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Sample records for synthesized dilaktam crown

  1. Dental crowns

    Science.gov (United States)

    ... than metal crowns Match the color of other teeth May be a good choice if you have a metal allergy Porcelain fused to metal crowns: Are made from porcelain covering a metal crown Metal makes the crown stronger Porcelain part is more prone to fracture than crowns made of all porcelain After the ...

  2. Selective sensing of mercury(II) using PVC-based membranes incorporating recently synthesized 1,3-alternate thiacalix[4]crown ionophore.

    Science.gov (United States)

    Mahajan, Rakesh Kumar; Kamal, Ajar; Kumar, Naresh; Bhalla, Vandana; Kumar, Manoj

    2013-05-01

    The construction and electrodes characteristics of poly(vinylchloride) (PVC)-based polymeric membrane electrode (PME) and coated graphite electrode (CGE), incorporating 1,3-alternate thiacalix[4]crown as ionophore for estimation of Hg(II) ions, are reported here. The best potential response was observed for PME-1 having membrane composition of: ionophore (6.2 mg), PVC (100.0 mg), 2-nitrophenyl octyl ether (2-NPOE; 200.0 mg), and sodium tetraphenyl borate (NaTPB; 2.0 mg); for CGE-1 with the membrane composition: ionophore (3.5 mg), PVC (40.0 mg), 2-NPOE (80.0 mg), and NaTPB (2.0 mg). The electrodes exhibits Nernstian slope of 29.16 mV/decade with PME-1 and 30.39 mV/decade with CGE-1 for Hg(II) ions over wide concentration range, i.e., 1.0 × 10(-1) to 5.0 × 10(-6) M with PME-1 and 1.0 × 10(-1) to 5.0 × 10(-7) M with CGE-1. Lower detection limits were found to be 9.77 × 10(-6) M for PME-1 and 7.76 × 10(-7) M for CGE-1 with response time varying from 10 to 20 s. Also, these electrodes work within pH range of 2.0-6.0 for PME-1 and 1.5-6.5 for CGE-1. Overall, CGE-1 has been found to be better than PME-1. CGE-1 has been used as indicator electrode for the potentiometric titration of Hg(II) ions with EDTA as well as successfully applied for determination of Hg(II) content in wastewater, insecticide, dental amalgam, and ayurvedic medicines samples with very good performance (0.9974 correlation coefficient in the comparison against volumetric method).

  3. Dinar-crown banknotes

    OpenAIRE

    Pantelić Svetlana

    2017-01-01

    Dinar-crown banknotes were: ½ dinars (i.e. 2 crowns), 1 dinar (i.e. 4 crowns), 5 dinars (i.e. 20 crowns), 10 dinars (i.e. 40 crowns), 20 dinars (i.e. 80 crowns), 100 dinars (i.e. 400 crowns), and 1000 dinars (i.e. 4000 crowns). The ½- and 1-dinar banknotes are assumed to have been issued in 1919, whereas the other five banknotes, according to one source, were released into circulation on 21.02.1920. Pursuant to the regulations, the replacement of the nostrified crown banknotes by the new crow...

  4. Dinar-crown banknotes

    Directory of Open Access Journals (Sweden)

    Pantelić Svetlana

    2017-01-01

    Full Text Available Dinar-crown banknotes were: ½ dinars (i.e. 2 crowns, 1 dinar (i.e. 4 crowns, 5 dinars (i.e. 20 crowns, 10 dinars (i.e. 40 crowns, 20 dinars (i.e. 80 crowns, 100 dinars (i.e. 400 crowns, and 1000 dinars (i.e. 4000 crowns. The ½- and 1-dinar banknotes are assumed to have been issued in 1919, whereas the other five banknotes, according to one source, were released into circulation on 21.02.1920. Pursuant to the regulations, the replacement of the nostrified crown banknotes by the new crown- dinar banknotes started on 3 February 1920 in Serbia and Montenegro and on 16 February 1920 in other parts of the country. All seven denominations of the dinar-crown banknotes were being withdrawn from circulation throughout a lengthy period of time from 21 February 1921 until May 1934. The first to be withdrawn were the 20-dinar banknotes, from 1 February to 30 April 1921, then the 5-dinar banknotes, from 20 July to 20 November 1922, and the 10-dinar banknotes, from 10 February to 10 June 1924. The 100-dinar (400-crown and 1000-dinar (4000-crown banknotes remained in circulation the longest. The withdrawal of the 100- and 1000-dinar banknotes started in 1929 and lasted until 25 May 1934. The 1924 rulebook on minting coins of ½, 1 and 2 dinars precisely defines their withdrawal from circulation and replacement by minted coins within one year after the last batch of minted coins gets released into circulation. However, in 1927 the decree of the Minister of Finance prescribed that the remaining paper banknotes be withdrawn from circulation on 30 September 1927 by being replaced by the metal coins of the same denominations.

  5. Crowns and Crypts

    Indian Academy of Sciences (India)

    The product was isolated to be dibenzo-. 18-Crown-6. Many other crowns were ... fashion with their lone pairs pointing inward towards the metal atom. The bonding M-O is largely ... Macrocycles, though extremely effective as polydentate ligands, are not essential for the production of stable alkali complexes; additional ...

  6. 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...

  7. 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.

  8. Crowns and Crypts

    Indian Academy of Sciences (India)

    biologically occurring natural compounds they are expected to provide insight into the biological phenomena occurring in living systems. For example, the mechanism of the sodium pump occurring across a cell membrane could be understood using the formation of the alkali metal-crown complex mecha- nism as a model.

  9. Crowns and Crypts

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 6; Issue 6. Crowns and Crypts - A Fascinating Group of Multidentate Macrocyclic Ligands. Debasis Bandyopadhyay. General Article Volume 6 Issue 6 June 2001 pp 71-79. Fulltext. Click here to view fulltext PDF. Permanent link:

  10. 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

  11. Selective crystallization of cations with crown ethers

    International Nuclear Information System (INIS)

    Heffels, Dennis Egidius

    2014-01-01

    The aim of this work was to study the selectivity and preferences of the incorporation of differently sized cations in the cavities of various crown ethers and the characterization of the resulting compounds. The coordination preferences of crown ethers with different cavities have long been known, and the impact of other effects on the structure formation have increasingly become the focus of attention. In this work a comparative overview of the coordination preferences depending on various factors was undertaken. The focus was mainly on the variation of the cavity of the crown ether in the presence of differently sized cations. In addition, the effects of the solvent and differently coordinating anions have been investigated. Within the framework of this work, basic coordination preferences could be detected with rare earth nitrates, which are affected particularly by the choice of the solvent. The formation of different types of structures could be controlled by varying the conditions such that the incorporation of the cation in the cavity of the crown ether was influenced and the formation of a particular type of structure can be influenced partly by the choice of solvent. In this case no direct preferences for the incorporation into the cavity of the crown ether in relation to the cation size were observed for rare earth cations. However, the coordination of the crown ether leads in each case - for lanthanides - to rather high coordination numbers. A total of five new rare earth complexes and two structural variants could be observed with crown ethers. In the study of the selectivity of the incorporation into the cavity, known structures were also reproduced and further structures were characterized but the crystal structures not entirely solved. With the use of monovalent cations such as potassium, lithium or silver a total of nine new compounds could be synthesized, while no clear preferences for the incorporation of certain cations were detected. The

  12. Calix salophen crown ethers as receptors for neutral molecules

    NARCIS (Netherlands)

    Reichwein, A.M.; Reichwein, Arjen M.; Verboom, Willem; Harkema, Sybolt; Spek, Anthony L.; Reinhoudt, David

    1994-01-01

    The calix[4]arene based salophen crown ethers 7 and 8 were synthesized as lipophilic carriers for neutral molecules. The X-ray structures of the H2O, CH3OH and (CH3)2SO complexes of 8a have been determined.

  13. Crowned dens syndrome

    Directory of Open Access Journals (Sweden)

    Norma Belfiore

    2012-10-01

    Full Text Available Introduction Microcrystalline deposition in peri-odontoid articular structures is mainly responsible for acute or chronic cervical pain and is known as “crowned dens syndrome”.Materials and methods We described two cases of acute cervical pain associated with onset of fever and peripheral acute monoarthritis. Cervical computed tomography (CT scan showed linear calcification of the retrodens ligament and calcium pyrophosphate dehydrate (CPPD crystals were found in synovial fluid of inflamed joints. Both patients were treated with anti-inflammatory drugs and colchicine.Discussion Calcium depositions around the odontoid process of the axis can be occasionally detected by radiological studies. They are frequently asymptomatic but sometimes can be associated with severe neurological abnormalities, fever and acute neck pain. CPPD crystals are usually deposited in joints and bursae but occasionally can disrupt these anatomical confines and deposit in periarticular tissues, sometimes forming large masses confused with tumours.Conclusions Acute onset of cervical neck pain associated with elevation of inflammatory indicators and/or signs of cervical myelopathy should suggest CT scans searching for microcrystal depositions in the peryodonthoid tissue. Differential diagnosis of fever of unknown origin (FUO should include crowned dens syndrome specially in the elderly after exclusion of several endocrine or metabolic disorders, infection diseases (meningitis, arthritis (psoriatic arthritis and ankylosing spondylitis and tumours (chordoma, meningioma, osteoblastoma.

  14. 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

  15. 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

  16. Crown rust control on oats

    International Nuclear Information System (INIS)

    Frey, K.J.; Browning, J.A.; Simons, M.D.

    1976-01-01

    Attempts have been made to test the relative effectiveness of EMS treatment for inducing tolerance to crown rust among oat strains Clintland-60 of different ploidy levels. One strain of diploid and one of tetraploid oats were treated with EMS. These two strains are as susceptible to damage from crown rust as are cultivars of hexaploid oats. Multiline cultivars of oats have been shown to provide adequate protection from economic loss due to crown-rust disease in Iowa. Since 1968, eleven multiline cultivars of oats have been released from the Iowa station for use in commercial production in the midwestern USA. During the past two winter seasons, the effectiveness of multiline oat cultivars against crown-rust disease has been researched in Texas, USA, which has a ''long rust season'' of about four months, not an Iowa ''short rust season''. The protection against crown rust afforded by the multiline cultivars appeared equally good in Texas and Iowa. The seasonal productions of crown-rust spores relative to completely resistant and susceptible checks were nearly identical in both environments. Fifteen new isolines of oats have been developed for use in multiline varieties, with seed supplies sufficiently large for immediate use

  17. Wave Forces on Crown Walls

    DEFF Research Database (Denmark)

    Pedersen, Jan; Burcharth, H. F.

    1993-01-01

    This paper presents some of the results from a large parametric laboratory study including more than 200 long-duration model tests. The study addresses both the wave forces imposed on the breakwater crown wall as well as the performance of the structure in reducing the wave overtopping. The testing...... programme includes variations of the sea state parameters and of the geometrical configuration of the breakwater and crown wall. Basic relations between forces/overtopping and the varied parameters are examined and preliminary design guidelines for structures within the tested range of variations...

  18. 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...

  19. Removal of failed crown and bridge

    OpenAIRE

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

    2012-01-01

    Crown and bridge have life span of many years but they fail for a number of reasons. Over the years, many devices have been designed to remove crowns and bridges from abutment teeth. While the removal of temporary crowns and bridges is usually very straightforward, the removal of a definitive cast crown with unknown cement is more challenging. Removal is often by destructive means. There are a number of circumstances, however, in which conservative disassembly would aid the practitioner in co...

  20. Equations to convert compacted crown ratio to uncompacted crown ratio for trees in the Interior West

    Science.gov (United States)

    Chris Toney; Matthew C. Reeves

    2009-01-01

    Crown ratio is the proportion of total tree length supporting live foliage. Inventory programs of the US Forest Service generally define crown ratio in terms of compacted or uncompacted measurements. Measurement of compacted crown ratio (CCR) involves envisioning the transfer of lower branches of trees with asymmetric crowns to fill holes in the upper portion of the...

  1. Synthesis and characterization of solid complex of thorium nitrate with dibenzo-24-crown-8

    International Nuclear Information System (INIS)

    Gan Xinmin; Tan Minyu

    1988-01-01

    The solid complex of thorium nitrate with dibenzo-24-crown-8 (DB24C8), having the composition Th(NO 3 ) 4 ·DB24C8·2H 2 O, has been synthesized in acetonitrile medium and characterized by elemental analysis, molar conductance, infrared spectra, differential thermal analyses(DTA)and thermogravimetry(TG)

  2. Synthesis of Novel 8-Hydroxyquinoline-Containing Diaz-18-Crown-6 Ligands and Analogues

    National Research Council Canada - National Science Library

    Su, Ning

    1999-01-01

    ...) were synthesized via a one-pot or stepwise Mannich reaction, reductive amination, or by reacting diaza-18-crown-6 with 5,7-dichloro-2-iodomethyl-8-quinolinol in the presence of N,N-diisopropylethylamine (Schemes 1 and 2...

  3. Crown structure of Picea omorika trees in the plantation

    OpenAIRE

    Krstić M.; Stavretović N.; Isajev V.; Bjelanović I.

    2012-01-01

    The study was carried out in Serbian spruce (Picea omorika Panč/Purkynĕ) plantations in the western Serbia. The paper presents results of the analysis of crown development. The following elements were analyzed: total tree height, height of the crown base, absolute and relative crown length, maximal crown diameter, coefficient of crown spreading and degree of crown girth. We discuss approaches to the modeling of tree crown growth and development, growing under favorable environmental and...

  4. Pericoronal radiolucency associated with incomplete crown

    International Nuclear Information System (INIS)

    Nah, Kyung Soo

    2013-01-01

    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.

  5. 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.

  6. Fracture resistance of various temporary crown materials.

    Science.gov (United States)

    Yilmaz, Asude; Baydaş, Seyfettin

    2007-01-01

    The aim of this study was to evaluate the fracture resistance of various provisional crown materials using an in vitro model test system. In the present study polycarbonate crowns, prefabricated by the manufacturer (3M Polycarbonate Crown), and the temporary crowns, fabricated in the dental laboratory environment, were fabricated using bis-acryl composite (Protemp II), autopolymerizing PMMA resin (BISICO Temp S), and heat-polymerized PMMA resin (Major C&B-V Dentine). All temporary crowns were stored in distilled water for 24 hours at room temperature prior to testing. The crowns were seated on metal dies, fabricated from Cr-Co alloy (AZ Dental, Konstanz, Germany), and then tested using the indenter of a Hounsfield testing machine (Hounsfield Tensometer, Hounsfield Test Equipment, Raydon, England). The tip of the indenter was located at a position one-third of the way down the inciso-palatine surface at 135 masculine. The data were statistically analyzed for differences using one-way analysis of variance (ANOVA) and the Tukey HSD test (P crowns were significantly different from the BISICO Temp S, Protemp II, and Major C&B-V Dentine (P crowns may be preferable to the other types of temporary crowns used in this study.

  7. All-ceramic crowns: bonding or cementing?

    Science.gov (United States)

    Pospiech, Peter

    2002-12-01

    Despite the wide variety of all-ceramic systems available today, the majority of dental practitioners hesitate to recommend and insert all-ceramic crowns. This article regards the nature of the ceramic materials, the principles of bonding and adhesion, and the clinical problems of the acid-etch technique for crowns. Advantages and disadvantages are discussed, and the influences of different factors on the strength of all-ceramic crowns are presented. Finally, the conclusion is drawn that conventional cementing of all-ceramic crowns is possible when the specific properties of the ceramics are taken into consideration.

  8. Incorporating crown dimensions into stem height and basal area for ...

    African Journals Online (AJOL)

    Four crown dimensions (crown diameter, crown projection area, crown length and crown ratio) were each incorporated into nonlinear individual tree total height and basal area increment models for African white wood (Triplochiton scleroxylon K. Schum). The basic height/basal area growth model was formulated as a ...

  9. Equations for predicting uncompacted crown ratio based on compacted crown ratio and tree attributes.

    Science.gov (United States)

    Vicente J. Monleon; David Azuma; Donald. Gedney

    2004-01-01

    Equations to predict uncompacted crown ratio as a function of compacted crown ratio, tree diameter, and tree height are developed for the main tree species in Oregon, Washington, and California using data from the Forest Health Monitoring Program, USDA Forest Service. The uncompacted crown ratio was modeled with a logistic function and fitted using weighted, nonlinear...

  10. FRACTURE-RESISTANT MONOLITHIC DENTAL CROWNS

    Science.gov (United States)

    Zhang, Yu; Mai, Zhisong; Barani, Amir; Bush, Mark; Lawn, Brian

    2016-01-01

    Objective To quantify the splitting resistance of monolithic zirconia, lithium disilicate and nanoparticle-composite dental crowns. Methods Fracture experiments were conducted on anatomically-correct monolithic crown structures cemented to standard dental composite dies, by axial loading of a hard sphere placed between the cusps. The structures were observed in situ during fracture testing, and critical loads to split the structures were measured. Extended finite element modeling (XFEM), with provision for step-by-step extension of embedded cracks, was employed to simulate full failure evolution. Results Experimental measurements and XFEM predictions were self consistent within data scatter. In conjunction with a fracture mechanics equation for critical splitting load, the data were used to predict load-sustaining capacity for crowns on actual dentin substrates and for loading with a sphere of different size. Stages of crack propagation within the crown and support substrate were quantified. Zirconia crowns showed the highest fracture loads, lithium disilicate intermediate, and dental nanocomposite lowest. Dental nanocomposite crowns have comparable fracture resistance to natural enamel. Significance The results confirm that monolithic crowns are able to sustain high bite forces. The analysis indicates what material and geometrical properties are important in optimizing crown performance and longevity. PMID:26792623

  11. Fracture-resistant monolithic dental crowns.

    Science.gov (United States)

    Zhang, Yu; Mai, Zhisong; Barani, Amir; Bush, Mark; Lawn, Brian

    2016-03-01

    To quantify the splitting resistance of monolithic zirconia, lithium disilicate and nanoparticle-composite dental crowns. Fracture experiments were conducted on anatomically-correct monolithic crown structures cemented to standard dental composite dies, by axial loading of a hard sphere placed between the cusps. The structures were observed in situ during fracture testing, and critical loads to split the structures were measured. Extended finite element modeling (XFEM), with provision for step-by-step extension of embedded cracks, was employed to simulate full failure evolution. Experimental measurements and XFEM predictions were self-consistent within data scatter. In conjunction with a fracture mechanics equation for critical splitting load, the data were used to predict load-sustaining capacity for crowns on actual dentin substrates and for loading with a sphere of different size. Stages of crack propagation within the crown and support substrate were quantified. Zirconia crowns showed the highest fracture loads, lithium disilicate intermediate, and dental nanocomposite lowest. Dental nanocomposite crowns have comparable fracture resistance to natural enamel. The results confirm that monolithic crowns are able to sustain high bite forces. The analysis indicates what material and geometrical properties are important in optimizing crown performance and longevity. Copyright © 2015 Academy of Dental Materials. All rights reserved.

  12. 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

    2017-05-31

    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.

  13. Comparison of internal fit between implant abutments and cast metal crowns vs laser-sintered crowns.

    Science.gov (United States)

    Kiliçarslan, Mehmet Ali; Özkan, Pelin; Uludag, Bülent; Mumcu, Emre

    2014-07-01

    A common problem related to cemented single crowns is the internal misfit, which may cause inadequate retention, especially when seated on the implant abutment. The aim of this study was to compare the internal fit of Co-Cr crowns using a traditional lost-wax casting technique from laser-sintered Co-Cr alloy crowns. Twelve metallic crowns per each technique were fabricated. The effect of the thickness of cement, originated internal gap was evaluated. Crowns were cemented on the implant abutments with resin cement, and the internal fit of crowns was measured at five areas with an optical microscope. The data were analyzed, and the means were compared with a t-test (pcrowns obtained through the lost wax method (min. 65.50 ± 9.54 μm and max. 313.46 ± 48.12 μm). The fit of the metal crown likely varies with the fabrication technique. The use of techniques that enable the adjustment of crown parameters, such as the laser sintering technique, maintains the desired fit between casting and implant abutments. This study investigated which technique affects the internal fit of cemented implant-supported crowns, comparing the use of lost wax casting and laser-sintered metal dental alloys. The results of this study indicate that the use of laser-sintered crowns can improve for crown accuracy.

  14. Lava zirconia crowns and bridges.

    Science.gov (United States)

    Suttor, D

    2004-01-01

    Ceramic restorations--suitable for the anterior as well as the posterior region, simultaneously satisfying the demand for high strength, longevity, and esthetics--are an increasingly important field for the dental professional. Because of its outstanding mechanical properties and esthetics with a proven track record in other industrial areas, zirconium oxide (zirconia) is emerging in the dental industry. As the manufacturing method of choice, CAD/CAM is important for the dental laboratory; however, in the final analysis, the primary focus will be on the material properties and the clinical performance of the result of the CAD/CAM process--in this case, zirconia crowns and bridges. This is especially true since some concepts do not require the acquisition of a CAD/CAM system at all.

  15. Fracture resistance of different primary anterior esthetic crowns

    OpenAIRE

    Al Shobber, Manar Zaki; Alkhadra, Thamer A.

    2017-01-01

    Purpose: Investigate and compare fracture resistance of four commercially available esthetic crowns. Methods: Sixty-four anterior crowns were used: NuSmile Primary crowns (NuSmile, Houston, Tex. USA) (16); Preveneered Cheng Crowns, (Orthodontic Technologies Inc., Houston, TX) (16); NuSmile ZR (NuSmile, Houston, Tex. USA); and Cheng Crowns zirconia (Orthodontic Technologies Inc., Houston, TX). Crowns were mounted and cemented on a negative replica and placed under servo hydraulic mechanical...

  16. Hardness characteristic of dental porcelain synthesized from Indonesian natural sand

    Science.gov (United States)

    Gunawan, J.; Taufik, D.; Takarini, V.; Hasratiningsih, Z.; Ramelan, A.

    2018-02-01

    Porcelain has been one of dental biomaterials which can be used to restore tooth structure. Veneer and jacket crown were the examples of dental porcelain restoration. Since wear resistance is related to the strength on its surface, then Vickers Hardness Test of the synthesized porcelain was applied subsequently. If the porcelain hardness number is too high, it should be considered that an abrasion of the opposing teeth could occur. On previous research, dental porcelain had been successfully synthesized from Indonesian natural sand. In this experiment, 5 samples were prepared from a mixture of 65w/o Pangaribuan feldspar, 25w/o Belitung silica, 5w/o Sukabumi kaolinite, and 5w/o potassium salt. This synthesized porcelain samples were invested on 5 cm diameter resin each. A kilogram of load was placed on top of each sample for 10 seconds on 7 different indented areas using ZwickRoell Indentec ZHVμ Micro Vickers. The average hardness number of synthesized dental porcelain made from Indonesian natural sand was 936.06 VHN which was higher than the average hardness number of porcelain restoration. In conclusion of the hardness test, synthesized dental porcelain made from Indonesian natural sand can potentially be used as a core, which shall support hardness and strength of the crown restoration.

  17. 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.

  18. Colorimetric values of esthetic stainless steel crowns.

    Science.gov (United States)

    Hosoya, Yumiko; Omachi, Koichi; Staninec, Michal

    2002-01-01

    The colorimetric values of two different kinds of esthetic stainless steel crowns were measured and compared with the colorimetric values of primary anterior teeth in Japanese children. The colorimetric values of resin composite-faced stainless steel crowns (Kinder Krown) and epoxy-coated stainless steel crowns (White Steel Crown) were measured with a color difference meter. The Commission Internationale de Eclairage L*, a*, b*, and delta E*ab values and Munsell value, chroma, and hue were calculated. The data were compared with previously reported colorimetric values of Japanese primary anterior teeth measured with the same color difference meter used in this study. Compared to Japanese primary anterior teeth, Kinder Krown Pedo I and Pedo II showed much higher L* values and lower hue; on the other hand, White Steel Crown showed much higher L*, a*, b* values, much higher value and chroma, and much lower hue. Color analysis revealed that the colors of the White Steel Crown and Kinder Krown Pedo I were substantially different from the color of Japanese primary anterior teeth. The color difference between Pedo II crowns and Japanese primary anterior teeth was relatively high, but the color of Pedo II might be acceptable for clinical use.

  19. Retention and surface changes of zirconia primary crowns with secondary crowns of different materials.

    Science.gov (United States)

    Turp, Işıl; Bozdağ, Ergün; Sünbüloğlu, Emin; Kahruman, Cem; Yusufoğlu, Ibrahim; Bayraktar, Gülsen

    2014-11-01

    To evaluate zirconia as a substitute for gold alloy in primary crowns facing secondary crowns manufactured with different materials, in terms of long-term retention force changes, wear, and phase transformation was aimed. A total of 12 groups, each containing six samples, consisting of gold alloy primary crown-electroformed gold secondary crowns (AA), zirconia primary crown-electroformed gold secondary crowns (ZA) and zirconia primary crown-casted non-precious alloy secondary crowns (ZC) with conus angles of 0°, 2°, 4°, and 6° were evaluated. Samples were subjected to 10,000 insertion-separation cycles in artificial saliva and retention force was measured. X-ray diffraction and scanning electron microscope analysis were performed on the sample surfaces. The highest retention forces were obtained from ZC-0° group (72.09-71.26 N) and the lowest were obtained from ZA-4° (12.73-19.44 N) and ZA-6° (5.36-19.73 N) groups in the beginning and after 10,000 cycles, respectively. Retention force increased as the conus angle decreased. The monoclinic phase ratio of the zirconia primary crowns decreased after the experiments. No wear was observed in zirconia primary crowns except for the ZC-0° and ZC-2° groups. The use of zirconia primary crowns resulted in a less excursive retention force. A more predictable and less excursive retention force can be obtained using a hard and rigid primary crown material like zirconia. Despite a lack of knowledge about the aging of zirconia without a veneer layer in the oral environment, zirconia primary crowns are more advantageous in terms of retention force development and wear.

  20. Two Supramolecular Inorganic–Organic Hybrid Crystals Based on Keggin Polyoxometalates and Crown Ethers

    Directory of Open Access Journals (Sweden)

    Jun Xiong

    2018-01-01

    Full Text Available New supramolecular structures were designed in this work using large-sized polyoxometalates (POMs and crown-ether-based supramolecular cations selected as building blocks. Two novel supramolecular inorganic–organic hybrids [(3-F-4-MeAnis([18]crown-6]2[SMo12O40]•CH3CN (1 and [(4-IAnis([18]crown-6]3[PMo12O40]•4CH3CN (2 (3-F-4-MeAnis = 3-fluoro-4-methylanilinium and 4-IAnis = 4-iodoanilinium were synthesized. Crystals 1 and 2 have been characterized by infrared spectroscopy (IR and elemental analysis (EA. Based on X-ray diffraction analysis, Crystals 1 and 2 were constructed through noncovalent bonding interactions and belong to different space groups due to the difference of the building blocks used. Supramolecular cations formed due to strong N–H···O hydrogen bonding interactions between the six oxygen atoms of [18]crown-6 molecules and nitrogen atoms of anilinium derivatives. Crystal 1 has two different supramolecular cations with an anti-paralleled arrangement that forms a dimer through weak hydrogen bonding interactions between adjacent [18]crown-6 molecules. Crystal 2 has three independent supramolecular cations that fill large spaces between the [PMo12O40] polyoxoanions forming a rhombus-shape packing arrangement in the ac plane. Crystals 1 and 2 are unstable at room temperature.

  1. Development of methods for immobilisation of crown ethers onto solid supports for separation of metal ions from solution

    International Nuclear Information System (INIS)

    Wagh, Sandip Janardan; Renjithkumar, A.U.; Maithania, K.N.; Mukhopadhyay, Sulekha; Shenoy, K.T.; Ghosh, Sunil Kumar

    2014-01-01

    Since the serendipitous discovery of dibenzo-18-crown-6 (1) by C.J. Pedersen in 1967, many significant developments have been made in the field of host-guest chemistry. The very important use of these molecules in nuclear industry is removal of metal ions selectively. The removal of 90 Sr from the nuclear waste solution is very essential in order to reduce the vitrification period. Dicyclohexyl 18 Crown 6 ether (hydrogenated form of 1) has been reported to be efficient selective ligand for recovery of 90 Sr from nitrate medium. The application of crown ether in liquid-liquid extraction mode has some issue related to choice of diluents and aqueous solubility. Both of these problems can be overcome by the incorporation of crown ethers onto polymers. Polymer supported reagents offer many advantages, including ease of handling and recoverability when used in the removal of toxic metal ions from the environment. Due to increased concern with the remediation of wastewater, polymer-supported reagents, including immobilized crown ethers, have been studied for the selective removal of targeted metal ions. This will allow ease of handling, recyclability and adaption to continuous processes. There are three principal methods by which crown ethers can be incorporated into polymer matrices a) step-growth mechanism; b) chain-growth mechanism; c) post-functionalization wherein a crown ether is covalently bound to a pre-formed polymer backbone. The last method requires the crown to have a reactive functional group that can bond to the polymer. The immobilisation of (1) and (2) onto a solid support zeocarb-226 via amide linkage is successfully achieved by our group. We have synthesized novel extraction chromatographic resins by covalently binding on polymeric substrate. The covalent bonding in synthesized polymeric material has characterized by the FTIR. The resultant material is providing a simple and effective means of isolating 90 Sr and 6 Li

  2. Internal fit evaluation of crowns prepared using a new dental crown fabrication technique: laser-sintered Co-Cr crowns.

    Science.gov (United States)

    Ucar, Yurdanur; Akova, Tolga; Akyil, Musa S; Brantley, William A

    2009-10-01

    Difficulties encountered during casting of base metal dental alloys limit their use. Application of these alloys might be enhanced if new techniques are used. The purpose of this study was to compare the internal fit of laser-sintered Co-Cr alloy crowns with base metal restorations prepared from another Co-Cr alloy and a Ni-Cr alloy using conventional casting techniques. Internal fit of laser-sintered Co-Cr crowns was compared with the fit of conventionally cast Ni-Cr and Co-Cr alloy crowns. Twelve crown-shaped specimens were prepared on a stainless steel die representing a prepared maxillary right central incisor for each group. Fit of crowns was evaluated using 2 different techniques: (1) weighing the light-body addition silicone that simulated a cement material, and (2) measuring the internal gap width on a die for longitudinally sectioned specimens. One-way ANOVA followed by Tukey multiple comparison test was used for statistical analysis (alpha=.05). Significantly higher mean (SD) light-body silicone weights (Pcrowns. However, no significant difference was found among the 3 alloy groups evaluated for the internal gap width of sectioned crown specimens.

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

    OpenAIRE

    Alsadon, O.; Patrick, D.; Johnson, A.; Pollington, S.; Wood, D.

    2017-01-01

    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 ...

  4. 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...

  5. Methods for evaluating crown area profiles of forest stands

    Science.gov (United States)

    Dubrasich, Michael E.; Hann, D.W.; Tappeiner, J. C.

    1997-01-01

    Canopy architectures of five structurally complex forest stands and three structurally simple forest stands in southwest Oregon and the Willamette Valley, Oregon, were evaluated and quantified through crown area profiles. Mixed conifer and mixed conifer hardwood stands across a range of sites were sampled for crown widths and heights. Crown width and shape equations were derived and used to quantify the stand crown area at incremental heights above the forest floor. Crown area profiles describe the spatial arrangement of aboveground forest vegetation and the total pore spaces between crowns. Plot by plot profiles were combined to produce vertical and horizontal displays of the stand crown area distribution. In complex stands, the forest space was moderately occupied by crowns from the forest floor up to heights over 30 m, producing uniform distributions of between-crown porosity. The structurally complex stands had between-crown porosity values of 70% to 90% for more than 23 vertical metres of canopy, and they had total between-crown porosities of 86% to 91%. The structurally simple stands had between-crown porosity values of 70% to 90% for less than 8 vertical metres of canopy, and they had total between-crown porosities of 69% to 85%. Variances in crown area indicate that variation in horizontal crown area (within heights) was larger in complex stands than in simple stands, but vertical crown areas (between heights) varied less in complex stands. The study provides a basis for discriminating between canopy architectures and for quantifying the porosity of forest canopies.

  6. Experimental and numerical modeling of shrub crown fire initiation

    Science.gov (United States)

    Watcharapong Tachajapong; Jesse Lozano; Shakar Mahalingam; Xiangyang Zhou; David Weise

    2009-01-01

    The transition of fire from dry surface fuels to wet shrub crown fuels was studied using laboratory experiments and a simple physical model to gain a better understanding of the transition process. In the experiments, we investigated the effects of varying vertical distances between surface and crown fuels (crown base height), and of the wind speed on crown fire...

  7. Long-term clinical performance of esthetic primary molar crowns.

    Science.gov (United States)

    Ram, Diana; Fuks, Anna B; Eidelman, Eliecer

    2003-01-01

    The aim of the study was to report the long-term clinical performance of esthetic primary molar crowns and compare them to that of stainless steel crowns (SSC). Twenty crowns (10 conventional and 10 esthetic) placed in 10 children who had participated in a previously reported study, were assessed again after 4 years. The crowns were evaluated clinically and radiographically according to the following parameters: gingival health, marginal extension, crown adequacy, proper occlusion, proximal contact, chipping of the facing (for esthetic crowns only), and cement removal. At the 4 year evaluation, all the esthetic crowns showed chipping of the facing. No difference was found for marginal extension, occlusion, crown adequacy and periodontal health between SSCs and the esthetic crowns. After 4 years, all the esthetic crowns presented chipping of the facing and, consequently, a very poor esthetic appearance.

  8. 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...

  9. Extraction separation of lithium isotopes with crown-ethers

    International Nuclear Information System (INIS)

    Tsivadze, A.Yu.; Demin, S.V.; Levkin, A.V.; Zhilov, V.I.; Nikol'skij, S.F.; Knyazev, D.A.

    1990-01-01

    By the method of extraction chromatography lithium isotope separation coefficients are measured during chemical isotope exchange between lithium aquocomplex and its complex in chloroform with crown-ethers: benzo-15-crown-5, 15crown-5, dicyclohexano-18-crown-6 and dibenzo-18-crown-6. Lithium perchlorate and trichloroacetate are the salts extracted. Values of 6 Li/ 7 Li isotope separation are 1.0032-1.020

  10. Comparison of the fracture strengths of metal-ceramic crowns and three ceromer crowns.

    Science.gov (United States)

    Ku, Chul-Whoi; Park, Sang-Won; Yang, Hong-So

    2002-08-01

    The fracture strength of a number of new ceromer systems for the fabrication of anterior fixed partial dentures is unknown. The purpose of this study was to compare the fracture strengths of metal-ceramic crowns and 3 types of ceromer crowns in a simulated anterior tooth preparation. A resin maxillary central incisor analog was prepared with a 5-degree convergence angle and a 90-degree, 1-mm shoulder. The incisal edge was reduced by 2 mm, and the axiogingival and axioincisal line angles were rounded. A mold of this tooth was made with vinyl polysiloxane impression material. Ten wax patterns were made from the mold and cast in a nickel-chromium alloy for the fabrication of metal dies, from which 10 metal-ceramic crowns were fabricated. Ten crowns for each of 3 ceromer systems (Artglass, Sculpture, and Targis) were fabricated from the same metal die. Each crown group was prepared, polymerized, air-particle abraded, and finished in accordance with the specific manufacturer's instructions. All 4 types of finished crowns were luted to the dies and embedded in polymethyl methacrylate resin blocks. Their fracture resistance was tested in a universal testing machine. The load was directed at the incisolingual line angle, at 130 degrees to the long axis of each specimen, until catastrophic failure occurred. A 7-mm-diameter rod was used to load the artificial crowns, with the center of the rod in contact with the crown surfaces. Analysis of variance and Tukey's multiple comparisons test (Pceromer crowns (1317 vs 602 N, respectively) (Pceromer crowns tested, although significantly lower than the values for metal-ceramic crowns, still exceeded normal occlusal forces.

