia ceramics with ultrasonic vibration assisted grinding and diamond grinding were conducted to analyze the feasibility of the new method.Effects of spindle speed on material removal rate,surface roughness and edge chipping size were studied,combined with the machining characteristics of dental prosthesis.The test results demonstrated that the ultrasonic vibration assisted grinding not only raises the material removal rate,but also reduces the surface roughness and restrains the edge chipping effectively,therefore,the ultrasonic vibration assisted grinding is a new method with higher efficiency and lower damage for machining presintered zirconia ceramics crowns.

  3. Fracture Strength of Aged Monolithic and Bilayer Zirconia-Based Crowns

    Directory of Open Access Journals (Sweden)

    Deborah Pacheco Lameira

    2015-01-01

    Full Text Available The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP crowns in monolithic (1.5 mm thickness and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n=10: Polished monolithic zirconia crowns (PM; Glazed monolithic zirconia crowns (GM; Bi-layer crowns (BL. Crowns were cemented with resin cement, submitted to artificial aging in a chewing simulator (2.5 million cycles/80 N/artificial saliva/37°C, and tested for fracture strength. Two remaining crowns referring to PM and GM groups were submitted to a chemical composition analysis to measure the level of yttrium after aging. One-way ANOVA and Tukey’s test (P=.05 indicated that monolithic zirconia crowns presented similar fracture strength (PM=3476.2 N ± 791.7; GM=3561.5 N ± 991.6, which was higher than bilayer crowns (2060.4 N ± 810.6. There was no difference in the yttrium content among the three surfaces evaluated in the monolithic crowns. Thus, monolithic zirconia crowns present higher fracture strength than bilayer veneered zirconia after artificial aging and surface finishing does not affect their fracture strength.

  4. Earth Pressure on Tunnel Crown

    DEFF Research Database (Denmark)

    Andersen, Lars

    Two different analyses have been carried out in order to find the vertical earth pressure, or overburden pressure, at the crown of a tunnel going through a dike. Firstly, a hand calculation is performed using a simple dispersion of the stresses over depth. Secondly, the finite‐element program...

  5. Earth Pressure on Tunnel Crown

    DEFF Research Database (Denmark)

    Andersen, Lars

    Two different analyses have been carried out in order to find the vertical earth pressure, or overburden pressure, at the crown of a tunnel going through a dike. Firstly, a hand calculation is performed using a simple dispersion of the stresses over depth. Secondly, the finite‐element program...

  6. Strength and marginal fit of full and partial porcelain crowns on Brånemark implants.

    Science.gov (United States)

    Kersten, S; Tiedemann, C

    2000-02-01

    The aim of the present study was to evaluate strength and marginal fit of different designed single crowns screwed on titanium implants (Brånemark) without the usage of any abutment. Seven test groups with 10 specimens each (standardized maxillary central incisor crowns) were fabricated of Empress (staining/veneering technique), metal-based Empress (staining/veneering technique), metal-based In-Ceram and metal ceramic (with/without cervical porcelain margin). The marginal fit of 5 specimens of each group was evaluated (SEM-Analysis) and the crowns were incisally loaded at a 30 degrees angle in a Zwick testing machine until fracture. The 5 remaining specimens underwent a marginal evaluation (SEM-analyses) before and after thermo-mechanical stressing (tms) and were loaded in the Zwick testing machine as well. All Empress ceramic crowns without metal reinforcement fractured during fixing procedure on the implant (32 N cm). The gap medians of the fixed crowns ranged from 11 microns (metal ceramic crowns) to 34 microns (metal ceramic crowns with porcelain margin). No significant differences in gap width were observed before and after tms. In the strength analyses screw-binding forces (SBF) of about 135 N were registered in all test groups. Fracture failure forces (FFF) reached up to 280 N. The indication of the crown designs presented in this study is limited in clinical use because of low stability and esthetics.

  7. Wear Behavior of Ceramic CAD/CAM Crowns and Natural Antagonists

    Directory of Open Access Journals (Sweden)

    Ella A. Naumova

    2017-02-01

    Full Text Available Objective: Evaluation of wear behavior of computer-aided design/computer-aided manufacturing (CAD/CAM crowns from various restorative materials and natural antagonists. Method: Full CAD/CAM crowns fabricated with nanoceramic resin (Lava Ultimate (LU, a glass ceramic in a resin interpenetrating matrix (Vita Enamic (VE and a lithium silicate reinforced ceramic enriched with zirconia (Vita Suprinity (VS were cemented on human molars. The crown and antagonists were subjected to simulated chewing. 3D data sets, before and after the chewing simulation, were generated and matched. Occlusal surface roughness, vertical and volume loss of the crowns and antagonists were analyzed. Results: Crown roughness was significantly different between the LU and VE groups after chewing simulation. Crown vertical loss differed in all groups. The highest crown volume loss was found in the LU group, and the lowest in the VE group. Comparisons between the LU and VE groups and the LU and VS groups were significantly different. The highest antagonist volume loss was reached in the VE group, the lowest was in the LU group. Conclusion: Roughness increased after chewing simulation. LU crowns are the most natural antagonist-friendly; these were the most susceptible to vertical and volume loss. Of the tested materials, the VE crowns are the most stable regarding occlusion.

  8. Measuring residual stress in ceramic zirconia-porcelain dental crowns by nanoindentation.

    Science.gov (United States)

    Zhang, Y; Allahkarami, M; Hanan, J C

    2012-02-01

    Residual stress plays a critical role in failure of ceramic dental crowns. The magnitude and distribution of residual stress in the crown system are largely unknown. Determining the residual stress quantitatively is challenging since the crown has such complex contours and shapes. This work explored the feasibility and validity of measuring residual stress of zirconia and porcelain in ceramic crowns by nanoindentation. Nanoindentation tests were performed on the cross-section of a crown for both porcelain and zirconia along four critical locations: the thickest, thinnest and medium porcelain thicknesses. Zirconia and porcelain pieces, chipped off from the crown and annealed at 400 °C, were used as reference samples. The residual stress was determined by comparing the measured hardness of the stressed sample with that of the reference sample. Nanoindentation impression images were acquired through a scanning probe microscope (SPM) equipped with a Hysitron Triboindenter. Zirconia showed large pile-up. Residual stress is determined along the thickness of crowns at the chosen locations for both porcelain and zirconia. The measured results were compared with the results from X-ray diffraction (XRD) and finite element modeling (FEM). Results show there are large amounts of residual stresses in the dental crown and their magnitude differs between locations due to the complex shape of the crown. The average residual stress readings were as high as -637 MPa and 323 MPa for zirconia and porcelain respectively.

  9. Reflectance signature on sunlit crown of conifers

    Institute of Scientific and Technical Information of China (English)

    王锦地; 李小文; 项月琴

    1997-01-01

    Based on the field measurements of the reflected radiation distribution on sunlit crown surface and crown structure, the analytical approximation model of path-scattering of light in a homogeneous layer is applied to the calculation of the reflectance signature of sunlit crown. The reflectance on the sunlit crown surface is considered as the weighted sum of the direct-to-hemisphere reflectance and the hemisphere-to-hemisphere reflectance. The validation results show that the calculated reflectance signature fits the field measurement very well This paper presents details of the validation and the feasibility of the model application to nonuniform medium, such as tree crown canopies.

  10. Crown lengthening: the periodontal-restorative connection.

    Science.gov (United States)

    Becker, W; Ochsenbein, C; Becker, B E

    1998-03-01

    Crown lengthening procedures are based on biologic principles that can be determinants for successful treatment. These procedures are fixed on an understanding of the biologic width. A few of the indications for crown lengthening are caries beneath the gingival margin, fractured teeth with insufficient clinical crown exposure, and teeth with excessive occlusal or incisal wear. This article describes flap designs, the use of a new bur probe for precise measurement of clinical crown exposure, and suturing methods for flap stabilization. Clinical documentation of patients with various clinical situations requiring crown lengthening is presented.

  11. Predicting tree crown defoliation using color-infrared orthophoto maps

    Directory of Open Access Journals (Sweden)

    Eigirdas M

    2013-01-01

    Full Text Available Orthophoto maps based on color-infrared aerial photography have been used by the Lithuanian forest inventory since 2001. This study aimed to investigate the opportunities for using these orthophoto maps to predict tree crown defoliation at the single tree and sample plot levels. The test area was located in the Aukstaitija National Park, eastern Lithuania, and it was photographed in the summer of 2008 using a Vexcel UltraCam D digital frame aerial camera to produce digital orthophoto maps with a 0.5 x 0.5 m ground sampling density. Some 1721 tree crowns (mainly pine, spruce and birch, located in 166 permanent sample plots, were identified and delineated on the orthophoto maps. Crown defoliation and other dendrometric characteristics were field-estimated for all of these trees in summer 2008. Judgments on the suitability of using color-infrared aerial photography based orthophotos to estimate tree crown defoliation were based on the accuracy of the defoliation prediction. Defoliation for each crown was predicted using the non-parametric k-Nearest Neighbor (k-NN method and characteristics extracted from the digital orthophoto maps as the auxiliary variables for prediction. Prediction accuracies were validated using the “Leave One Out” technique by comparing the predicted data with data from field-assessed crown defoliations. The lowest root mean square errors for the predicted tree crown defoliation values were 7.564 for pine trees, 9.166 for spruce and 7.712 for birch and the highest coefficients of correlation between field-estimated and predicted crown defoliations were 0.576, 0.600 and 0.386, respectively. However, there was no best performing solution for using the k-NN prediction found, as the best results were achieved using different approaches. Next, predicted and field estimated tree crown defoliation values were aggregated up to the sample plot level by taking an averaging of trees in the same sample plot. The root mean square error

  12. [Sunrise gold foil jacket crown].

    Science.gov (United States)

    Lecardonnel, A

    1989-09-01

    This technique permits the preparation of ceramic jacket crowns made on Sunrise laminated precious metal alloy. The Sunrise foil is gold-colored, made of 99% of precious metals and is 50 microns thick. The die is prepared in order to display a moderate and regular undercut beyond the cervical limit. The margin will be underlined with a red pencil. The Sunrise foil is cut according to predetermined templates. Then the foil is applied without burnishing, according to the technique of jacket crowns on platinum foil only by finger pressure. The double folding on closure is preferably done distally or mesially. Then, the metal base is disinserted, sandblasted with 100 microns aluminum oxide, replaced on its die, and placed in a rubber casing before being placed in the isostatic press, to be subjected to a pressure of 2,000 TSI (14 kg par cm2). Sunrise's orange color reinforces rather subtetly the overall color, making these reconstructions particularly esthetic. The color of the Sunrise metal does not require, therefore a too thick opaque. Any ceramic intended to be fired on a metal base, may be used in respecting its firing protocol. Sunrise, as any other technique of this type, require a careful preparation with a shoulder that has a rounded gingivoaxial line angle. Bridges may be built on the "thimbles" crowns, fitted on Sunrise cores, the pontics being made as a ceramo-metal framework.

  13. Molluscicidal action of the latex of Euphorbia splendens var. hislopii N.E.B. ("Christ's Crown") (Euphorbiaceae) against Lymnaea columella (Say, 1817) (Pulmonata: Lymnaeidae), intermediate host of Fasciola hepatica Linnaeus, 1758 (Trematode: Fasciolidae): 1- test in laboratory.

    Science.gov (United States)

    de Vasconcellos, Mauricio Carvalho; de Amorim, Alziro

    2003-06-01

    The latex action of Euphorbia splendens var. hislopii (Christ's Crown) against snails Lymnaea columella, intermediate host of Fasciola hepatica, derived from irrigation ditches of the Station of Pisciculture at Universidade Federal Rural do Rio de Janeiro, was studied in the laboratory. Lab bioassays, using aqueous solutions of the latex, varying between 0.1 and 10 mg/l, have proven molluscicidal activity of the product collected on the same day the tests were performed, during the four seasons of the year, finding the following lethal concentrations (LC90): 1.51 mg/l in the spring; 0.55 mg/l in the summer; 0.74 mg/l in the fall and 0.93 mg/l in winter, after 24 h exposure of the snails, showing significant differences among the seasons of the year (ANOVA test, F = 11.01, G.L.= 3/33, p < 0.05), as well as among the concentrations (ANOVA test, F = 27.38, G.L.= 11/33, p < 0.05). In the summer, mortality reached 100% from concentration at 0.6 mg/l, the same during fall and in winter as of 1 mg/l, while in spring it only reached 100% mortality as of 2 mg/l. Mortality in the controls was low, reaching 5% in the summer and winter and 10% in the fall and spring. None of the samples died. During the assay, with an aqueous solution of the latex at a concentration of 5 mg/l, in order to check the time of duration of the product effect, in the laboratory, it was observed that the molluscicidal activity remained stable up to the 15th day after the beginning of the test with 100% mortality of L. columella, gradually losing its effect until the 23rd day, when we no longer observed animal mortality. In the control group, there was a random daily variation in mortality rate ranging 0-50% after 48 h of observation for 30 days.

  14. Molluscicidal action of the latex of Euphorbia splendens var. hislopii N.E.B. ("Christ's Crown" (Euphorbiaceae against Lymnaea columella (Say, 1817 (Pulmonata: Lymnaeidae, intermediate host of Fasciola hepatica Linnaeus, 1758 (Trematode: Fasciolidae: 1- test in laboratory

    Directory of Open Access Journals (Sweden)

    Vasconcellos Mauricio Carvalho de

    2003-01-01

    Full Text Available The latex action of Euphorbia splendens var. hislopii (Christ's Crown against snails Lymnaea columella, intermediate host of Fasciola hepatica, derived from irrigation ditches of the Station of Pisciculture at Universidade Federal Rural do Rio de Janeiro, was studied in the laboratory. Lab bioassays, using aqueous solutions of the latex, varying between 0.1 and 10 mg/l, have proven molluscicidal activity of the product collected on the same day the tests were performed, during the four seasons of the year, finding the following lethal concentrations (LC90: 1.51 mg/l in the spring; 0.55 mg/l in the summer; 0.74 mg/l in the fall and 0.93 mg/l in winter, after 24 h exposure of the snails, showing significant differences among the seasons of the year (ANOVA test, F = 11.01, G.L.= 3/33, p < 0.05, as well as among the concentrations (ANOVA test, F = 27.38, G.L.= 11/33, p < 0.05. In the summer, mortality reached 100% from concentration at 0.6 mg/l, the same during fall and in winter as of 1 mg/l, while in spring it only reached 100% mortality as of 2 mg/l. Mortality in the controls was low, reaching 5% in the summer and winter and 10% in the fall and spring. None of the samples died. During the assay, with an aqueous solution of the latex at a concentration of 5 mg/l, in order to check the time of duration of the product effect, in the laboratory, it was observed that the molluscicidal activity remained stable up to the 15th day after the beginning of the test with 100% mortality of L. columella, gradually losing its effect until the 23rd day, when we no longer observed animal mortality. In the control group, there was a random daily variation in mortality rate ranging 0-50% after 48 h of observation for 30 days.

  15. [Artificial crowns influence upon edge parodontium status].

    Science.gov (United States)

    Zhulev, E N; Serov, A B

    2010-01-01

    With the aim of prosthetic treatment efficacy increase study of edge parodontium tissue reaction upon different types of artificial crowns was done and methods of chronic localized parodontitis prevention were developed. Changes of the main gingival fluid characteristics (amount, acidity, interleukine-1beta concentration) and indicators of microcirculation in edge parodontium of the teeth under the artificial crowns influence were disclosed. There were developed methods of chronic localized parodontitis prevention produced by artificial crowns edge.

  16. Pericoronal radiolucency associated with incomplete crown

    Energy Technology Data Exchange (ETDEWEB)

    Nah, Kyung Soo [Dept. of Oral and Maxillofacial Radiology, School of Dentistry, Pusan National University, Yangsan (Korea, Republic of)

    2013-12-15

    The author experienced 8 cases of pericoronal radiolucency involving an incomplete tooth crown that had not developed to form the cemento-enamel junction, and the underdeveloped crown sometimes appeared to be floating within the radiolucency radiographically. The first impression was that these cystic lesions had odontogenic keratocysts, but half of them turned out to be dentigerous cysts histopathologically. There has been no report concerning odontogenic cysts involving an incompletely developed crown. The purpose of this paper is to report that dentigerous cysts may develop before the completion of the cemento-enamel junction of a developing crown.

  17. The importance of crown dimensions to improve tropical tree biomass estimates.

    Science.gov (United States)

    Goodman, Rosa C; Phillips, Oliver L; Baker, Timothy R

    2014-06-01

    Tropical forests play a vital role in the global carbon cycle, but the amount of carbon they contain and its spatial distribution remain uncertain. Recent studies suggest that once tree height is accounted for in biomass calculations, in addition to diameter and wood density, carbon stock estimates are reduced in many areas. However, it is possible that larger crown sizes might offset the reduction in biomass estimates in some forests where tree heights are lower because even comparatively short trees develop large, well-lit crowns in or above the forest canopy. While current allometric models and theory focus on diameter, wood density, and height, the influence of crown size and structure has not been well studied. To test the extent to which accounting for crown parameters can improve biomass estimates, we harvested and weighed 51 trees (11-169 cm diameter) in southwestern Amazonia where no direct biomass measurements have been made. The trees in our study had nearly half of total aboveground biomass in the branches (44% +/- 2% [mean +/- SE]), demonstrating the importance of accounting for tree crowns. Consistent with our predictions, key pantropical equations that include height, but do not account for crown dimensions, underestimated the sum total biomass of all 51 trees by 11% to 14%, primarily due to substantial underestimates of many of the largest trees. In our models, including crown radius greatly improves performance and reduces error, especially for the largest trees. In addition, over the full data set, crown radius explained more variation in aboveground biomass (10.5%) than height (6.0%). Crown form is also important: Trees with a monopodial architectural type are estimated to have 21-44% less mass than trees with other growth patterns. Our analysis suggests that accounting for crown allometry would substantially improve the accuracy of tropical estimates of tree biomass and its distribution in primary and degraded forests.

  18. Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia.

    Science.gov (United States)

    Nakamura, Takashi; Sugano, Tsuyoshi; Usami, Hirofumi; Wakabayashi, Kazumichi; Ohnishi, Hiroshi; Sekino, Tohru; Yatani, Hirofumi

    2015-01-01

    The purpose of this study is to evaluate the fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia. Commercial semi-sintered zirconia, sintered dense zirconia and sintered hybrid zirconia were used. Sintered zirconia was milled using the CAD/CAM system, and semi-sintered zirconia was milled and sintered to fabricate molar crown frames. Completed frames were veneered with tooth-colored porcelain. The marginal and internal gaps between frames/crowns and abutments were measured. Each crown specimen was subjected to a fracture test. There were no significant differences in marginal and internal gap among all the frames and crowns. The crown with the hybrid zirconia frame had a 31-35% greater fracture load than that with the commercial or dense zirconia frame (pcrowns with a hybrid zirconia frame have a high fracture resistance.

  19. Five-year results of a prospective randomised controlled clinical trial of posterior computer-aided design-computer-aided manufacturing ZrSiO4 -ceramic crowns.

    Science.gov (United States)

    Passia, N; Stampf, S; Strub, J R

    2013-08-01

    The aim of this prospective randomised controlled clinical trial was to evaluate the clinical outcome of shrinkage-free ZrSiO4 -ceramic full-coverage crowns on premolars and molars in comparison with conventional gold crowns over a 5-year period. Two hundred and twenty-three patients were included and randomly divided into two treatment groups. One hundred and twenty-three patients were restored with 123 ZrSiO4 -ceramic crowns, and 100 patients received 100 gold crowns, which served as the control. All crowns were conventionally cemented with glass-ionomer cement. After an observation period of 6, 12, 24, 36, 48 and 60 months, the survival probability (Kaplan-Meier) for the shrinkage-free ZrSiO4 -ceramic crowns was 98·3%, 92·0%, 84·7%, 79% and 73·2% and for the gold crowns, 99%, 97·9%, 95·7%, 94·6% and 92·3%, respectively. The difference between the test and control group was statistically significant (P = 0·0027). The gold crowns showed a better marginal integrity with less marginal discoloration than the ceramic crowns. The most common failure in the ceramic crown group was fracture of the crown. The 60-month results of this prospective randomised controlled clinical trial suggest that the use of these shrinkage-free ZrSiO4 -ceramic crowns in posterior tooth restorations cannot be recommended.

  20. Effect of Different Luting Agents on the Retention of Lithium Disilicate Ceramic Crowns

    Directory of Open Access Journals (Sweden)

    Nicola Mobilio

    2015-04-01

    Full Text Available No studies are available that evaluate the retention of disilicate crowns according to different cementation procedures. The purpose of this study was to measure the retention of lithium disilicate crowns cemented using two different cementation systems. Twenty extracted mandibular premolars were prepared. Anatomic crowns were waxed and hot pressed using lithium disilicate ceramic. Teeth were divided into two groups (n = 10: (1 self-curing luting composite and (2 glass-ionomer cement (GIC. After cementation, the crowns were embedded in acrylic resin block with a screw base. Each specimen was pulled along the path of insertion in Universal Testing Machine. Failure load in Newtons (N and failure mode were recorded for each specimen. Failure mode was classified as decementation or fracture. Failure load data were analyzed using one-way analysis of variance (ANOVA. Failure modes were compared using Pearson’s Chi-square test. Mean failure load was 306.6(±193.8 N for composite group and 94.7(±48.2 N for GIC group (p = 0.004. Disilicate crown cemented with luting composite most often failed by fracture; otherwise, crown cemented with glass-ionomer cement most often failed by decementation (p = 0.02. Disilicate full crown cemented with luting composite showed higher failure load compared with conventional cementation with glass-ionomer cement.

  1. Clinical crown lengthening to improve implant results.

    Science.gov (United States)

    Kohner, J

    1992-01-01

    Clinical crown lengthening is used as an adjunct to implant procedures, and can help provide a better long-term prognosis by establishing proper occlusal planes and aiding in preparation of the abutment teeth. Crown lengthening procedures may be especially useful when caries or a fracture extends below the gingival margin, compromising impression taking and marginal fit.

  2. Crown lengthening: a surgical flap approach.

    Science.gov (United States)

    Lundergan, W; Hughes, W R

    1996-09-01

    In many instances it is not possible to place a restoration margin without encroaching on the periodontal attachment apparatus. A surgical crown-lengthening procedure can provide a good solution to this common clinical problem. This article discusses indication and contraindication for surgical crown-lengthening procedures and presents an appropriate surgical technique.

  3. Fracture resistance of zirconia-composite veneered crowns in comparison with zirconia-porcelain crowns.

    Science.gov (United States)

    Alsadon, Omar; Patrick, David; Johnson, Anthony; Pollington, Sarah; Wood, Duncan

    2017-02-11

    The objectives were to evaluate the fracture resistance and stress concentration in zirconia/composite veneered crowns in comparison to zirconia/porcelain crowns using occlusal fracture resistance and by stress analysis using finite element analysis method. Zirconia substructures were divided into two groups based on the veneering material. A static load was applied occlusally using a ball indenter and the load to fracture was recorded in Newtons (N). The same crown design was used to create 3D crown models and evaluated using FEA. The zirconia/composite crowns subjected to static occlusal load showed comparable results to the zirconia/porcelain crowns. Zirconia/composite crowns showed higher stress on the zirconia substructure at 63.6 and 50.9 MPa on the zirconia substructure veneered with porcelain. In conclusion, zirconia/composite crowns withstood high occlusal loads similar to zirconia/porcelain crowns with no significant difference. However, the zirconia/composite crowns showed higher stress values than the zirconia/porcelain crowns at the zirconia substructure.

  4. Treatment recommendations for single-unit crowns: Findings from The National Dental Practice-Based Research Network.

    Science.gov (United States)

    McCracken, Michael S; Louis, David R; Litaker, Mark S; Minyé, Helena M; Mungia, Rahma; Gordan, Valeria V; Marshall, Don G; Gilbert, Gregg H

    2016-11-01

    The objectives of this study were to quantify practitioner variation in likelihood to recommend a crown and test whether certain dentist, practice, and clinical factors are associated significantly with this likelihood. Dentists in The National Dental Practice-Based Research Network completed a questionnaire about indications for single-unit crowns. In 4 clinical scenarios, practitioners ranked their likelihood of recommending a single-unit crown. The authors used these responses to calculate a dentist-specific crown factor (range, 0-12). A higher score implied a higher likelihood of recommending a crown. The authors tested certain characteristics for statistically significant associations with the crown factor. A total of 1,777 of 2,132 eligible dentists (83%) responded. Practitioners were most likely to recommend crowns for teeth that were fractured, cracked, or endodontically treated or had a broken restoration. Practitioners overwhelmingly recommended crowns for posterior teeth treated endodontically (94%). Practice owners, practitioners in the Southwest, and practitioners with a balanced workload were more likely to recommend crowns, as were practitioners who used optical scanners for digital impressions. There is substantial variation in the likelihood of recommending a crown. Although consensus exists in some areas (posterior endodontic treatment), variation dominates in others (size of an existing restoration). Recommendations varied according to type of practice, network region, practice busyness, patient insurance status, and use of optical scanners. Recommendations for crowns may be influenced by factors unrelated to tooth and patient variables. A concern for tooth fracture-whether from endodontic treatment, fractured teeth, or large restorations-prompted many clinicians to recommend crowns. Copyright © 2016 American Dental Association. Published by Elsevier Inc. All rights reserved.

  5. Esthetic crown lengthening for maxillary anterior teeth.

    Science.gov (United States)

    Sonick, M

    1997-08-01

    In the maxillary anterior region, the gingival labial margin position is an important parameter in the achievement of an ideal smile. The relationship between the periodontium and the restoration is critical if gingival health and esthetics are to be achieved. Periodontal therapy is a necessary and useful adjunct when any anterior restoration is undertaken. Anterior surgical crown lengthening may be undertaken to avoid restorative margin impingement on the biologic width. Crown lengthening is also used to alter the gingival labial profiles. This article discusses the esthetic parameters of ideal gingival labial positions and presents a classification of crown-lengthening procedures and the procedure for a two-stage crown-lengthening technique. The two-stage crown-lengthening technique is surgically precise because healing is predictable.

  6. Dimethylammonium perchlorate 18-crown-6 monohydrate clathrate

    Directory of Open Access Journals (Sweden)

    Jia-Zhen Ge

    2010-07-01

    Full Text Available The reaction of dimethylamine, 18-crown-6, and perchloric acid in methanol yields the title compound, C2H8N+·ClO4−·C12H24O6·H2O. The dimethylammonium cation and the water molecule interact with the 18-crown-6 unit: N—H...O hydrogen bonds are formed between the ammonium NH2+ group and four O atoms of the crown ether, while the water molecule on the other side of 18-crown-6 ring forms O—H...O hydrogen bonds with two other O atoms of the crown ether. All conventional donors and acceptors in the cations are thus engaged in hydrogen bonding. The ClO4− anion is disordered over two sites, and occupancies for the disordered O atoms were fixed at 0.5. In the crystal, the cations and anions are arranged in alternating layers.

  7. Wave Forces and Overtopping on Crown Walls of Rubble Mound Breakwaters

    DEFF Research Database (Denmark)

    Pedersen, Jan

    in the coastal laboratory at Aalborg University. Based on analyses of experimental data a design method for assessing the maximum wave forces on the vertical face of the crown wall structures has been developed as well as new and more versatile design equation for the related overtopping discharges...... of rubble mound breakwater crown walls. This background motivated the initialization of the present study on wave imposed forces and wave overtopping on crown wall structures. The two subjects where investigated through an excessive parametric model study involving more than 370 long duration test series...

  8. Wear of double crown systems: electroplated vs. casted female part

    Directory of Open Access Journals (Sweden)

    Stefan Bayer

    2012-06-01

    Full Text Available OBJECTIVES: The wear of telescopic crowns is a common problem often reducing the patient's satisfaction with the denture and resulting in a renewal of the denture. The study aims to compare the wear behavior of conical crowns using electroplated copings (group E with standard telescopic crowns with cast female parts (group C. MATERIAL AND METHODS: 10 conical crowns were milled for each group of a cast gold alloy. The specimen of group E had a conicity of 2º. The cast secondary crowns of group C had a 0º design. The electroplated coping was established by direct electroforming. An apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long term wear period. The retention force value and the force-distance integral of the first 0.33 mm of each cycle were calculated. RESULTS: The retentive forces were significantly higher for group E and the integrals were significantly lower for this group except the integral at cycle 10,000. The changes of retention force and integral did not differ significantly between both groups in all phases. The change of the integrals as well as the integral at the particular cycles showed higher interquartile distances for group C. CONCLUSIONS: Within the limitations of this study the tested conical crowns showed clinically acceptable retentive properties. The values reached a range comparable to retentive elements tested in recent literature. The values of group C showed higher ranges. The force measured for group E was significantly higher than for group C but the integrals showed an opposite tendency. The results indicate that an exclusive analysis of the force is not sufficient as the integral is not equivalent to the force although it describes the retentive property of the system in a better way than the force over a distance is

  9. Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns

    Directory of Open Access Journals (Sweden)

    Adil Othman ABDULLAH

    Full Text Available ABSTRACT Objective This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. Material and Methods An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone “PEEK”, Telio CAD-Temp, and Protemp™4 (control group. The crowns were divided into four groups (n=10, Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. Results The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99 µm, PEEK 46.75 (±8.26 µm, Telio CAD-Temp 56.10 (±5.65 µm, and Protemp™4 193.07(±35.96 µm (P0.05. Conclusions CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns.

  10. Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns

    Science.gov (United States)

    ABDULLAH, Adil Othman; TSITROU, Effrosyni A; POLLINGTON, Sarah

    2016-01-01

    ABSTRACT Objective This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. Material and Methods An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone “PEEK”, Telio CAD-Temp, and Protemp™4 (control group). The crowns were divided into four groups (n=10), Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. Results The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99) µm, PEEK 46.75 (±8.26) µm, Telio CAD-Temp 56.10 (±5.65) µm, and Protemp™4 193.07(±35.96) µm (P0.05). Conclusions CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns. PMID:27383707

  11. The Effect of Different Finishing Lines on the Marginal Fitness of Full Contour Zirconia and Glass Ceramic CAD/CAM Crowns (An in-vitro study

    Directory of Open Access Journals (Sweden)

    ZAK Al-Zubaidi

    2015-09-01

    Full Text Available Purpose: The aim of this study was to evaluate the effect of two gingival finishing lines (90° shoulder and deep chamfer on the marginal fitness of two types of full anatomic all-ceramic crowns; zirconia crowns (Zikonzhan and glass ceramic crowns (IPS e-max CAD milled with CAD/CAM system. Materials and Methods: Two dentoform teeth of left maxillary first molar were prepared with chamfer finishing line (CFL and shoulder finishing line (SFL, respectively and duplicated to Nickel-Chromium master dies. Thirty two crowns were fabricated and grouped as follows: Group I: 8 zirconia crowns on CFL; Group II: 8 zirconia crowns on SFL; Group III: 8 glass ceramic crowns on CFL and Group IV: 8 glass ceramic crowns on SFL. Marginal gaps were measured at 4 indentations, each one was at center of each tooth surface and collectively 16 points were measured by using stereomicroscope (160X. The data were analyzed by One-way ANOVA and student t-tests. Results: Group I produced the least marginal gap (73.55µm; followed by Group II (92.60µm, and Group III (151.45µm and the highest marginal gap was recorded by Group IV (162.34µm. Statistical analysis of the data showed that SFL produced significantly greater marginal gap on zirconia crowns in comparison with CFL. However, in glass ceramic crowns, CFL revealed less marginal gap compared to SFL but statistically was not significant. On the other hand, glass ceramic crowns significantly produced a greater marginal gap in comparison to zirconia crowns regardless type of finishing line. Conclusions: deep chamfer margin could be more preferable finishing line than 90° shoulder especially for zirconia full crowns. Furthermore, zirconia crowns could be more advisable than glass ceramic crowns in respect to marginal adaptation.

  12. Enamel wear caused by monolithic zirconia crowns after 6 months of clinical use.

    Science.gov (United States)

    Stober, T; Bermejo, J L; Rammelsberg, P; Schmitter, M

    2014-04-01

    The purpose of this study was to evaluate enamel wear caused by monolithic zirconia crowns and to compare this with enamel wear caused by contralateral natural antagonists. Twenty monolithic zirconia crowns were placed in 20 patients requiring full molar crowns. For measurement of wear, impressions of both jaws were made at baseline after crown cementation and at 6-month follow-up. Mean and maximum wear of the occlusal contact areas of the crowns, of their natural antagonists and of the two contralateral natural antagonists were measured by the use of plaster replicas and 3D laser scanning methods. Wear differences were investigated by the use of two-sided paired Student's t-tests and by linear regression analysis. Mean vertical loss (maximum vertical loss in parentheses) was 10 (43) μm for the zirconia crowns, 33 (112) μm for the opposing enamel, 10 (58) μm for the contralateral teeth and 10 (46) μm for the contralateral antagonists. Both mean and maximum enamel wear were significantly different between the antagonists of the zirconia crowns and the contralateral antagonists. Gender and activity of the masseter muscle at night (bruxism) were identified as possible confounders which significantly affected wear. Under clinical conditions, monolithic zirconia crowns seem to be associated with more wear of opposed enamel than are natural teeth. With regard to wear behaviour, clinical application of monolithic zirconia crowns is justifiable because the amount of antagonistic enamel wear after 6 months is comparable with, or even lower than, that caused by other ceramic materials in previous studies.

  13. Evaluation of different sterilization and disinfection methods on commercially made preformed crowns

    Directory of Open Access Journals (Sweden)

    Yilmaz Y

    2008-01-01

    Full Text Available The aim of this study was to evaluate the changes caused by different sterilization or disinfection methods on the vestibular surface of four commercially made preformed crowns using stereomicroscopy and scanning electron microscopy (SEM. Preformed crowns (NuSmile Primary Anterior Crown (NSC, Kinder Krowns (KK, Pedo Pearls (PP and polycarbonate crowns (PC were sterilized and/or disinfected by one of the following techniques: no sterilization or disinfection (G1 control group; steam autoclaving at 134 °C (30 psi for 4 min (G2; steam autoclaving at 134 °C (30 psi for 12 min (G3; steam autoclaving at 121 °C (15 psi for 30 min (G4; and ultrasonication in a bath containing 4% Lysetol ® AF for 5 min at room temperature (chemical disinfection (G5. Scanning electron micrographs of the crowns were taken before and after their sterilization or disinfection. The changes on the vestibular surface were then scored for the presence or absence of crazing, contour alteration, fracturing, and vestibular surface changes. The data were analyzed statistically using the chi-square test. No changes were observed before and after sterilization or disinfection in the stereomicroscopic evaluation of the vestibular surface of the crowns. However, all methods in which steam autoclaving was used to sterilize the crowns caused significant (P < 0.05 crazing and contour alterations of the vestibular surface of the crowns when they were examined by SEM. Chemical disinfection using an aldehyde-free disinfectant is the preferred method of disinfection for crowns that have been used previously in other dental patients.

  14. Evaluation of different sterilization and disinfection methods on commercially made preformed crowns.

    Science.gov (United States)

    Yilmaz, Y; Guler, C

    2008-12-01

    The aim of this study was to evaluate the changes caused by different sterilization or disinfection methods on the vestibular surface of four commercially made preformed crowns using stereomicroscopy and scanning electron microscopy (SEM). Preformed crowns (NuSmile Primary Anterior Crown (NSC), Kinder Krowns (KK), Pedo Pearls (PP) and polycarbonate crowns (PC)) were sterilized and/or disinfected by one of the following techniques: no sterilization or disinfection (G1 control group); steam autoclaving at 134 degrees C (30 psi) for 4 min (G2); steam autoclaving at 134 degrees C (30 psi) for 12 min (G3); steam autoclaving at 121 degrees C (15 psi) for 30 min (G4); and ultrasonication in a bath containing 4% Lysetol AF for 5 min at room temperature (chemical disinfection) (G5). Scanning electron micrographs of the crowns were taken before and after their sterilization or disinfection. The changes on the vestibular surface were then scored for the presence or absence of crazing, contour alteration, fracturing, and vestibular surface changes. The data were analyzed statistically using the chi-square test. No changes were observed before and after sterilization or disinfection in the stereomicroscopic evaluation of the vestibular surface of the crowns. However, all methods in which steam autoclaving was used to sterilize the crowns caused significant (P < 0.05) crazing and contour alterations of the vestibular surface of the crowns when they were examined by SEM. Chemical disinfection using an aldehyde-free disinfectant is the preferred method of disinfection for crowns that have been used previously in other dental patients.

  15. Success of Hall technique crowns questioned.

    Science.gov (United States)

    Nainar, S M Hashim

    2012-01-01

    Hall technique is a method of providing stainless steel crowns for primary molars without tooth preparation and requires no local anesthesia. Literature review showed inconclusive evidence and therefore this technique should not be used in clinical practice.

  16. Activity relationships for aromatic crown ethers

    CERN Document Server

    Wilson, M J

    1998-01-01

    This thesis involves an investigation of aromatic crown ethers and a study of their binding constants for alkali metals. The study was motivated by the current needs of the semiconductor industry to improve the scavenging of mobile ions from fabricated circuits. A number of aromatic crown ethers have been sulphonated in an attempt to improve their water solubility and cation binding activity. These materials have been extensively studied and their binding activity determined. In collaboration with a molecular modelling study, the effect of ionisable sulphonate groups on the macrocycles' behaviour has been investigated. The broader issue of the effect of substituents in aromatic crown ethers has also been studied with the preparation of a wide range of substituted crown ethers. The cation binding activity of these materials has been found to bear a simple relationship to the electron withdrawing nature of the aromatic substituents. This relationship can be accurately monitored using electronic charge densities...

  17. Reliability of metalloceramic and zirconia-based ceramic crowns.

    Science.gov (United States)

    Silva, N R F A; Bonfante, E A; Zavanelli, R A; Thompson, V P; Ferencz, J L; Coelho, P G

    2010-10-01

    Despite the increasing utilization of all-ceramic crown systems, their mechanical performance relative to that of metal ceramic restorations (MCR) has yet to be determined. This investigation tested the hypothesis that MCR present higher reliability over two Y-TZP all-ceramic crown systems under mouth-motion fatigue conditions. A CAD-based tooth preparation with the average dimensions of a mandibular first molar was used as a master die to fabricate all restorations. One 0.5-mm Pd-Ag and two Y-TZP system cores were veneered with 1.5 mm porcelain. Crowns were cemented onto aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Mouth-motion fatigue was performed, and use level probability Weibull curves were determined. Failure modes of all systems included chipping or fracture of the porcelain veneer initiating at the indentation site. Fatigue was an acceleration factor for all-ceramic systems, but not for the MCR system. The latter presented significantly higher reliability under mouth-motion cyclic mechanical testing.

  18. Distribution of Wave Loads for Design of Crown Walls in Deep and Shallow Water

    DEFF Research Database (Denmark)

    Nørgaard, Jørgen Quvang Harck; Andersen, Thomas Lykke

    2014-01-01

    This paper puts forward a new method to determine horizontal wave loads on rubble mound breakwater crown walls with specific exceedance probabilities based on the formulae by Nørgaard et al. (2013) as well as presents a new modified version of the wave run-up formula by Van der Meer & Stam (1992......). Predictions from the method are compared to measured horizontal wave loads from scaled model tests, and the new method provides results which are in agreement with measured values as long as the wave loads on the crown wall are relatively impulsive. Another aim of the paper has been to compare...... the displacements of a crown wall exposed to wave loads with different exceedance probabilities in an overload situation (in this case the loads exceeded by 0.1 % and 1/250 of the incident waves). The comparison is made using the assumption that the Eigenfrequency of the crown wall and breakwater is significantly...

  19. Comparing Laser and Scalpel for Soft Tissue Crown Lengthening: A Clinical Study.

    Science.gov (United States)

    Farista, Sana; Kalakonda, Butchibabu; Koppolu, Pradeep; Baroudi, Kusai; Elkhatat, Esam; Dhaifullah, Essam

    2016-10-01

    Crown lengthening procedure is aimed at exposure of sufficient crown structure accomplished by a gingivectomy, an apically positioned flap with osseous resection or the use of lasers. Our present clinical study is aimed to assess the clinical effectiveness of a diode laser for functional crown lengthening procedure and to compare it with the conventional procedure using the scalpel. Fourteen patients including males and females, aged 20- 40 years were recruited and divided into two groups to undergo crown lengthening either with the scalpel or the laser. The data obtained was analyzed for intergroup comparison with an Unpaired t-test and intragroup comparison was determined by ANOVA.Analysis of the intergroup results for pain showcased that there was a significant difference (Pcrown lengthening performed with the scalpel.

  20. The Crown Bite Jumping Herbst.

    Science.gov (United States)

    Owen, Reuel

    2003-01-01

    The Crown Bite Jumping Herbst Appliance is evaluated and combined with Straight Wire Arch Fixed Orthodontics in treatment of Class II, Division I malocclusions. This article will evaluate a combined orthodontic approach of "straightening teeth" and an orthognathic approach of "moving jaws or making skeletal changes." Orthodontic treatment cannot be accomplished well without establishing a healthy temporomandibular joint. This is defined by Keller as a joint that is "noiseless, painless and has a normal range of motion without deviation and deflection." It is not prudent to separate orthodontic treatment as its own entity without being aware of the changes in the temporomandibular joint before, during and after treatment. In other words, "If you're doing orthodontics you're doing TMJ treatment." One should treat toward a healthy, beautiful face asking, "Will proposed treatment achieve this goal?" Treatment should be able to be carried out in an efficient manner, minimizing treatment time, be comfortable and affordable for the patient, and profitable for the dentist. The finished treatment should meet Andrews' Six Keys of Occlusion, or Loudon's Twelve Commandments. Above all, do no harm to the patient. We think that a specific treatment plan can embrace these tenets. The focus will be to show Class II treatment using a modified Herbst Appliance and fixed straight wire orthodontics.

  1. Clinical crown lengthening in the esthetic zone.

    Science.gov (United States)

    Camargo, Paulo M; Melnick, Philip R; Camargo, Luciano M

    2007-07-01

    Periodontal surgical procedures consisting of gingival flaps and osseous recontouring are indicated for crown lengthening of several contiguous teeth in the esthetic zone; both in cases where restorations are required and in cases where no restorations are planned, such as in patients with excessive gingival display due to altered passive eruption. Forced tooth eruption via orthodontic extrusion is the technique of choice when clinical crown lengthening is necessary on isolated teeth in the esthetic zone.

  2. Treatment of crown dilaceration: an interdisciplinary approach.

    Science.gov (United States)

    Subramaniam, P; Naidu, P

    2010-01-01

    Trauma to primary teeth can result in a wide range of disturbances to the underlying permanent teeth, such as dilaceration. Root dilacerations occur more commonly than crown dilacerations. This paper is a report of an 11-year-old girl with a missing maxillary left anterior tooth. Past history revealed premature loss of primary maxillary anterior teeth due to trauma. Radiographic examination revealed crown dilaceration of permanent maxillary left central incisor. An interdisciplinary approach in the management of this child is presented herewith.

  3. Comparison of Amount of Primary Tooth Reduction Required for Anterior and Posterior Zirconia and Stainless Steel Crowns.

    Science.gov (United States)

    Clark, Larkin; Wells, Martha H; Harris, Edward F; Lou, Jennifer

    2016-01-01

    To determine if aggressiveness of primary tooth preparation varied among different brands of zirconia and stainless steel (SSC) crowns. One hundred primary typodont teeth were divided into five groups (10 posterior and 10 anterior) and assigned to: Cheng Crowns (CC); EZ Pedo (EZP); Kinder Krowns (KKZ); NuSmile (NSZ); and SSC. Teeth were prepared, and assigned crowns were fitted. Teeth were weighed prior to and after preparation. Weight changes served as a surrogate measure of tooth reduction. Analysis of variance showed a significant difference in tooth reduction among brand/type for both the anterior and posterior. Tukey's honest significant difference test (HSD), when applied to anterior data, revealed that SSCs required significantly less tooth removal compared to the composite of the four zirconia brands, which showed no significant difference among them. Tukey's HSD test, applied to posterior data, revealed that CC required significantly greater removal of crown structure, while EZP, KKZ, and NSZ were statistically equivalent, and SSCs required significantly less removal. Zirconia crowns required more tooth reduction than stainless steel crowns for primary anterior and posterior teeth. Tooth reduction for anterior zirconia crowns was equivalent among brands. For posterior teeth, reduction for three brands (EZ Pedo, Kinder Krowns, NuSmile) did not differ, while Cheng Crowns required more reduction.

  4. Influence of thermomechanical fatigue loading on the fracture resistance of all-ceramic posterior crowns.

    Science.gov (United States)

    Senyilmaz, Dilek Pinar; Canay, Senay; Heydecke, Guido; Strub, Joerg Rudolf

    2010-06-01

    This study evaluated the fracture resistance and the survival rate of different all-ceramic crowns in-vitro after thermomechanical fatigue loading in comparison to porcelain-fused-to-metal posterior crowns. Sixteen crowns for human mandibular first molars were made of each of the following: Cercon, IPS-Empress 2 In-Ceram Zirconia, Procera AllZircon and porcelain-fused-to-metal. Half of the specimens of each group was thermocycled and dynamically loaded using a chewing simulator All samples were thereafter tested for the maximum fracture resistance. The survival rates after 1-2 million cycles in the artificial mouth were 100% in all the tested crown systems. The chewing simulation and thermocycling did not significantly decrease the fracture strength of the ceramic crowns (P>0.005). The median fracture load of Cercon, Procera AllZircon, In-Ceram Zirconia and PFM was significantly higher than IPS-Empress 2 both for loaded and non loaded groups (PZirconia and PFM was not significant (P>0.005). All-ceramic systems showed fracture load values similar to those of porcelain-fused-to-metal molar crowns and therefore may be considered for use in clinical studies.

  5. Seal capability of interim post and core crown with temporary cements

    Directory of Open Access Journals (Sweden)

    Guilherme Bönecker-Valverde

    2010-06-01

    Full Text Available The purpose of the present study was to evaluate the in vitro seal capability of interim post and core crown restorations. Eighty teeth were selected and divided into 8 groups. Four experimental groups received interim posts and core crowns. Half of each group was decoronated at the cementum-enamel junction, groups PCCH and PCZO. The other half was sectioned 2 mm coronal to the cementum-enamel junction, groups PCrZO and PCrCH. The interim post and core crowns were luted with Rely X Temp NE, groups PCrZO and PCZO; Hydro C was used for Groups PCrCH and PCCH. The control groups, PC and PCr, received uncoated post and core crowns; groups OTg and OT were left without interim post and core crowns and were totally open. Infiltration was accessed by dye exposure followed by demineralization of the teeth. The length of the infiltration was measured using digital images taken from the specimens. The images were inserted into the Image Tool 3.0 software. Kruskal-Wallis analysis of variance and Dunn's multiple comparison method were used to test for significant differences among test groups (P < .05. Groups PCrZO and PCrCH showed the least dye penetration, followed by groups PCZO and PCCH. Teeth restored with interim post and core crowns will be subject to leakage. Ethics Committee: 095/2008.

  6. An investigation of crown fuel bulk density effects on the dynamics of crown fire initiation in shrublands

    Science.gov (United States)

    Watcharapong Tachajapong; Jesse Lozano; Shankar Mahalingam; Xiangyang Zhou; David R. Weise

    2008-01-01

    Crown fire initiation is studied by using a simple experimental and detailed physical modeling based on Large Eddy Simulation (LES). Experiments conducted thus far reveal that crown fuel ignition via surface fire occurs when the crown base is within the continuous flame region and does not occur when the crown base is located in the hot plume gas region of the surface...

  7. Resistance of full veneer metal crowns with different forms of axial grooves

    Science.gov (United States)

    Hidayat, A. S.; Masulili, C.; Indrasari, M.

    2017-08-01

    Dental crowns or bridges can occasionally come loose or separate from the tooth during chewing, particularly when they are situated on small, short, and conical teeth. The main cause of this separation is a lack of retention and resistance to the tooth. There are several methods available to increase the retention and resistance of the crown during both inlay and onlay preparation, including parallelism, groove preparation, crown build-up, and surface roughness. The aim of this study was to determine the differences in resistance of full veneer metal crowns with various forms of groove preparation. The study involved the compressive strength testing of a total of 24 specimens, namely six specimens without groove preparation, six specimens with box-shaped grooves, six specimens with V-shaped grooves, and six specimens with half round grooves. The mean values of the metal crowns that separated from the teeth during testing were 27.97 ± 1.08 kgF for the crowns with box-shaped grooves, 6.15 ± 0.22 kgF for those with V-shaped grooves, 1.77 ± 0.12 kgF for those with half round grooves, and 0.95 ± 0.13 kgF for those without grooves. This study found that the resistance is best in crowns with box-shaped grooves, followed by those with V-shaped grooves, half round grooves, and those without groove. When clinicians are working on short and conical molar teeth, it is therefore recommended that box-shaped grooves are used to increase the resistance of the crown.

  8. Assessment of nickel release from stainless steel crowns.

    Directory of Open Access Journals (Sweden)

    Nahid Ramazani

    2014-06-01

    Full Text Available Adverse effects of dental materials, especially metals, have been an important issue in recent decades.The purpose of this study was to determine the amount of nickel released from stainless steel crowns in artificial saliva.In this in-vitro study, 270 stainless steel crowns were divided into five groups, each with nine subgroups. Each group (I to V was comprised of four, five, six, seven and eight crowns, respectively. Each subgroup was placed in a polyethylene jar containing artificial saliva and held in an incubator at 37°C for four weeks. The amount of released nickel was determined on days 1, 7, 14, 21 and 28, using an atomic absorption spectrophotometer. Wilcoxon Signed-Rank and Kruskal-Wallis with Dunn's post hoc tests (SPSS software, v. 18 were used for statistical analysis at a significance level of 0.05.The mean level of nickel on day 1 was more than that of day 7; this difference was statistically significant for all groups (P < 0.05, except for group II (P = 0.086. Also, the mean difference of released nickel between the groups was significant on day 1 (P = 0.006 and was insignificant on day 7 (P = 0.620. The nickel levels were zero on days 14, 21, and 28.The amount of nickel was below the toxic level and did not exceed the dietary intake.

  9. Urban Crowns: crown analysis software to assist in quantifying urban tree benefits

    Science.gov (United States)

    Matthew F. Winn; Sang-Mook Lee Bradley; Philip A. Araman

    2010-01-01

    UrbanCrowns is a Microsoft® Windows®-based computer program developed by the U.S. Forest Service Southern Research Station. The software assists urban forestry professionals, arborists, and community volunteers in assessing and monitoring the crown characteristics of urban trees (both deciduous and coniferous) using a single side-view digital photograph. Program output...

  10. Influence of application site of provisional cement on the marginal adaptation of provisional crowns

    Directory of Open Access Journals (Sweden)

    Mayra Cardoso

    2008-06-01

    Full Text Available INTRODUCTION: Marginal discrepancies may lead to cement washout and marginal leakage, damaging periodontal and pulp tissues or causing premature loss of the restoration. PURPOSE: This study evaluated the influence of application site of provisional cement on the marginal adaptation of provisional crowns. MATERIAL AND METHODS: Four different application sites of provisional cement (Temp Bond NE, Kerr Corporation were used for cementation of provisional crowns on phantom teeth prepared for full crown restorations, performing 4 experimental groups (n=10: cement applied to all internal surfaces of the crown (CAO; cement applied to all internal surfaces of the crown, except for the occlusal surface (CA; cement applied to the cervical crown margin (CM; and cement applied to the cervical tooth margin (TM. A comparison microscope (Mitutoyo America Corporation was used to measure the distances between the internal tangents of two circular marks, one made on the provisional crown and one made apical to the tooth preparation margin, in areas corresponding to buccal, lingual, mesial and distal surfaces. Marginal adaptation was determined before and after cementation, with 0.0001-mm accuracy. Data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. RESULTS: Mean values of marginal opening obtained for each group were: CAO: 145 µm; CA: 67 µm; CM: 46 µm; TM: 34 µm. CA, CM and TM presented significantly lower marginal openings than CAO (p<0.05. CONCLUSION: complete filling of the crown with provisional cement, including the occlusal surface, provided grater marginal discrepancies when compared to the other methods evaluated.

  11. Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

    Science.gov (United States)

    Anastassova-Yoshida, Yana; Nothdurft, Frank Phillip; von See, Constantin; Pospiech, Peter

    2016-01-01

    PURPOSE The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method. MATERIALS AND METHODS An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture. RESULTS The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly. CONCLUSION The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns. PMID:26949485

  12. In vitro failure of crowns produced by two CAD/CAM systems.

    Science.gov (United States)

    Donnelly, Thomas J; Burke, F J Trevor

    2011-09-01

    Previous laboratory studies have demonstrated satisfactory fracture resistance of all-ceramic crowns placed using a resin-composite luting material and a dentine bonding system. This study investigated the fracture resistance of teeth restored using CAD/CAM technology, namely, Zirconia Based crowns and Cerec produced feldspathic porcelain crowns, both luted with a self adhesive resin luting material (RelyX Unicem Clicker 3M ESPE). Standardized preparations were carried out on two groups often sound, unrestored, maxillary premolar teeth. Ceramic crowns were constructed to have a thickness of 2mm at their midline fissure. Compressive fracture resistance was determined for each group using a Universal Testing Machine. The failure modes were also examined visually and interpreted according to a chosen scale. Mean Compressive fracture resistance of 746 (147)N and 1630 (175)N were recorded for the Cerec and Lava groups respectively; differences were statistically significant (p < 0.001). The fracture resistance of teeth restored with Lava crowns is significantly greater than a similar group of teeth restored with Cerec crowns.

  13. A novel transferable individual tree crown delineation model based on Fishing Net Dragging and boundary classification

    Science.gov (United States)

    Liu, Tao; Im, Jungho; Quackenbush, Lindi J.

    2015-12-01

    This study provides a novel approach to individual tree crown delineation (ITCD) using airborne Light Detection and Ranging (LiDAR) data in dense natural forests using two main steps: crown boundary refinement based on a proposed Fishing Net Dragging (FiND) method, and segment merging based on boundary classification. FiND starts with approximate tree crown boundaries derived using a traditional watershed method with Gaussian filtering and refines these boundaries using an algorithm that mimics how a fisherman drags a fishing net. Random forest machine learning is then used to classify boundary segments into two classes: boundaries between trees and boundaries between branches that belong to a single tree. Three groups of LiDAR-derived features-two from the pseudo waveform generated along with crown boundaries and one from a canopy height model (CHM)-were used in the classification. The proposed ITCD approach was tested using LiDAR data collected over a mountainous region in the Adirondack Park, NY, USA. Overall accuracy of boundary classification was 82.4%. Features derived from the CHM were generally more important in the classification than the features extracted from the pseudo waveform. A comprehensive accuracy assessment scheme for ITCD was also introduced by considering both area of crown overlap and crown centroids. Accuracy assessment using this new scheme shows the proposed ITCD achieved 74% and 78% as overall accuracy, respectively, for deciduous and mixed forest.

  14. Evaluation of polymer inclusion membranes containing crown ethers for selective cesium separation from nuclear waste solution.

    Science.gov (United States)

    Mohapatra, P K; Lakshmi, D S; Bhattacharyya, A; Manchanda, V K

    2009-09-30

    Transport behaviour of (137)Cs from nitric acid feed was investigated using cellulose triacetate plasticized polymer inclusion membrane (PIM) containing several crown ether carriers viz. di-benzo-18-crown-6 (DB18C6), di-benzo-21-crown-7 (DB21C7) and di-tert-butylbenzo-18-crown-6 (DTBB18C6). The PIM was prepared from cellulose triacetate (CTA) with various crown ethers and plasticizers. DTBB18C6 and tri-n-butyl phosphate (TBP) were found to give higher transport rate for (137)Cs as compared to other carriers and plasticizers. Effect of crown ether concentration, nitric acid concentration, plasticizer and CTA concentration on the transport rate of Cs was also studied. The Cs selectivity with respect to various fission products obtained from an irradiated natural uranium target was found to be heavily dependent on the nature of the plasticizer. The present work shows that by choosing a proper plasticizer, one can get either good transport efficiency or selectivity. Though TBP plasticized membranes showed good transport efficiency, it displayed poor selectivities. On the other hand, an entirely opposite separation behaviour was observed with 2-nitrophenyloctylether (NPOE) plasticized membranes suggesting the possible application of the later membranes for the removal of bulk (137)Cs from the nuclear waste. The stability of the membrane was tested by carrying out transport runs for nearly 25 days.

  15. Influence of different post core materials on the color of Empress 2 full ceramic crowns

    Institute of Scientific and Technical Information of China (English)

    GE Jing; WANG Xin-zhi; FENG Hai-lan

    2006-01-01

    Background For esthetic consideration, dentin color post core materials were normally used for all-ceramic crown restorations. However, in some cases, clinicians have to consider combining a full ceramic crown with a metal post core. Therefore, this experiment was conducted to test the esthetical possibility of applying cast metal post core in a full ceramic crown restoration.Methods The color of full ceramic crowns on gold and Nickel-Chrome post cores was compared with the color of the same crowns on tooth colored post cores. Different try-in pastes were used to imitate the influence of a composite cementation on the color of different restorative combinations. The majority of patients could not detect any color difference less than △E 1.8 between the two ceramic samples. So, △E 1.8 was taken as the objective evaluative criterion for the evaluation of color matching and patients' satisfaction.Results When the Empress 2 crown was combined with the gold alloy post core, the color of the resulting material was similar to that of a glass fiber reinforced resin post core (△E = 0.3). The gold alloy post core and the try-in paste did not show a perceptible color change in the full ceramic crowns, which indicated that the color of the crowns might not be susceptible to change between lab and clinic as well as during the process of composite cementation. Without an opaque covering the Ni-Cr post core would cause an unacceptable color effect on the crown (△E = 2.0), but with opaque covering, the color effect became more clinically satisfactory (△E=1.8).Conclusions It may be possible to apply a gold alloy post core in the Empress 2 full ceramic crown restoration when necessary. If a non-extractible Ni-Cr post core exists in the root canal, it might be possible to restore the tooth with an Empress 2 crown after coveting the labial surface of the core with one layer of opaque resin cement.