  11. 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...

  12. Restoring crown fractures by direct composite layering using transparent strip crowns.

    Science.gov (United States)

    Eden, Ece; Taviloğlu, Engin

    2016-04-01

    Traumatic dental injuries are mostly seen at childhood and adolescence. The most common fracture in permanent anterior teeth is crown fracture. Esthetic and easy rehabilitation of these anterior teeth is possible using layering techniques and direct composite resin restorations. Shape, color and surface texture are the most important factors in restoring crown fractures esthetically. This article illustrates how to perform an esthetic composite resin restoration of crown fractures using strip crowns. The technique suggests using a strip crown as a mold for direct resin composite restoration. This provides a cost-effective treatment with operator friendly approach where most outstanding advantage is the minimum chair-side time with a single visit that is very important for young trauma patients. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  13. Indications & predisposing factors of crown lengthening surgery

    Directory of Open Access Journals (Sweden)

    Arghavan Amini-Behbahani

    2014-09-01

    Full Text Available Introduction: Since crown lengthening surgery could be accompanied by stress, pain and discomfort, knowledge about its predisposing factors could reduce the demands for such surgery.The aim of this study was to identify the most important indications of crown lengthening surgery in order to present new ideas to clinicians on how to reduce the need for this surgery. Methods: This cross-sectional study was done on 470 patients (aged 12-89 years referred for crown lengthening surgery. The patients' demographic data and their reasons for surgery, the teeth restoration condition and its type, condition of the opposite tooth, type of fractured cusp (posterior teeth, root canal therapy condition and quality, and size of existing intracanal posts were recorded in a data sheet. Data were analyzed by using SPSS software.The chi-square and fisher exact test were used for statistical analysis. The significant difference was p<0.05. Results: The most frequent indication in men and women was dental caries followed by tooth fracture.The second upper premolars and first lower molars needed crown lengthening surgery more often, respectively. Conclusions: Since dental caries and fracture are the most important factors that predispose teeth to crown lengthening surgery, controlling caries with a regular recall sequence can reduce the need for such surgery, especially in the elderly.

  14. Crown ether derivatives of EDTA: Pt. 6

    International Nuclear Information System (INIS)

    Liu Zhongqun; Qin Shengying; Chen Shaojin; Tan Lin

    1988-01-01

    EDTA-diaminodibenzo-18-crown-6 (cis- and trans-) condensation polymer is a new compound of crown ether derivatives of EDTA. In this paper the adsorption behaviors of U(IV) and U(VI) on this polymer from chloride solutions and effects of hydrochloric acid concentrations, salting-out agents and organic solvents on distribution coefficient (K d ) of uranium are investigated. Adsorption mechanism of uranyl ion (UO 2 2+ ) on this polymer was studied with IR spectra and by means of the adsorption behaviors of compounds of similar structure. Experimental results show that both polyether section and carboxyl groups in EDTA-diaminodibenzo-18-crown-6 take part in complexation with uranyl ion and synergistic effect appeared

  15. Explaining Synthesized Software

    Science.gov (United States)

    VanBaalen, Jeffrey; Robinson, Peter; Lowry, Michael; Pressburger, Thomas; Lau, Sonie (Technical Monitor)

    1998-01-01

    Motivated by NASA's need for high-assurance software, NASA Ames' Amphion project has developed a generic program generation system based on deductive synthesis. Amphion has a number of advantages, such as the ability to develop a new synthesis system simply by writing a declarative domain theory. However, as a practical matter, the validation of the domain theory for such a system is problematic because the link between generated programs and the domain theory is complex. As a result, when generated programs do not behave as expected, it is difficult to isolate the cause, whether it be an incorrect problem specification or an error in the domain theory. This paper describes a tool we are developing that provides formal traceability between specifications and generated code for deductive synthesis systems. It is based on extensive instrumentation of the refutation-based theorem prover used to synthesize programs. It takes augmented proof structures and abstracts them to provide explanations of the relation between a specification, a domain theory, and synthesized code. In generating these explanations, the tool exploits the structure of Amphion domain theories, so the end user is not confronted with the intricacies of raw proof traces. This tool is crucial for the validation of domain theories as well as being important in everyday use of the code synthesis system. It plays an important role in validation because when generated programs exhibit incorrect behavior, it provides the links that can be traced to identify errors in specifications or domain theory. It plays an important role in the everyday use of the synthesis system by explaining to users what parts of a specification or of the domain theory contribute to what pieces of a generated program. Comments are inserted into the synthesized code that document these explanations.

  16. 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.

  17. Widely tunable THz synthesizer

    Science.gov (United States)

    Hindle, F.; Mouret, G.; Eliet, S.; Guinet, M.; Cuisset, A.; Bocquet, R.; Yasui, T.; Rovera, D.

    2011-09-01

    The generation of cw-THz radiation by photomixing is particularly suited to the high resolution spectroscopy of gases; nevertheless, until recently, it has suffered from a lack of frequency metrology. Frequency combs are a powerful tool that can transfer microwave frequency standards to optical frequencies and a single comb has permitted accurate (10-8) THz frequency synthesis with a limited tuning range. A THz synthesizer composed of three extended cavity laser diodes phase locked to a frequency comb has been constructed and its utility for high resolution gas phase spectroscopy demonstrated. The third laser diode allows a larger tuning range of up to 300 MHz to be achieved without the need for large frequency excursions, while the frequency comb provides a versatile link to be established from any traceable microwave frequency standard. The use of a single frequency comb as a reference for all of the cw-lasers eliminates the dependency of synthesized frequency on the carrier envelope offset frequency. This greatly simplifies the frequency comb stabilization requirements and leads to a reduced instrument complexity.

  18. 21 CFR 872.3770 - Temporary crown and bridge resin.

    Science.gov (United States)

    2010-04-01

    ... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3770 Temporary crown and bridge resin. (a... polymethylmethacrylate, intended to make a temporary prosthesis, such as a crown or bridge, for use until a permanent...

  19. Relative Clinical Success of Bis-Acryl Composite Provisional Crowns.

    Science.gov (United States)

    Kozmacs, Carla; Baumann, Vanessa; Bunz, Oskar; Piwowarczyk, Andree

    2018-01-01

    The high demands on the clinical performance of a single-tooth provisional restoration necessitate that said performance be examined. The authors evaluated 24 teeth evaluated. Two test groups received bis-acrylic composite for provisional crowns (n = 12) and a single-unit, self-supporting, malleable, light-curing composite crown (n = 12). Final crowns (n = 24) served as paired controls. Evaluation of clinical success was measured using previously selected subcategories of FDI criteria. Statistical analysis was performed using McNemar's Test (α = 0.05). The null hypothesis of no improvement of the definitive crown relative to the provisionals was rejected at the 5% significance level (McNemar's P value provisional crowns, 75% received a clinically insufficient valuation, while only 8% of the definitive crowns did. The authors concluded that, independent of the manufacturing process, a bis-acrylic composite provisional crown cannot serve as a replacement for a conventionally manufactured definitive crown.

  20. The molecular genetics of crown gall tumorigenesis

    International Nuclear Information System (INIS)

    Hooykaas, P.J.J.; Schilperoort, R.A.

    1984-01-01

    The phytopathogenic bacteria Agrobacterium tumefaciens and A. rhizogenes are the causative agents of the widespread plant diseases ''crown gall'' and ''hairy root'' respectively. It is now well established that virulent strains of these bacterial species transfer a piece of bacterial DNA into plant cells, thereby transforming these into tumor cells. In research much attention has been paid to the agrobacteria for several reasons. First is the desire to develop a system for the genetic engineering of plant cells based on the natural system for gene transfer between Agrobacterium species and plant cells. Second, there is a striking resemblance between the etiology of animal cancers and the plant cancer crown gall that was recognized as early as in 1927. This led to basic studies on the process of plant tumor induction and on the recovery of plant cells from the tumorous state. A third important interest lies in crown gall as a disease that is the cause of economically important losses in agriculture an horticulture in Europe, North America, and Austrailia. Research has been aimed at finding means to prevent crown gall and to cure plants of this disease

  1. 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...

  2. 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.

  3. Two-body wear comparison of zirconia crown, gold crown, and enamel against zirconia.

    Science.gov (United States)

    Kwon, Min-Seok; Oh, Sang-Yeob; Cho, Sung-Am

    2015-07-01

    Full zirconia crowns have recently been used for dental restorations because of their mechanical properties. However, there is little information about their wear characteristics against enamel, gold, and full zirconia crowns. The purpose of this study was to compare the wear rate of enamel, gold crowns, and zirconia crowns against zirconia blocks using an in vitro wear test. Upper specimens were divided into three groups: 10 enamels (group 1), 10 gold crowns (group 2, Type III gold), and 10 zirconia crowns (group 3, Prettau(®)Zirkon 9H, Zirkonzahn, Italy). Each of these specimens was wear tested against a zirconia block (40×30×3mm(3)) as a lower specimen (30 total zirconia blocks). Each specimen of the groups was abraded against the zirconia block for 600 cycles at 1Hz with 15mm front-to-back movement on an abrading machine. Moreover, the load applied during the abrading test was 50N, and the test was performed in a normal saline emulsion for 10min. Three-dimensional images were taken before and after the test, and the statistical analysis was performed using the Krushal-Wallis test and Mann-Whitney test (p=0.05). The mean volume loss of group 1 was 0.47mm(3), while that of group 2 and group 3 was 0.01mm(3). The wear volume loss of enamels against zirconia was higher than that of gold and zirconia crowns. Moreover, according to this result, zirconia crowns are not recommended for heavy bruxers. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Method for synthesizing HMX

    Science.gov (United States)

    McGuire, Raymond R.; Coon, Clifford L.; Harrar, Jackson E.; Pearson, Richard K.

    1984-01-01

    A method and apparatus for electrochemically synthesizing N.sub.2 O.sub.5 cludes oxidizing a solution of N.sub.2 O.sub.4 /HNO.sub.3 at an anode, while maintaining a controlled potential between the N.sub.2 O.sub.4 /HNO.sub.3 solution and the anode. A potential of about 1.35 to 2.0 V vs. SCE is preferred, while a potential of about 1.80 V vs. SCE is most preferred. Thereafter, the N.sub.2 O.sub.5 is reacted with either 1.5-diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooctane (DADN) or 1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane (TAT) to form cyclotetramethylenetetraamine (HMX).

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

    NARCIS (Netherlands)

    Shembish, F.A.; Tong, H.; Kaizer, M.; Janal, M.N.; Thompson, V.P.; Opdam, N.J.M.; Zhang, Y.

    2016-01-01

    OBJECTIVE: 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. METHODS: Fully anatomically shaped monolithic resin composite molar crowns (Lava

  6. Digital photography for urban street tree crown conditions

    Science.gov (United States)

    Neil A. Clark; Sang-Mook Lee; William A. Bechtold; Gregory A. Reams

    2006-01-01

    Crown variables such as height, diameter, live crown ratio, dieback, transparency, and density are all collected as part of the overall crown assessment (USDA 2004). Transparency and density are related to the amount of foliage and thus the photosynthetic potential of the tree. These measurements are both currently based on visual estimates and have been shown to be...

  7. 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...

  8. Crown dilacerations - Two case reports | Rao | Nigerian Dental Journal

    African Journals Online (AJOL)

    Crown dilaceration is a relatively abnormal clinical finding when compared to root dilacerations. The incidence of crown dilacerations is stated to be as low as 3%. This report presents two cases of crown dilacerations in two different locations. A brief review of the literature pertinent to the condition, and the clinical and ...

  9. Synthesis and characterization of lanthanide (III) complexes of 4',5'- dibromobenzo-15-crown-5

    International Nuclear Information System (INIS)

    Wenkui Dong; Rudong Yang; Ling Ma

    1998-01-01

    Six new solid complexes of lanthanide(III) nitrates with 4',5'- dibromobenzo-15-crown-5 (Br 2 B15C5), [Ln(NO 3 ) 3 Br 2 B15C5] (Ln=La-Nd) and [Ln(NO 3 ) 3 (OH 2 ) 2 ]Br 2 B15C5CH 3 CN (Ln=Sm,Eu) have been synthesized and characterized by elemental analyses, IR and UV spectra, molar conductance measurements, TG-DTA and XRD. Coordination number of the lanthanide (III) ion for La(III), Ce(III), Pr(III) and Nd(III) complexes is found to be eleven. Sm(III) and Eu(III) ions are not directly bonded to the crown ether but are bonded by hydrogen bonds. (author)

  10. Proton-Ionizable Crown Ethers. A Short Review

    Science.gov (United States)

    1989-05-30

    Triazole’Subcyclic Unit 14. Proton-Ionizable Crown Ethers Containing Sulfonamide Groups 15. Miscellaneous Proton-Ionizable Crown Ethers 1. INTRODUCTION. ""Since...the diaza dinitrile crown. Subsequent hydrolysis produced the diacid 33 (Procedure E). 27 Monoaza-crowns 35-38 (Figure V, Table 5) were obtained by the...followed by hydrolysis of the cetidi to f the acid.3o Complextion by th~eam crownsJ hasJ boon extensively castudieon and transportat es of thos ecaions have

  11. Dentin-bonded all-ceramic crowns: current status.

    Science.gov (United States)

    Burke, F J; Qualtrough, A J; Hale, R W

    1998-04-01

    Dentin-bonded all-ceramic crowns employ contemporary techniques to lute the crown to the tooth using a resin luting material and dentin-bonding system. The advantages of these crowns are that they provide good esthetics and fracture resistance and can be used in cases of substantial tooth loss. Their principal disadvantages are that the luting procedure is more time-consuming and that these crowns should not be used where margins are subgingival. Dentin-bonded all-ceramic crowns may be a useful addition to the dentist's armamentarium, but long-term clinical studies are needed to fully assess their performance.

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

    Science.gov (United States)

    Nakamura, Keisuke; Harada, Akio; Inagaki, Ryoichi; Kanno, Taro; Niwano, Yoshimi; Milleding, Percy; Örtengren, Ulf

    2015-01-01

    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. Monolithic zirconia crowns (Lava Plus Zirconia, 3M/ESPE) with specified axial/occlusal thicknesses and lithium disilicate crowns (IPS e.max press, Ivoclar/Vivadent) with regular thickness were fabricated using a dental CAD/CAM system and a press technique, respectively. The crowns cemented onto dies were loaded until fracture. Based on measurements of the crown thickness made by micro-CT and the fracture load, multiple regression analysis was performed. It was revealed that the occlusal thickness significantly affected the fracture load (p zirconia crowns, the fracture load of the zirconia crowns with the occlusal thickness of 0.5 mm (5558 ± 522 N) was significantly higher than that of lithium disilicate crowns with an occlusal thickness of 1.5 mm (3147 ± 409 N). Within the limitations of the present study, it is suggested that monolithic zirconia crown with chamfer width of 0.5 mm and occlusal thickness of 0.5 mm can be used in the molar region in terms of fracture resistance.

  13. Cerec anterior crowns: restorative options with monolithic ceramic materials.

    Science.gov (United States)

    Reich, Sven; Fiedlar, Kurt

    2013-01-01

    The aim of this article is to discuss the different types of monolithic ceramic crowns that can be placed on anterior teeth with existing shoulder preparations. Anterior crowns were indicated for the teeth 12 to 22 in the present case. The patient, a 65-year-old male, had received all-ceramic crowns 20 years earlier, which had started to develop cracks and palatal fractures over the last few years. The patient's teeth were prepared and four sets of crowns were fabricated using different monolithic ceramic materials: IPS e.max CAD, Cerec Blocs C In, VITABLOCS Real Life, and ENAMIC. Both shade characterization and crystallization firing were performed on the monolithic lithium disilicate glass ceramic crowns. The silicate ceramic crowns received glaze firing alone. The crowns made of hybrid ceramic (ENAMIC) were treated with a polymer sealant.

  14. Crown structure of Picea omorika trees in the plantation

    Directory of Open Access Journals (Sweden)

    Krstić M.

    2012-01-01

    Full Text Available The study was carried out in Serbian spruce (Picea omorika Panč/Purkynĕ plantations in the western Serbia. The paper presents results of the analysis of crown development. The following elements were analyzed: total tree height, height of the crown base, absolute and relative crown length, maximal crown diameter, coefficient of crown spreading and degree of crown girth. We discuss approaches to the modeling of tree crown growth and development, growing under favorable environmental and stand conditions, without anomalies in development. In order to establish the relationship between analyzed factors, regression analyses were applied. Data fitting was by the analytic method, by the implementation of Prodan’s functions of growth, linear and parabolic function. Received models can be used for the simulation of various growth and developing processes in forest.

  15. Selective crystallization of cations with crown ethers; Selektive Kristallisation von Kationen mit Kronenethern

    Energy Technology Data Exchange (ETDEWEB)

    Heffels, Dennis Egidius

    2014-07-04

    The aim of this work was to study the selectivity and preferences of the incorporation of differently sized cations in the cavities of various crown ethers and the characterization of the resulting compounds. The coordination preferences of crown ethers with different cavities have long been known, and the impact of other effects on the structure formation have increasingly become the focus of attention. In this work a comparative overview of the coordination preferences depending on various factors was undertaken. The focus was mainly on the variation of the cavity of the crown ether in the presence of differently sized cations. In addition, the effects of the solvent and differently coordinating anions have been investigated. Within the framework of this work, basic coordination preferences could be detected with rare earth nitrates, which are affected particularly by the choice of the solvent. The formation of different types of structures could be controlled by varying the conditions such that the incorporation of the cation in the cavity of the crown ether was influenced and the formation of a particular type of structure can be influenced partly by the choice of solvent. In this case no direct preferences for the incorporation into the cavity of the crown ether in relation to the cation size were observed for rare earth cations. However, the coordination of the crown ether leads in each case - for lanthanides - to rather high coordination numbers. A total of five new rare earth complexes and two structural variants could be observed with crown ethers. In the study of the selectivity of the incorporation into the cavity, known structures were also reproduced and further structures were characterized but the crystal structures not entirely solved. With the use of monovalent cations such as potassium, lithium or silver a total of nine new compounds could be synthesized, while no clear preferences for the incorporation of certain cations were detected. The

  16. TRANSFORMATIONS OF BENZO-15-CROWN-5, [3.3]DIBENZO-18-CROWN-6 AND [4.4]DIBENZO-24-CROWN-8 IN AQUEOUS SOLUTIONS OF NITRIC ACID

    Directory of Open Access Journals (Sweden)

    S. M. Pluzhnik-Gladyr

    2015-02-01

    Full Text Available Peculiarities of benzo-15-crown-5 (I, [3.3]dibenzo-18-crown-6 (II, and [4.4]diben zo-24-crown-8 (III nitration by the dilute nitric acid and the mixture HCl-HNO3(4:1, «aqua regia» at room temperature are discussed. It was revealed that the «reactivity» of studied crown ethers (symbatically/antisymbatic to their hydrophili ci ty/lipophilicity is variated as follows: I>> III> II.

  17. Antagonist wear by polished zirconia crowns.

    Science.gov (United States)

    Hartkamp, Oliver; Lohbauer, Ulrich; Reich, Sven

    The aim of this in vivo study was to measure antagonist wear caused by polished monolithic posterior zirconia crowns over a 24-month period using the intraoral digital impression (IDI) technique. Thirteen zirconia crowns were placed in nine patients. The crowns and adjacent teeth were captured using an intraoral scanner (Lava C.O.S.). The corresponding antagonist teeth and the respective neighboring teeth were also scanned. Scanning was performed immediately after the restoration (baseline) as well as 12 and 24 months after crown placement. Geomagic Qualify software was used to superimpose the follow-up data sets onto the corresponding baseline data set, identify wear sites, and measure maximum vertical height loss in each individual wear site. Overall antagonist wear was then determined as the mean of wear rates measured in all of the individual antagonist units. In addition, wear rates in enamel and ceramic antagonists were analyzed as part of the scope of this study. The maximum mean wear with standard deviation (SD) in the overall sample with a total of nine patients, 13 antagonist units, and 98 evaluable wear sites was 86 ± 23 µm at 12 months, and 103 ± 39 µm at 24 months. The maximum mean wear in the enamel antagonist subgroup was 87 ± 41 µm at 12 months, and 115 ± 71 µm at 24 months; and in the ceramic antagonist subgroup 107 ± 22 µm at 12 months, and 120 ± 27 µm at 24 months. The wear rates determined in this study are comparable to those of existing studies. The IDI technique of wear analysis can be carried out in a practical manner and produces useful results.

  18. An Investigation Into the Integrity of Fit of Provisional Crowns Using Current Proprietary Temporary Crown Materials.

    Science.gov (United States)

    Taylor, Philip D; Georgakis, Georgios; Niggli, Jason

    2016-06-01

    Three methods of direct provisional crown construction were investigated for accuracy of marginal fit. A modified proprietary crown coping was compared to Bis GMA and isobutyl methacrylate resin provisional crowns with margins modified by using a flowable composite and 'bead on' isobutyl methacrylate respectively. Measurement was at 50x magnification at seven sites over the fit surface. Data was analyzed using SPSS version 13.0.1 and measurement compared using the Mann Whitney test set at a significance level of 0.05. Reliability was checked using the Bland Altman test. Statistical significant differences were found between the three groups. The order of best fit was Bis-GMA and flowable composite > isobutyl methacrylate with 'bead on' margins > Bis-GMA modified implant temporary coping. The clinical significance is that the Bis GMA and flowable composite combination can be used with equal confidence to traditional methods of temporarisation.

  19. Retention behavior of double-crown attachments with zirconia primary and secondary crowns.

    Science.gov (United States)

    Schwindling, Franz Sebastian; Stober, Thomas; Rustemeier, Rainer; Schmitter, Marc; Rues, Stefan

    2016-05-01

    To investigate whether adequate retention of zirconia conical crown (CC) attachments can be achieved, and to investigate their long-term retention. Sixteen individual zirconia primary crowns were produced with convergence angles of 1° or 2° (eight of each). After determination of the convergence angles of the primary crowns, monolithic zirconia secondary crowns were manufactured. To evaluate the retention behavior of all-zirconia CC, the crowns were fitted with forces from F=12.5-100 N. Force magnitudes during the loosening process (L) were then measured. L/F ratios were recorded and the coefficient of friction (μ0) was calculated. Long-term retention was tested with up to 50,000 cycles of denture integration at a speed of 30 mms(-1) and a fitting force magnitude of 53 N. Even when primary crowns were manufactured with the utmost care, the real convergence angles were greater than the nominal angles of the standardized burs (1° and 2°) by 0.28° (SD 0.11°). Without mechanical aging, mean L/F was 0.632 (SD 0.038) for 1° samples and 0.526 (SD 0.022) for 2° samples, indicative of high retentive forces of up to 63.2% of the fitting forces. When all the test results were used, best-fitting curves gave μ0=0.117 for new samples and μ0=0.126 for samples after 50,000 integration cycles. When the correct milling and sintering parameters are chosen, the retention behavior of zirconia CCs is adequate and stable. This innovative type of attachment is appealing because of the beneficial properties of zirconia and the efficient CAD/CAM-based manufacture. Copyright © 2016 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  20. [Comparison of the clinical effects of selective laser melting deposition basal crowns and cobalt chromium alloy base crowns].

    Science.gov (United States)

    Li, Jing-min; Wang, Wei-qian; Ma, Jing-yuan

    2014-06-01

    To evaluate the clinical effects of selective laser melting (SLM) deposition basal crowns and cobalt chromium alloy casting base crowns. One hundred and sixty eight patients treated with either SLM deposition basal crowns (110 teeth) or cobalt chromium alloy casting basal crowns (110 teeth) were followed-up for 1 month, 6 months, 12 months and 24 months. The revised standard of American Public Health Association was used to evaluate the clinical effect of restoration, including the color of porcelain crowns, gingival inflammation, gingival margin discoloration, and crack or fracture. Data analysis was conducted with SPSS 20 software package for Student's t test and Chi-square test. Six cases were lost to follow-up. The patients who were treated with SLM deposition basal crowns (104 teeth) and cobalt chromium alloy casting base crowns (101 teeth) completed the study. Patients were more satisfied with SLM deposition cobalt chromium alloy porcelain crowns. There was 1 prosthesis with poor marginal fit after 24 months of restoration in SLM crowns. There were 6 prostheses with edge coloring and 8 with poor marginal fit in cobalt chromium alloy casting base crowns, which was significantly different between the 2 groups(P<0.05). The SLM deposition copings results in smaller edge coloring and better marginal fit than those of cobalt-chrome copings. Patients are pleased with short-term clinical results.

  1. Fracture resistance of implant- supported monolithic crowns cemented to zirconia hybrid-abutments: zirconia-based crowns vs. lithium disilicate crowns.

    Science.gov (United States)

    Elshiyab, Shareen H; Nawafleh, Noor; Öchsner, Andreas; George, Roy

    2018-02-01

    The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials. Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between 5℃ and 55℃. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test. All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed. When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.

  2. 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.

  3. 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

  4. 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.

  5. 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...

  6. 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.

  7. Clinically relevant fracture testing of all-ceramic crowns.

    Science.gov (United States)

    Øilo, Marit; Kvam, Ketil; Tibballs, John E; Gjerdet, Nils Roar

    2013-08-01

    Fracture strength measured in vitro indicates that most all-ceramic crowns should be able to withstand mastication forces. Nevertheless, fractures are one of the major clinical problems with all-ceramic restorations. Furthermore, the fracture mode of all-ceramic crowns observed in clinical use differs from that found in conventional fracture strength tests. The aim of the present study was to develop and investigate a method that simulates clinical fracture behavior in vitro. 30 crowns with alumina cores were made to fit a cylindrical model with a molar-like preparation design. These crowns were randomly allocated to 3 tests groups (n=10). The crowns in group 1 were cemented to abutment models of epoxy and subsequently fractured by occlusal loading without contact damage. The crowns in group 2 were fractured by cementation with expanding cement. The crowns in group 3 were cemented on an abutment model of epoxy split almost in two and fractured by increasing the diameter of the model in the bucco-lingual direction. The fractured crowns were analyzed by fractographic methods and compared to a reference group of 10 crowns fractured in clinical use. The fracture modes of all the in vitro crowns were similar to clinical fracture modes. The fracture modes in group 1 were most closely matched to the clinical fractures. These crowns also fractured at clinically relevant loads. Laboratory tests that induce a distortion of the abutment model during occlusal loading without occlusal contact damage can simulate clinical fractures of all-ceramic crowns. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  8. 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

    2016-01-01

    Objective 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. Methods 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 electronic microscopes were used to examine the occlusal surface and subsurface damages, as well as the material microstructures. Results The resin composite crowns showed only minor occlusal damage during mouth-motion step-stress fatigue loading up to 1700 N. 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 450 N. Significance 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. PMID:26777092

  9. 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.

  10. Crown and bridge cements: clinical applications.

    Science.gov (United States)

    Bunek, Sabiha S; Powers, John M

    2012-12-01

    Cement selection can be confusing because factors such as substrate, the type of restoration, and patient needs must be considered. Some substrates require additional treatment before cementation. This article describes the most commonly used traditional crown and bridge cements (GI and RMGI) used for metal and metal-ceramic restorations, and resin cements used for all-ceramic restorations. Advantages, disadvantages, indications, and contraindications of cements have been reviewed. Recommended uses of cements for metal, ceramic, and laboratory composite restorations have been presented. General guidelines for surface treatment ot silica- and zirconia-based restorations when using resin cements have been discussed.

  11. Functionalized mesoporous silicas with crown ether moieties for selective adsorption of lithium ions in artificial sea water.

    Science.gov (United States)

    Sung, Soo Park; Moorthy, Madhappan Santha; Song, Hyun-Jin; Ha, Chang-Sik

    2014-11-01

    Lithium ion has been increasingly recognized in a wide range of industrial applications. In this work, we studied on the adsorption of Li+ in the artificial seawater with high selectivity using methyl-crown ether (AC-SBA-15) and aza-crown ether (HMC-SBA-15) moieties-functionalized mesoporous silica materials. First, methyl-crown ether and aza-crown ether moieties-functionalized mesoporous silica materials were synthesized via two-step post-synthesis process using a grafting method. The functionalized materials were employed to the metal ion adsorption from aqueous solution (artificial seawater) containing Li+, Co2+, Cr3+ and Hg2+. The prepared hybrid material showed high selectivity for Li+ ion in the artificial seawater at pH 8.0. The absorbed amount of Li+ was 73 times higher than Cr3+ for aza-crown ether containing AC-SBA-15 as an absorbent. The absorbed amount of Co2+ (4.5 x 10(-5) mol/g), Cr3+ (1.5 x 10(-5) mol/g) and Hg2+ (2.25 x 10(-4) mol/g) were remarkably lower than the case of Li+. On the other hand, the absorbed amount of various metal ions of HMC-SBA-15 with amine groups in alky chains and crown ether moieties were 1.1 x 10(-3) mol/g for Li+, 5.0 x 10(-5) mol/g for Co2+, 2.9 x 10(-4) mol/g for Cr3+, 2.8 x 10(-4) mol/g for Hg2+ mol/g, respectively.

  12. Posterior preveneered stainless steel crowns: clinical performance after three years.

    Science.gov (United States)

    O'Connell, Anne C; Kratunova, Evelina; Leith, Rona

    2014-01-01

    The purpose of this study was to evaluate the clinical performance of posterior preveneered stainless steel crowns after three years. NuSmile crowns and Kinder Krowns were randomly allocated on paired molars using a split-mouth design. Variables such as fracture, wear, gingival health, and esthetics were recorded. (Pcrowns in 14 children. After three years, 53 percent of crowns were fracture free compared to 81 percent at one year. There was minimal esthetic impact for most fractures due to the location of the veneer fracture, but five crowns had extensive fracture. No difference was reported in the clinical performance between the two crown types. Fracture was more likely to occur where the adjacent tooth was missing. Parents reported a satisfaction rating of 8.3 out of 10. Clinical performance of both crown types was similar and successful for three years. Facing fracture occurred in 47 percent of crowns but had minimal impact on the esthetic value or parental satisfaction in the majority of cases. These crowns offer an esthetic alternative to the traditional stainless steel crown, but parents should be alerted to the possibility of veneer loss over time.

  13. Adhesive Cementation Promotes Higher Fatigue Resistance to Zirconia Crowns.

    Science.gov (United States)

    Campos, F; Valandro, L F; Feitosa, S A; Kleverlaan, C J; Feilzer, A J; de Jager, N; Bottino, M A

    The aim of this study was to investigate the influence of the cementation strategy on the fatigue resistance of zirconia crowns. The null hypothesis was that the cementation strategy would not affect the fatigue resistance of the crowns. Seventy-five simplified molar tooth crown preparations were machined in glass fiber-filled epoxy resin. Zirconia crowns were designed (thickness=0.7 mm), milled by computer-aided design/computer-aided manufacturing, and sintered, as recommended. Crowns were cemented onto the resin preparations using five cementation strategies (n=15): ZP, luting with zinc phosphate cement; PN, luting with Panavia F resin cement; AL, air particle abrasion with alumina particles (125 μm) as the crown inner surface pretreatment + Panavia F; CJ, tribochemical silica coating as crown inner surface pretreatment + Panavia F; and GL, application of a thin layer of porcelain glaze followed by etching with hydrofluoric acid and silanization as crown inner surface pretreatment + Panavia F. Resin cement was activated for 30 seconds for each surface. Specimens were tested until fracture in a stepwise stress fatigue test (10,000 cycles in each step, 600 to 1400 N, frequency of 1.4 Hz). The mode of failure was analyzed by stereomicroscopy and scanning electron microscopy. Data were analyzed by Kaplan-Meier and Mantel-Cox (log rank) tests and a pairwise comparison (pzirconia layer. Finite element analysis showed the different stress distribution for the two models. Adhesive cementation of zirconia crowns improves fatigue resistance.

  14. Relation of Crown Width to Tree Diameter In Some Upland Hardwood Stands of Southern Illinois

    Science.gov (United States)

    Leon S. Minckler; Samuel F. Gingrich

    1970-01-01

    Crown width-d.b.h. relationships in well stocked, uneven-aged stands of oak and hickory were similar to those for open-grown trees and were independent of site, crown class, and species. The irregular crowns of forest grown trees interface and overlap, however, and measuring crown extensions to the branch tips tended to overestimate effective crown area

  15. SYNTHESES, SPECTROSCOPIC AND MAGNETIC PROPERTIES ...

    African Journals Online (AJOL)

    Preferred Customer

    SYNTHESES, SPECTROSCOPIC AND MAGNETIC PROPERTIES OF. POLYSTYRENE-ANCHORED COORDINATION COMPOUNDS OF. THIAZOLIDINONE. Dinesh Kumar1, Amit Kumar2* and Durga Dass3. 1Department of Chemistry, National Institute of Technology, Kurukshetra 136119, Haryana,. India. 2Department of ...

  16. Fully automated parallel oligonucleotide synthesizer

    Czech Academy of Sciences Publication Activity Database

    Lebl, M.; Burger, Ch.; Ellman, B.; Heiner, D.; Ibrahim, G.; Jones, A.; Nibbe, M.; Thompson, J.; Mudra, Petr; Pokorný, Vít; Poncar, Pavel; Ženíšek, Karel

    2001-01-01

    Roč. 66, č. 8 (2001), s. 1299-1314 ISSN 0010-0765 Institutional research plan: CEZ:AV0Z4055905 Keywords : automated oligonucleotide synthesizer Subject RIV: CC - Organic Chemistry Impact factor: 0.778, year: 2001

  17. Crowns cemented on crown preparations lacking geometric resistance form. Part II: effect of cement.

    Science.gov (United States)

    Proussaefs, Periklis

    2004-03-01

    This study evaluated the effect of different cements on resistance to dislodgment of crowns cemented on preparations lacking geometric resistance form. A preparation that offered no geometric resistance form, with 20 degrees total occlusal convergence (TOC), 0.9 mm wide shoulder finish line, and a 2.5 mm axial wall height was created on an ivorine tooth using a milling machine. Ten metal test specimen die replicas and 10 standardized metal crowns with recipient sites for the application of external forces through a universal testing machine were fabricated. The crowns were cemented on the dies under 5 and 10 kg external loads, the marginal openings measured, loaded to dislodgment, and cleaned of cement. The process was repeated using zinc oxide and eugenol (ZOE), zinc phosphate (ZPh), resin modified glass ionomer (RMGI), and composite resin (CR) cements. Marginal openings under 5 kg cementation loads were 74.63 (+/-15.04) for ZOE, 75.98 (+/-18.20) microm for ZPh, 98.58 (+/-22.62) microm for RMGI, and 105.82 (+/-20.07) microm for CR cements respectively; under 10 kg cementation loads they were 57.62 (+/-15.86) microm, 59.55 (+/-15.41) microm, 95.00 (+/-19.52) microm, 101.30 (+/-12.52) microm respectively. Oblique dislodgment forces, measured with a Universal testing machine, were 40.18 (+/- 6.76) N for ZOE, 215.65 (+/-45.79) N for ZPh, 165.43 (+/-19.53) N for RMGI, and 181.54 (+/-30.75) N for CR respectively when crowns were cemented under 5 kg loads. The corresponding values for 10 kg loads were 38.62 (+/-4.19), 274.86 (+/-54.22), 139.70 (+/-21.71), and 160.40 (+/-21.21) respectively. Only zinc phosphate cement produced statistically enhanced resistance when crowns were cemented under 10 kg force (p value = 0.035). Under the conditions of the present study only crowns cemented with zinc phosphate displayed increased resistance to dislodgment on preparations lacking resistance form.

  18. Usurpation of a Crowned Lapwing Vanellus coronatus nest by ...

    African Journals Online (AJOL)

    I report an instance of usurpation of a Crowned Lapwing Vanellus coronatus nest by a pair of African Wattled Lapwings Vanellus senegalensis. The nest, which originally contained a single Crowned Lapwing egg, eventually contained an additional three Wattled Lapwing eggs, before it was predated. Although parents of ...

  19. 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

  20. Evaluation of wild Juglans species for crown gall resistance

    Science.gov (United States)

    Paradox, the most widely used rootstock in CA walnut production, is highly susceptible to the causal agent of crown gall (CG) Agrobacterium tumefaciens. The bacterial pathogen induces the formation of large tumors around the crown of the tree resulting in a reduction in both vigor and yield. If left...

  1. Gloss and Surface Roughness of Anterior Pediatric Zirconia Crowns.

    Science.gov (United States)

    Theriot, Adrien L; Frey, Gary N; Ontiveros, Joe C; Badger, Gary

    2017-09-15

    The purpose of this study was to determine gloss and surface roughness (Ra) of pediatric anterior zirconia crowns. Gloss of labial and lingual surfaces of pediatric anterior zirconia crowns from three manufacturers was measured on 20 specimens using a small area gloss meter on each. Ra (μm) was measured using a contact-type surface profilometer. Data were evaluated by analysis of variance and pair-wise comparison at the 0.05 level of significance. There were statistically significant interactions between surface location and crown type for both gloss and Ra scores. NuSmile had higher mean gloss scores and lower mean Ra scores than both Kinder Krowns and EZCrowns. Kinder Krowns showed lower mean gloss scores and higher Ra scores than other crown groups. Among all crowns, there was a trend of higher mean gloss paired with lower mean surface roughness, and lower mean gloss paired with higher mean Ra. Hand smoothed followed by mechanically polished zirconia crowns (NuSmile) displayed the highest mean gloss and lowest mean Ra compared to hybrid polishedglazed zirconia crowns (Kinder Krowns, EZCrowns). Of the hybrid polished-glazed zirconia crowns, Kinder Krowns displayed the lowest mean gloss and highest mean Ra.

  2. Re/crowning the Jowo Śākyamuni

    DEFF Research Database (Denmark)

    Warner, Cameron

    2011-01-01

    of ritual observance and visions received.  In 1409, Tsongkhapa Lozang Drakpa  (1357-1419) crowned the Jowo, changing his doctrinal and iconographic representations.  I connect the controversy surrounding Tsongkhapa's decision to re/crown the Jowo in 1409 to the significance placed on authenticity...

  3. Relationships among alfalfa resistance to Sclerotinia crown and ...

    African Journals Online (AJOL)

    Sclerotinia crown and stem rot (SCSR) of alfalfa caused by Sclerotinia trifoliorum is one of the main constraints for efficient alfalfa cultivation in temperate climate all over the world. The resistance of 200 alfalfa accessions to Sclerotinia crown and stem rot was evaluated during 2010 to 2011 in the field nursery established in ...

  4. Evaluation of Vertical Marginal Adaptation of Provisional Crowns by ...

    African Journals Online (AJOL)

    Objective: To investigate and compare the degree of vertical marginal discrepancy of four provisional crown materials by digital microscope. Materials and Methods: A total of 100 provisional crowns were fabricated on standardized resin dies by direct technique of provisional fabrication, using four different provisional ...

  5. Short clinical crowns (SCC) - treatment considerations and techniques.

    Science.gov (United States)

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

    2012-10-01

    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.

  6. Spectrophotometric evaluation of crown fragment a year after ...

    African Journals Online (AJOL)

    Background: Crown fracture is the most common type of fracture and frequently affects the anterior teeth. Crown fractures have been treated in several ways depending on the location and kind of fracture. This case emphasizes reattachment of fractured fragments using fiber-reinforced post. Also this case report underlines ...

  7. Crown ratio models for tropical rainforests species in Oban division ...

    African Journals Online (AJOL)

    Crown ratio (CR) is a characteristic used to describe the crown size, which is an important element of forest growth and yield. It is often used as an important predictor variable for tree-level growth equations. It indicates tree vigour and is an important habitat variable. It is often estimated using allometry. Modified versions of ...

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

    International Nuclear Information System (INIS)

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

    2004-01-01

    Isothermal titration calorimetry has been applied to the determination of the thermodynamic parameters of binding of β-lactose, α,α-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 β-lactose. The associates are preferentially or completely entropy stabilized. The most stable associate is formed between α,α-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)

  9. [Clinical evaluation of zirconia crowns for single posterior teeth].

    Science.gov (United States)

    Chen, Yuanhua; Meng, Xiangfeng; Yu, Qing

    2014-06-01

    To observe and evaluate the clinical performance of zirconia crowns made by CEREC inLab computer aided design/computer aided manufacturing(CAD/CAM) for posterior teeth. A total of 242 patients were implanted with zirconia crowns fabricated by CEREC inLab CAD/CAM. The crowns were evaluated by Modified US Public Health Service criteria at baseline, 6, 12, 24, and 36 months. The chi-square test was used to analyze the survival rate. All but five crowns were evaluated by an independent evaluator at baseline, 6, 12, 24, and 36 months. The survival rate declined with time. The A score percentage was above 85% at 36 months. The single zirconia crowns fabricated by CEREC inLab CAD/CAM demonstrate satisfactory clinical performance during a short period.

  10. Triaquachlorido(18-crown-6barium chloride

    Directory of Open Access Journals (Sweden)

    Min-Min Zhao

    2012-03-01

    Full Text Available In the title compound, [BaCl(C12H24O6(H2O3]Cl, the BaII atom, the coordinating and free Cl− anions, one coordinating water molecule and two O atoms of an 18-crown-6 molecule lie on a mirror plane. The environment of the ten-coordinate Ba2+ ion is defined by one Cl atom, three water molecules and six O atoms from the macrocyclic ether. The macrocycle adopts a conformation with an approximate D3d symmetry. In the crystal, O—H...Cl hydrogen bonds link the complex cations and Cl− anions into a two-dimensional network parallel to (010. An intramolecular O—H...Cl hydrogen bond is also present.

  11. Gingival pigmentation beneath a metallic crown

    International Nuclear Information System (INIS)

    Sakai, T.; Hirayasu, R.; Sakai, H.; Hashimoto, N.

    1988-01-01

    Light and electron microscopic studies and energy dispersive X-ray analysis disclosed that the essential cause of gingival discoloration following the placement of a metallic crown, was marked deposition of melanin pigment. Deposition of melanin pigment was observed in epithelial cells, on basement membranes, and in fibroblasts, macrophages and among intercellular ground substance of the proprial layer. Brown or dark brown colored granules were observed in the deep portion of the proprial layer. Some metallic elements as silver and sulfur were detected. It was presumed that these materials were dental metals accidentally implanted in gingival tissues during the therapeutic procedure. The deposition of melanin pigment closely corresponded with mucosal tissue where these materials were present in the deep portion of the proprial layer. These findings suggested that these materials influenced the physiological metabolism of melanin and induced its pathological deposition in the proprial tissue. (author)

  12. EL CROWN HALL. CONTEXTO Y PROYECTO / The Crown Hall. Context and project

    Directory of Open Access Journals (Sweden)

    José Santatecla Fayós

    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

  13. [Comparison of adaptation of crowns of different lithium disilicate glass-ceramic].

    Science.gov (United States)

    Li, Kemeng; Ai, Hongjun; Yi, Zhe

    2016-05-01

    To evaluate the adaptation of different lithium disilicate glass-ceramic crown and whether different fabrication processes affect the adaptation of crowns. Thirty epoxy dies crowns were divided into 3 groups. They were cemented to domestic lithium disilicate glass-ceramic crowns in Group A, to IPS e.max CAD crowns in Group B and to IPS e.max Press crowns in Group C respectively. All crowns were cut by cutting machine. A confocal laser scanning microscope was used to measure the gap between crown tissue surface and die. There were significant differences in the three groups of measurement points(Pcrowns appeared to have clinically acceptable fit.

  14. Fracture strength of lithium disilicate crowns compared to polymer-infiltrated ceramic-network and zirconia reinforced lithium silicate crowns.

    Science.gov (United States)

    Sieper, Kim; Wille, Sebastian; Kern, Matthias

    2017-10-01

    The aim of this study was to evaluate the fracture strength of crowns made from current CAD/CAM materials. In addition the influence of crown thickness and chewing simulation on the fracture strength was evaluated. Crowns were fabricated from lithium disilicate, zirconia reinforced lithium silicate (ZLS-ceramic) and a polymer-infiltrated ceramic-network (PICN) with an occlusal thickness of 1.0mm or 1.5mm, respectively (n=16). Crowns were cemented on composite dies. Subgroups of eight specimens were loaded with 5kg in a chewing simulator for 1,200,000 cycles with thermal cycling. Finally, all specimens were loaded until fracture in a universal testing machine. Three-way ANOVA was used to detect statistical interaction. Differences regarding the materials were tested with two-way ANOVA, following one-way ANOVA and a post-hoc Tukey's-Test. All crowns survived the chewing simulation. The material had a significant influence on the fracture resistance (p≤0.05). Lithium disilicate achieved the highest values of fracture strength in almost all groups followed by ZLS-ceramic. PICN achieved the lowest values of fracture strength. Chewing simulation increased the fracture strength of thick lithium disilicate crown significantly. Greater occlusal thickness of all crown materials resulted in higher crown fracture strength before chewing simulation. After chewing simulation occlusal thickness of lithium disilicate and PICN crowns had no significant influence on the fracture strength. All crowns revealed fracture strength above the clinically expected loading forces. Therefore the durability of the tested CAD/CAM materials seems promising also in an occlusal thickness of 1.0mm. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Guided tooth preparation for a pediatric zirconia crown.

    Science.gov (United States)

    Lee, Ju-Hyoung

    2018-03-01

    Unesthetic primary incisors can produce negative self-perceptions in preschool-aged children. In recent years, because of increased esthetic demands, prefabricated zirconia crowns have become increasingly popular. However, zirconia crowns cannot be crimped, and the clinician must prepare the teeth to fit the zirconia crowns. Therefore, extended preparation and fitting times are necessary, especially for inexperienced practitioners. A 1- to 2-millimeter subgingival feather margin also is required. Gingival hemorrhage after subgingival preparation compromises the retention of zirconia crowns. In this clinical report, the author presents a step-by-step description of the clinical and laboratory procedures for restoring a discolored traumatized incisor with a zirconia crown. The author used a polyvinyl siloxane occlusal registration material as an impression material and made 2 identical casts. The author fabricated 3 reduction guides after prospective tooth preparation on the casts. The author rapidly prepared the discolored incisor with the reduction guides and ultrasonic burs. A zirconia crown provided an optimal esthetic result and gingival health. Because the reduction guides provided a visibility intraorally, fast tooth reduction, less trial placement, and passive adaptation of the crown were successful. Because the ultrasonic burs prevented gingival injuries, hemorrhage control was not necessary. The presented technique reduced the patient's discomfort and total chair time. Therefore, this alternative technique is helpful for inexperienced practitioners. Copyright © 2018 American Dental Association. Published by Elsevier Inc. All rights reserved.

  16. Review of Alberta Crown Crude Oil Marketing Program

    International Nuclear Information System (INIS)

    Crandall, G. R.; Kromm, R. B.

    1999-01-01

    This report contains an independent evaluation of the operations of the private marketing agents that are currently marketing the Alberta Crown's share of royalty crude oil. The evaluation includes a review of pricing performance, working relationship, current issues and the overall performance of the marketing arrangements during the fiscal years of 1997 and 1998. Overall, the outsourcing of sales of Crown production to agents is judged to be successful. For example, it has been noted that agents are becoming more aggressive in maintaining and increasing their margins. On the other hand, the increased level of aggressiveness in marketing, while tending to maximize Crown revenues, is also creating a potential conflict on how margins should be shared between the Crown and its agents. Also, there has been evidence of some management issues between the agents and the Crown concerning the extent to which the Crown should share in any increased value which the agent generates by increased third party marketing activities. These differences need to be addressed in order to maintain the strong performance of the marketing program. The consultants also recommend additional guidelines on risk management issues that more clearly define the Crown's risk tolerance. 2 tabs., 4 figs

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

    Directory of Open Access Journals (Sweden)

    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

  18. The repair of preveneered posterior stainless steel crowns.

    Science.gov (United States)

    Yilmaz, Yucel; Gurbuz, Taskin; Eyuboglu, Ozge; Belduz, Nihal

    2008-01-01

    This study's purposes were to determine the shear bond strength (SBS) for and to perform dye penetration (microleakage) and scanning electron microscopy (SEM) evaluations of preveneered posterior stainless steel crowns (SSCs) that were repaired using 2 different materials. Twenty-two crowns were used. They were stored in artificial saliva for 30 days and then thermocycled. A force was applied on the crowns' occlusal surfaces until the original veneer material appeared to be fractured. The fracture types and S8S values were recorded. The crowns were then repaired using Panavia opaque cement and Tetric Flow or Monoopaque and Tetric Flow. Twenty of the repaired crowns were subjected to dye penetration and SBS tests, and the remaining 2 were evaluated using SEM. Statistical analysis revealed no statistically significant differences in the results of either the S8S or the dye penetration test (P = .58 and P = 38, respectively). A statistically significant difference was found between original and repaired crowns regarding fracture extent (P = .02), but not failure type (P = .08). SEM evaluation showed that there was no observable gap at the interface of the original or repaired materials and the stainless steel base. Preveneered posterior stainless steel crowns may be repaired using either repair material types tested here.

  19. 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. © 2016 John Wiley & Sons Ltd.

  20. Retention of cast crown copings cemented to implant abutments.

    Science.gov (United States)

    Dudley, J E; Richards, L C; Abbott, J R

    2008-12-01

    The cementation of crowns to dental implant abutments is an accepted form of crown retention that requires consideration of the properties of available cements within the applied clinical context. Dental luting agents are exposed to a number of stressors that may reduce crown retention in vivo, not the least of which is occlusal loading. This study investigated the influence of compressive cyclic loading on the physical retention of cast crown copings cemented to implant abutments. Cast crown copings were cemented to Straumann synOcta titanium implant abutments with three different readily used and available cements. Specimens were placed in a humidifier, thermocycled and subjected to one of four quantities of compressive cyclic loading. The uniaxial tensile force required to remove the cast crown copings was then recorded. The mean retention values for crown copings cemented with Panavia-F cement were statistically significantly greater than both KetacCem and TempBond non-eugenol cements at each compressive cyclic loading quantity. KetacCem and TempBond non-eugenol cements produced relatively low mean retention values that were not statistically significantly different at each quantity of compressive cyclic loading. Compressive cyclic loading had a statistically significant effect on Panavia-F specimens alone, but increased loading quantities produced no further statistically significant difference in mean retention. Within the limitations of the current in vitro conditions employed in this study, the retention of cast crown copings cemented to Straumann synOcta implant abutments with a resin, glass ionomer and temporary cement was significantly affected by cement type but not compressive cyclic loading. Resin cement is the cement of choice for the definitive non-retrievable cementation of cast crown copings to Straumann synOcta implant abutments out of the three cements tested.

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

    Science.gov (United States)

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

    2017-05-01

    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

  2. Preventive and conservative prosthodontic treatment using overdenture and Richmond crown

    Directory of Open Access Journals (Sweden)

    Jevin Stivie Cialy

    2016-12-01

    Full Text Available Prosthodontic treatment aims to restore the chewing function (rehabilitation and to prevent tooth decay and bone resorption (preventive and conservative. As an example, treatment by overdenture and Richmond crown. Overdenture is a partial or complete removable denture covered and supported by one or more teeth, the tooth roots and/or dental implants. Richmond crown is fixed denture by post and crown system, in which the post part goes into the root canal and its crown covers the entire of original tooth crown surface. By retaining the original teeth and/or roots, it could improve the stability and retention of the denture, and defend proprioseptic of teeth and vertical dimensions. To provide information about preventive prosthodontic treatment and prevention by using overdenture and Richmond crown. Case Report: A 50 year old woman only has 44 teeth on the mandible which is indicated for the overdenture construction and loss teeth 13, 14, 17 and 27 on the maxilla with deep caries in teeth 22 which is indicated for a removable partial denture (RPDs construction by Richmond crown gear 22. On an early stage study, printing models is done. Then treatment of the root canal on teeth 22 and 44, followed by root canal preparation, core construction (cast post and Richmond crown on tooth 22 and bareroot preparation on tooth 44 for overdenture construction. The procedure followed by printing, recording bite to insertion. Choosing treatment either overdenture or Richmond crown is very important because it could mantain remain original teeth, thus it can help to improve the retention and stabilization.

  3. Information Retrieval for Ecological Syntheses

    Science.gov (United States)

    Bayliss, Helen R.; Beyer, Fiona R.

    2015-01-01

    Research syntheses are increasingly being conducted within the fields of ecology and environmental management. Information retrieval is crucial in any synthesis in identifying data for inclusion whilst potentially reducing biases in the dataset gathered, yet the nature of ecological information provides several challenges when compared with…

  4. Lanthanide crown ether complexes of p-sulfonatocalix[5]arene.

    Science.gov (United States)

    Dalgarno, Scott J; Hardie, Michaele J; Warren, John E; Raston, Colin L

    2004-08-21

    Two types of arrays are formed in water involving aza-crown ethers, p-sulfonatocalix[5]arene and europium(III) ions. One is a co-ordination polymer connecting calixarenes, sodium ions and lanthanide ions based on "ferris wheel" moieties incorporating aza-18-crown-6 and sodium ions. The second structure is a host-guest arrangement with di-protonated diaza-18-crown-6 in the cavity of the calixarenes as part of secondary coordination spheres of aquated europium(iii) ions.

  5. 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.

  6. 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....... The largest and most consistent reduction in noise level was however achieved with a diesel bowl type piston. The increased surface area as well as the larger crevice volumes of the experimental piston crowns generally resulted in lower IMEP than the flat piston. While the crevice volumes can be reduced...... reduction as well as heat losses....

  7. Retention force of secondary crowns to copings after temporary cementation: the effect of crown material and luting agent.

    Science.gov (United States)

    Mundt, Torsten; Heinemann, Friedhelm; Golecki, Gudrun; Schwahn, Christian; Biffar, Reiner

    2010-12-01

    Tooth-implant supported restorations can be temporarily cemented if the natural abutments are protected by permanently cemented copings. This in vitro study investigated the retention forces of pure titanium crowns to milled titanium alloy copings and of cobalt-chromium crowns to copings made of electroplated gold after cementation with different luting agents. Five specimens per group were cemented with acrylic-urethane cement (inner crown surface preisolated with petroleum jelly) and provisional zinc oxide cement. The retention was measured using a universal testing machine and a dental device for crown removal. The differences between groups were compared using analysis of variance. The pull-off forces for the cobalt-chromium secondary crowns cemented on gold copings using zinc oxide cement were significantly higher (mean=144.5 N) than the other crown-cement combinations (32.2-54.4 N), which showed no significant differences in the retention force. The impulse number and magnitude of the dental device was usually low and showed no substantial differences between the crown-cement combinations. It can be concluded that the results of the clinical removal method for prostheses differ from the results of the pull-off test. The question which luting agent is the better choice for retrievable restorations remains unanswered without further clinical and laboratory studies.

  8. 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.

  9. [Esthetic evaluation of Cerec 3D anterior crowns].

    Science.gov (United States)

    Yang, Jian; Feng, Hai-lan; Wei, Xiu-xia; Xing, Yan-xi; Jia, Lu; Zhou, Yong-sheng

    2012-03-27

    To observe the short-term effect of clinical application of Cerec 3D anterior crowns. A total of 16 patients were restored with 31 Cerec 3D anterior crowns. All restorations were stained before cementation. The evaluation started 1 week after luting. The restorations were examined in accordance with the modified US Public Health Service (USPHS) criteria at baseline and every 6 - 12 months. The observation period of 31 Cerec 3D anterior crowns varied from 8 to 33 months. The mean observation period was 22 months. All restorations scored A or B by modified USPHS standard. And 22 out of 31 restorations scored A for all criteria while 8 restorations scored B in color matching. Slight differences of translucency and chroma could be observed. Between baseline and follow-up examinations, insignificant shift from A-to B-rating occurred. Cerec 3D anterior crowns may achieve favorable short-term esthetic effects.

  10. 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.

  11. Probing supramolecular complexation of cetylpyridinium chloride with crown ethers

    Science.gov (United States)

    Saha, Subhadeep; Roy, Mahendra Nath

    2017-11-01

    Supramolecular complexations of cetylpyridinium chloride with three comparable cavity dimension based crown ethers, namely, dibenzo-18-crown-6, 18-crown-6 and dicyclohexano-18-crown-6 have been explored and adequately compared in acetonitrile with the help of conductivity in a series of temperatures to reveal the stoichiometry of the three host-guest complexes. Programme based mathematical treatment of the conductivity data affords association constants for complexations from which the thermodynamic parameters were derived for better comprehension about the process. The interactions at molecular level have been explained and decisively discussed by means of FT-IR and 1H NMR spectroscopic studies that demonstrate H-bond type interactions as the primarily force of attraction for the investigated supramolecular complexations.

  12. Luminescent Lariat Aza-Crown Ether Carboxylic Acid

    Directory of Open Access Journals (Sweden)

    Burkhard König

    2010-03-01

    Full Text Available Lariat ethers are interesting recognition motifs in supramolecular chemistry. The synthesis of a luminescent lariat aza-crown ether with a carboxyl group appended by azide-alkyne (Huisgen cycloaddition is presented.

  13. Sentencing dangerous offenders: policy and practice in the Crown Court

    OpenAIRE

    Henham, R

    2001-01-01

    Analysis of Crown Courts' use of protective sentencing powers under s.80(2)(b), s.85, and s.109 of 2000 Act and whether preference for s.85 reflects fundamental flaw in leaving determination of "dangerousness" to judiciary.

  14. Fractal approach to computer-analytical modelling of tree crown

    International Nuclear Information System (INIS)

    Berezovskaya, F.S.; Karev, G.P.; Kisliuk, O.F.; Khlebopros, R.G.; Tcelniker, Yu.L.

    1993-09-01

    In this paper we discuss three approaches to the modeling of a tree crown development. These approaches are experimental (i.e. regressive), theoretical (i.e. analytical) and simulation (i.e. computer) modeling. The common assumption of these is that a tree can be regarded as one of the fractal objects which is the collection of semi-similar objects and combines the properties of two- and three-dimensional bodies. We show that a fractal measure of crown can be used as the link between the mathematical models of crown growth and light propagation through canopy. The computer approach gives the possibility to visualize a crown development and to calibrate the model on experimental data. In the paper different stages of the above-mentioned approaches are described. The experimental data for spruce, the description of computer system for modeling and the variant of computer model are presented. (author). 9 refs, 4 figs

  15. Development of post-fire crown damage mortality thresholds in ponderosa pine

    Science.gov (United States)

    James F. Fowler; Carolyn Hull Sieg; Joel McMillin; Kurt K. Allen; Jose F. Negron; Linda L. Wadleigh; John A. Anhold; Ken E. Gibson

    2010-01-01

    Previous research has shown that crown scorch volume and crown consumption volume are the major predictors of post-fire mortality in ponderosa pine. In this study, we use piecewise logistic regression models of crown scorch data from 6633 trees in five wildfires from the Intermountain West to locate a mortality threshold at 88% scorch by volume for trees with no crown...

  16. Crown profile equations for stand-grown western hemlock trees in northwestern Oregon.

    Science.gov (United States)

    David D. Marshall; Gregory P. Johnson; David W. Hann

    2003-01-01

    Crown profile equations were developed for stand-grown western hemlock(Tsuga heterophylla (Raf.) Sarg.) in northwest Oregon. The profile model uses a segmented approach, dividing the crown into an upper and lower portion at the point of the largest crown width (LCW). The model explains about 86% of the variation in crown width when LCW is known but...

  17. Root-Crown Relations of Young Sugar Maple and Yellow Birch

    Science.gov (United States)

    Carl H. Tubbs

    1977-01-01

    Young forest-grown sugar maple and yellow birch (1 to 6 inches d.b.h.) crowns were mapped and roots excavated. Crown dimensions were compared. Sugar maple roots usually terminated within a few feet of the crown perimeter. Yellow birch roots frequently terminated well outside crown perimeters and roots of birch were more irregularly distributed than those of maple....

  18. Adhesively luted, metal-free composite crowns after five years.

    Science.gov (United States)

    Lehmann, Franziska; Spiegl, Katrin; Eickemeyer, Grit; Rammelsberg, Peter

    2009-12-01

    The effect of location and preparation design of abutment teeth and of preparation design on the survival and complication rate of metal-free, adhesively luted composite crowns (Artglass, Heraeus Kulzer) and their clinical performance was investigated in this controlled, randomized, prospective clinical study. After randomization, 114 single crowns (68 posterior, 46 anterior) were prepared either with a 0.5 mm chamfer finishing line or with a 0.5 mm shoulder combined with occlusal reduction of at least 1.5 mm. Buildups were made with a composite material, using the corresponding dentin adhesive. Crowns were manufactured on stone dies and intraorally adhesively luted with resin cement. Follow-up examinations were conducted after 1 month and 1, 2, 3, and 5 years. Documentation included failures and complications, occlusal contacts, plaque accumulation and patients' rating of esthetics and functionality. After 5 years, data for 83 single crowns had been obtained. Within an observation period of 5 years, 18 complications occurred, including 13 major failures which resulted in replacement of the crowns, and 5 minor complications which could be repaired. All loosened crowns (n = 2) were successfully re-cemented. The Cox Regression did not reveal any effect of location or preparation design on complication rate. Calculation of the Kaplan-Meier survival curve on the basis of major failures indicated a probability of survival of 96% after 3 years and 88.5% after 5 years. Four Artglass crowns had no contact in static occlusion after 5 years and plaque accumulation was significantly higher than for control teeth. esthetic and functional evaluation by patients revealed that acceptance was high. Metal-free composite crowns may be recommended for long-term temporary use. However, the complication rate and the increased plaque accumulation restrict the indication for permanent restorations.

  19. 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.

  20. Slow cooling protocol improves fatigue life of zirconia crowns.

    Science.gov (United States)

    Paula, Vitor G; Lorenzoni, Fabio C; Bonfante, Estevam A; Silva, Nelson R F A; Thompson, Van P; Bonfante, Gerson

    2015-02-01

    To compare the fatigue life and damage modes of zirconia crowns fabricated with and without framework design modification when porcelain veneered using a fast or slow cooling protocol. Composite resin replicas of a first molar full crown preparation were fabricated. Zirconia copings were milled as conventional (0.5mm even thickness, Zr-C, n=20,) or modified (lingual margin of 1.0mm thickness, 2.0mm height connected to two proximal struts of 3.5mm height, Zr-M, n=20). These groups were subdivided (n=10 each) according to the veneer cooling protocol employed: fast cooling (Zr-CFast and Zr-MFast) and slow cooling (Zr-CSlow and Zr-MSlow). Crowns were cemented and fatigued for 10(6) cycles in water. The number of cycles to failure was recorded and used to determine the interval databased 2-parameter probability Weibull distribution parameter Beta (β) and characteristic life value Eta (η). 2-parameter Weibull calculation presented β=5.53 and β=4.38 for Zr-MFast and Zr-CFast, respectively. Slow cooled crowns did not fail by completion of 10(6) cycles, thereby Weibayes calculation was applied. Increased fatigue life was observed for slow cooled crowns compared to fast cooled ones. Groups Zr-MFast and Zr-MSlow presented no statistical difference. Porcelain cohesive fractures were mainly observed in fast cooled groups. Slow cooled crowns presented in some instances inner cone cracks not reaching the zirconia/veneer interface. Improved fatigue life in tandem with the absence of porcelain fractures were observed in slow cooled crowns, regardless of framework design. Crowns fast cooled chiefly failed by porcelain cohesive fractures. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  1. 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.

  2. Mechanical performance of implant-supported posterior crowns.

    Science.gov (United States)

    de Kok, Paul; Kleverlaan, Cornelis J; de Jager, Niek; Kuijs, Ruud; Feilzer, Albert J

    2015-07-01

    The fracture of implant-supported restorations, especially of the veneering layer, is a common problem in dentistry. Monolithic ceramic or resin restorations might help solve this problem. The purpose of this in vitro study was to obtain additional insight into the risk of fracture of implant-supported restorations. Identical crowns (n=10) of 10 different ceramic and composite resin materials were cemented on conventional abutments on implant replicas embedded in polymethyl methacrylate blocks. The specimens were subjected to compressive load in a universal testing machine to record initial load to failure (ILF). Additionally, the flexural strength (FS), compressive strength (CS), and elastic modulus (E) of the investigated materials were determined. These results were used in a finite element analysis model of a composite resin and a lithium disilicate crown. Anatomic contour zirconia (Lava Plus) crowns had the highest ILF (6065 N), followed by lithium disilicate (IPS e.max) (2788 N) and the composite resin materials (Protemp 4, Majesty Flow, Telio CAD, Estenia C&B, Lava Ultimate, VITA Enamic) (2386 to 1935 N). Veneered zirconia (Lava) crowns showed the lowest ILF (1477 N). The highest FS, CS, and E were found for Lava Plus and IPS e.max. No direct relationship was found between ILF and the FS, CS, or E. The finite element analysis showed stresses that did not exceed the FS or CS of IPS e.max. The surface roughness of these crowns might have caused initial failure at relatively low stresses. In this laboratory study, monolithic implant-supported crowns showed a higher ILF than conventional veneered ceramic crowns. Monolithic ceramic restorations might perform better than composite resin crowns. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  3. Failure probability of three designs of zirconia crowns

    Science.gov (United States)

    Ramos, G. Freitas; Monteiro, E. Barbosa Carmona; Bottino, M.A.; Zhang, Y.; de Melo, R. Marques

    2015-01-01

    Objectives This study utilized a 2-parameter Weibull analysis for evaluation of lifetime of fully or partially porcelain-/glaze-veneered zirconia crowns after fatigue test. Methods Sixty 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 (100N, 3Hz) with a piston with hemispherical tip (Ø=6 mm) until the specimens failed or up to 2×106 cycles. Every 500,000 cycles intervals, the fatigue tests were interrupted, and stereomicroscopy (10 X) was used to inspect the specimens for damage. We performed Weibull analysis of interval data to calculate the number of failures in each interval. Results The types and number of failures according to the groups were: cracking (Traditional-13, Modified-6) and chipping (Traditional-4) of the feldspathic porcelain, followed by delamination (Traditional-1) at the veneer/core interface and debonding (Monollithic-2) at the cementation interface. Weibull parameters (beta, scale; and eta, shape), with a two-sided confidence interval of 95%, were: Traditional – 1.25 and 0.9 × 106cycles; 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. Conclusions The three crown designs presented significantly different behaviors under fatigue. The Modified and the Monolithic groups presented less probability to failure after 2×106cycles. PMID:26509988

  4. Variation in crown light utilization characteristics among tropical canopy trees.

    Science.gov (United States)

    Kitajima, Kaoru; Mulkey, Stephen S; Wright, S Joseph

    2005-02-01

    Light extinction through crowns of canopy trees determines light availability at lower levels within forests. The goal of this paper is the exploration of foliage distribution and light extinction in crowns of five canopy tree species in relation to their shoot architecture, leaf traits (mean leaf angle, life span, photosynthetic characteristics) and successional status (from pioneers to persistent). Light extinction was examined at three hierarchical levels of foliage organization, the whole crown, the outermost canopy and the individual shoots, in a tropical moist forest with direct canopy access with a tower crane. Photon flux density and cumulative leaf area index (LAI) were measured at intervals of 0.25-1 m along multiple vertical transects through three to five mature tree crowns of each species to estimate light extinction coefficients (K). Cecropia longipes, a pioneer species with the shortest leaf life span, had crown LAI <0.5. Among the remaining four species, crown LAI ranged from 2 to 8, and species with orthotropic terminal shoots exhibited lower light extinction coefficients (0.35) than those with plagiotropic shoots (0.53-0.80). Within each type, later successional species exhibited greater maximum LAI and total light extinction. A dense layer of leaves at the outermost crown of a late successional species resulted in an average light extinction of 61% within 0.5 m from the surface. In late successional species, leaf position within individual shoots does not predict the light availability at the individual leaf surface, which may explain their slow decline of photosynthetic capacity with leaf age and weak differentiation of sun and shade leaves. Later-successional tree crowns, especially those with orthotropic branches, exhibit lower light extinction coefficients, but greater total LAI and total light extinction, which contribute to their efficient use of light and competitive dominance.

  5. Catalytic method for synthesizing hydrocarbons

    Science.gov (United States)

    Sapienza, R.S.; Sansone, M.J.; Slegeir, W.A.R.

    A method for synthesizing hydrocarbons from carbon monoxide and hydrogen by contacting said gases with a slurry of a catalyst composed of palladium or platinum and cobalt supported on a solid phase is disclosed. The catalyst is prepared by heating a heterogeneous component of the palladium or platinum deposited on the solid support in a solution of cobalt carbonyl or precursors thereof. The catalyst exhibits excellent activity, stability in air, and produces highly desirable product fractions even with dilute gaseous reactants.

  6. Solid phase syntheses of oligoureas

    Energy Technology Data Exchange (ETDEWEB)

    Burgess, K.; Linthicum, D.S.; Russell, D.H.; Shin, H.; Shitangkoon, A.; Totani, R.; Zhang, A.J.; Ibarzo, J. [Texas A& M Univ., College Station, TX (United States)

    1997-02-19

    Isocyanates 7 were formed from monoprotected diamines 3 or 6, which in turn can be easily prepared from commercially available N-BOC- or N-FMOC-protected amino acid derivatives. Isocyanates 7, formed in situ, could be coupled directly to a solid support functionalized with amine groups or to amino acids anchored on resins using CH{sub 2}Cl{sub 2} as solvent and an 11 h coupling time at 25 {degree}C. Such couplings afforded peptidomimetics with an N-phthaloyl group at the N-terminus. The optimal conditions identified for removal of the N-phthaloyl group were to use 60% hydrazine in DMF for 1-3 h. Several sequences of amino acids coupled to ureas (`peptidic ureas`) and of sequential urea units (`oligoureas`) were prepared via solid phase syntheses and isolated by HPLC. Partition coefficients were measured for two of these peptidomimetics, and their water solubilities were found to be similar to the corresponding peptides. A small library of 160 analogues of the YGGFL-amide sequence was prepared via Houghten`s tea bag methodology. This library was tested for binding to the anti-{beta}-endorphin monoclonal antibody. Overall, this paper describes methodology for solid phase syntheses of oligourea derivatives with side chains corresponding to some of the protein amino acids. The chemistry involved is ideal for high-throughput syntheses and screening operations. 51 refs., 3 figs., 2 tabs.