  16. Effect of water temperature on the fit of provisional crown margins during polymerization: An in vitro study

    Directory of Open Access Journals (Sweden)

    Vivekanandan Ramkumar

    2012-01-01

    Full Text Available Aim: To evaluate the effect of water temperature on the marginal fit of bis-acrylic composite provisional crown during resin polymerization. Materials and Methods: Precisely machined 10 brass master dies were designed to simulate molar teeth. Five brass dies were selected and precisely machined to simulate all ceramic crown preparation. An acrylic jaw replica was made in which brass dies were arranged equidistant from each other. A custom-made metallic tray was fabricated on the acrylic jaw replica to make polyvinyl siloxane impression matrix. Bis-acrylic composite resin provisional crowns were made using polyvinyl siloxane impression matrix. Provisional crowns were polymerized at room temperature (Group I direct technique, on dental stone cast; Group I indirect technique crowns and at different water temperatures (Group II direct technique crowns. The vertical marginal gap between all the provisional crown margins and the finish line of brass dies was measured using a Research Stereomicroscope System. Results: The results were statistically analyzed using one-way analysis of variance (ANOVA test and Newman-Keul′s test. The results showed that crowns polymerized in 20°C and 30°C water had marginal gap approximately three times smaller than those polymerized in 30°C air, due to the reduced polymerization shrinkage. Conclusion: This study shows that crowns polymerized in 20°C and 30°C water had mean vertical marginal gap approximately three times smaller than those polymerized in 30°C air. It was approximately closer to that of crowns fabricated by indirect technique. Warmer water also supposedly hastens polymerization.

  17. Evaluation of tensile retention of Y-TZP crowns after long-term aging: effect of the core substrate and crown surface conditioning.

    Science.gov (United States)

    Amaral, R; Rippe, M; Oliveira, B G; Cesar, P F; Bottino, M A; Valandro, L F

    2014-01-01

    This study evaluated the effect of the core substrate type (dentin and composite resin) on the retention of crowns made of yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP), submitted to three inner surface conditionings. For this purpose, 72 freshly extracted molars were embedded in acrylic resin, perpendicular to the long axis, and prepared for full crowns: 36 specimens had crown preparations in dentin; the remaining 36 teeth had the crowns removed, and crown preparations were reconstructed with composite resin plus fiber posts with dimensions identical to the prepared dentin. The preparations were impressed using addition silicone, and 72 Y-TZP copings for the tensile test were produced. Cementation was performed with a dual-cured cement containing phosphate monomers. For cementation, the crown preparation (dentin or resin) was conditioned with the adhesive system, and the ceramic was subjected to one of three surface treatments: isopropyl alcohol, tribochemical silica coating, or thin low-fusing glassy porcelain layer application plus silanization. After 24 hours, all specimens were submitted to thermocycling (6000 cycles) and placed in a special tensile testing device in a universal testing machine to determine failure loads. The failure modes of all samples were analyzed under a stereomicroscope. Two-way analysis of variance showed that the surface treatment and substrate type (α=0.05) affected the tensile retention results. The dentin substrate presented the highest tensile retention values, regardless of the surface treatment. When the substrate was resin, the tribochemical silica coating and low-fusing glaze application plus silanization groups showed the higher retention values.

  18. Effect of Cervical Collar Removal on the Fracture Load of Anterior Zirconia Crowns.

    Science.gov (United States)

    Campos, Fernanda; Cardoso, Mayra; de Melo, Renata Marques; Bottino, Marco Antonio; Souza, Rodrigo Oa

    The objective of this study was to assess the influence of the extension of collar and fatigue cycling on the fracture load of anterior zirconia crowns. A total of 60 anterior full-crown preparations (central incisor) were machined in glass fiber-filled epoxy resin. Zirconia copings were designed and milled using computer-aided design/computer-assisted manufacture (thickness: buccal = 0.62 mm, lingual = 0.65 mm, incisal = 0.72 mm). The cervical collars (occlusogingival height = 0.8 mm, buccolingual width = 1.0 mm) were totally or partially (buccal face) removed for modified copings. They were randomly allocated to six groups according to the type of cervical collar design and the presence (or not) of fatigue cycling (n = 10). The veneering ceramic layer was pressed, and the crowns were cemented with resin cement. The samples were tested until fracture in a universal testing machine and analyzed by stereomicroscopy. Data were statistically analyzed by two-way analysis of variance and Tukey test (5%). Removal of the cervical collar significantly affected the fracture strength of zirconia crowns (P = .000), whereas fatigue cycling did not (P = .428). The mean failure load was lower in the groups with no collar. The most frequent failure modes were cracking of the veneer porcelain in collarless crowns and catastrophic failure in the others. The authors concluded that removal of the vestibular collar of zirconia copings in anterior crowns does not reduce the fracture load of the crowns. However, removal of the entire collar reduces the fracture load and cannot be recommended.

  19. The Retentive Strength of Cemented Zirconium Oxide Crowns after Dentin Pretreatment with Desensitizing Paste Containing 8% Arginine and Calcium Carbonate.

    Science.gov (United States)

    Pilo, Raphael; Harel, Noga; Nissan, Joseph; Levartovsky, Shifra

    2016-03-25

    The effect of dentin pretreatment with Desensitizing Paste containing 8% arginine and calcium carbonate on the retention of zirconium oxide (Y-TZP) crowns was tested. Forty molar teeth were mounted and prepared using a standardized protocol. Y-TZP crowns were produced using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. The 40 prepared teeth were either pretreated with Desensitizing Paste or not pretreated. After two weeks, each group was subdivided into two groups, cemented with either Resin Modified Glass Ionomer Cement (RMGIC) or Self Adhesive Resin Cement (SARC)). Prior to cementation, the surface areas of the prepared teeth were measured. After aging, the cemented crown-tooth assemblies were tested for retentive strength using a universal testing machine. The debonded surfaces of the teeth and crowns were examined microscopically at 10× magnification. Pretreating the dentin surfaces with Desensitizing Paste prior to cementation did not affect the retention of the Y-TZP crowns. The retentive values for RMGIC (3.04 ± 0.77 MPa) were significantly higher than those for SARC (2.28 ± 0.58 MPa). The predominant failure modes for the RMGIC and SARC were adhesive cement-dentin and adhesive cement-crown, respectively. An 8.0% arginine and calcium carbonate in-office desensitizing paste can be safely used to reduce post-cementation sensitivity without reducing the retentive strength of Y-TZP crowns.

  20. Comparative evaluation of shear bond strength of conventional composite resin and nanocomposite resin to sandblasted primary anterior stainless steel crown

    Directory of Open Access Journals (Sweden)

    Khatri A

    2007-06-01

    Full Text Available To evaluate and compare the shear bond strength of conventional composite resin and nanocomposite resin to sandblasted primary anterior stainless steel crown. The study samples consisted of 30 primary anterior stainless steel crowns (Unitek TM , size R4, embedded in resin blocks with crown, in test groups of 15 samples each. Mounting of the crown was done using resin block with one crown each. Sandblasting was done and the bonding agent Prime and Bond NT (Dentsply was applied on the labial surface of the primary anterior sandblasted crown. The composite resin and nanocomposite resin were placed into the well of Teflon jig and bonded to Stainless Steel Crowns. The cured samples were placed in distilled water and stored in incubator at 37°C for 48 hours. Shear bond strength was measured using universal testing machine (Hounsefield U.K. Model, with a capacity of 50 KN. Independent sample ′t′ test revealed a nonsignificant ( P < 0.385 difference between mean shear bond strength values of conventional and nanocomposite group. The bond strength values revealed that nanocomposite had slightly higher mean shear bond strength (21.04 ± 0.56 compared to conventional composite (20.78 ± 0.60. It was found that conventional composite resin and nanocomposite resin had statistically similar mean shear bond strength, with nanocomposite having little more strength compared to conventional composite.

  1. Effect of preparation taper and height on strength and retention of zirconia crowns.

    Science.gov (United States)

    Ersu, Bahadir; Narin, Duygu; Aktas, Guliz; Yuzugullu, Bulem; Canay, Senay

    2012-01-01

    This study aimed to determine the effect of the taper and height of tooth preparations on the fracture strength and retention of zirconia crowns. Sixty-four dies were designed to simulate a crown preparation. Dies were machined with a height of either 4 mm (n = 16) or 7 mm (n = 16) and a taper of either 6 degrees (n = 16) or 20 degrees (n = 16). Copings were created from Lava zirconia blanks. Retention tests were performed using a universal testing machine. Copings were recemented on the dies, thermocycled, and tested for fracture strength. Data were analyzed using factorial analysis of variance. Retention was greater in the taller and less-tapered preparation designs. Taller preparations showed superior fracture strength. Preparing posterior teeth with higher axial walls and less taper is recommended to achieve increased retention and strength for zirconia crowns.

  2. Needle-Age Related Variability in Nitrogen, Mobile Carbohydrates, and δ13C within Pinus koraiensis Tree Crowns

    Science.gov (United States)

    Yan, Cai-Feng; Han, Shi-Jie; Zhou, Yu-Mei; Wang, Cun-Guo; Dai, Guan-Hua; Xiao, Wen-Fa; Li, Mai-He

    2012-01-01

    For both ecologists and physiologists, foliar physioecology as a function of spatially and temporally variable environmental factors such as sunlight exposure within a tree crown is important for understanding whole tree physiology and for predicting ecosystem carbon balance and productivity. Hence, we studied concentrations of nitrogen (N), non-structural carbohydrates (NSC = soluble sugars + starch), and δ13C in different-aged needles within Pinus koraiensis tree crowns, to understand the needle age- and crown position-related physiology, in order to test the hypothesis that concentrations of N, NSC, and δ13C are needle-age and crown position dependent (more light, more photosynthesis affecting N, NSC, and δ13C), and to develop an accurate sampling strategy. The present study indicated that the 1-yr-old needles had significantly higher concentration levels of mobile carbohydrates (both on a mass and an area basis) and Narea (on an area basis), as well as NSC-N ratios, but significantly lower levels of Nmass (on a mass basis) concentration and specific leaf area (SLA), compared to the current-year needles. Azimuthal (south-facing vs. north-facing crown side) effects were found to be significant on starch [both on a mass (STmass) and an area basis (STarea)], δ13C values, and Narea, with higher levels in needles on the S-facing crown side than the N-facing crown side. Needle Nmass concentrations significantly decreased but needle STmass, STarea, and δ13C values significantly increased with increasing vertical crown levels. Our results suggest that the sun-exposed crown position related to photosynthetic activity and water availability affects starch accumulation and carbon isotope discrimination. Needle age associated with physiological activity plays an important role in determining carbon and nitrogen physiology. The present study indicates that across-scale sampling needs to carefully select tissue samples with equal age from a comparable crown position

  3. Stress and Reliability Analysis of a Metal-Ceramic Dental Crown

    Science.gov (United States)

    Anusavice, Kenneth J; Sokolowski, Todd M.; Hojjatie, Barry; Nemeth, Noel N.

    1996-01-01

    Interaction of mechanical and thermal stresses with the flaws and microcracks within the ceramic region of metal-ceramic dental crowns can result in catastrophic or delayed failure of these restorations. The objective of this study was to determine the combined influence of induced functional stresses and pre-existing flaws and microcracks on the time-dependent probability of failure of a metal-ceramic molar crown. A three-dimensional finite element model of a porcelain fused-to-metal (PFM) molar crown was developed using the ANSYS finite element program. The crown consisted of a body porcelain, opaque porcelain, and a metal substrate. The model had a 300 Newton load applied perpendicular to one cusp, a load of 30ON applied at 30 degrees from the perpendicular load case, directed toward the center, and a 600 Newton vertical load. Ceramic specimens were subjected to a biaxial flexure test and the load-to-failure of each specimen was measured. The results of the finite element stress analysis and the flexure tests were incorporated in the NASA developed CARES/LIFE program to determine the Weibull and fatigue parameters and time-dependent fracture reliability of the PFM crown. CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/Or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program.

  4. Clinical Evaluation and Parental Satisfaction with Pediatric Zirconia Anterior Crowns.

    Science.gov (United States)

    Holsinger, Daniel M; Wells, Martha H; Scarbecz, Mark; Donaldson, Martin

    2016-01-01

    The purpose of this study was to evaluate the clinical success of and parental satisfaction with anterior pediatric zirconia crowns. A retrospective analysis of maxillary anterior pediatric zirconia crowns was performed. Crowns were evaluated for retention, gingival health, color match, contour, marginal integrity, and opposing tooth wear. Parental satisfaction regarding the esthetics of the crowns and parental perception of the impact of treatment on the child's appearance and oral health were evaluated by questionnaire. Fifty-seven crowns were evaluated in 18 children. Eight teeth were lost to exfoliation, three were extracted due to pathology, and two crowns debonded, leaving 44 available for examination. The average crown age at time of examination was 20.8 months. Sixteen crowns (36 percent) displayed gingival inflammation and color mismatch. No recurrent caries or opposing tooth wear was noted. Parents reported high satisfaction with the color, size, and shape of the crowns. The majority of parents reported that crowns improved the appearance and oral health of their child (78 percent and 83 percent, respectively). Eight-nine percent of parents reported that they would highly recommend these crowns. Zirconia crowns are clinically acceptable restorations in the primary maxillary anterior dentition. Parental satisfaction with zirconia crowns is high.

  5. Surgical crown lengthening for function and esthetics.

    Science.gov (United States)

    Allen, E P

    1993-04-01

    Clinical crown lengthening is a useful procedure to provide tooth length for proper restoration of a tooth without compromising the periodontium or the retentive qualities of the restoration. It is also useful for enhancing maxillary anterior esthetics. Crown lengthening may be as simple as a limited removal of soft tissue or as complex as orthodontic extrusion followed by flap with osseous surgery on a tooth requiring endodontic therapy. Total treatment could thus involve endodontic, orthodontic, periodontic, and restorative procedures. Careful evaluation, case selection, treatment planning, and surgical treatment following the principles outlined in this article can achieve results that meet the functional and esthetic challenges of current dental practice.

  6. EL CROWN HALL. CONTEXTO Y PROYECTO

    Directory of Open Access Journals (Sweden)

    Laura Lizondo Sevilla

    2010-05-01

    Full Text Available RESUMEN El artículo enmarca el edificio del Crown Hall en el contexto docente y arquitectónico de Mies van der Rohe. Revisa sus inicios en la Bauhaus con su primera intervención en un espacio docente para la Bauhaus de Berlín en 1932, así como su marcha a Estados Unidos, los planteamientos arquitectónicos del campus del IIT y el proyecto del Crown Hall. El texto incide en el estudio del proceso proyectual del Crown Hall analizando la evolución de su concepción arquitectónica a través de las diferentes versiones del proyecto. Se constata la transición desde los primeros planteamientos arquitectónicos de los edificios del campus del IIT proyectados por Mies hacia el planteamiento del gran espacio unitario del Crown Hall. Este proyecto se puede entender desde la creciente importancia de la estructura, la claridad constructiva y el manejo del acero y vidrio como únicos materiales de la imagen del edificio y el carácter flexible y unitario del espacio. Finalmente se hace referencia al concepto del "espacio universal" en la arquitectura de Mies, como un concepto abstracto que supera los de flexibilidad de uso o unidad espacial, insinuando, a modo de reflexión, las principales variables que definirían el espacio universal miesiano.SUMMARY The article showcases the Crown Hall building in the educational and architectural context of Mies van der Rohe. It reviews his beginnings in the Bauhaus with his first intervention in an educational space for the Bauhaus of Berlin in 1932, as well as his sojourn to the United States, and the architectural approaches to the IIT campus and the Crown Hall project. The text touches on the study of the planning process for the Crown Hall, analysing the evolution of its architectural conception, through the different versions of the project. The article covers the transition from the first architectural approaches for the IIT campus buildings, planned by Mies, to the approach of the large unitary space of

  7. Treatment of crown dilaceration: An interdisciplinary approach

    Directory of Open Access Journals (Sweden)

    Subramaniam P

    2010-03-01

    Full Text Available Trauma to primary teeth can result in a wide range of disturbances to the underlying permanent teeth, such as dilaceration. Root dilacerations occur more commonly than crown dilacerations. This paper is a report of an 11-year-old girl with a missing maxillary left anterior tooth. Past history revealed premature loss of primary maxillary anterior teeth due to trauma. Radiographic examination revealed crown dilaceration of permanent maxillary left central incisor. An interdisciplinary approach in the management of this child is presented herewith.

  8. [The method of esthetic crown restoration with composite resin jacket crown in primary molars].

    Science.gov (United States)

    Doi, K; Shibui, N; Suda, M; Uehara, M; Karibe, H; Kondou, K

    1990-10-01

    The term "esthetics" has recently been also used in the dental field, and a field called esthetic dentistry is increasingly being noted. The number of not only adult but also pediatric patients who visit for treatment aiming at esthetic recovery is being increased. Inpedodontics, composite resin of the coronal color is generally used in the restoration of deciduous incisors. However, the method using metal crowns for the deciduous teeth is used for the deciduous molars at present. We applied a composite resin jacket crown to the deciduous molar in a way similar to that of esthetic crown restoration for the anterior teeth. The surgical procedure before crown preparation varied slightly according to the presence or absence of pulpal treatment of vital teeth and with non-vital teeth, but the application was performed as follows: 1) Desensitization of pulp, pulpal treatment and core construction. 2) Preparation of crown. 3) Selection, trial set and occlusal equilibration of a metal crown for the deciduous tooth. 4) Precision impression with a silicone impression material. 5) Removal of the metal crown for the deciduous tooth from the impression material. 6) Making of an under-cut to the abutment tooth on the buccal lingual side. 7) Filling of the impression with chemical polymerization resin. 8) Application of pressure in the oral cavity. 9) Adjustment of edge and crown forms. Thus, the preparation method for the composite resin jacket crown was relatively simple. Since this surgery, the patient has been followed up for 1 year and 6 months, and no specifically troublesome points have been observed clinically. The patient and her parents are satisfied with the results.(ABSTRACT TRUNCATED AT 250 WORDS)

  9. Fracture load and failure analysis of zirconia single crowns veneered with pressed and layered ceramics after chewing simulation.

    Science.gov (United States)

    Stawarczyk, Bogna; Ozcan, Mutlu; Roos, Malgorzata; Trottmann, Albert; Hämmerle, Christoph H F

    2011-01-01

    This study determined the fracture load of zirconia crowns veneered with four overpressed and four layered ceramics after chewing simulation. The veneered zirconia crowns were cemented and subjected to chewing cycling. Subsequently, the specimens were loaded at an angle of 45° in a Universal Testing Machine to determine the fracture load. One-way ANOVA, followed by a post-hoc Scheffé test, t-test and Weibull statistic were performed. Overpressed crowns showed significantly lower fracture load (543-577 N) compared to layered ones (805-1067 N). No statistical difference was found between the fracture loads within the overpressed group. Within the layered groups, LV (1067 N) presented significantly higher results compared to LC (805 N). The mean values of all other groups were not significantly different. Single zirconia crowns veneered with overpressed ceramics exhibited lower fracture load than those of the layered ones after chewing simulation.

  10. Wave Loads on Rubble Mound Breakwater Crown Walls in Long Waves

    DEFF Research Database (Denmark)

    Røge, Mads Sønderstrup; Færch Christensen, Nicole; Thomsen, Jonas Bjerg;

    2014-01-01

    This paper evaluates the formulae by Nørgaard et al. (2013) for predicting wave loads on rubble mound breakwater crown walls on new model tests. The formulae are tested outside their validation area by means of waves with a low wave steepness and low run-up height compared to the armour freeboard...

  11. Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns

    Directory of Open Access Journals (Sweden)

    Ahmed Attia

    2010-04-01

    Full Text Available OBJECTIVE: This study investigated the durability of repaired all-ceramic crowns after cyclic loading. MATERIAL AND METHODS: Eighty In-ceram zirconia crowns were fabricated to restore prepared maxillary premolars. Resin cement was used for cementation of crowns. Palatal cusps were removed to simulate fracture of veneering porcelain and divided into 4 groups (n = 20. Fracture site was treated before repair as follows: roughening with diamond bur, (DB; air abrasion using 50 µm Al2O3, (AA and silica coating using Cojet system followed by silane application, (SC. Control group (CG 20 specimens were left without fracture. Palatal cusps were repaired using composite resin. Specimens were stored in water bath at 37ºC for one week. Ten specimens of each group were subjected to cyclic loading. Fracture load (N was recorded for each specimen using a universal testing machine. Two-way analysis of variance (ANOVA and Tukey honestly significant difference (HSD test (a=.05 were used for statistical analysis. RESULTS: There was statistically significant difference between control and tested groups, (p<0.001. Post Hoc analysis with the Tukey HSD test showed that cyclic loading fatigue significantly decreased means fracture load of control and test groups as follows (CG, 950.4±62.6 / 872.3±87.4, P = 0.0004, (DB, 624.2 ±38 / 425.5± 31.7, P <.001, (AA, 711.5 ±15.5 / 490 ± 25.2, p <0.001 and (SC, 788.7 ± 18.1 / 610.2 ± 25.2, P <.001, while silica coating and silane application significantly increased fracture load of repaired crowns (p<0.05. CONCLUSION: Repair of fractured In-ceram zirconia crowns after chairside treatment of the fracture site by silica coating and silane application could improve longevity of repaired In-ceram zirconia crowns.

  12. Clinical and Radiographic Evaluation of Pulpotomized Primary Molars Restored with Stainless Steel Crown and Amalgam

    Directory of Open Access Journals (Sweden)

    Haghgoo R.

    2011-08-01

    Full Text Available Statement of Problem: Pulpotomy is the most common pulp treatment in primary teeth. Final restoration of the pulpotomized primary molar can affect the success rate of treatment. Purpose: The aim of this study was to evaluate the success rate of formocresol pulpotomy in primary molars restored with stainless steel crowns as compared to those restored with amalgam.Materials and Method: In this randomized clinical trial study, 110 primary molars to be treated with pulpotomy were treated by a conventional pulpotomy technique. Then these teeth were randomly divided into 2 groups: amalgam and crown. 55 teeth were restored by stainless steel crown and 55 by amalgam. The clinical and radiographic evaluation was done at 6-12-24 months. The data were analyzed by Exact Fisher test.Results: During the 6 months of evaluation, no clinical and radiographic failure was seen. In the 12 months of follow up in the amalgam group, 1 case showed swelling and furcal radiolucency. During the 24 months of evaluation, mobility was seen in 2 teeth in the crown group, and in the amalgam group radiolucency was seen in 1 case, mobility in 1 case, and internal resorption in 1 tooth. Exact Fisher test showed that there was no significant difference in the success rate of pulpotomized molars restored by stainless steel crown and amalgam.Conclusion: If the tooth is selected correctly for pulpotomy, SSC and amalgam restoration can be used as the final restoration.

  13. New atraumatic easy removal technique for permanently cemented crown

    Directory of Open Access Journals (Sweden)

    Pravinkumar G Patil

    2012-01-01

    Full Text Available Removal of a permanently cemented crown or fixed partial denture is a cumbersome procedure for a prosthodontist, especially when there is no purchase point available to remove it. The technique described in this article consists of sectioning of a crown on facial surface followed by removal of the crown with orthodontic plier. This technique does not damage the gingival/periodontal tissues or underlying tooth structure as the crown need not to be removed with jerky back-action force.

  14. Three different surgical techniques of crown lengthening: A comparative study

    OpenAIRE

    Ramya Nethravathy; Santhana Krishnan Vinoth; Ashwin Varghese Thomas

    2013-01-01

    Introduction: A short clinical crown may lead to poor retention form thereby leading to improper tooth preparation. Surgical crown lengthening procedure is done to increase the clinical crown length without violating the biologic width. Several techniques have been proposed for clinical crown lengthening which includes gingivectomy, apically displaced flap with or without resective osseous surgery, and surgical extrusion using periotome. Objective: The aim of this paper is to compare clinical...

  15. Comparison of Primary Molar Crown Dimensions with Stainless Steel Crowns in a Sample of Iranian Children.

    Science.gov (United States)

    Afshar, Hossein; Kamali Sabeti, Arghavan; Shahrabi, Mahdi

    2015-01-01

    Background and aims. Due to anatomic variation in tooth anatomy between populations, this study compared the buccolingual (BL) and mesiodistal (MD) dimensions of primary molars with those of stainless steel crowns (SSCs) in anIranian population. Materials and methods. Impressions were taken from both dental arches of children, and casts were poured. Teeth with caries, restoration, hypoplasia or other dental anomalies were excluded. 216 primary molars were selected and divided into 4 groups of 54 each (maxillary and mandibular first and second primary molars). MD/BL dimensions were measured using a digital caliper with 0.01 mm precision on casts and SCCs (3M brand). Data were assessed using paired t-test, post hoc test and ANOVA. P < 0.05 was considered statistically significant. Results. The MD dimension of the lower first molar SSC and the BL dimension of the lower second molar SSC had the least difference with the corresponding values of the respective teeth. The MD dimension of the upper second molar SSC and the BL dimension of the upper first molar SSC had the greatest difference with the corresponding values in the respective teeth. Comparison of the two different brands of SSCs for the upper first molar revealed that both types had significant differences with the teeth in terms of both MD (P = 0.0) and BL (P = 0.0) dimensions. Conclusion. In the studied population, best adaptation was seen in second lower molars and the least adaptationswere seen in first and second upper molars.

  16. Clinical crown lengthening - a case report.

    Science.gov (United States)

    Lipska, Weronika; Lipski, Marcin; Lisiewicz, Małgorzata; Gala, Andrzej; Gronkiewicz, Krzysztof; Darczuk, Dagmara; Chomyszyn-Gajewska, Maria

    2015-01-01

    Maintaining healthy parodontium during teeth restoration procedures is an indispensable condition for obtain- ing regular functionning and esthetics. Thus, the knowledge of correct anatomy and the influence of filling and complement on paradontium tissue is vital. Difficulty in maintaining appropriate gingival biological width (GBW) is a frequent problem encountered in this type of reconstruction. Preservation of unchanged biological width conditions predictible treatment result and, what is more, lack of inflammatory lesions in marginal parodontium. The ideal situation for parodontium is localizing the filling/complement border supragingivaly, which is at least 3 mm from alveolar process edge. In the case, when the above conditions are impossible to fulfil, elongation of clinical crown is a metod of choice. The effect is possible to achieve by surgical treatment or combined orthodontic - surgical treatment. Surgical treatment is faster and preferred procedure for indirect reconstruction, where achieving high clinical crown is necessary. Three clinical cases of performing method of surgical clinical crown elongation were presented in the article. Performing the described procedure enables correct tooth crown reconstruction and, what is most important, keeping individual toothing.

  17. 21 CFR 872.3330 - Preformed crown.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Preformed crown. 872.3330 Section 872.3330 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL... device also may be intended for use as a functional restoration for a badly decayed deciduous (baby...

  18. A Comparative Evaluation for Biologic Width following Surgical Crown Lengthening Using Gingivectomy and Ostectomy Procedure.

    Science.gov (United States)

    Ganji, Kiran Kumar; Patil, Veena Ashok; John, Jiji

    2012-01-01

    Surgical crown lengthening has been proposed as a means of facilitating restorative procedures and preventing injuries in teeth with structurally inadequate clinical crown or exposing tooth structure in the presence of deep, subgingival pathologies which may hamper the access for proper restorative measures. Histological studies utilizing animal models have shown that postoperative crestal resorption allowed reestablishment of the biologic width. However, very little has been done in humans. Aims. The purpose of the study was to evaluate the potential changes in the periodontal tissues, particularly the biologic width, following surgical crown lengthening by two surgical procedures before and after crown placement. Methods and Material. Twenty (20) patients who needed surgical crown lengthening to gain retention necessary for prosthetic treatment and/or to access caries, tooth fracture, or previous prosthetic margins entered the study. The following parameters were obtained from line angles of treated teeth (teeth requiring surgical crown lengthening) and adjacent sites: Plaque and Gingival Indices (PI) & (GI), Position of Gingival Margin from reference Stent (PGMRS), Probing depth (PD), and Biologic Width (BW). Statistical Analysis Used. Student "t" Test. Results. Initial baseline values of biologic width were 2.55 mm (Gingivectomy procedure B1 Group) and 1.95 mm (Ostectomy procedure B2 Group) and after surgical procedure the values were 1.15 mm and 1.25 mm. Conclusions. Within the limitations of the study the biologic width, at treated sites, was re-established to its original vertical dimension by 3 months. Ostectomy with apically positioned flap can be considered as a more effective procedure than Gingivectomy for Surgical Crown Lengthening.

  19. A Comparative Evaluation for Biologic Width following Surgical Crown Lengthening Using Gingivectomy and Ostectomy Procedure

    Directory of Open Access Journals (Sweden)

    Kiran Kumar Ganji

    2012-01-01

    Full Text Available Surgical crown lengthening has been proposed as a means of facilitating restorative procedures and preventing injuries in teeth with structurally inadequate clinical crown or exposing tooth structure in the presence of deep, subgingival pathologies which may hamper the access for proper restorative measures. Histological studies utilizing animal models have shown that postoperative crestal resorption allowed reestablishment of the biologic width. However, very little has been done in humans. Aims. The purpose of the study was to evaluate the potential changes in the periodontal tissues, particularly the biologic width, following surgical crown lengthening by two surgical procedures before and after crown placement. Methods and Material. Twenty (20 patients who needed surgical crown lengthening to gain retention necessary for prosthetic treatment and/or to access caries, tooth fracture, or previous prosthetic margins entered the study. The following parameters were obtained from line angles of treated teeth (teeth requiring surgical crown lengthening and adjacent sites: Plaque and Gingival Indices (PI & (GI, Position of Gingival Margin from reference Stent (PGMRS, Probing depth (PD, and Biologic Width (BW. Statistical Analysis Used. Student “t” Test. Results. Initial baseline values of biologic width were 2.55 mm (Gingivectomy procedure B1 Group and 1.95 mm (Ostectomy procedure B2 Group and after surgical procedure the values were 1.15 mm and 1.25 mm. Conclusions. Within the limitations of the study the biologic width, at treated sites, was re-established to its original vertical dimension by 3 months. Ostectomy with apically positioned flap can be considered as a more effective procedure than Gingivectomy for Surgical Crown Lengthening.

  20. Finkelstein Reaction in Functionalized Crown-ether Ionic Liquids

    Institute of Scientific and Technical Information of China (English)

    Xiao Hua WANG; Han Zhi WANG; Hui LIU; Yuan KOU

    2006-01-01

    Functional crown-ether ionic liquids were used as catalytic green solvents of Finkelstein reaction of 1-bromooctane and iodide. The rate and yield of the reaction were obvious improved compared with that using crown ether in water. No free crown ether loss was observed after reaction.

  1. 21 CFR 872.3770 - Temporary crown and bridge resin.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Temporary crown and bridge resin. 872.3770 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3770 Temporary crown and bridge resin. (a) Identification. A temporary crown and bridge resin is a device composed of a material, such...

  2. Evaluation of wild juglans species for crown gall resistance

    Science.gov (United States)

    A. tumefaciens is a soil-borne Gram-negative bacterium which causes crown gall on many dicotyledonous plant species including walnut. Crown gall symptoms on walnut are characterized by large tumors located near the crown of the tree but can occur near wounds caused by bleeding cuts or at the graft u...

  3. Evaluation of sampling strategies to estimate crown biomass

    Science.gov (United States)

    Krishna P Poudel; Hailemariam Temesgen; Andrew N Gray

    2015-01-01

    Depending on tree and site characteristics crown biomass accounts for a significant portion of the total aboveground biomass in the tree. Crown biomass estimation is useful for different purposes including evaluating the economic feasibility of crown utilization for energy production or forest products, fuel load assessments and fire management strategies, and wildfire...

  4. Applicability of non-destructive substitutes for leaf area in different stands of Norway spruce (Picea abies L. Karst.) focusing on traditional forest crown measures.

    Science.gov (United States)

    Laubhann, Daniel; Eckmüllner, Otto; Sterba, Hubert

    2010-09-30

    Since individual tree leaf area is an important measure for productivity as well as for site occupancy, it is of high interest in many studies about forest growth. The exact determination of leaf area is nearly impossible. Thus, a common way to get information about leaf area is to use substitutes. These substitutes are often variables which are collected in a destructive way which is not feasible for long term studies. Therefore, this study aimed at testing the applicability of using substitutes for leaf area which could be collected in a non-destructive way, namely crown surface area and crown projection area. In 8 stands of Norway spruce (Picea abies L. Karst.), divided into three age classes and two thinning treatments, a total of 156 trees were felled in order to test the relationship between leaf area and crown surface area and crown projection area, respectively. Individual tree leaf area of the felled sample trees was estimated by 3P-branch sampling with an accuracy of ±10%. Crown projection area and crown surface area were compared with other, more commonly used, but destructive predictors of leaf area, namely sapwood area at different heights on the bole. Our investigations confirmed findings of several studies that sapwood area is the most precise measure for leaf area because of the high correlation between sapwood area and the leaf area. But behind sapwood area at crown base and sapwood area at three tenth of the tree height the predictive ability of crown surface area was ranked third and even better than that of sapwood area at breast height (R(2) = 0.656 compared with 0.600). Within the stands leaf area is proportional to crown surface area. Using the pooled data of all stands a mixed model approach showed that additionally to crown surface area dominant height and diameter at breast height (dbh) improved the leaf area estimates. Thus, taking dominant height and dbh into account, crown surface area can be recommended for estimating the leaf area

  5. Advanced variable crown work roll contour and its crown control characteristics%先进变凸度工作辊辊形及其控制特性

    Institute of Scientific and Technical Information of China (English)

    李洪波; 张杰; 曹建国; 李慧慧; 周一中; 黄为民

    2011-01-01

    跟踪某2250 mm热轧生产线CVC辊形实际窜辊数据发现,连续变凸度(CVC)辊形常窜到两端极限位置.分析表明,CVC辊形的二次凸度调控能力随带钢宽度减小而呈二次方下降趋势,表现出对较窄带钢凸度控制能力的明显不足.Smart-Crown辊形也存在同样问题.提出一种新的先进变凸度(AVC)工作辊辊形曲线,其二次和四次凸度与窜辊量呈线性关系,且随着四次凸度控制能力的增大,二次凸度控制能力随带钢宽度的变化明显放缓,有助于提高宽带钢或超宽带钢轧机对不同宽度带钢的板形控制能力.%After industrially tracing and testing the shifting positions of continuously variable crown(CVC) work rolls for a 2 250 mm hot strip production line,it was found that CVC work rolls always worked at the limit positions.The analysis showed that the quadratic crown control capability of the CVC work roll contour declined quadratically with decreasing strip width,leading to an insufficient crown control capability to narrow strip steel,and so did SmartCrown work rolls.A new advanced variable crown(AVC) work roll was proposed,whose quadratic crown and quartic crown vary linearly with roll shifting positions.With the quartic crown control capability increasing,the quadratic crown control capability varies slowly with strip width,indicating that the new contour can improve the crown control capability of a wide strip or super wide strip rolling mill for different strip widths.

  6. Crown lengthening: basic principles, indications, techniques and clinical case reports.

    Science.gov (United States)

    Yeh, Simon; Andreana, Sebastiano

    2004-11-01

    Sometimes, in order to properly restore teeth, surgical intervention in the form of a crown-lengthening procedure is required. Crown lengthening is a periodontal resective procedure, aimed at removing supporting periodontal structures to gain sound tooth structure above the alveolar crest level. Periodontal health is of paramount importance for all teeth, both sound and restored. For the restorative dentist to utilize crown lengthening, it is important to understand the concept of biologic width, indications, techniques and other principles. This article reviews these basic concepts of clinical crown lengthening and presents four clinical cases utilizing crown lengthening as an integral part of treatments, to restore teeth and their surrounding tissues to health.

  7. Genetic analysis of seedling resistance to crown rust in five diploid oat (Avena strigosa) accessions.

    Science.gov (United States)

    Cabral, A L; Park, R F

    2016-02-01

    Crown rust, caused by Puccinia coronata Corda f. sp. avenae Eriks., is a serious menace in oats, for which resistance is an effective means of control. Wild diploid oat accessions are a source of novel resistances that first need to be characterised prior to introgression into locally adapted oat cultivars. A genetic analysis of resistance to crown rust was carried out in three diverse diploid oat accessions (CIav6956, CIav9020, PI292226) and two cultivars (Saia and Glabrota) of A. strigosa. A single major gene conditioning resistance to Australian crown rust pathotype (Pt) 0000-2 was identified in each of the three accessions. Allelism tests suggested that these genes are either the same, allelic, or tightly linked with less than 1 % recombination. Similarly, a single gene was identified in Glabrota, and possibly two genes in Saia; both cultivars previously reported to carry two and three crown rust resistance genes, respectively. The identified seedling resistance genes could be deployed in combination with other resistance gene(s) to enhance durability of resistance to crown rust in hexaploid oat. Current diploid and hexaploid linkage maps and molecular anchor markers (simple sequence repeat [SSR] and diversity array technology [DArT] markers) should facilitate their mapping and introgression into hexaploid oat.

  8. Aesthetic comparison between crowns made with Cubo and metal-ceramic systems

    Directory of Open Access Journals (Sweden)

    Lis Regina Carneiro HOPPEN

    2010-06-01

    Full Text Available Introduction and objective: The objective of this study was to verify the influence of different materials used in the construction of infrastructures on the aesthetic result of restorations with ceramic coating. Material and methods: A patient that needed a single prosthetic crown on the maxillary central incisors was selected for treatment, one in the right maxillary central incisor (11 and another in the dental implant (21.Metal-free (Cubo system and metal-ceramic (MC crowns were made for each tooth and submitted to blind review by 11 dentists, who answered a questionnaire about ratios of opacity and translucency of the crowns in the oral cavity of the patient, where each answer corresponded to one score.Data was submitted to Wilcoxon test (α = 0.05. Results: Therewas no significant statistical difference between the metal-ceramic and Cubo system crowns (11: p = 0.107; 21: p = 0.739. The analysis of the scores also showed that for the same type of infrastructure there was no significant statistical difference between 11 and 21 (Cubo: p = 0.206; MC: p = 0.102. Conclusion: Within the limits of this study, it was concluded that, according to the visual perception of the evaluators,prosthetic crowns made with metal infrastructure and with ceramic infrastructure showed to be aesthetically similar and satisfactory.

  9. Experimental Analyses for The Mechanical Behavior of Pressed All-Ceramic Molar Crowns with Anatomical Design

    Directory of Open Access Journals (Sweden)

    Porojan Liliana

    2017-01-01

    Full Text Available Ceramic restorations show considerable variation in strength and structural reliability regarding to the type of material, and design characteristics. The fracture of ceramics occurs with little or no plastic deformation, with cracks propagated in an unstable manner under applied tensile stresses. The aim of the study was to assess experimental analyses of pressed monolithic ceramic crowns with anatomical design used in the posterior areas in order to understand their mechanical behavior before following their clinical use. Experiments were conducted on a complete molar crown preparation. Experiments show different modes of fracture for the tested samples. Digital images from the fractured pieces of the crowns were used to verify the fragments in all cases final fracture occurred by splitting into two and often more parts. The graphically representation of the displacement depending on the load highlights a series of peaks that can be correlated with cracks occurred in crowns. The development of well-designed mechanical experiments could be useful to help to predict clinical survival of these new all-ceramic restorative techniques and materials. Because failure is often accompanied by complete cracking of the crowns, preliminary research should represents a compulsory goal.

  10. Crown dimensions and proximal enamel thickness of mandibular second bicuspids.

    Science.gov (United States)

    Fernandes, Sérgio Augusto; Vellini-Ferreira, Flávio; Scavone-Junior, Helio; Ferreira, Rívea Inês

    2011-01-01

    To achieve proper recontouring of anterior and posterior teeth, to obtain optimal morphology during enamel stripping, it is important to be aware of dental anatomy. This study aimed at evaluating crown dimensions and proximal enamel thickness in a sample of 40 extracted sound, human, mandibular, second bicuspids (20 right and 20 left). Mesiodistal, cervico-occlusal and buccolingual crown dimensions were measured using a digital caliper, accurate to 0.01 mm. Teeth were embedded in acrylic resin and cut along their long axes through the proximal surfaces to obtain 0.7 mm-thick central sections. Enamel thickness on the cut sections was measured using a perfilometer. Comparative analyses were carried out using the Student's-t test (α= 5%). The mean mesiodistal crown widths for right and left teeth were 7.79 mm (± 0.47) and 7.70 mm (± 0.51), respectively. Mean cervico-occlusal heights ranged from 8.31 mm (± 0.75) on the right to 8.38 mm (± 0.85) on the left teeth. The mean values for the buccolingual dimension were 8.67 mm (± 0.70) on the right and 8.65 mm (± 0.54) on the left teeth. The mean enamel thickness on the mesial surfaces ranged from 1.35 mm (± 0.22) to 1.40 mm (± 0.17), on the left and right sides, respectively. On the distal surfaces, the corresponding values were 1.44 mm (± 0.21) and 1.46 mm (± 0.12). No significant differences were found between measurements for right and left teeth. However, enamel thickness was significantly greater on the distal surfaces, compared with the mesial surfaces.

  11. Crown dimensions and proximal enamel thickness of mandibular second bicuspids

    Directory of Open Access Journals (Sweden)

    Sérgio Augusto Fernandes

    2011-08-01

    Full Text Available To achieve proper recontouring of anterior and posterior teeth, to obtain optimal morphology during enamel stripping, it is important to be aware of dental anatomy. This study aimed at evaluating crown dimensions and proximal enamel thickness in a sample of 40 extracted sound, human, mandibular, second bicuspids (20 right and 20 left. Mesiodistal, cervico-occlusal and buccolingual crown dimensions were measured using a digital caliper, accurate to 0.01 mm. Teeth were embedded in acrylic resin and cut along their long axes through the proximal surfaces to obtain 0.7 mm-thick central sections. Enamel thickness on the cut sections was measured using a perfilometer. Comparative analyses were carried out using the Student's-t test (α= 5%. The mean mesiodistal crown widths for right and left teeth were 7.79 mm (± 0.47 and 7.70 mm (± 0.51, respectively. Mean cervico-occlusal heights ranged from 8.31 mm (± 0.75 on the right to 8.38 mm (± 0.85 on the left teeth. The mean values for the buccolingual dimension were 8.67 mm (± 0.70 on the right and 8.65 mm (± 0.54 on the left teeth. The mean enamel thickness on the mesial surfaces ranged from 1.35 mm (± 0.22 to 1.40 mm (± 0.17, on the left and right sides, respectively. On the distal surfaces, the corresponding values were 1.44 mm (± 0.21 and 1.46 mm (± 0.12. No significant differences were found between measurements for right and left teeth. However, enamel thickness was significantly greater on the distal surfaces, compared with the mesial surfaces.

  12. The effect of retentive groove, sandblasting and cement type on the retentive strength of stainless steel crowns in primary second molars - An in vitro comparative study

    Directory of Open Access Journals (Sweden)

    M M Veerabadhran

    2012-01-01

    Full Text Available Purpose: This in vitro study was conducted to find out the effect of retentive groove, sand blasting and cement type on the retentive strength of stainless steel crowns in primary second molars. Materials and Methods: Thirty-two extracted intact human maxillary and mandibular primary second molars were embedded in aluminum blocks utilizing autopolymerising acrylic resin. After tooth preparation, the 3M stainless steel crown was adjusted to the prepared tooth. Then weldable buccal tubes were welded on the buccal and lingual surfaces of each crown as an attachment for the testing machine. A full factorial design matrix for four factors (retentive groove placement on the tooth, cement type, sandblasting and primary second molar at two levels each was developed and the study was conducted as dictated by the matrix. The lower and upper limits for each factor were without and with retentive groove placement on the tooth, GIC and RMGIC, without and with sandblasting of crown, maxillary and mandibular second primary molar. For those teeth for which the design matrix dictated groove placement, the retentive groove was placed on the middle third of the buccal surface of the tooth horizontally and for those crowns for which sandblasting of the crowns are to be done, sandblasting was done with aluminium oxide with a particle size of 250 mm. The crowns were luted with either GIC or RMGIC, as dictated by the design matrix. Then the retentive strength of each sample was evaluated by means of an universal testing machine. The obtained data was analyzed using ANOVA for statistical analysis of the data and ′t′- tests for pairwise comparison. Results: The mean retentive strength in kg/cm 2 stainless steel crowns luted with RMGIC was 19.361 and the mean retentive strength of stainless steel crowns luted with GIC was 15.964 kg/cm 2 with a mean difference of 3.397 kg/cm 2 and was statistically significant. The mean retentive strength in kg/cm 2 of stainless steel

  13. Stability of Monolithic Rubble Mound Breakwater Crown Walls Subjected to Impulsive Loading

    DEFF Research Database (Denmark)

    Nørgaard, Jørgen Harck; Andersen, Lars Vabbersgaard; Andersen, Thomas Lykke

    2012-01-01

    model tests. The outcome is a more reliable evaluation of the applicability of simple dynamic calculations for the estimation of sliding distances of rubble mound superstructures. This is of great practical importance since many existing rubble mound crown walls are subjected to increasing wave loads......This paper evaluates the validity of a simple onedimensional dynamic analysis as well as a FEM model to determine the sliding of a rubble mound breakwater crown wall. The evaluation is based on a case example with real wave load time series and displacements measured from two-dimensional physical...

  14. The effect of laser irradiation on retention of full cast crowns.

    Science.gov (United States)

    Al-Omari, W M; Palamara, J E; Almohammed, S N

    2013-03-01

    The objective of this work was to determine the effect on the retention force of full cast crowns cemented on short tooth preparations after preparation of dentine with an erbium, chromium: yttrium scandium gallium garnet (Er, Cr:YSGG) laser at different sub-ablative power settings. Thirty teeth were prepared for full cast crowns using a milling machine. The surface area for all preparations was measured. The surfaces of the preparations were irradiated with 0 (control), 0.25 and 0.75 W laser. The crowns were cemented with self-cure resin cement and tested for retention on a Hounsfield Tensometer machine. The 0.75 W power setting produced the highest failure load value (346.2 +/- 86.1 N) and was significantly higher than the other groups. There were no significant differences between the 0.25 W and 0 W control groups

  15. The influence of low-temperature degradation and cyclic loading on the fracture resistance of monolithic zirconia molar crowns.

    Science.gov (United States)

    Nakamura, K; Harada, A; Kanno, T; Inagaki, R; Niwano, Y; Milleding, P; Örtengren, U

    2015-07-01

    The present study analyzed the kinetics of low-temperature degradation (LTD) in zirconia, and evaluated the influence of LTD and cyclic loading on the fracture resistance of monolithic zirconia molar crowns. Bar-shaped zirconia specimens were divided into nine groups and autoclaved at 134°C for 0-200h to induce LTD. The surface fraction and penetration depth of the monoclinic phase were examined using X-ray diffraction and scanning electron microscopy. Monolithic zirconia molar crowns were prepared for crown fracture testing. The crowns were autoclaved for 0-100h (n=6) and cemented to dies. Six crown-die samples that were not autoclaved and six samples that were autoclaved for 100h were subjected to cyclic loading with a load of 300N for 240,000 cycles. All samples were tested in a load-to-failure test. The monoclinic fraction on the surface increased with autoclaving time and reached a plateau after 50h. The depth of the monoclinic phase increased without reaching a plateau. The fracture load of the crowns significantly decreased from 5683N (SD: 342) to 3975N (SD: 194) after 100h of autoclaving. Cyclic loading did not significantly affect the fracture resistance of the crowns in all cases. Kinetic analysis showed no linear correlation between the surface fraction and depth of the monoclinic phase after 50h of autoclaving. Even though LTD increased the monoclinic phase, resulting in lower strength, the fracture resistance of the monolithic zirconia crowns was still sufficient to withstand the loading conditions in the molar regions.

  16. Cross-Validation of a Short Form of the Marlowe-Crowne Social Desirability Scale.

    Science.gov (United States)

    Zook, Avery, II; Sipps, Gary J.

    1985-01-01

    Presents a cross-validation of Reynolds' short form of the Marlowe-Crowne Social Desirability Scale (N=233). Researchers administered 13 items as a separate entity, calculated Cronbach's Alpha for each sex, and computed test-retest correlation for one group. Concluded that the short form is a viable alternative. (Author/NRB)

  17. 4′-Formylbenzo-15-crown-5

    Directory of Open Access Journals (Sweden)

    Conrad Fischer

    2008-08-01

    Full Text Available In the title compound (systematic name: 17-formyl-2,5,8,11,14-pentaoxabicyclo[13.4.0]nonadeca-15,17,19-triene, C15H20O6, the 15-crown-5 ring adopts a twisted conformation. The formyl group is coplanar with the benzene ring. The crystal packing is stabilized by C—H...O interactions involving the C=O group and ether O atoms as acceptors and methylene CH groups as donors.

  18. Dental trauma. Combination injuries 1. The risk of pulp necrosis in permanent teeth with concussion injuries and concomitant crown fractures

    DEFF Research Database (Denmark)

    Lauridsen, Eva Fejerskov; Hermann, Nuno Vibe; Gerds, Thomas Alexander

    2012-01-01

    by the Kaplan–Meier method and Cox regression. Risk factors included in the analysis: gender, age, stage of root development, type of crown fracture, and response to electric pulp test (EPT) at the initial examination. The level of significance was set at 5%. Results:  The risk of PN was low in teeth......The reported risk of pulp necrosis (PN) is low in teeth with concussion injuries. A concomitant crown fracture may affect the risk of PN. Aim:  To analyze the influence of a crown fracture (with and without pulp exposure) on the risk of PN in teeth with concussion injury. Material:  The study...... included 469 permanent incisors with concussion from 358 patients (226 male, 132 female). Among these, 292 had a concomitant crown fracture (70 with and 222 without pulp exposure). All teeth were examined and treated according to standardized protocol. Statistical analysis:  The risk of PN was analyzed...

  19. The use of stainless steel crowns.

    Science.gov (United States)

    Seale, N Sue

    2002-01-01

    The stainless steel crown (SSC) is an extremely durable restoration with several clear-cut indications for use in primary teeth including: following a pulpotomy/pulpectomy; for teeth with developmental defects or large carious lesions involving multiple surfaces where an amalgam is likely to fail; and for fractured teeth. In other situations, its use is less clear cut, and caries risk factors, restoration longevity and cost effectiveness are considerations in decisions to use the SSC. The literature on caries risk factors in young children indicates that children at high risk exhibiting anterior tooth decay and/or molar caries may benefit by treatment with stainless steel crowns to protect the remaining at-risk tooth surfaces. Studies evaluating restoration longevity, including the durability and lifespan of SSCs and Class II amalgams demonstrate the superiority of SSCs for both parameters. Children with extensive decay, large lesions or multiple surface lesions in primary molars should be treated with stainless steel crowns. Because of the protection from future decay provided by their feature of full coverage and their increased durability and longevity, strong consideration should be given to the use of SSCs in children who require general anesthesia. Finally, a strong argument for the use of the SSC restoration is its cost effectiveness based on its durability and longevity.

  20. Surgical lengthening of the clinical tooth crown.

    Science.gov (United States)

    Planciunas, Liudvikas; Puriene, Alina; Mackeviciene, Grazina

    2006-01-01

    To understand why the crown lengthening may be desirable, a review of periodontal anatomy is in order. The odontologists know, but often underestimate importance of periodontal tissues health to restoration of defected teeth or dental arches. In order to avoid pathological changes, to predict treatment results more precisely, it is necessary to keep gingival biological width unaltered during teeth restoration. If there are less than 2 mm from restoration's margin to marginal bone clinical crown lengthening possibility should be considered in dental treatment plan. The choice depends on relationship of crown-root-alveolar bone and esthetical expectations. In order to keep margins of restoration supragingivally the distance from marginal bone to margins of restoration should not be less than 3 mm. Ideally the margins of restoration should be supragingivally or in the same level as marginal gingiva. When the margins of restoration are prepared subgingivally, the distance from marginal gingiva to margins of restoration should not be more than 0.7 mm. To continue dental treatment in operated area is recommended not earlier than in 4 weeks, and making restorations in esthetical area--not earlier than in 6 weeks.

  1. Comparison of fracture toughness of all-ceramic and metal-ceramic cement retained implant crowns: an in vitro study.

    Science.gov (United States)

    Rao, S; Chowdhary, R

    2014-12-01

    To evaluate the fracture toughness of cement-retained implant-supported metal-ceramic molar crown with that of all-ceramic crowns, fabricated using IPS Empress 2 and yttria-stabilized zirconia copings. An dental implant and abutment was embedded in a clear polymethyl methacrylate model. A wax pattern reproducing the anatomy and dimension of a mandibular molar was made using inlay wax. Copings were made from the manufacturers guidelines for zirconia, metal ceramic and empress crown, in total of 21 copings, which were built for the crowns with metal layering ceramics specified by the manufacturers. The polymethylmethacrylate block-implant abutment complex was mounted on universal testing machine, and a static continuos vertical compressive load with a crosshead speed of 0.5 mm/min was applied. The breaking load and the peak load (in kilo Newtons) were recorded. The fractures for group I (zirconia-ceramic) and group II (metal-ceramic) occurred on the mesio-buccal aspect of the crowns involving the veneered ceramic layer while the catastrophic/bulk fracture was not observed. The mean value of breaking load for zirconia-ceramic, metal-ceramic and IPS-empress 2 was 3.4335, 3.071 and 1.0673 kN respectively. The mean value of peak load for zirconia-ceramic, metal-ceramic and IPS-empress 2 was 4.7365, 3.2757 and 1.566 kN respectively. It can be concluded that the zirconia-ceramic crown with the fracture toughness of 4.7365 ± 2.2676 kN has sufficient strength to allow clinical testing of these crowns as an alternative for metal-ceramic crowns (3.2757 ± 0.4681 kN).

  2. Comparison of Primary Molar Crown Dimensions with Stainless Steel Crowns in a Sample of Iranian Children

    Directory of Open Access Journals (Sweden)

    Hossein Afshar

    2015-06-01

    Full Text Available Background and aims. Due to anatomic variation in tooth anatomy between populations, this study compared the buccolingual (BL and mesiodistal (MD dimensions of primary molars with those of stainless steel crowns (SSCs in anIranian population. Materials and methods. Impressions were taken from both dental arches of children, and casts were poured. Teeth with caries, restoration, hypoplasia or other dental anomalies were excluded. 216 primary molars were selected and divided into 4 groups of 54 each (maxillary and mandibular first and second primary molars. MD/BL dimensions were measured using a digital caliper with 0.01 mm precision on casts and SCCs (3M brand. Data were assessed using paired t-test, post hoc test and ANOVA. P < 0.05 was considered statistically significant. Results. The MD dimension of the lower first molar SSC and the BL dimension of the lower second molar SSC had the least difference with the corresponding values of the respective teeth. The MD dimension of the upper second molar SSC and the BL dimension of the upper first molar SSC had the greatest difference with the corresponding values in the respective teeth. Comparison of the two different brands of SSCs for the upper first molar revealed that both types had significant differences with the teeth in terms of both MD (P = 0.0 and BL (P = 0.0 dimensions. Conclusion. In the studied population, best adaptation was seen in second lower molars and the least adaptationswere seen in first and second upper molars.

  3. Quantitative characterization of clumping in Scots pine crowns.

    Science.gov (United States)

    Stenberg, Pauline; Mõttus, Matti; Rautiainen, Miina; Sievänen, Risto

    2014-09-01

    Proper characterization of the clumped structure of forests is needed for calculation of the absorbed radiation and photosynthetic production by a canopy. This study examined the dependency of crown-level clumping on tree size and growth conditions in Scots pine (Pinus sylvestris), and determined the ability of statistical canopy radiation models to quantify the degree of self-shading within crowns as a result of the clumping effect. Twelve 3-D Scots pine trees were generated using an application of the LIGNUM model, and the crown-level clumping as quantified by the crown silhouette to total needle area ratio (STAR(crown)) was calculated. The results were compared with those produced by the stochastic approach of modelling tree crowns as geometric shapes filled with a random medium. Crown clumping was independent of tree height, needle area and growth conditions. The results supported the capability of the stochastic approach in characterizing clumping in crowns given that the outer shell of the tree crown is well represented. Variation in the whole-stand clumping index is induced by differences in the spatial pattern of trees as a function of, for example, stand age rather than by changes in the degree of self-shading within individual crowns as they grow bigger.

  4. Flapless implant placement with crown lengthening procedure to correct crown height: a case report.

    Science.gov (United States)

    Jacobson, Nancy; Starr, Cliff

    2009-10-01

    Bone loss and soft tissue loss are common problems after tooth extraction and that can lead to excessive length of clinical crowns. This problem can be exacerbated by delaying implant placement after tooth extraction. In this case the opposite occurred. After flapless placement of a NobelDirect implant with immediate loading there was not enough vertical space for an esthetic restoration. Surgical crown lengthening was performed to create vertical space to place an esthetically pleasing restoration in harmony with the patient's existing dentition.

  5. Clinical outcomes of three different crown systems with CAD/CAM technology.

    Science.gov (United States)

    Batson, Emily R; Cooper, Lyndon F; Duqum, Ibrahim; Mendonça, Gustavo

    2014-10-01

    probing was affected by the explanatory variables. One-way ANOVA was used to assess marginal discrepancy values among the crown systems (α=.05 for all tests). Twelve metal ceramic, 10 lithium disilicate, and 10 zirconia restorations were fabricated for 22 participants. Zirconia restorations were significantly different from the other 2 crown systems (Pcontrol groups, or over time. The average horizontal marginal discrepancy was significantly different between lithium disilicate and zirconia crowns (P=.027), with zirconia crowns having the least amount of horizontal marginal discrepancy. Given the small sample size and limitations of this study, CAD/CAM-generated restorations for posterior teeth made from different materials had acceptable clinical results. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  6. Short clinical crowns (SCC) – treatment considerations and techniques

    OpenAIRE

    Sharma, Ashu; Rahul, G. R.; Poduval, Soorya T.; Shetty, Karunakar

    2012-01-01

    When the clinical crowns of teeth are dimensionally inadequate, esthetically and biologically acceptable restoration of these dental units is difficult. Often an acceptable restoration cannot be accomplished without first surgically increasing the length of the existing clinical crowns; therefore, successful management requires an understanding of both the dental and periodontal parameters of treatment. The complications presented by teeth with short clinical crowns demand a comprehensive tre...

  7. Fracture resistance of monolithic zirconia molar crowns with reduced thickness

    OpenAIRE

    Nakamura, Keisuke; Harada, A.; Inagaki, R.; Kanno, Taro; Niwano, Y; Milleding, Percy; Ørtengren, Ulf Thore

    2015-01-01

    This is the accepted manuscript version. Published version is available at Acta Odontologica Scandinavica Objectives. The purpose of the present study was to analyze the relationship between fracture load of monolithic zirconia crowns and axial/occlusal thickness, and to evaluate the fracture resistance of monolithic zirconia crowns with reduced thickness in comparison with that of monolithic lithium disilicate crowns with regular thickness. Materials and methods. Monolithic zi...