  7. Efficient scrambling-free synthesis of heteroleptic terbium triple-decker (porphyrinato)(crown-phthalocyaninates).

    Science.gov (United States)

    Birin, Kirill P; Gorbunova, Yulia G; Tsivadze, Aslan Yu

    2012-08-28

    New heteroleptic triple-decker terbium complexes of general structure [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[Br(4)TPP] (Tb-TD) and [Br(4)TPP]Tb[(15C5)(4)Pc]Tb[(15C5)(4)Pc] (Tb-TD*) (Br(4)TPP = tetrakis-meso-(4-bromophenyl)-porphyrin, (15C5)(4)Pc = tetra-(15-crown-5)-phthalocyanine) are synthesized with 48% and 57% yields, respectively. The triple-decker complexes were prepared by interaction of generated in situ terbium monoporphyrinate [Br(4)TPP]Tb(acac) and corresponding double-decker precursors. The heteroleptic double-decker precursor [Br(4)TPP]Tb[(15C5)(4)Pc] was prepared for the first time in a two step one-pot synthesis. No ligand scrambling was observed in the synthesis of Tb-TD, while 4% scrambling was determined in the case of Tb-TD*. High yields of target triple-decker complexes were achieved despite the presence of electron-donating crown-ether fragments with low thermal stability at the phthalocyanine deck. Analysis of lanthanide-induced paramagnetic shifts of protons of Tb-TD together with data of previously reported La, Pr, Nd and Eu analogues allowed precise separation of contributions of contact and dipolar lanthanide terms as well as verification of isostructurality of complexes within the series.

  8. Fracture load of different crown systems on zirconia implant abutments.

    Science.gov (United States)

    Albrecht, T; Kirsten, A; Kappert, H F; Fischer, H

    2011-03-01

    The purpose of this study was to evaluate the fracture load of single zirconia abutment restorations using different veneering techniques and materials. The abutment restorations were divided into 6 groups with 20 samples each: test abutments (control group A), lithium disilicate ceramic crowns bonded on incisor abutments (group B), leucite ceramic crowns bonded on incisor abutments (group C), premolar abutments directly veneered with a fluor apatite ceramic (group D (layered) and group E (pressed)) and premolar abutments bonded with lithium disilicate ceramic crowns (group F). The fracture load of the restorations was evaluated using a universal testing machine. Half of each group was artificially aged (chewing simulation and thermocycling) before evaluating the fracture load with the exception of the test abutments. The fracture load of the test abutments was 705 ± 43N. Incisor abutments bonded with lithium disilicate or leucite ceramic crowns (groups B and C) showed fracture loads of about 580N. Premolar restorations directly veneered with fluor apatite ceramic (groups D and E) showed fracture loads of about 850N. Premolar restorations bonded with lithium disilicate ceramic crowns (group F) showed fracture loads of about 1850N. The artificial ageing showed no significant influence on the strength of the examined restorations. All ceramic crowns made of lithium disilicate glass-ceramic, adhesively bonded to premolar abutments showed the highest fracture loads in this study. However, all tested groups can withstand physiological bite forces. Copyright © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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

    Science.gov (United States)

    Kortegaard, H E; Anthony Knudsen, T; Dahl, S; Agger, J F G; Eriksen, T

    2015-04-01

    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. 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. 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 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 · 8% in dogs without pulp exposure (n = 133) resulting in a significant (relative risk, 109 · 5; P < 0 · 001) risk of periapical pathology in teeth with pulp exposure compared to teeth without pulp exposure. The high risk of periapical pathology observed in teeth with pulp exposure confirms that these teeth should not be neglected in affected dogs. © 2015 British Small Animal Veterinary Association.

  10. Antimicrobial efficacy of chemical disinfectants on contaminated full metal crowns.

    Science.gov (United States)

    Orsi, Iara Augusta; Villabona, Camilo Andrés; Kameoka, Eliana; Ferreira, Marly Christiènne C G; Ito, Izabel Yoko; Saravia, Marta Estela

    2010-01-01

    Prosthetic restorations that have been tried in the patient's mouth are potential sources of infection. In order to avoid cross-infection, protocols for infection control should be established in dental office and laboratory. This study evaluated the antimicrobial efficacy of disinfectants on full metal crowns contaminated with microorganisms. Full crowns cast in a Ni-Cr alloy were assigned to one control group (n=6) and 5 experimental groups (n=18). The crowns were placed in flat-bottom glass balloons and were autoclaved. A microbial suspension of each type of strain - S. aureus, P. aeruginosa, S. mutans, E. faecalis and C. albicans- was aseptically added to each experimental group, the crowns being allowed for contamination during 30 min. The contaminated specimens were placed into recipients with the chemical disinfectants (1% and 2% sodium hypochlorite and 2% glutaraldehyde) for 5, 10 and 15 min. Thereafter, the crowns were placed into tubes containing different broths and incubated at 35ºC. The control specimens were contaminated, immersed in distilled water for 20 min and cultured in Thioglycollate broth at 35ºC. Microbial growth assay was performed by qualitative visual examination after 48 h, 7 and 12 days. Microbial growth was noticed only in the control group. In the experimental groups, turbidity of the broths was not observed, regardless of the strains and immersion intervals, thus indicating absence of microbial growth. In conclusion, all chemical disinfectants were effective in preventing microbial growth onto full metal crowns.

  11. 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...

  12. Fracture resistance and failure modes of CEREC endo-crowns and conventional post and core-supported CEREC crowns

    Directory of Open Access Journals (Sweden)

    Chia-Yu Chang

    2009-09-01

    Conclusion: The bonded ceramic endo-crowns showed a significantly higher fracture resistance than the classic reinforced and designed group and, therefore, offer a feasible alternative for severely damaged teeth.

  13. Crystalline smectic E phase revisited in case of symmetrical dibenzo-18-crown-6-ether azomethine dimers

    Science.gov (United States)

    Cozan, Vasile; Ardeleanu, Rodinel; Airinei, Anton; Timpu, Daniel

    2018-03-01

    Three symmetric azomethine dimers having dibenzo-18-crown-6-ether as internal moiety and halogens (F, Cl, Br) as terminal functional groups were synthesized and characterized by FTIR and 1H NMR spectroscopy. Their thermal behavior was investigated by polarized optical microscopy (POM) and DSC techniques. Interesting textures have been observed at cooling by POM as being representative for a soft crystalline smectic phase. X-ray diffraction measurements in powder at room temperature exhibited a map of reflections corresponding to crystal E phase. The influence of molecular parameters (interdigitation parameter γ, dipole moment, molecular polarizability, halogen radius) on thermal behavior was discussed. The UV-Vis investigations allowed evaluation of photostability and a bathochromic effect was noticed with the increasing of halogen atom radius. Also the values of optical band gap (Eg) are higher than those corresponding to conjugated Schiff bases.

  14. Synthesis and antimicrobial activity of new crown ethers of Schiff base type

    Directory of Open Access Journals (Sweden)

    MUSTAFA YILDIZ

    2007-03-01

    Full Text Available New crown ether ligands of the Schiff base type (4a–d were synthesized by the reaction of 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde with 6,7-dihydro-13H-dibenzo [e,h] [1,4]dioxonin-2,11-diamine (3. The structures of ligands were investigated by elemental analysis as well as IR, UV–visible, 1H-NMR, 13C-NMR and MS spectroscopic data. The antimicrobial and anti-yeast activities of the ligands were screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae UC57, Micrococcus luteus La 2971, Proteus vulgaris ATCC 8427, Pseudomonas aeruginosa ATCC 27853, Mycobacterium smegmatis CCM 2067, Bacillus cereus ATCC 7064, Listeria monocytogenes ATCC 15313, Candida albicans ATCC 10231, Kluyveromyces fragilis NRRL 2415, Rhodotorula rubra DSM 70403, Debaryomyces hansenii DSM 70238 and Hanseniaspora guilliermondii DSM 3432.

  15. 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.

  16. Fracture load of monolithic CAD/CAM lithium disilicate ceramic crowns and veneered zirconia crowns as a posterior implant restoration.

    Science.gov (United States)

    Kim, Jee Hwan; Lee, Su-Jeong; Park, Jun Sub; Ryu, Jae Jun

    2013-02-01

    To compare the fracture load and failure mode of the monolithic lithium disilicate crown (e.max group) and 2 types of veneered zirconia crowns, hand layer (ZV group) and heat pressed (ZP group), as a posterior implant-supported restoration. A total of 24 all-ceramic crowns for molar tooth were fabricated using the computer-aided design/computer-assisted manufacture (CAD/CAM) system. The e.max group crowns and zirconia copings for ZV and ZP groups were fabricated using a Cerec milling unit. The ZV group was fabricated using a hand-layer veneering method, and the ZP group using a heat-pressing method. All crowns were luted to the abutments, which were connected to implant fixtures, using resin cement. Fracture load was measured using the universal testing machine, and the fracture surface was evaluated by scanning electron microscopy. The ZP group showed significantly higher fracture load (5229.3 N) compared with the e.max group (3852.1 N) and ZV group (3100.3 N). All fractures in the ZV group occurred in the veneered layer. Monolithic CAD/CAM lithium disilicate crowns are applicable to posterior implant-supported restorations because the fracture load was higher than the average occlusal force.

  17. Crown fracture: Failure load, stress distribution, and fractographic analysis.

    Science.gov (United States)

    Campos, Roberto E; Soares, Paulo V; Versluis, Antheunis; de O Júnior, Osmir Batista; Ambrosano, Gláucia M B; Nunes, Isabella Ferola

    2015-09-01

    The outcomes from load-to-failure tests may not be applicable to clinical situations. The purpose of this study was to critically evaluate the efficacy of load-to-failure tests in the investigation of the fracture load and pattern of metal-free crowns. Four groups were formed from 128 bovine roots restored with metal posts, resin cores, and feldspathic, leucite, or lithium disilicate ceramic systems or polymer crowns. Each group was divided into 4 (n=8) according to the cement: zinc phosphate, self-adhesive resin, autopolymerizing resin, and glass ionomer. Mean fracture loads from compressive tests were submitted to ANOVA and Tukey HSD test. Finite element and fractographic analyses were performed and associated with the fracture load and pattern. Significantly higher fracture load values were obtained for the lithium disilicate ceramic, but finite element and fractographic analyses showed that the cement effect could not be determined. The finite element analysis showed the cement likely affected the fracture pattern, confirmed that stresses in the cements were little affected by the crown materials, and found that the stressed conditions were lowest in the lithium disilicate compared with other crowns for all cement combinations. The stressed conditions in the crowns depended more on the adhesive properties than on the elastic modulus of the cement materials. The level of the stressed condition in the crowns at the occlusal surface was about the same or higher than along their cement interface, consistent with the fractography, which indicated fractures starting at the load point. Higher stress levels in the crowns corresponded with a lower number of catastrophic fractures, and higher stresses in the cements seemed to reduce the number of catastrophic fracture patterns. The highest stressed conditions occurred along the occlusal surface for crown materials with a low elastic modulus or in combination with adhesive cements. The method used was not appropriate

  18. Method of synthesizing tungsten nanoparticles

    Science.gov (United States)

    Thoma, Steven G; Anderson, Travis M

    2013-02-12

    A method to synthesize tungsten nanoparticles has been developed that enables synthesis of nanometer-scale, monodisperse particles that can be stabilized only by tetrahydrofuran. The method can be used at room temperature, is scalable, and the product concentrated by standard means. Since no additives or stabilizing surfactants are required, this method is particularly well suited for producing tungsten nanoparticles for dispersion in polymers. If complete dispersion is achieved due to the size of the nanoparticles, then the optical properties of the polymer can be largely maintained.

  19. Ceramometal crowns and bridges. Focus on failures.

    Science.gov (United States)

    Bell, A M; Kurzeja, R; Gamberg, M G

    1985-10-01

    There are numerous factors that can have an adverse or beneficial effect upon the esthetic appearance of a ceramometal restoration. Some of these factors are beyond the influence of the dentist unless he or she is aware of them. As knowledgable practicing dentists, they have the ability to prescribe for their patients in such a manner as to achieve greater success and, in turn, greater patient acceptance and recognition. These are the rewards of a successful crown and bridge practice, and the ceramometal restoration is the basic state of the art prosthesis in present use. Knowing how to take a shade under the proper lighting conditions is generally well taught as part of the dental school curriculum, but the knowledge that shade guides are manufactured with built in idiosyncrasies of color variations from guide to guide is an enlightening experience. O'Brien of the Department of Dental Materials at the University of Michigan School of Dentistry clearly demonstrated the variabilities of color intensities between porcelain manufacturers. Laboratory technicians have been frustrated by the inconsistency of shades of porcelains from one lot number to another. It is now more fully understood that fluorescence is an important factor in patient satisfaction, as patients observe and have their restorations seen under differing lighting conditions. The type of alloy used in the ceramometal combination can have an effect upon the esthetic result. The wider use of silver-palladium alloys requires that the porcelain employed be of a nongreening nature, or else the final glazed prosthesis will give off a greenish cast. The ability of the opaque to block out the metal substructure while blending with the gingival and incisal shades eliminates the graying out, which can be esthetically objectionable to the patient. However, one of the most important considerations in aesthetic ceramometal restorations is the correct anatomy, placement, and harmonious blending with the oral and

  20. Direct composite restoration of permanent anterior teeth uncomplicated crown fractures

    Directory of Open Access Journals (Sweden)

    Ashley Evans Nicholas

    2018-01-01

    Full Text Available An uncomplicated crown fracture is a fracture that involves only the tooth enamel or the dentin and tooth enamel without any damage or exposure to the pulp. Crown fracture of the anterior teeth usually caused by traumatic forces such as falls, accidents, violence, or sports activities. Traumatic injuries of the oral region frequently involve the anterior teeth, especially maxillary incisors due to the anatomic factors which may affect the functional and aesthetical values of the teeth. The objective of this literature study was to know more about uncomplicated crown fracture of the anterior teeth and its restoration. This research was a literature study performed by researching, highlighting various interesting facts and compiling the relevant published journals. The most common and ideal direct restoration of the anterior teeth was the composite resin restoration. The anterior teeth restoration was considered to be a complex and challenging case to solves due to the fact that besides reconstructing the tooth and regaining the function, the aesthetical aspect was also becoming the main objectives. The permanent anterior teeth uncomplicated crown fracture was the most common case of tooth fractures which was mainly caused by traumatic injuries such as falls, accidents, excessive forces, violence, and also sports activities. Dental injuries of the anterior teeth also affected the aesthetical properties and the function of the tooth. Composite resin restoration was able to performed directly on the permanent anterior teeth uncomplicated crown fracture.

  1. The use of stainless steel crowns: a systematic literature review.

    Science.gov (United States)

    Seale, N Sue; Randall, Ros

    2015-01-01

    The purpose was to review the published literature on stainless steel crowns (SSCs) from 2002 to the present as an update to an earlier review published in 2002. Included were published papers on clinical studies, case series, and laboratory testing on SSCs (including esthetic SSCs and the Hall technique) in peer-reviewed journals. Study quality and strength of evidence presented were assessed for papers reporting clinical results for SSCs as a primary study outcome using a list of weighting criteria. Sixty-one papers fulfilled the inclusion criteria (24 papers on 22 clinical studies, three case reports, 21 reviews and surveys, and 13 laboratory testing reports on SSCs and esthetic preformed metal crowns for primary and permanent molar teeth). Ten clinical studies achieved weighting scores ranging from 68 percent to 26 percent, with the two highest scoring studies (68 percent and 63 percent) considered good quality. Within the confines of the studies reviewed, primary molar esthetic crowns and SSCs had superior clinical performance as restoratives for posterior primary teeth, and the Hall technique was shown to have validity. No clinical studies were available on zirconia crowns. Further well-designed prospective studies on primary molar esthetic crowns and the Hall technique are needed.

  2. 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.

  3. Effect of cements on fracture resistance of monolithic zirconia crowns

    Science.gov (United States)

    Nakamura, Keisuke; Mouhat, Mathieu; Nergård, John Magnus; Lægreid, Solveig Jenssen; Kanno, Taro; Milleding, Percy; Örtengren, Ulf

    2016-01-01

    Abstract Objectives The present study investigated the effect of cements on fracture resistance of monolithic zirconia crowns in relation to their compressive strength. Materials and methods Four different cements were tested: zinc phosphate cement (ZPC), glass-ionomer cement (GIC), self-adhesive resin-based cement (SRC) and resin-based cement (RC). RC was used in both dual cure mode (RC-D) and chemical cure mode (RC-C). First, the compressive strength of each cement was tested according to a standard (ISO 9917-1:2004). Second, load-to-failure test was performed to analyze the crown fracture resistance. CAD/CAM-produced monolithic zirconia crowns with a minimal thickness of 0.5 mm were prepared and cemented to dies with each cement. The crown–die samples were loaded until fracture. Results The compressive strength of SRC, RC-D and RC-C was significantly higher than those of ZPC and GIC (p crown between the groups. Conclusion The values achieved in the load-to-failure test suggest that monolithic zirconia crowns with a minimal thickness of 0.5 mm may have good resistance against fracture regardless of types of cements. PMID:27335900

  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. Fracture Strength After Fatigue Loading of Lithium Disilicate Pressed Zirconia Crowns.

    Science.gov (United States)

    Kim, So-Yeun; Choi, Jae-Won; Ju, Sung-Won; Ahn, Jin-Soo; Yoon, Mi-Jung; Huh, Jung-Bo

    2016-01-01

    The aim of this study was to evaluate the fracture resistance of fatigued lithium disilicate pressed zirconia crowns versus other ceramic crowns. Lithium disilicate pressed zirconia, fluorapatite pressed zirconia, monolithic lithium disilicate, and monolithic zirconia crowns were fabricated. Cyclic and static loadings were applied to the mesiobuccal cusp tip after thermocycling and fracture strengths were recorded. Fatigued lithium disilicate pressed zirconia crowns were found to have a fracture resistance of 9,117.81 ± 727.04 N, compared with 9,240.61 ± 887.21 N for monolithic zirconia crowns, 3,030.18 ± 1,505.83 N for fluorapatite pressed zirconia crowns, and 4,173.94 ± 877.46 N for monolithic lithium disilicate crowns (P = .001). This in vitro study shows that fatigued lithium disilicate pressed zirconia and monolithic zirconia crowns have better fracture resistance than fluorapatite pressed zirconia and monolithic lithium disilicate crowns.

  6. 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...

  7. Chipping Resistance of Graded Zirconia Ceramics for Dental Crowns

    Science.gov (United States)

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

    2012-01-01

    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. PMID:22232142

  8. Microleakage of core materials for complete cast gold crowns.

    Science.gov (United States)

    Tjan, A H; Chiu, J

    1989-06-01

    This study evaluated the microleakage patterns of complete cast-gold crowns cemented onto teeth rebuilt with pin-retained cores made from cast gold, amalgam, composite resin, and silver-reinforced glass ionomer by using three different cements (zinc phosphate, glass ionomer, and resin cement). Crowns cemented onto unrebuilt tooth preparations with zinc phosphate cement served as controls. The cemented specimens were thermocycled between 4 degrees and 50 degrees C in waterbaths. They were then embedded in epoxy resin and sectioned. The extent of marginal microleakage was evaluated with a stereomicroscope and scored. The findings indicated that the type of luting agent used appeared to affect microleakage more than the core material. No significant differences in the degree of microleakage were found under crowns cemented onto teeth rebuilt with the four core materials when cemented with the same luting cement.

  9. A zirconia implant-crown system: a case report.

    Science.gov (United States)

    Kohal, Ralf J; Klaus, Gerold

    2004-04-01

    Exposed metal crown margins in the porcelain-fused-to-metal technique might be an esthetic problem. Therefore, all-ceramic crown systems are used for restoring teeth and dental implants. In addition, the gray color of a titanium implant might hamper the esthetic appearance of the entire reconstruction in cases of thin peri-implant soft tissue or tissue retraction. To further improve the esthetic aspect of dental implants, efforts are undertaken to develop implant systems fabricated out of tooth-colored materials that are biocompatible and able to withstand masticatory forces. One such material may be zirconia. The present article presents a case in which an all-ceramic custom-made zirconia implant-crown system was used for the replacement of a single tooth.

  10. Retention of crowns cemented on implant abutments with temporary cements.

    Science.gov (United States)

    Nagasawa, Yuko; Hibino, Yasushi; Nakajima, Hiroshi

    2014-01-01

    This study was to examine the retentive force of crowns to implant abutments with commercial temporary cements. Six different temporary cements were investigated. Cast crowns were cemented to the abutments using each cement and their retentive forces to abutments were determined 7 or 28 days after cementing (n=10). The retentive force of the cements to abutments varied widely among the products [27-109 N (7-day), 18-80 N (28-days)]. The retentive force of all the cements was not reduced as the time elapsed, except for two products tested. The polycarboxylate cements and paste-mixing type eugenol-free cements revealed comparable retentive force after 28 days of storage. The powder-liquid type cements showed a positive correlation (pcement between the retentive force and compressive strength. Mechanical strength of temporary cements could not be a prominent predicting factor for retention of the crowns on the abutments.

  11. 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

  12. 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.

  13. Provisional crown failures in dental school predoctoral clinics.

    Science.gov (United States)

    Hyde, Jeffrey D; Bader, James A; Shugars, Daniel A

    2007-11-01

    Following a preliminary study indicating that at least 10 percent of single-unit crown temporary restorations failed in patients who received treatment by predoctoral students, a comprehensive examination of provisional crown failure was initiated to identify strategies to reduce the failure rate. For all provisionalized, natural tooth, single-unit crown preparations in University of North Carolina School of Dentistry predoctoral clinics for one year (N=1008), we noted tooth type, type of crown, student level, faculty coverage experience, treatment clinic, temporary material and luting agent, and retreatment (failure) of the provisional restoration. For failures, we also noted the stage of crown preparation at failure and the time since initial placement of the temporary. We analyzed these data using simple cross-tabs and logistic regression on need for retreatment (alpha =0.05). The failure rate was 18.75 percent (N=189). The median time to failure was twelve days; the 25(th) and 75(th) percentiles were six and twenty-six days. Significant risk factors, in order of odds ratio estimates, were molar tooth, second- or third-year student, and inexperienced faculty. Most provisional failures occurred during the final preparation phase of treatment. Provisional restoration failure is more frequent than was initially suspected from preliminary studies. Strategies for institutional intervention to reduce provisional restoration failure include greater attention to evaluating provisional crowns placed by inexperienced students (sophomores and juniors) and placing more emphasis on the retentiveness of provisional restorations reused following the final impression. Review of provisional evaluation procedures is also indicated for faculty who do not routinely supervise these procedures.

  14. Immediate esthetic crown with a facet of the extracted element.

    Science.gov (United States)

    Di Giacomo, Giovanni de Almeida Prado; Magalhães, Amanda; Ajzen, Sergio

    2014-07-01

    The present report describes a case of implant loading with an immediate temporary crown. The buccal crown surface was removed from the extracted tooth to obtain an aesthetically satisfactory result. After periodontal treatment, tooth 21 appeared proclined and showed Grade 3 mobility, indicating the need for its extraction. The remaining bone was imaged using computed tomography, and virtual surgical planning was performed using these results. The implant was immediately loaded postextraction into the fresh alveolus without a graft and flap procedure. The temporary tooth, which was manufactured using the extracted buccal surface, was a simple, fast, and low cost procedure that produced an excellent esthetic outcome.

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

    DEFF Research Database (Denmark)

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

    2012-01-01

    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...... 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...

  16. Evaluation of retention of cemented laser-sintered crowns on unmodified straight narrow implant abutments.

    Science.gov (United States)

    Kilicarslan, Mehmet Ali; Ozkan, Pelin

    2013-01-01

    A common problem with cemented crowns is inadequate retention at the crown-abutment interface. The aim of this study was to compare the retention of new laser-sintered cobalt-chromium alloy crowns to the retention of cobalt-chromium alloy crowns fabricated with a traditional casting technique with and without an alloy primer. Twenty-four metallic crowns per casting technique were fabricated, and surface roughness values were recorded with a profilometer. Alloy primer was applied to half the specimens, and all crowns were luted with resin cement. After 24 hours, specimens were subjected to tensile force application with a universal testing machine. The effect of the cement amount was evaluated with an analytic balance. The results were compared using the Kruskal-Wallis multiple-comparison test. The Spearman correlation was used to determine correlations between crown retention and cement weight. The laser-sintered crowns (2.72 μm) were rougher than conventionally cast crowns. The mean load to failure values were as follows: 455.10 ± 192.69 Ncm for conventional crowns, 565.52 ± 112.87 Ncm for conventional crowns with alloy primer, 534.78 ± 130.15 Ncm for laser-sintered crowns, and 678.60 ± 212.83 Ncm for laser-sintered crowns with alloy primer. Laser-sintered crowns (10.10 ± 2.15 mg) showed a significant difference in terms of cement weight compared with cast crowns. In addition, negative correlations were found for retention and cement weight between all groups, except for the laser-sintered group without alloy primer. Retentive forces were significantly higher for laser-sintered crowns than for conventionally cast crowns. An increase in the surface roughness and the application of alloy primers led to an increase in the adhesive bonding of resin cements to metal alloys. It was concluded that a reduction in cement weight improved retention.

  17. 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.

  18. Synthese de champs sonores adaptative

    Science.gov (United States)

    Gauthier, Philippe-Aubert

    La reproduction de champs acoustiques est une approche physique au probleme technologique de la spatialisation sonore. Cette these concerne l'aspect physique de la reproduction de champs acoustiques. L'objectif principal est l'amelioration de la reproduction de champs acoustiques par "synthese de champs acoustiques" ("Wave Field Synthesis", WFS), une approche connue, basee sur des hypotheses de champ libre, a l'aide du controle actif par l'ajout de capteurs de l'erreur de reproduction et d'une boucle fermee. Un premier chapitre technique (chapitre 4) expose les resultats d'appreciation objective de la WFS par simulations et mesures experimentales. L'effet indesirable de la salle de reproduction sur les qualites objectives de la WFS fut illustre. Une premiere question de recherche fut ensuite abordee (chapitre 5), a savoir s'il est possible de reproduire des champs progressifs en salle dans un paradigme physique de controle actif: cette possibilite fut prouvee. L'approche technique privilegiee, "synthese de champs adaptative" ("Adaptive Wave Field Synthesis" [AWFS]), fut definie, puis simulee (chapitre 6). Cette approche d'AWFS comporte une originalite en controle actif et en reproduction de champs acoustiques: la fonction cout quadratique representant la minimisation des erreurs de reproduction inclut une regularisation de Tikhonov avec solution a priori qui vient de la WFS. L'etude de l'AWFS a l'aide de la decomposition en valeurs singulieres (chapitre 7) a permis de comprendre les mecanismes propres a l'AWFS. C'est la deuxieme principale originalite de la these. L'algorithme FXLMS (LMS et reference filtree) est modifie pour l'AWFS (chapitre 8). Le decouplage du systeme par decomposition en valeurs singulieres est illustre dans le domaine du traitement de signal et l'AWFS basee sur le controle independant des modes de rayonnement est simulee (chapitre 8). Ce qui constitue la troisieme originalite principale de cette these. Ces simulations du traitement de signal

  19. Changes in retention force with electroplated copings on conical crowns: a comparison of gold and zirconia primary crowns.

    Science.gov (United States)

    Bayer, Stefan; Kraus, Dominik; Keilig, Ludger; Gölz, Lina; Stark, Helmut; Enkling, Norbert

    2012-01-01

    The aim of this study was to examine the wear behavior of conical crowns with electroplated gold copings that are used to connect implants and teeth to a removable denture. Gold alloy and zirconium dioxide ceramic crowns were compared. Fifteen crowns each were milled for two groups: gold alloy and zirconium dioxide. Each specimen had a 2-degree taper. The electroplated coping was established by direct electroforming. The retentive forces and the correlating distance during insertion and separation were measured after 10,000 wear cycles were applied. The wear testing was separated into 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 0.3 mm of each cycle were calculated. The changes in retention force and integral did not differ significantly between both groups in the start and the initial wear phase. No differences were seen in force development during the long-term wear period. Only the force-distance integral showed a significant difference: the median values of the gold crowns increased slightly, and they decreased slightly for the zirconia crowns. The median force values never fell below 6 N for gold and 4 N for zirconia. Within the limitations of this study, the tested conical crowns showed clinically acceptable retentive properties. As with other retentive elements for dentures, the specimens tested showed the greatest amount of change in retentive forces during the first 2,000 cycles. The development of retention force in both groups was not significantly different. However, the zirconia specimens showed reduced variability, which is preferable in clinical practice.

  20. Fluorescence Sensing Properties of Thiazolobenzo-crown Ether Incorporating Coumarin

    International Nuclear Information System (INIS)

    Lee, Sang Hoon; Helal, Aasif; Kim, Hong Seok

    2010-01-01

    A new coumarin-thiazolobenzo-crown ether based fluorogenic chemosensor BTC (1) was reported. The ion-selective binding properties of 1 with different alkali, alkaline earth metals and transitional metals were investigated in an ethanol- DMSO system. BTC (1) showed the highest binding constant toward Hg 2+ over Ag + , Pb 2+ and Cu 2+

  1. Fracture Resistance Force of Primary Molar Crowns Milled from ...

    African Journals Online (AJOL)

    2018-04-04

    Apr 4, 2018 ... and porcelain‑based ceramic blocks, metal alloy blocks, and various composite ... Mete, et al.: Primary molar CAD/CAM crowns brittleness, tendency to fracturing, and attrition on the enamel of the antagonist tooth.[9‑13] To overcome its ..... Yilmaz A, Ozdemir CE, Yilmaz Y. A delayed hypersensitivity reaction ...

  2. Effect of detachment time of pineapple ( Ananas comosus L .) crown ...

    African Journals Online (AJOL)

    A limiting factor to large scale production of pineapple is the scarcity of planting materials. The use of pineapple crown as a propagation material is common, but with no regard to length of time after detachment. A study was conducted in the late seasons of 2007 and 2008 at the Teaching and Research Farm Ekiti State ...

  3. Fracture Resistance Force of Primary Molar Crowns Milled from ...

    African Journals Online (AJOL)

    2018-04-04

    Apr 4, 2018 ... are used.[8]. Glass‑ceramic material that is widely used with. CAD/CAM technologies has both advantages such as the esthetic appearance, color stability, biocompatibility, and life‑long durability and disadvantages such as. Original Article. Introduction. Stainless steel crowns (SSCs) were introduced by.

  4. CAD/CAM technology for implant abutments, crowns, and superstructures.

    Science.gov (United States)

    Kapos, Theodoros; Evans, Christopher

    2014-01-01

    The aim of this systematic review was to compare implant prostheses fabricated by computer-assisted design and computer-assisted manufacturing (CAD/CAM) with conventionally fabricated implant prostheses when assessing esthetics, complications (biologic and mechanical), patient satisfaction, and economic factors. Electronic searches for clinical studies focusing on long-term follow-up were performed using the PubMed and Ovid search engines. Concentrating on the restorative aspect of the CAD/CAM technology applicable to implant dentistry, pertinent literature was divided into articles related to implant abutments, crowns, and frameworks. A total of 18 articles satisfied the inclusion criteria. Two articles reported on CAD/CAM crowns, six on abutments, and 10 on implant-supported CAD/CAM frameworks. The mean survival rate for CAD/CAM crowns was 98.85% and for CAD/CAM abutments 100%. The mean survival rate for CAD/CAM frameworks was 95.98%. Based on the current literature, CAD/CAM fabricated crowns, abutments, and frameworks demonstrate survival rates comparable to conventionally fabricated prostheses. Implant survival appears unaffected by fabrication technique. Since this technology encompasses several manufacturing variations, a new definition might be necessary to accurately define the processes under which the CAD/CAM restorations are fabricated. "Complete CAD/CAM product" where no or minimal manual intervention is employed could be a possible term.

  5. Evaluaton of Wild Juglans Species for Crown Gall Resistance

    Science.gov (United States)

    Crown Gall disease of walnut is caused by the ubiquitous soil-borne bacterium, Agrobacterium tumefaciens, which is able to transfer a specific piece of its own DNA into the genome of the plant host cell. The result of this genetic transformation is the autonomous undifferentiated massive growth of ...

  6. Loading capacity of zirconia implant supported hybrid ceramic crowns.

    Science.gov (United States)

    Rohr, Nadja; Coldea, Andrea; Zitzmann, Nicola U; Fischer, Jens

    2015-12-01

    Recently a polymer infiltrated hybrid ceramic was developed, which is characterized by a low elastic modulus and therefore may be considered as potential material for implant supported single crowns. The purpose of the study was to evaluate the loading capacity of hybrid ceramic single crowns on one-piece zirconia implants with respect to the cement type. Fracture load tests were performed on standardized molar crowns milled from hybrid ceramic or feldspar ceramic, cemented to zirconia implants with either machined or etched intaglio surface using four different resin composite cements. Flexure strength, elastic modulus, indirect tensile strength and compressive strength of the cements were measured. Statistical analysis was performed using two-way ANOVA (p=0.05). The hybrid ceramic exhibited statistically significant higher fracture load values than the feldspar ceramic. Fracture load values and compressive strength values of the respective cements were correlated. Highest fracture load values were achieved with an adhesive cement (1253±148N). Etching of the intaglio surface did not improve the fracture load. Loading capacity of hybrid ceramic single crowns on one-piece zirconia implants is superior to that of feldspar ceramic. To achieve maximal loading capacity for permanent cementation of full-ceramic restorations on zirconia implants, self-adhesive or adhesive cements with a high compressive strength should be used. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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

    NARCIS (Netherlands)

    van Unen, D.J.; Engbersen, Johannes F.J.; Reinhoudt, David

    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

  8. Mandibular molar crown-topography, a biological predisposing ...

    African Journals Online (AJOL)

    Mandibular molar crown-topography, a biological predisposing factor to development of caries – a post-mortem analysis of 2500 extracted lower permanent molars at ... (12.57%), distol surface attack 1,528 (12.22%) buccal surface attack 926 (7.40%), lingual surface attack 59 (0.47%) occlusal surface attack 6540 (52.32%).

  9. Bio-inspired ion selective crown-ether polymer membranes

    NARCIS (Netherlands)

    Tas, Sinem

    2016-01-01

    Development of unctional membranes that are capable of selectively recognizing and transporting ions have key importance for the recovery and separation of specific icons (e.d. K+, Li+, Na+) from multicomponent mixtures. In this thesis, new membrane materials based on crown ether-metal ion

  10. Management of crown-of-thorns sea star (

    NARCIS (Netherlands)

    Bos, A.R.; Gumanao, G.S.; Mueller, B.; Saceda-Cardoza, M.M.E.

    2013-01-01

    Removals of crown-of-thorns sea stars (Acanthaster planci L) are crucial initiatives in limiting the damage to coral reefs during outbreaks, but have often been unable to control the populations. We hypothesized that reef topography and exact timing of removals (before reproduction) determine their

  11. Novel Ordered Crown Ether-Containing Polyimides for Ion Conduction

    Science.gov (United States)

    Irvin, Jennifer A.; Stasko, Daniel; Fallis, Stephen; Guenthner, Andrew J.; Webber, Cynthia; Blackwell, John; Chvalun, Sergei N.

    2003-01-01

    We report the synthesis and characterization of thermally-stable polyimides for use as battery and fuel cell electrolyte membranes. Dianhydrides used were 1,4,5,8- naphthalenetetracarboxylic dianhydride and/or 4,4'-(hexafluoroisopropylidene)diphthalic anhydride. Diamines used were anti-4,4-diaminodibenzo-l8-crown-6, 4,4'- diaminodibenzo-24-crown-8, 2,2-bis(4-aminophenyl)hexafluoropropane, and/or 2,5- diaminobenzenesulfonic acid. The polymers were characterized using electrochemical impedance spectroscopy (EIS), thermal analysis and X-ray diffraction. Polymers containing the hexafluoroisopropylidene (HFIP) group were soluble in common organic solvents, while polymers without the HFIP group were very poorly soluble. Sulfonation yields polymers that are sparingly soluble in aqueous base and/or methanol. Degree of sulfonation, determined by titration, was between one and three sulfonate groups per repeat unit. Proton conductivity was determined as a function of water content, with a maximum conductivity of l x 10(exp -2) per centimeter when fully hydrated. Crown ether-containing polymers exhibit a high degree of order that may be indicative of crown ether channel formation, which may facilitate Li(+) transport for use in battery membranes.