  8. Zirconia crowns - the new standard for single-visit dentistry?

    Science.gov (United States)

    Wiedhahn, Klaus; Fritzsche, Günter; Wiedhahn, Claudine; Schenk, Olaf

    2016-01-01

    Zirconia crowns combine the advantages of metal restorations, such as minimally invasive tooth preparation and ease of cementation, with those of full ceramic crowns, such as low thermal conductivity and tooth color. With the introduction of a high-speed sintering procedure, it is possible to produce and cement zirconia crowns and small monolithic bridges in a Cerec Single Visit procedure. This new procedure is compared to established chairside methods.

  9. Characterization of Microsolvated Crown Ethers from Broadband Rotational Spectroscopy

    Science.gov (United States)

    Perez, Cristobal; Schnell, Melanie; Blanco, Susana; Lopez, Juan Carlos

    2016-06-01

    Since they were first synthetized, crown ethers have been extensively used in organometallic chemistry due to their unparalleled binding selectivity with alkali metal cations. From a structural point of view, crown ethers are heterocycles containing oxygen and/or other heteroatoms, although the most common ones are formed from ethylene oxide unit. Crown ethers are conventionally seen as being hydrophilic inside and hydrophobic outside when the structures found for the metal cation complexes are considered. However, crown ethers are extremely flexible and in isolation may present a variety of stable conformations so that their structure may be easily adapted in presence of a strong ligand as an alkali metal cation minimize the energy of the resulting complex. Water can be considered a soft ligand which interacts with crown ethers through moderate hydrogen bonds. It is thus interesting to investigate which conformers are selected by water to form complexes, the preferred interaction sites and the possible conformational changes due to the presence of one or more water molecules. Previous studies identified microsolvated crown ethers but in all cases with a chromophore group attached to the structure. Here we present a broadband rotational spectroscopy study of microsolvated crown ethers produced in a pulsed molecular jet expansion. Several 1:1 and 1:2 crown ether:water aggregates are presented for 12-crown-4, 15-crown-5 and 18-crown-6. Unambiguous identification of the structures has been achieved using isotopic substitution within the water unit. The subtle changes induced in the structures of the crown ether monomer upon complexation and the hydrogen-bonding network that hold them together will be also discussed. F. Gámez, B. Martínez-Haya, S. Blanco,J. C. López and J. L. Alonso, Phys. Chem. Chem. Phys. 2014, 14 12912-12918 V. A. Shubert, C.W. Müller and T. Zwier, J. Phys. Chem. A 2009, 113 8067-8079

  10. CROWN FUNCTIONALIZED LINEAR POLYSILOXANE PLATINUM COMPLEX AS HYDROSILYLATION CATALYST

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuanyin; LU Xueran; GONG Shuling; ZHANG Baolian

    1994-01-01

    A modified method of preparing crown functionalized linear polysiloxane has been described.4'-allylbenzo-15-crown-5 was subjected to hydrosilylation with methyldichlorosilane,followed by polycondensation with silanol-terminated polydimethylsiloxane to give the title crown functionalized linear polysiloxane. It was found that the polysiloxane could be coordinated with platinum salt to form platinum complex, which could catalyze the hydrosilylation of olefins with triethoxysilane efficiently.

  11. Short clinical crowns (SCC) – treatment considerations and techniques

    OpenAIRE

    Sharma, Ashu; G. R. Rahul; Poduval, Soorya T.; Shetty, Karunakar

    2012-01-01

    When the clinical crowns of teeth are dimensionally inadequate, esthetically and biologically acceptable restoration of these dental units is difficult. Often an acceptable restoration cannot be accomplished without first surgically increasing the length of the existing clinical crowns; therefore, successful management requires an understanding of both the dental and periodontal parameters of treatment. The complications presented by teeth with short clinical crowns demand a comprehensive tre...

  12. Shear Bond Strength of Orthodontic Brackets Bonded to Zirconium Crowns

    Science.gov (United States)

    Mehmeti, Blerim; Azizi, Bleron; Kelmendi, Jeta; Iljazi-Shahiqi, Donika; Alar, Željko

    2017-01-01

    Background An increasing demand for esthetic restorations has resulted in an increased use of all-ceramic restorations, such as zirconium. However, one of the challenges the orthodontist must be willing to face is how to increase bond strength between the brackets and various ceramic restorations.Bond strength can beaffected bybracket type, by the material that bracketsaremade of, and their base surface design or retention mode. ​ Aim: of this study was to perform a comparative analysis of the shear bond strength (SBS) of metallic and ceramic orthodontic brackets bonded to all-zirconium ceramic surfaces used for prosthetic restorations, and also to evaluate the fracture mode of these two types of orthodontic brackets. Material and methods Twenty samples/semi-crowns of all-zirconium ceramic, on which orthodontic brackets were bonded, 10 metallic and 10 ceramic polycrystalline brackets, were prepared for this research. SBS has been testedby Universal Testing Machine, with a load applied using a knife edged rod moving at a fixed rate of 1 mm/min, until failure occurred. The force required to debond the brackets was recorded in Newton, then SBS was calculated to MPa. In addition, the samples were analyzed using a digital camera magnifier to determine Adhesive Remnant Index (ARI). Statistical data were processed using t-test, and the level of significance was set at α = 0.05. Results Higher shear bond strength values were observed in metallic brackets bonded to zirconium crowns compared tothoseof ceramic brackets, with a significant difference. During the test, two of the ceramic brackets were partially or totally damaged. Conclusion Metallic brackets, compared to ceramic polycrystalline brackets, seemed tocreate stronger adhesion with all-zirconium surfaces due to their better retention mode. Also, ceramic brackets showed higher fragility during debonding. PMID:28827846

  13. Crown lengthening and restorative treatment in mutilated molars.

    Science.gov (United States)

    Parashis, A; Tripodakis, A

    1994-03-01

    Crown lengthening has been advocated as a treatment modality to restore teeth with a clinical crown reduced subsequent to different kinds of trauma. Multirooted teeth, however, present certain anatomic features, such as the furcation area and corresponding interradicular bone, the retromolar area, and the external oblique ridge, that may limit the possibility for soft tissue and bone reduction and minimize the effectiveness of crown-lengthening procedures. This article describes surgical modifications to overcome the anatomic difficulties that multirooted teeth present when crown lengthening is required. Furthermore, root resection is discussed as an alternative to conventional surgery when the latter is not possible.

  14. Complexes of Diquat with Dibenzo-24-Crown-8

    Institute of Scientific and Technical Information of China (English)

    LI Shijun; HUANG Feihe; SLEBODNICK Carla; ASHRAF-KHORASSANI Mehdi; GIBSON Harry W.

    2009-01-01

    The complexation between dibenzo-24-crown-8(1)and diquat(2)was investigated in detail by NMR,MS andlated,in which a single molecule of diquat is enclosed in the concave cavity provided by two dibenzo-24-crown-8 host molecules.Both results are different from the previously assumed stoichiometry of the complexation between dibenzo-24-crown-8 and diquat.This result enriches the range of host-guest complexes based on dibenzo-24crown-8 and provides new opportunities for developing more complicated structures and chemosensors for diquat.

  15. Basal ganglia - thalamus and the crowning enigma

    Directory of Open Access Journals (Sweden)

    Marianela eGarcia-Munoz

    2015-11-01

    Full Text Available When Hubel (1982 referred to layer 1 of primary visual cortex as …a ‘crowning mystery’ to keep area-17 physiologists busy for years to come... he could have been talking about any cortical area. In the 80’s and 90’s there were no methods to examine this neuropile on the surface of the cortex: a tangled web of axons and dendrites from a variety of different places with unknown specificities and doubtful connections to the cortical output neurons some hundreds of microns below. Recently, three changes have made the crowning enigma less of an impossible mission: the clear presence of neurons in layer 1 (L1, the active conduction of voltage along apical dendrites and optogenetic methods that might allow us to look at one source of input at a time. For all of those reasons alone, it seems it is time to take seriously the function of L1. The functional properties of this layer will need to wait for more experiments but already L1 cells are GAD67 positive, i.e., inhibitory! They could reverse the sign of the thalamic glutamate (GLU input for the entire cortex. It is at least possible that in the near future normal activity of individual sources of L1 could be detected using genetic tools. We are at the outset of important times in the exploration of thalamic functions and perhaps the solution to the crowning enigma is within sight. Our review looks forward to that solution from the solid basis of the anatomy of the basal ganglia output to motor thalamus. We will focus on L1, its afferents, intrinsic neurons and its influence on responses of pyramidal neurons in layers 2/3 and 5. Since L1 is present in the whole cortex we will provide a general overview considering evidence mainly from the somatosensory cortex before focusing on motor cortex.

  16. Comparison of Implant-Supported Crown Length Measured on Digitized Casts and Intraoral Radiographs

    NARCIS (Netherlands)

    Meijer, Henny J. A.; Telleman, Gerdien; Gareb, Chawan; Den Hartog, Laurens; Vissink, Arjan; Raghoebar, Gerry M.

    2012-01-01

    Correct measurement of crown length is important for calculating the crown-implant ratio. The aim of this study was to compare the length of implant-supported crowns measured on digitized casts and intraoral radiographs. Crown lengths were studied in 50 patients with 86 implant-supported crowns in t

  17. Microwave-assisted fast and efficient synthesis of some crown ethers

    Institute of Scientific and Technical Information of China (English)

    Ahmad Ziafati; Hossein Eshghi; Omolbanin Sabzevari

    2009-01-01

    13-Crown-4, 16-crown-5, dibenzo-12-crown-4 and dibenzo-14-crown-4 were synthesized by a one-pot microwave-assisted procedure in good yields. Irradiation of diols and dichlorides in the presence of sodium hydroxide in DMSO gave title crown ethers presumably within a template effect.

  18. Guided esthetic crown lengthening: case reports.

    Science.gov (United States)

    Borges, Ivan; Ribas, Tania Rocha Cabral; Duarte, Poliana Mendes

    2009-01-01

    It is well-recognized that excessive gingival display can have a negative impact on a patient's smile. Excessive gingival display due to gingival enlargement or altered passive eruption (dentogingival cause) can be corrected effectively through periodontal surgeries. This article describes two successful esthetic crown-lengthening surgeries that were guided by an acetate template to better predict the outcomes of the surgical procedures in relation to the symmetry and harmony of the gingival contour. This article also highlights the importance of utilizing an interdisciplinary approach to obtain an optimum esthetic result for restorative treatments in the anterior maxilla.

  19. Pediatric Preformed Metal Crowns - An Update

    Directory of Open Access Journals (Sweden)

    Sangameshwar Sajjanshetty

    2013-01-01

    Full Text Available Stainless Steel crowns (SSC were introduced in 1947 by the Rocky Mountain Company and popularized by Humphrey in 1950. Prefabricated SSC can be adapted to individual primary teeth and cemented in place to provide a definitive restoration. The SSC is extremely durable, relatively inexpensive, subject to minimal technique sensitivity during placement, and offers the advantage of full coronal coverage. SSC are often used to restore primary and permanent teeth in children and adolescents where intracoronal restorations would otherwise fail. This article brings the update of this definitive restoration.

  20. Crowned Ionic Liquids for Biomolecular Interaction Analysis.

    Science.gov (United States)

    Tseng, Ming-Chung; Yuan, Tsu-Chun; Li, Zhuo; Chu, Yen-Ho

    2016-11-15

    On the basis of affinity recognition with positively charged side chains in peptides and proteins, a series of crowned 1,2,3-triazolium ionic liquids (CIL 1-6) was developed and found to be capable of quantitatively extracting peptides and proteins from the aqueous layer into the ionic liquid phase. All of the synthesized CIL 1-6 are liquid at room temperature. This is the first example of biomolecular recognition of both lysine- and arginine-containing peptides and proteins by CILs in pure ionic liquid phase.

  1. Correlation between margin fit and microleakage in complete crowns cemented with three luting agents

    Directory of Open Access Journals (Sweden)

    Paulo Henrique Orlato Rossetti

    2008-02-01

    Full Text Available Microleakage can be related to margin misfit. Also, traditional microleakage techniques are time-consuming. This study evaluated the existence of correlation between in vitro margin fit and a new microleakage technique for complete crowns cemented with 3 different luting agents. Thirty human premolars were prepared for full-coverage crowns with a convergence angle of 6 degrees, chamfer margin of 1.2 mm circumferentially, and occlusal reduction of 1.5 mm. Ni-Cr cast crowns were cemented with either zinc phosphate (ZP (S.S. White, resin-modified glass-ionomer (RMGI (Rely X Luting Cement or a resin-based luting agent (RC (Enforce. Margin fit (seating discrepancy and margin gap was evaluated according to criteria in the literature under microscope with 0.001 mm accuracy. After thermal cycling, crowns were longitudinally sectioned and microleakage scores at tooth-cement interface were obtained and recorded at ×100 magnification. Margin fit parameters were compared with the one-way ANOVA test and microleakage scores with Kruskal-Wallis and Dunn's tests (alpha=0.05. Correlation between margin fit and microleakage was analyzed with the Spearman's test (alpha=0.05. Seating discrepancy and marginal gap values ranged from 81.82 µm to 137.22 µm (p=0.117, and from 75.42 µm to 78.49 µm (p=0.940, respectively. Marginal microleakage scores were ZP=3.02, RMGI=0.35 and RC=0.12 (p0.05. Conclusion: Margin fit parameters and microleakage showed no strong correlations; cast crowns cemented with RMGI and RC had lower microleakage scores than ZP cement.

  2. [An esthetic crown lengthening technic of the clinical crown. Rapid orthodontic extrusion].

    Science.gov (United States)

    Blase, D; Bercy, P

    1993-01-01

    Rapid orthodontic root extrusion is an esthetic technique for clinical crown lengthening. Associated with periodontal surgery, it exposes subgingival lesions and preserves an harmonious gingivo-osseous morphology. This conservative technique is easy to apply by the general dentist as it requires non specialised material.

  3. The influence of tooth preparation and crown manipulation on the mechanical retention of stainless steel crowns.

    Science.gov (United States)

    Rector, J A; Mitchell, R J; Spedding, R H

    1985-01-01

    The belief that close adaptation of the metal margins to tooth surfaces in the undercut areas is the most important retentive feature, was borne out in this study. The type of preparation did not affect the retention of stainless steel crowns.

  4. Effect of framework design on crown failure.

    Science.gov (United States)

    Bonfante, Estevam A; da Silva, Nelson R F A; Coelho, Paulo G; Bayardo-González, Daniel E; Thompson, Van P; Bonfante, Gerson

    2009-04-01

    This study evaluated the effect of core-design modification on the characteristic strength and failure modes of glass-infiltrated alumina (In-Ceram) (ICA) compared with porcelain fused to metal (PFM). Premolar crowns of a standard design (PFMs and ICAs) or with a modified framework design (PFMm and ICAm) were fabricated, cemented on dies, and loaded until failure. The crowns were loaded at 0.5 mm min(-1) using a 6.25 mm tungsten-carbide ball at the central fossa. Fracture load values were recorded and fracture analysis of representative samples were evaluated using scanning electron microscopy. Probability Weibull curves with two-sided 90% confidence limits were calculated for each group and a contour plot of the characteristic strength was obtained. Design modification showed an increase in the characteristic strength of the PFMm and ICAm groups, with PFM groups showing higher characteristic strength than ICA groups. The PFMm group showed the highest characteristic strength among all groups. Fracture modes of PFMs and of PFMm frequently reached the core interface at the lingual cusp, whereas ICA exhibited bulk fracture through the alumina core. Core-design modification significantly improved the characteristic strength for PFM and for ICA. The PFM groups demonstrated higher characteristic strength than both ICA groups combined.

  5. Dental trauma. Combination injuries 2. The risk of pulp necrosis in permanent teeth with subluxation injuries and concomitant crown fractures

    DEFF Research Database (Denmark)

    Lauridsen, Eva Fejerskov; Hermann, Nuno Vibe; Gerds, Thomas Alexander

    2012-01-01

    age, crown fracture type, mobility and response to an electric pulp test (EPT) at the initial examination. Results:  Teeth with immature root development: The risk of PN was increased in teeth with a concomitant enamel fracture (log-rank test: P = 0.002), enamel–dentin fracture (log-rank test: P ...The reported risk of pulp necrosis (PN) is generally low in teeth with subluxation injuries. A concomitant crown fracture may increase the risk of PN in such teeth. Aim:  To analyse the influence of a concomitant trauma-related infraction, enamel-, enamel–dentin- or enamel–dentin–pulp fracture...... on the risk of PN in permanent teeth with subluxation injury. Material and Methods:  The study included 404 permanent incisors with subluxation injury from 289 patients (188 male, 101 female). Of these teeth, 137 had also suffered a concomitant crown fracture. All the teeth were examined and treated according...

  6. MULTISEASONAL TREE CROWN STRUCTURE MAPPING WITH POINT CLOUDS FROM OTS QUADROCOPTER SYSTEMS

    Directory of Open Access Journals (Sweden)

    S. Hese

    2017-08-01

    Full Text Available OTF (Off The Shelf quadro copter systems provide a cost effective (below 2000 Euro, flexible and mobile platform for high resolution point cloud mapping. Various studies showed the full potential of these small and flexible platforms. Especially in very tight and complex 3D environments the automatic obstacle avoidance, low copter weight, long flight times and precise maneuvering are important advantages of these small OTS systems in comparison with larger octocopter systems. This study examines the potential of the DJI Phantom 4 pro series and the Phantom 3A series for within-stand and forest tree crown 3D point cloud mapping using both within stand oblique imaging in different altitude levels and data captured from a nadir perspective. On a test site in Brandenburg/Germany a beach crown was selected and measured with 3 different altitude levels in Point Of Interest (POI mode with oblique data capturing and deriving one nadir mosaic created with 85/85 % overlap using Drone Deploy automatic mapping software. Three different flight campaigns were performed, one in September 2016 (leaf-on, one in March 2017 (leaf-off and one in May 2017 (leaf-on to derive point clouds from different crown structure and phenological situations – covering the leaf-on and leafoff status of the tree crown. After height correction, the point clouds where used with GPS geo referencing to calculate voxel based densities on 50 × 10 × 10 cm voxel definitions using a topological network of chessboard image objects in 0,5 m height steps in an object based image processing environment. Comparison between leaf-off and leaf-on status was done on volume pixel definitions comparing the attributed point densities per volume and plotting the resulting values as a function of distance to the crown center. In the leaf-off status SFM (structure from motion algorithms clearly identified the central stem and also secondary branch systems. While the penetration into the

  7. A 3-year follow-up study of all-ceramic single and multiple crowns performed in a private practice: a prospective case series

    Directory of Open Access Journals (Sweden)

    Gianluca M. Tartaglia

    2011-01-01

    Full Text Available OBJECTIVES: Zirconia-based prostheses are commonly used for aesthetic crown and fixed restorations, although follow-up data are limited, especially for implant-supported crowns. The aim of this study was to evaluate the threeyear clinical results of the installation of 463 zirconia core crowns by a general dental private practice. METHODS: This study followed 142 patients (69 men and 73 women; aged 28-82 years who had received 248 single crowns (202 tooth-supported, 36 implant-supported and 225 multiple units of up to six elements (81 toothsupported, 144 implant-supported. Clinical events, including fracture and loss of retention, secondary caries, and marginal integrity, were recorded. The overall failure rate was computed for the fractured and lost prostheses. Aesthetic, functional, and biological properties were rated, and patient satisfaction was investigated. RESULTS: During the three-year follow-up period, four patients were lost from the study (18 crowns, 4% of the total crowns. Three of the zirconia prostheses suffered fractures in more than three units (11 crowns; one- vs. three-year follow-up, p,0.05, Wilcoxon signed-rank test, and the cumulative prosthesis survival rate was 98.2%. Twelve units lost retention and were re-cemented, and no secondary caries of the abutment teeth were reported. The aesthetic, functional, and biological properties were generally well-rated, and there were no differences between tooth- and implant-supported crowns. The lowest scores were given regarding the anatomical form of the crowns, as some minor chipping was reported. Relatively low scores were also given for the periodontal response and the adjacent mucosa. Overall, patient satisfaction was high. CONCLUSIONS: At the three-year follow-up, the zirconia-core crowns appeared to be an effective clinical solution as they had favorable aesthetic and functional properties. Only the marginal fit of the prostheses should be improved upon.

  8. Fracture Strength of Zirconia and Alumina Ceramic Crowns Supported by Implants.

    Science.gov (United States)

    Traini, Tonino; Sorrentino, Roberto; Gherlone, Enrico; Perfetti, Federico; Bollero, Patrizio; Zarone, Ferdinando

    2015-07-01

    Due to the brittleness and limited tensile strength of the veneering glass-ceramic materials, the methods that combine strong core material (as zirconia or alumina) are still under debate. The present study aims to evaluate the fracture strength and the mechanism of failure through fractographic analysis of single all-ceramic crowns supported by implants. Forty premolar cores were fabricated with CAD/CAM technology using alumina (n = 20) and zirconia (n = 20). The specimens were veneered with glass-ceramic, cemented on titanium abutments, and subjected to loading test until fracture. SEM fractographic analysis was also performed. The fracture load was 1165 (±509) N for alumina and 1638 (±662) N for zirconia with a statistically significant difference between the two groups (P = 0.026). Fractographic analysis of alumina-glass-ceramic crowns, showed the presence of catastrophic cracks through the entire thickness of the alumina core; for the zirconia-glass-ceramic crowns, the cracks involved mainly the thickness of the ceramic veneering layer. The sandblast procedure of the zirconia core influenced crack path deflection. Few samples (n = 3) showed limited microcracks of the zirconia core. Zirconia showed a significantly higher fracture strength value in implant-supported restorations, indicating the role played by the high resistant cores for premolar crowns.

  9. Short clinical crowns (SCC) – treatment considerations and techniques

    Science.gov (United States)

    Rahul, G. R.; Poduval, Soorya T.; Shetty, Karunakar

    2012-01-01

    When the clinical crowns of teeth are dimensionally inadequate, esthetically and biologically acceptable restoration of these dental units is difficult. Often an acceptable restoration cannot be accomplished without first surgically increasing the length of the existing clinical crowns; therefore, successful management requires an understanding of both the dental and periodontal parameters of treatment. The complications presented by teeth with short clinical crowns demand a comprehensive treatment plan and proper sequencing of therapy to ensure a satisfactory result. Visualization of the desired result is a prerequisite of successful therapy. This review examines the periodontal and restorative factors related to restoring teeth with short clinical crowns. Modes of therapy are usually combined to meet the biologic, restorative, and esthetic requirements imposed by short clinical crowns. In this study various methods for treating short clinical crowns are reviewed, the role that restoration margin location play in the maintenance of periodontal and dental symbiosis and the effects of violation of the supracrestal gingivae by improper full-coverage restorations has also been discussed. Key words:Short clinical crown, surgical crown lengthening, forced eruption, diagnostic wax up, alveoloplasty, gingivectomy. PMID:24558561

  10. Synthesis and Cation Complexation of Lariat Calix[4 ] crowns

    Institute of Scientific and Technical Information of China (English)

    SHI Zheng-Wei; JIN Chuan-Ming; LU Guo-Yuan

    2003-01-01

    @@ Calixcrowns carrying bridging polyethyleneoxy moieties on the lower rim, which combine calixarene and crown ether in a single molecule, are a novel class of host compounds which have attracted increasing attention because of their increased ability for selective complexation of cations and neutral molecules compared with crown ethers or cal ixarenes.

  11. [Surgical crown lengthening procedures. Preparatory step for fixed prosthesis].

    Science.gov (United States)

    Parashis, A O; Tripodakis, A P

    1990-04-01

    Necessary restorative requirements for full coverage are adequate axial wall height of the preparation for retention as well as sufficient vertical width of sound tooth structure cervically for the crown margins. In cases where adequate healthy tooth structure does not exist coronally to the epithelial attachment due to various crown damages, the margins of the crown might traumatize the periodontal attachment and the periodontium will be jeopardized iatrogenically. Teeth with inadequate axial Reight of the clinical crown, subgingival caries, vertical or horizontal fractures will require surgical crown lengthening procedures before prosthetic treatment is performed. These procedures may either involve only the soft tissues or bone remodeling as well. Irrespective of the procedure, crown lengthening must be performed with the objective of at least 3 mm. of healthy tooth structure coronally to the bone. This width will permit the formation of a new dentinogingival junction and the existence of 1-2 m.m. of sound tooth structure coronally to the new attachment line for the construction of a biologically acceptable crown margin. The purpose of this article is to discuss the clinical problem and underline the importance of crown lengthening procedures as a preparatory step for prosthetic treatment in fixed partial dentures.

  12. Reduction of HCCI combustion noise through piston crown design

    DEFF Research Database (Denmark)

    Pedersen, Troels Dyhr; Schramm, Jesper

    2010-01-01

    Seven shapes of piston crowns have been evaluated for their ability to reduce HCCI knock and transmission of combustion noise to the engine. The performance of each piston crown was evaluated with measurements of cylinder pressure, engine vibration and acoustic sound pressure measured one meter a...

  13. Isotope effects of hafnium in solvent extraction using crown ethers

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Toshiyuki; Moriyama, Hirotake [Research Reactor Institute, Kyoto University, Osaka (Japan); Hirata, Takafumi [Laboratory for Planetary Sciences, Tokyo Institute of Technology, Tokyo (Japan); Nishizawa, Kazushige [Department of Nuclear Engineering, Graduate School of Engineering, Osaka University, Osaka (Japan)

    2001-06-01

    Hafnium isotopes were fractionated in a liquid-liquid extraction system by using seven types of crown ethers, tributyl phosphate, or {omicron}-diethoxybenzene. The largest isotope effect was observed in the isotope pair of {sup 177}Hf-{sup 179}Hf with dibenzo-24-crown-8; the isotope enrichment factor was observed to be 0.0129{+-}0.0032. (author)

  14. SILICA-BOUND CROWN ETHERS PLATINUM COMPLEX AS HYDROSILYLATION CATALYST

    Institute of Scientific and Technical Information of China (English)

    CHEN Yuanyin; MENG Lingzhi; LI Liping; LUO Jieqi; HU Jinchang

    1993-01-01

    Silica-bound 15-Crown-5, 18-Crown-6 with a spacer of propyloxymethyl and their platinum complexes have been synthesized. It was found that they were efficient catalysts for the hydrosilylation of olefins with triethoxysilane in the temperature range of 60 to 130 ℃ .

  15. An interdisciplinary approach to treat crown-root-fractured tooth

    Directory of Open Access Journals (Sweden)

    Ying Chun Sun

    2013-01-01

    Full Text Available Restoration of a crown-root subgingival fractured tooth, especially at anterior aesthetic zones is still a great challenge for restorative dentists. Crown lengthening procedure alone has the disadvantage of high gingival curve of the final restoration, which was not discontinuous to adjacent teeth and thus compromise cosmetic outcomes. The objective of this report is to display a new interdisciplinary approach which combining endodontic root canal treatment, orthodontic extrusion, periodontal crown lengthening surgery and prosthodontic post-core-crown restoration procedures to restore a crown-root subgingival fractured maxillary central incisor and achieved a satisfied cosmetic result. Computer-based spectrophotometer was also used to accurately select colour without objective interference to achieve ideal cosmetic effects.

  16. Biologic rationale of esthetic crown lengthening using innovative proportion gauges.

    Science.gov (United States)

    Fletcher, Paul

    2011-01-01

    Research shows that practitioners tend to underestimate the amount of tooth structure that must be exposed during a crown lengthening procedure. In the anterior portion of the mouth, this can lead to biologic width problems and subsequent cosmetic issues. This paper presents a biologically based, step-by-step approach to periodontal esthetic crown lengthening. Using a series of innovative measuring gauges, the ideal clinical crown length of a tooth as well as the proper occlusogingival placement of the interproximal papilla will be determined based on established, documented tooth proportion relationships. The biologic crown length of the tooth, defined as the distance from the incisal edge to the bone crest, will subsequently be determined as a function of the clinical crown length, with the ultimate goals being adequate tooth structure for the placement of a restorative margin, establishment of a healthy dentogingival complex, and the placement of an esthetically pleasing definitive restoration.

  17. An interdisciplinary approach to treat crown-root-fractured tooth.

    Science.gov (United States)

    Sun, Ying Chun; Li, Ying; Tong, Jian; Gao, Ping

    2013-07-01

    Restoration of a crown-root subgingival fractured tooth, especially at anterior aesthetic zones is still a great challenge for restorative dentists. Crown lengthening procedure alone has the disadvantage of high gingival curve of the final restoration, which was not discontinuous to adjacent teeth and thus compromise cosmetic outcomes. The objective of this report is to display a new interdisciplinary approach which combining endodontic root canal treatment, orthodontic extrusion, periodontal crown lengthening surgery and prosthodontic post-core-crown restoration procedures to restore a crown-root subgingival fractured maxillary central incisor and achieved a satisfied cosmetic result. Computer-based spectrophotometer was also used to accurately select colour without objective interference to achieve ideal cosmetic effects.

  18. Effect of Initial Crown on Shape of Hot Rolled Strip

    Institute of Scientific and Technical Information of China (English)

    HU Yu; GONG Dian-yao; JIANG Zheng-yi; XU Jian-zhong; ZHANG Dian-hua; LIU Xiang-hua

    2009-01-01

    Based on the influence coefficient method, the effect of entry strip crown on the shape of hot rolled strip was analyzed using the software of roll elastic deformation simulation. According to the practical condition of a domestic hot roiled strip plant, the unit strip crown change from the first stand to the last stand was calculated when the entry crown of hot strip varies. The calculated result shows that the entry strip crown does not significantly affect the target strip crown at the exit of the last finishing stand in respect to a fixed strip shape control reference (such as bending force). The calculation was analyzed, and the research is helpful in modeling strip shape setup and shape control.

  19. Calorimetric study of binding of some disaccharides with crown ethers

    Energy Technology Data Exchange (ETDEWEB)

    Davydova, Olga I.; Lebedeva, Nataliya Sh.; Parfenyuk, Elena V

    2004-11-01

    Isothermal titration calorimetry has been applied to the determination of the thermodynamic parameters of binding of {beta}-lactose, {alpha},{alpha}-trehalose and sucrose with 15-crown-5 and 18-crown-6 in water at 298.15 K. The formation of 1:1 molecular associates has been found for the systems studied except 18-crown-6 and {beta}-lactose. The associates are preferentially or completely entropy stabilized. The most stable associate is formed between {alpha},{alpha}-trehalose and 18-crown-6. The obtained values of thermodynamic parameters of binding are discussed from the point of view of solute-solvent interactions as well as conformational and structural peculiarities of the disaccharides (DS) and crown ethers (CE)

  20. Structural Study of Mismatched Disila-Crown Ether Complexes

    Directory of Open Access Journals (Sweden)

    Kirsten Reuter

    2017-02-01

    Full Text Available Mismatched complexes of the alkali metals cations Li+ and Na+ were synthesized from 1,2-disila[18]crown-6 (1 and 2 and of K+ from 1,2,4,5-tetrasila[18]crown-6 (4. In these alkali metal complexes, not all crown ether O atoms participate in the coordination, which depicts the coordination ability of the C-, Si/C-, and Si-bonded O atoms. Furthermore, the inverse case—the coordination of the large Ba2+ ion by the relatively small ligand 1,2-disila[15]crown-5—was investigated, yielding the dinuclear complex 5. This structure represents a first outlook on sandwich complexes based on hybrid crown ethers.

  1. Predation on crown-of-thorns starfish larvae by damselfishes

    Science.gov (United States)

    Cowan, Zara-Louise; Dworjanyn, Symon A.; Caballes, Ciemon F.; Pratchett, Morgan S.

    2016-12-01

    Examining the functional response of predators can provide insight into the role of predation in structuring prey populations and ecological communities. This study explored feeding behaviour and functional responses of planktivorous damselfishes when offered captive reared larvae of crown-of-thorns starfish, Acanthaster sp., with the aim of determining whether these predators could ever play a role in moderating outbreaks of Acanthaster sp. We examined predatory behaviour of 11 species of planktivorous damselfish, testing: (1) the relationship between predator size and predation rate, both within and among fish species; (2) consumption rates on larvae of Acanthaster sp. versus larvae of a common, co-occurring coral reef asteroid Linckia laevigata; (3) maximal feeding rates upon both Acanthaster sp. and L. laevigata; and (4) functional responses of planktivorous fishes to increasing densities of Acanthaster sp. Consumption rates of crown-of-thorns larvae by damselfishes were independent of predator size; however, there was a significant negative relationship between predator size and consumption rate of L. laevigata, when pooling across all predatory species. Some damselfishes, including Acanthochromis polyacanthus and Amblyglyphidodon curacao, consumed larval Acanthaster sp. at a greater rate than for L. laevigata. Most predatory species (all except A. curacao and Pomacentrus amboinensis) exhibited a Type II functional response whereby the increasing feeding rate decelerated with increasing prey density. In addition to revealing that a wide range of planktivorous fishes can prey upon larvae of Acanthaster sp., these data suggest that planktivorous damselfishes may have the capacity to buffer against population fluctuations of Acanthaster sp. Importantly, predators with Type II functional responses often contribute to stability of prey populations, though planktivorous fishes may be swamped by an abnormally high influx of larvae, potentially contributing to the

  2. Validizace Marlowe-Crowne škály sociální desirability v českém prostředí

    OpenAIRE

    Přibáňová, Tereza

    2014-01-01

    Diploma thesis deals with the process of validization of Marlowe-Crowne social desirability scale in the Czech context. Despite the fact that social desirability represents an error, which can disrupt validity of obtained data, there is no official Czech version of Marlowe-Crowne scale that could be used in surveys. The aim of this thesis is to create Czech translation of the scale and test its functionality. The Marlowe-Crowne scale is introduced from a theoretical point of view firstly, is ...

  3. Establishment of crown-root domain borders in mouse incisor.

    Science.gov (United States)

    Juuri, Emma; Saito, Kan; Lefebvre, Sylvie; Michon, Frederic

    2013-10-01

    Teeth are composed of two domains, the enamel-covered crown and the enamel-free root. The understanding of the initiation and regulation of crown and root domain formation is important for the development of bioengineered teeth. In most teeth the crown develops before the root, and erupts to the oral cavity whereas the root anchors the tooth to the jawbone. However, in the continuously growing mouse incisor the crown and root domains form simultaneously, the crown domain forming the labial and the root domain the lingual part of the tooth. While the crown-root border on the incisor distal side supports the distal enamel extent, reflecting an evolutionary diet adaptation, on the incisor mesial side the root-like surface is necessary for the attachment of the interdental ligament between the two incisors. Therefore, the mouse incisor exhibits a functional distal-mesial asymmetry. Here, we used the mouse incisor as a model to understand the mechanisms involved in the crown-root border formation. We analyzed the cellular origins and gene expression patterns leading to the development of the mesial and distal crown-root borders. We discovered that Barx2, En1, Wnt11, and Runx3 were exclusively expressed on the mesial crown-root border. In addition, the distal border of the crown-root domain might be established by cells from a different origin and by an early Follistatin expression, factor known to be involved in the root domain formation. The use of different mechanisms to establish domain borders gives indications of the incisor functional asymmetry.

  4. Separation of americium (III) and strontium (II) using TEHDGA and 18-crown-6

    Energy Technology Data Exchange (ETDEWEB)

    Sinharoy, Prithwish; Khan, Pasupati Nath; Nair, Deepika; Jagasia, Poonam; Dhami, P.S.; Kaushik, C.P.; Banerjee, Kalyan [Bhabha Atomic Research Centre, Mumbai (India). Nuclear Recycle Group; Anitha, M. [Bhabha Atomic Research Centre, Mumbai (India). Rare Earth Development Section; Sharma, J.N. [Bhabha Atomic Research Centre, Mumbai (India). Process Development Div.

    2017-06-01

    This work describes extraction of Am(III) and Sr(II) together with tetra(2-ethylhexyl) diglycolamide (TEHDGA) and selective back-extraction of strontium with a strontium complexant, 18-crown-6, leading to their separation from each other. 0.3 M TEHDGA+5% isodecyl alcohol/n-dodecane was used to extract Am(III) and Sr(II) from 4 M nitric acid into organic phase with very high D (D{sub Am}=1000, D{sub Sr}=22) and 0.1 M 18-crown-6 dissolved in 4 M nitric acid is used for selective stripping of Sr(II) from loaded extract phase. Am(III) left in the extract phase was then stripped with 0.01 M nitric acid. Stripping of Sr(II) was found to increase with increase in 18-crown-6 concentration, at 0.1 M 18-crown-6 dissolved in 4 M nitric acid, 83% of the loaded strontium (D{sub Sr}=0.20) was back-extracted in a single contact while loss of Am(III) was 0.8% (D{sub Am}=122.45). Stoichiometry limit of 1:1 was observed between strontium and 18-crown-6. Strontium was precipitated and separated from the complexant by Na{sub 2}SO{sub 4} or Na{sub 2}CO{sub 3}. This process was tested with simulated solution of high level waste and found suitable for quantitative recovery of strontium with high purity.

  5. An Update on Crown Lengthening. Part 2: Increasing Clinical Crown Height to Facilitate Predictable Restorations.

    Science.gov (United States)

    Kalsi, Harpoonam Jeet; Bomfim, Deborah Iola; Darbar, Ulpee

    2015-04-01

    This is the second paper in this two-part series. Paper one provided an overview of managing gingival tissue excess and paper two will focus on increasing clinical crown height to facilitate restorative treatment. Crown lengthening is a surgical procedure aimed at the removal of gingival tissue with or without adjunctive bone removal. The different types of procedure undertaken will be discussed over the two papers. In order to provide predictable restorations, care must be taken to ensure the integrity of the margins. If this is not taken into account it can lead to an impingement on the biologic width, which may in turn lead to chronic inflammation resulting in recession or the development of periodontal problems which can be hard to manage. Clinical Relevance: This paper aims to reinforce the need for thorough diagnosis and treatment planning and provides an overview of the various procedures that can be undertaken.

  6. Biological restoration: A 4/5 crown

    Directory of Open Access Journals (Sweden)

    Monize Ferreira Figueiredo de Carvalho

    2013-01-01

    Full Text Available Dental caries is one of the most prevalent conditions in humans; the purpose of restorative dentistry is to recreate the anatomy of the affected tooth thus the use of fragments from natural teeth as an effective restorative method. A maxillary first premolar left was prepared for an inverted 4/5 crown due to involvement of the vestibular face, after prepared received an allogeneic collage with similar color and dimension. Follow-up after 12 months indicated a stable restoration. Clinically, the site was without signs of caries, migration of the fragment or marginal infiltration. Biological restoration is a viable alternative for reestablishing function and esthetics to damaged/decayed teeth and therefore, biological restoration as an alternative to other restorative options.

  7. Earliest known crown-group salamanders.

    Science.gov (United States)

    Gao, Ke-Qin; Shubin, Neil H

    2003-03-27

    Salamanders are a model system for studying the rates and patterns of the evolution of new anatomical structures. Recent discoveries of abundant Late Jurassic and Early Cretaceous salamanders are helping to address these issues. Here we report the discovery of well-preserved Middle Jurassic salamanders from China, which constitutes the earliest known record of crown-group urodeles (living salamanders and their closest relatives). The new specimens are from the volcanic deposits of the Jiulongshan Formation (Bathonian), Inner Mongolia, China, and represent basal members of the Cryptobranchidae, a family that includes the endangered Asian giant salamander (Andrias) and the North American hellbender (Cryptobranchus). These fossils document a Mesozoic record of the Cryptobranchidae, predating the previous record of the group by some 100 million years. This discovery provides evidence to support the hypothesis that the divergence of the Cryptobranchidae from the Hynobiidae had taken place in Asia before the Middle Jurassic period.

  8. Dentist material selection for single-unit crowns: Findings from the National Dental Practice-Based Research Network.

    Science.gov (United States)

    Makhija, Sonia K; Lawson, Nathaniel C; Gilbert, Gregg H; Litaker, Mark S; McClelland, Jocelyn A; Louis, David R; Gordan, Valeria V; Pihlstrom, Daniel J; Meyerowitz, Cyril; Mungia, Rahma; McCracken, Michael S

    2016-12-01

    Dentists enrolled in the National Dental Practice-Based Research Network completed a study questionnaire about techniques and materials used for single-unit crowns and an enrollment questionnaire about dentist/practice characteristics. The objectives were to quantify dentists' material recommendations and test the hypothesis that dentist's and practice's characteristics are significantly associated with these recommendations. Surveyed dentists responded to a contextual scenario asking what material they would use for a single-unit crown on an anterior and posterior tooth. Material choices included: full metal, porcelain-fused-to-metal (PFM), all-zirconia, layered zirconia, lithium disilicate, leucite-reinforced ceramic, or other. 1777 of 2132 eligible dentists responded (83%). The top 3 choices for anterior crowns were lithium disilicate (54%), layered zirconia (17%), and leucite-reinforced glass ceramic (13%). There were significant differences (p<0.05) by dentist's gender, race, years since graduation, practice type, region, practice busyness, hours worked/week, and location type. The top 3 choices for posterior crowns were all-zirconia (32%), PFM (31%), and lithium disilicate (21%). There were significant differences (p<0.05) by dentist's gender, practice type, region, practice busyness, insurance coverage, hours worked/week, and location type. Network dentists use a broad range of materials for single-unit crowns for anterior and posterior teeth, adopting newer materials into their practices as they become available. Material choices are significantly associated with dentist's and practice's characteristics. Decisions for crown material may be influenced by factors unrelated to tooth and patient variables. Dentists should be cognizant of this when developing an evidence-based approach to selecting crown material. Copyright © 2016 Elsevier Ltd. All rights reserved.

  9. Odontoplasty associated with clinical crown lengthening in management of extensive crown destruction

    OpenAIRE

    2012-01-01

    Aim: The aim of this study was to evaluate the clinical outcome of teeth submitted to odontoplasty during clinical crown lengthening surgery (CCLS), when compared to their contralateral non-operated teeth. Materials and Methods: Fourteen patients submitted to odontoplasty during CCLS were evaluated according to plaque index, bleeding on probing, probing depth and final restoration outcome (total success, relative success and failure). Results: The mean follow-up period was 13.57 (± 8....

  10. Correlation between maxillary central incisor crown morphology and mandibular dental arch form in normal occlusion subjects.

    Science.gov (United States)

    Paranhos, Luiz Renato; Lima, Carolina Souto; da Silva, Ricardo Henrique Alves; Daruge Júnior, Eduardo; Torres, Fernando Cesar

    2012-01-01

    The aim of this study was to evaluate the correlation between the morphology of the mandibular dental arch and the maxillary central incisor crown. Cast models from 51 Caucasian individuals, older than 15 years, with optimal occlusion, no previous orthodontic treatment, featuring 4 of the 6 keys to normal occlusion by Andrews (the first being mandatory) were observed. The models were digitalized using a 3D scanner, and images of the maxillary central incisor and mandibular dental arch were obtained. These were printed and placed in an album below pre-set models of arches and dental crowns, and distributed to 12 dental surgeons, who were asked to choose which shape was most in accordance with the models and crown presented. The Kappa test was performed to evaluate the concordance among evaluators while the chi-square test was used to verify the association between the dental arch and central incisor morphology, at a 5% significance level. The Kappa test showed moderate agreement among evaluators for both variables of this study, and the chi-square test showed no significant association between tooth shape and mandibular dental arch morphology. It may be concluded that the use of arch morphology as a diagnostic method to determine the shape of the maxillary central incisor is not appropriate. Further research is necessary to assess tooth shape using a stricter scientific basis.

  11. Odontoplasty associated with clinical crown lengthening in management of extensive crown destruction

    Directory of Open Access Journals (Sweden)

    Márcio K da Cruz

    2012-01-01

    Full Text Available Aim: The aim of this study was to evaluate the clinical outcome of teeth submitted to odontoplasty during clinical crown lengthening surgery (CCLS, when compared to their contralateral non-operated teeth. Materials and Methods: Fourteen patients submitted to odontoplasty during CCLS were evaluated according to plaque index, bleeding on probing, probing depth and final restoration outcome (total success, relative success and failure. Results: The mean follow-up period was 13.57 (± 8.00 months, and ranged from 6 to 24 months. Twelve cases presented total success of the final rehabilitation and 2 cases presented relative success. The cases of relative success were due to the necessity for a new periodontal intervention (scalling. No differences were observed with respect to periodontal parameters (P>0.05 and the patients that showed relative success presented generalized poor oral hygiene. Conclusions: The odontoplasty during clinical crown lengthening surgery is a feasible procedure in the management of extensive crown destruction.

  12. Retentive strength of luting cements for stainless steel crowns: an in vitro study.

    Science.gov (United States)

    Subramaniam, Priya; Kondae, Sapna; Gupta, Kamal Kishore

    2010-01-01

    The present study evaluated and compared the retentive strength of three luting cements. A total of forty five freshly extracted human primary molars were used in this study. The teeth were prepared to receive stainless steel crowns. They were then randomly divided into three groups, of fifteen teeth each, so as to receive the three different luting cements: conventional glass ionomer resin modified glass ionomer and adhesive resin. The teeth were then stored in artificial saliva for twenty four hours. The retentive strength of the crowns was determined by using a specially designed Instron Universal Testing Machine (Model 1011). The data was statistically analyzed using ANOVA to evaluate retentive strength for each cement and Tukey test for pair wise comparison. It was concluded that retentive strength of adhesive resin cement and resin modified glass ionomer cement was significantly higher than that of the conventional glass ionomer cement.

  13. Synthesis, characterization and antibacterial activity of new complexes of some lanthanide ions with 15-crown-5 and 18-crown-6

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    Hussein Al-Amery

    2016-05-01

    Full Text Available Complexes of some lanthanide picrates (Ln3+ = Pr3+, Nd3+ and Dy3+ with 15-crown-5 and 18-crown-6 were synthesized and characterized by elemental analysis, ICP-AES, FTIR, 1H-NMR, 13C-NMR and UV-Visible spectrophotometric methods, thermal analysis (TGA & DTG, magnetic susceptibility , molar conductance and melting points. Also an in-vitro study on pathogenic gram positive (Staphylococcus aureus and pathogenic gram negative bacteria (Escherichia coli, Salmonella and pseudomonas aeruginosa was performed and the results were compared to those of a broad spectrum antibiotic (Chloramphinicol. The complexes of 15-crown-5 have the general formula [Ln(15C52(Pic]Pic2.nH2O where (Ln3+ = Nd3+ and Dy3+, (Pic = Picrate anion and (n = 2 or 4 except for Pr3+ complex which has the formula [Pr(15C5]Pic3.H2O , the 18-crown-6 complexes have the general formula [Ln(18C6]Pic3 where (Ln3+ = Pr3+ and Nd3+ except for Dy3+ complex which has the formula [Dy(18C6(Pic]Pic2.3H2O. In 15-crown-5 complexes both Nd3+ and Dy3+ were coordinated with two 15-crown-5 ligands and one picrate anion through its phenolic oxygen and the oxygen of it’s ortho nitro group, except for Pr3+ which was coordinated with only one 15-crown-5 ligand leaving three picrate anions as counter ions. In 18-crown-6 complexes both Pr3+ and Nd3+ were coordinated with one 18-crown-6 ligand leaving all the three picrate anions as counter ions outside the coordination sphere, except for the Dy3+ complex which was coordinated with one 18-crown-6 ligand and one picrate anion.

  14. Three different surgical techniques of crown lengthening: A comparative study

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    Ramya Nethravathy

    2013-01-01

    Full Text Available Introduction: A short clinical crown may lead to poor retention form thereby leading to improper tooth preparation. Surgical crown lengthening procedure is done to increase the clinical crown length without violating the biologic width. Several techniques have been proposed for clinical crown lengthening which includes gingivectomy, apically displaced flap with or without resective osseous surgery, and surgical extrusion using periotome. Objective: The aim of this paper is to compare clinically the three different surgical techniques of crown lengthening procedures. Materials and Methods: Fifteen patients who reported to the department of Periodontology, were included in the study. Patients were randomly divided into three groups, which include patients who underwent gingivectomy (Group A, apically repositioned flap (Group B and surgical extrusion using periotome (Group C. Clinical measurements such as clinical crown length, gingival zenith, interdental papilla height were taken at baseline and at 3 rd month post-operatively. Results: Clinical and radiographic evaluation at 3 rd month suggest that surgical extrusion technique offers several advantages over the other conventional surgical techniques such as preservation of the interproximal papilla, gingival margin position and no marginal bone loss. Conclusions: This technique can be used to successfully treat a grossly damaged crown structure as a result of tooth fracture, dental caries and iatrogenic factors especially in the anterior region, where esthetics is of great concern.

  15. [Ready-made crowns in the deciduous dentition].

    Science.gov (United States)

    Schulte, A

    1999-01-01

    The following review of the literature on "prefabricated crowns for deciduous teeth" attempts to highlight the benefits and limitations of this treatment modality. The use of prefabricated crowns is indicated in the following situations: severe destruction of the clinical crown, deep approximal cavities, bilateral approximal cavities, circumferential caries, history of root canal treatment, and need for fixed space retention. Compared to amalgam restorations involving two or more surfaces, prefabricated crowns on deciduous molar teeth gave very high survival rates. They consist of a chromium-nickel-steel alloy and are reported to have an acceptable gingival tolerance profile. In contrast to the Anglo-American countries this treatment modality is quite uncommon in Germany. A probable reason for this reservation could be that many clinicians often fail to see the need for a filling in the deciduous dentition. Besides, many dentists are reluctant to use local anesthesia in children, which is inevitable in preparing and fitting a prefabricated crown. In the United States and UK dentists are less frequently confronted with this problem, as complex treatments are often carried out under nitrous oxide sedation or insufflation anesthesia. Modern filling materials have been introduced which have the potential to narrow the indications for prefabricated stainless steel crowns. Against this background, future studies are necessary to compare the survival rates of prefabricated crowns and modern filling materials.

  16. Marginal Assessment of Crowns by the Aid of Parallel Radiography

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    Farnaz Fattahi

    2015-03-01

    Full Text Available Introduction: Marginal adaptation is the most critical item in long-term prognosis of single crowns. This study aimed to assess the marginal quality as well asthe discrepancies in marginal integrity of some PFM single crowns of posterior teeth by employing parallel radiography in Shiraz Dental School, Shiraz, Iran. Methods: In this descriptive study, parallel radiographies were taken from 200 fabricated PFM single crowns of posterior teeth after cementation and before discharging the patient. To calculate the magnification of the images, a metallic sphere with the thickness of 4 mm was placed in the direction of the crown margin on the occlusal surface. Thereafter, the horizontal and vertical space between the crown margins, the margin of preparations and also the vertical space between the crown margin and the bone crest were measured by using digital radiological software. Results: Analysis of data by descriptive statistics revealed that 75.5% and 60% of the cases had more than the acceptable space (50µm in the vertical (130±20µm and horizontal (90±15µm dimensions, respectively. Moreover, 85% of patients were found to have either horizontal or vertical gap. In 77% of cases, the margins of crowns invaded the biologic width in the mesial and 70% in distal surfaces. Conclusion: Parallel radiography can be expedient in the stage of framework try-in to yield some important information that cannot be obtained by routine clinical evaluations and may improve the treatment prognosis

  17. Silica crown refractory corrosion in glass melting furnaces

    Directory of Open Access Journals (Sweden)

    Balandis A.

    2011-01-01

    Full Text Available The critical parameters of silica refractories, such as compressive strength, bulk, density, quantity of silica, microstructure and porosity were evaluated of unused and used bricks to line the crowns of glass furnaces, when the rate of corrosion of crowns were about 2 times greater. The change of these parameters, the chemical composition and formation of the microcracks in the used silica refractories material were studied. It was established that the short time at service of container glass furnace crown can be related to low quality of silica brick: high quantity of CaO and impurities, low quantity of silica, low quantity of silica, transferred to tridymite and cristobalite and formation of 5-10 μm and more than 100 μm cracks in the crown material. The main reason of corrosion high quality silica bricks used to line the crown of electrovacuum glass furnace is the multiple cyclic change of crown temperature at 1405 - 1430°C range in the initial zone of crown and at 1575 - 1605°C range in the zone of highest temperatures.

  18. Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics.

    Science.gov (United States)

    Nasrin, S; Katsube, N; Seghi, R R; Rokhlin, S I

    2017-01-01

    This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the

  19. Comparison of the fit of cast gold crowns fabricated from the digital and the conventional impression techniques

    Science.gov (United States)

    Jeon, Young-Chan; Jeong, Chang-Mo

    2017-01-01

    PURPOSE The purpose of this study was to compare the fit of cast gold crowns fabricated from the conventional and the digital impression technique. MATERIALS AND METHODS Artificial tooth in a master model and abutment teeth in ten patients were restored with cast gold crowns fabricated from the digital and the conventional impression technique. The forty silicone replicas were cut in three sections; each section was evaluated in nine points. The measurement was carried out by using a measuring microscope and I-Soultion. Data from the silicone replica were analyzed and all tests were performed with α-level of 0.05. RESULTS 1. The average gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly. 2. In marginal and internal axial gap of cast gold crowns, no statistical differences were found between the two impression techniques. 3. The internal occlusal gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly. CONCLUSION Both prostheses presented clinically acceptable results with comparing the fit. The prostheses fabricated from the digital impression technique showed more gaps, in respect of occlusal surface. PMID:28243386

  20. Crown lengthening procedure in the management of amelogenesis imperfecta.

    Science.gov (United States)

    Kalaivani, S; Manohar, Jenish; Shakunthala, P; Sujatha, S; Rajasekaran, S A; Karthikeyan, B; Kalaiselvan, S

    2015-08-01

    Full mouth rehabilitation includes a promising treatment planning and execution thus fulfilling esthetic, occlusal, and functional parameters maintaining the harmony of the stomatognathic system. Crown lengthening procedures have become an integral component of the esthetic armamentarium and are utilized with increasing frequency to enhance the appearance of restorations placed in the esthetic zone. Crown lengthening plays a role to create healthy relationship of the gingiva and bone levels so as to gain access to more of the tooth which can be restored, if it is badly worn, decayed or fractured, below the gum line. This paper highlights the full mouth crown lengthening procedure performed on a patient with amelogenesis imperfecta.

  1. Analysis of CVC roll contour and determination of roll crown

    Institute of Scientific and Technical Information of China (English)

    Guang Xu; Xianjun Liu; Jiarong Zhao; Junwei Xiong

    2007-01-01

    Mathematical analysis of continuous variable crown (CVC) roll contour used in CSP production line was conducted and the roll contour function of CVC roll was obtained. The validation with actual CVC roll contour shows that the calculation values of the roll contour function and the actual roll contour parameters given by equipment provider are the same, which proves that the roll contour function of CVC rolls given in this article is correct. The nonlinear relationship between the roll crown of CVC rolls and roll shift amounts was deduced. The concept of crown extremum was given.

  2. Crown lengthening procedure in the management of amelogenesis imperfecta

    Science.gov (United States)

    Kalaivani, S.; Manohar, Jenish; Shakunthala, P.; Sujatha, S.; Rajasekaran, S. A.; Karthikeyan, B.; Kalaiselvan, S.

    2015-01-01

    Full mouth rehabilitation includes a promising treatment planning and execution thus fulfilling esthetic, occlusal, and functional parameters maintaining the harmony of the stomatognathic system. Crown lengthening procedures have become an integral component of the esthetic armamentarium and are utilized with increasing frequency to enhance the appearance of restorations placed in the esthetic zone. Crown lengthening plays a role to create healthy relationship of the gingiva and bone levels so as to gain access to more of the tooth which can be restored, if it is badly worn, decayed or fractured, below the gum line. This paper highlights the full mouth crown lengthening procedure performed on a patient with amelogenesis imperfecta. PMID:26538965

  3. Unique case of a geminated supernumerary tooth with trifid crown

    Energy Technology Data Exchange (ETDEWEB)

    Ather, Amber; Ather, Hunaiza; Sheth, Sanket Milan; Muliya, Vidya Saraswathi [Manipal College of Dental Sciences, Manipal (Korea, Republic of)

    2012-09-15

    Gemination, a relatively uncommon dental anomaly, is characterized by its peculiar representation as a tooth with a bifid crown and a common root and root canal. It usually occurs in primary dentition. To come across gemination in a supernumerary tooth is a rare phenomenon. The purpose of this paper is to present a unique case of hyperdontia wherein gemination in an impacted supernumerary tooth resulted in a trifid crown unlike the usual bifid crown. The role of conventional radiographs as well as computed tomography, to accurately determine the morphology and spatial location, and to arrive at a diagnosis, is also emphasized in this paper.

  4. Achieving optimal outcomes with all-zirconia crowns.

    Science.gov (United States)

    Christensen, John Juel

    2014-01-01

    All-zirconia crowns are enjoying an unprecedented popularity. Dental laboratories are acquiring new equipment and adopting novel techniques, some of which require a learning curve. As a result, some crowns fabricated by computer-aided design/computer-aided manufacturing technology may come back to the dentist with unsatisfactory features. Dentists should carefully examine each crown under magnification prior to delivery to the patient. The dentist and dental laboratory should establish a close partnership with clear communication to yield the most favorable outcome for the patient.

  5. Effect of axial groove and resin luting cements on the retention of complete cast metal crowns

    Directory of Open Access Journals (Sweden)

    K Rajkumar

    2009-01-01

    Full Text Available Background : The design of the tooth preparation and the cementing medium are important consid-erations in the retention of crowns and fixed partial dentures. The purpose of this invitro study was to determine the effect of axial groove on the retention of complete cast metal crowns using two resin luting cements. Methods: Forty freshly extracted intact human molar teeth were prepared in their long axis to receive complete cast metal crowns. The specimens were randomly divided into two groups (one control and one study group. An axial groove of uniform size and shape was made on the prepared teeth under the study group. Axial surface area of prepared teeth specimens was measured. Complete cast metal crowns were fabricated for each specimen. Specimens of each group were divided into subgroups of 10 samples and were cemented with two resin luting cements, RelyX Unicem® and Calibra®, re-spectively. The cemented crowns were loaded in tension using a Universal Instron testing machine. The maximal tensile strength was recorded. Data were compared using the Mann-Whitney U test (α=0.05. Results: No significant differences in the tensile stress values were noted between the control (mean: 5.76±0.392 MPa and study (mean: 5.93±0.751 MPa groups cemented with RelyX Unicem. No sig-nificant differences in the tensile stress values were noted between the control (mean: 4.92±0.641 MPa and study (mean: 5.15 ±0.478 MPa groups cemented with Calibra. However, significant dif-ference in the tensile stress values was found between the two resin cements in the control and study groups. Conclusion: Axial groove placed in tooth preparations for resin bonded complete cast metal crowns had no statistically significant effect on retention. The use of (RelyX Unicem® yielded greater reten-tion values when compared to Calibra®.