  12. Chemical constituent analysis of the crown-of-thorns starfish ...

    African Journals Online (AJOL)

    The crown-of-thorns starfish Acanthaster planci is a major management issue on coral reefs and the exploring of effective control methods to the starfish is an interesting goal. In this study, the chemical constituent of the starfish were analyzed and the toxicity of the starfish was tested when it was used as mice diet.

  13. Towards an optimized method of olive tree crown volume measurement.

    Science.gov (United States)

    Miranda-Fuentes, Antonio; Llorens, Jordi; Gamarra-Diezma, Juan L; Gil-Ribes, Jesús A; Gil, Emilio

    2015-02-04

    Accurate crown characterization of large isolated olive trees is vital for adjusting spray doses in three-dimensional crop agriculture. Among the many methodologies available, laser sensors have proved to be the most reliable and accurate. However, their operation is time consuming and requires specialist knowledge and so a simpler crown characterization method is required. To this end, three methods were evaluated and compared with LiDAR measurements to determine their accuracy: Vertical Crown Projected Area method (VCPA), Ellipsoid Volume method (VE) and Tree Silhouette Volume method (VTS). Trials were performed in three different kinds of olive tree plantations: intensive, adapted one-trunked traditional and traditional. In total, 55 trees were characterized. Results show that all three methods are appropriate to estimate the crown volume, reaching high coefficients of determination: R2 = 0.783, 0.843 and 0.824 for VCPA, VE and VTS, respectively. However, discrepancies arise when evaluating tree plantations separately, especially for traditional trees. Here, correlations between LiDAR volume and other parameters showed that the Mean Vector calculated for VCPA method showed the highest correlation for traditional trees, thus its use in traditional plantations is highly recommended.

  14. Diet of nesting African Crowned Eagles Stephanoaetus coronatus in ...

    African Journals Online (AJOL)

    The aim of this study was to investigate the species composition of prey caught in the forest, savanna and emerging habitats in which African Crowned Eagles Stephanoaetus coronatus breed in KwaZulu-Natal province, South Africa. At the 17 nest sites, the remains of 195 prey individuals were collected. The five dominant ...

  15. Notes on African Crowned Eagle Stephanoaetus coronatus diet in ...

    African Journals Online (AJOL)

    Our study reports on contrasts in prey items from African Crowned Eagle Stephanoaetus coronatus nesting in forest (n = 1) and savanna (n = 2) biomes in KwaZulu-Natal, South Africa. At least 12 taxa were identified at a forest nest, of which 92.1% were neonate/juvenile. Bovids and procaviids represented 73.7% and 19.6% ...

  16. Towards an Optimized Method of Olive Tree Crown Volume Measurement

    Science.gov (United States)

    Miranda-Fuentes, Antonio; Llorens, Jordi; Gamarra-Diezma, Juan L.; Gil-Ribes, Jesús A.; Gil, Emilio

    2015-01-01

    Accurate crown characterization of large isolated olive trees is vital for adjusting spray doses in three-dimensional crop agriculture. Among the many methodologies available, laser sensors have proved to be the most reliable and accurate. However, their operation is time consuming and requires specialist knowledge and so a simpler crown characterization method is required. To this end, three methods were evaluated and compared with LiDAR measurements to determine their accuracy: Vertical Crown Projected Area method (VCPA), Ellipsoid Volume method (VE) and Tree Silhouette Volume method (VTS). Trials were performed in three different kinds of olive tree plantations: intensive, adapted one-trunked traditional and traditional. In total, 55 trees were characterized. Results show that all three methods are appropriate to estimate the crown volume, reaching high coefficients of determination: R2 = 0.783, 0.843 and 0.824 for VCPA, VE and VTS, respectively. However, discrepancies arise when evaluating tree plantations separately, especially for traditional trees. Here, correlations between LiDAR volume and other parameters showed that the Mean Vector calculated for VCPA method showed the highest correlation for traditional trees, thus its use in traditional plantations is highly recommended. PMID:25658396

  17. Towards an Optimized Method of Olive Tree Crown Volume Measurement

    Directory of Open Access Journals (Sweden)

    Antonio Miranda-Fuentes

    2015-02-01

    Full Text Available Accurate crown characterization of large isolated olive trees is vital for adjusting spray doses in three-dimensional crop agriculture. Among the many methodologies available, laser sensors have proved to be the most reliable and accurate. However, their operation is time consuming and requires specialist knowledge and so a simpler crown characterization method is required. To this end, three methods were evaluated and compared with LiDAR measurements to determine their accuracy: Vertical Crown Projected Area method (VCPA, Ellipsoid Volume method (VE and Tree Silhouette Volume method (VTS. Trials were performed in three different kinds of olive tree plantations: intensive, adapted one-trunked traditional and traditional. In total, 55 trees were characterized. Results show that all three methods are appropriate to estimate the crown volume, reaching high coefficients of determination: R2 = 0.783, 0.843 and 0.824 for VCPA, VE and VTS, respectively. However, discrepancies arise when evaluating tree plantations separately, especially for traditional trees. Here, correlations between LiDAR volume and other parameters showed that the Mean Vector calculated for VCPA method showed the highest correlation for traditional trees, thus its use in traditional plantations is highly recommended.

  18. Protonation of benzo-18-crown-6: Extraction and DFT study

    Czech Academy of Sciences Publication Activity Database

    Toman, Petr; Makrlík, E.; Vaňura, P.; Kašička, Václav

    2011-01-01

    Roč. 225, č. 2 (2011), s. 265-270 ISSN 0942-9352 R&D Projects: GA ČR(CZ) GAP205/10/2280 Institutional research plan: CEZ:AV0Z40500505; CEZ:AV0Z40550506 Keywords : protonation * nitrobenzene * benzo-18-crown-6 Subject RIV: CD - Macromolecular Chemistry Impact factor: 1.568, year: 2011

  19. Evaluating host resistance to Macrophomina crown rot in strawberry

    Science.gov (United States)

    Macrophomina crown rot, caused by the soilborne fungus Macrophomina phaseolina, is an emerging pathogen in California strawberry production. When established, the pathogen can cause extensive plant decline and mortality. Host resistance will be a critical tool for managing this disease and guiding ...

  20. Evolution of the mandibular third premolar crown in early Australopithecus.

    Science.gov (United States)

    Delezene, Lucas K; Kimbel, William H

    2011-06-01

    The Pliocene hominins Australopithecus anamensis and Australopithecus afarensis likely represent ancestor-descendent taxa--possibly an anagenetic lineage--and capture significant change in the morphology of the canine and mandibular third premolar (P(3)) crowns, dental elements that form the canine honing complex in nonhuman catarrhines. This study focuses on the P(3) crown, highlighting plesiomorphic features in A. anamensis. The A. afarensis P(3) crown, in contrast, is variable in its expression of apomorphic features that are characteristic of geologically younger hominins. Temporal variation characterizes each taxon as well. The A. anamensis P(3) from Allia Bay, Kenya expresses apomorphic character states, shared with A. afarensis, which are not seen in the older sample of A. anamensis P(3)s from Kanapoi, Kenya, while spatiotemporal differences in shape exist within the A. afarensis hypodigm. The accumulation of derived features in A. afarensis results in an increased level of P(3) molarisation. P(3) molarisation did not evolve concurrent with postcanine megadontia and neither did the appearance of derived aspects of P(3) occlusal form coincide with the loss of canine honing in hominins, which is apparent prior to the origin of the genus Australopithecus. A. afarensis P(3) variation reveals the independence of shape, size, and occlusal form. The evolution of the P(3) crown in early Australopithecus bridges the wide morphological gap that exists between geologically younger hominins on the one hand and extant apes and Ardipithecus on the other. Copyright © 2011 Elsevier Ltd. All rights reserved.

  1. New die design for dimensional accuracy assessment of crown castings.

    Science.gov (United States)

    Low, Danny

    2003-01-01

    The aim of this study was to introduce a newly designed die for ceramometal restoration, and to compare the dimensional accuracy with the traditional complete-crown design. Two methods of dimensional accuracy assessment, vertical axial discrepancy and transverse diametral percentage, were compared. Patterns were prepared from two different die designs--complete crown and ceramometal. Two investments available for titanium crown casting were used, Titavest CB and T-invest C & B. Titanium castings were made from each investment with a high-pressure casting machine. Vertical axial discrepancy of casting was determined by measuring the discrepancy for each set of wax patterns and their castings on the same die under a traveling microscope. Dimensional accuracy was expressed as vertical axial discrepancy and by transforming the vertical axial discrepancy into transverse diametral percentage. Both dies produced undersized castings with T-invest C & B and oversized castings with Titavest CB. Dimensional accuracy assessment of the two different types of crown casting design showed no significant difference in vertical axial discrepancy. Compared to the traditional transverse diametral percentage calculation, the vertical axial discrepancy assessment is independent of the die's dimensions. The two types of investment materials studied resulted in castings with different dimensional accuracies.

  2. Evaluation of Vertical Marginal Adaptation of Provisional Crowns by ...

    African Journals Online (AJOL)

    2018-01-30

    Jan 30, 2018 ... Department of Prosthetic Dental Sciences, College of Dentistry,. King Saud University, Riyadh, Kingdom of Saudi Arabia. E‑mail: malrifaiy@hotmail.com. How to cite this article: Al Rifaiy MQ. Evaluation of vertical marginal adaptation of provisional crowns by digital microscope. Niger J Clin Pract. 2017 ...

  3. Grey Crowned Cranes Balearica regulorum in urban areas of Uganda

    African Journals Online (AJOL)

    The greatest threat to birds in tropical Africa is habitat change; often a result of unsus- tainable agricultural practices (BirdLife International 2013a) and this certainly applies to Grey Crowned Cranes Balearica regulorum, whose primary breeding habitat — sea- sonal swamps — is increasingly being converted into cultivation ...

  4. Long-term survival of extensive amalgams and posterior crowns.

    Science.gov (United States)

    Smales, R J; Hawthorne, W S

    1997-01-01

    There is very little information available from private dental practices on the comparative survivals of extensive posterior amalgam restorations and posterior crowns placed in the same patient population. Therefore, the present retrospective study examined the performance of such restorations at three long-established Adelaide city practices. Life-table survival estimates were generated for 160 extensive amalgams, 96 cast gold crowns and 174 ceramometal crowns. The restorations were placed by 20 dentists at various times in 100 patients who attended the practices on a regular basis for around 25 years on average. There were no significant differences found in the survival times for both types of crowns, with around 70% still being present at 20 years. However, the median survival time for the extensive amalgams was much lower, at 14.6 years. Despite these differences in survival times, the extensive amalgam restorations survived for longer than is usually expected. In this present study, the survival findings have implications for the most cost-effective dental treatments of large lesions in posterior teeth.

  5. The impact of capture, domestication and trade on Black Crowned ...

    African Journals Online (AJOL)

    The inland delta of the Niger, a vast floodplain, is the only refuge of Black Crowned Cranes in Mali. This study, centred on the regions of Mopti, Tenenkou and Youwarou, aimed to: (1) census the number of cranes in the delta and in captivity in the towns of Mopti and Bamako; (2) examine exploitation at different levels (local ...

  6. 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

  7. Asymptomatic ''crowned dens'' calcification in CT images for the craniovertebral junction

    International Nuclear Information System (INIS)

    Kubota, Gen; Mori, Masataka; Fukushima, Tatsuro

    2007-01-01

    Calcification around the odontoid process suggests 'crowned dens' syndrome, when accompanied with acute occipital headache or neck pain and with inflammatory signs. We retrospectively searched for calcification around the odontoid process in routine CT images of 282 patients emcompassing the craniovertebral junction, and found 13 (4.6%) had 'crowned dens' calcifications with neither characteristic symptoms nor signs suggestive for crowned dens' syndrome. Females of older ages frequently showed asymptomatic crowned dens' calcifications. (author)

  8. Autologous reattachment of complicated crown fractures using intra canal anchorage: Report of two cases

    OpenAIRE

    Kashetty Panchakshari Bharath; Raju Umaji Patil; Haalaswamy Vishwanath Kambalimath; Ashokan Alexander

    2015-01-01

    Crown fractures are most common form of dental trauma sustained by children and adolescents. Major portion of these crown fractures are uncomplicated. Complicated crown fractures though infrequent and account only 4-16%, is an enigma to any clinician. Autologus reattachment of the tooth fragment is a simple and conservative procedure in managing such crown fractures. The present article intends to report the successful clinical management of Autologus tooth fragment reattachment in two compli...

  9. In vitro performance of full-contour zirconia single crowns.

    Science.gov (United States)

    Beuer, Florian; Stimmelmayr, Michael; Gueth, Jan-Frederik; Edelhoff, Daniel; Naumann, Michael

    2012-04-01

    Zirconia based restorations exhibited high failure rates due to veneering-porcelain fractures. Milling to full-contour might be an alternative approach for zirconia restorations. The aim of this study was to evaluate full-contour zirconia crowns in terms of light-transmission, contact wear (restoration and antagonist) and load-bearing capacity. Powder build-up veneered zirconia substructures and CAD/CAM-veneered zirconia substructures served as controls. Four different kinds of crowns were fabricated on 12 metal dies: zirconia substructure with powder build-up porcelain (veneering technique), zirconia substructure with CAD/CAM generated veneering (sintering technique), full-contour zirconia glazed (glazed full-contour) and full-contour zirconia polished (polished full-contour). All crowns had the same dimensions. After light-transmission was measured the crowns were cemented on the corresponding metal dies. The specimens were loaded according to a special wear method in the chewing simulator (120,000 mechanical cycles, 5 kg load, 0.7 mm sliding movement, 320 thermocycles). Wear of the restoration and the antagonist were measured. All specimens were loaded until failure. One-way ANOVA and a LSD post-hoc test were used to compare data at a level of 5%. Polished full-contour showed significantly higher light transmission than the other groups (p=0.003; ANOVA). Polished full-contour exhibited significantly less contact wear at the restoration (p=0.01; ANOVA) and higher contact wear at the antagonist (p=0.016; ANOVA) compared to the other groups. Glazed full-contour zirconia showed similar contact wear at the antagonist compared to veneering technique (p=0.513, post-hoc LSD). Crowns with conventional veneering showed significantly lower load-bearing capacity (pzirconia to full-contour with glazed surface might be an alternative to traditionally veneered restorations. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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

    International Nuclear Information System (INIS)

    Sivaiah, M.V.; Krishna, R.M.; Murthy, G.S.; Venkatesan, K.A.; Sasidhar, P.

    2005-01-01

    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 d ) of 599 and 1007 ml g -1 were obtained, respectively, for the extraction of cesium and strontium from 0.1 M nitric acid by Ben-Crown; K 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 -1 ) intercalated in bentonite. The enthalpy change (ΔH 0 ) for the extraction of cesium and strontium was found to be exothermic. (authors)

  11. Bud development and shoot morphology in relation to crown location

    Science.gov (United States)

    Kukk, Maarja; Sõber, Anu

    2015-01-01

    Plant architecture is shaped by endogenous growth processes interacting with the local environment. The current study investigated crown development in young black alder trees, assessing the effects of local light conditions and branch height on individual bud mass and contents. In addition, we examined the characteristics of parent shoots [the cross-sectional area (CSA) of stem and total leaf area, shoot length, the number of nodes, the number and total mass of buds per shoot] and leaf–stem as well as bud–stem allometry, as several recent studies link bud development to hydraulic architecture. We sampled shoots from top branches and two lower-crown locations: one subjected to deep shade and the other resembling the upper branches in light availability. Sampling was carried out three times between mid-July and late October, spanning from the early stages of bud growth to dormancy. Individual bud mass and shoot characteristics varied in response to light conditions, whereas leaf–stem allometry depended on branch height, most likely compensating for the increasing length of hydraulic pathways. Despite the differences in individual bud mass, the number of preformed leaves varied little across the crown, indicating that the plasticity in shoot characteristics was mainly achieved by neoformation. The relationship between total bud mass and stem CSA scaled similarly across crown locations. However, scaling slopes gradually decreased throughout the sampling period, driven by bud rather than by stem growth. This suggests that the allometry of total bud mass and CSA of stem is regulated locally, instead of resulting from crown-level processes. PMID:26187607

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

    Science.gov (United States)

    Kwon, Taek-Ka; Pak, Hyun-Soon; Han, Jung-Suk; Lee, Jai-Bong; Kim, Sung-Hun

    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 duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns. RESULTS The mean fracture strengths were as follows: 54.9 ± 15.6 N for the Lava CAD/CAM zirconia crowns and 87.0 ± 16.0 N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (Pzirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain. CONCLUSION The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain. PMID:23755332

  13. 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.

  14. Enhancing a eucalypt crown condition indicator driven by high spatial and spectral resolution remote sensing imagery

    Science.gov (United States)

    Evans, Bradley; Lyons, Tom; Barber, Paul; Stone, Christine; Hardy, Giles

    2012-01-01

    Individual crown condition of Eucalyptus gomphocephala was assessed using two classification models to understand changes in forest health through space and time. Using high resolution (0.5 m) digital multispectral imagery, predictor variables were derived from textural and spectral variance of all pixels inside the crown area. The results estimate crown condition as a surrogate for tree health against the total crown health index. Crown condition is derived from combining ground-based crown assessment techniques of density, transparency, dieback, and the regrowth of foliage. This object-based approach summarizes the pixel data into mean crown indices assigned to crown objects which became the carrier of information. Models performed above expectations, with a significant weighted Cohen's kappa (κ>0.60 and p<0.001) using 70% of available data. Using in situ data for model development, crown condition was predicted forwards (2010) and backwards (2007) in time, capturing trends in crown condition and identifying decline in the healthiest between 2008 and 2010. The results confirm that combining spectral and textural information increased model sensitivity to small variations in crown condition. The methodology provides a cost-effective means for monitoring crown condition of this or other eucalypt species in native and plantation forests.

  15. Tree crown structure indicators in a natural uneven-aged mixed coniferous forest in northeastern Mexico

    Science.gov (United States)

    Javier Jimenez-Perez; Oscar Aguirre-Calderon; Horst Kramer

    2006-01-01

    Characterization of tree crown structure provides critical information to assess a variety of ecological conditions for multiple purposes and applications. For biomass growth, for example, tree crowns have basic physiological functions: assimilation, respiration, and transpiration. How tree crowns spatially interact and grow can bring about a seamless landscape of...

  16. The use of Hall technique preformed metal crowns by specialist paediatric dentists in the UK

    OpenAIRE

    Roberts, A; McKay, A; Albadri, S

    2018-01-01

    Examines treatment planning involving Hall technique preformed metal crowns by specialists in paediatric dentistry. Explores clinical situations in which specialists in paediatric dentistry feel it is appropriate or not to fit Hall technique preformed metal crowns. Investigates which types of carious lesions are being treated with Hall technique preformed metal crowns by specialists in paediatric dentistry.

  17. 18-Crown-6 and Dibenzo-18-crown-6 Assisted Extraction of Cesium from Water into Room Temperature Ionic Liquids and Its Correlation with Stability Constants for Cesium Complexes

    Directory of Open Access Journals (Sweden)

    Igor Vladimirovich Pletnev

    2009-12-01

    Full Text Available The pH-profiles of the extraction of Cs+ into four conventional (1-butyl-3-methylimidazolium hexafluorophosphate and bis[trifluoromethylsulphonyl]imides of 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, and 1-(2-ethylhexyl-3- methylimidazolium and two novel (trioctylmethylammonium salicylate and tetrahexylammonium dihexylsulfosuccinate room temperature ionic liquids have been determined both in the absence and in the presence of crown ether (18-crown-6 or dibenzo-18-crown-6. The pH-profiles of distribution ratio of crown ethers have been established in the same conditions. The relationship of cesium extraction efficiency both with the stability of its complexes with crown ethers and crown ethers’ distribution ratio has been clarified.

  18. Perception of Paralinguistic Traits in Synthesized Voices

    DEFF Research Database (Denmark)

    Baird, Alice Emily; Hasse Jørgensen, Stina; Parada-Cabaleiro, Emilia

    the paralinguistic traits of the synthesized voice. Using a corpus of 13 synthesized voices, constructed from acoustic concatenative speech synthesis, we assessed the response of 23 listeners from differing cultural backgrounds. Evaluating if the perception shifts from the known ground–truths, we asked listeners......Along with the rise of artificial intelligence and the internet-of-things, synthesized voices are now common in daily–life, providing us with guidance, assistance, and even companionship. From formant to concatenative synthesis, the synthesized voice continues to be defined by the same traits we...

  19. 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.

  20. 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.

  1. Tensile bond strength of ceramic crowns to dentin using resin cements.

    Science.gov (United States)

    Simon, James F; de Rijk, Waldemar G; Hill, Jennifer; Hill, Nathaniel

    2011-01-01

    This study measured the bond strength of the self-adhesive resin cements and a bonded resin cement for crowns bonded to extracted teeth with preparations having a total taper greater than 30 degrees. A crown pull-off test was used with direction of pull along the path of insertion. The CAD/CAM system Cerec was used to create crowns with the pull-off loop as an integral part of the crown structure. One hundred extracted human molars were prepared for all-ceramic crowns with a 1.5-mm shoulder, greater than 30-degree axial wall convergence, a flat occlusal surface and 3 to 5 mm occlusal/ gingival height. All-ceramic crowns were cemented with five different self-adhesive cements (Rely X Unicem, Maxcem Elite, BisCem, SmartCem 2, and G-Cem) and one bonded resin cement (Multilink). Forfour cements (excluding GCem and Multilink) there were 2 groups, one with HF etching and one without ceramic surface treatment. The crowns were then subject to tensile stress until either the crown fractured or the crown was lifted off from the tooth. For several cements, the bond strength exceeded the tensile strength of the all-ceramic crown; thus, the crown fractured, leaving the cemented part of the crown on the tooth. The effect of ceramic surface etching was not statistically significant at p = 0.05; however, for each cement, the treated crowns showed a lower coefficient of variance (COV). For this study, the COV ranged from 24.9 % to 97.9 %. Loads ranged from 41.3 to 190.3 N. Some of the new self-etching resin cements can create bonds to non-retentive crown preparations that are stronger than the strength of a ceramic crown; however, these high bond strengths may not be able to be achieved consistently.

  2. Clinical Evaluation of Monolithic Zirconia Crowns: A Short-Term Pilot Report.

    Science.gov (United States)

    Kitaoka, Aki; Akatsuka, Ryo; Kato, Hiroaki; Yoda, Nobuhiro; Sasaki, Keiichi

    This study aimed to prospectively evaluate the clinical performance of monolithic zirconia crowns made of yttria-stabilized tetragonal zirconia polycrystal. A total of 26 crowns placed on premolar or molar teeth in 18 patients were evaluated at the time of crown placement and at 2 weeks, 6 months, 1 year, and 2 years after placement. Twenty-five crowns rated as satisfactory according to the California Dental Association quality evaluation system. Most of the abutment and antagonist teeth showed good periodontal condition. An enamel cracking occurred on one antagonist tooth 1 year after placement. Monolithic zirconia crowns can be a clinically acceptable prosthetic option.

  3. 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.

  4. 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 ...

  5. Clinical evaluation of and parental satisfaction with resin-faced stainless steel crowns.

    Science.gov (United States)

    Roberts, C; Lee, J Y; Wright, J T

    2001-01-01

    This study evaluated the clinical success and parental acceptance of anterior primary dentition caries treatment with prefabricated resin-faced stainless steel crowns. A retrospective analysis of maxillary anterior primary dentition caries treatment using Whiter Biter II Crowns was performed. Each crown was evaluated for retention, fracture, interface failure, color match, marginal integrity, and surface texture. Parental satisfaction regarding the esthetics of the crowns was evaluated by survey. Thirty-eight crowns were evaluated in 12 children. The average crown age at time of examination was 20.7 months. Three teeth were lost to trauma with all other crowns remaining intact. Twelve crowns (32%) showed loss of at least some facial resin. Nine crowns (24%) had complete loss of the resin facing. Overall parental satisfaction with the treatment was excellent, however, satisfaction with crown esthetics received the lowest rating. While parental satisfaction with treatment of anterior primary dentition caries with prefabricated resin-faced stainless steel crowns is excellent, the high failure rate of the resin facings is problematic.

  6. Effect of water temperature on the fit of provisional crown margins during polymerization.

    Science.gov (United States)

    Ogawa, T; Aizawa, S; Tanaka, M; Matsuya, S; Hasegawa, A; Koyano, K

    1999-12-01

    When fabricating a provisional crown with the direct technique, dentists are concerned with margin discrepancies that result from polymerization shrinkage. This in vitro study examined the effect of water temperature on the fit of provisional crown margins during resin polymerization. The experiment was designed to simulate a direct technique to fabricate provisional crowns. After mixing autopolymerizing methyl methacrylate resin, the material was placed in a preformed polycarbonate crown. The crown was seated on a prepared premolar-shaped die with a shoulder margin. After 1 minute and 50 seconds, the crown was removed and polymerization was continued under the following conditions: 20 degrees C air, and water at 0 degrees C, 10 degrees C, 20 degrees C, 30 degrees C, 40 degrees C, 60 degrees C, and 80 degrees C. Six minutes after polymerization, the crown was trimmed and reseated on the die. Discrepancy of crown margin was measured with a 3-dimensional digitizer. Margin discrepancy varied with the condition during resin-polymerization (ANOVA, P crowns polymerized in 20 degrees C and 30 degrees C water revealed the best margin fit, showing 3 times more accurate margin fit than those polymerized in 20 degrees C air (Bonferroni/Dunn procedure, P provisional crowns using the direct technique. Water temperatures of 20 degrees C and 30 degrees C produced the best fit at the margin of the provisional crown.

  7. 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.

  8. The marginal fit of selective laser melting-fabricated metal crowns: an in vitro study.

    Science.gov (United States)

    Xu, Dan; Xiang, Nan; Wei, Bin

    2014-12-01

    The selective laser melting technique is attracting interest in prosthetic dentistry. The marginal fit is a key criterion for fixed restorations. The purpose of the study was to evaluate the marginal fit of cast cobalt-chromium alloy crowns versus the fit of selective laser melting-fabricated crowns. The marginal gap widths of 36 single crowns (18 selective laser melting-fabricated cobalt-chromium metal crowns and 18 cobalt-chromium cast crowns) were determined with a silicone replica technique. Each crown specimen was cut into 4 sections, and the marginal gap width of each cross section was evaluated by stereomicroscopy (× 100). The Student t test was used to evaluate whether significant differences occurred in the marginal gap widths between the selective laser melting-fabricated and cast cobalt-chromium metal crowns (α=.05). The mean marginal gap width of the cast crowns (170.19 μm) was significantly wider than that of the selective laser melting-fabricated crowns (102.86 μm). Selective laser melting-fabricate cobalt-chromium dental crowns found improved marginal gap widths compared with traditional cast crowns. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  9. Composites comprising biologically-synthesized nanomaterials

    Science.gov (United States)

    Curran, Seamus; Dias, Sampath; Blau, Werner; Wang, Jun; Oremland, Ronald S; Baesman, Shaun

    2013-04-30

    The present disclosure describes composite materials containing a polymer material and a nanoscale material dispersed in the polymer material. The nanoscale materials may be biologically synthesized, such as tellurium nanorods synthesized by Bacillus selenitireducens. Composite materials of the present disclosure may have optical limiting properties and find use in optical limiting devices.

  10. Perception of Paralinguistic Traits in Synthesized Voices

    DEFF Research Database (Denmark)

    Baird, Alice Emily; Hasse Jørgensen, Stina; Parada-Cabaleiro, Emilia

    2017-01-01

    Along with the rise of artificial intelligence and the internet-of-things, synthesized voices are now common in daily–life, providing us with guidance, assistance, and even companionship. From formant to concatenative synthesis, the synthesized voice continues to be defined by the same traits we...

  11. Crown ethers as size-selective synergists in solvent extraction systems: a new selectivity parameter

    International Nuclear Information System (INIS)

    Kinard, W.F.; McDowell, W.J.

    1981-01-01

    Mixtures of macrocyclic polyethers (crown ethers) and organic-phase-soluble liquid cation exchangers have been found to produce a synergistic effect in the extraction of metal ions. The synergistic effect is size selective; that is, it tends to be greatest for those ions that best fit the crown ether cavity. The mixtures of a liquid cation exchanger and a crown ether also allow metal ion extraction from common mineral-acid anion systems (NO 3 - , Cl - , SO 4 2- ) that would be impossible with the crown ether alone, because of the difficulty of solubilizing those anions in nonpolar solvents. This cooperation makes the use of crown ethers as size-selective coordinators available for process applications. Size selectivity of compounds such as crown ethers may thus become a useful new parameter in designing selective solvent extraction systems. Results are reported for alkali (including Cs) and alkaline earth (including Sr) extraction by HDEHP mixed with various crown ethers. (author)

  12. 18F-fluorination by crown ether-metal fluoride

    International Nuclear Information System (INIS)

    Irie, T.; Fukushi, K.; Ido, T.; Kasida, Y.; Nozaki, T.

    1982-01-01

    18 F-Fluorination by ''naked'' 18 F - anion produced by complexing anhydrous K 18 F, which was prepared from aqueous 18 F, with 18 -Crown-6 was described for preparing 18 F-21-fluoroprogesterone. In order to find out optimum conditions in this labelling method, various factors were investigated such as the solubility of KF in organic solvents containing 18 -Crown-6 and its reactivity for the nucleophilic displacement of 21-mesylate of progesterone. Chloroform was a good solvent in solubilization of KF and its reactivity. Problems in this labelling procedure were also examined, such as a supporter for transferring the labelled anhydrous K 18 F and reaction vessels. Use of a Teflon reaction vessel resulted in a good radiochemical yield based on the starting activity of $ 18 water. (author)

  13. 18F-fluorination by crown ether-metal fluoride

    International Nuclear Information System (INIS)

    Irie, T.; Fukushi, K.; Ido, T.; Kasida, Y.; Nozaki, T.

    1984-01-01

    For non-carrier-added 18 F-labeling of organic compounds, details were studied concerning the previously developed KF-crown ether method. In the modified method, a minute amount of KOH instead of carrier KF is added for the preparation of the anhydrous 18 F from aqueous carrier-free 18 F. The following factors were examined in order to determine optimum conditions for the preparation of the anhydrous non-carrier-added 18 F and the labeling synthesis with it: effects of the vessel on the evaporation of the 18 F-KOH solution and the amount of added KOH for the conversion of aqueous 18 F to anhydrous 18 F, the solubilized activity of the 18 F obtained by the evaporation in organic solutions containing 18-Crown-6 and the labeling reaction, as exemplified by the synthesis of 21-fluoroprogesterone. (author)

  14. 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.

  15. 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.

  16. Design algorithm for generatrix profile of cylindrical crowned rollers

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    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.

  17. Increasing the thermopower of crown-ether-bridged anthraquinones

    Science.gov (United States)

    Ismael, Ali K.; Grace, Iain; Lambert, Colin J.

    2015-10-01

    We investigate strategies for increasing the thermopower of crown-ether-bridged anthraquinones. The novel design feature of these molecules is the presence of either (1) crown-ether or (2) diaza-crown-ether bridges attached to the side of the current-carrying anthraquinone wire. The crown-ether side groups selectively bind alkali-metal cations and when combined with TCNE or TTF dopants, provide a large phase-space for optimising thermoelectric properties. We find that the optimum combination of cations and dopants depends on the temperature range of interest. The thermopowers of both 1 and 2 are negative and at room temperature are optimised by binding with TTF alone, achieving thermpowers of -600 μV K-1 and -285 μV K-1 respectively. At much lower temperatures, which are relevant to cascade coolers, we find that for 1, a combination of TTF and Na+ yields a maximum thermopower of -710 μV K-1 at 70 K, whereas a combination of TTF and Li+ yields a maximum thermopower of -600 μV K-1 at 90 K. For 2, we find that TTF doping yields a maximum thermopower of -800 μV K-1 at 90 K, whereas at 50 K, the largest thermopower (of -600 μV K-1) is obtain by a combination TTF and K+ doping. At room temperature, we obtain power factors of 73 μW m-1 K-2 for 1 (in combination with TTF and Na+) and 90 μW m-1 K-2 for 2 (with TTF). These are higher or comparable with reported power factors of other organic materials.We investigate strategies for increasing the thermopower of crown-ether-bridged anthraquinones. The novel design feature of these molecules is the presence of either (1) crown-ether or (2) diaza-crown-ether bridges attached to the side of the current-carrying anthraquinone wire. The crown-ether side groups selectively bind alkali-metal cations and when combined with TCNE or TTF dopants, provide a large phase-space for optimising thermoelectric properties. We find that the optimum combination of cations and dopants depends on the temperature range of interest. The

  18. Theobrominium perchlorate dibenzo-18-crown-6 3.25-hydrate

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    Vladislav Kulikov

    2013-07-01

    Full Text Available The co-crystal, C7H9N4O2+·ClO4−·C20H24O6·3.25H2O, consists of theobrominium (3,7-dimethyl-2,6-dioxo-1H-purin-9-ium cations, perchlorate anions and dibenzo-18-crown-6 and water molecules. The crown ether is in a bent conformation, in which the planes of the aromatic rings subtend an angle of 63.7 (1°. Intermolecular O—H...O hydrogen bonding between the water molecules and the O atoms of the cyclic ether delimit an empty space reminiscent of a hollow cage. The water molecules are additionally linked to the cations by N—H...O hydrogen bonding. One of the positions of the water molecules is occupied only fractionally (25% and is located outside this framework.

  19. [Finite element analysis of the maxillary central incisor with traditional and modified crown lengthening surgery and post-core restoration in management of crown-root fracture].

    Science.gov (United States)

    Zhen, M; Wei, Y P; Hu, W J; Rong, Q G; Zhang, H

    2016-06-01

    To construct three-dimensional finite element models with modified crown lengthening surgery and post-core restoration in management of various crown-root fracture types, to investigate the intensity and distribution of stressin models mentioned above, and to compare and analyze the indications of traditional and modified crown lengthening surgeries from the mechanic point of view. Nine three-dimensional finite element models with modified crown lengthening surgery and post-core restoration were established and analyzed by micro-CT scanning technique, dental impression scanner, Mimics 10.0, Geomagic studio 9.0 and ANSYS 14.0 software. The von Mises stress of dentin, periodontal ligament, alveolar bone, post and core, as well as the periodontal ligament area and threshold limit value were calculated and compared with the findings of traditional crown lengthening models which had been published earlierby our research group. The von Mises stress intensity of modified crown lengthening models were: dentin>post>core>alveolar bone>periodontal ligament. The maximum von Mises stress of dentin(44.37-80.58 MPa)distributed in lingual central shoulder. The periodontal ligament area of the modified crown lengthening surgery was reduced by 6% to 28%, under the same crown-root fracture conditions, the periodontal ligament area of modified crown lengthening models was larger than that of the traditional crown lengthening models. In modified crown lengthening surgery models, the von Mises stress of periodontal ligament of B3L1m, B3L2m, B3L3m models exceeded their limit values, however, the von Mises stress of periodontal ligament of the B2L2c, B2L3c, B3L1c, B3L2c, B3L3c models exceeded their limit values in traditional crown lengthening surgery models. The modified crown lengthening surgery conserves more periodontal supporting tissues, which facilitates the long-term survival of teeth. The indication of modified crown lengthening surgery is wider than traditional method. The

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

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    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

  1. [Fracture toughness of zirconia ceramic crowns made by feather-edge tooth preparation design].

    Science.gov (United States)

    Mirković, Nemanja; Gostović, Aleksandra Spadijer; Lazić, Zoran; Trifković, Branka

    2012-07-01

    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. 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 mmn 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. 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 2000 N, what was double beyond a recommended value. The mean value of fracture toughness in the feather-edge group was 2090 N, and in shoulder group it was 2214 N. 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 gingival inflammatory response.

  2. Synthesis and Characterisation of Macrocyclic Diamino Chiral Crown Ethers

    Directory of Open Access Journals (Sweden)

    Janet L. Scott

    2004-05-01

    Full Text Available A benign and efficient synthesis of chiral macrocyclic ‘aza-crown’ ethers of varying ring size is reported. The synthesis involves a Schiff base condensation of ether linked dialdehydes of varying chain length and (1R,2R-(–-1,2-diaminocyclohexane under mild conditions to yield the macrocycles, which are subsequently reduced to yield the diamino analogues.

  3. 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....

  4. Provisional Crown Dislodgement during Scuba Diving: A Case of Barotrauma

    OpenAIRE

    Gulve, Meenal Nitin; Gulve, Nitin Dilip

    2013-01-01

    Changes in ambient pressure, for example, during flying, diving, or hyperbaric oxygen therapy, can lead to barotrauma. Although it may seem that this issue was neglected in dental education and research in recent decades, familiarity with and understanding of these facts may be of importance for dental practitioners. We report the case of a patient who experienced barotrauma involving dislodgement of a provisional crown during scuba diving. Patients who are exposed to pressure changes as a pa...

  5. In vitro evaluation of the marginal integrity of CAD/CAM interim crowns.

    Science.gov (United States)

    Kelvin Khng, Kwang Yong; Ettinger, Ronald L; Armstrong, Steven R; Lindquist, Terry; Gratton, David G; Qian, Fang

    2016-05-01

    The accuracy of interim crowns made with computer-aided design and computer-aided manufacturing (CAD/CAM) systems has not been well investigated. The purpose of this in vitro study was to evaluate the marginal integrity of interim crowns made by CAD/CAM compared with that of conventional polymethylmethacrylate (PMMA) crowns. A dentoform mandibular left second premolar was prepared for a ceramic crown and scanned for the fabrication of 60 stereolithical resin dies, half of which were scanned to fabricate 15 Telio CAD-CEREC and 15 Paradigm MZ100-E4D-E4D crowns. Fifteen Caulk and 15 Jet interim crowns were made on the remaining resin dies. All crowns were cemented with Tempgrip under a 17.8-N load, thermocycled for 1000 cycles, placed in 0.5% acid fuschin for 24 hours, and embedded in epoxy resin before sectioning from the mid-buccal to mid-lingual surface. The marginal discrepancy was measured using a traveling microscope, and dye penetration was measured as a percentage of the overall length under the crown. The mean vertical marginal discrepancy of the conventionally made interim crowns was greater than for the CAD/CAM crowns (P=.006), while no difference was found for the horizontal component (P=.276). The mean vertical marginal discrepancy at the facial surface of the Caulk crowns was significantly greater than that of the other 3 types of interim crowns (Pcrowns was significantly larger than that of the other 3 types, with no difference at the lingual margins (P=.150). The mean percentage dye penetration for the Paradigm MZ100-E4D crowns was significantly greater and for Jet crowns significantly smaller than for the other 3 crowns (Pcrowns at the facial surface and with the horizontal marginal discrepancies of the Caulk interim crowns at the lingual surface (Pcrowns fabricated by CAD/CAM as compared with PMMA crowns; however, this difference was not observed for the horizontal component. The percentage dye penetration was correlated with vertical and horizontal

  6. 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.

  7. 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.

    2010-01-01

    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. PMID:20660796

  8. Plant responses to Agrobacterium tumefaciens and crown gall development

    Science.gov (United States)

    Gohlke, Jochen; Deeken, Rosalia

    2014-01-01

    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 tumors. 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 tumor 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. PMID:24795740

  9. Assessment of nickel release from stainless steel crowns.

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    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.

  10. 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.

  11. 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.

  12. Immediate maxillary lateral incisor implants with nonocclusal loading provisional crowns.

    Science.gov (United States)

    Peñarrocha, Miguel; Lamas, Joana; Peñarrocha, Maria; Garcia, Berta

    2008-01-01

    This clinical report series describes a treatment modality involving immediately placed dental implants in maxillary lateral incisor sites using noncemented immediate provisional crowns retained with calcinable copings (prosthetic complement used in preparing the metal for the definitive prosthesis). Ten implants were placed in eight patients for the replacement of maxillary lateral incisors: two immediate and eight corresponding to cases of agenesis. All were subjected to immediate rehabilitation with provisional acrylic resin crowns in nonocclusal loading. One implant failed 3 weeks after placement due to acute local trauma. The other nine remained functional within the mouth, with normal clinical and radiological characteristics after a minimum of 12-month follow-up. Immediate placement of implant fixed provisional restorations retained by friction in maxillary lateral incisors offers an esthetic solution, eliminates the need for a removable provisional restoration, and avoids implant failures associated with excess cement or screw loosening. Moreover, in the case of extractions, immediate placement and provisionalization of implants in maxillary lateral incisors can effectively optimize the peri-implant esthetic results by maintaining the existing hard and soft tissue architecture of the replaced tooth. As no cement or screws are required, and the provisional crowns are placed in nonocclusal loading, the risk of complications is minimized.

  13. In vitro study of fracture strength of provisional crown materials.

    Science.gov (United States)

    Karaokutan, Isil; Sayin, Gulsum; Kara, Ozlem

    2015-02-01

    The purpose of this report was to evaluate the effect of the fabrication method and material type on the fracture strength of provisional crowns. A master model with one crown (maxillary left second premolar) was manufactured from Cr-Co alloy. The master model was scanned, and the data set was transferred to a CAD/CAM unit (Yenamak D50, Yenadent Ltd, Istanbul, Turkey) for the Cercon Base group. For the other groups, temporary crowns were produced by direct fabrication methods (Imident, Temdent, Structur Premium, Takilon, Systemp c&b II, and Acrytemp). The specimens were subjected to water storage at 37℃ for 24 hours, and then they were thermocycled (TC, 5000×, 5-55℃) (n=10). The maximum force at fracture (Fmax) was measured in a universal test machine at 1 mm/min. Data was analyzed by non-parametric statistics (α=.05). Fmax values varied between 711.09-1392.1 N. In the PMMA groups, Takilon showed the lowest values (711.09 N), and Cercon Base showed the highest values (959.59 N). In the composite groups, Structur Premium showed the highest values (1392.1 N), and Acrytemp showed the lowest values (910.05 N). The composite groups showed significantly higher values than the PMMA groups (P=.01). Composite-based materials showed significantly higher fracture strengths than PMMA-based materials. The CAD-CAM technique offers more advantages than the direct technique.

  14. Descriptive statistics of tree crown condition in the Southern United States and impacts on data analysis and interpretation

    Science.gov (United States)

    KaDonna C. Randolph

    2006-01-01

    The U.S. Department of Agriculture Forest Service, Forest Inventory and Analysis Program (FIA) utilizes visual assessments of tree crown condition to monitor changes and trends in forest health. This report describes and discusses distributions of three FIA crown condition indicators (crown density, crown dieback, and foliage transparency) for trees in the Southern...

  15. Comparative evaluation of marginal leakage of provisional crowns cemented with different temporary luting cements: In vitro study

    Directory of Open Access Journals (Sweden)

    Sheen Juneja Arora

    2016-01-01

    Conclusion: The temporary cements with eugenol showed more microleakage than those without eugenol. SC-10 crowns showed more microleakage compared to Protemp 4 crowns. SC-10 crowns cemented with Kalzinol showed maximum microleakage and Protemp 4 crowns cemented with HY bond showed least microleakage.

  16. Synthesis of l-threitol-based crown ethers and their application as enantioselective phase transfer catalyst in Michael additions.

    Science.gov (United States)

    Rapi, Zsolt; Nemcsok, Tamás; Pálvölgyi, Ádám; Keglevich, György; Grün, Alajos; Bakó, Péter

    2017-06-01

    A few new l-threitol-based lariat ethers incorporating a monoaza-15-crown-5 unit were synthesized starting from diethyl l-tartrate. These macrocycles were used as phase transfer catalysts in asymmetric Michael addition reactions under mild conditions to afford the adducts in a few cases in good to excellent enantioselectivities. The addition of 2-nitropropane to trans-chalcone, and the reaction of diethyl acetamidomalonate with β-nitrostyrene resulted in the chiral Michael adducts in good enantioselectivities (90% and 95%, respectively). The substituents of chalcone had a significant impact on the yield and enantioselectivity in the reaction of diethyl acetoxymalonate. The highest enantiomeric excess (ee) values (99% ee) were measured in the case of 4-chloro- and 4-methoxychalcone. The phase transfer catalyzed cyclopropanation reaction of chalcone and benzylidene-malononitriles using diethyl bromomalonate as the nucleophile (MIRC reaction) was also developed. The corresponding chiral cyclopropane diesters were obtained in moderate to good (up to 99%) enantioselectivities in the presence of the threitol-based crown ethers. © 2017 Wiley Periodicals, Inc.

  17. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

    Science.gov (United States)

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-08-01

    Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

  18. In vitro microleakage of luting cements and crown foundation material.

    Science.gov (United States)

    Lindquist, T J; Connolly, J

    2001-03-01

    Microleakage is a concern for the long-term prognosis of a cemented crown and foundation. The aims of this investigation were, first, to evaluate microleakage of zinc phosphate cement and resin-reinforced glass ionomer cement under ideal (dry) versus contaminated (wet) conditions, and second, to compare 3 foundations under both ideal and contaminated conditions. One hundred forty extracted molar teeth were cleaned and mounted. Tooth preparations for complete veneer cast crowns were completed with a chamfer finish line. A mesial surface class II cavity preparation 4 mm wide buccolingually and 2 mm deep was made in each tooth. Seven restorative groups were formed: amalgam/cavity varnish, amalgam/dentinal bonding agent, and composite/dentinal bonding agent, each with dry and contaminated groups, and a seventh group of class II cavity preparations without foundations. Finish lines for crown margins were refined 1.5 mm gingival to the restoration. Artificial crowns were cast in type III gold. Treatment groups were divided into 4 cement groups: dry and contaminated zinc phosphate cement and dry and contaminated resin-reinforced glass ionomer cement. The specimens were thermocycled and immersed in erythrosine B solution for 24 hours. Subsequently, they were rinsed, and their coronal portions were embedded in clear resin. Teeth were sectioned mesiodistally, and standard photomicrographs were made. The microleakage of each restoration and crown was measured. The least foundation microleakage was recorded for amalgam/dentinal bonding agents (ideal group) and composite/dentinal bonding agents (ideal group). The most microleakage was observed within the group without a foundation. In cement groups, the control and experiment sides were evaluated separately but displayed the same order of finding. The least leakage was recorded with resin-reinforced glass ionomer cement (ideal group); the most microleakage was noted with zinc phosphate cement (ideal group). An interaction was

  19. Retention of metal-ceramic crowns with contemporary dental cements.

    Science.gov (United States)

    Johnson, Glen H; Lepe, Xavier; Zhang, Hai; Wataha, John C

    2009-09-01

    New types of crown and bridge cement are in use by practitioners, and independent studies are needed to assess their effectiveness. The authors conducted a study in three parts (study A, study B, and study C) and to determine how well these new cements retain metal-ceramic crowns. The authors prepared teeth with a 20-degree taper and a 4-millimeter length. They cast high-noble metal-ceramic copings, then fitted and cemented them with a force of 196 newtons. The types of cements they used were zinc phosphate, resin-modified glass ionomer, conventional resin and self-adhesive modified resin. They thermally cycled the cemented copings, then removed them. They recorded the removal force and calculated the stress of dislodgment by using the surface area of each preparation. They used a single-factor analysis of variance to analyze the data (alpha = .05). The mean stresses necessary to remove crowns, in megapascals, were 8.0 for RelyX Luting (3M ESPE, St. Paul, Minn.), 7.3 for RelyX Unicem (3M ESPE), 5.7 for Panavia F (Kuraray America, New York) and 4.0 for Fuji Plus (GC America, Alsip, Ill.) in study A; 8.1 for RelyX Luting, 2.6 for RelyX Luting Plus (3M ESPE) and 2.8 for Fuji CEM (GC America) in study B; and 4.9 for Maxcem (Kerr, Orange, Calif.), 4.0 for BisCem (Bisco, Schaumburg, Ill.), 3.7 for RelyX Unicem Clicker (3M ESPE), 2.9 for iCEM (Heraeus Kulzer, Armonk, N.Y.) and 2.3 for Fleck's Zinc Cement (Keystone Industries, Cherry Hill, N.J.) in study C. Powder-liquid versions of new cements were significantly more retentive than were paste-paste versions of the same cements. The mean value of crown removal stress for the new self-adhesive modified-resin cements varied appreciably among the four cements tested. All cements retained castings as well as or better than did zinc phosphate cement. Powder-liquid versions of cements, although less convenient to mix, may be a better clinical choice when crown retention is an issue. All cements tested will retain castings

  20. Inter-organ defense networking: Leaf whitefly sucking elicits plant immunity to crown gall disease caused by Agrobacterium tumefaciens.

    Science.gov (United States)

    Park, Yong-Soon; Ryu, Choong-Min

    2015-01-01

    Plants have elaborate defensive machinery to protect against numerous pathogens and insects. Plant hormones function as modulators of defensive mechanisms to maintain plant resistance to natural enemies. Our recent study suggests that salicylic acid (SA) is the primary phytohormone regulating plant responses to Agrobacterium tumefaciens infection. Tobacco (Nicotiana benthamiana Domin.) immune responses against Agrobacterium-mediated crown gall disease were activated by exposure to the sucking insect whitefly, which stimulated SA biosynthesis in aerial tissues; in turn, SA synthesized in aboveground tissues systemically modulated SA secretion in root tissues. Further investigation revealed that endogenous SA biosynthesis negatively modulated Agrobacterium-mediated plant genetic transformation. Our study provides novel evidence that activation of the SA-signaling pathway mediated by a sucking insect infestation has a pivotal role in subsequently attenuating Agrobacterium infection. These results demonstrate new insights into interspecies cross-talking among insects, plants, and soil bacteria.

  1. 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...... 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......, 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 (ptooth (p=.415...

  2. Twenty-year follow-up of metal-ceramic single crowns: a retrospective study.

    Science.gov (United States)

    Näpänkangas, Ritva; Raustia, Aune

    2008-01-01

    The aim of this clinical retrospective study was to evaluate the survival and success of single metal-ceramic crowns after 20 years. The biologic and technical complications as well as patient satisfaction were recorded. Fifty patients treated with 100 single metal-ceramic crowns attended the clinical 20-year follow-up examination. The mean follow-up time was 18.8 years (17.5 to 20.5 years). Twenty-one teeth with single crowns were extracted because of root fractures or esthetic or periodontal reasons. Ninety-seven percent of the subjects had no complaints about the esthetics of the crowns. The most common clinical findings were supragingival crown margins caused by gingival recessions, gingival bleeding on probing, and occlusal wear in opposing teeth. The success of the crowns after 20 years was 75%, and the survival was 78%. In the 20-year follow-up of single metal-ceramic crowns, there were few biologic and technical complications, and patients were satisfied with the crowns. Crown removal was in most cases the result of root fractures in single crowns with endodontic posts.

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

    Science.gov (United States)

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

    2014-01-01

    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. PMID:24698209

  4. 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.

  5. Strength of CAD/CAM-generated esthetic ceramic molar implant crowns.

    Science.gov (United States)

    Wolf, Daniel; Bindl, Andreas; Schmidlin, Patrick R; Lüthy, Heinz; Mörmann, Werner H

    2008-01-01

    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. 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) and zirconia (2) abutments: noncemented (a) and with nonadhesive cement (b) or 2 adhesive resin-based cements (c) and (d). In addition, 15 molar crowns with 5.5-mm occlusal thickness were seated on short zirconia abutments (3) using cements (c) and (d). All crowns had the identical occlusal morphology and were loaded with a crosshead speed of 0.5 mm/min until fracture. Load data were analyzed using 2-way ANOVA, the Scheffé test, and Weibull probability of failure analysis. Fracture loads of 1.5-mm occlusal thickness crowns (a, b, c, d) were higher (P crowns (except for group ld). Occlusal 5.5-mm crowns on short zirconia abutments had similar (2c) or less (2d) strength than the respective 1.5-mm crowns. Nonadhesive crowns (1b, 2b) were weaker (P crowns (1c, 1d, 2c, 2d). Fracture loads of 0.5- and 1.5-mm crowns were significantly higher on titanium than on zirconia abutments with both cements. Adhesive cement d generally showed higher fracture loads than c on both titanium and zirconia. Esthetic ceramic CAD/CAM molar implant crowns gained high strength with adhesive cements on both titanium and zirconia implant abutments compared to nonadhesive cementation.

  6. 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.

  7. Separation of calcium-48 isotope by crown ether chromatography using ethanol/hydrochloric acid mixed solvent.

    Science.gov (United States)

    Okumura, Shin; Umehara, Saori; Fujii, Yasuhiko; Nomura, Masao; Kaneshiki, Toshitaka; Ozawa, Masaki; Kishimoto, Tadafumi

    2015-10-09

    Benzo-18-crown-6 ether resin embedded in porous silica beads was synthesized and used as the packing material for chromatographic separation of (48)Ca isotope. The aim of the present work is to develop efficient isotope enrichment process for double β decay nuclide (48)Ca. To this end, ethanol/HCl mixed solvent was selected as the medium for the chromatographic separation. Adsorption of calcium on the resin was studied at different HCl concentrations and different ethanol mixing ratios in batch-wise experiments. A very interesting phenomenon was observed; Ca adsorption is controlled not by the overall HCl concentration of the mixed solvent, but by the initial concentration of added HCl solution. Calcium break-through chromatography experiments were conducted by using 75v/v% ethanol/25v/v% 8M HCl mixed solvent at different flow rates. The isotope separation coefficient between (48)Ca and (40)Ca was determined as 3.8×10(-3), which is larger than that of pure HCl solution system. Discussion is extended to the chromatographic HETP, height equivalent to a theoretical plate. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Macrocyclic Gd(3+) complexes with pendant crown ethers designed for binding zwitterionic neurotransmitters.

    Science.gov (United States)

    Oukhatar, Fatima; Meudal, Hervé; Landon, Céline; Logothetis, Nikos K; Platas-Iglesias, Carlos; Angelovski, Goran; Tóth, Éva

    2015-07-27

    A series of Gd(3+) complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd(3+) chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen-type macrocycle that binds the Ln(3+) ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM(-1)  s(-1) at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by (1) H relaxometric titrations of the Gd(3+) complexes and by luminescence measurements on the Eu(3+) and Tb(3+) analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu(3+) complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non-amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Inclusion separation of alkali metals in emulsion liquid membranes by nanobaskets of calix[4]crown-3

    Directory of Open Access Journals (Sweden)

    B. Mokhtari

    2012-12-01

    Full Text Available Nano-assisted inclusion separation of alkali metals from basic solutions was reported by an inclusion-facilitated emulsion liquid membrane process. The novelty of this study is application of nanobaskets of calixcrown in the selective and efficient separation of alkali metals as both the carrier and the surfactant. For this purpose, two diacids, p-tert-butylcalix[4]arene-1,2-crown-3 in the cone and the 1,2alternate conformation, as well as another diacid, p-tert-butylcalix[4]arene-1,2-thiacrown-3 in the cone conformation, were synthesized. Their inclusion-extraction parameters were optimized, including the calixcrown scaffold (04, 4 wt% as the carrier/demulsifier, commercial kerosene as the diluent in the membrane, sulphonic acid (0.2 M and ammonium carbonate (0.4 M as the strip and the feed phases; the phase and the treat ratios were 0.8 and 0.3, mixing speed (300 rpm, and initial solute concentration (100 mg/L. The selectivity of the membrane was examined for more than ten interfering cations was examined and the results reveled that, under the optimized operating condition, the degree of inclusion-extraction of alkali metals was as high as 98-99%.

  10. Syntheses, molecular and crystalline architectures, and ...

    Indian Academy of Sciences (India)

    Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base. SUBHASIS ROYa, SOMNATH CHOUBEYa, SUMITAVA KHANa, KISHALAY BHARa,. PARTHA MITRAb and BARINDRA ...

  11. Synthese en chemotherapeutisch onderzoek van sulfanilamidopyrimidinen

    NARCIS (Netherlands)

    Grevenstuk, Anton Bernard

    1942-01-01

    In order to investigate the influence of substitution in the pyrimidine nucleous on the activity of the three isomeric sulfanilamidopyrimidines (2, 5 and 6), a number of substituted sulfanilamidopyrimidines were synthesized and tested on chemotherapeutic activity. ... Zie: Summary

  12. CAMAC programmable-control frequency synthesizer

    International Nuclear Information System (INIS)

    Yumaguzin, T.Kh.; Vyazovkin, D.E.; Nazirov, Eh.P.; Tuktarov, R.F.

    1989-01-01

    Synthesizer allows to set frequency with 0.015% accuracy and to scan it with variable step. Frequency controlled divider with further summing-up of divided frequency with fundamental one is used in synthesizer, and it has allowed to use digit of the input code and to obtain 3-4 MHz frequency range. Variation of operation flowsheet in the other frequency range is possible. K-155 and K-531 series microcircuits were used during development

  13. Raman assisted lightwave synthesized frequency sweeper

    DEFF Research Database (Denmark)

    Pedersen, Anders Tegtmeier; Rottwitt, Karsten

    2010-01-01

    We present a Lightwave Synthesized Frequency Sweeper comprising a Raman amplifier for loss compensation. The generated pulse train contains 123 pulses and has a flat signal level as well as a low noise level.......We present a Lightwave Synthesized Frequency Sweeper comprising a Raman amplifier for loss compensation. The generated pulse train contains 123 pulses and has a flat signal level as well as a low noise level....

  14. Psychoacoustic Analysis of Synthesized Jet Noise

    Science.gov (United States)

    Okcu, Selen; Rathsam, Jonathan; Rizzi, Stephen A.

    2013-01-01

    An aircraft noise synthesis capability is being developed so the annoyance caused by proposed aircraft can be assessed during the design stage. To make synthesized signals as realistic as possible, high fidelity simulation is required for source (e.g., engine noise, airframe noise), propagation and receiver effects. This psychoacoustic study tests whether the jet noise component of synthesized aircraft engine noise can be made more realistic using a low frequency oscillator (LFO) technique to simulate fluctuations in level observed in recordings. Jet noise predictions are commonly made in the frequency domain based on models of time-averaged empirical data. The synthesis process involves conversion of the frequency domain prediction into an audible pressure time history. However, because the predictions are time-invariant, the synthesized sound lacks fluctuations observed in recordings. Such fluctuations are hypothesized to be perceptually important. To introduce time-varying characteristics into jet noise synthesis, a method has been developed that modulates measured or predicted 1/3-octave band levels with a (<20Hz) LFO. The LFO characteristics are determined through analysis of laboratory jet noise recordings. For the aft emission angle, results indicate that signals synthesized using a generic LFO are perceived as more similar to recordings than those using no LFO, and signals synthesized with an angle-specific LFO are more similar to recordings than those synthesized with a generic LFO.

  15. Direct and indirect single electron transfer (SET-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

    Directory of Open Access Journals (Sweden)

    Dae Won Cho

    2014-02-01

    Full Text Available In this review, we describe direct and indirect photochemical approaches that have been developed for the preparation of phthalimide- and naphthalimide-based, lariat-type crown ethers. The direct route utilizes a strategy in which nitrogen-linked side chains containing polyethoxy-tethered phthalimides and naphthalimides, possessing terminal α-trialkylsilyl groups, are synthesized utilizing concise routes and UV-irradiation to form macrocyclic ring systems. In contrast, the indirect route developed for the synthesis of lariat-type crown ethers employs sequences in which SET-promoted macrocyclization reactions of α-trialkylsilyl-terminated, polyethoxy-tethered phthalimides and naphthalimides are followed by a side chain introduction through substitution reactions at the amidol centers in the macrocyclic ethers. The combined observations made in these investigations demonstrate the unique features of SET-promoted photocyclization reactions that make them well-suited for the use in the synthesis of functionalized crown ethers. In addition, while some limitations exist for the general use of SET-photochemical reactions in large-scale organic synthesis, important characteristics of the photoinduced macrocyclization reactions make them applicable to unique situations in which high temporal and spatial control is required.

  16. Fracture Resistance of Monolithic High Translucency Zirconia Implant-Supported Crowns.

    Science.gov (United States)

    Brizuela-Velasco, Aritza; Diéguez-Pereira, Markel; Álvarez-Arenal, Ángel; Chávarri-Prado, David; Solaberrieta, Eneko; Fernández-González, Felipe J; Chento-Valiente, Yelko; Santamaría-Arrieta, Gorka

    2016-10-01

    To evaluate the resistance to axial forces of screw-retained monolithic high translucency zirconia (mHTZr) crowns compared with high translucency zirconia + feldspathic ceramic (HTZrC) crowns, low translucency zirconia + feldspathic ceramic (LTZrC) crowns, and metal-ceramic (MC) crowns, and also to observe the different fracture patterns between all groups. Twenty-four crowns were fabricated (6 of each group) and loaded until failure, using a testing machine with a 5.0-kN load cell. Mean fracture results varied between 1092.7 N (LTZrC group) and 3439.7 N (mHTZr group). No statistically significant differences were found between the HTZrC, LTZrC, and MC groups. However, statistically significant differences (P zirconia implant-supported crowns proved to be the toughest group studied when an axial force was applied. Fracture patterns varied between different materials, chipping being the most common occurrence.

  17. [Clinical evaluation of the zirconia all ceramic crowns in 40 consecutive patients].

    Science.gov (United States)

    Qi, Bing; He, Yan

    2016-06-01

    To investigate clinical application, aesthetics, stability and bio-compatibility of zirconia all-ceramic crowns in prosthodontic patients. Computer aided design and manufacturing techniques were used to make zirconia all ceramic crowns in 40 patients. They were divided into 2 groups according to the thickness of the gingival thickness. After 12 months of clinical observation, the aesthetics, stability, and bio-compatibility were evaluated by the crown color, crown edge fitness, losing ratio and gingival health. The data were analyzed using SPSS 13.0 software package. Slight marginal discrepancy was observed in 2 zirconia all ceramic crowns, no evidence of decay was observed at 1 year. Zirconia all ceramic crowns have a low fracture rate, good biological properties and excellent esthetic properties. It is ideal esthetic prosthesis.

  18. Holographic evaluation of the marginal fits of complete crowns loaded at the central fossa

    Science.gov (United States)

    Chen, Terry Y.; Chang, Guan L.; Wu, Shih H.

    1995-05-01

    In dentistry, a defect of cementation on the margins of crowns accumulates bacterial plaque easily. This can result in recurrent caries and periodontal disease. In this paper holographic interferometry was applied to evaluate the effect of masticatory force on various complete crowns. Four complete molar crowns made from different materials (Au alloy, Pd-Ag alloy, Ni-Cr alloy, and porcelain fused to metal) were tested. The out-of-plane displacements of the crown specimens were measured by the method of multiple observations. The displacements measured range from 6 to 10 micrometers under normal load (25 N). However, the marginal openings of all four crowns were estimated to be less than 0.2 micrometers . In addition the defect of the crown was examined.

  19. Holographic evaluation of the marginal fit of complete crowns loaded at central fossa

    Science.gov (United States)

    Chen, Terry Y.; Chang, Guan L.; Wu, Shih H.

    1993-07-01

    In dentistry, the defect of cementation on the margins of crowns accumulates bacterial plaque easily. This can result in recurrent caries and periodontal disease. In this paper holographic interferometry is applied to study the effect of masticatory force on various complete crowns. Four complete molar crowns made from different casting materials (Au, Pd-Ag, Ni-Cr, and PFM) were tested. The horizontal displacements of two points near the margin, measured by the method of multiple observations, could be as large as 15 micrometers under normal load (25 kgw). However, the marginal discrepancy of all four crowns estimated were quite small (cementation between the crown and the tooth is quite good. Nevertheless, when the load was increased to 45 kgw, a defect of cementation was found on the Pd-Ag crown.

  20. MOLECULAR CLIPS BASED ON THE CROWN ETHERS: PROSPECTIVE RECEPTORS FOR THE Sr2+CATIONS REMOVAL

    Directory of Open Access Journals (Sweden)

    A. Yu. Lyapunov

    2015-04-01

    Full Text Available Strontium cation complexation with diphenylglycoluril-based molecular clips containing 12-crown-4, 15-crown-5, 18-crown-6 and 21-crown-7 residues was qualitatively studied by FAB mass-spectrometry. It was found that at low concentrations of Sr2+ cations molecular clip with fragments of 15-crown-5 is the most effective, and it is assumed that it is due to the formation of the most stable «sandwich-type» complex. The higher removal degree with an excess of Sr2+ cations is observed in the case of molecular clips with fragments of 18-crown-6 due to the formation of 1:2 composition complexes.

  1. Fracture Resistance of Non-Metallic Molar Crowns Manufactured with CEREC 3D

    Science.gov (United States)

    Madani, Dalia A.

    Objectives. To compare fracture strength and fatigue resistance of ceramic (ProCAD, Ivoclar-Vivadent) (C) and resin composite (Paradigm MZ100, 3M/ ESPE) (R) crowns made with CEREC-3D. Methods. A prepared ivorine molar tooth was duplicated to produce 40 identical prepared specimens made of epoxy resin (Viade). Twenty (C) crowns and 20 (R) were cemented to their dies using resin cement. Ten of each group were subjected to compressive loading to fracture. The remaining 10 of each group were subjected to mechanical cyclic loading for 500,000 cycles. The survivors were subjected to compressive loading to fracture. Results. No significant difference in mean fracture load was found between the two materials. However, only 30% of the (C) crowns vs. 100% of the (R) crowns survived the cyclic loading test. Conclusions. (R) crowns demonstrated higher fatigue Resistance than (C) crowns in-vitro and might better resist cracking in-vivo.

  2. Bis(hydroxyammonium hexachloridoplatinate(IV–18-crown-6 (1/2

    Directory of Open Access Journals (Sweden)

    Evgeny Bulatov

    2014-01-01

    Full Text Available In the title complex, (NH3OH2[PtCl6]·2C12H24O6, the PtIV atom is coordinated by six chloride anions in a slightly distorted octahedral geometry. The Pt—Cl bond lengths are comparable to those reported for other hexachloridoplatinate(IV species. The hydroxyammonium groups act as linkers between the [PtCl6]2− anion and the crown ether molecules. The anion is linked to two hydroxyammonium cations via O—H...Cl hydrogen bonds and each hydroxyammonium moiety is linked to a crown ether molecule by hydrogen bonds between ammonium H atoms and 18-crown-6 O atoms. The crown ether molecules have the classic crown shape in which all O atoms are located in the inner part of the crown ether ring and all –CH2– groups are turned to the outside.

  3. 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.

  4. Crown retention and flexural strength of eight provisional cements.

    Science.gov (United States)

    Lawson, Nathaniel C; Burgess, John O; Mercante, Donald

    2007-12-01

    Few studies have compared the retention of resin-based and zinc-oxide noneugenol provisional cements. Crown retention testing is difficult and variable; therefore, a simpler method of testing by using flexural strength is indicated. The purpose of this study was to measure the retention of base metal alloy castings to dentin provided by 8 provisional cements (3 resin-based and 5 zinc oxide) and correlate the retention to their flexural strength. Flexural strength specimens (2.5 x 2.5 x 22 mm) were made of each cement. The specimens were placed in a 3-point bending testing mode and loaded at 1 mm/min until failure. Ten extracted teeth were milled to a standardized complete crown preparation, fitted with Rexillium III castings, and cemented with each provisional cement. The specimens were subjected to a tensile load (1 mm/min) until failure in a universal testing machine. The flexural strength for each cement was calculated in MPa and correlated to the retention. A 1-way ANOVA and Tukey HSD post hoc analysis were used to determine significant intergroup differences (alpha=.05). Linear regression was used to correlate flexural strength and crown retention (alpha=.05). Significant differences were found in the flexural strengths and retention provided by the various cements. Flexure strength was correlated with cement retention for resin-based cements (r=0.998) but not zinc-oxide noneugenol cements (r=0.058). Based on a 20-degree preparation, stronger cements provide increased retention. Therefore, the desired amount of retention should be based on both the cement and a clinical evaluation of the preparation.

  5. 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.

  6. DNA methylation mediated control of gene expression is critical for development of crown gall tumors.

    Directory of Open Access Journals (Sweden)

    Jochen Gohlke

    Full Text Available Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA-encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes. High levels of abscisic acid (ABA in crown galls regulate expression of drought stress responsive genes and mediate drought stress acclimation, which is essential for wild-type-like tumor growth. An impact of epigenetic processes such as DNA methylation on crown gall development has been suggested; however, it has not yet been investigated comprehensively. In this study, the methylation pattern of Arabidopsis thaliana crown galls was analyzed on a genome-wide scale as well as at the single gene level. Bisulfite sequencing analysis revealed that the oncogenes Ipt, IaaH, and IaaM were unmethylated in crown galls. Nevertheless, the oncogenes were susceptible to siRNA-mediated methylation, which inhibited their expression and subsequently crown gall growth. Genome arrays, hybridized with methylated DNA obtained by immunoprecipitation, revealed a globally hypermethylated crown gall genome, while promoters were rather hypomethylated. Mutants with reduced non-CG methylation developed larger tumors than the wild-type controls, indicating that hypermethylation inhibits plant tumor growth. The differential methylation pattern of crown galls and the stem tissue from which they originate correlated with transcriptional changes. Genes known to be transcriptionally inhibited by ABA and methylated in crown galls became promoter methylated upon treatment of A. thaliana with ABA. This suggests that the high ABA levels in crown galls may mediate DNA methylation and regulate expression of genes involved in drought stress protection. In summary, our studies provide evidence that epigenetic processes

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

    OpenAIRE

    Naumova, Ella A.; Schneider, Stephan; Arnold, Wolfgang H.; Piwowarczyk, Andree

    2017-01-01

    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 c...