  6. Comparison of retention of provisional crowns cemented with temporary cements containing stannous fluoride and sodium fluoride-an in vitro study.

    Science.gov (United States)

    Sachin, Bhuvana

    2013-12-01

    The objective of this study was to evaluate the effect of the addition of stannous fluoride (SnF2) and sodium fluoride (NaF) to luting cements on the retention of provisional crowns. Provisional crowns were fabricated using methyl methacrylate and bis-acryl composite resin for 32 chamfer prepared molars. For control group A, crowns were cemented with Freegenol and RelyX Temp NE non-eugenol cements. For test group B, crowns were cemented using the above cements with the addition of SnF2. For test group C, crowns were cemented using the above cements with the addition of NaF. The specimens were thermocycled and retention test was conducted after 7 days. The addition of SnF2 significantly increased the retentive strength of both the cements in the range of 27-48 %, whereas addition of NaF decreased the retentive strength of both the cements in the range of 14-23 %. SnF2 can be mixed with non-eugenol luting cements to improve the retention of both methyl methacrylate and bis-acryl composite crowns. The different effects of NaF and SnF2 on retention indicate that it may be useful to have two different types of provisional luting cements for short-term and long-term cementation, as appropriate.

  7. Comparison of Marginal Circumference of Two Different Pre-crimped Stainless Steel Crowns for Primary Molars After Re-crimping

    Directory of Open Access Journals (Sweden)

    Hossein Afshar

    2016-08-01

    Full Text Available Objectives: It is not clear what type of pre-crimped crown is more successful in achieving greater marginal adaptation following re-crimping. This study aimed to assess the changes in the circumference of 3M ESPE and MIB pre-crimped stainless steel crowns (SSCs for the primary maxillary and mandibular first and second molars following re-crimping.Materials and Methods: This was an in-vitro, experimental study. Initial photographs were obtained from the margins of 3M and MIB SSCs for the upper and lower primary molars using a digital camera. Crown margins were crimped by applying 0.2N force using 114 and 137 pliers. Post-crimping photographs were also obtained and the changes in crown circumference after crimping were calculated using AutoCad software. The percentage of reduction in the circumference of crowns for each tooth was statistically analyzed based on the type of crown using student t-test. The effect of crown design and the associated teeth on the decreased circumference percentage was statistically analyzed by two-sided ANOVA.Results: The percentage of reduction in lower E SSC circumference was 3.71±0.39% in MIB and 6.29±0.62% in 3M crowns. These values were 3.55±0.55% and 7.15±1.13% for the lower Ds, and 3.95±0.43 and 6.24±0.85% for the upper Ds, respectively. For the upper Es, these values were found to be 3.12±0.65% and 5.14±0.94%, respectively. For each tooth, a significant difference was found between MIB and 3M SSCs in terms of the percentage of reduction in crown circumference following crimping. The magnitude of this reduction was smaller in MIB compared to 3M SSCs (P<0.001.Conclusion: Considering the significant reduction in the marginal circumference of pre-crimped SSCs following re-crimping, it appears that this manipulation must be necessarily performed for MIB and 3M pre-crimped SSCs. By using 3M SSCs, higher marginal adaptation can be achieved following crimping.

  8. Unidirectional infiltration method to produce crown for dental prosthesis application

    Energy Technology Data Exchange (ETDEWEB)

    Pontes, F.H.D.; Taguchi, S.P. [Universidade de Sao Paulo (EEL/DEMAR/USP), Lorena, SP (Brazil). Escola de Engenharia; Borges Junior, L.A. [Centro Universitario de Volta Redonda, RJ (Brazil); Machado, J.P.B. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil); Santos, C. [ProtMat Materiais Avancados, Guaratingueta, SP (Brazil)

    2009-07-01

    Alumina ceramics have been used in dental prosthesis because it is inert, presents higher corrosion and shear resistance when compared to metals, excellent aesthetic, and mechanical resistance. In this work it was produced an infrastructure material for applications in dental crowns, obtained by glass infiltration in alumina preform. Various oxides, among that, rare-earth oxide produced by Xenotime, were melted at 1450 deg C and heat treatment at 700 deg C to obtain the glass (REglass). The alumina was pre-sintered at 1100 deg C cut and machined to predetermine format (unidirectional indirect infiltration) and finally conducted to infiltration test. The alumina was characterized by porosity (Hg-porosity and density) and microstructure (SEM). The glass wettability in alumina was determined as function of temperature, and the contact angle presented a low value (θ<90 deg), showing that glass can be infiltrated spontaneously in alumina. The infiltration test was conducted at glass melting temperature, during 30, 60, 180, 360 minutes. After infiltration, the samples were cut in longitudinal section, ground and polished, and analyzed by XRD (crystalline phases), SEM (microstructure) and EDS (composition).The REglass presents higher infiltration height when compared to current processes (direct infiltration), and homogeneous microstructure, showing that it is a promising method used by prosthetics and dentists. (author)

  9. Effects of coronal substrates and water storage on the microhardness of a resin cement used for luting ceramic crowns

    Directory of Open Access Journals (Sweden)

    Luana Menezes de MENDONÇA

    2014-07-01

    Full Text Available Composite resin and metallic posts are the materials most employed for reconstruction of teeth presenting partial or total destruction of crowns. Resin-based cements have been widely used for cementation of ceramic crowns. The success of cementation depends on the achievement of adequate cement curing. Objectives: To evaluate the microhardness of Variolink® II (Ivoclar Vivadent, Schaan, Liechtenstein, used for cementing ceramic crowns onto three different coronal substrate preparations (dentin, metal, and composite resin, after 7 days and 3 months of water storage. The evaluation was performed along the cement line in the cervical, medium and occlusal thirds on the buccal and lingual aspects, and on the occlusal surface. Material and Methods: Thirty molars were distributed in three groups (N=10 according to the type of coronal substrate: Group D- the prepared surfaces were kept in dentin; Groups M (metal and R (resin- the crowns were sectioned at the level of the cementoenamel junction and restored with metallic cast posts or resin build-up cores, respectively. The crowns were fabricated in ceramic IPS e.max® Press (Ivoclar Vivadent, Schaan, Liechtenstein and luted with Variolink II. After 7 days of water storage, 5 specimens of each group were sectioned in buccolingual direction for microhardness measurements. The other specimens (N=5 were kept stored in deionized water at 37ºC for three months, followed by sectioning and microhardness measurements. Results: Data were first analyzed by three-way ANOVA that did not reveal significant differences between thirds and occlusal surface (p=0.231. Two-way ANOVA showed significant effect of substrates (p<0.001 and the Tukey test revealed that microhardness was significantly lower when crowns were cemented on resin cores and tested after 7 days of water storage (p=0.007. Conclusion: The type of material employed for coronal reconstruction of preparations for prosthetic purposes may influence the

  10. Marginal gap, cement thickness, and microleakage of 2 zirconia crown systems luted with glass ionomer and MDP-based cements.

    Science.gov (United States)

    Sener, Isil; Turker, Begum; Valandro, Luiz Felipe; Ozcan, Mutlu

    2014-01-01

    This in vitro study evaluated the marginal gap, cement thickness, and microleakage of glass-ionomer cement (GIC) and phosphate monomer-containing resin cement (MDP-RC) under 2 zirconia crown systems (Cercon and DC-Zirkon). Forty human premolars were prepared for all-ceramic zirconia crowns with a 1 mm circumferential finish line and a 1.5 mm occlusal reduction. The crowns (n = 10 per group) from each zirconia system were randomly divided into 2 groups and cemented either with GIC (Vivaglass CEM) or MDP-RC (Panavia F 2.0) cement. The cemented crowns were thermocycled 5000 times (5°-55°C). The crowns were immersed in 0.5% basic fuchsine dye solution for 24 hours and sectioned buccolingually and mesiodistally. Specimens were examined under optical microscope (100X). Data were analyzed using Student t-test and chi-square tests (α = 0.05). Mean marginal gap values for Cercon (85 ± 11.4 μm) were significantly higher than for DC-Zircon (75.3 ± 13.2 μm) (P = 0.018). The mean cement thickness values of GIC (81.7 ± 13.9 μm) and MDP-RC (78.5 ± 12.5 μm) were not significantly different (P = 0.447). Microleakage scores did not demonstrate significant difference between GIC (P = 0.385) and MDP-RC (P = 0.631) under Cercon or DC-Zircon. Considering the cement thickness values and microleakage scores obtained, both zirconia crown systems could be cemented in combination with either GIC or MDP-RC.

  11. Investigation of the time-dependent wear behavior of veneering ceramic in porcelain fused to metal crowns during chewing simulations.

    Science.gov (United States)

    Guo, Jiawen; Tian, Beimin; Wei, Ran; Wang, Weiguo; Zhang, Hongyun; Wu, Xiaohong; He, Lin; Zhang, Shaofeng

    2014-12-01

    The excessive abrasion of occlusal surfaces in ceramic crowns limits the service life of restorations and their clinical results. However, little is known about the time-dependent wear behavior of ceramic restorations during the chewing process. The aim of this in vitro study was to investigate the dynamic evolution of the wear behavior of veneering porcelain in PFM crowns as wear progressed, as tested in a chewing simulator. Twenty anatomical metal-ceramic crowns were prepared using Ceramco III as the veneering porcelain. Stainless steel balls served as antagonists. The specimens were dynamically loaded in a chewing simulator with 350N up to 2.4×10(6) loading cycles, with additional thermal cycling between 5 and 55°C. During the testing, several checkpoints were applied to measure the substance loss of the crowns' occlusal surfaces and to evaluate the microstructure of the worn areas. After 2.4×10(6) cycles, the entire wear process of the veneering porcelain in the PFM crowns revealed three wear stages (running-in, steady and severe wear stages). The occlusal surfaces showed traces of intensive wear on the worn areas during the running-in wear stage, and they exhibited the propagation of cracks in the subsurface during steady wear stage. When the severe wear stage was reached, the cracks penetrated the ceramic layer, causing the separation of porcelain pieces. It also exhibited a good correlation among the microstructure, the wear loss and the wear rate of worn ceramic restorations. The results suggest that under the conditions of simulated masticatory movement, the wear performance of the veneering porcelain in PFM crowns indicates the apparent similarity of the tribological characteristics of the traditional mechanical system. Additionally, the evaluation of the wear behavior of ceramic restorations should be based on these three wear stages.

  12. Extraction of tree crowns from mobile laser scanning data using a marked point process model

    Science.gov (United States)

    Li, Jonathan; Yu, Yongtao; Guan, Haiyan; Gong, Zheng

    2016-03-01

    For the purpose of realistic visualisation in 3D city models, we present a marked point process based method for extracting tree-crowns from mobile laser scanning (MLS) data. First, we apply a modified IDW interpolation to generate a geo-referenced feature image, by which a histogram analysis is applied to separate high objects(e.g. trees and lightpoles) from low objects(e.g. road, ground, low vegetation). Next, we calculate grey differences of each pixel with its neighbors to find the local maxima as potential tree-crown seeds, and then use a grouping-and-centralizing procedure to remove the redundants from the seeds. Finally, we employ a marked point process to the generated geo-referenced image via the seeds. Two experiments have been conducted to test the efficiency and feasibility of our tree-extraction algorithm using RIEGL VMX-450 MLS data.

  13. Synthesis of Crown Ethers Containing a Rubicene Moiety

    Directory of Open Access Journals (Sweden)

    Mario Smet

    2000-03-01

    Full Text Available A symmetrically disubstituted derivative of the highly fluorescing and photostable rubicene was incorporated in a macrocycle using high dilution conditions and a hydroxyrubicene was functionalized with a modified aminobenzo-15-crown-5.

  14. Supramolecular metal complex systems based on crown-substituted tetrapyrroles

    Energy Technology Data Exchange (ETDEWEB)

    Tsivadze, Aslan Yu [Institute of Physical Chemistry, Russian Academy of Sciences, Moscow (Russian Federation)

    2004-01-31

    The characteristic features of the structures and properties of crown-substituted porphyrinates and phthalocyaninates are considered. Interactions of these compounds with alkali metal salts yield supramolecular ensembles. The factors determining the architecture of such ensembles are described.

  15. Heavy metal accumulation in Melilotus officinalis under crown Olea ...

    African Journals Online (AJOL)

    STORAGESEVER

    2008-11-05

    Nov 5, 2008 ... African Journal of Biotechnology Vol. 7 (21), pp. ... crown Olea europaea L forest irrigated with wastewater .... industrial effluent from Tehran and used for irrigation during 7 ..... Assessment for Central and Eastern Europe.

  16. Acetylene–ammonia–18-crown-6 (1/2/1

    Directory of Open Access Journals (Sweden)

    Tobias Grassl

    2012-10-01

    Full Text Available The title compound, C2H2·C12H24O6·2NH3, was formed by co-crystallization of 18-crown-6 and acetylene in liquid ammonia. The 18-crown-6 molecule has threefold rotoinversion symmetry. The acteylene molecule lies on the threefold axis and the whole molecule is generated by an inversion center. The two ammonia molecules are also located on the threefold axis and are related by inversion symmetry. In the crystal, the ammonia molecules are located below and above the crown ether plane and are connected by intermolecular N—H...O hydrogen bonds. The acetylene molecules are additionally linked by weak C—H...N interactions into chains that propagate in the direction of the crystallographic c axis. The 18-crown-6 molecule [occupancy ratio 0.830 (4:0.170 (4] is disordered and was refined using a split model.

  17. Resistance in tomato and wild relatives to crown and root rot caused by Phytophthora capsici.

    Science.gov (United States)

    Quesada-Ocampo, L M; Hausbeck, M K

    2010-06-01

    Phytophthora capsici causes root, crown, and fruit rot of tomato, a major vegetable crop grown worldwide. The objective of this study was to screen tomato cultivars and wild relatives of tomato for resistance to P. capsici. Four P. capsici isolates were individually used to inoculate 6-week-old seedlings (1 g of P. capsici-infested millet seed per 10 g of soilless medium) of 42 tomato cultivars and wild relatives of tomato in a greenhouse. Plants were evaluated daily for wilting and death. All P. capsici isolates tested caused disease in seedlings but some isolates were more pathogenic than others. A wild relative of cultivated tomato, Solanum habrochaites accession LA407, was resistant to all P. capsici isolates tested. Moderate resistance to all isolates was identified in the host genotypes Ha7998, Fla7600, Jolly Elf, and Talladega. P. capsici was frequently recovered from root and crown tissue of symptomatic inoculated seedlings but not from leaf tissue or asymptomatic or control plants. The phenotype of the recovered isolate matched the phenotype of the inoculum. Pathogen presence was confirmed in resistant and moderately resistant tomato genotypes by species-specific polymerase chain reaction of DNA from infected crown and root tissue. Amplified fragment length polymorphisms of tomato genotypes showed a lack of correlation between genetic clusters and susceptibility to P. capsici, indicating that resistance is distributed in several tomato lineages. The results of this study create a baseline for future development of tomato cultivars resistant to P. capsici.

  18. The energetic characterization of pineapple crown leaves.

    Science.gov (United States)

    Braga, R M; Queiroga, T S; Calixto, G Q; Almeida, H N; Melo, D M A; Melo, M A F; Freitas, J C O; Curbelo, F D S

    2015-12-01

    Energetic characterization of biomass allows for assessing its energy potential for application in different conversion processes into energy. The objective of this study is to physicochemically characterize pineapple crown leaves (PC) for their application in energy conversion processes. PC was characterized according to ASTM E871-82, E1755-01, and E873-82 for determination of moisture, ash, and volatile matter, respectively; the fixed carbon was calculated by difference. Higher heating value was determined by ASTM E711-87 and ash chemical composition was determined by XRF. The thermogravimetric and FTIR analyses were performed to evaluate the thermal decomposition and identify the main functional groups of biomass. PC has potential for application in thermochemical processes, showing high volatile matter (89.5%), bulk density (420.8 kg/m(3)), and higher heating value (18.9 MJ/kg). The results show its energy potential justifying application of this agricultural waste into energy conversion processes, implementing sustainability in the production, and reducing the environmental liabilities caused by its disposal.

  19. Surgical crown lengthening: a periodontal and restorative interdisciplinary approach.

    Science.gov (United States)

    Parwani, Simran R; Parwani, Rajkumar N

    2014-01-01

    Surgical crown lengthening helps to provide an adequate retention form for proper tooth preparation, thus enabling dentists to create esthetically pleasing and healthy restorations. Long-term stability requires accurate diagnosis and development of a comprehensive treatment plan in each case. This sequence of events stresses the importance of communication between the restorative dentist and the periodontist. This article presents 2 cases that involve surgical crown lengthening (including mucoperiosteal flap and ostectomy) for the restoration of teeth.

  20. Crown lengthening procedure in the management of amelogenesis imperfecta

    OpenAIRE

    2015-01-01

    Full mouth rehabilitation includes a promising treatment planning and execution thus fulfilling esthetic, occlusal, and functional parameters maintaining the harmony of the stomatognathic system. Crown lengthening procedures have become an integral component of the esthetic armamentarium and are utilized with increasing frequency to enhance the appearance of restorations placed in the esthetic zone. Crown lengthening plays a role to create healthy relationship of the gingiva and bone levels s...

  1. Polymorph of dibenzo-24-crown-8 and its mercury complex

    OpenAIRE

    Crochet, Aurélien; Kottelat, Emmanuel; Fleury, Antoine; Neuburger, Markus; Fromm, Katharina M.

    2011-01-01

    Dibenzo-24-crown-8 is studied herein as a flexible ligand able to adopt different conformations, as well as for the complexation of mercury. The recrystallization of dibenzo-24-crown-8 (DB24C8) from dry THF gives a new polymorphic structure of this ligand. This new structure is described and compared to the literature compound. Additionally, coordination of this ligand to mercury iodide HgI₂ is studied.

  2. Consequences of crown shortening canine teeth in Greenland sled dogs

    DEFF Research Database (Denmark)

    Kortegaard, H E; Anthony Knudsen, T; Dahl, S

    2015-01-01

    OBJECTIVES: To evaluate the consequences of crown shortening, focusing on the prevalence of pulp exposure and periapical pathology in Greenland sled dogs that had had their canine crowns shortened at an early age. METHODS: Five cadaver heads and 54 sled dogs underwent an oral examination for dental...... fractures and pulp exposure of canines. All canines were radiographed and evaluated for periapical pathology. RESULTS: The prevalence of canine pulp exposure in 12 (5 heads and 7 dogs) crown shortened dogs was 91 · 7%, and 21 · 3% in 47 not-crown shortened dogs. A significant (P ... exposure of the canines in the crown shortened group compared to the not-crown shortened group was seen with a relative risk of 4 · 3 on a dog basis and a relative risk of 12 · 2 on a tooth basis. In dogs with pulp exposure of canines (n = 51) the prevalence of periapical pathology was 82 · 4%, but only 0...

  3. Evaluation of the Effect of Surgical Crown Lengthening on Periodontal Parameters

    OpenAIRE

    2015-01-01

    Background: Surgical crown lengthening is needed for teeth with subgingival caries, fractured teeth, insufficient crown length, and deep subgingival margin of failed restorations. Since there is no agreement on the effects of crown lengthening surgery on gingival parameters, the purpose of this study was to evaluate periodontal parameters in patients who needed crown lengthening surgery. Methods: Twenty patients who had healthy periodontium and needed surgical crown lengthening were included ...

  4. Smart Crown 技术的研究与应用%Study and Application of Smart Crown Technology

    Institute of Scientific and Technical Information of China (English)

    王振华; 王玲珑; 焦广亮

    2012-01-01

    The work principle and technological characteristics of Smart Crown profile control technology were introduced. The roll equivalent crown equation was deduced by Smart Crown roll shape curve equivalent. Production practice proves that the plate profile control capability is greatly improved, roll wear is uniformity and working time is longer after using Smart Crown technology.%介绍了Smart Crown板形控制技术的原理及技术特点,根据Smart Crown辊型曲线方程推导了轧辊等效凸度方程.生产实践证明,使用Smart Crown工作辊后,轧机板形控制能力显著提高,轧辊磨损均匀,工作周期显著延长.

  5. Comparative evaluation of feldespatic crowns fitness made from additional silicon impression and gypsum cast by CAD/CAM

    Directory of Open Access Journals (Sweden)

    Faramarz Zakavi

    2015-05-01

    Full Text Available Background and Aims: Marginal fit is one of the key factors in the success of fixed restoration. The aim of this study was to evaluate the fitness of feldespatic crowns made from additional silicon impression and gypsum cast by CAD/CAM.   Materials and Methods: 10 intact extracted upper premolar teeth were used for this experimental study. After preparation of the mounted teeth with radial shoulder finish line, 2 Vita Mark II feldespatic CAD/CAM machined crowns were fabricated for each tooth (one from scanning the additional silicone impression of the prepared tooth and the other one from the plaster model. Marginal gap of each crown was measured using SEM in two points on the mesial and 2 points on the buccal surface. Data were analyzed using Paired t-test with SPSS version 17 software (P<0.05.   Results: The mean of marginal gaps in crowns fabricated from additional silicone and model plaster were (155.13±37.11 and (130.18±12.35, respectively. However, no significant difference emerged between marginal gaps of the two methods (P=0.055. Also, the mean of marginal gaps in crowns fabricated from additional silicone and model plaster was higher in mesial (157.82±44.41 compared to buccal (127.50±24.26 region (P=0.003.   Conclusion: Marginal fit was not significantly differen ce between crown s made of the plaster casts and silicone molds and both methods showed the same results .

  6. The Effects of New Design of Access Hole on Porcelain Fracture Resistance of Implant-Supported Crowns

    Directory of Open Access Journals (Sweden)

    Reza Derafshi

    2015-03-01

    Full Text Available Statement of the Problem: One disadvantage of cement-retained crowns is the lack of predictable irretrievability. This problem can be overcome through designing a screw access hole in the metal substructure of cement-retained restora-tion and using porcelain stain to define this area. Purpose: This study aimed to evaluate the influence of existence of screw access hole on porcelain fracture resistance of metal-ceramic implant-supported crowns. Materials and Method: Thirty six standardized metal-ceramic crowns were fabri-cated and divided into 3 groups (n=12; group 1 conventional cement-retained metal-ceramic crowns as control group, group 2 cement-retained MC crowns in which porcelain stain was used to define the location of screw access channel, and group 3 cement-retained metal-ceramic crowns in the metal substructure of which a hole and ledge was designed in the location of screw access channel. The specimens were cemented (TempBond, Kerr to their dedicated abutments. A hole was made in the location of screw access channel in group 2 and 3 and filled with photo-polymerized composite resin (3M; ESPE. All specimens were thermocycled and loaded in universal testing machine at crosshead speed of 2mm/min until fracture. Mean values of load at fracture were calculated in each group and compared with One-way ANOVA (α=0.05. Results: Mean value of the load required to fracture the restorations was 1947±487 N in group 1, 1927±539 N in group 2, and 2170±738 N in group 3. No statistically significant difference was found between the fracture resistance values of the three groups (p> 0.05 Conclusion: Presence of screw access channel in cement-retained implant restora-tions does not compromise fracture resistance.

  7. Composite crown-form crowns for severely decayed primary molars: a technique for restoring function and esthetics.

    Science.gov (United States)

    Ram, D; Peretz, B

    2000-01-01

    Current developments in esthetic dentistry center around new techniques and materials that improve the ability of the clinician to provide esthetic services. This article describes a step-by-step method of placing composite crown-form crowns on severely decayed primary mandibular molars. The described technique allows for restoring, as close as possible, form and function lost to caries in an esthetic mode in cases of severely decayed primary molars that would have required stainless steel crowns had they been treated traditionally. Disadvantages of this treatment mode are that dryness may not be prevented in the proximal margins, especially where subgingival carious involvement is encountered and the margin areas may be contaminated with gingival fluid or blood. Although no long-term follow-up has been reported for the technique, when strong opposition by the parent or child to the stainless steel crown is encountered, and a desire for esthetic restoration is strongly expressed, the composite crown-form crowns may be considered as an alternative.

  8. Comparative photophysical behaviour of naphthalene-linked crown ethers and aza crown ethers of varying cavity dimensions

    Indian Academy of Sciences (India)

    Subhodip Samanta; Pinki Saha Sardar; Shyam Sundar Maity; Anirban Pal; Maitrayee Basu Roy; Sanjib Ghosh

    2007-03-01

    A comparative time-resolved emission studies of several naphtho-crown ethers I-V, where metal ions can be complexed in a predetermined orientation with respect to the naphthalene (Naph) - plane and naphthalene-linked aza crown ethers (L1 and L2) have been presented. In both the systems, crown ethers and aza crown ethers, naphthalene fluorescence gets quenched. In the systems I to V, the quenching is mainly due to efficient spin-orbit coupling (SOC) leading to greater population of the lowest triplet state of naphthalene. This SOC depends on the orientation of the crown ring with respect to the Naph--plane. However, in the systems L1 and L2, the quenching is due to photoinduced electron transfer (PET) from nitrogen lone pair of the aza crown ring to naphthalene moiety and consequent exciplex formation. The results have been interpreted using the time-resolved emission studies of all the compounds in various solvents, their alkali metal ion complexes, and protonated ligands.

  9. Archaeobatrachian paraphyly and pangaean diversification of crown-group frogs.

    Science.gov (United States)

    Roelants, Kim; Bossuyt, Franky

    2005-02-01

    Current models for the early diversification of living frogs inferred from morphological, ontogenetic, or DNA sequence data invoke very different scenarios of character evolution and biogeography. To explore central controversies on the phylogeny of Anura, we analyzed nearly 4000 base pairs of mitochondrial and nuclear DNA for the major frog lineages. Likelihood-based analyses of this data set are congruent with morphological evidence in supporting a paraphyletic arrangement of archaeobatrachian frogs, with an (Ascaphus + Leiopelma) clade as the sister-group of all other living anurans. The stability of this outcome is reinforced by screening for phylogenetic bias resulting from site-specific rate variation, homoplasy, or the obligatory use of distantly related outgroups. Twenty-one alternative branching and rooting hypotheses were evaluated using a nonparametric multicomparison test and parametric bootstrapping. Relaxed molecular clock estimates situate the emergence of crown-group anurans in the Triassic, approximately 55 million years prior to their first appearance in the fossil record. The existence of at least four extant frog lineages on the supercontinent Pangaea before its breakup gains support from the estimation that three early splits between Laurasia- and Gondwana-associated families coincide with the initial rifting of these landmasses. This observation outlines the potential significance of this breakup event in the formation of separate Mesozoic faunal assemblages in both hemispheres.

  10. Trend of traumatic crown injuries and associated factors in preschool children

    Directory of Open Access Journals (Sweden)

    Bernardo Antonio AGOSTINI

    Full Text Available Abstract The aim of this study was to assess trends in traumatic crown injuries (TCIs, their prevalence, and association with socioeconomic and clinical factors in preschool children over a 5-year period. A series of cross-sectional surveys was conducted in Santa Maria, Brazil, on children attending a National Day of Children’s Vaccination. The same protocol was used in all surveys conducted in 2008, 2010, and 2013. Clinical examinations were performed to evaluate types of traumatic crown injuries using the O’brien index. A semi-structured questionnaire was answered by the parents. It provided information about several socioeconomic factors as well as the parents’ perception of their child’s oral health. The chi-square for trends test was used to verify changes in TCI prevalence throughout the years. The association between socioeconomic and clinical factors with TCI was assessed by the Poisson regression analysis. A total of 1,640 children were examined. The prevalence of TCIs decreased significantly from 2008 to 2013 (10.12%; p < 0.001. Central incisors were the most vulnerable to injury, independent of the year. Moreover, older children and those with inadequate lip coverage were more likely to present with some traumatic dental injury (p < 0.001. prevalence of traumatic crown injuries decreased following the years, however TCI remain an important subject to consider when planning oral health policies.

  11. Backup roll contour of a SmartCrown tandem cold rolling mill

    Institute of Scientific and Technical Information of China (English)

    Guanghui Yang; Jianguo Cao; Jie Zhang; Shenghui Jia; Renwei Tan

    2008-01-01

    SmartCrown was a new system developed by VAI for improving the strip profile and flatness control first applied in 1700mm tandem cold rolling mills at Wuhan Iron & Steel (Group) Corporation (WISCO). After tracing and testing, the application of the conventional crown backup roll matching the SmartCrown work roll of the production mill led to heavy and nonuniform wear, and the edge spalling of the backup roll often occurred. A 3-dimension finite element model of roll stacks was established, which was used to analyze the above-mentioned problems, and it was found that the main reason was the highly nonuniform contact pressure distribution between the work roll and the backup roll. A new FSR (flexible shape backup roll) was developed and applied in 1700mm tandem cold rolling mills. A lot of good actual effects of FSR, such as evident improvement in profile and flatness of strips,non-occurring edge spalling, wear uniform, and remarkable decrease in roll consumption were validated by long-term industrial applications.

  12. Measurement of lower canine clinical crown index in male and female for gender identification

    Directory of Open Access Journals (Sweden)

    Rita Dewi Handayani

    2007-11-01

    Full Text Available The purpose of this research was to acquire the value index of clinical crown lower jaw canine male and female, and to prove whether the index of male's canine is bigger than female's. The samples of the research was the students of Faculty of Dentistry Universitas Padjadjaran class of 1998 until 2001 by using proportional random sampling method according to the criteria and also adjust with the numbers of male and female composition in per class. The characteristic of the research was analytical descriptive with survey technique. The result of t test statistic measurement was that index of clinical crown tower jaw canine of mate was 1.50 and female was 1.21, by using reliance 95%. The inference of the research showed that the index of clinical crown lower jaw canine of male was significantly bigger than female's. The result of the research can be used as auxiliary data from the techniques to process gender identification in odontology forensic.

  13. Marginal distortion of thermally incompatible metal ceramic crowns with overextended margins.

    Science.gov (United States)

    Nakamura, Y; Anusavice, K J

    1998-01-01

    The present study tested the hypothesis that metal ceramic crowns with a varying axial height are more susceptible to marginal distortion during mechanical and thermal processing treatments than crowns with a uniform axial height. Copings of Pd-Cu-Ga alloy with buccal margin extensions of 0, 1.5, and 3.0 mm were prepared. Oxidized copings were veneered with experimental opaque porcelain with a mean thermal contraction coefficient (25 degrees C to 500 degrees C) that was either 2.1 ppm/degree C below (delta alpha = +2.1 ppm/degree C) or 0.1 ppm/degree C above (delta alpha = -0.1 ppm/degree C) that of the alloy. Nine groups of six specimens each were prepared for analysis. Eighteen copings from these 54 specimens were used as porcelain-free controls. All specimens were subjected to a 10-step procedure including grinding, oxidation, firing of four opaque porcelain layers (O1: 0.15 mm; O2: 0.15 mm; O3: 0.5 mm; O4: 0.5 mm), glazing, abrasive blasting for 15 seconds, removal of ceramic by dissolution in hydrogen fluoride, and a postannealing treatment. The control specimens were also subjected to this procedure with the exception of the firing of four layers of porcelain, which were not applied. Marginal gap width was determined using a measuring microscope at a magnification of 30x. Analysis of variance revealed a significant difference in mean gap width as a function of axial length. The largest gap change was associated with a 3.0-mm buccal extension and the negative mismatch condition (delta alpha < 0). Marginal distortion of crowns decreases as the axial length becomes more uniform. Analysis of crown distortion based on differences in the mean contraction coefficients of metal and porcelain alone is not recommended because it ignores the effects of metal grinding, metal sandblasting, and transient stress.

  14. The fit of crowns produced using digital impression systems.

    Science.gov (United States)

    Vennerstrom, Micael; Fakhary, Mobin; Von Steyern, Per Vult

    2014-01-01

    Compare the marginal and internal fit of crowns manufactured using four different digital impression systems with crowns manufactured using conventional impression technique, that served as a control group. Fifty all-ceramic crowns were fabricated using 50 standardized dies divided into five groups, each group representing one impression system. Each crown was cemented onto its respective model and sectioned into four segments.The marginal and internal fit were measured at 8 predefined points. A total of 1567 measurements were made, statistically analyzed and compared with crowns fabricated using the five systems. The following was found: (1) No significant difference was found with regard to mar ginal gap when comparing the control group to any of the digital systems. (2) Lava™ had smaller marginal gaps than CEREC® and iTero®, (3) CEREC and Lava had smaller gaps in the chamfer compared to iTero and the control, (4) E4D® showed smaller gaps than CEREC at measuring points 4-8 and CEREC a smaller gap at point 2, (5) Lava showed smaller gaps than CEREC at measuring points 1,3 and 5-8. (6) Lava had smaller gaps than iTero at measuring points 1-4,7 and 8. All differences presented were significant. In conclusions, crowns manufactured using digital impressions present a marginal and internal fit equal to, or better than, crowns made using a conventional impression method.The marginal and internal fit of reconstructions made using digital impression techniques could improve with a lower initial setting of the spacer.

  15. Evaluation of marginal and internal gaps of metal ceramic crowns obtained from conventional impressions and casting techniques with those obtained from digital techniques.

    Science.gov (United States)

    Rai, Rathika; Kumar, S Arun; Prabhu, R; Govindan, Ranjani Thillai; Tanveer, Faiz Mohamed

    2017-01-01

    Accuracy in fit of cast metal restoration has always remained as one of the primary factors in determining the success of the restoration. A well-fitting restoration needs to be accurate both along its margin and with regard to its internal surface. The aim of the study is to evaluate the marginal fit of metal ceramic crowns obtained by conventional inlay casting wax pattern using conventional impression with the metal ceramic crowns obtained by computer-aided design and computer-aided manufacturing (CAD/CAM) technique using direct and indirect optical scanning. This in vitro study on preformed custom-made stainless steel models with former assembly that resembles prepared tooth surfaces of standardized dimensions comprised three groups: the first group included ten samples of metal ceramic crowns fabricated with conventional technique, the second group included CAD/CAM-milled direct metal laser sintering (DMLS) crowns using indirect scanning, and the third group included DMLS crowns fabricated by direct scanning of the stainless steel model. The vertical marginal gap and the internal gap were evaluated with the stereomicroscope (Zoomstar 4); post hoc Turkey's test was used for statistical analysis. One-way analysis of variance method was used to compare the mean values. Metal ceramic crowns obtained from direct optical scanning showed the least marginal and internal gap when compared to the castings obtained from inlay casting wax and indirect optical scanning. Indirect and direct optical scanning had yielded results within clinically acceptable range.

  16. The reproducibility and accuracy of internal fit of Cerec 3D CAD/CAM all ceramic crowns.

    LENUS (Irish Health Repository)

    D'Arcy, Brian L

    2009-06-01

    The objective of this study was to evaluate the reproducibility and accuracy of internal fit using Cerec 3D CAD\\/CAM (computer aided design\\/computer aided manufacturing) all-ceramic crowns and to investigate the proximal contact point areas between the crowns and neighbouring teeth, in terms of location and the presence or absence of contact. A total of 48 crowns were milled and divided into two groups of twenty-four each. One group consisted of testing a Control die and the other group consisted of testing single Replica stone die duplicates of the Control die. The Internal Marginal Gap, Axio-Occlusal Transition Gap and Occlusal Gap were measured on each crown in both groups. No significant differences were identified between the mean thickness of the Marginal Gap, the Axio-Occlusal Transition Gap and the Occlusal Gap of the Control die when compared with the Replica dies indicating uniformity and consistency of the accuracy of fit and therefore die replication.

  17. Intellectual ability correlates of the Marlowe-Crowne Social Desirability Scale.

    Science.gov (United States)

    Evans, R G; Forbach, G B

    1982-02-01

    The hypothesis that the Marlowe-Crowne Scale would be negatively related to a variety of intellectual ability measures was investigated in a sample of college students. As predicted, MC scores were negatively correlated with measures of intelligence (Quick Test), associational ability (Remote Associates Test), and academic achievement (course grades). These results suggest that the vulnerable self-esteem and defensiveness traditionally ascribed to high versus low MC scorers may at least in part, reflect a history of poorer performance in intellectual and academically related activities.

  18. Microbiological and microscopic analysis of the pulp of non-vital traumatized teeth with intact crowns

    Directory of Open Access Journals (Sweden)

    Kely Firmino Bruno

    2009-10-01

    Full Text Available OBJECTIVE: This study evaluated the presence of microorganisms and analyzed microscopically the pulp of 20 traumatized human teeth with intact crowns and clinical diagnosis of pulp necrosis, based on the association of at least three of the clinical criteria: crown discoloration, negative response to thermal and electric pulp vitality tests, positive response to vertical and horizontal percussion, pain on palpation or mobility. MATERIAL AND METHODS: Microbiological collection was performed from the root canals to evaluate the presence of microorganisms. The pulp samples were stained with hematoxylin and eosin (H.E. for histological evaluation of possible morphological alterations. RESULTS: Analysis of results was performed by statistical tests (linear regression test and diagnostic analysis and subjective analysis of the sections stained with H.E. and revealed that only 15% of the sample did not exhibit microbial development. The time elapsed between dental trauma and onset of endodontic intervention ranged from 15 days to 31 months; the percussion test presented high sensitivity (80% for detection of microorganisms in the root canal of traumatized teeth; 3 teeth (15% did not present pulp tissue, being characterized as complete autolysis; analysis of pulp samples was performed on the other 17 cases, among which 3 (15% exhibited partial necrosis without possibility of repair and 14 presented complete necrosis; none of the clinical criteria employed for the diagnosis of pulp necrosis in traumatized teeth was pathognomonic. CONCLUSIONS: The present results allowed the following conclusions: with regard to microbiological findings, 85% of teeth presented microorganisms in the root canal, despite the presence of an intact crown. Concerning the microscopic findings, 100% of traumatized teeth presented pulp necrosis; the pulp vitality tests based on pulp response to heat, cold and vertical percussion were the most reliable to diagnose pulp necrosis in

  19. Modeling the spatial distribution of forest crown biomass and effects on fire behavior with FUEL3D and WFDS

    Science.gov (United States)

    Russell A. Parsons; William Mell; Peter McCauley

    2010-01-01

    Crown fire poses challenges to fire managers and can endanger fire fighters. Understanding of how fire interacts with tree crowns is essential to informed decisions about crown fire. Current operational crown fire predictions in the United States assume homogeneous crown fuels. While a new class of research fire models, which model fire behavior with computational...

  20. Comparative evaluation of bond strengths of different core materials with various luting agents used for cast crown restorations.

    Science.gov (United States)

    Nayakar, Ramesh P; Patil, Narendra P; Lekha, K

    2012-09-01

    The coronal cast restoration continues to be used commonly to restore mutilated, endodontically treated teeth. The tensile bond strength of luting cements is of critical importance as many of failures are at the core and the crown interface. An invitro study with aim to evaluate and compare bond strengths of luting cements between different core materials and cast crowns. A total of 45 extracted identical mandibular second premolars were endodontically treated and divided into 3 groups of 15 each. Specimens in first group were restored with cast post and core (Group C), and specimens in second group were restored with stainless steel parapost and composite core material (Group B) and specimens in third group were restored with stainless steel parapost and glass ionomer core build (Group G). Standardized crown preparation was done for all the specimens to receive cast crowns. Each group was further divided into 3 subgroups and were cemented using 3 different luting cements namely, resin cement, polycarboxylate cement, glass ionomer cement (Type I). The samples of each subgroup (n = 5) were subjected to tensile testing using Universal Testing Machine at a crosshead speed of 2 mm/min till the dislodgement of crown from the core surface was observed. The bond strengths were significantly different according one way ANOVA (F-150.76 and p < 0.0000). The results of the study showed that the specimens cemented with resin cement in cast core, composite core and glass ionomer core exhibited significantly higher bond strengths as compared to specimens cemented with glass ionomer and polycarboxylate cement. Composite resin core and resin cement combinations were superior to all other cement and core combinations tested.

  1. Digital modeling technology for full dental crown tooth preparation.

    Science.gov (United States)

    Dai, Ning; Zhong, Yicheng; Liu, Hao; Yuan, Fusong; Sun, Yuchun

    2016-04-01

    A dental defect is one of the most common oral diseases, and it often requires a full crown restoration. In this clinical operation, the dentist must manually prepare the affected tooth for the full crown so that it has a convergence angle between 4° and 10°, no undercuts, and uniform and even shoulder widths and depths using a high speed diamond bur in the patient׳s mouth within one hour, which is a difficult task that requires visual-manual operation. The quality of the tooth preparation has an important effect on the success rate of the subsequent prosthodontic treatment. This study involved research into digital modeling technology for full dental crown tooth preparation. First, the margin line of the tooth preparation was designed using a semi-automatic interactive process. Second, the inserting direction was automatically computed. Then, the characteristic parameters and the constraints on the tooth preparation were defined for the model. Next, the shoulder and axial surface of the tooth preparation were formed using parametric modeling. Finally, the implicit surface of a radial basis function was used to construct the tooth preparation׳s occlusal surface. The experimental results verified that the method of digital modeling for full crown preparation proposed in this study can quickly and accurately implement personalized designs of various parameters, such as the shoulder width and the convergence angle; it provides a digital design tool for full crown preparation.

  2. Biology and control of the raspberry crown borer (Lepidoptera: Sesiidae).

    Science.gov (United States)

    McKern, Jacquelyn A; Johnson, Donn T; Lewis, Barbara A

    2007-04-01

    This study explored the biology of raspberry crown borer, Pennisetia marginata (Harris) (Lepidoptera: Sesiidae), in Arkansas and the optimum timing for insecticide and nematode applications. The duration of P. marginata's life cycle was observed to be 1 yr in Arkansas. Insecticide trials revealed that bifenthrin, chlorpyrifos, imidacloprid, metaflumizone, and metofluthrin efficacy were comparable with that of azinphosmethyl, the only labeled insecticide for P. marginata in brambles until 2005. Applications on 23 October 2003 for plots treated with bifenthrin, chlorpyrifos, and azinphosmethyl resulted in >88% reduction in larvae per crown. Applications on 3 November 2004 of metaflumizone, metofluthrin, and bifenthrin resulted in >89% reduction in larvae per crown. Applications on 7 April 2005 for metofluthrin, imidacloprid, bifenthrin, metaflumizone, and benzoylphenyl urea resulted in >64% reduction in the number of larvae per crown. Applications on 6 May 2004 did not reduce larval numbers. The optimum timing for treatments was found to be between October and early April, before the larvae tunneled into the crowns of plants. Applying bifenthrin with as little as 468 liters water/ha (50 gal/acre) was found to be as effective against larvae as higher volumes of spray. Nematode applications were less successful than insecticides. Nematode applications of Steinernemafeltiae, Steinernema carpocapsae, and Heterorhabditis bacteriophora reduced larvae counts per plant by 46, 53, and 33%, respectively.

  3. Crown sealing and buckling instability during water entry of spheres

    KAUST Repository

    Marston, J. O.

    2016-04-05

    We present new observations from an experimental investigation of the classical problem of the crown splash and sealing phenomena observed during the impact of spheres onto quiescent liquid pools. In the experiments, a 6 m tall vacuum chamber was used to provide the required ambient conditions from atmospheric pressure down to of an atmosphere, whilst high-speed videography was exploited to focus primarily on the above-surface crown formation and ensuing dynamics, paying particular attention to the moments just prior to the surface seal. In doing so, we have observed a buckling-type azimuthal instability of the crown. This instability is characterised by vertical striations along the crown, between which thin films form that are more susceptible to the air flow and thus are drawn into the closing cavity, where they atomize to form a fine spray within the cavity. To elucidate to the primary mechanisms and forces at play, we varied the sphere diameter, liquid properties and ambient pressure. Furthermore, a comparison between the entry of room-temperature spheres, where the contact line pins around the equator, and Leidenfrost spheres (i.e. an immersed superheated sphere encompassed by a vapour layer), where there is no contact line, indicates that the buckling instability appears in all crown sealing events, but is intensified by the presence of a pinned contact line. © 2016 Cambridge University Press.

  4. Museum security and the Thomas Crown Affair.

    Energy Technology Data Exchange (ETDEWEB)

    Michaud, E. C. (Nuclear Engineering Division)

    2010-01-01

    Over the years, I've daydreamed about stealing a Vermeer, a Picasso, or Rembrandt. It tickles me, as much as watching the reboot of The Thomas Crown Affair. Why is it, do you suppose, so much fun to think about stealing a world renowned piece off the wall of a major metropolitan museum? Is it the romantic thoughts of getting away with it, walking past infrared detectors, and pressure sensors ala Indiana Jones with the sack of sand to remove the idol without triggering the security system? Is it the idea of snatching items with such fantastic prices, where the romance of possessing an item of such value is less intoxicating than selling it to a private collector for it to never be seen again? I suspect others share my daydreams as they watch theater or hear of a brazen daylight heist at museums around the world, or from private collections. Though when reality sets in, the mind of the security professional kicks in. How could one do it, why would one do it, what should you do once it's done? The main issue a thief confronts when acquiring unique goods is how to process or fence them. They become very difficult to sell because they are one-of-a-kind, easy to identify, and could lead to the people involved with the theft. The whole issue of museum security takes up an ironic twist when one considers the secretive British street artist 'Banksy'. Banksy has made a name for himself by brazenly putting up interesting pieces of art in broad daylight (though many critics don't consider his work to be art) on building walls, rooftops, or even museums. I bring him up for a interesting take on what may become a trend in museum security. In March of 2005, Banksy snuck a piece of his called 'Vandalized Oil Painting' into the Brooklyn Museum's Great Historical Painting Wing, plus 3 other pieces into major museums in New York. Within several days, 2 paintings had been torn down, but 2 stayed up much longer. In his home country of the UK, a

  5. AB INITIO INVESTIGATION OF 12-CROWN-4 AND BENZO-12-CROWN-4 COMPLEXES WITH Li+, Na+, K+, Zn2+, Cd2+, AND Hg2+

    Directory of Open Access Journals (Sweden)

    Yahmin Yahmin

    2010-06-01

    Full Text Available The structure and binding energies of 12-crown-4 and benzo-12-crown-4 complexes with Li+, Na+, K+, Zn2+, Cd2+, and Hg2+were investigated with ab initio calculations using Hartree-Fock approximation and second-order perturbation theory. The basis set used in this study is lanl2mb. The structure optimization of cation-crown ether complexes was evaluated at HF/lanl2mb level of theory and interaction energy of the corresponding complexes was calculated at MP2/lanl2mb level of theory (MP2/lanl2mb//HF/lanl2mb. Interactions of the crown ethers and the cations were discussed in term of the structure parameter of crown ether. The binding energies of the complexes show that all complex formed from transition metal cations is more stable than the complexes formed from alkali metal cations.   Keywords: 12-crown-4, benzo-12-crown-4, alkali metals, transition metals

  6. Displacement of Monolithic Rubble-Mound Breakwater Crown-Walls

    DEFF Research Database (Denmark)

    Nørgaard, Jørgen Harck; Andersen, Lars Vabbersgaard; Andersen, Thomas Lykke

    2012-01-01

    studies on caisson breakwaters, but correction terms are suggested in the present paper to obtain almost equal measured and estimated displacements. This is of great practical importance since many existing rubble-mound crown-walls are subjected to increasing wave loads due to rising sea water level from......This paper evaluates the validity of a simple one-dimensional dynamic analysis as well as a Finite-Element model to determine the sliding of a rubble-mound breakwater crown-wall. The evaluation is based on a case example with real wave load time-series and displacements measured from two...... of the accumulated sliding distance of crown-wall superstructures, which is in contrast to findings from previous similar studies on caisson breakwaters. The calculated sliding distance is approximately three times larger than the measured one when using the original one-dimensional model suggested in previous...

  7. Laser-assisted flapless crown lengthening: a case series.

    Science.gov (United States)

    McGuire, Michael K; Scheyer, E Todd

    2011-01-01

    As part of the paradigm shift toward more minimally invasive surgical procedures, increasing numbers of references to laser-mediated flapless crown lengthening are noted in the published literature. The vast majority of these references are noncontrolled case reports or technique-focused articles. Therefore, prospective, randomized controlled studies that objectively examine the safety and efficacy of flapless crown lengthening are lacking. The current case series represents an initial attempt to examine some of the clinical issues posed by this minimally invasive flapless approach. Ultimately, only well-designed controlled clinical trials can yield the type of evidence-based data necessary to categorize this approach to crown lengthening as standard-of-care treatment.

  8. Dimethylammonium tetrachloridoferrate(III 18-crown-6 clathrate

    Directory of Open Access Journals (Sweden)

    Ping Ping Shi

    2010-07-01

    Full Text Available The reaction of dimethylamine hydrochloride, 18-crown-6 and ferric chloride in ethanol yields the title compound, (C2H8N[FeCl4]·C12H24O6, which exhibits an unusual supramolecular structure. The protonated dimethylamine contains one NH2+ group, resulting in a 1:1 supramolecular rotator–stator structure (CH3—NH2+—CH3(18-crown-6, through N—H...O hydrogen-bonding interactions between the ammonium group of the cation and the O atoms of the crown ether. In the crystal, all three components lie on a common crystallographic mirror plane normal to [010].

  9. Chipping resistance of graded zirconia ceramics for dental crowns.

    Science.gov (United States)

    Zhang, Y; Chai, H; Lee, J J-W; Lawn, B R

    2012-03-01

    A serious drawback of veneering porcelains is a pronounced susceptibility to chipping. Glass-infiltrated dense zirconia structures can now be produced with esthetic quality, making them an attractive alternative. In this study, we examined the hypothesis that such infiltrated structures are much more chip-resistant than conventional porcelains, and at least as chip-resistant as non-infiltrated zirconia. A sharp indenter was used to produce chips in flat and anatomically correct glass-infiltrated zirconia crown materials, and critical loads were measured as a function of distance from the specimen edge (flat) or side wall (crown). Control data were obtained on zirconia specimens without infiltration and on crowns veneered with porcelains. The results confirmed that the resistance to chipping in graded zirconia is more than 4 times higher than that of porcelain-veneered zirconia and is at least as high as that of non-veneered zirconia.

  10. Crowned odontoid process and osteoarthrosis of the anterior atlantoaxial joint

    Energy Technology Data Exchange (ETDEWEB)

    Skaane, P.; Klott, K.J.

    1981-01-01

    Crowned odontoid process and osteoarthrosis of the anterior atlantoaxial joint. The so-called peridentale aureole ( crowned odontoid ), a horseshoelike calcification around the odontoid process, can occasionally be shown on transbuccal views of the occipito-atlantoaxial region, but is commonly only seen on a.p. tomography in patients with osteoarthrosis of the anterior atlantoxial joint. Tomographic examinations reveal that these irregular horseshoe-like calcifications around the odontoid peg represent mainly the osteophyte formation on the superior border of the anterior arch of the atlas. These calcifications are often surrounding a smaller calcification on the tip of the odontoid peg sometimes with a bucket-handle appearance corresponding to the ostephyte formation on the odontoid process. The peridentale aureole or crowned odontoid process is easily overlooked unless tomography is performed, and misinterpretations are possible if the radiologist is not familiar with this appearance of osteoarthrosis and some other joint diseases of the anterior atlantoaxial joint.

  11. Uniform versus asymmetric shading mediates crown recession in conifers.

    Directory of Open Access Journals (Sweden)

    Amanda L Schoonmaker

    Full Text Available In this study we explore the impact of asymmetrical vs. uniform crown shading on the mortality and growth of upper and lower branches within tree crowns, for two conifer species: shade intolerant lodgepole pine (Pinus contorta and shade tolerant white spruce (Picea glauca. We also explore xylem hydraulics, foliar nutrition, and carbohydrate status as drivers for growth and expansion of the lower and upper branches in various types of shading. This study was conducted over a two-year period across 10 regenerating forest sites dominated by lodgepole pine and white spruce, in the lower foothills of Alberta, Canada. Trees were assigned to one of four shading treatments: (1, complete uniform shading of the entire tree, (2 light asymmetric shading where the lower 1/4-1/3 of the tree crown was shaded, (3 heavy asymmetric shading as in (2 except with greater light reduction and (4 control in which no artificial shading occurred and most of the entire crown was exposed to full light. Asymmetrical shading of only the lower crown had a larger negative impact on the bud expansion and growth than did uniform shading, and the effect was stronger in pine relative to spruce. In addition, lower branches in pine also had lower carbon reserves, and reduced xylem-area specific conductivity compared to spruce. For both species, but particularly the pine, the needles of lower branches tended to store less C than upper branches in the asymmetric shade, which could suggest a movement of reserves away from the lower branches. The implications of these findings correspond with the inherent shade tolerance and self-pruning behavior of these conifers and supports a carbon based mechanism for branch mortality--mediated by an asymmetry in light exposure of the crown.

  12. Synthesis and adsorption properties of chitosan-crown ether resins

    Institute of Scientific and Technical Information of China (English)

    彭长宏; 陈艺锋; 唐谟堂

    2003-01-01

    Two kinds of novel chitosan-crown ether resins, Schiff base type chitosan-benzo-15-crown-5 (CTS-B15)and chitosan-benzo-18-crown-6 (CTS-B18), were synthesized through the reaction between -NH2 in chitosan and -CHO in 4′-formyl benzo-crown ethers. Their structures were characterized by elemental analysis and FT-IR spectra analysis. The elemental analysis results show that the mass fractions of nitrogen in CTS-B15 and CTS-B18 are much lower than those of chitosan. The results of FT-IR spectra of CTS-B15 and CTS-B18 reveal that there exist characteristic peak of C= N, N-H and Ar, and characteristic peak of pyr anoside in the chain of chitosan-crown ether resins, showing that the structures of chitosan-crown ethers are as expected. The adsorption properties of CTS-B15 and CTS-B18 for Pd2+ , Cu2 + and Hg2+ were studied and the experimental results show that these adsorbents have both good adsorption characterization and especially high particular adsorption selectivity for Pd2+ when Cu2+ and Hg2+ are in coexistence, and the coefficients of selectivity of CTS-B15 and CTS-B18 for metal ions are KPd2+/cu2+ =7.56, KPd2+/Hg2+ = 68.00, Kcu2+/Hg2+ = 9.00 and KPd2+/cu2+ = 6.00, KPd2+/Hg2+ = 19. 00, Kcu2+/Hg2+ = 3.00, respectively.

  13. The Microleakage of Polycarboxylate, Glass Ionomer and Zinc Phosphate Cements for Stainless Steel Crowns of Pulpotomized Primary Molars

    Directory of Open Access Journals (Sweden)

    Mahkameh Mirkarimi

    2013-01-01

    Full Text Available Background: Microleakage in Stainless Steel Crowns (SSC margins leads to seepage of oral fluids and bacteria and it is one of the reasons for treatments failures. The aim of this study was to assess the effect of zinc phosphate, glass Ionomer and polycarboxylate cements on microleakage of stainless steel crowns for primary pulpotomized molar teeth. Materials and Methods: In this experimental in vitro study, 60 extracted primary molar teeth were randomly divided in to three groups (n=20. Stainless steel crowns were fitted for each tooth after pulpotomy procedures. Crowns were luted with a zinc phosphate, glass ionomer or polycarboxylate cement. All specimens were stored in 100% humidity at 37o C for 1 hour and termocycled 500 times (5ºC to 55ºC with a 30 seconds dwell time and then immersed in 0.5% basic fuschin solution for 24 hours. The specimens were sectioned buccolingually and each section was evaluated for microleakage under a stereomicroscope.Results: In zinc phosphate group 45% of spicemens and in glass ionomer group there was 5% of spicemens showed leakage extending on to occlusal aspect and in polycarboxylate group none of the spicemens had this situation. According to the kruskal wallis test in all groups there were significant differences in microleakage (p< 0.001.Conclusion: The use of zinc phosphate cement resulted in the highest percentage of microleakage. The microleakage of SSCs cemented with polycarboxylate and glass ionomer were similar.

  14. Effect of the Crystallization Process on the Marginal and Internal Gaps of Lithium Disilicate CAD/CAM Crowns

    Directory of Open Access Journals (Sweden)

    Jae-Hong Kim

    2016-01-01

    Full Text Available The aim of this study is to quantify the effect of the crystallization process on lithium disilicate ceramic crowns fabricated using a computer-aided design/computer-aided manufacturing (CAD/CAM system and to determine whether the effect of crystallization is clinically acceptable by comparing values of fit before and after the crystallization process. The mandibular right first molar was selected as the abutment for the experiments. Fifteen working models were prepared. Lithium disilicate crowns appropriate for each abutment were prepared using a commercial CAD/CAM system. Gaps in the marginal area and 4 internal areas of each crown were measured twice—before and after crystallization—using the silicone replica technique. The mean values of fit before and after crystallization were analyzed using a paired t-test to examine whether the conversion that occurred during crystallization affected marginal and internal gaps (α=0.05. Gaps increased in the marginal area and decreased in the internal areas after crystallization. There were statistically significant differences in all of the investigated areas (P<0.05. None of the values for marginal and internal fit of lithium disilicate CAD/CAM crowns after crystallization exceeded 120 μm, which is the clinically acceptable threshold.

  15. [Estimating nonstructural carbon content of tree crown considering its spatial variability: A case study on Juglans mandshurica and Ulmus japonica].

    Science.gov (United States)

    Cheng, Fang-yan; Wang, Chuan-kuan

    2015-08-01

    Using Juglans mandshurica and Ulmus japonica as test materials, we examined the variability in nonstructural carbohydrates (NSC) concentrations in the branches with different basal diameters with a branch analysis method and explored potential errors in estimating the crown-scale NSC content introduced from various sampling protocols. The results showed that organs significantly influenced the crown NSC concentrations for both species. The mean concentrations of the sum of soluble sugars and starch (TNC) of the leaves, new twigs, old branches, and dead branches were 17.6%, 12.6%, 5.7% and 2.9%, respectively. Most of the NSC concentrations in leaves and new twigs varied insignificantly with basal diameter, age, length and height of the branch. However, the NSC concentration in old branches increased significantly with decreasing the basal diameter, age and length of the branch, and with increasing the relative height of the branch. Among the branch traits, basal diameter was the best predictor for the NSC concentration of the old branch (the R2 between 0.87 and 0.95). The mean TNC contents of leaves, new branches, and old branches for the two species accounted for 28%, 2% and 70% of the crown TNC content, respectively. Considering the effect of the spatial variability in the estimation of NSC content, we recommend the sampling protocol that applies the NSC concentration of new twigs and old branches with a diameter of 3 cm to up-scale the crown NSC content as a simple and practical method.