  8. Clinical evaluations of cast gold alloy, machinable zirconia, and semiprecious alloy crowns: A multicenter study.

    Science.gov (United States)

    Park, Ji-Man; Hong, Yong-Shin; Park, Eun-Jin; Heo, Seong-Joo; Oh, Namsik

    2016-06-01

    Few studies have compared the marginal and internal fits of crowns fabricated from machinable palladium-silver-indium (Pd-Ag-In) semiprecious metal alloy. The purpose of this clinical study was to evaluate and compare the marginal and internal fits of machined Pd-Ag-In alloy, zirconia, and cast gold crowns. A prospective clinical trial was performed on 35 participants and 52 abutment teeth at 2 centers. Individuals requiring prosthetic restorations were treated with gold alloy or zirconia crowns (2 control groups) or Pd-Ag-In alloy crowns (experimental group). A replica technique was used to evaluate the marginal and internal fits. The buccolingual and mesiodistal cross-sections were measured, and a noninferiority comparison was conducted. The mean marginal gaps were 68.2 μm for the gold crowns, 75.4 μm for the zirconia crowns, and 76.9 μm for the Pd-Ag-In alloy crowns. In the 5 cross-sections other than the distal cross-section, the 2-sided 95% confidence limits for the differences between the Pd-Ag-In alloy crowns and the 2 control groups were not larger than the 25-μm noninferiority margin. The control groups displayed smaller internal gaps in the line angle and occlusal spaces compared with the Pd-Ag-In crown group. The marginal gaps of machinable Pd-Ag-In alloy crowns did not meet the noninferiority criterion in the distal margin compared with zirconia and gold alloy crowns. Nonetheless, all 3 crowns had clinically applicable precision. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  9. A Comparison of Marginal Fit Between Lithium-Disilicate Press and CAD Fabricated Crowns

    Science.gov (United States)

    2014-05-27

    KBC, Nicholls JI. Evaluation of the marginal fit of a zirconia ceramic computer-aided machined (CAM) crown system. J Prosthet Dent 2010;104:216-27. 7...Workshops _Abstract _Other 6. Title: "A comparison of marginal fit between lithium-disilicate press and CAD fabricated crowns " 7. Intended...thesis manuscript entitled: "A comparison of marginal fit between lithium-disilicate press and CAD fabricated crowns " Is appropriately acknowledged

  10. 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.

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

    Science.gov (United States)

    Lameira, Deborah Pacheco; 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 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. PMID:26576423

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

    OpenAIRE

    Mobilio, Nicola; Fasiol, Alberto; Mollica, Francesco; Catapano, Santo

    2015-01-01

    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)...

  13. Fatigue resistance and microleakage of CAD/CAM ceramic and composite molar crowns.

    Science.gov (United States)

    Kassem, Amr S; Atta, Osama; El-Mowafy, Omar

    2012-01-01

    The aim of this study was to determine effect of compressive cyclic loading on fatigue resistance and microleakage of monolithic CAD/CAM molar ceramic and composite crowns. Thirty-two extracted molars were prepared to receive CEREC crowns according to manufacturer's guidelines using a special paralleling device (Parallel-A-Prep). Sixteen feldspathic ceramic crowns (VITABLOCS Mark II) (VMII) and 16 resin-composite crowns (Paradigm-MZ100 blocks) (PMZ) were milled using a CEREC-3D machine. Eight crowns of each group were cemented to their respective teeth using self-etching resin cement (Panavia-F-2.0) (PAN), and eight were cemented using self-adhesive resin cement (RelyX-Unicem-Clicker) (RXU). Following storage for 1 week in water, specimens were subjected to uniaxial compressive cyclic loading in an Instron testing machine at 12 Hz for 1,000,000 cycles. Load was applied at the central fossa, and the cycle range was 60-600 N. Specimens were then subjected to microleakage testing. Data were statistically analyzed using factorial ANOVA and Post Hoc (Tukey HSD) tests. All composite crowns survived compressive cyclic loading without fracture, while three ceramic crowns from the subgroup cemented with RXU developed surface cracks at the center of occlusal surfaces, extending laterally. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other three subgroups (p crowns were more fatigue-resistant than VMII ceramic crowns. Cement type had a significant effect on fatigue resistance of the ceramic crowns but not the composite ones. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other subgroups (p < 0.05). © 2011 by The American College of Prosthodontists.

  14. Biomechanical three-dimensional finite element analysis of monolithic zirconia crown with different cement type

    OpenAIRE

    Ha, Seung-Ryong

    2015-01-01

    PURPOSE The objective of this study was to evaluate the influence of various cement types on the stress distribution in monolithic zirconia crowns under maximum bite force using the finite element analysis. MATERIALS AND METHODS The models of the prepared #46 crown (deep chamfer margin) were scanned and solid models composed of the monolithic zirconia crown, cement layer, and prepared tooth were produced using the computer-aided design technology and were subsequently translated into 3-dimens...

  15. In Vitro Fit and Cementation Resistance of Provisional Crowns for Single Implant-Supported Restorations

    OpenAIRE

    Moris,Izabela Cristina Maurício; Oliveira,Juliana Elias de; Faria,Adriana Cláudia Lapria; Ribeiro,Ricardo Faria; Rodrigues,Renata Cristina Silveira

    2015-01-01

    Abstract: This study aimed to verify marginal fit and the effect of cement film thickness standardization on retention of provisional crowns made with prefabricated acrylic cylinders on abutments, using two temporary luting agents subjected or not to mechanical cycling. Provisional crowns were made from bis-acryl (Luxatemp Fluorescence) or methyl methacrylate (Duralay) resins on acrylic cylinders and marginal fit and cement film thickness were evaluated. For retention evaluation, crowns were ...

  16. Radiochemical determination of 210Pb using crown ether

    International Nuclear Information System (INIS)

    Vajda, N.; Bodizs, D.; Vodicska, M.

    1994-01-01

    Gamma spectrometric determination of 210 Pb following chemical separation has been performed very precisely and with high sensitivity, due to the low and constant self-absorption of the chemically pure sample. A simple and quick method for the chemical separation of lead using crown ether has been developed. Its four steps are described in detail. The new method was verified using phosphate ore and gypsum samples that were measured in an interlaboratory comparison and with a standard reference material. This method can also be used for self-absorption correction in direct gamma spectrometry of 210 Pb. (N.T.) 4 refs.; 2 figs.; 2 tabs

  17. Suppressing Nonradiative Recombination in Crown-Shaped Quantum Wells

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ju, Gunwu [Gwangju Institute of Science and Technology; Korea Institute of Science and Technology; Na, Byung Hoon [Samsung Advanced Institute of Technology; Hwang, Hyeong-Yong [Gwangju Institute of Science and Technology; Jho, Young-Dahl [Gwangju Institute of Science and Technology; Myoung, NoSoung [Gwangju Institute of Science and Technology; Yim, Sang-Youp [Gwangju Institute of Science and Technology; Kim, Hyung-jun [Korea Institute of Science and Technology; Lee, Yong Tak [Gwangju Institute of Science and Technology

    2018-02-06

    We examined the structural and optical properties of a crown-shaped quantum well (CSQW) to suppress nonradiative recombination. To reduce carrier loss in defect traps at the well/barrier interface, the CSQW was designed to concentrate carriers in the central region by tailoring the bandgap energy. Temperature-dependent photoluminescence measurements showed that the CSQW had a high activation energy and low potential fluctuation. In addition, the long carrier lifetime of the CSQW at high temperatures can be interpreted as indicating a decrease in carrier loss at defect traps.

  18. Provisional Crown Dislodgement during Scuba Diving: A Case of Barotrauma.

    Science.gov (United States)

    Gulve, Meenal Nitin; Gulve, Nitin Dilip

    2013-01-01

    Changes in ambient pressure, for example, during flying, diving, or hyperbaric oxygen therapy, can lead to barotrauma. Although it may seem that this issue was neglected in dental education and research in recent decades, familiarity with and understanding of these facts may be of importance for dental practitioners. We report the case of a patient who experienced barotrauma involving dislodgement of a provisional crown during scuba diving. Patients who are exposed to pressure changes as a part of their jobs or hobbies and their dentists should know the causes of barotrauma. In addition, the clinician must be aware of the possible influence of pressure changes on the retention of dental components.

  19. Stress distribution difference between Lava Ultimate full crowns and IPS e.max CAD full crowns on a natural tooth and on tooth-shaped implant abutments.

    Science.gov (United States)

    Krejci, Ivo; Daher, René

    2017-04-01

    The goal of this short communication is to present finite element analysis comparison of the stress distribution between CAD/CAM full crowns made of Lava Ultimate and of IPS e.max CAD, adhesively luted to natural teeth and to implant abutments with the shape of natural teeth. Six 3D models were prepared using a 3D content-creating software, based on a micro-CT scan of a human mandibular molar. The geometry of the full crown and of the abutment was the same for all models representing Lava Ultimate full crowns (L) and IPS e.max CAD full crowns (E) on three different abutments: prepared natural tooth (n), titanium abutment (t) and zirconia abutment (z). A static load of 400 N was applied on the vestibular and lingual cusps, and fixtures were applied to the base of the models. After running the static linear analysis, the post-processing data we analyzed. The stress values at the interface between the crown and the abutment of the Lt and Lz groups were significantly higher than the stress values at the same interface of all the other models. The high stress concentration in the adhesive at the interface between the crown and the abutment of the Lava Ultimate group on implants might be one of the factors contributing to the reported debondings of crowns.

  20. 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 (pFracture 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, pfracture. 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.

  1. Radium separation through complexation by aqueous crown ethers and ion exchange or solvent extraction

    Energy Technology Data Exchange (ETDEWEB)

    Chiarizia, R.; Dietz, M.L.; Horwitz, E.P. [Argonne National Lab., IL (United States). Chemistry Div.; Burnett, W.C. [Florida State Univ., Tallahassee, FL (United States). Dept. of Oceanography

    1997-11-01

    The effect of three water-soluble, unsubstituted crown ethers (15-crown-5 (15C5), 18-crown-6 (18C6) and 21-crown-7 (21C7)) on the uptake of Ca, Sr, Ba and Ra cations by a sulfonic acid cation exchange resin, and on the extraction of the same cations by xylene solutions of dinonylnaphthalenesulfonic acid (HDNNS) from aqueous hydrochloric acid solutions has been investigated. The crown ethers enhance the sorption of the larger cations by the ion exchange resin, thereby improving the resin selectivity over calcium, a result of a synergistic interaction between the crown ether and the ionic functional groups of the resin. Similarly, the extraction of the larger alkaline earth cations into xylene by HDNNS is strongly synergized by the presence of the crown ethers in the aqueous phase. Promising results for intra-Group IIa cation separations have been obtained using each of the three crown ethers as the aqueous ligands and the sulfonic acid cation exchange resin. Even greater separation factors for the radium-calcium couple have been measured with the crown-ethers and HDNNS solutions in the solvent extraction mode. The application of the uptake and extraction results to the development of radium separation schemes is discussed and a possible flowchart for the determination of {sup 226}Ra/{sup 228}Ra in natural waters is presented.

  2. 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.

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

    OpenAIRE

    Lameira, Deborah Pacheco; Silva, Wilkens Aur?lio 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...

  4. 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. Copyright © 2011 Elsevier Ltd. All rights reserved.

  5. Finite element analysis of the influence of geometry and design of zirconia crowns on stress distribution.

    Science.gov (United States)

    Anami, Lilian Costa; Lima, Julia Magalhaes da Costa; Corazza, Pedro Henrique; Yamamoto, Eron Toshio Colauto; Bottino, Marco Antonio; Borges, Alexandre Luiz Souto

    2015-02-01

    To evaluate the influence of the geometry and design of prosthetic crown preparations on stress distribution in compression tests, using finite element analysis (FEA). Six combinations of 3D drawings of all-ceramic crowns (yttria-stabilized zirconia framework and porcelain veneer) were evaluated: F, flat preparation and simplified crown; FC, flat preparation and crown with contact point; FCM, flat preparation and modified crown; A, anatomical preparation and simplified anatomical crown framework; AC, anatomical preparation and crown with contact point; and ACM, anatomical preparation and modified crown. Bonded contact types at all interfaces with the mesh were assigned, and the material properties used were according to the literature. A 200 N vertical load was applied at the center of each model. The maximum principal stresses were quantitatively and qualitatively analyzed. The highest values of tensile stress were observed at the interface between the ceramics in the region under the load application for the simplified models (F and A). Reductions in stress values were observed for the model with the anatomical preparation and modified infrastructure (ACM). The stress distribution in the flat models was similar to that of their respective anatomical models. The modified design of the zirconia coping reduces the stress concentration at the interface with the veneer ceramic, and the simplified preparation can exert a stress distribution similar to that of the anatomical preparation at and near the load point, when load is applied to the center of the crown. © 2014 by the American College of Prosthodontists.

  6. 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......+ , with a detection limit of 10-5 M without inference from other ions (Na+ , Li+ , NH4+ and Ca2+) in concentrations up to 2.5 × 10-2 M. Similar sensing was achieved with functionalized disposable SPE electrodes. The results demonstrate that RGO-crown[6] is a conductive material full of promise for application...

  7. Extracting oil palm crown from WorldView-2 satellite image

    Science.gov (United States)

    Korom, A.; Phua, M.-H.; Hirata, Y.; Matsuura, T.

    2014-02-01

    Oil palm (OP) is the most commercial crop in Malaysia. Estimating the crowns is important for biomass estimation from high resolution satellite (HRS) image. This study examined extraction of individual OP crown from a WorldView-2 image using twofold algorithms, i.e., masking of Non-OP pixels and detection of individual OP crown based on the watershed segmentation of greyscale images. The study site was located in Beluran district, central Sabah, where matured OPs with the age ranging from 15 to 25 years old have been planted. We examined two compound vegetation indices of (NDVI+1)*DVI and NDII for masking non-OP crown areas. Using kappa statistics, an optimal threshold value was set with the highest accuracy at 90.6% for differentiating OP crown areas from Non-OP areas. After the watershed segmentation of OP crown areas with additional post-procedures, about 77% of individual OP crowns were successfully detected in comparison to the manual based delineation. Shape and location of each crown segment was then assessed based on a modified version of the goodness measures of Möller et al which was 0.3, indicating an acceptable CSGM (combined segmentation goodness measures) agreements between the automated and manually delineated crowns (perfect case is '1').

  8. Polyaza crown ether as non-nucleosidic building blocks in DNA-conjugates

    DEFF Research Database (Denmark)

    Jakobsen, Ulla; Rohr, Katja; Madsen, Rasmus K

    2007-01-01

    The synthesis of amphiphilic polyaza crown ether monomers X (palmityl-substituted), Y (cholesteryl-substituted) and Z (dipalmityl-subtituted) and their incorporation into oligonucleotides are described. Their effects on thermal duplex stability were investigated by UV melting curve analysis....... Thermal denaturation experiments showed remarkable stabilization of dsDNA by polyaza crown ether monomers when incorporated in opposite positions. The series of polyaza crown ether monomers (X, Y, and Z) with different lipophilicity showed a trend of increased stability of the corresponding ds......DNA with increasing lipophilicity of the polyaza crown ether monomer....

  9. 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

    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...

  10. Extracting oil palm crown from WorldView-2 satellite image

    International Nuclear Information System (INIS)

    Korom, A; Phua, M-H; Hirata, Y; Matsuura, T

    2014-01-01

    Oil palm (OP) is the most commercial crop in Malaysia. Estimating the crowns is important for biomass estimation from high resolution satellite (HRS) image. This study examined extraction of individual OP crown from a WorldView-2 image using twofold algorithms, i.e., masking of Non-OP pixels and detection of individual OP crown based on the watershed segmentation of greyscale images. The study site was located in Beluran district, central Sabah, where matured OPs with the age ranging from 15 to 25 years old have been planted. We examined two compound vegetation indices of (NDVI+1)*DVI and NDII for masking non-OP crown areas. Using kappa statistics, an optimal threshold value was set with the highest accuracy at 90.6% for differentiating OP crown areas from Non-OP areas. After the watershed segmentation of OP crown areas with additional post-procedures, about 77% of individual OP crowns were successfully detected in comparison to the manual based delineation. Shape and location of each crown segment was then assessed based on a modified version of the goodness measures of Möller et al which was 0.3, indicating an acceptable CSGM (combined segmentation goodness measures) agreements between the automated and manually delineated crowns (perfect case is '1')

  11. Effect of misfit of cement-retained implant single crowns on crestal bone changes.

    Science.gov (United States)

    Chen, Chun-Jung; Papaspyridakos, Panos; Guze, Kevin; Singh, Medha; Weber, Hans-Peter; Gallucci, German O

    2013-01-01

    The purpose of this clinical study was to compare peri-implant crestal bone levels between misfitting (overhanging/open margin) cement-retained implant single crowns (SCs) vs accurately fitted implant SCs. Seventeen subjects were divided into two groups: test group (misfitting crowns, n = 10) and control group (accurately fitted crowns, n = 7). Crestal bone level changes were assessed using digital software. The average differences in mean bone loss within and between the two groups were statistically significant. Cement-retained implant SCs with marginal misfit resulted in more crestal bone loss than accurately fitted crowns after a mean of 3 years in function.

  12. Using an Existing Crown to Repair a Damaged Cast Post and Core Restoration

    OpenAIRE

    Arabolu, Manikya; Nair, K Chandrasekharan; Raheel, Syed Ahmed; Tarakji, Bassel; Azzeghaiby, Saleh Nasser; Nassani, Mohammad Zakaria

    2014-01-01

    A fractured coronal tooth structure beneath an intact crown is a common clinical occurrence. If the underlying root is healthy, the tooth is restored with a post and core followed by refabrication of the crown. This paper describes a technique of using the existing intact crown for the above-mentioned situation. A 34-year-old female was referred with a fractured right canine with an intact crown. A post was found fractured in the canal which was subsequently retrieved. A new fiber post was ce...

  13. 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.

  14. CAD/CAM glass ceramics for single-tooth implant crowns: a finite element analysis.

    Science.gov (United States)

    Akça, Kvanç; Cavusoglu, Yeliz; Sagirkaya, Elcin; Aybar, Buket; Cehreli, Murat Cavit

    2013-12-01

    To evaluate the load distribution of CAD/CAM mono-ceramic crowns supported with single-tooth implants in functional area. A 3-dimensional numerical model of a soft tissue-level implant was constructed with cement-retained abutment to support glass ceramic machinable crown. Implant-abutment complex and the retained crown were embedded in a Ø 1.5 × 1.5 cm geometric matrix for evaluation of mechanical behavior of mono-ceramic CAD/CAM aluminosilicate and leucite glass crown materials. Laterally positioned axial load of 300 N was applied on the crowns. Resulting principal stresses in the mono-ceramic crowns were evaluated in relation to different glass ceramic materials. The highest compressive stresses were observed at the cervical region of the buccal aspect of the crowns and were 89.98 and 89.99 MPa, for aluminosilicate and leucite glass ceramics, respectively. The highest tensile stresses were observed at the collar of the lingual part of the crowns and were 24.54 and 25.39 MPa, respectively. Stresses induced upon 300 N static loading of CAD/CAM aluminosalicate and leucite glass ceramics are below the compressive strength of the materials. Impact loads may actuate the progress to end failure of mono-ceramic crowns supported by metallic implant abutments.

  15. Considerations during crown reattachment procedure over the pulpal exposure: case report

    Directory of Open Access Journals (Sweden)

    Bona Kim

    2012-11-01

    Full Text Available Crown reattachment is the most conservative treatment which can be used to restore fractured tooth, presumably with sufficient strength, while maintaining original contour, incisal translucency, and reducing chair time and cost. However, in case of crown fracture with pin-point pulp exposure, we should cautiously minimize the irritation to the pulp and consider pre-treatment pulpal status, choice of pulp capping materials, choice of bonding system and treatment sequence during crown reattachment procedures. This case reports the considerations while crown reattachment with direct pulp capping using calcium hydroxide (Dycal, Dentsply Caulk.

  16. 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

  17. Resin composite repair for implant-supported crowns.

    Science.gov (United States)

    Bonfante, Estevam A; Suzuki, Marcelo; Hirata, Ronaldo; Bonfante, Gerson; Fardin, Vinicius P; Coelho, Paulo G

    2017-08-01

    This study evaluated the reliability of implant-supported crowns repaired with resin composites. Fifty-four titanium abutments were divided in three groups (n = 18 each) to support resin nanoceramic molar crowns, as follows: (LU) (Lava Ultimate, 3M ESPE); LU repaired with either a direct or an indirect resin composite. Samples were subjected to mouth-motion accelerated-life testing in water (n = 18). Cumulative damage with a use stress of 300 N was used to plot Weibull curves for group comparison. Reliability was calculated for a mission of 100,000 cycles at 400 N load. Beta values were 0.83 for LU, 0.31 and 0.27 for LU repaired with Filtek and Ceramage, respectively. Weibull modulus for LU was 9.5 and η = 1047 N, m = 6.85, and η = 1002 N for LU repaired with Ceramage, and m = 4.65 and η = 766 N for LU repaired with Filtek (p material, and detailed fractography is presented. The performance of resin nanoceramic material repaired with an indirect composite was maintained after accelerated-life testing compared to unrepaired controls. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1481-1489, 2017. © 2016 Wiley Periodicals, Inc.

  18. 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.

  19. Coordinate geometry method for capturing and evaluating crown preparation geometry.

    Science.gov (United States)

    Tiu, Janine; Waddell, J Neil; Al-Amleh, Basil; Jansen van Vuuren, Wendy-Ann; Swain, Michael V

    2014-09-01

    A validated universal method requiring no human input is needed to capture and evaluate preparation geometries in a manner that can be used to see the correlation of different parameters. The purpose of this study was to present a method of capturing and evaluating crown preparation geometry. One manually machined acrylic resin block and 9 randomly selected preparations for ceramic complete crowns prepared by general dentists were selected and prepared. The specimens were scanned (3D scanner; Nobel Biocare), and buccolingual and mesiodistal cross section images were collected. The images were imported into digitizing software (Engauge Digitizer 4.1) to convert the outlines into x and y coordinates. Six points were chosen by using a set of algorithms, and the resulting parameters were calculated. The acrylic resin block was milled with a 12 degree total occlusal convergence (TOC) instrument producing a 12.83 degree TOC. For the other specimens, average TOC values ranged from 18 degrees to 52 degrees. The mean average margin width was 0.70 mm, and the mean average base dimension was 6.23 mm. The surface area/volume ratio, resistance length, and limiting taper were also calculated. The method described provides a basis for accurately evaluating preparation geometry without human input. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  20. Induced mutations for tolerance of oats to crown rust

    International Nuclear Information System (INIS)

    Simons, M.D.; Frey, K.J.

    1977-01-01

    Seeds of three oat (Avena sativa and A. abyssinica) strains were treated with ethyl methanesulphonate (EMS), and crown rust (caused by Puccinia coronata var. avenae) tolerance ratios of M 5 -derived lines were compared with untreated checks. Tolerance ratios of mutant lines tended to be distributed in both plus and minus directions. No mutant oat line had a significant increase in grain yield, but many showed significantly depressed yields. With C.I. 6665, only five of 130 mutagen-derived lines were not significantly below the check for grain yield; one of these had significantly improved tolerance. Re-treatment of selected strains from a previous EMS treatment (original cultivar was Clintland-60) gave one M 5 -derived oat line (of 100 tested) that was equal to Clintland-60 in grain yield and sustained no damage from crown rust (i.e. it had a tolerance ratio of 100). EMS treatment of the highly susceptible tetraploid C.I. 2110 resulted in both significantly increased and reduced tolerance. (author)

  1. Short implants supporting single crowns in atrophic jaws.

    Science.gov (United States)

    Al-Ansari, Asim

    2014-09-01

    PubMed-Medline, Web of Science, Cochrane Library, ProQuest Dissertations and Theses, LILACS, Ebsco-Dentistry and Oral Sciences Source, Scirus, Embase, Scopus and Journal Ovid databases were searched. In addition hand searching of 14 relevant journals was undertaken along with screening of the reference lists of screened article and reviews. Randomised controlled clinical trials (RCTs), controlled clinical trials (CCTs), prospective cohort studies and case series were included. Studies where short (biological failure proportion (BFP), prosthetic failure proportion (PFP) and radiographic marginal bone loss (MBL) were 5.9% (95% CI: 3.7-9.2%), 3.8% (95%CI: 1.9-7.4%), 2.8% (95%CI: 1.4-5.7%) and 0.83 mm (95%CI: 0.54-1.12 mm) respectively. Quantitative analysis showed that placement in the mandible (p = 0.0002) and implants with length ≤ 8 mm (p = 0.01) increased FP, BFP and MBL, whereas qualitative assessment revealed that crown-to-implant ratio did not influence MBL. Within the limitations of the present systematic review with meta-analysis, it is suggested that single crowns supported by short implants are an acceptable and predictable option in the short- and long-term treatment of the atrophic jaws.

  2. The confusing array of tooth-colored crowns.

    Science.gov (United States)

    Christensen, Gordon J

    2003-09-01

    The venerable PFM crown or fixed prosthesis still dominates the tooth-colored restoration market. However, use of PFMs is declining slightly, as the many new all-ceramic and resin-based composite crowns and fixed-prosthesis products flood the market. Several situations may indicate the use of materials other than PFM. They include patients requiring a high level of esthetic acceptability, patients with proven or perceived allergies to the metals used in dentistry and bruxing or clenching patients with metal allergies or desire to eliminate metal from their mouths. PFM restorations have been proven during 40 years of successful use. They provide acceptable esthetics for most situations, minimal fracture during service, proven ability to serve in multiple-unit situations and excellent fit, and the profession has detailed knowledge of these restorations' advantages, disadvantages and physical characteristics. PFM restorations have only a few well-known negative characteristics. Be cautious as you elect to move from the reliability and positive history of PFM to relatively unknown types of restorations.

  3. [Preliminary evaluation of clinical effect of computer aided design and computer aided manufacture zirconia crown].

    Science.gov (United States)

    Wang, Yu-guang; Xing, Yan-xi; Sun, Yu-chun; Zhao, Yi-jiao; Lü, Pei-jun; Wang, Yong

    2013-06-01

    To evaluate clinical effects of computer aided design and computer aided manufacturing (CAD/CAM) milled zirconia crown in three aspects: aesthetic, contact wear and fracture. Sixty patients were divided into two groups.In one group, 35 full contour CAD/CAM zirconia crown were made on molars of 30 patients. The manufacturing process of zirconia crown was as follow. First, the three dimensional(3-D) data of working models, antagonist impression and check records were acquired by 3-D laser scanning Dental wings S50. Then full contour zirconia crowns, which had functional occlusal contacts with antagonistic teeth, and appropriate contact with adjacent teeth were designed with Zeno-CAD(V4.2.5.5.12919) software. ZENOSTAR Zr pure zirconia material was milled in digital controlled machine WIELAND 4030 M1.In the end, the zirconia crown were completed with the method of second sintering and polishing. After clinical try-in, the crown was cemented.In the control group, thirty gold alloy full crown were made and cemented on molars of 30 patients. According to the modified U S Public Health Service Criteria(USPHS) evaluation standard, all crowns were evaluated on the same day, at three months, half a year, one year and two years following delivery. There were three aspects we were focusing on in the evaluation: aesthetic, contact wear(restoration and antagonist), and fracture. In all the prosthesis we evaluated during the 24 months, no fracture was found. Contact wear of crowns varies according to different antagonist teeth. The zirconia crowns show privilege in aesthesis, toughness and anti-wearing.However, there is contact wear on antagonistic natural teeth. Thus it is a good choice when full zirconia crowns are indicated on two antagonistic teeth in both jaws.

  4. Load-bearing capacity and the recommended thickness of dental monolithic zirconia single crowns.

    Science.gov (United States)

    Sun, Ting; Zhou, Shanyu; Lai, Renfa; Liu, Ruoyu; Ma, Shuyuan; Zhou, Zhiying; Longquan, Shao

    2014-07-01

    The aim of this study was to evaluate the load bearing capacity and a reasonable thicknesss of dental monolithic zirconia crowns. Polymethyl methacrylate (PMMA) abutment tooth specimens were made by CAD/CAM technic. Monolithic zirconia crowns (MZC), monolithic lithium disilicate crowns (MLC), layered zirconia crowns (LZC) and metal ceramic crowns(MCC), of which the occlusal thickness was 1.5mm were thereafter fabricated and cemented on the abutment tooth specimens. MCC with occlusal thicknesses of 0.6mm, 0.8mm, 1.00mm, 1.2mm were also made. All specimens underwent load-to-fracture test. Weibull parameters (σ0) and (m) were calculated. Fracture modes were also evaluated. The mean fracture load was 1863.16±116.81 for MLC, 2284.77±355.60 for MCC, 2308.0±510.94 for LZC, 4109.93±610.18 for MZC (1.5mm), 3068.31±233.88 for MZC (1.2mm), 2429.88±315.03 for MZC (1.0mm), 1814.60±68.21 for MZC (0.8mm) and 1308.38±111.38 for MZC (0.6mm). The fracture load of MZC was significantly higher than MCC, LZC and MLC (P0.05). Monolithic zirconia crowns exhibit higher fracture loads than monolithic lithium disilicate crowns, layered zirconia crowns and metal ceramic crowns. The fracture resistance of monolithic zirconia crowns with a thickness of 1.0mm can be equal to metal ceramic crowns. Doubling the monolithic zirconia core from 0.6mm to 1.5mm increases the fracture resistance of this restorative system threefold. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Effect of Intraoral Mechanical Cleaning Techniques on Bond Strength of Cast Crowns to Metal Cores.

    Science.gov (United States)

    AlZain, Sahar; Kattadiyil, Mathew T; AlHelal, Abdulaziz; Alqahtani, Ali

    2017-11-30

    To evaluate the effect of cleaning of metal cores from provisional cement, using an intraoral airborne-particle abrasion method, on the bond strength of permanent resin cement with cast crowns to cores. Thirty stainless steel models of a standard complete crown tooth preparation were fabricated. Thirty Type III gold crowns were fabricated. Each cast crown corresponded to one stainless steel crown preparation model. All crowns were cemented with noneugenol zinc oxide cement and stored for 7 days at 37°C. All crowns were debonded, and the cement was cleaned with airborne-particle abrasion using 50 μm aluminum oxide at 4.1 bar (0.41 MPa) followed by ultrasonic cleaning. Based on the mechanical cleaning technique of the remaining provisional cement on surfaces of cast cores, specimens were equally divided into 3 groups: hand cleaning (HC) with a dental excavator, hand cleaning followed by polishing using a brush and pumice (BP), and hand cleaning followed by intraoral airborne-particle abrasion (APA). All crowns were then cemented to their corresponding cores using universal resin cement. All crowns were stored for 7 days at 37°C. An Instron universal testing machine was used to record the bond strength of crowns. Airborne-particle abrasion method for intraoral mechanical cleaning revealed a statistically significantly higher bond strength compared to the other two methods. When comparing the three methods of provisional cement cleaning from metal cores, airborne-particle abrasion resulted in the highest bond strength for cast crowns. © 2017 by the American College of Prosthodontists.

  6. Displacement of screw-retained single crowns into implants with conical internal connections.

    Science.gov (United States)

    Yilmaz, Burak; Seidt, Jeremy D; McGlumphy, Edwin A; Clelland, Nancy L

    2013-01-01

    Internal conical implant-abutment connections without platforms may lead to axial displacement of crowns during screw tightening. This displacement may affect proximal contacts, incisal edge position, or occlusion. This study aimed to measure the displacement of screw-retained single crowns into an implant in three dimensions during screw tightening by hand or via torque driver. A stereolithic acrylic resin cast was created using computed tomography data from a patient missing the maxillary right central incisor. A 4.0- × 11-mm implant was placed in the edentulous site. Five porcelain-fused-to-metal single crowns were made using "cast-to" abutments. Crowns were tried on the stereolithic model, representing the patient, and hand tightened. The spatial relationship of crowns to the model after hand tightening was determined using three-dimensional digital image correlation (3D DIC), an optical measurement technique. The crowns were then tightened using a torque driver to 20 Ncm and the relative crown positions were again recorded. Testing was repeated three times for each crown, and displacement of the crowns was compared between the hand-tightened and torqued states. Commercial image correlation software was used to analyze the data. Mean vertical and horizontal crown displacement values were calculated after torqueing. The interproximal contacts were evaluated before and after torquing using an 8-μm aluminum foil shim. There were vertical and horizontal differences in crown positions between hand tightening and torqueing. Although these were small in magnitude, detectable displacements occurred in both apical and facial directions. After hand tightening, the 8-μm shim could be dragged without tearing. However, after torque tightening, the interproximal contacts were too tight and the 8-μm shim could not be dragged without tearing. Differences between hand tightening and torque tightening should be taken into consideration during laboratory and clinical

  7. Fracture Strength and Failure Mode of Maxillary Implant-Supported Provisional Single Crowns : A Comparison of Composite Resin Crowns Fabricated Directly Over PEEK Abutments and Solid Titanium Abutments

    NARCIS (Netherlands)

    Santing, H.J.; Meijer, Henny J.A.; Raghoebar, G.M.; Ozcan, M.

    2012-01-01

    Background: Polyetheretherketone (PEEK) temporary abutments have been recently introduced for making implant-supported provisional single crowns. Little information is available in the dental literature on the durability of provisional implant-supported restorations. Purpose: The objectives of this

  8. Retention Load Values of Telescopic Crowns Made of Y-TZP and CoCr with Y-TZP Secondary Crowns: Impact of Different Taper Angles

    Directory of Open Access Journals (Sweden)

    Susanne Merk

    2016-05-01

    Full Text Available This study aimed to examine and compare the retention load values (RL of different telescopic crown assemblies (Y-TZP and CoCr primary crowns with electroformed and Y-TZP secondary crowns each with three different taper angles (0°, 1° and 2°. Thirty Y-TZP primary crowns with electroformed gold copings (Z/G group and Y-TZP secondary crowns (Z/Z group and 30 CoCr primary crowns with electroformed gold copings (C/G group and Y-TZP secondary crowns (C/Z group, each with taper angles of 0°, 1° and 2°, were fabricated, respectively. With the exception of the electroformed gold copings, all specimens were Computer-Aided-Design/Computer-Aided-Manufacturing (CAD/CAM-milled, then sintered and afterwards manually adapted. In order to stabilize the gold copings, they were fixed in a tertiary structure. The secondary crowns were constructed with a hook, which ensured self-alignment with an upper chain. Afterwards, 20 pull-off test cycles were performed in a universal testing machine under artificial saliva and after weighing the secondary crowns with a 5 kg object for 20 s. Data were analyzed by one-way and two-way Analysis of Variance (ANOVA. C/Z with 1° showed higher (p = 0.009 RL than 0° and 2° tapers. C/G at 1° also showed higher (p = 0.001 RL than at tapers of 0° and 2°. Z/G and C/G at 0° showed lower RL than Z/Z and C/Z (p < 0.001. Primary crowns had no impact on the 0° group. Z/G showed lower RL as compared to C/Z within the 1° group (p = 0.007 and Z/Z in the 2° group (p = 0.006. The primary crown material had no influence on RL. Electroformed copings showed lower RL. Further investigations for 1° as well as for the long-term performance after thermomechanical aging are necessary.

  9. Three-dimensional finite element analysis of molars with thin-walled prosthetic crowns made of various materials.

    Science.gov (United States)

    Dejak, Beata; Młotkowski, Andrzej; Langot, Cezary

    2012-04-01

    The aim of the study was to compare the strength of thin-walled molar crowns made of various materials under simulation of mastication. Five 3D FE models of the first lower molar with the use of contact elements were created: intact tooth; tooth with a zirconia crown; tooth with a porcelain crown; tooth with a gold alloy crown and tooth with a composite crown. The computer simulations of mastication were conducted. For the models, equivalent stresseswere calculated using the modified von Mises failure criterion (mvM). Contact stresses at the adhesive interface between the cement and tooth structure under the crowns were analyzed. Equivalent stresses in the crowns, did not exceed the tensile strength of their material. The mvM stresses in resin cement under the zirconia crown were 1.3 MPa, and under the composite crown they increased over 6 times. The tensile and shear contact stressesunder the stiff crowns (ceramics and gold alloy), were several times lower than those under the composite one. The maximum mvM stresses in the tooth structure for the zirconia crown were only 2.8 MPa, whereas for the composite crown were 6.4 MPa. The higher elastic modulus the crown was, the lower the equivalent stresses occurred in the composite luting cement and in the tooth structures. Also contact stresses decreased with the increasing stiffness of the crowns. Under physiological loads, the thin-walled crowns perfectly luted to molars, made of zirconia ceramic, gold alloys and composite resin are resistant to failure. Prosthetic crowns made of stiff materials are less prone to debonding than those made of composite resin. Prosthetic crowns made of a material with a higher elastic modulus than enamel will strengthen the dental structures of molar teeth. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  10. An in vivo evaluation of fit of zirconium-oxide based ceramic single crowns, generated with two CAD/CAM systems, in comparison to metal ceramic single crowns.