  16. Barodontalgia: a review, and the influence of simulated diving on microleakage and on the retention of full cast crowns.

    Science.gov (United States)

    Lyons, K M; Rodda, J C; Hood, J A

    1999-03-01

    This paper reviews the causes of barodontalgia and reports on a study that indicates a possible cause of barodontalgia in the diver. In the study, extracted teeth had full cast crowns cemented with either a zinc phosphate, a glass ionomer, or a resin cement, and simulated diving to 30 m (3.0 atmospheres) was performed. During simulated diving, the teeth were pressure cycled 15 times to 3 atmospheres and microleakage was monitored. The force required to dislodge the crown was then tested; a significant difference was found between the zinc phosphate and the glass ionomer cement groups (p < 0.01). No difference was found between the resin cement groups. Microleakage was also detected in the zinc phosphate and glass ionomer cement groups and was found to occur sooner, and to a greater extent with zinc phosphate. No microleakage was detected in the resin cement experimental group. This study showed that the retention of full cast crowns to extracted teeth is reduced after pressure cycling and that microleakage does occur if the crowns are cemented with either zinc phosphate cement or glass ionomer cement.

  17. Identification of urban tree crown in a tropical environment using WorldView-2 data: problems and perspectives

    Science.gov (United States)

    Gomes, Marília F.; Maillard, Philippe

    2013-10-01

    With the availability of high-resolution satellite data, much research has been focused on the automatic detection and classi cation of individual tree crowns. Most of these studies were applied to temperate climates of the northern hemisphere, especially for forests of coniferous. Very few studies have been applied to the detection of trees in the tropical regions, least of all in the urban environment. Urban trees play a major role in maintaining or even improving the quality of life in cities by their contribution to the quality of the air, by absorbing rain water, by refreshing the air through transpiration and providing shadow. In this study we explored the potential of high-resolution WorldView-2 satellite data for the identi cation of urban individual tree crowns in the city of Belo Horizonte, Minas Gerais, Brazil, through an object-oriented approach. Irrelevant areas were masked (e.g. buildings, asphalt, shadows, exposed soil) using a threshold of NDVI. Three di erent approaches were tested to isolate and delineate individual tree crowns: region growing, watershed and template matching. For the rst two approaches several parameters were tested to nd the best result for the isolation of the individual tree crowns. An in-house program has been developed for template matching using a set of seven di erent templates of di erent species. A set of 300 individual tree crowns were visually interpreted in the WorldView-2 image to serve as validation and to compare the performance of the three di erent approaches. Then, the comparison was performed between the visual interpretation and the results of each approach by calculating the di erence between the areas as a ratio of the validated area. Our results show that the region growing approach provided the best results, with an accuracy of over 80%.

  18. Crowning glory: public law, power and the monarchy

    OpenAIRE

    Murphy, Thérèse; Whitty, Noel

    2000-01-01

    ‘New public law’ has a keen interest in the deployment of power and the shifting nature of the public and private. In this article, we argue that the historical legacy of the Crown has hindered the ability of public lawyers to respond to changes in modes of governance in the UK. The constitutional law textbook tradition has played a key role in limiting critiques of the Crown because of the obfuscation that surrounds the legal and political status of the Monarch. However, instead of discounti...

  19. Biologic width and crown lengthening: case reports and review.

    Science.gov (United States)

    Oh, Se-Lim

    2010-01-01

    The biologic width includes both the connective tissue attachment and the junctional epithelium and has a mean dimension of approximately 2 mm. Invading the biologic width with a restoration can result in localized crestal bone loss, gingival recession, localized gingival hyperplasia, or a combination of these three. When restoring teeth that have subgingival caries or fractures below the gingival attachment, a clinical crown-lengthening procedure is needed to establish the biologic width. This article presents three case reports that utilized crown-lengthening procedures.

  20. Synthesis of Schiff Base Calix[4]arene Crowns

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    This letter reports the synthesis of Schiff base calix[4]arene crowns containing m-xylylene phenol subunit, in which calix[4]arene Schiff base crowns 2a, 2b and 2c were formed by 1:1 condensation of calix[4]arene diamine 1 with dialdehydes (2, 6-diformyl-4-chlorophenol 3a, 2, 6-diformyl-4-methylphenol 3b, 2, 6-diformyl-4-tert-butylphenol 3c) under high dilute condition in refluxing anhydrous ethanol in 65-70% yield.

  1. CROWN: A service grid middleware with trust management mechanism

    Institute of Scientific and Technical Information of China (English)

    HUAI Jinpeng; HU Chunming; LI Jianxin; SUN Hailong; WO Tianyu

    2006-01-01

    Based on a proposed Web service-based grid architecture, a service grid middleware system called CROWN is designed in this paper. As the two kernel points of the middleware, the overlay-based distributed grid resource management mechanism is proposed, and the policy-based distributed access control mechanism with the capability of automatic negotiation of the access control policy and trust management and negotiation is also discussed in this paper. Experience of CROWN testbed deployment and application development shows that the middleware can support the typical scenarios such as computing-intensive applications, data-intensive applications and mass information processing applications.

  2. Stars and Nebulae in the Southern Crown

    Science.gov (United States)

    2000-10-01

    The R Coronae Australis complex of young stars and interstellar gas clouds is one of the nearest star-forming regions, at a distance of approx. 500 light-years from the Sun. It is seen in the southern constellation of that name (The "Southern Crown"). Images of this sky area were recently obtained with the Wide Field Imager (WFI) , a 67-million pixel digital camera that is installed at the 2.2-m MPG/ESO Telescope at ESO's La Silla Observatory. Some of these exposures have been combined into a magnificent colour image, here reproduced as PR Photo 25a/00 . The field shown measures about 4.7 x 4.7 light-years 2. It displays the central part of the complex, its brightest stars, and the nebulosity that they illuminate. The interstellar clouds that are associated with the complex are visible all across this field and also beyond its borders (on other exposures), due to the obscuring effect of the dust particles that "dim" the light of stars behind these clouds. This effect is particularly noticeable in the lower left corner where very few stars are seen. R Coronae Australis , the bright star from which the entire complex is named, is located at the center of the field and illuminates the reddish nebula around it. The bright star in the lower part, illuminating a somewhat bluer nebula, is known as TY Coronae Australis . The brightness of these two stars and several others in the same field is variable. They belong to the so-called "T Tauri" class , a type that is quite common in star-forming regions. T Tauri stars are in the early stages of stellar evolution and display various observable characteristics of this phase, e.g. emission at visible and infrared wavelengths due to the accretion of matter left over from their formation, as well as X-ray emission. The nebulosity seen in this picture is mostly due to reflection of the stellar light by small dust particles. The stars in the R Coronae Australis complex do not emit sufficient ultraviolet light to ionize a substantial

  3. Influence of cervical finish line type on the marginal adaptation of zirconia ceramic crowns.

    Science.gov (United States)

    Comlekoglu, Muharrem; Dundar, Mine; Ozcan, Mutlu; Gungor, Mehmet; Gokce, Bulent; Artunc, Celal

    2009-01-01

    The current study evaluated the effect of different cervical finish line designs on the marginal adaptation of a zirconia ceramic. Four different marginal finish lines (c: chamfer, mc: mini-chamfer, fe: feather-edge and s: rounded shoulder) were prepared on phantom incisors. Die models for each preparation group (N = 28, n = 7 per finish line design group) were made of epoxy resin. Y-TZP (ICE Zirkon) frameworks were manufactured by a copy-milling system (Zirconzahn) using prefabricated blanks and tried on the master models for initial adaptation of the framework; they were then sintered, followed by veneering (Zirconzahn). The finished crowns were cemented with a polycarboxylate cement (Poly F) under 300 g load and ultrasonically cleaned. The specimens were sliced and the marginal gap was measured, considering absolute marginal opening (AMO) and marginal opening (MO) for each coping under a stereomicroscope with image processing software (Lucia). The measurements were statistically analyzed using the Kruskal Wallis, Mann Whitney and Wilcoxon Signed Ranks tests at a significance level of alpha = 0.01. Means of AMO measurement (microm) for the feather-edge finish line (87 +/- 10) was significantly lower than that of the chamfer (144 +/- 14), shoulder (114 +/- 16) and mini-chamfer finish line types (114 +/- 11) (p finish line (68 +/- 9) (p finish line type had an influence on the marginal adaptation of the tested zirconia ceramic. Although the feather-edge finish line resulted in lower AMO and MO values, with its proven mechanical disadvantage, it cannot be recommended in clinical applications of zirconia crowns. This type of finish line has acted solely as a control group to test the null hypothesis in the current study. For better marginal adaptation, both shoulder and mini-chamfer finish line types could be suggested for zirconia crowns.

  4. Stem and Crown Characteristics of Norway Spruce [Picea abies (L. Karst] Populations from Romanian Carpathians

    Directory of Open Access Journals (Sweden)

    Marius BUDEANU

    2013-12-01

    Full Text Available To establish the most important Norway spruce Romanian populations, open-pollinated progeny of ten plus trees originating from 33 seed stands mapped in the Romanian Carpathians have been evaluated for stem and crown characteristics at the age of 30 years, in two field trials: one established in their natural range (Breţcu trial, while the second was located outside of their natural range, in Subcarpathian lands (Avrig trial. Significant (p < 0.05 differences were found among the seed stands in both sites for most of the characteristics, suggesting an additive genetic control with different levels of significance depending on the evaluated trait and the testing site. Location analysis also revealed a highly significant population x locality interaction for all traits. The same populations behave differently to the change of the ecological conditions. In the Avrig trial higher values were recorded than in the Breţcu trial for the tree slenderness coefficient (19%, crown slenderness coefficient (13.6% and crown lateral area (9.4%. Although outside of their natural area, pruning height (m increased 6.4%, however pruning height ratio (% decreases by 1%, compared to the test established in their natural range. The populations from the Eastern Carpathians stand out by showing sustained growth and superior wood quality, while the populations from the Western Romanian Carpathians have generally smaller differences between the mean values of analysed traits in both field trials. Qualitative characteristics that influence the stability of stands to windthrow and snowbreak showed low levels of correlations to ecological gradients of the originating location of tested seed stands.

  5. Response to Proximal Restorations Placed Either Subgingivally or Following Crown Lengthening in Patients with No History of Periodontal Disease.

    Science.gov (United States)

    Oppermann, Rui Vicente; Gomes, Sabrina Carvalho; Cavagni, Juliano; Cayana, Ezymar Gomes; Conceição, Ewerton Nocchi

    2016-01-01

    The purpose of this study was to compare the impact of resin restorations placed supragingivally or impinging periodontal biologic width (PBW). Ten patients (aged 19 to 35 years) with at least two contralateral teeth (premolars and molars) in need of proximal subgingival restorations participated. Test group (TG) (impingement of PBW with transsurgical restorations) and control croup (CG) (supragingival restorations after crown lengthening) were randomly assigned. Visible plaque (VP), bleeding on probing (BOP), periodontal probing depth (PPD), and clinical attachment loss (CAL) were evaluated at baseline and at 45, 90, and 180 days, and by transperiodontal probing at baseline and 180 days. Generalized estimating equations, Wald test, and t test were used (P ≤ .05). VP and BOP were reduced and maintained at low levels (less than 10% from day 45 on). PPD initially reduced in the TG. At day 180, no intra- or intergroup differences were observed (P > .05). CAL was higher in the CG after surgery (P crown lengthening.

  6. Reactions of 15-crown-5 and bis-15-crown-5 ethers with metal acetylacetonate ions in the gas phase

    Energy Technology Data Exchange (ETDEWEB)

    Timofeev, O.S.; Bogatskii, A.V.; Gren, A.I.; Lobach, A.V.; Nekarsov, Y.S.; Zagorevskii, D.V.

    1985-05-20

    A study was carried out on the ion-molecule reactions of ions arising in the dissociation of ferric, cobaltic, chromic, manganous, neodymium(II), gallium(III), and indium(III) acetylacetonates upon electron impact with 15-crown-5 and bis-15-crown-5. The ratio of the yields of (acac)x-1 /SUP M+L/ ions is determined by the case of reduction of M /SUP x+1+/ to M /SUP x+/ and for (acac)/sub 3/M complexes, this ratio decreases in the series Nd, In, GA > Cr > Fe, Co. The rate constant for the formation of acacCoL/sup +/ ions is greater than for acacFeL/sup +/ ions. The possibility of fixing transition metals in unstable oxidation states by crown ethers is demonstrated in the case of nickel.

  7. Reliability estimation for single-unit ceramic crown restorations.

    Science.gov (United States)

    Lekesiz, H

    2014-09-01

    The objective of this study was to evaluate the potential of a survival prediction method for the assessment of ceramic dental restorations. For this purpose, fast-fracture and fatigue reliabilities for 2 bilayer (metal ceramic alloy core veneered with fluorapatite leucite glass-ceramic, d.Sign/d.Sign-67, by Ivoclar; glass-infiltrated alumina core veneered with feldspathic porcelain, VM7/In-Ceram Alumina, by Vita) and 3 monolithic (leucite-reinforced glass-ceramic, Empress, and ProCAD, by Ivoclar; lithium-disilicate glass-ceramic, Empress 2, by Ivoclar) single posterior crown restorations were predicted, and fatigue predictions were compared with the long-term clinical data presented in the literature. Both perfectly bonded and completely debonded cases were analyzed for evaluation of the influence of the adhesive/restoration bonding quality on estimations. Material constants and stress distributions required for predictions were calculated from biaxial tests and finite element analysis, respectively. Based on the predictions, In-Ceram Alumina presents the best fast-fracture resistance, and ProCAD presents a comparable resistance for perfect bonding; however, ProCAD shows a significant reduction of resistance in case of complete debonding. Nevertheless, it is still better than Empress and comparable with Empress 2. In-Ceram Alumina and d.Sign have the highest long-term reliability, with almost 100% survivability even after 10 years. When compared with clinical failure rates reported in the literature, predictions show a promising match with clinical data, and this indicates the soundness of the settings used in the proposed predictions. © International & American Associations for Dental Research.

  8. Zirconia- versus metal-based, implant-supported abutments and crowns

    DEFF Research Database (Denmark)

    Hosseini, Mandana

    studies have reported on aesthetic, biological, biomechanical and patient-reported outcomes of implant-supported single-tooth restorations of various biomaterials. The aim of the present thesis was to investigate the clinical performance of zirconia-based implant-supported single-tooth restorations...... was to test the reliability and validity of six aesthetic parameters used at the Copenhagen Dental School to assess the aesthetic outcome of implant-supported restorations. The aims of study III and IV were to compare the influence of different abutment and crown materials on biological, biomechanical...

  9. Psychometric properties of the Marlowe-Crowne social desirability scale with adult male sexual offenders.

    Science.gov (United States)

    Tatman, Anthony W; Swogger, Marc T; Love, Keisha; Cook, Michelle D

    2009-03-01

    This research project investigates the factor structure, reliability, and validity of the Marlowe-Crowne Social Desirability Scale (MCSDS) when used with a sample of convicted, adult male sexual offenders. Results confirm the two-factor structure (Denial and Attribution) originally proposed by the authors (Study 1, n = 247). Results also reveal that the full-scale MCSDS has strong internal consistency estimates (Study 1), discriminant and convergent validity (Study 2, n = 91), and test-retest reliability over a 3-week period (Study 3, n = 74). Information is provided to aid evaluators' interpretation of MCSDS full-scale and factor scores when used with male adult sexual offenders.

  10. Impact of Gluma Desensitizer on the tensile strength of zirconia crowns bonded to dentin: an in vitro study.

    Science.gov (United States)

    Stawarczyk, Bogna; Hartmann, Leonie; Hartmann, Rahel; Roos, Malgorzata; Ender, Andreas; Ozcan, Mutlu; Sailer, Irena; Hämmerle, Christoph H F

    2012-02-01

    This study tested the impact of Gluma Desensitizer on the tensile strength of zirconia crowns bonded to dentin. Human teeth were prepared and randomly divided into six groups (N = 144, n = 24 per group). For each tooth, a zirconia crown was manufactured. The zirconia crowns were cemented with: (1) Panavia21 (PAN), (2) Panavia21 combined with Gluma Desensitizer (PAN-G), (3) RelyX Unicem (RXU), (4) RelyX Unicem combined with Gluma Desensitizer (RXU-G), (5) G-Cem (GCM) and (6) G-Cem combined with Gluma Desensitizer (GCM-G). The initial tensile strength was measured in half (n = 12) of each group and the other half (n = 12) subjected to a chewing machine (1.2 Mio, 49 N, 5°C/50°C). The cemented crowns were pulled in a Universal Testing Machine (1 mm/min, Zwick Z010) until failure occurred and tensile strength was calculated. Data were analyzed with one-way and two-way ANOVA followed by a post hoc Scheffé test, t test and Kaplan-Meier analysis with a Breslow-Gehan analysis test (α = 0.05). After the chewing simulation, the self-adhesive resin cements combined with Gluma Desensitizer showed significantly higher tensile strength (RXU-G, 12.8 ± 4.3 MPa; GCM-G, 13.4 ± 6.2 MPa) than PAN (7.3 ± 1.7 MPa) and PAN-G (0.9 ± 0.6). Within the groups, PAN, PAN-G and RXU resulted in significantly lower values when compared to the initial tensile strength; the values of all other test groups were stable. In this study, self-adhesive resin cements combined with Gluma Desensitizer reached better long-term stability compared to PAN and PAN-G after chewing simulation.

  11. Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study

    Science.gov (United States)

    Mokhtarpour, Hadi; Eftekhar Ashtiani, Reza; Mahshid, Minoo; Tabatabaian, Farhad; Alikhasi, Marzieh

    2016-01-01

    Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P zirconia-based crowns decreased the fracture load. PMID:27651885

  12. Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study.

    Science.gov (United States)

    Mokhtarpour, Hadi; Eftekhar Ashtiani, Reza; Mahshid, Minoo; Tabatabaian, Farhad; Alikhasi, Marzieh

    2016-01-01

    Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P zirconia-based crowns decreased the fracture load.

  13. Influence of finish line on the marginal seal of nanohybrid composite crowns after periodontal scaling: a microleakage study.

    Science.gov (United States)

    Angerame, D; De Biasi, M; Del Lupo, V; Bevilacqua, L; Zarone, F; Sorrentino, R

    2015-10-01

    The aim of the present microleakage study was to assess the sealing ability of nanohybrid composite crowns with different finish lines exposed to simulated mechanical periodontal treatment (SMPT). After sample size calculation (α=0.05; β=0.20; δ=1.0; σ=0.8), sixty extracted mandibular molars were divided into four groups (N.=15): G1, 90° shoulder; G2, beveled 90° shoulder; G3, 90° shoulder and SMPT; G4, beveled 90° shoulder and SMPT. Tooth preparations were carried out by means of diamond burs and Arkansas stones. The buildup of crowns was performed with a nanohybrid composite on master casts obtained after polyether impressions and crowns were cemented with self-adhesive cement. Groups G3 and G4 were subjected to the equivalent of five years of semestral mechanical periodontal scaling with Gracey curettes (2-mm long strokes, 5 N). Samples were immersed into a methylene blue supersaturated solution for 10 minutes. Microleakage was measured by stereomicroscopic observation of multiple sections of the samples and leakage data underwent statistical analysis with non-parametric tests. Marginal microleakage was 1.53±1.27% and 17.60±12.72% of the length of the adhesive interface in G1 and G2, respectively. SMPT reduced dye penetration (P<0.001) with G3 not leaking at all and G4 leaking along the 5.58±1.84% of the adhesive interface. The bevel preparation significantly worsened the marginal seal both in control and treated crowns (P<0.001). Microleakage of nanohybrid composite crowns increased by adding a bevel to a 90° shoulder preparation and diminished after SMPT.

  14. The comparative evaluation of the translucency of crowns fabricated with three different all-ceramic materials: an in vitro study.

    Science.gov (United States)

    Sravanthi, Y; Ramani, Y V; Rathod, Asha M; Ram, Sabita M; Turakhia, Hetal

    2015-02-01

    All-ceramic crowns with different core materials of different strength and aesthetics are available in recent years. The aesthetics of the crown depends mainly on the shade and translucency. Clinician should be aware of the quality and characteristics of these materials so that they will be able to opt for good material for successful clinical use. The aim of this study was to evaluate and compare the translucency of crowns fabricated with three different commercially available all-ceramic materials viz. Alumina - CAD-CAM Procera, Lithium disilicate - Pressable IPS e.max Press, Zirconia - CAD-CAM Lava. All-ceramic crowns (5 per each group and total of 15 samples) were made of Alumina - CAD-CAM Procera (Group I), Lithium disilicate - Pressable IPS e.max Press (Group II), Zirconia - CAD-CAM Lava (Group III) and veneered with their respective layering ceramic. Evaluation for the Translucency (CR=Yb/Yw) over the White (Yw) and Black (Yb) backgrounds at the Incisal, Middle, Cervical, Mesial and Distal thirds of each crown were done using the Spectrophotometer. The results obtained were statistically analyzed by Paired t-test (pfair idea to clinician for the choice of material in different zones during replacement and suitability for restoration in aesthetic zone. Selection of all ceramic system depends on the translucency needed for successful prosthesis of artificial tooth so that it mimics patient's natural dentition. The qualitative measurement of translucency will give the evidence for the clinicians during selection of high or low value translucent tooth for successful replacement. Lithium disilicate - Pressable IPS e.max Press is having better translucency in comparison with other two materials in our study.

  15. Laser pediatric crowns performed without anesthesia: a contemporary technique.

    Science.gov (United States)

    Jacboson, B; Berger, J; Kravitz, R; Patel, P

    2003-01-01

    Extensive caries resulting in the need for a stainless steel crown in primary teeth may now be prepared with the use of the WaterlaseTM YSGG Laser, (Biolase) hard and soft-tissue laser. The use of the laser eliminates the need for local anesthesia, thereby providing optimal patient comfort and compliance.

  16. Modeling hardwood crown radii using circular data analysis

    Science.gov (United States)

    Paul F. Doruska; Hal O. Liechty; Douglas J. Marshall

    2003-01-01

    Cylindrical data are bivariate data composed of a linear and an angular component. One can use uniform, first-order (one maximum and one minimum) or second-order (two maxima and two minima) models to relate the linear component to the angular component. Crown radii can be treated as cylindrical data when the azimuths at which the radii are measured are also recorded....

  17. Antibacterial activity of plant defensins against alfalfa crown rot pathogens

    Science.gov (United States)

    Alfalfa (Medicago sativa) is the fourth most widely grown crop in the United States. Alfalfa crown rot is a disease complex that severely decreases alfalfa stand density and productivity in all alfalfa-producing areas. Currently, there are no viable methods of disease control. Plant defensins are sm...

  18. Material choice for restorative dentistry: inlays, onlays, crowns, and bridges.

    Science.gov (United States)

    Small, Bruce W

    2006-01-01

    New materials--specifically the new CAD/CAM zirconia-based systems--are available now for restorative dentistry. When esthetics are not a factor, gold remains the standard, particularly for intracoronal restorations and full posterior coverage. Tooth-colored crowns made with zirconia are new and offer great promise for the future, although more long-term in vivo studies are necessary.

  19. Why do crown ethers activate enzymes in organic solvents?

    NARCIS (Netherlands)

    Unen, van Dirk-Jan; Engbersen, Johan F.J.; Reinhoudt, David N.

    2002-01-01

    One of the major drawbacks of enzymes in nonaqueous solvents is that their activity is often dramatically low compared to that in water. This limitation can be largely overcome by crown ether treatment of enzymes. In this paper, we describe a number of carefully designed new experiments that have im

  20. Classification system for conventional crown and fixed partial denture failures.

    Science.gov (United States)

    Manappallil, John Joy

    2008-04-01

    The dental literature is replete with reports on the many aspects of failure encountered with traditional fixed prosthodontic treatment, including longitudinal survival studies of crowns and fixed partial dentures and reasons for failures. However, criteria for grading or classifying the type and severity of these failures are inadequate. A classification system for conventional fixed prosthodontic failures based on severity is presented.

  1. Analysis of "Babar Loses His Crown." Technical Report No. 169.

    Science.gov (United States)

    Green, G. M.; And Others

    This report presents the text analysis of "Babar Loses His Crown," a story for beginning readers. (The techniques used in arriving at the analysis are presented in a Reading Center Technical Report, Number 168, "Problems and Techniques of Text Analysis.") Tables are given for a statistical lexical analysis and for a syntactic…

  2. SIERPIENSKI & CROWN SQUARE FRACTAL SHAPES SLOTTED MICROSTRIP PATCH ANTENNA

    Directory of Open Access Journals (Sweden)

    Dr. Yogesh Bhomia

    2014-01-01

    Full Text Available A new Sierpienski & Crown Square Fractal Shapes Slotted Microstrip Patch Antenna is proposed. A patch antenna is a narrowband, wide-beam antenna. These antennas are low profile, conformal to planar and non-planar surface, simple and inexpensive to manufacture using modern printed circuit technology, mechanically robust when mounted on rigid surface, compatible with MMIC designs and when the particular shape and mode are selected they are very versatile in terms of resonant frequency, polarization, field pattern and impedance. Microstrip patch antenna consist of a very thin metallic strip (patch placed a small fraction of a wavelength above a ground plane. The patch is generally made of conducting material such as copper or gold and can take any possible shape. This paper presents a design of Sierpienski & Crown Square Fractal Shapes Slotted Microstrip Patch Antenna and experimentally studied on IE3D software. This design is achieved by cutting Sierpienski & Crown Square Fractal Shapes Slottes in a patch. With Sierpienski & Crown Square Fractal Shapes patch antenna is designed on a FR4 substrate of thickness 1.524 mm and relative permittivity of 4.4 and mounted above the ground plane at a height of 6 mm. Bandwidth as high as 36.6% are achieved with stable pattern characteristics, such as gain and cross polarization, within its bandwidth. Impedance bandwidth, antenna gain and return loss are observed for the proposed antenna. Details of the measured and simulated results are presented and discussed.

  3. Evaluation of sampling strategies to estimate crown biomass

    Directory of Open Access Journals (Sweden)

    Krishna P Poudel

    2015-01-01

    Full Text Available Background Depending on tree and site characteristics crown biomass accounts for a significant portion of the total aboveground biomass in the tree. Crown biomass estimation is useful for different purposes including evaluating the economic feasibility of crown utilization for energy production or forest products, fuel load assessments and fire management strategies, and wildfire modeling. However, crown biomass is difficult to predict because of the variability within and among species and sites. Thus the allometric equations used for predicting crown biomass should be based on data collected with precise and unbiased sampling strategies. In this study, we evaluate the performance different sampling strategies to estimate crown biomass and to evaluate the effect of sample size in estimating crown biomass. Methods Using data collected from 20 destructively sampled trees, we evaluated 11 different sampling strategies using six evaluation statistics: bias, relative bias, root mean square error (RMSE, relative RMSE, amount of biomass sampled, and relative biomass sampled. We also evaluated the performance of the selected sampling strategies when different numbers of branches (3, 6, 9, and 12 are selected from each tree. Tree specific log linear model with branch diameter and branch length as covariates was used to obtain individual branch biomass. Results Compared to all other methods stratified sampling with probability proportional to size estimation technique produced better results when three or six branches per tree were sampled. However, the systematic sampling with ratio estimation technique was the best when at least nine branches per tree were sampled. Under the stratified sampling strategy, selecting unequal number of branches per stratum produced approximately similar results to simple random sampling, but it further decreased RMSE when information on branch diameter is used in the design and estimation phases. Conclusions Use of

  4. Estimating tree crown widths for the primary Acadian species in Maine

    Science.gov (United States)

    Matthew B. Russell; Aaron R. Weiskittel

    2012-01-01

    In this analysis, data for seven conifer and eight hardwood species were gathered from across the state of Maine for estimating tree crown widths. Maximum and largest crown width equations were developed using tree diameter at breast height as the primary predicting variable. Quantile regression techniques were used to estimate the maximum crown width and a constrained...

  5. Restoration of the Severely Decayed Tooth Using Crown Lengthening with Simultaneous Tooth-Preparation

    OpenAIRE

    2010-01-01

    This clinical case describes a treatment approach that combines, in a single appointment, a crown lengthening procedure and the final crown preparation for the restoration of a severely decayed tooth. This approach allows for a more accurate placement of the crown margin in relation to the bone crest while reducing treatment time.

  6. Restoration of the severely decayed tooth using crown lengthening with simultaneous tooth-preparation.

    Science.gov (United States)

    Park, Jun-Beom

    2010-04-01

    This clinical case describes a treatment approach that combines, in a single appointment, a crown lengthening procedure and the final crown preparation for the restoration of a severely decayed tooth. This approach allows for a more accurate placement of the crown margin in relation to the bone crest while reducing treatment time.

  7. Crown Ether Complexes with H3O+ and NH4+: Proton Localization and Proton Bridge Formation

    NARCIS (Netherlands)

    Hurtado, P.; Gamez, F.; Hamad, S.; Martinez-Haya, B.; Steill, J. D.; Oomens, J.

    2011-01-01

    The complexes formed by crown ethers with hydronium and ammonium cations are of key relevance for the understanding of their supramolecular behavior in protic solvents. In this work, the complexes of the 15-crown-5 (15c5) and 18-crown-6 (18c6) ethers with H3O+ and NH4+ and their deuterated variants

  8. Field evaluation of switchgrass seedlings divergently selected for crown node placement

    NARCIS (Netherlands)

    Elbersen, H.W.; Ocumpaugh, W.R.; Hussey, M.A.; Sanderson, M.A.; Tischler, C.R.

    1999-01-01

    Excessive crown node elevation of warm-season grass seedlings is a major limitation to successful establishment. Crown node placement at or above the soil surface limits the opportunity for adventitious root development at the crown node. Switchgrass (Panicum virgatum L.) germplasm selected for low-

  9. A technique for sampling low shrub vegetation, by crown volume classes

    Science.gov (United States)

    Jay R. Bentley; Donald W. Seegrist; David A. Blakeman

    1970-01-01

    The effects of herbicides or other cultural treatments of low shrubs can be sampled by a new technique using crown volume as the key variable. Low shrubs were grouped in 12 crown volume classes with index values based on height times surface area of crown. The number of plants, by species, in each class is counted on quadrats. Many quadrats are needed for highly...

  10. First report of Fusarium hostae causing crown rot of wheat (Triticum spp.) in Turkey

    Science.gov (United States)

    Crown rot disease of wheat is caused by a complex of Fusarium species. To identify species associated with crown rot in Turkey, crowns and stems of bread wheat (Triticum aestivum L.) and durum wheat (T. durum Desf.) were collected from the Central and Southeast Anatolia, Black Sea, Aegean, Mediterr...

  11. Dioxygen affinities and catalytic oxidation activities of cobalt complexes with Schiff bases containing crown ether

    NARCIS (Netherlands)

    Sun, B.; Chen, J.R.; Hu, J.Y.; Li, X.J.

    2006-01-01

    The stoichiometry of dioxygen uptake of Co complexes with 4',5'-bis-(5-chloro-2-hydroxyphenylmethylideneimino)benzo-12-crown-4 (la), 4',5'-bis(2-hydroxyphenylmethylideneimino)benzo-12-crown-4(1b), 4',5'-bis-(5-methoxy-2-hydroxyphenylmethylideneimino)benzo-12-crown-4 (1c), 4',5'-bis-(5-chloro-2-hydro

  12. 18-Crown[6]ether functionalized reduced graphene oxide for membrane-free ion selective sensing

    DEFF Research Database (Denmark)

    Olsen, Gunnar; Ulstrup, Jens; Chi, Qijin

    The focus of this work is on the synthesis of a 1-Aza-18-crown[6]ether functionalized reduced graphene oxide (RGO-crown[6]) with specific K+ binding sites on the RGO surface. Glassy carbon electrodes (GCE) functionalized with RGO-crown[6] weretested for selective potentiometric sensing of K...

  13. Preformed resin-veneered stainless steel crowns for restoration of primary incisors.

    Science.gov (United States)

    Croll, T P; Helpin, M L

    1996-05-01

    Stainless steel crown forms with bonded resin veneers for primary incisors are commercially available to dentists. This type of preveneered crown was developed to serve as a convenient, durable, reliable, and esthetic solution to the difficult challenge of restoring severely carious primary incisors. This article describes preveneered crowns, reviews their advantages and disadvantages, and details a technique for placement of such restorations.

  14. Comparison of repair methods for ceramic-fused-to-metal crowns

    NARCIS (Netherlands)

    Ozcan, M.; Van Der Sleen, J.M.; Kurunmaki, H.; Vallittu, P.K.

    2006-01-01

    Purpose: The objective of this study was to evaluate the effect of four repair methods on the fracture load of repaired ceramic-fused-to-metal crowns. Materials and Methods: Metal-ceramic crowns were fractured, and the failure load was measured. The fractured metal-ceramic crowns (n = 9) were assign

  15. Comparison of repair methods for ceramic-fused-to-metal crowns

    NARCIS (Netherlands)

    Ozcan, M.; Van Der Sleen, J.M.; Kurunmaki, H.; Vallittu, P.K.

    2006-01-01

    Purpose: The objective of this study was to evaluate the effect of four repair methods on the fracture load of repaired ceramic-fused-to-metal crowns. Materials and Methods: Metal-ceramic crowns were fractured, and the failure load was measured. The fractured metal-ceramic crowns (n = 9) were

  16. Demonstration of a crown ether process for partitioning strontium from high level liquid waste (HLLW)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jianchen; Jing, Shan; Chen, Jing [Tsinghua Univ., Beijing (China). Inst. of Nuclear and New Energy Technology (INET); Tsinghua Univ., Beijing (China). Beijing Key Lab of Radioactive Waste Treatment

    2016-05-01

    Chinese HLLW with a higher-salt liquid that was generated via plutonium uranium recovery by extraction (PUREX) processing was temporarily stored in stainless steel tanks and is waiting for treatment. The volume and heat-loading of the glass block are reduced if the strontium, cesium, actinides and other long-life radioactive elements, such as Tc in the HLLW, are partitioned before the HLLW verification. This process is beneficial to preserve the capacity of the geological disposal repository and to minimize long-term hazards. The process of partitioning strontium from Chinese HLLW using Dicyclohexano-18Crown-6(DCH18C-6) was developed in past decades, including such fundamental studies as the small scale cold and hot test. In this work, new studies are introduced, including the cold and the long time hot cascade tests, using a miniature centrifugal contactor set and the pilot-scale cold test using pulse extraction columns. The results indicate that the crown process is promising for partitioning strontium from Chinese HLLW.

  17. Phytophthora Root and Crown Rot on Apples in Bulgaria

    Directory of Open Access Journals (Sweden)

    Mariana Nakova

    2010-01-01

    Full Text Available Phytophthora is a genus of Oomycota responsible for some of the most serious diseases with great economic impact (Judelson and Blanco, 2005. While 54 species were found in the 20th century (Erwin and Ribeiro, 1996 another 51-54 new species have been identified(Brasier, 2008 since the year 2000. They are spread worldwide and have broad range of host plants – fruit trees, citrus, forest and park species. Phytophthora can cause serious damages in orchards and nurseries of apples, cherries, etc. In Bulgaria they have been found first on young apples and cherries (1998-1999 in Plovdiv region (Nakova, 2003. Surveys have been done for discovering disease symptoms in Plovdiv and Kjustendil regions. Isolates have been obtained from infected plant material (roots and stem bases applying baiting bioassay (green apples, variety Granny Smith and/or PARP 10 selective media. Phytophthora strains were identified based on standard morphology methods – types of colonies on PDA, CMA, V 8, type and size of sporangia, oogonia and antheridia, andoospores. Cardial temperatures for their growth were tested on CMA and PDA.For molecular studies, DNA was extracted from mycelium using the DNA extraction kit.DNA was amplified using universal primers ITS 6 and ITS 4. Amplification products concentrations were estimated by comparison with the standard DNA. Sequencing was done at the Scottish Crop Research Institute (SCRI, Dundee, Scotland. Phytophthora root and crown rot symptoms first appear in early spring. Infected trees show bud break delay, have small chlorotic leaves, and branches die all of a sudden. Later symptoms are found in August-September. Leaves of the infected trees show reddish discoloration and drop down. Both symptoms are connected with lesions (wet, necrotic in appearance at stem bases of the trees.Disease spread was 2-3% in most gardens, only in an apple orchard in Bjaga (Plovdiv region it was up to 8-10%. Morphologically, the isolates acquired from

  18. Unusual extraction behaviour of crown ether when intercalated in bentonite

    Energy Technology Data Exchange (ETDEWEB)

    Sivaiah, M.V.; Krishna, R.M.; Murthy, G.S. [Andhra Univ., Nuclear Chemistry Section, Waltair (India); Venkatesan, K.A. [Indira Gandhi Centre for Atomic Research, Fuel Chemistry Div., Kapakkam (India); Sasidhar, P. [Atomic Energy Regulatory Board, Safety Research Institute, Kalpakkam (India)

    2005-04-01

    Di-cyclo-hexano-18-crown-6 (DCH18C6) has been intercalated in bentonite and the product, Ben-Crown, characterized by micro-elemental analysis, TG-DTA analysis, X-ray diffraction and IR spectroscopy. The permanent negative charge present in the bentonite layer has been exploited for more efficient extraction of cesium and strontium by Ben-Crown at nitric acid concentrations ({<=} 1.0 M) that gave only a meagre extraction when either DCH18C6 or bentonite alone were employed. The extraction of cesium and strontium has been investigated as a function of time, temperature, and the concentrations of nitric acid, metal ion and sodium nitrate. An unusual extraction phenomenon was observed at low concentrations of nitric acid ({<=} 1.0 M) in the absence of any organo-philic agents. Rapid extraction of the metal ion was followed by the establishment of an equilibrium, which occurred after 150 min. Distribution coefficients (K{sub d}) of 599 and 1007 ml g{sup -1} were obtained, respectively, for the extraction of cesium and strontium from 0.1 M nitric acid by Ben-Crown; K{sub d} decreased with an increase in the temperature or in the concentrations of nitric acid and sodium nitrate. The extraction data were fitted by the Langmuir adsorption model and the apparent experimental exchange capacity obtained by linear regression analysis was in good agreement with the amount of crown ether (0.22 mmol g{sup -1}) intercalated in bentonite. The enthalpy change ({delta}H{sup 0}) for the extraction of cesium and strontium was found to be exothermic. (authors)

  19. Wear characteristics of trimethylolpropane trimethacrylate filler-containing resins for the full crown restoration of primary molars.

    Science.gov (United States)

    Wada, Kanae; Ikeda, Eri; Wada, Junichiro; Inoue, Go; Miyasaka, Munenaga; Miyashin, Michiyo

    2016-01-01

    Although the demand for aesthetic restoration of primary molars has increased, the full-crown restorations using resin and the details of the wear characteristics of trimethylolpropane trimethacrylate (TMPT) filler containing resins for primary molars are not well understood. This study was conducted to determine whether new light-cured composite resin (Fantasista) and 4-META/MMATBB resin (Bondfill SB) are appropriate for full crown restoration of primary molars by evaluating their wear characteristics. Both resins products contain TMPT filler. The properties of the resins were evaluated through in vitro impacting-sliding wear tests; the wear properties of the opposing enamel specimens used in the tests were also studied. The properties of the resins were compared with those of Litefill, MetafilC, and Clearfil FII, which had been evaluated previously. Fantasista exhibited simple shape of wear that was suggestive of a higher wear resistance than that of Litefill. Fantasista caused the least damage to the antagonistic primary enamel.

  20. All- Ceramic Crown Preparation and the Remained wall Thickness of the Pulp Chamber

    Directory of Open Access Journals (Sweden)

    Mohammadzadeh Akhlaghi N.

    2012-12-01

    Full Text Available tatement of Problem: A minimally invasive method of preparation is essential to prevent tooth structure weakening and pulp irritation; especially for mandibular anterior single-tooth all-ceramic crowns. According to many investigations, one of the most important reasons of pulp injury caused by tooth preparation for different restorative procedures is reduced “remained wall thickness” (RWT. In order to protect the pulp from irritation, it is necessary to maintain a 0.5 mm of RWT.Purpose: The purpose of the present study was to evaluate the effect of all-ceramic crown preparation on pulp chamber RWT of mandibular incisors.Materials and Method: Mesiodistal and buccolingual initial images of 24 ex-tracted mandibular incisors were provided. The pulp chamber initial wall thick-nesses of buccal, lingual and proximal surfaces of cervical, 1and 2 mm above the cervical areas and also the incisal surfaces of incisal sections were measured using digital radiography and Photoshop software. After all-ceramic crown preparation, images were provided at the same initial positions. The initial and remained pulp chamber wall thicknesses were statistically evaluated and analyzed by ANOVA, paired t-test and a post hoc Tukey test.Results: Repeated measures ANOVA showed that the mean of pre- or post-preparation wall thicknesses were not significantly different for each surface at the three horizontal levels (p> 0.05. However, there were significant differences between the surfaces for each section. Comparison of pre- and post-preparation wall thicknesses revealed significant differences (p< 0.05. Proximal surfaces of cervical sections had the least RWT (0.42±0.12.Conclusion: According to the results of the present study, the least amount of initial and remained wall thicknesses of pulp chamber were related to the proximal surfaces, particularly in cervical areas. Therefore a reduction of preparation to 0.7 mm is suggested to prevent future pulp injury for

  1. Comparative fracture strength analysis of Lava and Digident CAD/CAM zirconia ceramic crowns

    OpenAIRE

    Kwon, Taek-Ka; Pak, Hyun-Soon; Yang, Jae-Ho; Han, Jung-Suk; Lee, Jai-Bong; Kim, Sung-Hun; Yeo, In-Sung

    2013-01-01

    PURPOSE All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident. MATERIALS AND METHODS Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also ...

  2. Failure analysis of various monolithic posterior aesthetic dental crowns using finite element method

    Science.gov (United States)

    Porojan, Liliana; Topală, Florin

    2017-08-01

    The aim of the study was to assess the effect of material stiffness and load on the biomechanical performance of the monolithic full-coverage posterior aesthetic dental crowns using finite element analysis. Three restorative materials for monolithic dental crowns were selected for the study: zirconia; lithium disilicate glass-ceramic, and resin-based composite. Stresses were calculated in the crowns for all materials and in the teeth structures, under different load values. The experiments show that dental crowns made from all this new aesthetic materials processed by CAD/CAM technologies would be indicated as monolithic dental crowns for posterior areas.

  3. An In Vivo Evaluation of the Fit of Zirconium-Oxide Based, Ceramic Single Crowns with Vertical and Horizontal Finish Line Preparations.

    Science.gov (United States)

    Vigolo, Paolo; Mutinelli, Sabrina; Biscaro, Leonello; Stellini, Edoardo

    2015-12-01

    Different types of tooth preparations influence the marginal precision of zirconium-oxide based ceramic single crowns. In this in vivo study, the marginal fits of zirconium-oxide based ceramic single crowns with vertical and horizontal finish lines were compared. Forty-six teeth were chosen in eight patients indicated for extraction for implant placement. CAD/CAM technology was used for the production of 46 zirconium-oxide-based ceramic single crowns: 23 teeth were prepared with vertical finishing lines, 23 with horizontal finishing lines. One operator accomplished all clinical procedures. The zirconia crowns were cemented with glass ionomer cement. The teeth were extracted 1 month later. Marginal gaps along vertical planes were measured for each crown, using a total of four landmarks for each tooth by means of a microscope at 50× magnification. On conclusion of microscopic assessment, ESEM evaluation was completed on all specimens. The comparison of the gap between the two types of preparation was performed with a nonparametric test (two-sample Wilcoxon rank-sum test) with a level of significance fixed at p finish line preparations, the median value of the gap was 35.45 μm (Iqr, 0.33); for the vertical finish line group, the median value of the gap was 35.44 μm (Iqr, 0.40). The difference between the two groups was not statistically significant (two-sample Wilcoxon rank-sum test, p = 0.0872). Within the limitations of this study, the gaps of the zirconium-oxide-based ceramic CAD/CAM crowns with vertical and horizontal finish line preparations were not different. © 2015 by the American College of Prosthodontists.

  4. The effects of scaling and root planing on the marginal gap and microleakage of indirect composite crowns prepared with different finish lines: an in vitro study.

    Science.gov (United States)

    Angerame, D; Sorrentino, R; Cettolin, D; Zarone, F

    2012-01-01

    The present in vitro study aimed to assess the effects of root surface mechanical instrumentation on the marginal integrity and adaptation of resin composite crowns. The following null hypotheses were tested: no differences exist between finish line and 1) marginal gap or 2) marginal microleakage before and after manual mechanical periodontal maintenance. A total of 56 intact human mandibular molars were randomly distributed into four groups and subjected to standardized tooth preparations for indirect composite crowns with different marginal finish lines (90° shoulder, beveled 90° shoulder, feather edge, chamfer). One-half of the specimens was used as a control and remained untreated, and the remaining half was subjected to root surface procedures simulating five years of semestral mechanical supportive periodontal treatment. The marginal gap and microleakage were evaluated and statistically analyzed. The specimens used as controls showed lower mean marginal gaps than those subjected to the simulated periodontal treatment, whereas the latter showed lower microleakage than the control crowns. Statistically significant differences were recorded for both the experimental variables. The root surface procedures resulted in altered surfaces of the composite crowns. The marginal gap increased after the treatment, whereas the marginal microleakage was reduced. The 90° shoulder and the chamfer preparation could be considered a viable option to fabricate composite crowns, but the beveled 90° shoulder and the feather edge should not be recommended.

  5. Assessment of occlusion after placement of stainless steel crowns in children - a pilot study.

    Science.gov (United States)

    Gallagher, S; O'Connell, B C; O'Connell, A C

    2014-10-01

    Many stainless steel crowns (SSCs) disrupt the occlusion in children, but stabilisation appears to occur within a short period post-placement. The extent and mechanism of these short-term occlusal changes in children are unknown. This study sought to determine whether placement of a SSC changes the maximum intercuspation position (MIP) in children, whether the MIP returns to normal within 4 weeks and whether local anaesthesia had an effect on the child's ability to achieve MIP. The T-Scan(®) III was used for the measurement of occlusal contacts. Reliability and reproducibility of the system was determined using a calibration exercise where MIP recordings were taken of eleven children not undergoing any dental treatment. For the main study, the percentage of total occlusal force on each tooth was recorded in 20 children preoperatively, after local anaesthesia, after SSC placement and 4 weeks postoperatively. There was no significant difference in MIP (P = 0·435) preoperatively and post-administration of local anaesthesia. There was a significant difference between the preoperative force on a tooth and the reading after crown placement (P = 0·0013, Wilcoxon test). By 4 weeks, there was no significant difference overall between post-SSC placement and the preoperative value for the tooth (P = 0·3). Administration of local anaesthesia did not affect the ability of a child to attain MIP. Maximum intercuspation position was disturbed by the placement of a SSC in seven of 20 cases. When MIP was disturbed, in most cases, it returned to preoperative status within 4 weeks of crown placement.

  6. Internal fit of two all-ceramic systems and metal-ceramic crowns

    Science.gov (United States)

    MARTINS, Leandro Moura; LORENZONI, Fabio Cesar; de MELO, Alcides Oliveira; da SILVA, Luciana Mendonça; de OLIVEIRA, José Luiz G.; de OLIVEIRA, Pedro Cesar Garcia; BONFANTE, Gerson

    2012-01-01

    Objectives The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. Material and Methods Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey's multiple comparison test (p<0.05). Results No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. Conclusions The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS. PMID:22666843

  7. Internal fit of two all-ceramic systems and metal-ceramic crowns

    Directory of Open Access Journals (Sweden)

    Leandro Moura Martins

    2012-04-01

    Full Text Available OBJECTIVES: The aim of this study was to investigate the internal fit (IF of glass-infiltrated alumina (ICA - In-Ceram Alumina, yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD, and metal-ceramic (MC - Ni-Cr alloy crowns. MATERIAL AND METHODS: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each according to the core material used (metal, ICA or Y-TZP. The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS, axial space (AS and total mean (TM using two-way ANOVA with Tukey ’s multiple comparison test (p<0.05. RESULTS: No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. CONCLUSIONS: The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

  8. Wear of primary teeth caused by opposed all-ceramic or stainless steel crowns

    Science.gov (United States)

    Bae, Ik-Hyun; Noh, Tae-Hwan; Ju, Sung-Won; Lee, Tae-Kyoung; Ahn, Jin-Soo; Jeong, Tae-Sung

    2016-01-01

    PURPOSE This study was conducted to evaluate the effects of full-coverage all-ceramic zirconia, lithium disilicate glass-ceramic, leucite glass-ceramic, or stainless steel crowns on antagonistic primary tooth wear. MATERIALS AND METHODS There were four study groups: the stainless steel (Steel) group, the leucite glass-ceramic (Leucite) group, the lithium disilicate glass-ceramic (Lithium) group, and the monolithic zirconia (Zirconia) group. Ten flat crown specimens were prepared per group; opposing teeth were prepared using primary canines. A wear test was conducted over 100,000 chewing cycles using a dual-axis chewing simulator and a 50 N masticating force, and wear losses of antagonistic teeth and restorative materials were calculated using a three-dimensional profiling system and an electronic scale, respectively. Statistical significance was determined using One-way ANOVA and Tukey's test (P.05). CONCLUSION Leucite glass-ceramic and lithium disilicate glass-ceramic cause more primary tooth wear than stainless steel or zirconia. PMID:26949487

  9. Microleakage of Different Self-Adhesive Materials for Lithium Disilicate CAD/CAM Crowns

    Directory of Open Access Journals (Sweden)

    Ella A. Naumova

    2015-06-01

    Full Text Available Objectives: To evaluate the microleakage and marginal gap of various luting materials after cementing ceramic crowns. Methods: Cervical margins of human molars were designed as circular chamfers. Cementation of full-contour ceramic crowns was conducted with zinc-phosphate cement (Harvard cement, resin cement (Panavia F 2.0 and self-adhesive resin cements (RelyX Unicem, BifixSE, MaxCem Elite, PermaCem2.0, G-Cem. Aging of specimens was performed in artificial saliva, at 37 °C for four weeks and thermocycling. The marginal gap was measured with a scanning electron microscope and silver precipitation within the microleakage. All data were compared statistically. Results: Independent of the margin preparation, the highest median value for microleakage was 320.2 μm (Harvard cement, and the lowest was 0 μm (Panavia F 2.0. The median value for enamel was 0 µm and for dentin 270.9 μm (p < 0.001, which was independent of the luting material. The marginal and absolute marginal gaps were not significantly different between the tested materials. There was no correlation between microleakage and the marginal gaps. Conclusion: Significant differences in microleakage were found between the tested luting materials (p < 0.05. Independent from the luting materials, the microleakage in dentin showed significantly higher values than in enamel.

  10. Modified Y-TZP core design improves all-ceramic crown reliability.

    Science.gov (United States)

    Silva, N R F A; Bonfante, E A; Rafferty, B T; Zavanelli, R A; Rekow, E D; Thompson, V P; Coelho, P G

    2011-01-01

    This study tested the hypothesis that all-ceramic core-veneer system crown reliability is improved by modification of the core design. We modeled a tooth preparation by reducing the height of proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. The CAD-based tooth preparation was replicated and positioned in a dental articulator for core and veneer fabrication. Standard (0.5 mm uniform thickness) and modified (2.5 mm height lingual and proximal cervical areas) core designs were produced, followed by the application of veneer porcelain for a total thickness of 1.5 mm. The crowns were cemented to 30-day-aged composite dies and were either single-load-to-failure or step-stress-accelerated fatigue-tested. Use of level probability plots showed significantly higher reliability for the modified core design group. The fatigue fracture modes were veneer chipping not exposing the core for the standard group, and exposing the veneer core interface for the modified group.

  11. A Randomized Controlled Trial of Crown Therapy in Young Individuals with Amelogenesis Imperfecta.

    Science.gov (United States)

    Pousette Lundgren, G; Morling Vestlund, G I; Trulsson, M; Dahllöf, G

    2015-08-01

    Amelogenesis imperfecta (AI) is a rare, genetically determined defect in enamel mineralization. Existing treatment recommendations suggest resin-composite restorations until adulthood, although such restorations have a limited longevity. New crown materials allow for minimal preparation techniques. The aim of this study was to compare the quality and longevity of 2 crown types-Procera and IPS e.max Press-in adolescents and young adults with AI. A secondary aim was to document adverse events. We included 27 patients (11 to 22 y of age) with AI in need of crown therapy in a randomized controlled trial using a split-mouth technique. After placing 119 Procera crowns and 108 IPS e.max Press crowns following randomization, we recorded longevity, quality, adverse events, and tooth sensitivity. After 2 y, 97% of the crowns in both crown groups had excellent or acceptable quality. We found no significant differences in quality between Procera and IPS e.max Press crowns. Tooth sensitivity was significantly reduced after crown therapy (P < 0.001). Endodontic complications occurred in 3% of crowns. The results show that it is possible to perform crown therapy with excellent results and without severe complications in young patients with AI. The study is registered at http://www.controlled-trials.com (ISRCTN70438627).

  12. OsCAND1 Is Required for Crown Root Emergence in Rice

    Institute of Scientific and Technical Information of China (English)

    Xiao-Fei Wang; Fen-Fang He; Xiao-Xia Ma; Chuan-Zao Mao; Charlie Hodgman; Chun-Gui Lu; Ping Wu

    2011-01-01

    Crown roots are main components of the fibrous root system and important for crops to anchor and absorb water and nutrition. To understand the molecular mechanisms of crown root formation,we isolated a rice mutant defective in crown root emergence designated as Oscand1 (named after the Arabidopsis homologous gene AtCAND1). The defect of visible crown root in the Oscand1 mutant is the result of cessation of the G2/M cell cycle transition in the crown root meristem. Map-based cloning revealed that OsCAND1 is a homolog of Arabidopsis CAND1. During crown root primordium development,the expression of OsCAND1 is confined to the root cap after the establishment of fundamental organization. The transgenic plants harboring DR5::GUS showed that auxin signaling in crown root tip is abnormal in the mutant. Exogenous auxin application can partially rescue the defect of crown root development in Oscand1. Taken together,these data show that OsCAND1 is involved in auxin signaling to maintain the G2/M cell cycle transition in crown root meristem and,consequently,the emergence of crown root. Our findings provide new information about the molecular regulation of the emergence of crown root in rice.

  13. Changes in the periodontal condition after replacement of swaged crowns by metal.

    Science.gov (United States)

    Plotniece-Baranovska, Anita; Soboleva, Una; Rogovska, Irena; Apse, Peteris

    2006-01-01

    Evidence based clinical studies have shown exact recommended design for artificial crown reconstruction with acceptable long-term results taking into an account the biological price. Previous histological and clinical studies proved that fixed prostheses might influence the periodontal condition of crowned teeth, if not all biological criteria have been considered. The aim of the present study was to assess the periodontal condition of the crowned teeth after stainless steel swaged crowns were replaced by cast metal ceramic crowns. Participants were selected at the Institute of Stomatology, Stradin's University. Selection criteria included need to replace existing swaged crowns by metal ceramic crowns for patients with absence of any systemic disease. Following symptoms of periodontal condition were examined - presence of inflammation (clinical signs, probing) and pocket depth. Assessments were carried out at four different points of time (first appointment after replacement existing swaged crowns by temporary crowns; two weeks after cementation of permanent metal ceramic restoration; after three month; after six month). Overall bleeding score "2" and "3" at the first measurement was observed in majority of study population. Bleeding scores between the 1st and the 4th measurement was significantly lower (pcrowns by metal ceramic improves gingival health and leads to better long-term prognosis for restored teeth. It is recommended that swaged crowns be replaced with more biologically friendly crowns.

  14. Wear of metal-free resin composite crowns after three years in service.

    Science.gov (United States)

    Zenthöfer, Andreas; Rammelsberg, Peter; Schmitt, Clemens; Ohlmann, Brigitte

    2013-01-01

    To compare differences between the wear behavior of two types of metal-free resin composite crown with a control after three years in clinical service. Sixty-six participants needing one to three posterior single crowns were fitted with 120 crowns. Abutment teeth were randomly assigned to three groups: 40 resin composite crowns with fiber-reinforced framework, 40 resin composite crowns without fiber-reinforced framework, and 40 metal-ceramic crowns. To assess wear, gypsum replicas of the crowns were fabricated and scanned with a 3D laser scanner at baseline and after three years. Differences between the groups were analyzed by use of mixed-effects regression models. Wear of resin composite crowns with fiber-reinforced framework (p=0.0043) and resin composite crowns without framework (p=0.0246) was significantly greater than in the metal-ceramic group. Wear of metal-free resin composite crowns after three years was significantly greater than that of metal-ceramic crowns, but the wear was still clinically acceptable.

  15. Canopy Fuel Load Mapping of Mediterranean Pine Sites Based on Individual Tree-Crown Delineation

    Directory of Open Access Journals (Sweden)

    Giorgos Mallinis

    2013-12-01

    Full Text Available This study presents an individual tree-crown-based approach for canopy fuel load estimation and mapping in two Mediterranean pine stands. Based on destructive sampling, an allometric equation was developed for the estimation of crown fuel weight considering only pine crown width, a tree characteristic that can be estimated from passive imagery. Two high resolution images were used originally for discriminating Aleppo and Calabrian pines crown regions through a geographic object based image analysis approach. Subsequently, the crown region images were segmented using a watershed segmentation algorithm and crown width was extracted. The overall accuracy of the tree crown isolation expressed through a perfect match between the reference and the delineated crowns was 34.00% for the Kassandra site and 48.11% for the Thessaloniki site, while the coefficient of determination between the ground measured and the satellite extracted crown width was 0.5. Canopy fuel load values estimated in the current study presented mean values from 1.29 ± 0.6 to 1.65 ± 0.7 kg/m2 similar to other conifers worldwide. Despite the modest accuracies attained in this first study of individual tree crown fuel load mapping, the combination of the allometric equations with satellite-based extracted crown width information, can contribute to the spatially explicit mapping of canopy fuel load in Mediterranean areas. These maps can be used among others in fire behavior prediction, in fuel reduction treatments prioritization and during active fire suppression.

  16. A comparative evaluation of the effect of dentin desensitizers on the retention of complete cast metal crowns

    Directory of Open Access Journals (Sweden)

    Saili M Chandavarkar

    2015-01-01

    Full Text Available Context: Desensitizers are used to reduce dentin hypersensitivity. They affect the surface texture of prepared dentin and may alter the retention of fixed restorations. Aims: The aim was to evaluate the effect of dentin desensitizers on the retention of complete cast metal crowns luted with glass ionomer cement. Subjects and Methods: Fifty freshly extracted human premolars were subjected to standardized tooth preparation (20° total convergence, 4 mm axial height with a computer numerically controlled machine. Individual cast metal crowns were fabricated from a base metal alloy. Dentin desensitizers included none (control, a glutaraldehyde (GLU based primer (Gluma desensitizer, casein phosphopeptide (CPP-amorphous calcium phosphate (ACP (GC Mousse, erbium, chromium: YSGG laser (Waterlase MD Turbo, Biolase and Pro-Argin (Colgate Sensitive Pro-Relief desensitizing polishing paste. After desensitization, crowns were luted with glass ionomer cement and kept for 48 h at 37°C in 100% relative humidity. The samples were tested using a universal testing machine by applying a load at a crosshead speed of 0.5 mm/min. Statistical Analysis Used: Statistical analysis included One-way ANOVA, followed by the Scheffe post-hoc test with P < 0.05. Results: All dentin desensitizers showed significantly different values: Pro-Argin (4.10 Megapascals [Mpa] < CPP-ACP (4.01 mpa < GLU based primer (3.87 Mpa < Virgin dentin (3.65 Mpa < LASER (3.37 Mpa. Conclusions : On comparing the effect of prepared virgin dentin, GLU based primer, CPP-ACP, LASER and Pro-Argin on the retention of complete cast metal crowns luted with glass ionomer cement on prepared teeth, it can be concluded that Pro-Argin and CPP-ACP showed the best retention in this in vitro study.

  17. Antimutagenic effect of crown ethers on heavy metal-induced sister chromatid exchanges.

    Science.gov (United States)

    Cai, M Y; Arenaz, P

    1998-01-01

    Macrocyclic polyethers (crown ethers) are a family of compounds that possess the ability to complex with and transport metal ions across membranes. Because of their unique ionophoric characteristic, they have wide application in industry and research, chemistry and biology. In the current investigation the relationship between heavy metal mutagenesis and crown ether co-mutagenicity and/or antimutagenicity in mammalian cells has been examined using sister chromatid exchange (SCE) as the cytogenetic end point. Chinese hamster ovary cells were treated with lead or cadmium, with and without selected crown ethers. Several genotoxic end points, including SCEs were scored and statistically compared. We report here that most of the crown ethers studied had little or no influence on lead- or cadmium-induced SCEs or chromosome aberrations. On the other hand, the substituted crown ether dicyclohexyl 21-crown-7 significantly decreased both spontaneous and metal-induced SCE frequencies, suggesting that this crown ether may possess antimutagenic activity.

  18. Detection, quantification and modelling of small-scale lateral translocation of throughfall in tree crowns of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

    Science.gov (United States)

    Frischbier, Nico; Wagner, Sven

    2015-03-01

    The redistribution of precipitation in forests depends on the amount of above-canopy precipitation and is characterised by high small-scale variability. Although higher and lower values of net forest precipitation at small scales are typically averaged at larger spatial scales, the small-scale variability of throughfall needs to be understood because subordinate ecological processes in the forest ecosystem, e.g., regeneration of tree species, often take place at the same small scale. High stemflow amounts and canopy driplines at the crown edge of particular tree species can only be explained by lateral flow processes within tree crowns. This study tests the hypothesis that lateral water translocation within the crown can be determined from simultaneous records of precipitation at defined measurement points below and above the canopy by taking single-tree characteristics such as species and crown width into account. Spatially explicit simultaneous measurements of gross precipitation (above-canopy reference) and throughfall were conducted repeatedly at 175 measurements points in a mixed European beech-Norway spruce stand for a total of 26 individual rain events. Subsequent analysis with a new regression approach resulted in an estimated average canopy storage capacity of 3.5 mm and 5.8 mm for beech (leaf-bearing period) and spruce stands, respectively. Values of calculated lateral flow showed considerable variability between individual measurement points. The highest discharge amounts were observed at positions below the inner beech crowns during the leaf-bearing period. For an exemplary rainfall event with a gross precipitation of 25 mm, the predicted discharge ranged from 5 mm underneath the inner beech crown to about zero near the crown edge. A comparison with the measured values indicated that the predicted amount of lateral flow, which could be translated into stemflow for single beech trees, was realistic. However, for the same rainfall event, lateral flow in

  19. Root type matters: measurements of water uptake by seminal, crown and lateral roots of maize

    Science.gov (United States)

    Ahmed, Mutez Ali; Zarebanadkouki, Mohsen; Kaestner, Anders; Carminati, Andrea

    2016-04-01

    Roots play a key role in water acquisition and are a significant component of plant adaptation to different environmental conditions. Although maize (Zea mays L.) is one of the most important crops worldwide, there is limited information on the function of different root segments and types in extracting water from soils. Aim of this study was to investigate the location of root water uptake in mature maize. We used neutron radiography to image the spatial distribution of maize roots and trace the transport of injected deuterated water (D2O) in soil and roots. Maize plants were grown in aluminum containers filled with a sandy soil that was kept homogeneously wet throughout the experiment. When the plants were five weeks-old, we injected D2O into selected soil regions. The transport of D2O was simulated using a diffusion-convection numerical model. By fitting the observed D2O transport we quantified the diffusion coefficient and the water uptake of the different root segments. The model was initially developed and tested with two weeks-old maize (Ahmed et. al. 2015), for which we found that water was mainly taken up by lateral roots and the water uptake of the seminal roots was negligible. Here, we used this method to measure root water uptake in a mature maize root system. The root architecture of five weeks-old maize consisted of primary and seminal roots with long laterals and crown (nodal) roots that emerged from the above ground part of the plant two weeks after planting. The crown roots were thicker than the seminal roots and had fewer and shorter laterals. Surprisingly, we found that the water was mainly taken up by the crown roots and their laterals, while the lateral roots of seminal roots, which were the main location of water uptake of younger plants, stopped to take up water. Interestingly, we also found that in contrast to the seminal roots, the crown roots were able to take up water also from their distal segments. We conclude that for the two weeks

  20. Spectrophotometric analysis of crown discoloration induced by MTA- and ZnOE-based sealers

    Directory of Open Access Journals (Sweden)

    Konstantinos Ioannidis

    2013-04-01

    Full Text Available Crown discoloration can be induced by root canal sealer remnants following root canal treatment. Objective: The aim of this study was to evaluate chromatic alterations in human tooth crowns induced by a Mineral Trioxide Aggregate-based sealer (MTA Fillapex® and a commonly used ZnOE-based sealer (Roth-811. The tested null hypothesis was that the application of the materials did not induce clinically perceptible crown discoloration (Ho: CIE color difference ΔE<3.7. Material and Methods: Forty five fully developed, intact, mandibular third molars were sectioned 1 mm below the cemento-enamel junction. The pulp chambers were chemomechanically debrided via the cervical access. The specimens were randomly assigned into three groups Group 1: MTA Fillapex, Group 2: Roth 811, Group 3: Negative control (unfilled and immersed in individually marked vials containing distilled water up to the cervix (37±1°C. The spectral reflectance lines were recorded by utilizing a UV-VIS spectrophotometer equipped with integration sphere in the visual spectrum at baseline, 1 week, 1 and 3 months after material placement. Data were transformed into values of the CIE L*a*b* color system and the corresponding ΔE values were calculated. Statistical analysis was performed using two-way mixed ANOVA models, at p=0.05 level of significance. Results: A statistically significant increase in a* and b* chromatic parameters of the MTA Fillapex Group was measured. However, ΔE values did not exceed the human eye perceptibility threshold (set at ΔE<3.7 during the experimental period (ΔEt3=2.88. In Roth-811 Group, a statistically significant decrease in L* and a statistically significant increase in a* and b* chromatic parameters was measured, during all observation periods. Resultant ΔE values exceeded the human eye perceptibility threshold after 1 week (ΔEt1=5.65. Conclusions: Application of MTA Fillapex in tooth crowns resulted in minimal color alterations, while Roth 811

  1. Design algorithm for generatrix profile of cylindrical crowned rollers

    Directory of Open Access Journals (Sweden)

    Creţu Spiridon

    2017-01-01

    Full Text Available The cross-section of roller profile controls the pressure distribution in the contact area and radically affects the roller bearings basic dynamic load rating and rating lives. Today the most used roller profiles are the logarithmic profile and cylindrical-crowned (ZB profile. The logarithmic profile has a continuous evolution with no discontinuities till the intersection with the end fillet while ZB profile has two more discontinuities at the intersections points between the crowning circle and straight line generatrix. Using a semianalytical method, a numerical study has been carried out to find the optimum ZB profile for rollers incorporated in cylindrical rollers bearings. The basic reference rating life (L10_r has been used as optimization criterion.

  2. A new flapless technique for crown lengthening after orthodontic extrusion.

    Science.gov (United States)

    Braga, Giovanni; Bocchieri, Anna

    2012-02-01

    Orthodontic extrusion (OE), which is performed in many different clinical situations to move a tooth or its periodontal tissues coronally, is often associated with supracrestal fiberotomy and root planing (OEFRP) or followed by surgical crown lengthening. The OEFRP procedure must be carried out every 2 weeks during the entire extrusive orthodontic phase, and precise control of the technique itself can be quite difficult, especially when this approach is to be performed on a limited portion of the root perimeter in teeth affected by angular defects. The aim of this study was to show a new nonsurgical crown-lengthening technique, performed shortly after the completion of OE, to simultaneously achieve proper hard and soft tissue architecture. Three different illustrative situations (periodontal pocket, root fracture, and root perforation) are described.

  3. Fabrication of all-ceramic crowns by a new method.

    Science.gov (United States)

    Masuda, Takayuki; Kakimoto, Kazutoshi; Takahashi, Kazuya; Komasa, Yutaka

    2016-01-01

    A new method of all-ceramic production using alumina coping has been developed. The present study investigates the influence of secondary firing (glass infiltration firing) conditions. Samples of porcelain build-up without secondary firing were also assessed. The suitability of coping that included secondary firing was found to be affected by the rate of temperature increase during the secondary firing. However, cracking developed in the fired porcelain if porcelain was built up onto secondarily-fired coping. In contrast, cracking did not occur with coping that was not secondarily fired. The bending strength after porcelain build-up was 70 MPa or higher, suggesting the possibility of clinical applications as an anterior crown. These findings establish that this is method of producing all-ceramic crowns that allows for low-cost manufacture in a short period of about 1 h.

  4. Fracture resistance of teeth restored with dentin-bonded crowns.

    Science.gov (United States)

    Burke, F J; Watts, D C

    1994-05-01

    While dentin-bonded crowns may hold esthetic advantages over metal-ceramic restorations, and minimal tooth preparation may also be appropriate, resistance to fracture of the restored unit is an important consideration. Dentin-bonded crowns were placed on standardized preparations in two groups of 10 maxillary premolar teeth in vitro. The preparations differed only in degree of taper. The restored specimens were subjected to compressive loading at 1 mm/min from a steel bar placed along the midline fissure. Mean fracture loads of 0.77 kN (6-degree taper) and 0.71 kN (8-degree taper) were recorded for the groups of prepared teeth, and a mean fracture load of 0.97 kN was obtained for a group of unprepared controls. Statistical analysis indicated that there was no significant difference between the fracture load of the 6-degree taper group and that of the sound control teeth.

  5. Crown structure modifications in relation to air pollution

    Energy Technology Data Exchange (ETDEWEB)

    Bussotti, Filippo (Laboratory of Forest Botany, Department of Plant Biology, University of Florence, (Italy)); Brogi, Lamberto (Agriculture and Forestry Department, Florence, (Italy)); Grossoni, Paolo (Institute of Silviculture, University of Florence, (Italy)); Cozzi, Alberto (Linnaea-ambiente s.r.l., Florence, (Italy)); Gellini, Romano (Laboratory of Forest Botany, Department of Plant Biology, University of Florence (Italy))

    1993-07-01

    Analysis of crown structure and crown modifications plays a role of primary importance in surveys of 'new types of forest damage', since it is a decisive parameter in assessing the health status of a tree. Several forms of ramification alterations have been described in central and northern European species (Norway spruce, beech, Durmast oak, English oak, birch). This study examines the situation in Tuscany and offers a description of the alterations found in the main species typical of the Mediterranean region (Turkey oak, pubescent oak, holm oak, stone pine). The article discusses the potential impact of these alterations on the most typical forest formations, the ones which characterize the Tuscan landscape, and it describes the modifications already under way.

  6. Modeling tree crown dynamics with 3D partial differential equations.

    Science.gov (United States)

    Beyer, Robert; Letort, Véronique; Cournède, Paul-Henry

    2014-01-01

    We characterize a tree's spatial foliage distribution by the local leaf area density. Considering this spatially continuous variable allows to describe the spatiotemporal evolution of the tree crown by means of 3D partial differential equations. These offer a framework to rigorously take locally and adaptively acting effects into account, notably the growth toward light. Biomass production through photosynthesis and the allocation to foliage and wood are readily included in this model framework. The system of equations stands out due to its inherent dynamic property of self-organization and spontaneous adaptation, generating complex behavior from even only a few parameters. The density-based approach yields spatially structured tree crowns without relying on detailed geometry. We present the methodological fundamentals of such a modeling approach and discuss further prospects and applications.

  7. Modeling Tree Crown Dynamics with 3D Partial Differential Equations

    Directory of Open Access Journals (Sweden)

    Robert eBeyer

    2014-07-01

    Full Text Available We characterize a tree's spatial foliage distribution by the local leaf area density. Considering this spatially continuous variable allows to describe the spatiotemporal evolution of the tree crown by means of 3D partial differential equations. These offer a framework to rigorously take locally and adaptively acting effects into account, notably the growth towards light. Biomass production through photosynthesis and the allocation to foliage and wood are readily included in this model framework. The system of equations stands out due to its inherent dynamic property of self-organization and spontaneous adaptation, generating complex behavior from even only a few parameters. The density-based approach yields spatially structured tree crowns without relying on detailed geometry. We present the methodological fundamentals of such a modeling approach and discuss further prospects and applications.

  8. Gilded Silver Crown with Double-dragon Pattern

    Institute of Scientific and Technical Information of China (English)

    1996-01-01

    Unearthed from a Liao tomb at Zhangjia Yingzi, Jianping County, Liaoning Province in 1956, this gilded silver crown with double-dragon pattern is 19 cm high and 20.9 cm in diameter. Its shape is suggestive of a mountain: higher in the middle and lower on both sides. On the front is a carving in the shape of a pearl surrounded by an S-shape pattern symbolizing good fortune. There is a lively dragon on either side. The complete design is based on the old theme "two dragons play with a pearl." Traditions of the Qidan, an ancient nationality of northern China, are evident in the design of the crown. It is recorded in

  9. Positional changes of maxillary central incisors following orthodontic treatment using single-crown implants as fixed reference markers

    DEFF Research Database (Denmark)

    Brahem Ben, Elissa; Holm, Bente; Sonnesen, L

    2017-01-01

    . MATERIALS AND METHODS: Fifty-seven patients - thirty-seven with (test group) and twenty without pre-implant orthodontic treatment (control group) - were rehabilitated with 89 single-crown implants in the upper maxilla. Clinical and radiographic data, clinical photographs, and dental casts were collected......OBJECTIVES: This follow-up study (1) compares tooth displacement of central incisors in patients with and without pre-implant orthodontic treatment and (2) investigates whether sex, age, or orthodontic retention have an effect on tooth displacement after the insertion of single-crown implants...... during baseline examinations after prosthetic rehabilitation and at the final follow-up examination at least 5 years later. A total of 114 dental casts were digitalized and aligned using a software program to measure changes in the positions of the central incisors. RESULTS: After a follow-up period...

  10. The Head that Wears a Crown

    DEFF Research Database (Denmark)

    Hansen, Bertel Teilfeldt

    2014-01-01

    of conflict onset in countries that have recently experienced conflict. I test this proposition using a difference-in-difference model on an original dataset of the ethnicities of elected presidents in all the world’s countries from 1975 to 2010. The result is a robust and substantial increase in the risk...... of conflict onset in the period immediately following a change in the ethnic group holding presidency. The effect is greatest in the aftermath of previous conflicts and slowly tapers off over time. Further, shifts where the winning and losing ethnic groups are of similar sizes exhibit the largest and most...

  11. The Effect of abutment wall modification, filling material & copying design on retention of cement retained implant supported crown

    Directory of Open Access Journals (Sweden)

    Shima Aalaei

    2016-12-01

    Full Text Available Background and aim: Factors which can effect of tooth supported crowns are well known. On the other side, low information are existed about retention of implant supported crowns. The aim of the present study was to evaluate the effect of abutment wall modification, filling material & copying design on retention of cement retained implant supported crown. Materials and methods: In this study, 4 straight abutments were attached to their implant analogues and were embedded in the acrylic resin block. Abutments were modified to one, two, three and four walls. Then, two type copying were made: conventional and with metal extension in two screw access cavity. Access cavities were filled incompletely by three methods: copying with extension spread into the access cavity without material and conventional copying with polytetrafluoroethylene (PTFE or composite. Then cemented with temporary agent (TempBond. Required tensile force for separation of copying was measured by universal testing machine. Data were analyzed using ANOVA as statistical test. Results: About findings of this research, no significant difference were detected among two methods of filling of access cavity and engaging screw access channel (P>0.05. Four wall abutment shown significantly higher retention than the others (P<0.05 and three other abutments have no significant difference in retention. Conclusion: The type of filling material of access cavity (PTFE and composite and engaging of the copying design have no significant effects on the cemented retained of implant supported restoration but existence of all four septums increase the veneer retention significantly.

  12. How resilient are southwestern ponderosa pine forests after crown fires?

    OpenAIRE

    Savage, Van M.; Mast, J N

    2005-01-01

    The exclusion of low-severity surface fire from ponderosa pine (Pinus ponderosa P. & C. Lawson) forests of the Southwest has changed ecosystem structure and function such that severe crown fires are increasingly causing extensive stand mortality. This altered fire regime has resulted from the intersection of natural drought cycles with human activities that have suppressed natural fires for over a century. What is the trajectory of forest recovery after such fires? This study explores the reg...

  13. Structured mayhem: personal experiences of the Crown Court

    OpenAIRE

    Jacobson, Jessica; Hunter, G.; Kirby, Amy

    2015-01-01

    Synopsis: A CJA briefing on the sometimes harrowing experiences of victims, witnesses and defendants in a wide-ranging series of Crown Court cases. Structured Mayhem is a digest of a remarkable piece of research carried by the Institute for Criminal Policy Research. Featuring extensive interviews with court users it furnishes a stark reminder that, for all the progress made in recent years, our courts all too often still cause huge frustration and distress to victims and witnesses, and also d...

  14. Bonded composite resin crowns for primary incisors: technique update.

    Science.gov (United States)

    Croll, T P

    1990-02-01

    A technique for restoration of carious primary maxillary incisors with a hybrid visible light-curing composite resin and a dentinal bonding agent is described. Careful use of this technique and the new materials can provide a restoration that is esthetic and resistant to fracture and displacement. The technique requires careful preparation of the operative field and precise handling of the restorative materials. The method is illustrated by the placement of bonded composite resin crowns in a 3-year-old boy.

  15. 12-Crown-4 Ether Improves Rechargeable Lithium Cells

    Science.gov (United States)

    Nagasubramanian, Ganesan; Attia, Alan I.

    1992-01-01

    Experiments show addition of 12-crown-4 ether (12Cr4) to thin film of polyethylene oxide (PEO) and LiBF4 reduces charge-transfer resistance of film and enhances performance of electrochemical cell in which film is electrolyte, anode is lithium, and cathode is LixCoO2. By increasing conductivity of the electrolyte, 12Cr4 reduces polarization loss; enabling cell to sustain higher current. Result is new type of rechargeable lithium cell.

  16. Laboratory fire behavior measurements of chaparral crown fire

    Science.gov (United States)

    C. Sanpakit; S. Omodan; D. Weise; M Princevac

    2015-01-01

    In 2013, there was an estimated 9,900 wildland fires that claimed more than 577,000 acres of land. That same year, about 542 prescribed fires were used to treat 48,554 acres by several agencies in California. Being able to understand fires using laboratory models can better prepare individuals to combat or use fires. Our research focused on chaparral crown fires....

  17. Negatively charged crown ethers for binding paraquat in water

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A water soluble negatively charged fluorescent 1,4-benzo-1,5-naphtho-36-crown-10-based host has been devised and synthesized.As shown by proton NMR,ESI mass spectrometry and UV-vis spectroscopy,it binds paraquat with a 1:1 stoichiometry and an association constant of 4.50(±0.02) ×103 M-1 in water.Its complexation with paraquat in water was further investigated by fluorescence emission spectroscopy.The results revealed that when paraquat was added to the water solution of the host,the fluorescence emission of the host was quenched by the charge transfer between the crown ether host and paraquat guest.A similar bis-p-phenylene-34-crown-10-based host was synthesized as a contrasting host.Lacking the naphthalene unit,the second host binds paraquat with a 1:1 stoichiometry and a lower association constant,1.04(±0.04) ×103 M-1,in water.This demonstrated that the naphthalene unit could not only act as a strong fluorescence group but also improve the π-πstacking interactions between the host and guest.

  18. Plant responses to Agrobacterium tumefaciens and crown gall development

    Directory of Open Access Journals (Sweden)

    Jochen eGohlke

    2014-04-01

    Full Text Available Agrobacterium tumefaciens causes crown gall disease on various plant species by introducing its T-DNA into the genome. Therefore, Agrobacterium has been extensively studied both as a pathogen and an important biotechnological tool. The infection process involves the transfer of T-DNA and virulence proteins into the plant cell. At that time the gene expression patterns of host plants differ depending on the Agrobacterium strain, plant species and cell-type used. Later on, integration of the T-DNA into the plant host genome, expression of the encoded oncogenes, and increase in phytohormone levels induce a fundamental reprogramming of the transformed cells. This results in their proliferation and finally formation of plant tumours. The process of reprogramming is accompanied by altered gene expression, morphology and metabolism. In addition to changes in the transcriptome and metabolome, further genome-wide (‘omic’ approaches have recently deepened our understanding of the genetic and epigenetic basis of crown gall tumour formation. This review summarizes the current knowledge about plant responses in the course of tumor development. Special emphasis is placed on the connection between epigenetic, transcriptomic, metabolomic and morphological changes in the developing tumor. These changes not only result in abnormally proliferating host cells with a heterotrophic and transport-dependent metabolism, but also cause differentiation and serve as mechanisms to balance pathogen defense and adapt to abiotic stress conditions, thereby allowing the coexistence of the crown gall and host plant.

  19. Surgical crown lengthening: a 12-month study - radiographic results

    Directory of Open Access Journals (Sweden)

    Daniela Eleutério Diniz

    2007-08-01

    Full Text Available OBJECTIVE: The purpose of this study was to perform a radiographic follow-up evaluation after a 12-month healing period, following crown lengthening surgery. MATERIAL AND METHODS: Twenty-three periodontally healthy subjects (mean age 32.5 years that required crown lengthening surgery in premolars were recruited. In a total of 30 premolars, full thickness flaps, osseous resection, and flap suturing were performed. The restorative margin was defined in the pre-surgical phase and maintained unaltered during the healing period, serving as a reference point. Standardized bitewing radiographs were taken before and after osseous reduction, and at 2, 3, 6, and 12-month healing periods. RESULTS: Intact lamina dura was observed at both mesial and distal alveolar crests only from the 3rd month. At 12-months, all alveolar crests presented lamina dura. The overall mean distance from the restorative margin to the alveolar crest achieved after osseous resection was 3.28±0.87 mm at mesial and 2.81±0.51 mm at distal sites. No significant radiographic changes in the bone crest were observed during a 12-month healing period. CONCLUSION: The findings of this study suggest that the radiographic proximal bone level observed on bitewing radiographs following crown lengthening surgery can be used as a reference to predict the future level of the healed alveolar crest.

  20. SURGICAL CROWN LENGTHENING: A 12-MONTH STUDY - RADIOGRAPHIC RESULTS*

    Science.gov (United States)

    Diniz, Daniela Eleutério; Okuda, Kalizia Marcela; Fonseca, Clarissa Ribeiro; Gonzalez, Marly Kimie Sonohara; Greghi, Sebastião Luiz Aguiar; do Valle, Accácio Lins; Lauris, José Roberto Pereira

    2007-01-01

    Objective The purpose of this study was to perform a radiographic follow-up evaluation after a 12-month healing period, following crown lengthening surgery. Material and methods Twenty-three periodontally healthy subjects (mean age 32.5 years) that required crown lengthening surgery in premolars were recruited. In a total of 30 premolars, full thickness flaps, osseous resection, and flap suturing were performed. The restorative margin was defined in the pre-surgical phase and maintained unaltered during the healing period, serving as a reference point. Standardized bitewing radiographs were taken before and after osseous reduction, and at 2, 3, 6, and 12-month healing periods. Results Intact lamina dura was observed at both mesial and distal alveolar crests only from the 3rd month. At 12-months, all alveolar crests presented lamina dura. The overall mean distance from the restorative margin to the alveolar crest achieved after osseous resection was 3.28±0.87 mm at mesial and 2.81±0.51 mm at distal sites. No significant radiographic changes in the bone crest were observed during a 12-month healing period. Conclusion The findings of this study suggest that the radiographic proximal bone level observed on bitewing radiographs following crown lengthening surgery can be used as a reference to predict the future level of the healed alveolar crest. PMID:19089145

  1. Study of an NC system of machining crown gears

    Science.gov (United States)

    Xu, Xiaogang; Wang, Huaqing; Yan, Jian; Gao, Shenyou

    2005-12-01

    Crown gear couplings are usually used in metallurgy and steel rolling equipments, which is manufactured by duplicating processing in common. The method makes the manipulator work hard, and the efficiency is low. The machining precision is limited to the shape of the mold and it is difficult to control the movement of machines table. This work stated an NC system to use hobbing machine. It consists of an industrial control computer, grating sensor, servo- motor and its driver source, servo driver card and other I/O equipments of inputting and outputting. The grating sensor was installed in the axial direction to trace the instantaneous position of gob rest. The radial movement of the machine table was controlled by a servomotor. When the computer captures the axial signal, this system controls the machine table by moving ahead or backwards according to the calculated value of interpolation theory. Thus, two dimensions (axial and radial) associated movement was realized while the crown gear was processed. The feature of the system is that a grating sensor used in the axial direction replaces the servomotor. By making a little change in the mechanism of the machine, NC can be implement and its redesign cost is very low. The design software has an interpolation function for a circular arc and line. The system has been used on a Y1380 gear hobbing machine, and the correlative software of machining crown gear has been designed as well. Satisfactory results have been obtained, showing facility and reliability in practical operation.

  2. Slide crown lengthening procedure using wide surface incisions and cyanoacrylate.

    Science.gov (United States)

    Szymaitis, Dennis W

    2011-01-01

    This article introduces the slide crown lengthening procedure (SCLP), which incorporates surgical design features to overcome present crown lengthening procedure (CLP) shortcomings. The result is a 75% decrease in required surgery on adjacent teeth and a corresponding 75% reduction in surgical time. Other advantages include a reduction in surgical morbidity, improvement in terminal esthetics, and fewer teeth subject to papillae removal and apically repositioned gingiva. The 20 to 30 degree incision forming the slide is the pivotal feature; it allows effortless flap positioning. This incision angle enables wide surface incisions to adhere flaps together by producing stronger fibrin clots, decreasing tissue retraction angles, and reforming disrupted fibrin clots as incision sides slide while maintaining contact. This enhanced fibrin clot eliminates the need for sutures. The slide produced by the 20 to 30 degree incision functions for crown lengthening on all sites (facial, lingual, or palatal). This versatile surgical design introduces a new healing dimension that adapts to and provides benefits for other dental surgeries, such as gingival grafts, endodontic surgery, implants, and extractions.

  3. Clinical marginal and internal adaptation of CAD/CAM milling, laser sintering, and cast metal ceramic crowns.

    Science.gov (United States)

    Tamac, Ece; Toksavul, Suna; Toman, Muhittin

    2014-10-01

    Metal ceramic crowns are widely used in clinical practice, but comparisons of the clinical adaptation of restorations made with different processing techniques are lacking. The purpose of this study was to compare the clinical marginal and internal adaptation of metal ceramic crowns fabricated with 3 different techniques: computer-aided design and computer-aided manufacturing (CAD/CAM) milling (CCM), direct metal laser sintering (DMLS), and traditional casting (TC). Twenty CCM, 20 DMLS, and 20 TC metal ceramic crowns were fabricated for 42 patients. Before luting the crowns, silicone replicas were obtained to measure marginal gap and internal adaptation that was evaluated at 3 regions: axial wall, axio-occlusal angle, and occlusal surface. Measurements were made with a reflected light binocular stereomicroscope at 20× magnification and analyzed with 1-way analysis of variance (ANOVA) and the Bonferroni post hoc test (α=.05). The mean marginal gap values were 86.64 μm for CCM, 96.23 μm for DMLS, and 75.92 μm for TC. The means at the axial wall region were 117.5 μm for the CCM group, 139.02 μm for the DMLS group, and 121.38 μm for the TC group. One-way ANOVA revealed no statistically significant differences among the groups for measurements at the marginal gap (P=.082) and the axial wall region (P=.114). The means at the axio-occlusal region were 142.1 μm for CCM, 188.12 μm for DMLS, and 140.63 μm for TC, and those at the occlusal surface region were 265.73 μm for CCM, 290.39 μm for DMLS, and 201.09 μm for TC. The mean values of group DMLS were significantly higher at the axio-occlusal region and the occlusal surface region than those of other groups (Pmetal ceramic crowns performed similarly in terms of clinical marginal and axial wall adaptation. The cement film thickness at the occlusal region and axio-occlusal region were higher for DMLS crowns. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc

  4. Crown Group Lejeuneaceae and Pleurocarpous Mosses in Early Eocene (Ypresian) Indian Amber.

    Science.gov (United States)

    Heinrichs, Jochen; Scheben, Armin; Bechteler, Julia; Lee, Gaik Ee; Schäfer-Verwimp, Alfons; Hedenäs, Lars; Singh, Hukam; Pócs, Tamás; Nascimbene, Paul C; Peralta, Denilson F; Renner, Matt; Schmidt, Alexander R

    2016-01-01

    Cambay amber originates from the warmest period of the Eocene, which is also well known for the appearance of early angiosperm-dominated megathermal forests. The humid climate of these forests may have triggered the evolution of epiphytic lineages of bryophytes; however, early Eocene fossils of bryophytes are rare. Here, we present evidence for lejeuneoid liverworts and pleurocarpous mosses in Cambay amber. The preserved morphology of the moss fossil is inconclusive for a detailed taxonomic treatment. The liverwort fossil is, however, distinctive; its zig-zagged stems, suberect complicate-bilobed leaves, large leaf lobules, and small, deeply bifid underleaves suggest a member of Lejeuneaceae subtribe Lejeuneinae (Harpalejeunea, Lejeunea, Microlejeunea). We tested alternative classification possibilities by conducting divergence time estimates based on DNA sequence variation of Lejeuneinae using the age of the fossil for corresponding age constraints. Consideration of the fossil as a stem group member of Microlejeunea or Lejeunea resulted in an Eocene to Late Cretaceous age of the Lejeuneinae crown group. This reconstruction is in good accordance with published divergence time estimates generated without the newly presented fossil evidence. Balancing available evidence, we describe the liverwort fossil as the extinct species Microlejeunea nyiahae, representing the oldest crown group fossil of Lejeuneaceae.

  5. Crown Group Lejeuneaceae and Pleurocarpous Mosses in Early Eocene (Ypresian Indian Amber.

    Directory of Open Access Journals (Sweden)

    Jochen Heinrichs

    Full Text Available Cambay amber originates from the warmest period of the Eocene, which is also well known for the appearance of early angiosperm-dominated megathermal forests. The humid climate of these forests may have triggered the evolution of epiphytic lineages of bryophytes; however, early Eocene fossils of bryophytes are rare. Here, we present evidence for lejeuneoid liverworts and pleurocarpous mosses in Cambay amber. The preserved morphology of the moss fossil is inconclusive for a detailed taxonomic treatment. The liverwort fossil is, however, distinctive; its zig-zagged stems, suberect complicate-bilobed leaves, large leaf lobules, and small, deeply bifid underleaves suggest a member of Lejeuneaceae subtribe Lejeuneinae (Harpalejeunea, Lejeunea, Microlejeunea. We tested alternative classification possibilities by conducting divergence time estimates based on DNA sequence variation of Lejeuneinae using the age of the fossil for corresponding age constraints. Consideration of the fossil as a stem group member of Microlejeunea or Lejeunea resulted in an Eocene to Late Cretaceous age of the Lejeuneinae crown group. This reconstruction is in good accordance with published divergence time estimates generated without the newly presented fossil evidence. Balancing available evidence, we describe the liverwort fossil as the extinct species Microlejeunea nyiahae, representing the oldest crown group fossil of Lejeuneaceae.

  6. Novel potentiometric sensor for monitoring beryllium based on naphto-9-crown-3.

    Science.gov (United States)

    Ganjali, Mohammad Reza; Daftari, Azadeh; Faal-Rastegar, Majid; Moghimi, Abolghasem

    2003-03-01

    A novel poly(vinyl chloride) (PVC) membrane electrode based on naphto-9-crown-3 was prepared and tested for the selective detection of beryllium ions. A suitable lipophilicity of the carrier and appropriate coordination ability were found to be essential for designing an electrode with good response characteristics. A PVC membrane with 9% naphtho-9-crown-3 carrier, 58% o-NPOE plasticizer, 3% tetraphenylborate anionic excluder and 30% poly(vinyl chloride) satisfied these requirements. The proposed sensor displayed a linear response to beryllium over a wide concentration range of 1.0 x 10(-1)-8.0 x 10(-6) M with a Nernstian slope of 29.5 mV per decade. The electrode showed very short response time (<15 s) and could be used in the pH range 3.5-9.0. The selectivity coefficient for alkali, alkaline earth, transition and heavy metal ions was smaller than 4.0 x 10(-4). The sensor was successfully used as an indicator electrode in the potentiometric titration of Be2+ with EDTA. The proposed Be(II) sensor was also used for the determination of Be2+ ions in binary mixtures.

  7. Antibacterial properties of amalgam and composite resin materials used as cores under crowns.

    Science.gov (United States)

    Al Ghadban, A; Al Shaarani, F

    2012-06-01

    The Aim of this Study was to compare the bacterial growth in the bulk of both amalgam and fluoridated composite resin materials used as cores under crowns at core's surface (in the superficial area of the bulk) and depth levels. With 24 lower premolars, 12 of them were restored with metal posts and amalgam cores (group 1). The rest were restored with glass Fiber-reinforced Composite (FRC) posts and fluoridated composite resin cores (group 2). All specimens were covered with aluminium crowns cemented with resin cement, and then they were soaked in natural saliva for three months. Excoriations abraded from the superficial and the depth areas of the core materials were cultured under aerobic conditions on blood agar plates. After incubation for 2 days, colonies formed on the plates were identified, and the CFU mg(-1) counts were recorded accordingly. Statistical analysis was performed using an independent sample T test. The mean values of CFU mg(-1) counts in group 2 excoriations (surface 39.75, and depth 9.75) were higher than the group 1 excoriations (surface 1.67, and depth 0.42). This study supports the use of amalgam for building up cores due to its antibacterial properties. Composite resin, however, enhanced sizable bacterial growth despite the presence of fluoride.

  8. Dynamics of indole-3-acetic acid oxidase activity in suspension culture of sunflower crown-gall

    Directory of Open Access Journals (Sweden)

    Zofia Chirek

    2014-02-01

    Full Text Available IAA oxidase activity was determined in several growth phases of a suspension culture of sunflower crown-gall. During the short phase of intensive growth (zero passage - PO a negative correlation was noted between enzymatic activity and the rate of growth. IAA oxidase activity increased to a certain level is not a factor limiting cell division. For protraction of the phase of intensive growth (first passage - P1, however, a decrease in the activity of this enzyme seems indispensable. IAA oxidase activity in the tested culture is under the control of inhibitors present in the cells and medium. High enzyme inhibition was observed in PO cells during the phase, of intensive growth and in P1 at the beginning and in the middle part of this phase. These results suggest' that the -auxin level determined in earlier studies in sunflower crown-gall culture is controlled by the IAA oxidase set. During the long phase of intensive growth (P1 this control is of negative feedback type.

  9. Influence of implant position on clinical crown length and peri-implant soft tissue dimensions at implant-supported single crowns replacing maxillary central incisors

    DEFF Research Database (Denmark)

    Peng, Min; Fei, Wei; Hosseini, Mandana

    2013-01-01

    The aims of the present study were to evaluate the influence of implant position on clinical crown length and marginal soft tissue dimensions at implant-supported single crowns of maxillary central incisors, and to validate the papilla index score (PIS). Twenty-five patients, who had lost one of ...

  10. Influence of implant position on clinical crown length and peri-implant soft tissue dimensions at implant-supported single crowns replacing maxillary central incisors

    DEFF Research Database (Denmark)

    Peng, Min; Fei, Wei; Hosseini, Mandana

    2013-01-01

    as controls. Paired sample t-testand Pearson´s correlation analysis were used to analyze implant position, dimension of crownand papilla fill.Cohen’s ¿ andSpearman correlation were used to validate the PIS.The implant-supported crown was statistically longer than the contra-lateral tooth......The aims of the present study were to evaluate the influence of implant position on clinical crown length and marginal soft tissue dimensions at implant-supported single crowns of maxillary central incisors, and to validate the papilla index score (PIS). Twenty-five patients, who had lost one......, and there was significant correlation between the oro-facial position of the implant and the crown length difference (r=.607, p=.001). The distalpapilla was significantly shorter than the mesialpapilla at implant-supported crowns (p

  11. Effect of GLUMA desensitizer on the retention of full metal crowns cemented with Rely X U200 self-adhesive cement

    Science.gov (United States)

    Lawaf, Shirin; Jalalian, Ezatallah; Roshan, Roshanak

    2016-01-01

    PURPOSE Considering the importance of retention in the success and long-term clinical service of fixed partial dentures (FPDs) as well as the existing controversy regarding the effect of GLUMA desensitizer on the retention of full metal crowns cemented with RelyX U200 self-adhesive cement, this study aimed to assess the effect of GLUMA desensitizer on the retention of full metal crowns cemented using RelyX U200. MATERIALS AND METHODS In this experimental study, 20 sound human premolars were prepared; a 0.5 mm chamfer finish line was prepared above the cementoenamel junction. The teeth were randomly assigned to two groups: a desensitizer group (n = 10, treated with GLUMA desensitizer) and a control (n = 10, no surface treatment). Full metal crowns were fabricated of base metal alloy and had a ring. All crowns were cemented with RelyX U200 and subjected to retention test by using a universal testing machine. The data were analyzed using SPSS version 20 and independent t-test. RESULTS The mean tensile bond strength was significantly higher in the GLUMA desensitizer group (230.63 ± 63.8 N) compared to the control group (164.45 ± 39.3 N) (P≤.012). CONCLUSION GLUMA desensitizer increases the tensile bond strength of RelyX U200 self-adhesive cement to dentin. PMID:27826391

  12. Evaluation of marginal and internal gaps of metal ceramic crowns obtained from conventional impressions and casting techniques with those obtained from digital techniques

    Directory of Open Access Journals (Sweden)

    Rathika Rai

    2017-01-01

    Full Text Available Background: Accuracy in fit of cast metal restoration has always remained as one of the primary factors in determining the success of the restoration. A well-fitting restoration needs to be accurate both along its margin and with regard to its internal surface. Aim: The aim of the study is to evaluate the marginal fit of metal ceramic crowns obtained by conventional inlay casting wax pattern using conventional impression with the metal ceramic crowns obtained by computer-aided design and computer-aided manufacturing (CAD/CAM technique using direct and indirect optical scanning. Materials and Methods: This in vitro study on preformed custom-made stainless steel models with former assembly that resembles prepared tooth surfaces of standardized dimensions comprised three groups: the first group included ten samples of metal ceramic crowns fabricated with conventional technique, the second group included CAD/CAM-milled direct metal laser sintering (DMLS crowns using indirect scanning, and the third group included DMLS crowns fabricated by direct scanning of the stainless steel model. The vertical marginal gap and the internal gap were evaluated with the stereomicroscope (Zoomstar 4; post hoc Turkey's test was used for statistical analysis. One-way analysis of variance method was used to compare the mean values. Results and Conclusion: Metal ceramic crowns obtained from direct optical scanning showed the least marginal and internal gap when compared to the castings obtained from inlay casting wax and indirect optical scanning. Indirect and direct optical scanning had yielded results within clinically acceptable range.

  13. Effect of tooth preparation on microleakage of stainless steel crowns placed on primary mandibular first molars with reduced mesiodistal dimension.

    Directory of Open Access Journals (Sweden)

    Nahid Ramazani

    2015-02-01

    Full Text Available Incomplete adaptation of stainless steel crown margins leads to microleakage. The aim of this study was to evaluate the effect of tooth preparation on microleakage of stainless steel crowns (SSCs placed on mesiodistally reduced primary mandibular first molars.In this In vitro study, 60 primary mandibular first molars with reduced mesiodistal dimension were selected. Pulp cavities were filled with amalgam and occlusal surfaces were reduced. The samples were randomly divided into two groups (groups P and BLP. Standard preparation was done in group P with only proximal reduction. In group BLP, after reducing the proximal undercuts, buccal and lingual surfaces were slightly reduced. Occlusal one-third of the buccal surfaces was beveled in both groups. Then, the SSCs of the primary maxillary and mandibular first molars were fitted and cemented in P and BLP groups, respectively. After immersing the samples into deionized water, thermo-cycling, and immersion in 2% basic fuchsin, the samples were sectioned buccolingually. The mesial halves were evaluated microscopically for microleakage in both buccal and lingual margins. Data were analyzed using Mann-Whitney U test in SPSS 19 at the significant level of 0.05.There was a significant difference in microleakage of the buccal margin (P=0.003; whereas, the difference observed in the lingual margin was not significant (P=0.54.We suggest reduction of buccal and lingual surfaces of mesiodistally reduced primary mandibular first molars and placing lower (mandibular crowns.

  14. Effect of the Crystallization Process on the Marginal and Internal Gaps of Lithium Disilicate CAD/CAM Crowns.

    Science.gov (United States)

    Kim, Jae-Hong; Oh, Seunghan; Uhm, Soo-Hyuk

    2016-01-01

    The aim of this study is to quantify the effect of the crystallization process on lithium disilicate ceramic crowns fabricated using a computer-aided design/computer-aided manufacturing (CAD/CAM) system and to determine whether the effect of crystallization is clinically acceptable by comparing values of fit before and after the crystallization process. The mandibular right first molar was selected as the abutment for the experiments. Fifteen working models were prepared. Lithium disilicate crowns appropriate for each abutment were prepared using a commercial CAD/CAM system. Gaps in the marginal area and 4 internal areas of each crown were measured twice-before and after crystallization-using the silicone replica technique. The mean values of fit before and after crystallization were analyzed using a paired t-test to examine whether the conversion that occurred during crystallization affected marginal and internal gaps (α = 0.05). Gaps increased in the marginal area and decreased in the internal areas after crystallization. There were statistically significant differences in all of the investigated areas (P crystallization exceeded 120 μm, which is the clinically acceptable threshold.

  15. Linear mixed-effects models to describe individual tree crown width for China-fir in Fujian Province, southeast China.

    Directory of Open Access Journals (Sweden)

    Xu Hao

    Full Text Available A multiple linear model was developed for individual tree crown width of Cunninghamia lanceolata (Lamb. Hook in Fujian province, southeast China. Data were obtained from 55 sample plots of pure China-fir plantation stands. An Ordinary Linear Least Squares (OLS regression was used to establish the crown width model. To adjust for correlations between observations from the same sample plots, we developed one level linear mixed-effects (LME models based on the multiple linear model, which take into account the random effects of plots. The best random effects combinations for the LME models were determined by the Akaike's information criterion, the Bayesian information criterion and the -2logarithm likelihood. Heteroscedasticity was reduced by three residual variance functions: the power function, the exponential function and the constant plus power function. The spatial correlation was modeled by three correlation structures: the first-order autoregressive structure [AR(1], a combination of first-order autoregressive and moving average structures [ARMA(1,1], and the compound symmetry structure (CS. Then, the LME model was compared to the multiple linear model using the absolute mean residual (AMR, the root mean square error (RMSE, and the adjusted coefficient of determination (adj-R2. For individual tree crown width models, the one level LME model showed the best performance. An independent dataset was used to test the performance of the models and to demonstrate the advantage of calibrating LME models.

  16. Biological control of crown gall on grapevine and root colonization by nonpathogenic Rhizobium vitis strain ARK-1.

    Science.gov (United States)

    Kawaguchi, Akira

    2013-01-01

    A nonpathogenic strain of Rhizobium vitis ARK-1 was tested as a biological control agent for grapevine crown gall. When grapevine roots were soaked in a cell suspension of strain ARK-1 before planting in the field, the number of plants with tumors was reduced. The results from seven field trials from 2009 to 2012 were combined in a meta-analysis. The integrated relative risk after treatment with ARK-1 was 0.15 (95% confidence interval: 0.07-0.29, P0.001), indicating that the disease incidence was significantly reduced by ARK-1. In addition, the results from four field trials from 2007 to 2009 using R. vitis VAR03-1, a previously reported biological control agent for grapevine crown gall, were combined in a meta-analysis. The integrated relative risk after treatment with VAR03-1 was 0.24 (95% confidence interval: 0.11-0.53, P0.001), indicating the superiority of ARK-1 in inhibiting grapevine crown gall over VAR03-1 under field conditions. ARK-1 did not cause necrosis on grapevine shoot explants. ARK-1 established populations on roots of grapevine tree rootstock and persisted inside roots for two years.

  17. Synthesis and spectroscopic characterization of Y-shaped fluorophores with an imidazole core containing crown ether moieties

    Energy Technology Data Exchange (ETDEWEB)

    Doğru, Ümit; Öztürk Ürüt, Gülsiye, E-mail: gulsiye.ozturk@deu.edu.tr; Bayramin, Dilek

    2015-07-15

    In this study three new Y-shaped fluorophores, 4,5-(2,2'-diphenyl)vinyl-{2-[(1,4,7,10-tetraoxa-13-azacyclopentadecyl) phenyl]}-1H-imidazole (1a), 4,5-{[2,2'-bis(4-methoxyphenyl)vinyl]-[2-(1,4,7,10-tetraoxa-13- azacyclopentadecyl)-phenyl]}-1H-imidazole (1b) and 4,5-(2,2'-diphenyl)vinyl-{2-(1,4,7,10,13-benzopentaoxacyclopentadecyl)} -1H-imidazole (1c) were synthesized. 1,6-Diphenylhexa-1,5-diene-3,4-dione (2a) and 1,6-bis(4-methoxyphenyl)hexa-1,5-diene-3,4-dione (2b) were synthesized as preliminary fluorophores and then reacted with 4-formylbenzo-aza-15-crown-5 (3a) and 4-formylbenzo-15-crown-5 (3b) to obtain the three Y-shaped fluorophores 1a, 1b and 1c. 4-formylbenzo-aza-15-crown-5 and 4-formylbenzo-15-crown-5 intermediates were synthesized with Vilsmeier–Haack reaction. The photophysical properties such as maximum absorption wavelengths, maximum emission wavelengths, Stokes' shifts, singlet energies, fluorescence quantum yields and photostabilities of the compounds were investigated by measuring absorption and emission spectra in a series of solvents of varying polarities of toluene (TOL), dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate (EA), acetonitrile (ACN), and N,N-dimethylformamide (DMF). The three compounds 1a, 1b and 1c exhibited emission maxima in the 412–677 nm range. All the derivatives synthesized exhibited excellent photostability in all the solvents tested. - Highlights: • Three new Y-shaped fluorophores were synthesized for the first time. • Their absorption and emission properties were investigated. • All the derivatives synthesized exhibited excellent photostability.

  18. In vitro Evaluation of Stainless Steel Crowns cemented with Resin-modified Glass Ionomer and Two New Self-adhesive Resin Cements

    Science.gov (United States)

    Shashibhushan, KK; Poornima, P; Reddy, VV Subba

    2016-01-01

    Aims To assess and compare the retentive strength of two dual-polymerized self-adhesive resin cements (RelyX U200, 3M ESPE & SmartCem2, Dentsply Caulk) and a resin-modified glass ionomer cement (RMGIC; RelyX Luting 2, 3M ESPE) on stainless steel crown (SSC). Materials and methods Thirty extracted teeth were mounted on cold cured acrylic resin blocks exposing the crown till the cemento-enamel junction. Pretrimmed, precontoured SSC was selected for a particular tooth. Standardized tooth preparation for SSC was performed by single operator. The crowns were then luted with either RelyX U200 or SmartCem2 or RelyX Luting 2 cement. Retentive strength was tested using Instron universal testing machine. The retentive strength values were recorded and calculated by the formula: Load/Area. Statistical analysis One-way analysis of variance was used for multiple comparisons followed by post hoc Tukey’s test for groupwise comparisons. Unpaired t-test was used for intergroup comparisons. Results RelyX U200 showed significantly higher retentive strength than rest of the two cements (p 0.05). Conclusion The retentive strength of dual-polymerized self-adhesive resin cements was better than RMGIC, and RelyX U200 significantly improved crown retention when compared with SmartCem2 and RelyX Luting 2. How to cite this article Pathak S, Shashibhushan KK, Poornima P, Reddy VVS. In vitro Evaluation of Stainless Steel Crowns cemented with Resin-modified Glass Ionomer and Two New Self-adhesive Resin Cements. Int J Clin Pediatr Dent 2016;9(3):197-200. PMID:27843249

  19. Stress and Deformation Analysis of Cylinder-Crown Integrated Hydraulic Press with Large Capacity

    Institute of Scientific and Technical Information of China (English)

    Weiwei Zhang; Xiaosong Wang; Zhongren Wang

    2015-01-01

    Cylinder⁃crown integrated hydraulic press ( CCIHP ) is a new press structure. The hemispherical hydraulic cylinder also functions as a main portion of crown, which has lower weight and higher section modulus compared with the conventional hydraulic cylinder and press crown. In order to design cylinder⁃crown integrated hydraulic press with large capacity, the theoretical design of hemispherical hydraulic cylinder was first proposed, and the structural parameters of 150 MN CCIHP were listed. Then the simulation was carried out to analyze the stress and deformation of CCIHP , and weight comparison was conducted between CCIHP and conventional press. It is shown that the weight reduction for hydraulic cylinder and press crown is about 20%compared with that for conventional press, and the stress and deformation are both within the range of constraints including strength and stiffness conditions. It is possible to manufacture cylinder⁃crown integrated hydraulic press with large capacity.

  20. RICHMOND CROWN - FOR RESTORATION OF BADLY MUTILATED POSTERIOR TEETH : A CASE REPORT

    Directory of Open Access Journals (Sweden)

    Yadav

    2015-07-01

    Full Text Available Restoration of badly broken endodontically treated teeth is a common problem in restorative dentistry. Such teeth often require additional support from the root canal by means of a post and core restoration. In cases where tooth structure is significantly lost full coverage restorations for posterior teeth are necessary to achieve proper tooth form and function. Badly broken teeth with minimal or no crown structure require added retention and support. The Richmond crown can be a good treatment alternative for restoration of such teeth. The Richmond crown was introduced in 1878 and incorporated a threaded tube in the canal with a screw retained crown. It was later modified to eliminate the threaded tube and was redesigned as a one piece dowel and crown. This case report shows restoration of badly mutilated posterior teeth with Richmond crown.

  1. Analysis of Temperature Field and Thermal Crown of Roll During Hot Rolling by Simplified FEM

    Institute of Scientific and Technical Information of China (English)

    GUO Zhong-feng; LI Chang-sheng; XU Jian-zhong; LIU Xiang-hua; WANG Guo-dong

    2006-01-01

    Thermal crown of roll is an important factor, which affects strip profile. It is necessary to analyze the temperature field and thermal crown of roll for hot strip mill. A new simplified finite element method (FEM) was used to analyze the temperature field and thermal crown of roll, and corresponding models were built according to the practical boundary conditions. Transient roll temperature field and thermal crown were simulated by ANSYS FEM software with considering transient thermal contact and complex boundary condition. Temperature and thermal crown variations on roll surface nodes were obtained. The thermal crown results of roll obtained by FEM simulation were in good agreement with the measured data, indicating that simplified FEM models and results were correct.

  2. Effect of Load Distribution on Strip Crown in Hot Strip Rolling

    Institute of Scientific and Technical Information of China (English)

    Hongshuang DI; Jianzhong XU; Dianyao GONG; Xianghua LIU; Guodong WANG; Xiaoming HE; Liying BA

    2004-01-01

    In order to establish precision model, a software to calculate the strip crown of four-high hot rolling mill was developed by using affecting function method according to the strip crown calculation theory. The effect of work roll diameter, unit width rolling load, roll bending force, work roll crown, initial strip crown and reduction, etc, on load distribution effect rate was simulated by using the software. The results show that the load distribution effect rate increases with the increase of strip width, work roll diameter, unit width rolling load, roll bending force, work roll crown, initial strip crown and reduction. Based on the simulation results, base value of load distribution effect rate and fitting coefficients of six power polynomial of load distribution effect rate modification coefficient were determined considering all of the above parameters. A simplified mathematical model for calculating load distribution effect rate was established.

  3. Model Building of the Initial Crown Effect Rate in 4-High Mill

    Institute of Scientific and Technical Information of China (English)

    Jianzhong XU; Dianyao GONG; Wencai ZHANG; Xianwen CHANG; Xianghua LIU; Guodong WANG

    2005-01-01

    The code for calculating the crown effect rate of hot strip steel was developed using the effect function method.The effect of the initial crown on the crown of the product in hot strip rolling was investigated. The coefficients of a polynomial of degree six for calculating the base value of initial crown effect rate in 4-high mill were determined and the compensation factors of per unit width rolling force, bending force, work roll crown and draft on the initial crown effect rate were given. The difference between the calculation result by established model and theoretical value obtained by effect function method was 4.88 μm when the strip width was 1.85 m.

  4. CVC热连轧机的板凸度计算模型%New Crown Setup Model of CVC Hot Strip Mill

    Institute of Scientific and Technical Information of China (English)

    刘立忠; 吕程; 刘相华; 王国栋

    2001-01-01

    针对中国宝山钢铁集团公司CVC热连轧机组,提出一种新的板凸度分配设定方法。首先计算出热连轧机组总的轧件比例凸度变化值,然后按各机架压下率占整个机组总压下率的比例,将总比例凸度变化值分配给各机架,进而可计算出各机架轧后板凸度通过适当分配各机架的板比例凸度和板凸度,可在不产生板形缺陷的条件下,充分发挥CVC轧机的能力,以期得到符合要求板凸度的成品采用此方法进行板凸度分配设定,同时结合辊系弹性变形模型、工作辊热凸度计算模型、CVC工作辊横移设定模型、负荷分配模型等,开发了计算板凸度调整和CVC工作辊横移设定的软件利用所开发的软件对现场生产条件进行计算,其结果优于现场设定结果%A new crown setup model of CVC Hot Strip Mill(HSM) was developed according to the field condition of Bao Steel Inc.,China. The scale of the proportional crown value fluctuation of the whole HSM was calculated in the beginning and then it was assigned to each stand according to the proportion of the reduction ratio of this stand to the whole reduction ratios. As a result,the crown after each stand can be calculated. With the appropriate setup of the proportion crown and the crown,to each stand,keeping the flatness under control and the on-gauge plate can be achieved during the CVC Hot Strip Mill. A software was developed based on the new crown setup model together with the roll elastic deformation model,work roll thermal crown model,CVC work roll shifting model and load distribution model. The software can be used to simulate the crown setup and roll shifting of Hot Strip Mill offline. The software was tested in the field condition and the results were much better than the previous field setup.

  5. A Market-Window Analysis for Crown-Cut Broccoli Produced in Southwest Virginia

    OpenAIRE

    Dillard, John; Kmak, Heather; Russ, M.J.; Coale, Charles W., Jr.; Bratsch, Tony; Reaves, Dixie Watts

    2006-01-01

    This research determines the profitability for farmers of marketing film-wrapped Crown-Cut broccoli in Southwest Virginia. Historical price data was collected in three eastern terminal markets (Atlanta, Baltimore, and Philadelphia) for Crown-Cut and bunched broccoli from October 1998 to January 2005. Cost-of-production budgets were estimated for Crown-Cut broccoli. The economic data was entered into a market window analysis and the profitability of each market was evaluated. The profitability...

  6. Comparison of crown fire modeling systems used in three fire management applications

    OpenAIRE

    Scott, J. H.

    2006-01-01

    The relative behavior of surface-crown fire spread rate modeling systems used in three fire management applications—CFIS (Crown Fire Initiation and Spread), FlamMap and NEXUS— is compared using fire environment characteristics derived from a dataset of destructively measured canopy fuel and associated stand characteristics. Although the surface-crown modeling systems predict the same basic fire behavior characteristics (type of fire, spread rate) using the same basic fire environment characte...

  7. Strategic Marketing Plan For Wedding Store : Case: Golden Crown Wedding Store, China

    OpenAIRE

    Wu, Fan

    2013-01-01

    ABSTRACT Wu, Fan 2012. Strategic Marketing Plan for Golden Crown Wedding Store. Case: Golden Crown Wedding Store, China. Bachelor’s Thesis. Kemi-Tornio University of Applied Sciences. Business and Culture. Pages 39. Appendices 1- 2. The objective of this thesis is to build a strategic marketing plan for the Golden Crown Wedding Store. The strategic marketing plan and the analysis of the situation of the market are the main part of the thesis. This thesis will help the case company to ...

  8. Variation in needle nutrient concentrations in the crown of Scots pine on peatland.

    OpenAIRE

    Finér, Leena

    1994-01-01

    Variation in needle nutrient concentrations with age and vertical location in the crown was studied in three Scots pine stands growing on peat soils in eastern Finland. The concentrations of N, P, Fe and Zn decreased down the crown and those of Ca and Mn increased. Potassium and magnesium concentration patterns differed between sites. Potassium and Mg concentrations were highest in the current needles at all heights in the crown, which was presumably due to retranslocation from the older nee...

  9. Determination of the age of oil palm from crown projection area detected from WorldView-2 multispectral remote sensing data: The case of Ejisu-Juaben district, Ghana

    Science.gov (United States)

    Chemura, Abel; van Duren, Iris; van Leeuwen, Louise M.

    2015-02-01

    Information about age of oil palm is important in sustainability assessments, carbon mapping, yield projections and precision agriculture. The aim of this study was to develop and test an approach to determine the age of oil palm plantations (years after planting) by combining high resolution multispectral remote sensing data and regression techniques using a case study of Ejisu-Juaben district of Ghana. Firstly, we determined the relationship between age and crown projection area of oil palms from sample fields. Secondly, we did hierarchical classification using object based image analysis techniques on WorldView-2 multispectral data to determine the crown projection areas of oil palms from remote sensing data. Finally, the crown projection areas obtained from the hierarchical classification were combined with the field-developed regression model to determine the age of oil palms at field level for a wider area. Field collected data showed a strong linear relationship between age and crown area of oil palm up to 13 years beyond which no relationship was observed. A user's accuracy of 80.6% and a producer's accuracy of 68.4% were obtained for the delineation of oil palm crowns while for delineation of non-crown objects a user's accuracy of 65.6% and a producer's accuracy of 78.6% were obtained, with an overall accuracy of 72.8% for the OBIA delineation. Automatic crown projection area delineation from remote sensing data produced crown projection areas which closely matched the field measured crown areas except for older oil palms (13+ years) where the error was greatest. Combining the remote sensing detected crown projection area and the regression model accurately estimated oil palm ages for 27.9% of the fields and had an estimation error of 1 year or less for 74.6% of the fields and an error of a maximum 2 years for 92.4% of the fields. The results showed that 6 and 11 year old oil palm stands were dominating age categories in the study area. Although the method

  10. Alkaline-side extraction of technetium from tank waste using crown ethers and other extractants

    Energy Technology Data Exchange (ETDEWEB)

    Bonnesen, P.V.; Moyer, B.A.; Presley, D.J.; Armstrong, V.S.; Haverlock, T.J.; Counce, R.M.; Sachleben, R.A.

    1996-06-01

    The chemical development of a new crown-ether-based solvent-extraction process for the separation of (Tc) from alkaline tank-waste supernate is ready for counter-current testing. The process addresses a priority need in the proposed cleanup of Hanford and other tank wastes. This need has arisen from concerns due to the volatility of Tc during vitrification, as well as {sup 99}Tc`s long half-life and environmental mobility. The new process offers several key advantages that direct treatability--no adjustment of the waste composition is needed; economical stripping with water; high efficiency--few stages needed; non-RCRA chemicals--no generation of hazardous or mixed wastes; co-extraction of {sup 90}Sr; and optional concentration on a resin. A key concept advanced in this work entails the use of tandem techniques: solvent extraction offers high selectivity, while a subsequent column sorption process on the aqueous stripping solution serves to greatly concentrate the Tc. Optionally, the stripping solution can be evaporated to a small volume. Batch tests of the solvent-extraction and stripping components of the process have been conducted on actual melton Valley Storage Tank (MVST) waste as well as simulants of MVST and Hanford waste. The tandem process was demonstrated on MVST waste simulants using the three solvents that were selected the final candidates for the process. The solvents are 0.04 M bis-4,4{prime}(5{prime})[(tert-butyl)cyclohexano]-18-crown-6 (abbreviated di-t-BuCH18C6) in a 1:1 vol/vol blend of tributyl phosphate and Isopar{reg_sign} M (an isoparaffinic kerosene); 0.02 M di-t-BuCH18C6 in 2:1 vol/vol TBP/Isopar M and pure TBP. The process is now ready for counter-current testing on actual Hanford tank supernates.

  11. Estimation of stand crown cover using a generalized crown diameter model: application for the analysis of Portuguese cork oak stands stocking evolution

    Directory of Open Access Journals (Sweden)

    Paulo JA

    2016-06-01

    Full Text Available A generalized non-linear tree crown diameter model was developed with the aim of allowing the computation of tree crown diameter over a large range of tree dimensions, and allowing its inclusion in forest growth and yield models. The model was formulated to provide biological meaning to the predicted values. Due to the nested structure of the data analyzed (trees within stands, both mixed- and fixed-effect models were developed. Since tree crown diameter is not frequently measured in forest inventories, the validation of the mixed model was carried out by considering the population specific response. The results demonstrate that when the measurements required for the mixed model calibration are not available, the use of the fixed effect model results in less biased and more accurate estimates. The fixed model was applied to the data from the two last Portuguese National Forest Inventories (NFI to analyze the change in stand crown cover and assess the stocking evolution of cork oak stands in Portugal between 1996 and 2006. Results showed an increase in the frequency of stands with crown cover lower than 20%, as well as a decrease in the frequency of stands with crown cover between 20 and 40%. Average crown cover values were significantly different in the two NFI, with a decrease from 28.0 to 26.5% over the considered period.

  12. A tree canopy height delineation method based on Morphological Reconstruction—Open Crown Decomposition

    Science.gov (United States)

    Liu, Q.; Jing, L.; Li, Y.; Tang, Y.; Li, H.; Lin, Q.

    2016-04-01

    For the purpose of forest management, high resolution LIDAR and optical remote sensing imageries are used for treetop detection, tree crown delineation, and classification. The purpose of this study is to develop a self-adjusted dominant scales calculation method and a new crown horizontal cutting method of tree canopy height model (CHM) to detect and delineate tree crowns from LIDAR, under the hypothesis that a treetop is radiometric or altitudinal maximum and tree crowns consist of multi-scale branches. The major concept of the method is to develop an automatic selecting strategy of feature scale on CHM, and a multi-scale morphological reconstruction-open crown decomposition (MRCD) to get morphological multi-scale features of CHM by: cutting CHM from treetop to the ground; analysing and refining the dominant multiple scales with differential horizontal profiles to get treetops; segmenting LiDAR CHM using watershed a segmentation approach marked with MRCD treetops. This method has solved the problems of false detection of CHM side-surface extracted by the traditional morphological opening canopy segment (MOCS) method. The novel MRCD delineates more accurate and quantitative multi-scale features of CHM, and enables more accurate detection and segmentation of treetops and crown. Besides, the MRCD method can also be extended to high optical remote sensing tree crown extraction. In an experiment on aerial LiDAR CHM of a forest of multi-scale tree crowns, the proposed method yielded high-quality tree crown maps.

  13. Release and systemic accumulation of heavy metals from preformed crowns used in restoration of primary teeth.

    Science.gov (United States)

    Kodaira, Hiroe; Ohno, Kohachiro; Fukase, Naoko; Kuroda, Midori; Adachi, Shiki; Kikuchi, Motohiro; Asada, Yoshinobu

    2013-01-01

    Preformed crowns for restoration of primary teeth are used in various treatments and are essential for restoring the crowns of primary molars. However, there are concerns that mechanical, chemical, and thermal stimulation may cause release of components of such crowns. We examined systemic accumulation of heavy metals associated with preformed crowns (3M Stainless Steel Primary Molar Crowns) used in primary tooth restoration. The participants were 37 children who had visited the Pediatric Dental Clinic of Tsurumi University Dental Hospital. They were divided into two groups: 22 participants without a history of being fitted with a preformed crown for primary tooth restoration (controls), and 15 participants with preformed crowns for primary tooth restoration. Analysis of hair samples showed a significant difference in the level of the trace element Cr - an important component of the preformed crowns - between children with and without preformed crowns, but no significant differences in Fe or Ni levels. Levels of the trace elements Ni, Cr, and Fe were within allowable ranges, indicating that these minerals were not likely to be harmful.

  14. Accidental swallowing of a gold cast crown during orthodontic tooth separation.

    Science.gov (United States)

    Kharbanda, O P; Varshney, P; Dutta, U

    1995-01-01

    Accidental swallowing of a gold cast crown that became loose after separation with brass wire for orthodontic band placement, is reported. The intervention to remove the ingested crown subsequent to its location in the GI tract on immediate radiographic examination of chest and abdomen included endoscopic examination. Since the crown had past distal to the duodenum it was decided to keep a watch on its movement by daily radiographic examination. The crown passed with excreta on the 5th day uneventfully. Literature on ingestion of foreign bodies of dental origin is reviewed. Possible emergencies and their management is discussed.

  15. Sex Identification of Red-crowned Crane by the Polymerase Chain Reaction

    Institute of Scientific and Technical Information of China (English)

    LI Jian-hong; LI Shu-ling; BAO Jun; BAI Xiu-juan

    2004-01-01

    Sex determining gene primers of Oriental White Stork were used to amplify sex-linked gene of the Red-crowned Crane's W chromosome-specific by PCR for sex identification. The sexes of 7 couples of grown Red-crowned Cranes and 15 youngs were identified. Through DNA sequence analysis, the identity is 94.77% between Red-crowned Crane and Oriental White Stork. The results of this study suggest that the application of the polymerase chain reaction technique is practicable for determining sex in the Red-crowned Crane.

  16. Fracture Strength of Aged Monolithic and Bilayer Zirconia-Based Crowns

    OpenAIRE

    Deborah Pacheco Lameira; Silva, Wilkens Aurélio Buarque e; Silva, Frederico Andrade e; De Souza, Grace M.

    2015-01-01

    The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP) crowns in monolithic (1.5 mm thickness) and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer) configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n = 10): Polished monolithic zirconia crowns (PM); Glazed mo...

  17. Failure modes and fracture origins of porcelain veneers on bilayer dental crowns.

    Science.gov (United States)

    Liu, Yihong; Liu, Guanghua; Wang, Yong; Shen, James Zhijian; Feng, Hailan

    2014-01-01

    The aims of this study were to determine the fracture origins and crack paths in the porcelain of clinically failed bilayer ceramic restorations and to reveal the correlation between the porcelain failures and material properties. Three clinically failed crowns of each material (bilayer zirconia crowns, galvano-ceramic crowns, and porcelain-fused-to-metal crowns) were collected and underwent failure analysis. The fractures found in porcelain veneers showed several characteristics including wear, Hertzian cone crack, chipping off, and delamination. The results indicated that the fracture origins and features of the porcelain in bilayer ceramic restorations might be affected by the rigidity of core materials and thickness of copings.

  18. Twenty-nine-month follow-up of a paediatric zirconia dental crown.

    Science.gov (United States)

    Lopez Cazaux, Serena; Hyon, Isabelle; Prud'homme, Tony; Dajean Trutaud, Sylvie

    2017-06-14

    The aim of this paper is to present the long-term follow-up of one paediatric zirconia crown on a deciduous molar. Preformed crowns are part of the armamentarium in paediatric dentistry. In recent years, aesthetic alternatives to preformed metal crowns have been developed, first preveneered crowns and then zirconia crowns. This paper describes the restoration of a primary molar with a zirconia crown (EZ-Pedo, Loomis, California, USA) in an 8-year-old boy. In this clinical case, the protocol for the implementation and maintenance of zirconia crowns is detailed. The patient was followed up for 29 months until the natural exfoliation of his primary molar. The adaptation of the zirconia crown, the gingival health and the wear on the opposing tooth were considered. In this case, the paediatric zirconia crown allowed sustainable functional restoration while restoring a natural appearance of the tooth. © BMJ Publishing Group Ltd (unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

  19. On the radiation stability of crown ethers in ionic liquids.

    Energy Technology Data Exchange (ETDEWEB)

    Shkrob, I.; Marin, T.; Dietz, M. (Chemical Sciences and Engineering Division); (Benedictine Univ.); (Univ. of Wisconsin at Milwaukee)

    2011-04-14

    Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in such separations. It is desirable that the extraction efficacy obtained with such solvents should not deteriorate in the strong radiation fields generated by decaying radionuclides. This deterioration will depend on the extent of radiation damage to both the IL solvent and the CE solute. While radiation damage to ILs has been extensively studied, the issue of the radiation stability of crown ethers, particularly in an IL matrix, has not been adequately addressed. With this in mind, we have employed electron paramagnetic resonance (EPR) spectroscopy to study the formation of CE-related radicals in the radiolysis of selected CEs in ILs incorporating aromatic (imidazolium and pyridinium) cations. The crown ethers have been found to yield primarily hydrogen loss radicals, H atoms, and the formyl radical. In the low-dose regime, the relative yield of these radicals increases linearly with the mole fraction of the solute, suggesting negligible transfer of the excitation energy from the solvent to the solute; that is, the solvent has a 'radioprotective' effect. The damage to the CE in the loading region of practical interest is relatively low. Under such conditions, the main chemical pathway leading to decreased extraction performance is protonation of the macrocycle. At high radiation doses, sufficient to increase the acidity of the IL solvent significantly, such proton complexes compete with the solvent cations as electron traps. In this regime, the CEs will rapidly degrade as the result of H abstraction from the CE ring by the released H atoms. Thus, the radiation dose to which a CE/IL system is exposed must be maintained at a level sufficiently low to avoid this regime.

  20. Unicuspid and bicuspid tooth crown formation in squamates.

    Science.gov (United States)

    Handrigan, Gregory R; Richman, Joy M

    2011-12-15

    The molecular and developmental factors that regulate tooth morphogenesis in nonmammalian species, such as snakes and lizards, have received relatively little attention compared to mammals. Here we describe the development of unicuspid and bicuspid teeth in squamate species. The simple, cone-shaped tooth crown of the bearded dragon and ball python is established at cap stage and fixed in shape by the differentiation of cells and the secretion of dental matrices. Enamel production, as demonstrated by amelogenin expression, occurs relatively earlier in squamate teeth than in mouse molars. We suggest that the early differentiation in squamate unicuspid teeth at cap stage correlates with a more rudimentary tooth crown shape. The leopard gecko can form a bicuspid tooth crown despite the early onset of differentiation. Cusp formation in the gecko does not occur by the folding of the inner enamel epithelium, as in the mouse molar, but by the differential secretion of enamel. Ameloblasts forming the enamel epithelial bulge, a central swelling of cells in the inner enamel epithelium, secrete amelogenin at cap stage, but cease to do so by bell stage. Meanwhile, other ameloblasts in the inner enamel epithelium continue to secrete enamel, forming cusp tips on either side of the bulge. Bulge cells specifically express the gene Bmp2, which we suggest serves as a pro-differentiation signal for cells of the gecko enamel organ. In this regard, the enamel epithelial bulge of the gecko may be more functionally analogous to the secondary enamel knot of mammals than the primary enamel knot. Copyright © 2011 Wiley Periodicals, Inc., A Wiley Company.

  1. Crown condition assessment at the CONECOFOR Permanent Monitoring Plots

    Directory of Open Access Journals (Sweden)

    Renzo NIBBI

    2002-09-01

    Full Text Available A detailed crown condition assessment is currently being carried out at the CONECOFOR (CONtrollo ECOsistemi FORestali, Control of Forest Ecosystems plots. The assessment began in 1996, and during the first two years (1996 and 1997 an assessment form based on previous regional experience was used; in 1998 the new official EU form was adopted. The resulting loss of comparability means that only a few indices can be used in the temporal series 1996-1999. Much effort was devoted to Quality Assurance (QA procedures. The QA program is structured as follows: (i specific field manuals have been adopted and are continuously updated; (ii a national training and intercalibration course (NT&IC is undertaken yearly before beginning the assessment campaign;( iii field checks are carried out yearly on a large number of plots. The results of the QA program have shown that for several indices the quality objectives were not reached, but the quality of the data is improving with time. To express the change in crown conditions in each area, a complex index (CCI = Crown Condition Index was adopted. This index is the result of the sum of the relativized values of all the common indices used during the four years. The following parameters were used: transparency, ramification type, leaf colour alteration extension, leaf damage extension, alteration of leaf distension extension. The range within which the CCI fluctuates was evaluated taking into account all the observations carried out at a given plot throughout the years. The number of cases over a given threshold (outliers was calculated for each year. The threshold for outliers was calculated as the median value plus 2 times the range of the interquartile value. All individual cases exceeding this value are considered outliers. The results are presented for all the areas in which the data set is complete for the four years. The yearly fluctuations are discussed and related to possible causes.

  2. The Effect of two Shading Techniques on Value of Zirconia-Based Crowns

    Directory of Open Access Journals (Sweden)

    Ahmad Hassan Ahangari

    2015-06-01

    Full Text Available Statement of the Problem: By introducing the coloring liquids, it is claimed that it is possible to make the color of frameworks fabricated from zirconium oxide ex-tremely close to the natural tooth color. Purpose: The purpose of this research was to evaluate the effect of two staining techniques on value changing in zirconia crowns. Materials and Method: Three groups A, B, and C, each containing ten zirconia crowns, were used. The zirconium cores samples were fabricated by a CAD/CAM device. Group A was left uncolored, Groups B was submerged for two minutes in A2 coloring liquid and Group C was stained with brush. Then all cores were sintered and the porcelain was applied by using the layering technique. Ultimately, the crowns color was determined using a spectrophotometer. Their color changing (∆E and value changing (∆L in relation to A2 color were also assessed. The data were analyzed with one-sample t-test, post-hoc Tukey, and one-way ANOVA tests with significant level set at 0.05. Results: The mean value in all groups was higher than the value obtained from A2 color samples (p= 0.001. The highest mean value was 78.31±1.22 belonging to group C (staining with brush and the lowest mean value was 76.99±0.65 belonging to group B (submerging. The results of post-hoc Tukey regarding both ∆E and ∆L variables showed a significant difference between groups A (uncolored and C (staining with brush with P∆E=0.006 and P∆L=0.039, respectively. A significant difference between group B (submerging technique and C (staining with brush were shown when these two variables were compared (P∆E=0.001, P∆L=0.015. Conclusion: Due to the higher value increase in surface staining (brush, it is rec-ommended to use the submerging technique for staining zirconia cores.

  3. Cervical end preparation design on collarless metal ceramic crown to the decrease of bacterial colony

    Directory of Open Access Journals (Sweden)

    Edy Machmud

    2010-09-01

    Full Text Available Background: Cervical end preparation design is an important procedure in fixed partial denture. If the cervical end preparation design is inadequate, dental plaque will easily be formed and this may indicate the beginning of periodontal disease. Purpose: This study was aimed to analyze the effect of cervical end preparation design on collarless metal ceramic crown towards the decrease of bacterium colony number. Methods: This study was quasi-experimental study applying pre and post test on a control group involving 48 subjects with shoulder, bevel shoulder, and deep chamfer cervical end preparation. The bacterium colonies were examined on the 1st, 7th, and 21st days after the insertion of collarless metal ceramic crown. Results: The study showed that bacterium colony increased significantly in deep chamfer and bevel shoulder preparation design between the treatment group and the control group (p<0.05. In shoulder preparation there was not significant different between the treatment group and the control group (p>0.05. Conclusion: Compared to the bevel shoulder and deep chamfer, shoulder design is the best design for collarless metal ceramic crown restoration.Latar belakang: Desain preparasi tepi servikal merupakan suatu tahap yang sangat menentukan dalam pembuatan gigi tiruan cekat. Apabila desain preparasi tepi servikal tidak adekuat dapat menyebabkan pembentukan plak gigi pada daerah tersebut. Keadaan ini merupakan tahap awal terjadinya penyakit periodontal. Tujuan: Untuk menganalisis pengaruh desain preparasi tepi servikal yang dibuat pada mahkota collarless metal ceramic untuk mengurangi jumlah bakterium koloni. Metode: Penelitian ini adalah penelitian eksperimental semu dengan metode pre and post test dan kelompok kontrol terhadap 48 subyek penelitian. Dilakukan preparasi gigi dan pembuatan akhiran preparasi tepi servikal shoulder, bevel shoulder, dan deep chamfer pada subyek penelitian. Pemeriksaan koloni bakteri dilakukan pada hari ke-1

  4. Fluorescence properties of crown ethers with phenylbenzothiozole pendant group

    Science.gov (United States)

    Kapoor, S.; Sapre, A. V.; Kumar, S.; Mashraqui, S. H.; Mukherjee, T.

    2005-06-01

    Photophysical characteristics of 2-phenylbenzothiazole (PBT) substituted crown ether (CRE-PBT) molecules have been investigated in various polar protic solvents. Large Stokes' and good solvatochromic shifts have been observed for CRE-PBT molecules. It is seen that in these molecules, the fluorescence lifetimes and quantum yields increase as compared to the pristine PBT molecule. Temperature-dependence studies have been carried out to understand the effect of CRE substitution and the role of C-C single bond rotation on the fluorescence quantum yield and lifetime.

  5. Electric field gradient and electronic properties of crown thioether compounds

    Energy Technology Data Exchange (ETDEWEB)

    Camargo Dalmatti Alves Lima, Filipe, E-mail: flima@if.usp.br; Rodrigues do Nascimento, Rafael; Brown Goncalves, Marcos [Universidade de Sao Paulo, Instituto de Fisica (Brazil); Cottenier, Stefaan [Ghent University, Center for Molecular Modeling (Belgium); Caldas, Marilia Junqueira; Petrilli, Helena Maria [Universidade de Sao Paulo, Instituto de Fisica (Brazil)

    2010-04-15

    We compare published TDPAC experiments on {sup 111}Cd in the crown thioether C{sub 6}H{sub 12}S{sub 3}AgCl with ab-initio electronic structure calculations performed within the framework of the Density Functional Theory using the Projector Augmented Wave method. We conclude from this comparison that the Cd atom at the very moment of the TDPAC experiment is positively charged, and we point out to a methodological difference between reproducing experimental electric-field gradients in molecules versus solid metals.

  6. FEM Calculation of Work Roll Temperature and Thermal Crown

    Institute of Scientific and Technical Information of China (English)

    KONG Xiang-wei; XU Jian-zhong; YE He-zhou; WANG Guo-dong; LIU Xiang-hua; HE Xiao-ming; BA Li-ying

    2004-01-01

    The simulation of the work roll temperature field was carried out by means of ANSYS software, and the thermal crown of the roll along its axis was obtained. The thermal-structural coupled element and contact element were introduced. In the simulation of work roll temperature field, the convert boundary condition and the transient thermal contact between the roll and strip were studied. Besides, the dynamic variation of the work roll temperature and the transient temperature distribution of the work roll during hot rolling were investigated. The calculated results were in good agreement with the measured data.

  7. Re/crowning the Jowo Śākyamuni

    DEFF Research Database (Denmark)

    Warner, Cameron

    2011-01-01

    From the eleventh century to the present, the Jowo (jo bo) Śākyamuni statue has served as a perduring index of Tibetan Buddhist ecclesiastical history.  Tibetan writers employed the Jowo as a discursive site where religio-political paradigms were negotiated and transformed through accounts......, firstness, and ritual efficacy in Tibetan cosmology.  I follow the history of the Jowo's crown into the present, including the voices of those Tibetans who blame the 1951 Chinese invasion of Tibet on repercussions of Tsongkhapa's controversial decision.  A multidisciplinary perspective, combining texts...

  8. The Vitruvius' Tale of Archimedes and the Golden Crown

    CERN Document Server

    Sparavigna, Amelia Carolina

    2011-01-01

    The paper discusses the tale that we can find in "The Architecture" by Vitruvius, on a method used by Archimedes to determine the percentage of gold and silver in a crown. The method is based on the immersion of bodies, allowing the evaluation of their volume in the case of irregular shapes. The measurement, as reported in "The Architecture", seems to be difficult to realize. But, using a vessel for a water-clock, the approach that Vitruvius described is possible. Here the discussion and experiments.

  9. Infrared Imagery of Crown-Fire Dynamics during FROSTFIRE.

    Science.gov (United States)

    Coen, Janice; Mahalingam, Shankar; Daily, John

    2004-09-01

    A thorough understanding of crown-fire dynamics requires a clear picture of the three-dimensional winds in and near the fire, including the flaming combustion zone and the convective updrafts produced by the fire. These observations and analyses present a unique high-spatial-resolution and high-temporal-resolution perspective of the motions within crown fires propagating up a forested 20° slope under light winds of 3 m s-1 during the FROSTFIRE experiment in interior Alaska. The purpose of this work is to calculate combustion-zone winds and examine mechanisms for the rapid propagation of crown fires. An infrared imager was used to detect high-temperature regions produced by incandescent soot particles in and near the fire and to produce a sequence of high-frequency (60 Hz), high-resolution (0.375 m × 0.8 m) two-dimensional images of temperature. An image-flow-analysis technique was applied to these data to derive wind fields in the image plane. Maximum updrafts of 32 60 m s-1 accompany maximum downdrafts of 18 30 m s-1. Horizontal wind speeds of 12 28 m s-1 show strong inflow into the base of the convective updrafts and imply recirculation of air and incomplete combustion products from the fire. Motions were more complex than a single large convective plume or many buoyant tree-scale plumes rising separately. Instead, repeated examples of narrow flaming fingers, representing a scale larger than individual trees, initially burst upslope along the ground for tens of meters at speeds up to 28 48 m s-1 before turning upward. These bursts exceeded ambient environmental winds, those considered to be driving the fire, by a factor of 10 and were low enough to propagate the crown fire actively by both igniting and preheating/ drying canopy fuel ahead of the fire. Average spread rates were 0.75 1.11 m s-1, with a peak 10-s spread rate of 1.26 m s-1. This powerful, dynamic mechanism of fire spread could explain firefighter reports of being overtaken by “fireballs.”

  10. 4′-Formyl­benzo-15-crown-5

    Science.gov (United States)

    Fischer, Conrad; Helas, Stefanie F.; Seichter, Wilhelm; Weber, Edwin; Ibragimov, Bakhtiyar T.

    2008-01-01

    In the title compound (systematic name: 17-formyl-2,5,8,11,14-penta­oxabicyclo­[13.4.0]nona­deca-15,17,19-triene), C15H20O6, the 15-crown-5 ring adopts a twisted conformation. The formyl group is coplanar with the benzene ring. The crystal packing is stabilized by C—H⋯O inter­actions involving the C=O group and ether O atoms as acceptors and methyl­ene CH groups as donors. PMID:21203259

  11. [Micromorphology of decayed tooth tissues covered with artificial crown].

    Science.gov (United States)

    Lutskaia, I K; Zinovenko, O G; Shved, I A

    2014-01-01

    Pathomorphological changes in dentine covered with artificial crown were studied in 40 decalcified teeth extracted from patients aged 35-61 years. The study of the decayed dentin microscopic structure revealed the uniform mineralization of dentinal tubules in 20% of cases, while in the absence of visually apparent caries it was present in 80% of cases. Irregular dentin structure was seen in 45% of caries cases and in 30% of observations with no signs of caries. Predentine distrophy and odontoblasts elimination in the decayed teeth was found in 55% of the observations while in the absence of caries lesions these features were seen in 70% of cases.

  12. Zirconia- versus metal-based, implant-supported abutments and crowns

    DEFF Research Database (Denmark)

    Hosseini, Mandana

    was to test the reliability and validity of six aesthetic parameters used at the Copenhagen Dental School to assess the aesthetic outcome of implant-supported restorations. The aims of study III and IV were to compare the influence of different abutment and crown materials on biological, biomechanical......To restore oral functions in patients with missing teeth, single-tooth implants are a well-documented treatment option. Along with high survival rates, aesthetic factors have become an important clinical outcome variable for evaluating treatment success of implant-supported restorations. Thus...... studies have reported on aesthetic, biological, biomechanical and patient-reported outcomes of implant-supported single-tooth restorations of various biomaterials. The aim of the present thesis was to investigate the clinical performance of zirconia-based implant-supported single-tooth restorations...

  13. Crown-of-Thorns Starfish Larvae Can Feed on Organic Matter Released from Corals

    Directory of Open Access Journals (Sweden)

    Ryota Nakajima

    2016-10-01

    Full Text Available Previous studies have suggested that Crown-of-Thorns starfish (COTS larvae may be able to survive in the absence of abundant phytoplankton resources suggesting that they may be able to utilize alternative food sources. Here, we tested the hypothesis that COTS larvae are able to feed on coral-derived organic matter using labeled stable isotope tracers (13C and 15N. Our results show that coral-derived organic matter (coral mucus and associated microorganisms can be assimilated by COTS larvae and may be an important alternative or additional food resource for COTS larvae through periods of low phytoplankton biomass. This additional food resource could potentially facilitate COTS outbreaks by reducing resource limitation.

  14. A comparison of the marginal and internal adaptation of titanium and gold-platinum-palladium metal ceramic crowns.

    Science.gov (United States)

    Valderrama, S; Van Roekel, N; Andersson, M; Goodacre, C J; Munoz, C A

    1995-01-01

    The marginal and internal adaptation of metal ceramic crowns fabricated by electrical discharge machining and conventional metal ceramic alloys were compared. The crowns were cemented using zinc phosphate cement, embedded in epoxy resin, and sectioned in two planes: diagonal and buccolingual. The crowns were then measured at nine sites. The results showed that there were no statistical differences between the external marginal opening of the titanium and the gold-platinum-palladium crowns. The overall marginal discrepancies for the restorations in this study were 61 microns (+/- 34 microns) for the titanium metal ceramic crowns and 47 microns (+/- 17 microns) for the gold-platinum-palladium metal ceramic crowns.

  15. Ion-Pair Complexation with Dibenzo[21]Crown-7 and Dibenzo[24]Crown-8 bis-Urea Receptors.

    Science.gov (United States)

    Mäkelä, Toni; Kiesilä, Anniina; Kalenius, Elina; Rissanen, Kari

    2016-09-26

    Synthesis and ion-pair complexation properties of novel ditopic bis-urea receptors based on dibenzo[21]crown-7 (R(1) ) and dibenzo[24]crown-8 (R(2) ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3 /[D6 ]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb(+) or Cs(+) , with the halide affinity increasing in order I(-) crown-ether scaffold, whereas R(2) has a compact, folded conformation. Computational studies of the ion-pair complexes of R(2) show that the interaction energies of the complexes increase in the order CsI

  16. Marginal integrity of two zirconia-based crowns before and after porcelain veneering

    Directory of Open Access Journals (Sweden)

    Sakineh Nikzad

    2013-04-01

    Full Text Available Background and Aims: The marginal integrity of fixed restorations always is a major matter of concern for dental clinicians. Any cause of distortion, including veneering processes, in the marginal integrity is supposed to be detrimental for long-term success of fixed dental prostheses. The aim of this in vitro study was to compare the marginal adaptation of two different full ceramic restoration systems (Zirkouzahu&Cercon and possible changes in marginal integrity following the multiple veneering process. Materials and Methods: Twelve all-ceramic crowns in the form of coping were fabricated on a pre-made standard metal die with finish line of shoulder preparation from two commercial systems: Cercon® and Zirkonzahn®. The specimens were not cemented. The Crown/Die discrepancy were measured by means of a precise stereo microscope (accuracy±0.1 μm, at various points (n=12 selected along circumferential margin of the restorations. Same procedure was accomplished after applying the veneering porcelain. The mean gap dimensions were calculated and data were analyzed by multivariate (b test. Results: Mean marginal gap dimensions before and after veneering porcelain firing cycles, for Cercon® were (59.67±13.46 µm and (63.75±14.16 µm and for Zirkonzahn® were (65.81±24.37 µm and (64.74±21.94 µm, respectively. Hotelling trace Multivariate(b test method showed that the rate of mismatching marginal integrity in two groups (Cercon® and Zirkonzahn® had no significant difference before and after porcelain firing (P>0.05. Conclusion: Within the limitation of this study, the marginal integrity of both systems were seems to be within the clinically acceptable standard dimension, i.e. 120μm.The marginal gap of both all-ceramic systems were not affected by veneering porcelain firing cycles.

  17. Transcript profiling of crown rootless1 mutant stem base reveals new elements associated with crown root development in rice

    Directory of Open Access Journals (Sweden)

    Van Anh Le Thi

    2011-08-01

    Full Text Available Abstract Background In rice, the major part of the post-embryonic root system is made of stem-derived roots named crown roots (CR. Among the few characterized rice mutants affected in root development, crown rootless1 mutant is unable to initiate crown root primordia. CROWN ROOTLESS1 (CRL1 is induced by auxin and encodes an AS2/LOB-domain transcription factor that acts upstream of the gene regulatory network controlling CR development. Results To identify genes involved in CR development, we compared global gene expression profile in stem bases of crl1 mutant and wild-type (WT plants. Our analysis revealed that 250 and 236 genes are down- and up-regulated respectively in the crl1 mutant. Auxin induces CRL1 expression and consequently it is expected that auxin also alters the expression of genes that are early regulated by CRL1. To identify genes under the early control of CRL1, we monitored the expression kinetics of a selected subset of genes, mainly chosen among those exhibiting differential expression, in crl1 and WT following exogenous auxin treatment. This analysis revealed that most of these genes, mainly related to hormone, water and nutrient, development and homeostasis, were likely not regulated directly by CRL1. We hypothesized that the differential expression for these genes observed in the crl1 mutant is likely a consequence of the absence of CR formation. Otherwise, three CRL1-dependent auxin-responsive genes: FSM (FLATENNED SHOOT MERISTEM/FAS1 (FASCIATA1, GTE4 (GENERAL TRANSCRIPTION FACTOR GROUP E4 and MAP (MICROTUBULE-ASSOCIATED PROTEIN were identified. FSM/FAS1 and GTE4 are known in rice and Arabidopsis to be involved in the maintenance of root meristem through chromatin remodelling and cell cycle regulation respectively. Conclusion Our data showed that the differential regulation of most genes in crl1 versus WT may be an indirect consequence of CRL1 inactivation resulting from the absence of CR in the crl1 mutant. Nevertheless

  18. Monolithic zirconia dental crowns. Internal fit, margin quality, fracture mode and load at fracture.

    Science.gov (United States)

    Schriwer, Christian; Skjold, Anneli; Gjerdet, Nils Roar; Øilo, Marit

    2017-09-01

    Dental all-ceramic restorations of zirconia, with and without an aesthetic veneering layer, have become a viable alternative to conventional metal-ceramic restorations. The aim of this study was to evaluate whether factors of the production methods or the material compositions affect load at fracture, fracture modes, internal fit or crown margins of monolithic zirconia crowns. Sixty crowns made from six different commercially available dental zirconias were produced to a model tooth with a shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. The crown margin quality was assessed by light microscopy on an ordinal scale. The cemented crowns were loaded centrally in the occlusal fossa with a horizontal steel cylinder with a diameter of 13mm at 0.5mm/min until fracture. Fractographic analysis was performed on the fractured crowns. There were statistically significant differences among the groups regarding crown margins, internal fit and load at fracture (p<0.05, Kruskall Wallis). Fracture analyses revealed that all fractures started cervically and propagated to the occlusal surface similar to clinically observed fractures. There was statistically significant correlation between margin quality and load at fracture (Spearman's rank correlation, p<0,05). Production method and material composition of monolithic zirconia crowns affect internal fit, crown margin quality and the load at fracture. The hard-machined Y-TZP zirconia crowns had the best margin quality and the highest load at fracture. Reduction of margin flaws will improve fracture strength of monolithic zirconia crowns and thereby increase clinical success. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  19. Metabolic changes in Avena sativa crowns recovering from freezing.

    Science.gov (United States)

    Henson, Cynthia A; Duke, Stanley H; Livingston, David P

    2014-01-01

    Extensive research has been conducted on cold acclimation and freezing tolerance of fall-sown cereal plants due to their economic importance; however, little has been reported on the biochemical changes occurring over time after the freezing conditions are replaced by conditions favorable for recovery and growth such as would occur during spring. In this study, GC-MS was used to detect metabolic changes in the overwintering crown tissue of oat (Avena sativa L.) during a fourteen day time-course after freezing. Metabolomic analysis revealed increases in most amino acids, particularly proline, 5-oxoproline and arginine, which increased greatly in crowns that were frozen compared to controls and correlated very significantly with days after freezing. In contrast, sugar and sugar related metabolites were little changed by freezing, except sucrose and fructose which decreased dramatically. In frozen tissue all TCA cycle metabolites, especially citrate and malate, decreased in relation to unfrozen tissue. Alterations in some amino acid pools after freezing were similar to those observed in cold acclimation whereas most changes in sugar pools after freezing were not. These similarities and differences suggest that there are common as well as unique genetic mechanisms between these two environmental conditions that are crucial to the winter survival of plants.

  20. Clergy, nobility and crown in Decadência

    Directory of Open Access Journals (Sweden)

    Yi Liu

    2006-01-01

    Full Text Available In the current work I intend to inquire into the internal motives that led the Portuguese seaborne empire to decadence. After making a brief review of the historiography about the decline of Estado da Índia, I proceed to the analysis of the Crown-Church-Nobility triangle in the course of os Descobrimentos, and of their respective roles in the evolution of Portuguese empire. The absolutization of the crown, the over-expansion of the clergy and the empowerment of the aristocracy became the most conspicuous and longstanding features in the Portuguese social fabric after the country launched herself into maritime undertakings, which crippled her agriculture and retarded the industrialization. As a consequence, the rise of bourgeoisie and the transformation of mercantilist economy into the capitalist were obstructed, and a strong adventurous but non-productive spirit mixed with disdain of manual work prevailed both in metropolis and in overseas territories. In conclusion, the Portuguese decadence commenced from within rather than from without, and far prior to Dutch intrusions in Portuguese Asia, which only accelerated the decline.

  1. Metabolic changes in Avena sativa crowns recovering from freezing.

    Directory of Open Access Journals (Sweden)

    Cynthia A Henson

    Full Text Available Extensive research has been conducted on cold acclimation and freezing tolerance of fall-sown cereal plants due to their economic importance; however, little has been reported on the biochemical changes occurring over time after the freezing conditions are replaced by conditions favorable for recovery and growth such as would occur during spring. In this study, GC-MS was used to detect metabolic changes in the overwintering crown tissue of oat (Avena sativa L. during a fourteen day time-course after freezing. Metabolomic analysis revealed increases in most amino acids, particularly proline, 5-oxoproline and arginine, which increased greatly in crowns that were frozen compared to controls and correlated very significantly with days after freezing. In contrast, sugar and sugar related metabolites were little changed by freezing, except sucrose and fructose which decreased dramatically. In frozen tissue all TCA cycle metabolites, especially citrate and malate, decreased in relation to unfrozen tissue. Alterations in some amino acid pools after freezing were similar to those observed in cold acclimation whereas most changes in sugar pools after freezing were not. These similarities and differences suggest that there are common as well as unique genetic mechanisms between these two environmental conditions that are crucial to the winter survival of plants.

  2. Alkali-crown ether complexes at metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Thontasen, Nicha; Deng, Zhitao; Rauschenbach, Stephan [Max Planck Institute for Solid State Research, Stuttgart (Germany); Levita, Giacomo [University of Trieste, Trieste (Italy); Malinowski, Nikola [Max Planck Institute for Solid State Research, Stuttgart (Germany); Bulgarian Academy of Sciences, Sofia (Bulgaria); Kern, Klaus [Max Planck Institute for Solid State Research, Stuttgart (Germany); EPFL, Lausanne (Switzerland)

    2010-07-01

    Crown ethers are polycyclic ethers which, in solution, selectively bind cations depending on the size of the ring cavity. The study of a single host-guest complex is highly desirable in order to reveal the characteristics of these specific interactions at the atomic scale. Such detailed investigation is possible at the surface where high resolution imaging tools like scanning tunneling microscopy (STM) can be applied. Here, electrospray ion beam deposition (ES-IBD) is employed for the deposition of Dibenzo-24-crown-8 (DB24C8)-H{sup +}, -Na{sup +} and -Cs{sup +} complexes on a solid surface in ultrahigh vacuum (UHV). Where other deposition techniques have not been successful, this deposition technique combines the advantages of solution based preparation of the complex ions with a highly clean and controlled deposition in UHV. Single molecular structures and the cation-binding of DB24C8 at the surface are studied in situ by STM and MALDI-MS (matrix assisted laser desorption ionization mass spectrometry). The internal structure of the complex, i.e. ring and cavity, is observable only when alkali cations are incorporated. The BD24C8-H{sup +} complex in contrast appears as a compact feature. This result is in good agreement with theoretical models based on density functional theory calculations.

  3. Hierarchical patterns of paternity within crowns of Albizia julibrissin (Fabaceae).

    Science.gov (United States)

    Pardini, Eleanor A; Hamrick, J L

    2007-01-01

    The floral architecture and phenology of the tree species Albizia julibrissin (Fabaceae) offer the potential for flowers within inflorescences to share common pollen donors. Patterns of paternity within individual tree crowns may differ among isolated individuals and those in populations due to differences in pollinator foraging behavior. To determine how genetic diversity is partitioned within individual seed pools and whether these patterns differ among isolated and population trees, we obtained all fruits from three inflorescences from four clusters from three isolated trees and from three population trees in Athens, Georgia. We assayed 14 polymorphic allozymes to genotype all progeny within singly sired fruits to determine the multilocus genotype of each fruit's pollen donor. Inflorescences had multiple pollen donors, but simulation analyses revealed that redundancy of pollen donors tended to be more likely within inflorescences than randomly across the crown. Analysis of genetic and genotypic diversity indicated that individual maternal trees received pollen from many donors in uneven frequencies. Results suggest that isolated trees receive pollen from slightly fewer pollen donors and experience more within-plant pollinator movement than trees in populations. However, isolated trees receive qualitatively similar pollen from many sources, suggesting that these trees are not effectively isolated and that pollen moves long distances in this species.

  4. Purification and characterization of a pineapple crown leaf thiol protease.

    Science.gov (United States)

    Singh, L Rupachandra; Devi, Th Premila; Devi, S Kunjeshwori

    2004-02-01

    A thiol protease was isolated and purified from the crown leaf of pineapple, Ananas comosus (L.) Merr. cv. Queen, by an immunoaffinity procedure. After the purification to electrophoretic homogeneity, the enzyme was characterized with respect to some of its physico-chemical and kinetic properties. The molecular weight of the protease (22.4-22.9 kDa), Km (97 microM) and kcat (8.8 s(-1)) for its esterolytic cleavage of the synthetic protease substrate N(alpha)-CBZ-L-lysine p-nitrophenyl ester, the concentration of its thiol activator L-cysteine required for half maximal activation A0.5 (9.9 microM), optimum pH (6.5) for its proteolytic action on azocasein, T(1/2) (60 degrees C) for inactivation by heating the enzyme (35.5 microg protein/mL) in citrate buffer pH 6.0 for 15 min, and SH-group content (0.98 mol/mol enzyme) were determined. Most of these physicochemical and kinetic properties were found to be similar to those of the already well-characterized stem bromelain (EC 3.4.22.32). Thus, the immunoaffinity purified crown leaf protease appeared to be closely related to stem bromelain.

  5. Research on work roll thermal crown in cold rolling mill

    Science.gov (United States)

    Song, Lei; Shen, Mingang; Chen, Xuebo; Wang, Junsheng

    2013-05-01

    The factors which have influence on the work roll thermal crown in cold strip rolling are discussed. The heat transferring in three directions (radial axis and circumference) were considered for calculating the work roll thermal deformation. Therefore, it is a three dimensions unstable system for the work roll temperature calculation. The plastic deformation work and friction heat are calculated by the divided element and digital integration method. The simplified calculation model is built for the heat transferring along work roll. There are four zones for work roll heat transferring: roll gap zone air cooling zone emulsion zone rolls contact zone. The heat transferring between the zones is decided by the temperature difference. The inter temperature field and thermal deformation of work roll can be calculated by two-dimension finite difference method. The work roll temperature and thermal crown of actual application cold rolling mill are analyzed by the model. By the comparison between calculated values and measured values, the work roll thermal calculation model can meet the accuracy requirement of on-line control.

  6. High-Resolution Airborne UAV Imagery to Assess Olive Tree Crown Parameters Using 3D Photo Reconstruction: Application in Breeding Trials

    Directory of Open Access Journals (Sweden)

    Ramón A. Díaz-Varela

    2015-04-01

    Full Text Available The development of reliable methods for the estimation of crown architecture parameters is a key issue for the quantitative evaluation of tree crop adaptation to environment conditions and/or growing system. In the present work, we developed and tested the performance of a method based on low-cost unmanned aerial vehicle (UAV imagery for the estimation of olive crown parameters (tree height and crown diameter in the framework of olive tree breeding programs, both on discontinuous and continuous canopy cropping systems. The workflow involved the image acquisition with consumer-grade cameras on board a UAV and orthomosaic and digital surface model generation using structure-from-motion image reconstruction (without ground point information. Finally, geographical information system analyses and object-based classification were used for the calculation of tree parameters. Results showed a high agreement between remote sensing estimation and field measurements of crown parameters. This was observed both at the individual tree/hedgerow level (relative RMSE from 6% to 20%, depending on the particular case and also when average values for different genotypes were considered for phenotyping purposes (relative RMSE from 3% to 16%, pointing out the interest and applicability of these data and techniques in the selection scheme of breeding programs.

  7. The relationship between sports activities and permanent incisor crown fractures in a group of school children aged 7-9 and 11-13 in Ankara, Turkey.

    Science.gov (United States)

    Cetinbaş, Tuğba; Yildirim, Gözde; Sönmez, Hayriye

    2008-10-01

    The objective of the study was to determine the distribution, aetiology of the crown fractures of permanent anterior teeth in children aged 7-9 and 11-13 years and to identify the role of participation in sports associated with crown fractures. The study population comprised 2570 students from 10 primary schools randomly selected from five municipalities in Ankara, Turkey. Two paediatric dentists examined all permanent maxillary and mandibular incisors for evidence of fracture and completed a standardized examination form to obtain information on the age, gender, severity of incisor injury and frequency and type of sports participation for each child, as well as whether or not children used mouthguards during sports activities. Chi-square and z-tests were used to determine differences. A total of 191 (7.43%) of the 2570 subjects examined were affected by dental trauma. The proportion of fractured incisors was significantly higher in males than in females among older children (P < 0.01). Out of a total of 222 fractured teeth, 84% involved the maxillary central incisors. Bicycling caused significantly higher rates of crown fractures than other types of sports (P < 0.05). The percentage of incisal fractures caused by sports-related accidents was 14.14%. The number of children interested in sports is high, and the sports chosen are generally contact sports. The high rate (14.14%) of crown injuries caused by sports activities supports these findings.

  8. Dental trauma. Combination injuries 3. The risk of pulp necrosis in permanent teeth with extrusion or lateral luxation and concomitant crown fractures without pulp exposure

    DEFF Research Database (Denmark)

    Lauridsen, Eva Fejerskov; Hermann, Nuno Vibe; Gerds, Thomas Alexander;

    2012-01-01

    Aim: To analyze the influence of a crown fracture without pulp exposure on the risk of pulp necrosis (PN) in teeth with extrusion or lateral luxation. Material and methods: The study included 82 permanent incisors with extrusion from 78 patients (57 male, 21 female) and 179 permanent incisors......, and response to electric pulp test at the initial examination. Results: A concomitant crown fracture significantly increased the risk of PN in teeth with lateral luxation. For teeth with immature root development (hazard ratio: 10 [95% confidence interval (CI): 1.1–100] P = 0.04), the overall risk increased...... increased from 56.5% (95% CI: 37.7–75.4) to 76.5% (95% CI: 58.9–94) in case of a concomitant crown fracture, but the difference was not statistically significant (P > 0.05). Conclusion: A concomitant crown fracture without pulp exposure significantly increased the risk of PN in teeth with lateral luxation...

  9. Accuracy of LiDAR-based tree height estimation and crown recognition in a subtropical evergreen broad-leaved forest in Okinawa, Japan

    Directory of Open Access Journals (Sweden)

    Azita Ahmad Zawawi

    2015-04-01

    Full Text Available Aim of study: To present an approach for estimating tree heights, stand density and crown patches using LiDAR data in a subtropical broad-leaved forest. Area of study: The study was conducted within the Yambaru subtropical evergreen broad-leaved forest, Okinawa main island, Japan. Materials and methods: A digital canopy height model (CHM was extracted from the LiDAR data for tree height estimation and a watershed segmentation method was applied for the individual crown delineation. Dominant tree canopy layers were estimated using multi-scale filtering and local maxima detection. The LiDAR estimation results were then compared to the ground inventory data and a high resolution orthophoto image for accuracy assessment. Main results: A Wilcoxon matched pair test suggests that LiDAR data is highly capable of estimating tree height in a subtropical forest (z = 4.0, p = 0.345, but has limitation to detect small understory trees and a single tree delineation. The results show that there is a statistically significant different type of crown detection from LiDAR data over forest inventory (z = 0, p = 0.043. We also found that LiDAR computation results underestimated the stand density and overestimated the crown size. Research highlights: Most studies involving crown detection and tree height estimation have focused on the analysis of plantations, boreal forests and temperate forests, and less was conducted on tropical and/or subtropical forests. Our study tested the capability of LiDAR as an effective application for analyzing a highly dense forest

  10. Marginal fit of all-ceramic crowns fabricated using two extraoral CAD/CAM systems in comparison with the conventional technique.

    Science.gov (United States)

    Alqahtani, Fawaz

    2017-01-01

    The purpose of this study was to determine the effect of two extraoral computer-aided design (CAD) and computer-aided manufacturing (CAM) systems, in comparison with conventional techniques, on the marginal fit of monolithic CAD/CAM lithium disilicate ceramic crowns. This is an in vitro interventional study. The study was carried out at the Department of Prosthodontics, School of Dentistry, Prince Sattam Bin Abdul-Aziz University, Saudi Arabia, from December 2015 to April 2016. A marginal gap of 60 lithium disilicate crowns was evaluated by scanning electron microscopy. In total, 20 pressable lithium disilicate (IPS e.max Press [Ivoclar Vivadent]) ceramic crowns were fabricated using the conventional lost-wax technique as a control group. The experimental all-ceramic crowns were produced based on a scan stone model and milled using two extraoral CAD/CAM systems: the Cerec group was fabricated using the Cerec CAD/CAM system, and the Trios group was fabricated using Trios CAD and milled using Wieland Zenotec CAM. One-way analysis of variance (ANOVA) and the Scheffe post hoc test were used for statistical comparison of the groups (α=0.05). The mean (±standard deviation) of the marginal gap of each group was as follows: the Control group was 91.15 (±15.35) µm, the Cerec group was 111.07 (±6.33) µm, and the Trios group was 60.17 (±11.09) µm. One-way ANOVA and the Scheffe post hoc test showed a statistically significant difference in the marginal gap between all groups. It can be concluded from the current study that all-ceramic crowns, fabricated using the CAD/CAM system, show a marginal accuracy that is acceptable in clinical environments. The Trios CAD group displayed the smallest marginal gap.

  11. Durability and Weibull Characteristics of Lithium Disilicate Crowns Bonded on Abutments with Knife-Edge and Large Chamfer Finish Lines after Cyclic Loading.

    Science.gov (United States)

    Cortellini, Davide; Canale, Angelo; Souza, Rodrigo O A; Campos, Fernanda; Lima, Julia C; Özcan, Mutlu

    2015-12-01

    The aim of this study was to evaluate the durability of lithium disilicate crowns bonded on abutments prepared with two types of finish lines after long-term cyclic loading. Pressed lithium disilicate all-ceramic molar crowns were bonded (Variolink II) to epoxy abutments (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) (N = 20) with either knife-edge (KE) or large chamfer (LC) finish lines. Each assembly was submitted to cyclic loading (1,200,000×; 200 N; 1 Hz) in water and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA. Weibull distribution values including the Weibull modulus (m), characteristic strength (0), probability of failure at 5% (0.05), 1% (0.01), and correlation coefficient were calculated. Type of finish line did not significantly influence the mean fracture strength of pressed ceramic crowns (KE: 1655 ± 353 N; LC: 1618 ± 263 N) (p = 0.7898). Weibull distribution presented lower shape value (m) of KE (m = 5.48; CI: 3.5 to 8.6) compared to LC (m = 7.68; CI: 5.2 to 11.3). Characteristic strengths (0) (KE: 1784.9 N; LC: 1712.1 N) were higher than probability of failure at 5% (0.05) (KE: 1038.1 N; LC: 1163.4 N) followed by 1% (0.01) (KE: 771 N; LC: 941.1 N), with a correlation coefficient of 0.966 for KE and 0.924 for LC. Type V failures (severe fracture of the crown and/or tooth) were more common in both groups. SEM findings showed that fractures occurred mainly from the cement/ceramic interface at the occlusal side of the crowns. Lithium disilicate ceramic crowns bonded onto abutment teeth with KE preparation resulted in similar fracture strength to those bonded on abutments with LC finish line. Pressed lithium disilicate ceramic crowns may not require invasive finish line preparations since finish line type did not impair the strength after aging conditions. © 2015 by the American College of

  12. Large acceleration of α-chymotrypsin-catalyzed dipeptide formation by 18-crown-6 in organic solvents

    NARCIS (Netherlands)

    Unen, van Dirk-Jan; Engbersen, Johan F.J.; Reinhoudt, David N.

    1998-01-01

    The effects of 18-crown-6 on the synthesis of peptides catalyzed by α-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and L-phe

  13. Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry

    NARCIS (Netherlands)

    Eikemo, H.; Klemsdal, S.S.; Riisberg, I.; Bonants, P.J.M.; Stensvand, A.; Tronsmo, A.M.

    2004-01-01

    Analysis of 44 isolates of Phytophthora cactorum, isolated from strawberry and other hosts, by AFLP showed that the crown rot pathotype is different from leather rot isolates and from P. cactorum isolated from other hosts. 16 of 23 crown rot isolates, including isolates from Europe, Japan, Australia

  14. Multipodal coordination of a tetracarboxylic crown ether with NH4+: A vibrational spectroscopy and computational study

    NARCIS (Netherlands)

    Hurtado, P.; Gamez, F.; Hamad, S.; Martinez-Haya, B.; Steill, J. D.; Oomens, J.

    2012-01-01

    The elucidation of the structural requirements for molecular recognition by the crown ether (18-crown-6)-2,3,11,12-tetracarboxylic acid (18c6H(4)) and its cationic complexes constitutes a topic of current fundamental and practical interest in catalysis and analytical sciences. The flexibility of the

  15. An alternative method for estimating crown characteristics of urban trees using digital photographs

    Science.gov (United States)

    Matthew F. Winn; Philip A. Araman

    2012-01-01

    The USDA Forest Service Forest Inventory and Analysis (FIA) program has concluded that statewide urban forest inventories are feasible based on a series of pilot studies initiated in 2001. However, much of the tree crown data collected during inventories are based on visual inspection and therefore highly subjective. In order to objectively determine the crown...

  16. Investigating assumptions of crown archetypes for modelling LiDAR returns

    NARCIS (Netherlands)

    Calders, K.; Lewis, P.; Disney, M.; Verbesselt, J.; Herold, M.

    2013-01-01

    LiDAR has the potential to derive canopy structural information such as tree height and leaf area index (LAI), via models of the LiDAR signal. Such models often make assumptions regarding crown shape to simplify parameter retrieval and crown archetypes are typically assumed to contain a turbid

  17. Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry

    NARCIS (Netherlands)

    Eikemo, H.; Klemsdal, S.S.; Riisberg, I.; Bonants, P.J.M.; Stensvand, A.; Tronsmo, A.M.

    2004-01-01

    Analysis of 44 isolates of Phytophthora cactorum, isolated from strawberry and other hosts, by AFLP showed that the crown rot pathotype is different from leather rot isolates and from P. cactorum isolated from other hosts. 16 of 23 crown rot isolates, including isolates from Europe, Japan, Australia

  18. Investigating assumptions of crown archetypes for modelling LiDAR returns

    NARCIS (Netherlands)

    Calders, K.; Lewis, P.; Disney, M.; Verbesselt, J.; Herold, M.

    2013-01-01

    LiDAR has the potential to derive canopy structural information such as tree height and leaf area index (LAI), via models of the LiDAR signal. Such models often make assumptions regarding crown shape to simplify parameter retrieval and crown archetypes are typically assumed to contain a turbid mediu

  19. 76 FR 62016 - Endangered and Threatened Wildlife and Plants; Red-Crowned Parrot

    Science.gov (United States)

    2011-10-06

    ... (Prosopeia splendens), great green macaw (Ara ambiguus), grey-cheeked parakeet (Brotogeris pyrrhoptera... haematuropygia), red-crowned parrot (Amazona viridigenalis), scarlet macaw (Ara macao), white cockatoo (Cacatua... distinguished by bright yellow-green cheek areas, bright red on the crown (top of head) and lores (area...

  20. Zirconia crowns--an esthetic and resistant restorative alternative for ECC affected primary teeth.

    Science.gov (United States)

    Planells del Pozo, P; Fuks, A B

    2014-01-01

    The present report discusses briefly the problem of ECC in very young children and the recommended approaches for prevention and treatment. The esthetic restoration of the maxillary incisors with Zirconia Nu Smile crowns is described. It is also stressed that the luxation injury two months after placement did not damage the appearance nor the stability of the crowns.

  1. Comparison of Clinical Effects of Au-Pt Based and Ni-Cr Based Porcelain Crowns

    Institute of Scientific and Technical Information of China (English)

    Li-chun Wu; Ye Shi; Teng Ma

    2012-01-01

    Objective To compare the long-term clinical effects of two kinds of crowns and bridges made of porcelain fused to Au-Pt alloy and Ni-Cr alloy.Methods A total of 131 teeth (64 patients) were rehabilitated using porcelain-fused-to-metal crowns,among which 59 were rehabilitated with Au-Pt alloy metal ceramic crown and 72 with Ni-Cr alloy metal ceramic crown.The porcelain fracture,shade,marginal adaptation,gingival discoloration,and gingival status after finishing restoration and 36 months of follow-up were evaluated.Results After 36 months of restoration,porcelain fused to Au-Pt alloy crown showed better clinical effects than porcelain fused to Ni-Cr alloy crown in shade,marginal adaptation,gingival discoloration,as well as gingival status (all P<0.05).Conclusion The Au-Pt alloy ceramic crown is superior to Ni-Cr alloy ceramic crown in long-term clinical effects.

  2. Evaluation of the occlusal contact of crowns fabricated with the bite impression method.

    Science.gov (United States)

    Makino, Sachi; Okada, Daizo; Shin, Chiharu; Ogura, Reiko; Ikeda, Masaomi; Miura, Hiroyuki

    2013-09-30

    In prosthodontic treatment, reconstruction of a proper occlusal contact relationship is very important as well as reconstruction of a proper interproximal relationship and marginal fitness. Unfortunately, occlusal relationships are sometimes lost in the process of occlusal adjustment of crowns. The purpose of this study was to compare the occlusal contacts of single crown fabricated by two different types of impression techniques. Nine subjects, whose molars required treatment with crown restoration, were enrolled in this study. Full cast crowns were fabricated using two types of impression techniques: the conventional impression method (CIM) and the bite impression method (BIM). The occlusal contacts of crowns were precisely evaluated at the following stages: after occlusal adjustment on the articulator (Step 0), before occlusal adjustment in the mouth (Step 1), after occlusal adjustment at the intercuspal position (Step 2), and after occlusal adjustment during lateral and protrusive excursions (Step 3). The number of occlusal contacts of the crowns on the functional cusps fabricated with BIM was significantly greater than that with CIM after occlusal adjustment. For this reason, the crowns fabricated with BIM might have a more functionally desirable occlusal surface compared to the crowns fabricated with CIM.

  3. In vitro evaluation of the marginal fit of different all-ceramic crowns

    Directory of Open Access Journals (Sweden)

    Munir Tolga Yucel

    2013-09-01

    Conclusion: In-Ceram all-ceramic crowns showed the largest marginal gap, and Celay crowns showed the smallest marginal gap in both die groups. The marginal discrepancies found in this study were all within the clinically acceptable standard of 120 μm.

  4. Crown ether activation of cross-linked subtilisin Carlsberg crystals in organic solvents

    NARCIS (Netherlands)

    Unen, van Dirk-Jan; Sakodinskaya, Inna K.; Engbersen, Johan F.J.; Reinhoudt, David N.

    1998-01-01

    The activity of cross-linked subtilisin Carlsberg crystals in the catalysis of peptide bond formation can be significantly enhanced by pretreatment of the enzyme crystals with crown ethers. Soaking of the enzyme crystals in a solution of crown ether in acetonitrile followed by evaporation of the sol

  5. Tree crown delineation from high resolution airborne LiDAR based on densities of high points

    NARCIS (Netherlands)

    Rahman, M.Z.A.; Gorte, B.G.H.

    2009-01-01

    Tree detection and tree crown delineation from Airborne LiDAR has been focusing mostly on utilizing the canopy height model (CHM). This paper presents a method for individual tree crown delineation based on densities of high points (DHP) from the high resolution Airborne LiDAR. The DHP method relies

  6. Clinical Performance of Pedo Jacket Crowns in Maxillary Anterior Primary Teeth.

    Science.gov (United States)

    Castro, Aimee; Badr, Sherine B Y; El-Badrawy, Wafa; Kulkarni, Gajanan

    2016-09-15

    To assess the clinical performance of Pedo Jacket crowns for restoration of carious primary anterior teeth. A total of 129 carious primary incisors and canines of 48 children younger than 71 months of age- were restored with Pedo Jacket crowns and resin-modified glass ionomer cementation. They were assessed for: ease of use; presence of recurrent decay; wear; partial or complete loss of the crown; color stability; gingival health; and overall clinical success over a 12-month follow-up. The patient's behavior at the restorative appointment during crown placement was also assessed. An overall clinical success of 89.5 percent of the teeth in 87.3 percent of the children was seen one year later. The crowns were easy to use, even in uncooperative children. The color stability, wear, plaque accumulation, and gingival health were acceptable. Discoloration, wear, or complete loss of the crown were found in 13.1 percent, 5.4 percent, and 7.6 percent of children, respectively. Although not statistically significant, failures were associated with poor patient cooperation at the time of crown placement, poor oral hygiene, or operator error. Pedo Jacket crowns are a viable treatment alternative for carious maxillary primary anterior teeth.

  7. Structures of dioxobipyridil-12-crown-4 and its complexes with silver (I) and copper (II) cations

    Science.gov (United States)

    Starova, Galina L.; Denisova, Anna S.; Dem'yanchuk, Evgeniya M.

    2008-02-01

    The structures of dioxobipyridil-12-crown-4 ( bpy-CO-crown) and its complexes with copper (II) and silver (I) cations have been determined using single crystal X-ray-diffraction. The results have been compared with the literature data on the complexes of dcmbpy and its complex with silver (I) and copper (II) cations.

  8. Characterization of mesenchymal progenitor cells in crown and root pulp from human mesiodentes.

    Science.gov (United States)

    Sato, M; Toriumi, T; Watanabe, N; Watanabe, E; Akita, D; Mashimo, T; Akiyama, Y; Isokawa, K; Shirakawa, T; Honda, M J

    2015-01-01

    Mesiodentes are usually found in the central position of the upper or lower jaw as supernumerary teeth. Here, we obtained 10 mesiodentes and three permanent teeth (PT) and separated the dental pulp (DP) from these into crown and root portions. We then characterized and compared the isolated crown portion-derived cells (crown cells) with root portion-derived cells (root cells) using a range of in vitro assays. Crown cells and root cells were examined for cell surface marker expression, colony-forming unit-fibroblast (CFU-F), cell proliferation, cell cycle characteristics and markers, and osteogenic and adipogenic differentiation. The proportion of CD105-positive cells (CD105(+) cells) in the crown cells vs the root cells varied among the mesiodentes, but not among the PT. When there were more CD105(+) cells in the root cells than in the crown cells, the root cells showed higher CFU-F, proliferation capacity, and osteogenic differentiation capacity. In contrast, when the crown cells contained more CD105(+) cells than the root cells, the crown cells showed the higher CFU-F, proliferation capacity, and osteogenic differentiation capacity. In addition, the sorted CD105(+) cells showed higher CFU-F and proliferation capacity than the sorted CD105(-) cells. These results indicated that proportion of CD105(+) cells is an effective means of characterizing DP-derived cells in mesiodentes. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  9. A Psychometric Investigation of the Marlowe-Crowne Social Desirability Scale Using Rasch Measurement

    Science.gov (United States)

    Seol, Hyunsoo

    2007-01-01

    The author used Rasch measurement to examine the reliability and validity of 382 Korean university students' scores on the Marlowe-Crowne Social Desirability Scale (MCSDS; D. P. Crowne and D. Marlowe, 1960). Results revealed that item-fit statistics and principal component analysis with standardized residuals provide evidence of MCSDS'…

  10. Development of Reliable and Valid Short Forms of the Marlowe-Crowne Social Desirability Scale.

    Science.gov (United States)

    Reynolds, William M.

    1982-01-01

    Developed, on the basis of responses from 608 undergraduate students to the 33-item Marlowe-Crowne Social Desirability Scale, three short forms of the scale. Comparisons made between the short forms examined in this investigation suggest the 13-item form as a viable substitute for the regular 33-item Marlowe-Crowne scale. (Author)

  11. A Reliability Generalization Study of the Marlowe-Crowne Social Desirability Scale.

    Science.gov (United States)

    Beretvas, S, Natasha; Meyers, Jason L.; Leite, Walter L.

    2002-01-01

    Conducted a reliability generalization study of the Marlowe-Crowne Social Desirability Scale (D. Crowne and D. Marlowe, 1960). Analysis of 93 studies show that the predicted score reliability for male adolescents was 0.53, and reliability for men's responses was lower than for women's. Discusses the need for further analysis of the scale. (SLD)

  12. Rapid crown root development confers tolerance to zinc deficiency in rice

    Directory of Open Access Journals (Sweden)

    Amrit Kaur eNanda

    2016-03-01

    Full Text Available Zinc (Zn deficiency is one of the leading nutrient disorders in rice (Oryza sativa. Many studies have identified Zn efficient rice genotypes, but causal mechanisms for Zn deficiency tolerance remain poorly understood. Here we report a detailed study of the impact of Zn deficiency on crown root development of rice genotypes, differing in their tolerance to this stress. Zn deficiency delayed crown root development and plant biomass accumulation in both Zn efficient and inefficient genotypes, with the effects being much stronger in the latter. Zn efficient genotypes had developed new crown roots as early as three days after transplanting (DAT to a Zn deficient field and that was followed by a significant increase in total biomass by 7 DAT. Zn-inefficient genotypes developed few new crown roots and did not increase biomass during the first seven days following transplanting. This correlated with Zn efficient genotypes retranslocating a higher proportion of shoot Zn to their roots, compared to Zn inefficient genotypes. These latter genotypes were furthermore not efficient in utilizing the limited Zn for root development. Histological analyses indicated no anomalies in crown tissue of Zn-efficient or inefficient genotypes that would have suggested crown root emergence was impeded. We therefore conclude that the rate of crown root initiation was differentially affected by Zn deficiency between genotypes. Rapid crown root development, following transplanting, was identified as a main causative trait for tolerance to Zn deficiency and better Zn retranslocation from shoot to root was a key attribute of Zn-efficient genotypes.

  13. Surface fire effects on conifer and hardwood crowns--applications of an integral plume model

    Science.gov (United States)

    Matthew Dickinson; Anthony Bova; Kathleen Kavanagh; Antoine Randolph; Lawrence Band

    2009-01-01

    An integral plume model was applied to the problems of tree death from canopy injury in dormant-season hardwoods and branch embolism in Douglas fir (Pseudotsuga menziesii) crowns. Our purpose was to generate testable hypotheses. We used the integral plume models to relate crown injury to bole injury and to explore the effects of variation in fire...

  14. Test

    DEFF Research Database (Denmark)

    Bendixen, Carsten

    2014-01-01

    Bidrag med en kortfattet, introducerende, perspektiverende og begrebsafklarende fremstilling af begrebet test i det pædagogiske univers.......Bidrag med en kortfattet, introducerende, perspektiverende og begrebsafklarende fremstilling af begrebet test i det pædagogiske univers....

  15. A feasible, aesthetic quality evaluation of implant-supported single crowns: an analysis of validity and reliability

    DEFF Research Database (Denmark)

    Hosseini, Mandana; Gotfredsen, Klaus

    2012-01-01

    OBJECTIVES: To test the reliability and validity of six aesthetic parameters and to compare the professional- and patient-reported aesthetic outcomes. MATERIAL AND METHODS: Thirty-four patients with 66 implant-supported premolar crowns were included. Two prosthodontists and 11 dental students......,24) were found between patient and professional evaluations. CONCLUSIONS: The feasibility, reliability and validity of the CIS make the parameters useful for quality control of implant-supported restorations. The professional- and patient-reported aesthetic outcomes had no significant correlation....

  16. A feasible, aesthetic quality evaluation of implant-supported single crowns: an analysis of validity and reliability

    DEFF Research Database (Denmark)

    Hosseini, Mandana; Gotfredsen, Klaus

    2012-01-01

    OBJECTIVES: To test the reliability and validity of six aesthetic parameters and to compare the professional- and patient-reported aesthetic outcomes. MATERIAL AND METHODS: Thirty-four patients with 66 implant-supported premolar crowns were included. Two prosthodontists and 11 dental students......,24) were found between patient and professional evaluations. CONCLUSIONS: The feasibility, reliability and validity of the CIS make the parameters useful for quality control of implant-supported restorations. The professional- and patient-reported aesthetic outcomes had no significant correlation....

  17. Complication rate of molar crowns: a practice-based clinical evaluation.

    Science.gov (United States)

    Rinke, S; Schäfer, S; Roediger, M

    2011-01-01

    This practice-based study evaluates the initial clinical performance of conventionally luted metal-ceramic and zirconia molar crowns fabricated with a prolonged cooling period of the veneering porcelain. Forty-nine patients were treated (group A: high precious alloy + low fusing porcelain; group B: zirconia crowns). All zirconia crowns were veneered with a modified porcelain firing cycle including a 6-minute cooling period. Ninety-two restorations (74 vital abutments/18 nonvital abutments) were evaluated after a mean observation period of 18.2 +/- 4.6 months. No complete failures or loss of vitality were recorded in either group. Two events were recorded in group A (1 loss of retention/1 minor ceramic chipping zirconia crowns fabricated with a modified porcelain firing. The modified firing of the zirconia porcelain seems to decrease the risk for early ceramic chipping in the molar area, leading to a technical complication rate comparable to that of metal-ceramic crowns.

  18. A delayed hypersensitivity reaction to a stainless steel crown: a case report.

    Science.gov (United States)

    Yilmaz, A; Ozdemir, C E; Yilmaz, Y

    2012-01-01

    Stainless steel crowns are commonly used to restore primary or permanent teeth in pediatric restorative dentistry. Here, we describe a case of a delayed hypersensitivity reaction, which manifested itself as perioral skin eruptions, after restoring the decayed first permanent molar tooth of a 13-year-old Caucasian girl with a preformed stainless steel crown. The eruptions completely healed within one week after removal of the stainless steel crown. The decayed tooth was then restored with a bis-acryl crown and bridge. Since no perioral skin eruptions occurred during the six-month follow-up, we presume that the cause of the perioral skin eruptions was a delayed hypersensitivity reaction, which was triggered by the nickel in the stainless steel crown.

  19. Zirconia crowns for rehabilitation of decayed primary incisors: an esthetic alternative.

    Science.gov (United States)

    Ashima, G; Sarabjot, K Bhatia; Gauba, K; Mittal, H C

    2014-01-01

    Esthetic management of extensively decayed primary maxillary anterior teeth requiring full coronal coverage restoration is usually challenging to the pediatric dentists especially in very young children. Many esthetic options have been tried over the years each having its own advantages, disadvantages and associated technical, functional or esthetic limitations. Zirconia crowns have provided a treatment alternative to address the esthetic concerns and ease of placement of extra-coronal restorations on primary anterior teeth. The present article presents a case where grossly decayed maxillary primary incisors were restored esthetically and functionally with ready made zirconia crowns (ZIRKIZ, HASS Corp; Korea). After endodontic treatment the decayed teeth were restored with zirconia crowns. Over a 30 months period, the crowns have demonstrated good retention and esthetic results. Dealing with esthetic needs in children with extensive loss of tooth structure, using Zirconia crowns would be practical and successful. The treatment described is simple and effective and represents a promising alternative for rehabilitation of decayed primary teeth.

  20. Sorbents based on crown ethers: preparation and application for the sorption of strontium

    Science.gov (United States)

    Bezhin, N. A.; Dovhyi, I. I.

    2015-12-01

    The key approaches to the synthesis of crown ether-based sorbents, including immobilization both with and without covalent bonding, are reviewed. Examples of sorbent preparation using anodic oxidation, chemical modification of polymers, polycondensation reactions, chemical modification of inorganic supports and radiochemical synthesis for covalent bonding of crown ether moieties are considered. Immobilization methods without covalent bonding including support synthesis in the presence of crown ethers, impregnation of supports with a crown ether solution and the use of powdered crown ether as a sorbent are presented. The applications of sorbents for selective removal of strontium from solutions of radioactive waste and spent nuclear fuel, for radiochemical analysis (determination of strontium in water, soil and biological materials) and for separation of strontium and yttrium isotopes are discussed. The bibliography includes 114 references.

  1. QTL analysis of crown rust resistance in perennial ryegrass under conditions of natural and artificial infection

    DEFF Research Database (Denmark)

    Schejbel, Britt; Jensen, Louise Friis Bach; Xing, Yongzhong;

    2007-01-01

    as well as by artificial pathogen inoculations using a detached leaf assessment. The broad sense heritability values for the field, detached leaf and combined assays were 0.42, 0.56, and 0.64, respectively, indicating a good potential for selection for crown rust resistance. A total of six QTLs were......Crown rust is an economically devastating disease of perennial ryegrass. Both artificial crown rust inoculations, with the possibility of several selection cycles in one year, as well as marker-assisted selection can be used for more efficient breeding of new resistant cultivars. The objective...... of this study was to map quantitative trait loci (QTL) for response to crown rust infection in perennial ryegrass. In order to identify relevant markers for response to crown rust infection, QTL mapping was performed on a ryegrass mapping population which was evaluated for resistance in the field for two years...

  2. Comparison of marginal fit of Lava CAD/CAM crown-copings with two finish lines.

    Science.gov (United States)

    Re, Dino; Cerutti, Francesca; Augusti, Gabriele; Cerutti, Antonio; Augusti, Davide

    2014-01-01

    Marginal fit is valued as one of the most important criteria for the clinical quality and success of all-ceramic crowns. The aim of this in vitro study was to investigate the marginal fit of Lava Zirconia crown-copings on chamfer and shoulder preparations. Two acrylic model teeth were selected to simulate the clinical preparations: one molar was prepared with a chamfer finish line (C) and one premolar was prepared with a rounded shoulder finish line (RS). Each resin model was duplicated 10 times using silicon-based impression material and poured in type IV dental stone for the fabrication of working dies. A total of 20 copings were divided into two groups (n = 10 for each finish line). Fifty measuring locations were chosen randomly along the margin on the dies and the gap width - vertical marginal discrepancy - was measured under a light microscope with a magnification of x100. Measurements were made without cementation. The mean marginal gap widths and standard deviations were calculated and a one-way analysis of variance (ANOVA) was performed for different types of preparations in order to detect differences (α = 0.05). The mean marginal gap was 30 ± 3 μm for the C group and 28 ± 4 μm for the RS group. The one-way ANOVA showed no statistical significant difference between the two groups (P = 0.23). Within the limitations of this study, the marginal discrepancies were all within the clinical acceptable standard set at 120 μm. Chamfer and shoulder preparations did not show differences regarding the gap dimension. Bur design is an easily selected parameter before natural tooth preparation. Both tested finish lines are able to help clinicians in obtaining acceptable marginal fit values for the investigated zirconia copings.

  3. The quality of working impressions for the fabrication of fixed prosthodontics prostheses (crown and bridgework

    Directory of Open Access Journals (Sweden)

    Ahmad Syahir Ahmad Zu Saifudin

    2014-01-01

    Full Text Available Objective: The study was carried out to assess the quality of working impressions sent to commercial laboratories for fabrication of fixed prostheses. Materials and Methods: Impressions (n: 200 received by four dental laboratories were evaluated by two calibrated examiners. The type of work, tray designs, impression materials and techniques were recorded for each impression. Quality data on crucial details of the tooth preparations, voids at tooth preparations, tears along the finished margin line and flow of materials were documented and each criterion scored either with 2 (Good, 1 (Acceptable or 0 (Unacceptable. The Chi-square test for independence was done for relationship analysis of the impression defects and different type of impression materials. Results: From 200 examined impressions, 53.9% were for crown works, 35.9% bridge works, 1.4% posts and cores and 8.8% for other types of work. The impression materials used were polyether (39.5% and polyvinyl-siloxane (60.5%. The two main types of trays were metal stock (48.5% and disposable plastic (37.5%. Impression techniques were monophase one-step technique (50.0%, putty wash two-steps technique (23.5%, putty wash one-step technique (15.5% and dual phase one-step technique (11.0%. Overall, 64.5% of the impressions sent had unacceptable quality (0 score recorded for at least one criteria. The proportions of impression defects were significant to the type of impression materials (P < 0.05. Conclusion: The percentage of unacceptable impressions (64.5% sent to the laboratories is a serious concern, as it contributes to the inaccuracy of the crown and bridgeworks provided to patients.

  4. Design and supramolecular structure of crystal associates of polyfluoroarylenediamines and 18-crown-6 (2:1)

    Science.gov (United States)

    Vaganova, Tamara A.; Gatilov, Yurij V.; Malykhin, Sergej E.; Pishchur, Denis P.; Larichev, Yurii V.; Rodionov, Vladimir I.; Malykhin, Evgenij V.

    2017-04-01

    The possibility of co-crystallization of polyfluoroaromatic meta-diamines with 18-crown-6 in the 2:1 ratio was tested using a large group of substrates with various frameworks (benzene, naphthalene, and pyridine) and substituents (H, Cl, CF3). Co-crystals of 2:1 stoichiometry were obtained from hexafluoro-2,7-naphthylenediamine, 4-trifluoromethyltrifluoro- and 2-trifluoromethyl-4,6-difluro-1,3-phenylenediamines, 4-chlorodifluoro-2,6-diaminopyridine. According to X-ray crystallographic data, associates of CF3-containing polyfluorophenylenediamines are 2D assemblies connected via synthon Car-N-H … Ocr. Polyfluorinated 2,7-diaminonaphthalene and 2,6-diamino-4-chloropyridine form 1D assemblies, in which the π-stacking of the naphthylenediamine molecules and the hydrogen bond Car-N-H … Npy, respectively, are the additional structure-supporting interactions. The co-crystallization of 18-crown-6 with less electron withdrawing arylenediamines gives only associates of stoichiometry 1:1 irrespective of the components ratio and the solvent nature. To rationalize the different co-crystallization behavior of the arylenediamines, the co-crystal structures were studied using a special version of the DFT, which accounts for the van der Waals interactions. The calculated difference between the specific sublimation enthalpies for the 1:1 and 2:1 associates was suggested to be a measure of the preferable co-crystallization ratio: the both types of associates are formed when |ΔΔHsubl| is smaller than 15 J g-1, a higher value indicates a significant energy preference for one of the structures. The experimental melting enthalpy values (DSC data) for the 1:1 and 2:1 co-crystals based on the same diamine are quite similar.

  5. Influence of marginal fit and cement types on microleakage of all-ceramic crown systems

    Directory of Open Access Journals (Sweden)

    Ece Yüksel

    2011-06-01

    Full Text Available The purpose of this study was to evaluate the effects of both marginal fit and cementing with different luting agents on the microleakage of all-ceramic crown systems. Thirty-six extracted upper central incisors were prepared for full-coverage crowns and were divided into three groups. Group 1: CAD/CAM-fabricated ZrO2, Group 2: Heat-pressed lithium-disilicate, and Group 3: Cast Cr-Co copings as the control group. Copings were made following standard techniques, and groups were assigned cementation with either self-adhesive resin cement (A or glass-ionomer luting cement (B. The specimens were subjected to thermocycling, immersed in basic fuchsin solution, sectioned mesiodistally and buccolingually. The surface of each section was digitally photographed under a stereomicroscope. Microleakage was scored using a five-point scale, and the marginal gap was measured using image analysis software. Data were statistically analyzed using 2-way ANOVA, Kruskal-Wallis, and Mann-Whitney U tests (α: 0.05. The marginal discrepancy of each group was 82.7 ± 7 µm, 92.6 ± 4 µm and 96.5 ± 7 µm respectively. Group 1 showed significantly smaller gaps than Group 3 (P = 0.042. Self-adhesive resin cement (A showed a lower level of microleakage than glass-ionomer luting cement (B in all groups (P = 0.029. Microleakage scores of '0' were 83% for 1A, 50% for 1B, 50% for 2A, 16% for 2B, 33% for 3A and none for 3B. Marginal discrepancy and cement type both had significant effects on microleakage. Lower levels of microleakage were recorded with self-adhesive resin cement, while CAD/CAM-fabricated ZrO2 copings showed smaller marginal discrepancy and less microleakage in comparison to cast Cr-Co.

  6. Mirror-image anterior crown fabrication with computer-aided design and rapid prototyping technology: a clinical report.

    Science.gov (United States)

    Cho, Seok-Hwan; Chang, Won-Gun

    2013-02-01

    This clinical report describes the fabrication of a maxillary central incisor single crown with rapid prototyping (RP) technology. A patient with a recently replaced metal ceramic crown had discomfort due to the nonanatomic lingual contour of the crown. With computer-aided design (CAD) software and rapid prototyping (RP) technology, the shape of the contralateral central incisor was duplicated and reproduced to make a mirror-image for a new crown. The prosthodontic planning and treatment approach are discussed.

  7. Spectrum of choices to restore the smile of a child: An update on current pediatric anterior crowns

    Directory of Open Access Journals (Sweden)

    Amit Kumar Sahu

    2016-01-01

    Full Text Available Esthetic treatment of severely damaged primary teeth is one of the greatest challenges to pediatric dentists. A wide variety of full coverage esthetic crowns for primary teeth are commercially available in the market. A practitioner should choose convenient, durable, and reliable solution which is fulfilled with complete knowledge of different crown forms. This article on esthetic crowns for children gives an outline of various anterior crowns in a tabular form, reviews their composition, advantages, disadvantages, and selection criteria.

  8. Time-dependent fracture probability of bilayer, lithium-disilicate-based, glass-ceramic, molar crowns as a function of core/veneer thickness ratio and load orientation.

    Science.gov (United States)

    Anusavice, Kenneth J; Jadaan, Osama M; Esquivel-Upshaw, Josephine F

    2013-11-01

    Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure. The aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6mm reduces the time-dependent fracture probability (Pf) of bilayer crowns with a lithium-disilicate-based glass-ceramic core, and (2) oblique loading, within the central fossa, increases Pf for 1.6-mm-thick crowns compared with vertical loading. Time-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass-ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic). Predicted fracture probabilities (Pf) for centrally loaded 1.6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8mm/0.8mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4mm/1.2mm). CARES/Life results support the proposed crown design and load orientation hypotheses. The application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures. Copyright © 2013 Academy of Dental Materials. All rights reserved.

  9. Co-inoculation with rhizobia and AMF inhibited soybean red crown rot: from field study to plant defense-related gene expression analysis.

    Directory of Open Access Journals (Sweden)

    Xiang Gao

    Full Text Available BACKGROUND: Soybean red crown rot is a major soil-borne disease all over the world, which severely affects soybean production. Efficient and sustainable methods are strongly desired to control the soil-borne diseases. PRINCIPAL FINDINGS: We firstly investigated the disease incidence and index of soybean red crown rot under different phosphorus (P additions in field and found that the natural inoculation of rhizobia and arbuscular mycorrhizal fungi (AMF could affect soybean red crown rot, particularly without P addition. Further studies in sand culture experiments showed that inoculation with rhizobia or AMF significantly decreased severity and incidence of soybean red crown rot, especially for co-inoculation with rhizobia and AMF at low P. The root colony forming unit (CFU decreased over 50% when inoculated by rhizobia and/or AMF at low P. However, P addition only enhanced CFU when inoculated with AMF. Furthermore, root exudates of soybean inoculated with rhizobia and/or AMF significantly inhibited pathogen growth and reproduction. Quantitative RT-PCR results indicated that the transcripts of the most tested pathogen defense-related (PR genes in roots were significantly increased by rhizobium and/or AMF inoculation. Among them, PR2, PR3, PR4 and PR10 reached the highest level with co-inoculation of rhizobium and AMF. CONCLUSIONS: Our results indicated that inoculation with rhizobia and AMF could directly inhibit pathogen growth and reproduction, and activate the plant overall defense system through increasing PR gene expressions. Combined with optimal P fertilization, inoculation with rhizobia and AMF could be considered as an efficient method to control soybean red crown rot in acid soils.

  10. A comparative study of retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements with stainless steel crowns - an in vitro study.

    Science.gov (United States)

    Raghunath Reddy, M H; Subba Reddy, V V; Basappa, N

    2010-01-01

    An in vitro study was conducted to compare the retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements using Instron universal testing machine. Thirty preformed and pretrimmed stainless steel crowns were used for cementation on 30 extracted human primary molars which were divided into three groups of 10 teeth in each group. Then the teeth were stored in artificial saliva and incubated at 37°C for 24 h. A load was applied on to the crown and was gradually increased till the crown showed dislodgement, and then the readings were recorded using Instron recorder and analyzed for statistical significance. The surface area of crown was measured by graphical method. The retentive strength was expressed in terms of kg/cm 2 , which was calculated by the equation load divided by area. Retentive strengths of zinc phosphate (ranged from a minimum of 16.93 to amaximum of 28.13 kg/cm 2 with mean of 21.28 kg/cm 2 ) and glass ionomer cement (minimum of 13.69 - 28.15 kg/cm 2 with mean of 20.69 kg/cm 2 ) were greater than that of polycarboxylate cement (minimum of 13.26 - 22.69 kg/cm 2 with mean of 16.79 kg/cm 2 ). Negligible difference (0.59 kg/cm 2 ) of retentive strength was observed between zinc phosphate (21.28 kg/cm 2 ) and glass ionomer cements (20.69 kg/cm 2 ). Glass ionomer cements can be recommended for cementation of stainless steel crowns because of its advantages and the retentive strength was almost similar to that of zinc phosphate cement.

  11. A comparative study of retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements with stainless steel crowns - An in vitro study

    Directory of Open Access Journals (Sweden)

    Raghunath Reddy M

    2010-01-01

    Full Text Available An in vitro study was conducted to compare the retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements using Instron universal testing machine. Thirty preformed and pretrimmed stainless steel crowns were used for cementation on 30 extracted human primary molars which were divided into three groups of 10 teeth in each group. Then the teeth were stored in artificial saliva and incubated at 37°C for 24 h. A load was applied on to the crown and was gradually increased till the crown showed dislodgement, and then the readings were recorded using Instron recorder and analyzed for statistical significance. The surface area of crown was measured by graphical method. The retentive strength was expressed in terms of kg/cm 2 , which was calculated by the equation load divided by area. Retentive strengths of zinc phosphate (ranged from a minimum of 16.93 to amaximum of 28.13 kg/cm 2 with mean of 21.28 kg/cm 2 and glass ionomer cement (minimum of 13.69 - 28.15 kg/cm 2 with mean of 20.69 kg/cm 2 were greater than that of polycarboxylate cement (minimum of 13.26 - 22.69 kg/cm 2 with mean of 16.79 kg/cm 2 . Negligible difference (0.59 kg/cm 2 of retentive strength was observed between zinc phosphate (21.28 kg/cm 2 and glass ionomer cements (20.69 kg/cm 2 . Glass ionomer cements can be recommended for cementation of stainless steel crowns because of its advantages and the retentive strength was almost similar to that of zinc phosphate cement.

  12. Automatic Tree-Crown Detection in Challenging Scenarios

    Science.gov (United States)

    Bulatov, Dimitri; Wayand, Isabell; Schilling, Hendrik

    2016-06-01

    In this paper, a new procedure for individual tree detection and modeling is presented. The input of this procedure consists of a normalized digital surface model NDSM, and a possibly error-prone classification result. The procedure is modular so that the functionality, the advantages and the disadvantages for every single module will be explained. The most important technical contributions of the paper are: Employing watershed transformation combined with classification results, applying hotspots detectors for identifying treetops in groups of trees, and correcting NDSM by detecting and geometric reconstruction of small anomalies, such as earth walls. Two minor contributions are made up by a detailed literature research on available methods for individual tree detection and estimation of tree-crowns for clearly identified trees in order to reduce arbitrariness by assigning trees to one of the few types in the output model.

  13. An update on crown lengthening. Part 1: Gingival tissue excess.

    Science.gov (United States)

    Kalsi, Harpoonam Jeet; Hussain, Zahra; Darbar, Ulpee

    2015-03-01

    This is the first article in a two-part series which aims to provide an overview of the different techniques used to increase clinical crown height. In the first paper, the focus will be on the management of patients who present with gingival tissue excess. The different aetiologies are discussed and illustrated with clinical cases, following which a range of procedures that may be employed in the management of these patients are presented. With an increasingly ageing population, more patients are taking regular medications prescribed from their general medical practitioner, and so having a working knowledge of the specific drugs that may cause gingival enlargement is essential. Clinical Relevance: When patients with gingival tissue excess present in primary or secondary care, a clinician must have a good knowledge of the possible causes of the condition, as well as an idea of how the patient may be managed.

  14. Stainless steel crown aspiration during sedation in pediatric dentistry.

    Science.gov (United States)

    Adewumi, A; Kays, David W

    2008-01-01

    Foreign body aspiration (FBA) causes death in more than 300 children every year in the United States. Morbidity and mortality are increased in children due to narrow airways and immature protective mechanisms. Factors to consider in pediatric dentistry are: (1) the patient's age and behavior; (2) presence and extent of disability; (3) local anesthesia; (4) body positioning; and (5) loose teeth. FBA requires prompt recognition and early treatment to minimize potentially serious and sometimes fatal consequences. The purpose of this case report was to describe the aspiration of a stainless steel crown in a 5-year-old boy during conscious sedation. It also discusses how a prompt and accurate diagnosis, early referral, and immediate treatment helped prevent serious complications.

  15. Fragment Reattachment after Atypical Crown Fracture in Maxillary Central Incisor

    Directory of Open Access Journals (Sweden)

    Vanessa Torraca Peraro Vaz

    2014-01-01

    Full Text Available Background. Fracture by trauma is one of the most common types of dental injury in the permanent dentition among children and teenagers. Aim. The aim of this study was to report the treatment performed to an atypical dental trauma case in a maxillary central incisor of a young patient by means of reattachment of the tooth fragment. Case Description. A 12-year-old male patient suffered a vertical crown fracture to the maxillary right central incisor. After clinical and radiographic examinations, a conservative restorative treatment which consisted in the reattachment of the tooth fragment with flow resin was performed in order to preserve the dental element and to obtain maximum aesthetics. Conclusion. The reattachment of fractured fragment is a fast and easy technique that can be used successfully as an option to restore dental element which suffered trauma. Clinical Significance. This technique restores the aesthetics and function of the dental element with minimal discomfort to the patient.

  16. The stainless steel crown debate: friend or foe?

    Science.gov (United States)

    Uston, Karen A; Estrella, Maria Regina P

    2011-01-01

    In this article, we will explore the use of the stainless steel crown (SSC) in dentistry today. For the pediatric population, many factors can affect the choice of restoration, such as the variations between primary and permanent tooth morphology, oral environment, and patient selection. The current literature and dentistry guidelines encourage dentists to make an informed decision when determining the restoration recommended for a carious primary molar. To further help educate dental providers on the topic of SSCs the following items will be reviewed: the indications; techniques for placement; advantages; and drawbacks when compared to alternative restorative materials. Regardless of personal opinion, the SSC should continue to be recognized for its efficiency, cost-effectiveness, and successful treatment modality.

  17. Rehabilitation of complicated crown-root fracture by invisible approach

    Directory of Open Access Journals (Sweden)

    V Leela Rani

    2016-01-01

    Full Text Available Dental trauma is one of the most common and significant problems met in all dental offices almost every day. In particular, injury to the anterior teeth is more vulnerable as it may affect the psychosocial behavior, severe emotional complications can occur leading to disturbances in their mental attitude. Cosmetic (lingual orthodontics is the recent development in the field of dentistry in the last few decades. Patients are more concerned about their appearance during the treatment and are affected by psychosocial issues because of labially placed brackets, thus leading to the evolution of lingual orthodontic appliances. In this article, we are sharing our clinical experience treating a complicated crown-root fracture using the lingual orthodontic technique.

  18. Management of Crown Root Fracture by Interdisciplinary Approach

    Directory of Open Access Journals (Sweden)

    K. Radhakrishnan Nair

    2013-01-01

    Full Text Available Fracture of tooth after trauma is distressing to a person because of the discomfort and pain due to pulpal injury. Crown root fractures of anterior teeth cause concomitant periodontal injury and there will be concern about appearance, and aesthetics. Management of pulpal and periodontal tissue relieves pain and restoration of tooth form regains patients confidence. Restoration of fractured tooth will be accepted readily if it is minimally invasive, less expensive, and aesthetically acceptable. Reattachment is an option for restoration of anterior teeth compared to other artificial replacements because of its appearance as natural. This method is favourable when the fractured fragment is intact and available. Utilization of pulp space for retention of fragment is achieved by the insertion of a dentine bonding post. This case report describes a case of tooth reattachment after trauma in which the pulp space is utilized to bond a fiber-reinforced post for retention after periodontal tissue management.

  19. Rehabilitation of complicated crown-root fracture by invisible approach

    Science.gov (United States)

    Rani, V. Leela; Rajalingam, S.; Hemalatha, R.; Jananee, J.

    2016-01-01

    Dental trauma is one of the most common and significant problems met in all dental offices almost every day. In particular, injury to the anterior teeth is more vulnerable as it may affect the psychosocial behavior, severe emotional complications can occur leading to disturbances in their mental attitude. Cosmetic (lingual) orthodontics is the recent development in the field of dentistry in the last few decades. Patients are more concerned about their appearance during the treatment and are affected by psychosocial issues because of labially placed brackets, thus leading to the evolution of lingual orthodontic appliances. In this article, we are sharing our clinical experience treating a complicated crown-root fracture using the lingual orthodontic technique. PMID:27829773

  20. Effect of wheel traffic and green manure treatments on forage yield and crown rot in alfalfa (Medicago sativa)

    Science.gov (United States)

    Harvesting alfalfa (Medicago sativa) results in mechanical wheel traffic on plants, which may damage crowns and increase the opportunity for entry of pathogens causing crown rot. Developing resistance to crown rot is problematic due to the large number of pathogens involved. Incorporation of plant b...

  1. A Rare Case of Crowned Dens Syndrome Mimicking Aseptic Meningitis

    Directory of Open Access Journals (Sweden)

    Teruyuki Takahashi

    2013-03-01

    Full Text Available Background: Crowned dens syndrome (CDS, related to microcrystalline deposition in the periodontoid process, is the main cause of acute or chronic cervical pain. Microcrystal-line deposition most often consists of calcium pyrophosphate dehydrate crystals and/or hydroxyapatite crystals. Case Presentation: This report describes the case of an 89-year-old woman who presented with sudden onset, high fever, severe occipital headache, and neck stiffness. A laboratory examination revealed a markedly elevated white blood cell count (11,100/µl and C-reactive protein level (23.8 mg/dl. These clinical findings suggested severe infection such as meningitis with sepsis. However, the results of blood culture, serum endotoxin, and procalcitonin were all negative, and cerebrospinal fluid studies revealed only a slight abnormality. The patient was first diagnosed with meningitis and treated with antiviral and antibiotic agents as well as non-steroidal anti-inflammatory drugs, but they only had limited effects. A cervical plain computed tomography (CT scan and its three-dimensional (3D reconstruction detected a remarkable crown-like calcification surrounding the odontoid process. On the basis of the CT findings, the patient was diagnosed as a severe case of CDS and was immediately treated with corticosteroids. The patient's condition drastically improved within a week after one course of corticosteroid therapy. Conclusion: Some atypical symptoms of CDS are misleading and may be misdiagnosed as meningitis, as happened in our case. A CT scan, especially a 3D-CT scan, is necessary and useful for a definitive diagnosis of CDS. CDS should be considered as a differential diagnosis of a possible etiology for fever, headache, and cervical pain of unknown origin.

  2. 4 '-acetyl benzo-15-crown-5 2-naphthyloxyacetyl hydrazone

    Institute of Scientific and Technical Information of China (English)

    ZHOU Yan-qing; WEI Tai-bao; ZHANG You-ming; ZONG Guo-qiang

    2004-01-01

    Aryloxyacetic acid and its derivatives often possess many important biological activities.Some of them are used as herbicides and plant-growth regulators. In continuation of our previous work on synthesis and biological activities1,2,3, we decided to design series of compounds containing the aryloxyacetyl group and crown ether to study the variation of bioactivities and the effect of the substituents on the ability of the crown ether to bind metal ions4,5. Recently, we determined related crystal structures6,7,8 , in order to study both bioactivities and coordination behaviour. In view of these encouraging results, the structure of the title compound (Figure 1), was obtained and is reported here.Figure 1 The molecule configuration and atom-numbering schem for the title compound,showing ellipsoids at the 50% probability level.Crystals of the ritle compound, C28H32N2O7, is monoclinic, space group P2(1)/c, a = 8.808(3), b =24.579(7), c =11.984(4), α = 90.00, β = 97.248(6), γ = 90.00, Z = 4, Dx= 1. 313 Mg m-3 ,Mo K α, λ =0.71073 , = 9.5mm-1 , F(000) = 1080, T =293(2) K, R = 0.0594, wR=0.1184 for 2575reflections [I>2 σ (Ⅰ) ] .The title compound adopts a syn-anti conformation, which enables N2-H...O6 intermolecule hydrogen bonds to be formed between centrosymmetrically related molecules. The resulting eight-membered rings join these molecules together as characteristic dimmers.

  3. Olive Crown Porosity Measurement Based on Radiation Transmittance: An Assessment of Pruning Effect

    Science.gov (United States)

    Castillo-Ruiz, Francisco J.; Castro-Garcia, Sergio; Blanco-Roldan, Gregorio L.; Sola-Guirado, Rafael R.; Gil-Ribes, Jesus A.

    2016-01-01

    Crown porosity influences radiation interception, air movement through the fruit orchard, spray penetration, and harvesting operation in fruit crops. The aim of the present study was to develop an accurate and reliable methodology based on transmitted radiation measurements to assess the porosity of traditional olive trees under different pruning treatments. Transmitted radiation was employed as an indirect method to measure crown porosity in two olive orchards of the Picual and Hojiblanca cultivars. Additionally, three different pruning treatments were considered to determine if the pruning system influences crown porosity. This study evaluated the accuracy and repeatability of four algorithms in measuring crown porosity under different solar zenith angles. From a 14° to 30° solar zenith angle, the selected algorithm produced an absolute error of less than 5% and a repeatability higher than 0.9. The described method and selected algorithm proved satisfactory in field results, making it possible to measure crown porosity at different solar zenith angles. However, pruning fresh weight did not show any relationship with crown porosity due to the great differences between removed branches. A robust and accurate algorithm was selected for crown porosity measurements in traditional olive trees, making it possible to discern between different pruning treatments. PMID:27213391

  4. Modelling initial mortality of Abies religiosa in a crown fire in Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Temiño-Villota, S.; Rodríguez-Trejo, D.A.; Molina Terrén, D.M.; Ryan, K.

    2016-07-01

    Aim of the study: The objectives of this work were to determine which morphological and fire severity variables may help explain the mortality of adult Abies religiosa (Kunth) Schltdl. & Cham., to model the probability of this species after being affected by crown fire, and to obtain more elements to classify the sacred fir in terms of fire resistance. This type of studies are relevant to estimate the impact of crown fires on the climax forests that forms this species. Area of study: The burned forest was located in the southern Mexico City, borough. Material and methods: Morphological variables and fire severity indicators were collected for 335 Abies religiosa trees burned by a mixed severity fire. Logistic regression was used to analyze data and develop models that best explained tree mortality. Main results: Survival was 26.9%. The models for height (p≤0.0001), diameter at breast height (p=0.0082), crown length (p≤0.0001) and crown base height (p≤0.0001) were significant, with a negative relationship between each one of these variables and probability of mortality. The significant severity variables were lethal scorch height (p≤0.0001) and crown kill (p≤ 0.0001), which have a direct relationship with probability of mortality. Highlights: This species is moderately fire-resistant. Crown kill ≥ 70% markedly increases mortality. Silvicultural activities such as pruning, thinning and fuel management can reduce the risk of crown fires. (Author)

  5. Identification of genes involved in the response of banana to crown rot disease.

    Science.gov (United States)

    Lassois, Ludivine; Frettinger, Patrick; de Lapeyre de Bellaire, Luc; Lepoivre, Philippe; Jijakli, Haissam

    2011-01-01

    Variations in banana susceptibility to crown rot disease have been observed but the molecular mechanisms underlying these quantitative host-pathogen relationships are still unknown. This study was designed to compare gene expression between crowns of banana fruit showing a high susceptibility (S(+)) and crowns showing a low susceptibility (S(-)) to the disease. Comparisons were performed at two situation times: i) between crowns (S(+) and S(-)) collected 1 h before inoculation and ii) between crowns (S+ and S-) collected 13 days after inoculation. Gene expression comparisons were performed with cDNA-amplified fragment length polymorphism (AFLP) and results were confirmed by real-time reverse-transcription polymerase chain reaction. Among genes identified as differentially expressed between S(+) and S(-) crowns, two were involved in signal transduction, three in proteolytic machinery, two had similarity to pathogenesis-related protein 14, one to a CCR4-associated factor protein, and one to a cellulose synthase. Paradoxically, the overexpression of the cellulose synthase gene was associated with banana showing a high susceptibility in both pre- and post-inoculation situations. Finally, the cDNA-AFLP identified a gene that seems to be associated with the quantitative banana responses to crown rot disease; this gene encodes a dopamine-β-monooxygenase, which is involved in the catecholamine pathway. To our knowledge, this work is the first to address both pre- and post-infection gene expression with the same host-pathogen combination and distinct susceptibility levels.

  6. Olive Crown Porosity Measurement Based on Radiation Transmittance: An Assessment of Pruning Effect

    Directory of Open Access Journals (Sweden)

    Francisco J. Castillo-Ruiz

    2016-05-01

    Full Text Available Crown porosity influences radiation interception, air movement through the fruit orchard, spray penetration, and harvesting operation in fruit crops. The aim of the present study was to develop an accurate and reliable methodology based on transmitted radiation measurements to assess the porosity of traditional olive trees under different pruning treatments. Transmitted radiation was employed as an indirect method to measure crown porosity in two olive orchards of the Picual and Hojiblanca cultivars. Additionally, three different pruning treatments were considered to determine if the pruning system influences crown porosity. This study evaluated the accuracy and repeatability of four algorithms in measuring crown porosity under different solar zenith angles. From a 14° to 30° solar zenith angle, the selected algorithm produced an absolute error of less than 5% and a repeatability higher than 0.9. The described method and selected algorithm proved satisfactory in field results, making it possible to measure crown porosity at different solar zenith angles. However, pruning fresh weight did not show any relationship with crown porosity due to the great differences between removed branches. A robust and accurate algorithm was selected for crown porosity measurements in traditional olive trees, making it possible to discern between different pruning treatments.

  7. Modelling initial mortality of Abies religiosa in a crown fire in Mexico

    Directory of Open Access Journals (Sweden)

    Salomé Temiño-Villota

    2016-04-01

    Full Text Available Aim of study: The objectives of this work were to determine which morphological and fire severity variables may help explain the mortality of adult Abies religiosa (Kunth Schltdl. & Cham., to model the probability of this species after being affected by crown fire, and to obtain more elements to classify the sacred fir in terms of fire resistance. This type of studies are relevant to estimate the impact of crown fires on the climax forests that forms this species.Area of study: The burned forest was located in the southern Mexico City, borough.Material and methods: Morphological variables and fire severity indicators were collected for 335 Abies religiosa trees burned by a mixed severity fire. Logistic regression was used to analyze data and develop models that best explained tree mortality.Main results: Survival was 26.9%. The models for height (p≤0.0001, diameter at breast height (p=0.0082, crown length (p≤0.0001 and crown base height (p≤0.0001 were significant, with a negative relationship between each one of these variables and probability of mortality. The significant severity variables were lethal scorch height (p≤0.0001 and crown kill (p≤ 0.0001, which have a direct relationship with probability of mortality.Highlights: This species is moderately fire-resistant. Crown kill ≥ 70% markedly increases mortality. Silvicultural activities such as pruning, thinning and fuel management can reduce the risk of crown fires.

  8. Analysis of crown widths in subjects with congenitally missing maxillary lateral incisors.

    Science.gov (United States)

    Mirabella, A Davide; Kokich, Vincent G; Rosa, Marco

    2012-12-01

    The aim of the study was to test the hypothesis that the gene defect causing congenital absence of maxillary lateral incisors also causes narrowing of the dentition. A total of 81 patients with one or two congenitally missing lateral incisors were retrieved; 52 (64.2 per cent) patients presented bilateral agenesis, whereas 29 (35.8 per cent) had unilateral agenesis. The control group consisted of 90 consecutively treated patients. The largest mesiodistal crown dimension for all teeth, except for the maxillary second and third molars, was measured on plaster casts using a digital caliper to the nearest 10th of a millimetre. Statistical testing was performed using the analysis of variance model (P < 0.05) to test for differences in the mesiodistal dimension between the sample and the control group. Significance has been assessed using a P-value threshold level of 5 per cent. Agenesis of maxillary lateral incisors was found to be a significant predictor of tooth size. Patients who were missing maxillary lateral incisors had smaller teeth compared to control subjects, except for the maxillary right and left first molars. This finding was true for both unilateral and bilateral lateral incisor agenesis. Interaction between maxillary lateral incisor agenesis and gender was not significant. Patients with congenitally missing lateral incisors have narrower teeth than patients without any dental anomalies, except for maxillary first molars. A higher prevalence of microdontic contralateral incisors was found in patients with unilateral agenesis with respect to the control group.

  9. Eleven-Year Retrospective Survival Study of 275 Veneered Lithium Disilicate Single Crowns.

    Science.gov (United States)

    Simeone, Piero; Gracis, Stefano

    2015-01-01

    The aim of the present clinical retrospective study was to evaluate the long-term survival and clinical performance of veneered lithium disilicate single restorations in anterior and posterior areas after up to 11 years. Following a rigid protocol, 275 lithium disilicate single crowns (35 IPS Empress II and 240 e.max Press) were cemented over 11 years, in 106 patients, using an adhesive technique; of these 106 were anterior (38.5%) and 169 posterior (61.5%) teeth. Teeth receiving endodontic therapy and composite reconstruction (50%) and teeth with preexisting metalceramic crowns, called prosthetic retreatments (PR; 65%), were included as well. Of the 106 patients enrolled in the study, 25 (23.5%) were diagnosed with bruxism habits, and 7 of these patients (6.6% of all patients) received full-mouth single lithium disilicate restorations (FMR). The exclusion criteria for this retrospective clinical study were: monolithic lithium disilicate crowns, teeth with cast post and cores, implant-supported all-ceramic crowns, active periodontitis, and/or poor oral hygiene. Clinical reevaluation was performed by the clinicians who prepared and luted them during maintenance appointments between January 2012 and October 2013. Number of restoration failures and characteristics of failures were recorded. Marginal adaptation and marginal discoloration were evaluated based on the Cvar-Ryge criteria. The overall cumulative survival rate was 98.2%. The failures recorded were the result of either mechanical failure or debonding. Five crowns failed mechanically-three because of chipping and two because of core fracture-and were replaced. None of the failed crowns was associated with the bruxers with FMR. A total of 15 crowns debonded (5.5% of all crowns); however, 11 belonged to the same patient who had endodontically treated and reconstructed abutments. In this retrospective clinical evaluation of up to 132 months, veneered lithium disilicate single crowns had a low failure rate.

  10. Early complications and performance of 327 heat-pressed lithium disilicate crowns up to five years

    Science.gov (United States)

    2016-01-01

    PURPOSE The prospective follow-up aimed to assess the performance of lithium disilicate crowns and clinical reasons of adverse events compromising survival and quality. MATERIALS AND METHODS 58 patients were treated with 375 heat-pressed monolithic crowns, which were bonded with resin cement. Annual recalls up to five years included a complete dental examination as well as quality assessment using CDA-criteria. Any need for clinical intervention led to higher complication rate and any failure compromised the survival rate. Kaplan-Meier-method was applied to all crowns and a dataset containing one randomly selected crown from each patient. RESULTS Due to drop-outs, 45 patients (31 females, 14 males) with the average age of 43 years (range = 17–73) who had 327 crowns (176 anterior, 151 posterior; 203 upper jaw, 124 lower jaw) were observed and evaluated for between 4 and 51 months (median = 28). Observation revealed 4 chippings, 3 losses of retention, 3 fractures, 3 secondary caries, 1 endodontic problem, and 1 tooth fracture. Four crowns had to be removed. Survival and complication rate was estimated 98.2% and 5.4% at 24 months, and 96.8% and 7.1% at 48 months. The complication rate was significantly higher for root canal treated teeth (12%, P<.01) at 24 months. At the last observation, over 90% of all crowns showed excellent ratings (CDA-rating Alfa) for color, marginal fit, and caries. CONCLUSION Heat pressed lithium disilicate crowns showed an excellent performance. Besides a careful luting, dentists should be aware of patients' biological prerequisites (grade of caries, oral hygiene) to reach full success with these crowns. PMID:27350853

  11. Fracture resistance of a selection of full-contour all-ceramic crowns: an in vitro study.

    Science.gov (United States)

    Zesewitz, Tim F; Knauber, Andreas W; Northdurft, Frank P

    2014-01-01

    This study aimed to evaluate the fracture resistance of monolithic single crowns made from zirconia (ZI), lithium disilicate (LS2), or feldspar ceramic (FC). Five groups of crowns representing a maxillary first molar were made with the appropriate dimensions according to the manufacturer's instructions. The ZI and LS2 crowns were luted adhesively or cemented conventionally on a metal abutment tooth analog. The feldspar ceramic crowns were luted adhesively. All specimens underwent axial loading until fracture. The crowns in the ZI groups possessed the highest fracture resistance independent of the mode of fixation.

  12. Effect of the shades of background substructures on the overall color of zirconia-based all-ceramic crowns

    OpenAIRE

    Suputtamongkol, Kallaya; Tulapornchai, Chantana; Mamani, Jatuphol; Kamchatphai, Wannaporn; Thongpun, Noparat

    2013-01-01

    PURPOSE The objective of this study was to determine the effect of the color of a background substructure on the overall color of a zirconia-based all-ceramic crown. MATERIALS AND METHODS Twenty one posterior zirconia crowns were made for twenty subjects. Seven premolar crowns and six molar crowns were cemented onto abutments with metal post and core in the first and second group. In the third group, eight molar crowns were cemented onto abutments with a prefabricated post and composite core ...

  13. The Influence of Implant Abutment Surface Roughness and the Type of Cement on Retention of Implant Supported Crowns

    Science.gov (United States)

    Reddy, M. Sushender; Reddy, C. Rajaneesh; Pithani, Padmaja; R, Santosh Kumar; Kulkarni, Ganesh

    2015-01-01

    Objectives: To provide relative data on the retentive characters of the commonly used cements on different implant abutment surfaces. Materials and Methods: A total of 20 implant abutments were divided into 2 groups. Ten implants were unaltered and ten were air borne particle abraded with 50μ aluminium oxide. Three luting agents (Tempbond, IRM and ImProv) were used to secure the crowns to abutments. All the crowns were removed from the abutment with an Instron machine at 0.5mm per minute and tensile bond strengths were recorded. Statistical analysis was performed using Anova, Paired t-test and Post-Hoc tests. Results: IRM showed the highest mean tensile strength among the three cements when used with treated and untreated implant abutment surfaces. Change in the abutment surface roughness had no effect on the mean tensile bond strength of TempBond and IRM cements, whereas ImProv cement showed reduced tensile strength with sandblasted surface. Conclusion: When increased retention is required IRM cement with either sandblasted or milled surface could be used and when retrievability is required cements of choice could be either TempBond or ImProv. PMID:25954694

  14. Strength of CAD/CAM-generated esthetic ceramic molar implant crowns

    OpenAIRE

    D. Wolf; Bindl, A; Schmidlin, P.R; Lüthy, H; Mörmann, W H

    2008-01-01

    PURPOSE: One-visit in-office CAD/CAM fabrication of esthetic ceramic crowns as a superstructure for posterior implants is quite new. The aim of the study was to evaluate the strength of esthetic ceramic CAD/CAM crowns with varied occlusal thickness and seated with adhesive and nonadhesive cements on titanium and zirconia abutments. MATERIALS AND METHODS: Esthetic ceramic CAD/CAM-generated molar crowns (n = 15 per group) with occlusal thicknesses of 0.5 mm and 1.5 mm were seated on titanium (1...

  15. Formation of the biologic width following crown lengthening in nonhuman primates.

    Science.gov (United States)

    Oakley, E; Rhyu, I C; Karatzas, S; Gandini-Santiago, L; Nevins, M; Caton, J

    1999-12-01

    The purpose of this study was to determine if and how the biologic width is reestablished following surgical crown lengthening. Crown-lengthening surgery was performed on the right or left maxillary and mandibular central and lateral incisors of three adult monkeys, with contralateral teeth serving as unoperated controls. Twelve weeks after surgery, tissue blocks were removed for histologic analysis. The results of a histometric evaluation indicate that the biologic width is reestablished following surgical crown lengthening. The junctional epithelium generally migrates to the apical level of root planing. Space for the supracrestal connective tissue fiber groups is created by crestal resorption of alveolar bone.

  16. A biological approach to crown fracture: Fracture reattachment: A report of two cases.

    Science.gov (United States)

    Vijayaprabha, K; Marwah, Nikhil; Dutta, Samir

    2012-09-01

    The development of adhesive dentistry has allowed dentists to use the patient's own fragment to restore the fractured tooth, which is considered to be the most conservative method of treatment of crown fracture allowing restoration of original dental anatomy, thus rehabilitating function and esthetics in a short time by preserving dental tissues. The tooth fragment reattachment is preferred over full coverage crowns or composite resin restoration because it conserves sound tooth structure, and is more esthetic, maintaining the original anatomy and translucency, and the rate of incisal wear also matches that of original tooth structure. Presented here is a report of two cases of crown fracture managed by reattachment procedures.

  17. Multidisciplinary and esthetic approach to clinical crown lengthening: report of a case.

    Science.gov (United States)

    Ngan, P; Knobloch, L

    1993-12-01

    This paper describes the combined efforts of an orthodontist, periodontist, and a restorative dentist to save an unrestorable tooth by clinical crown lengthening. A maxillary lateral incisor, originally treatment planned for extraction, was treated with orthodontic extrusion, circumferential fiberotomy, and metal-ceramic crown restoration. To maximize the esthetic appearance of the tooth during orthodontic treatment, an acrylic resin facing was designed together with the orthodontic appliance used to facilitate vertical extrusion. Clinical crown lengthening may be used as an alternative approach to the treatment of severely broken down anterior teeth.

  18. Study and application of crown feedback control in hot strip rolling

    Institute of Scientific and Technical Information of China (English)

    Xiaodong Wang; Anrui He; Quan Yang; Zhi Xie; Hongtao Yang

    2007-01-01

    Crown feedback control is one part of the automatic shape control (ASC) system. On the basis of large simulation researches conducted, a linear crown feedback control model was put forward and applied in actual strip rolling. According to its successful operation in the ASP 1700 hot strip mill of Angang Group for one year and also from the statistical results of several crown measurements, it can be definitely said that this control model is highly effective and shows stable performance. The control effectiveness of different gauges of strips with the feedback control is found to increase by 10%-30% compared with that without feedback control.

  19. Internal fit of two all-ceramic systems and metal-ceramic crowns

    OpenAIRE

    Leandro Moura Martins; Fabio Cesar Lorenzoni; Alcides Oliveira de Melo; Luciana Mendonça da Silva; José Luiz G. de Oliveira; Pedro Cesar Garcia de Oliveira; Gerson Bonfante

    2012-01-01

    Objectives: The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. Material and Methods: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns wa...

  20. An esthetic technique for veneering anterior stainless steel crowns with composite resin.

    Science.gov (United States)

    Wiedenfeld, K R; Draughn, R A; Welford, J B

    1994-01-01

    The restoration of primary anterior teeth presents complicated esthetic and retention problems to the clinician. A technique is described for the chairside veneering of composite resin to stainless steel crowns, which results in well contoured restorations with superior durability and esthetics. A trimmed and fitted stainless steel crown can be veneered in three to five minutes. This provides the adaptability and gingival contour benefits of the stainless steel crown in conjunction with the cosmetics of the composite facings. The technique described produced composite veneers with a mean sheer bond strength of 3520 PSI (24.4 Mpa).