    Science.gov (United States)

    Biscaro, Leonello; Bonfiglioli, Roberto; Soattin, Massimo; Vigolo, Paolo

    2013-01-01

    The purpose of this study was to assess in vivo the marginal fit of single crowns produced using two CAD/CAM all-ceramic systems, in comparison to more traditional metal ceramic crowns. Thirty vital, caries-free, and previously untreated teeth were chosen in five patients who needed extraction for implant placement and therefore were included in this study. In the control group (C), 10 regular metal ceramic crowns with porcelain occlusal surfaces were fabricated. In the other two groups (Z and E), CAD/CAM technology was used for the fabrication of 20 zirconium-oxide-based ceramic single crowns with two systems. All zirconia crowns were cemented with glass-ionomer cement, always following the manufacturer's instructions. The same dentist carried out all clinical phases. 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 a magnification of 50×. On completion of microscopic evaluation, representative specimens from each group were prepared for ESEM evaluation. Mean and standard deviations of the four landmarks (mesial, distal, buccal, palatal) at each single crown were calculated for each group. Multivariate analysis of variance (MANOVA) was performed to determine whether the four landmarks, taken into consideration together, differed between groups. Two-way ANOVA was performed to study in detail, for each landmark, how the three systems used to produce the FPDs affected the gap measurements. Differences were considered to be significant at p compared to more traditional metal ceramic crowns. © 2012 by the American College of Prosthodontists.

  11. Concise total syntheses of (+/-)-strychnine and (+/-)-akuammicine.

    Science.gov (United States)

    Sirasani, Gopal; Paul, Tapas; Dougherty, William; Kassel, Scott; Andrade, Rodrigo B

    2010-05-21

    Concise total syntheses of Strychnos alkaloids strychnine (1) and akuammicine (2) have been realized in 13 and 6 operations, respectively. Key steps include (1) the vinylogous Mannich reaction; (2) a novel, sequential one-pot spirocyclization/intramolecular aza-Baylis-Hillman reaction; and (3) a Heck cyclization. The synthesis of 1 proceeds via the Wieland-Gumlich aldehyde (26).

  12. Ferromagnetic Behavior in Zinc Ferrite Nanoparticles Synthesized ...

    African Journals Online (AJOL)

    Zinc ferrite have been produced and used by humans since long time, however understanding of ZnFe2O4 as a nano structured materials is very useful in order to be used for technological applications. ZnFe2O4 structural, magnetic and electrical properties are different when synthesized using different techniques.

  13. Biosynthesis of silver nanoparticles synthesized by Aspergillus

    Indian Academy of Sciences (India)

    In the present study, biosynthesis of silver nanoparticles and its antioxidant, antimicrobial and cytotoxic activities were investigated. Silver nanoparticles were extracellularly synthesized using Aspergillus flavus and the formation of nanoparticles was observed after 72 h of incubation. The results recorded from colour ...

  14. nanoparticles synthesized by citrate precursor m

    African Journals Online (AJOL)

    user

    Abstract. Ni0.5M0.5Fe2O4 (M = Co, Cu) ferrite nanoparticles were synthesized using citrate precursor method. The citrate precursor was annealed at temperatures 400oC, 450oC, 500oC and 550oC. The annealed powders were characterized using X-ray diffractometer. (XRD) and vibrating sample magnetometer (VSM).

  15. Biological activities of synthesized silver nanoparticles from ...

    Indian Academy of Sciences (India)

    The C. halicacabum leaf extract synthesized AgNPs efficiency were tested against different bacterial pathogens MTCC-426 Proteus vulgaris, MTCC-2453 Pseudomonas aeruginosa, MTCC-96 Staphylococcus aureus, MTCC-441 Bacillus subtilis andMTCC-735 Salmonella paratyphi, and fungal pathogens Alternaria solani ...

  16. Syntheses of copper complexes of nicotinohydroxamic and ...

    African Journals Online (AJOL)

    Nicotinohydroxamic acid (NHA) and isonicotinohydroxamic acid (INHA) were synthesized, characterized by electronic and spectral studies,magnetic measurements and their pKa determined spectrophotometrically as 8.68 ± 0.02 in aqueous medium of 0.1mol dm-3 I=ionic strength. The composition of the complexes was ...

  17. Syntheses, molecular and crystalline architectures, and ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 125; Issue 4. Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base. Subhasis Roy Somnath Choubey Sumitava Khan ...

  18. Biological activities of synthesized silver nanoparticles

    Indian Academy of Sciences (India)

    The C. halicacabum leaf extract synthesized AgNPs efficiency were tested against different bacterial pathogens MTCC-426 Proteus vulgaris, MTCC-2453 Pseudomonas aeruginosa, MTCC-96 Staphylococcus aureus, MTCC-441 Bacillus subtilis andMTCC-735 Salmonella paratyphi, and fungal pathogens Alternaria solani ...

  19. Method and apparatus for synthesizing filamentary structures

    Science.gov (United States)

    Height, Murray J [Somerville, MA; Howard, Jack B [Winchester, MA; Vandersande, John B [Newbury, MA

    2008-02-26

    Method and apparatus for producing filamentary structures. The structures include single-walled nanotubes. The method includes combusting hydrocarbon fuel and oxygen to establish a non-sooting flame and providing an unsupported catalyst to synthesize the filamentary structure in a post-flame region of the flame. Residence time is selected to favor filamentary structure growth.

  20. Cytotoxicity of Nanoliposomal Cisplatin Coated with Synthesized ...

    African Journals Online (AJOL)

    Purpose: To evaluate the cytotoxicity of pegylated nanoliposomal cisplatin on human ovarian cancer cell line A2780CP. Methods: Synthesized methoxypolyethylene glycol (mPEG) propionaldehyde was characterized by 1Hnuclear magnetic resonance (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) and used ...

  1. Syntheses, molecular and crystalline architectures, and ...

    Indian Academy of Sciences (India)

    Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base ... The complexes display intraligand (-*) fluorescence in the solid state and in DMF solutions at room temperature.

  2. Cytotoxicity of Nanoliposomal Cisplatin Coated with Synthesized ...

    African Journals Online (AJOL)

    Methods: Synthesized methoxypolyethylene glycol (mPEG) propionaldehyde was characterized by 1H- nuclear magnetic resonance (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) and used as coating agent for the preparation of liposomal nanodrug formulation by reverse phase evaporation method.

  3. Biosynthesis of silver nanoparticles synthesized by Aspergillus ...

    Indian Academy of Sciences (India)

    In the present study, biosynthesis of silver nanoparticles and its antioxidant, antimicrobial and cytotoxic activities were investigated. Silver nanoparticles were extracellularly synthesized using Aspergillus flavus and the formation of nanoparticles was observed after 72 h of incubation. The results recorded from colour ...

  4. Synthese et caracterisation par spectroscopie infrarouge et ...

    African Journals Online (AJOL)

    ABSTRACT:- About six new Molybdato adducts of tin tetrahalide and tin(IV) organometallics have been synthesized and characterized. Their infrared and Mössbauer study allow us to suggest discrete structures with only one polydentate ligand or two types of ligands of different symmetries in the same adduct. KEYWORDS: ...

  5. 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...

  6. A semi-empirical model for predicting crown diameter of cedrela ...

    African Journals Online (AJOL)

    A semi-empirical model relating age and breast height has been developed to predict individual tree crown diameter for Cedrela odorata (L) plantation in the moist evergreen forest zones of Ghana. The model was based on field records of 269 trees, and could determine the crown cover dynamics, forecast time of canopy ...

  7. 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.

  8. Randomized clinical study of wear of enamel antagonists against polished monolithic zirconia crowns.

    Science.gov (United States)

    Esquivel-Upshaw, J F; Kim, M J; Hsu, S M; Abdulhameed, N; Jenkins, R; Neal, D; Ren, F; Clark, A E

    2018-01-01

    To test the hypothesis that there is no difference in the in vivo maximum wear of enamel opposing monolithic zirconia crowns, enamel opposing porcelain fused to metal crowns and enamel opposing enamel. Thirty patients needing single crowns were randomized to receive either a monolithic zirconia or metal-ceramic crown. Two non-restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned for baseline data. Polyvinylsiloxane impressions were obtained and poured in white stone. Patients were recalled at six-months and one-year for re-impression. Stone models were scanned using a tabletop laserscanner to determine maximum wear. Statistical analysis was performed using Mann-Whitney U to determine any significant differences between the wear of enamel against zirconia and metal-ceramic crowns. Sixteen zirconia and 14 metal-ceramic crowns were delivered. There were no statistical differences in mean wear of crown types (p=0.165); enamel antagonists (p=0.235) and enamel controls (p=0.843) after one year. Monolithic zirconia exhibited comparable wear of enamel compared with metal-ceramic crowns and control enamel after one year. This study is clinically significant because the use of polished monolithic zirconia demonstrated comparable wear of opposing enamel to metal-ceramic and enamel antagonists. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Polyacrylonitrile (PAN)/crown ether composite nanofibers for the selective adsorption of cations

    NARCIS (Netherlands)

    Tas, Sinem; Kaynan, Ozge; Ozden-Yenigun, Elif; Nijmeijer, Dorothea C.

    2016-01-01

    In this study, we prepared electrospun polyacrylonitrile (PAN) nanofibers functionalized with dibenzo-18-crown-6 (DB18C6) crown ether and showed the potential of these fibers for the selective recovery of K+ from other both mono- and divalent ions in aqueous solutions. Nanofibers were characterized

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

    Science.gov (United States)

    Fusarium crown rot, caused by a complex of Fusarium spp., is a yield-limiting disease of wheat world-wide, especially in dry Mediterranean climates. In order to identify Fusarium species associated with crown rot of wheat, a survey was conducted in summer 2013 in the major wheat growing regions of T...

  11. Occlusal convergence and strain distribution on the axial surface of cemented gold crowns.

    Science.gov (United States)

    Asbia, S; Ibbetson, R; Reuben, R L

    2008-01-01

    The overall thrust of this work is concerned with the performance of the adhesives used to simulate cementation of gold crowns onto nickel chromium dies under static and dynamic compression. A measurement system, based on the mounting of strain gauges on the outer surface of the crowns, has been developed allowing an indirect semi-quantitative estimate of the state of adhesion. This paper reports an investigation of the effect of increased total occlusal convergence (TOC) of the nickel chromium dies from 12 degrees to 24 degrees with different degrees of cementation, a) un-cemented, b) partially cemented and c) fully cemented. Four nickel chromium dies (12 degrees TOC) and five nickel chromium dies (24 degrees TOC) for each convergence were fabricated using the lost wax technique. The axial height of all dies was 6mm. Two miniature gauges were installed on opposing axial surfaces of each gold crown 1 mm above the crown margin. Axial loading and unloading of the crowns was repeated five times for each crown and the values for strain recorded. The results showed an increase in strain at the axial surfaces with increasing TOC, providing useful design information for the durability of restorative crowns. These findings, along with the findings of earlier work are consistent with a simple model of load transfer between the crown and the die.

  12. Influence of Cusp Inclination and Type of Retention on Fracture Load of Implant-Supported Crowns.

    Science.gov (United States)

    Rocha, Cibele Oliveira de Melo; Longhini, Diogo; Pereira, Rodrigo de Paula; Arioli, João Neudenir

    2017-01-01

    There are few informations about the influence of cusp inclination on the fracture strength of implant-supported crowns. The study aimed to evaluate the influence of cusp inclination and retention type on fracture load in implant-supported metal-ceramic single crowns. Sixty crowns were made, classified as cemented and screw-retained with screw access hole (SAH) sealed or not. Standard (33°) and reduced (20°) cusp inclinations were tested for each group (n=10). To support crowns of a mandibular second molar, analogs of external hexagon implants 5.0 were used. The fracture load was measured in a universal testing machine EMIC DL2000 (10 kN load cell; 0.5 mm/min). Two-way ANOVA (retention and cusp inclination) followed by post hoc Tukey's honest significant difference test was used for the statistical analyses (a=0.05). Crowns with reduced cusp inclination exhibited significantly higher fracture load (pcrowns with standard cusp inclination. Cemented crowns showed significantly higher fracture load (pcrowns. The interaction among these factors was not significant (p>0.05) for the fracture load. The sealing of SAH did not influence the fracture load of screw-retained crowns (p>0.05). In conclusion, fracture load of implant-supported metal-ceramic crowns was influenced by retention and cusp inclination, and there was no influence of the sealing of SAH.

  13. distribution and types of artificial crown s and bridges prescribed at a ...

    African Journals Online (AJOL)

    *0bjectives: To determine the types and dstribution of artificial crowns and fixed partial dentures, to analyse the age and gender distribution of patients receiving these prostheses and to compare results with studies elsewhere. ' Materials and methods: The present study consists ofpatients who received crowns and fixed ...

  14. Crown area equations for 13 species of trees and shrubs in northern California and southwestern Oregon

    Science.gov (United States)

    Fabian C.C. Uzoh; Martin W. Ritchie

    1996-01-01

    The equations presented predict crown area for 13 species of trees and shrubs which may be found growing in competition with commercial conifers during early stages of stand development. The equations express crown area as a function of basal area and height. Parameters were estimated for each species individually using weighted nonlinear least square regression.

  15. A comparison of tree crown condition in areas with and without gypsy moth activity

    Science.gov (United States)

    KaDonna C. Randolph

    2007-01-01

    This study compared the crown condition of trees within and outside areas of gypsy moth defoliation in Virginia via hypothesis tests of mean differences for five U.S. Department of Agriculture (USDA) Forest Service Forest Inventory and Analysis phase 3 crown condition indicators. Significant differences were found between the trees located within and outside gypsy moth...

  16. Optical effects of different colors of artificial gingiva on ceramic crowns.

    Science.gov (United States)

    Wang, Jian; Lin, Jin; Gil, Mindy; Da Silva, John D; Wright, Robert; Ishikawa-Nagai, Shigemi

    2013-08-01

    The interaction between gingival color and the shade of ceramic restorations has never been fully studied. The purpose of this study is to investigate the optical effects of altering artificial gingival color on the ceramic crown shade in the cervical area. Thirty-one all-ceramic crowns of different shades were used in this study with six different artificial gingival colors. Using a spectrophotometer (Crystaleye(®) Olympus, Japan), we measured the shade of crowns in cervical areas with each of six different artificial gingiva. The crown color measured in the presence of pink artificial gingiva (control) was compared with the crown color with five other artificial gingiva. color difference values ΔE* were calculated and compared between the control group and test groups and the correlation of the artificial gingival color with the crown color was also assessed. Significant differences were found in the mean L* and a* values of all-ceramic crowns at the cervical regions in all six gingival color groups (pcolors of artificial gingiva generated clinically detectable shade differences in the cervical region of ceramic crowns. Copyright © 2013. Published by Elsevier Ltd.

  17. Practical tools for assessing potential crown fire behavior and canopy fuel characteristics

    Science.gov (United States)

    Martin E. Alexander; Miguel G. Cruz

    2015-01-01

    This presentation recapitulates the main points made at a technology and information transfer workshop held in advance of the conference that provided overviews of two software applications, developed by the authors, for use in assessing crown fire behavior and canopy fuel characteristics. These are the Crown Fire Initiation and Spread (CFIS) software system and the...

  18. Crown characteristics of juvenile loblolly pine 6 years after application of thinning and fertilization

    Science.gov (United States)

    Shufang Yu; Jim L. Chambers; Zhenmin Tang; James P. Barnett

    2003-01-01

    Total foliage dry mass and leaf area at the canopy hierarchical level of needle, shoot, branch and crown were measured in 48 trees harvested from a 14-year-old loblolly pine (Pinus taeda L.) plantation, six growing seasons after thinning and fertilization treatments. In the unthinned treatment, upper crown needles were heavier and had more leaf area...

  19. Evaluation of the Three-year Experience with All-ceramic Crowns with Polycrystalline Ceramic Cores

    Directory of Open Access Journals (Sweden)

    Lenka Vavřičková

    2013-01-01

    Full Text Available The objective of the study was to evaluate the clinical outcomes of all-ceramic crowns three years after placement of the restoration in the oral cavity. The aim of the present clinical study were surveyed the Procera®, Cercon® and LAVA™ systems. In total, 121 crowns were followed in 33 patients (7 men and 26 women with an average age of 53.5 years. The eighty crowns were placed in anterior and forty one crowns in posterior teeth. The crowns were fabricated in two dental laboratories and delivered in two private dental practices. The clinical trial was conducted according to American Dental Association guidelines. The patients were requested to provide their consent to the regular clinical examination including radiographic and photographic records.  A total of 102 crowns were made of zirconium oxide ceramic cores – 58 Cercon®; 43 LAVA™, while 19 crowns were made of aluminum oxide cores Procera®. The veneering ceramic LAVA™ Ceram was used. The success rate was analyzed using Kaplan-Meier statistics and, in our case, the overall three-year success rate reached 96.7%.  All-ceramic crowns with polycrystalline ceramic cores have low susceptibility to fracture, in this study just 3.3%.

  20. Rainfall interception by tree crown and leaf litter: an interactive process

    Science.gov (United States)

    Xiang Li; Qingfu Xiao; Jianzhi Niu; Salli Dymond; E. Gregory McPherson; Natalie van Doorn; Xinxiao Yu; Baoyuan Xie; Kebin Zhang; Jiao Li

    2017-01-01

    Rainfall interception research in forest ecosystems usually focuses on interception by either tree crown or leaf litter, although the 2 components interact when rainfall occurs. A process-based study was conducted to jointly measure rainfall interception by crown and litter and the interaction between the 2 interception processes for 4 tree species (...

  1. 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,

  2. 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

  3. Genome-Wide Association Mapping of Crown Rust Resistance in Oat Elite Germplasm.

    Science.gov (United States)

    Klos, Kathy Esvelt; Yimer, Belayneh A; Babiker, Ebrahiem M; Beattie, Aaron D; Bonman, J Michael; Carson, Martin L; Chong, James; Harrison, Stephen A; Ibrahim, Amir M H; Kolb, Frederic L; McCartney, Curt A; McMullen, Michael; Fetch, Jennifer Mitchell; Mohammadi, Mohsen; Murphy, J Paul; Tinker, Nicholas A

    2017-07-01

    Oat crown rust, caused by f. sp. , is a major constraint to oat ( L.) production in many parts of the world. In this first comprehensive multienvironment genome-wide association map of oat crown rust, we used 2972 single-nucleotide polymorphisms (SNPs) genotyped on 631 oat lines for association mapping of quantitative trait loci (QTL). Seedling reaction to crown rust in these lines was assessed as infection type (IT) with each of 10 crown rust isolates. Adult plant reaction was assessed in the field in a total of 10 location-years as percentage severity (SV) and as infection reaction (IR) in a 0-to-1 scale. Overall, 29 SNPs on 12 linkage groups were predictive of crown rust reaction in at least one experiment at a genome-wide level of statistical significance. The QTL identified here include those in regions previously shown to be linked with seedling resistance genes , , , , , and and also with adult-plant resistance and adaptation-related QTL. In addition, QTL on linkage groups Mrg03, Mrg08, and Mrg23 were identified in regions not previously associated with crown rust resistance. Evaluation of marker genotypes in a set of crown rust differential lines supported as the identity of . The SNPs with rare alleles associated with lower disease scores may be suitable for use in marker-assisted selection of oat lines for crown rust resistance. Copyright © 2017 Crop Science Society of America.

  4. 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.

  5. [Comparative adaptation of crowns of selective laser melting and wax-lost-casting method].

    Science.gov (United States)

    Li, Guo-qiang; Shen, Qing-yi; Gao, Jian-hua; Wu, Xue-ying; Chen, Li; Dai, Wen-an

    2012-07-01

    To investigate the marginal adaptation of crowns fabricated by selective laser melting (SLM) and wax-lost-casting method, so as to provide an experimental basis for clinic. Co-Cr alloy full crown were fabricated by SLM and wax-lost-casting for 24 samples in each group. All crowns were cemented with zinc phosphate cement and cut along longitudinal axis by line cutting machine. The gap between crown tissue surface and die was measured by 6-point measuring method with scanning electron microscope (SEM). The marginal adaptation of crowns fabricated by SLM and wax-lost-casting were compared statistically. The gap between SLM crowns were (36.51 ± 2.94), (49.36 ± 3.31), (56.48 ± 3.35), (42.20 ± 3.60) µm, and wax-lost-casting crowns were (68.86 ± 5.41), (58.86 ± 6.10), (70.62 ± 5.79), (69.90 ± 6.00) µm. There were significant difference between two groups (P < 0.05). Co-Cr alloy full crown fabricated by wax-lost-casting method and SLM method provide acceptable marginal adaptation in clinic, and the marginal adaptation of SLM is better than that of wax-lost-casting method.

  6. Large acceleration of a-chymotrypsin-catalyzed dipeptide formation by 18-crown-6 in organic solvents

    NARCIS (Netherlands)

    van Unen, D.J.; Engbersen, Johannes F.J.; Reinhoudt, David

    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

  7. NMR and theoretical study of the cooperative interaction of hydrated proton with dibenzo-24-crown-8

    Czech Academy of Sciences Publication Activity Database

    Kříž, Jaroslav; Dybal, Jiří; Budka, J.; Makrlík, E.

    2008-01-01

    Roč. 46, č. 11 (2008), s. 1015-1024 ISSN 0749-1581 R&D Projects: GA AV ČR 1ET400500402 Institutional research plan: CEZ:AV0Z40500505 Keywords : dibenzo-24- crown-8 * NMR exchange dynamics * crown protonation * DFT calculations Subject RIV: CD - Macromolecular Chemistry Impact factor: 1.443, year: 2008

  8. Fracture strength and failure mode of maxillary implant-supported provisional single crowns: a comparison of composite resin crowns fabricated directly over PEEK abutments and solid titanium abutments.

    Science.gov (United States)

    Santing, Hendrik Jacob; Meijer, Henny J A; Raghoebar, Gerry M; Özcan, Mutlu

    2012-12-01

    Polyetheretherketone (PEEK) temporary abutments have been recently introduced for making implant-supported provisional single crowns. Little information is available in the dental literature on the durability of provisional implant-supported restorations. The objectives of this study were to evaluate the fracture strength of implant-supported composite resin crowns on PEEK and solid titanium temporary abutments, and to analyze the failure types. Three types of provisional abutments, RN synOcta Temporary Meso Abutment (PEEK; Straumann), RN synOcta Titanium Post for Temporary Restorations (Straumann), and Temporary Abutment Engaging NobRplRP (Nobel Biocare) were used, and provisional screw-retained crowns using composite resin (Solidex) were fabricated for four different locations in the maxilla. The specimens were tested in a universal testing machine at a crosshead speed of 1 mm/minute until fracture occurred. The failure types were analyzed and further categorized as irreparable (Type 1) or reparable (Type 2). No significant difference was found between different abutment types. Only for the position of the maxillary central incisor, composite resin crowns on PEEK temporary abutments showed significantly lower (p Provisional crowns on PEEK abutments showed similar fracture strength as titanium temporary abutments except for central incisors. Maxillary right central incisor composite resin crowns on PEEK temporary abutments fractured below the mean anterior masticatory loading forces reported to be approximately 206 N. © 2010 Wiley Periodicals, Inc.

  9. 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.

  10. Clinical evaluation of two different methods of stainless steel esthetic crowns.

    Science.gov (United States)

    Yilmaz, Yucel; Koçoğullari, Mutlu Elçin

    2004-01-01

    The purpose of this study was to compare the clinical success of stainless steel crowns (SSCs) made esthetic by open facing or veneering on posterior primary teeth. Thirty-three crowns (18 open-face and 15 veneered) were placed and followed up for 18 months with semiannual evaluations. Crowns made esthetic with the open-face method showed a success of 95%, while the veneered crowns showed a success of 80% based on greater than two thirds facing retention. Statistical evaluation by 2 proportion test showed no significant difference between groups (P>.05). In addition, a statistically significant difference was found between upper and lower crowns by Fisher's exact test (Pcrowns exhibited a higher success rate than those in the lower arch.

  11. In vitro fracture resistance of composite-resin-veneered zirconia crowns.

    Science.gov (United States)

    Peampring, Chaimongkon; Aksornmuang, Juthatip; Sanohkan, Sasiwimol

    2017-01-01

    The aim of this study is to investigate the fracture load to failure and damage mode of the composite resin-veneered zirconia crowns preparing with two different zirconia surface treatments compared conventional porcelain-veneered zirconia crowns. Metallic molar-shape dies prepared with 10° convergence angle a 1.5 mm deep chamfer finish line were used. Two groups of composite-resin-veneered zirconia crowns were prepared using different surface treatment (Group A - sandblasting and Group B - glaze-on technique). Group C (conventional porcelain-veneered zirconia crowns) was served as control. Load to failure test was performed to evaluate the fracture resistance of the crowns using a universal testing machine. One-way ANOVA was used to evaluate the differences of mean values ( P zirconia coping exposed. Group B and C showed significant higher load to failure than Group A. Four specimens of Group A revealed the delamination of composite resin veneering.

  12. 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.

  13. Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry.

    Science.gov (United States)

    Eikemo, Håvard; Klemsdal, Sonja S; Riisberg, Ingvild; Bonants, Peter; Stensvand, Arne; Tronsmo, Anne M

    2004-03-01

    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, and New Zealand, were identical in an analysis based on 96 polymorphic bands from seven primer combinations. Leather rot isolates of strawberry could not be distinguished from isolates from other hosts. The pathogenicity test of all 44 isolates on strawberry plants mostly gave unambiguous results, except for three American isolates, which seemed to have reduced aggressiveness compared to the crown rot isolates. These isolates also differed in the AFLP analysis. Comparing information on the origin of the isolates with results from the pathogenicity test, showed that isolates from strawberry fruits or petioles could be either leather rot or crown rot pathotypes. None of the isolates from hosts other than strawberry caused crown rot symptoms in strawberry.

  14. [Cervical adaptation of complete cast crowns of various metal alloys, with and without die spacers].

    Science.gov (United States)

    Stephano, C B; Roselino, R F; Roselino, R B; Campos, G M

    1989-01-01

    A metallic replica from a dental preparation for crown was used to make 8 class-IV stone dies. The wax patterns for the casting of the crowns were obtained in two conditions: a) from the stone die with no spacer; and b) from the stone die with an acrylic spacer. Thus, 64 metallic crowns were casted, using 4 different alloys: DURACAST (Cu-Al), NICROCAST (Ni-Cr) and DURABOND (Ni-Cr), and gold. The casted crowns were fitted in the metallic replica and measured as to the cervical discrepance of fitting. The results showed that the use of die spacers decreases the clinical discrepancies of fitting of the casted crowns (in a statistically significant level), no matter the metallic alloy employed.

  15. Vonlays: a conservative esthetic alternative to full-coverage crowns.

    Science.gov (United States)

    McLaren, Edward A; Figueira, Johan; Goldstein, Ronald E

    2015-04-01

    Porcelain veneers have long been a popular restorative option that have evolved into a well-accepted treatment that can be fabricated in various ways. Onlays are another common treatment modality used in contemporary dentistry to restore large areas of decay and to replace old restorations. With the availability of newer high-strength materials such as lithium disilicate and processing technologies like CAD/CAM and heat pressing, dental professionals are now able to produce highly esthetic, high-strength restorations that blend seamlessly with the natural dentition while also withstanding posterior occlusal forces. This has resulted in innovative methods of providing minimally invasive dentistry. One such approach is a combination restoration the authors call a "vonlay," which, as demonstrated in this case report, can be used as an alternative to coverage crowns to restore damaged posterior teeth.

  16. Rehabilitation of complicated crown-root fracture by invisible approach.

    Science.gov (United States)

    Rani, V Leela; Rajalingam, S; Hemalatha, R; Jananee, J

    2016-10-01

    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.

  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. Provisional Crown Dislodgement during Scuba Diving: A Case of Barotrauma

    Directory of Open Access Journals (Sweden)

    Meenal Nitin Gulve

    2013-01-01

    Full Text Available Changes in ambient pressure, for example, during flying, diving, or hyperbaric oxygen therapy, can lead to barotrauma. Although it may seem that this issue was neglected in dental education and research in recent decades, familiarity with and understanding of these facts may be of importance for dental practitioners. We report the case of a patient who experienced barotrauma involving dislodgement of a provisional crown during scuba diving. Patients who are exposed to pressure changes as a part of their jobs or hobbies and their dentists should know the causes of barotrauma. In addition, the clinician must be aware of the possible influence of pressure changes on the retention of dental components.

  19. AUTOMATIC TREE-CROWN DETECTION IN CHALLENGING SCENARIOS

    Directory of Open Access Journals (Sweden)

    D. Bulatov

    2016-06-01

    Full Text Available 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.

  20. 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.

  1. Effect of core thickness differences on post-fatigue indentation fracture resistance of veneered zirconia crowns.

    Science.gov (United States)

    Alhasanyah, Abdulrahman; Vaidyanathan, Tritala K; Flinton, Robert J

    2013-07-01

    Despite the excellent esthetics of veneered zirconia crowns, the incidence of chipping and fracture of veneer porcelain on zirconia crowns has been recognized to be higher than in metal ceramic crowns. The objective of this investigation was to study the effect of selected variations in core thickness on the post-fatigue fracture resistance of veneer porcelain on zirconia crowns. Zirconia crowns for veneering were prepared with three thickness designs of (a) uniform 0.6-mm thick core (group A), (b) extra-thick 1.7 mm occlusal core support (group B), and (c) uniform 1.2-mm thick core (group C). The copings were virtually designed and milled by the CAD/CAM technique. Metal ceramic copings (group D) with the same design as in group C were used as controls. A sample size of N = 20 was used for each group. The copings were veneered with compatible porcelain and fatigue tested under a sinusoidal loading regimen. Loading was done with a 200 N maximum force amplitude under Hertzian axial loading conditions at the center of the crowns using a spherical tungsten carbide indenter. After 100,000 fatigue cycles, the crowns were axially loaded to fracture and maximum load levels before fracture was recorded. One-way ANOVA (P crowns. Extra-thick occlusal core support for porcelain veneer may significantly reduce the veneer chipping and fracture of zirconia crowns. This is suggested as an important consideration in the design of copings for zirconia crowns. © 2013 by the American College of Prosthodontists.

  2. Risk factors for technical and biological complications with zirconia single crowns.

    Science.gov (United States)

    Rinke, Sven; Lange, Katharina; Roediger, Matthias; Gersdorff, Nikolaus

    2015-11-01

    This practice-based study evaluated the clinical performance and risk factors for biological and technical complications with conventionally luted zirconia crowns. Sixty-eight patients (39 female) with a total of 323 restorations placed on 219 vital teeth, 69 endodontically treated teeth (ETT), and 41 implants (incisors, 96; premolars, 89; molars, 138; observational period, 79.7 ± 14.2 months) underwent a clinical follow-up examination and were included in the study. Time-dependent survival (in situ), success (event free), and veneering ceramic fracture (VCF) rates were calculated and analyzed relative to the following risk factors: smoking status, location of the crown, and type of abutment. Fifty-three complete failures were recorded. A significant influence of the abutment type on survival could be detected (p = 0.033): ETT demonstrated a significantly (p = 0.029) lower 7-year survival rate (73.8%, 95% confidence interval [95% CI] 0.600-0.876) than crowns placed on implants (90.0%, 95% CI 0.814-0.990). The success rate of the crowns was significantly influenced by the location of the restoration (p = 0.0058). A total of 75.6% (95% CI 0.648-0.864) of the anterior crowns remained event free, compared to 50.4% (95% CI 0.388-0.621) of the molar crowns. Furthermore, the location of the crowns affected the VCF rate (p = 0.018, event-free anterior teeth 95.2% (95% CI 0.880-1), event-free molars 80.9% (95% CI 0.706-0.913)). Survival and success rates were significantly influenced by the type of abutment and the location of the restoration. More complete failures should be expected for crowns placed on ETT, while crowns on molars demonstrated more biological and technical complications than anterior zirconia crowns.

  3. Effect of cement space on the marginal fit of CAD-CAM-fabricated monolithic zirconia crowns.

    Science.gov (United States)

    Kale, Ediz; Seker, Emre; Yilmaz, Burak; Özcelik, Tuncer Burak

    2016-12-01

    Monolithic zirconia crowns fabricated with computer-aided design and computer-aided manufacturing (CAD-CAM) have recently become a common practice for the restoration of posterior teeth. The marginal fit of monolithic zirconia crowns may be affected by different cement space parameters set in the CAD software. Information is scarce regarding the effect of cement space on the marginal fit of monolithic zirconia crowns fabricated with CAD-CAM technology. The purpose of this in vitro study was to evaluate the effect of cement space on the marginal fit of CAD-CAM-fabricated monolithic zirconia crowns before cementation. Fifteen right maxillary first molar typodont teeth with standardized anatomic preparations for complete-coverage ceramic crowns were scanned with a 3-dimensional laboratory scanner. Crowns were designed 3-dimensionally using software and then milled from presintered monolithic zirconia blocks in a computer numerical control dental milling machine. The cement space was set at 25 μm around the margins for all groups, and additional cement space starting 1 mm above the finish lines of the teeth was set at 30 μm for group 25-30, 40 μm for group 25-40, and 50 μm for group 25-50 in the CAD software. A total of 120 images (3 groups, 5 crowns per group, 8 sites per crown) were measured for vertical marginal discrepancy under a stereoscopic zoom microscope and the data were statistically analyzed with 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05). The results showed that different cement space values had statistically significant effect on the mean vertical marginal discrepancy value of tested crowns (Pzirconia crowns. The marginal fit improved as the cement space decreased. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  4. Reduction of load-bearing capacity of all-ceramic crowns due to cement aging.

    Science.gov (United States)

    Lu, Chenglin; Wang, Raorao; Mao, Shuangshuang; Arola, Dwayne; Zhang, Dongsheng

    2013-01-01

    The purpose of this study was to investigate how water aging of the resin cement influences the stress distribution in all-ceramic crowns and if there is an increase in the propensity for crown failure. The failure of all-ceramic crowns attributed to cement degradation was explored using a combination of experimental and numerical methods. Sectioned all-ceramic crown specimens were fabricated of IPS e.max Ceram/e.max Press (CP) and Vita VM9/Cercon zirconia (VZ), and then stored in either air or distilled water for 30 days. Monotonic contact loads were applied to fracture near the buccal cusp ridge of each sample. Deformation within the crown layers during loading was analyzed by means of Digital Image Correlation (DIC). A 3D finite element model of the restoration including veneer, core, cement and tooth substrate was developed to evaluate the stress distribution in the crowns before and after cement degradation. There was a significant decrease (pcement water absorption in the CP crowns. In contrast, there was no significant influence of cement aging on fracture modes and fracture loads (p>0.05) in the VZ crowns. Finite element analysis showed that regardless of the crown types, the stress distribution is identical by degradation in Young's modulus of the cement. However, core/substrate debonding results in a change of the stress distribution and a significant increase in the magnitude. Water aging causes reduction of stiffness and bonding strength of cement agents. Degradation in bonding strength and stiffness could potentially lead to stress redistribution in the restored crown and reduce the load-bearing capacity of all-ceramic restorations after years of service. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. 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.

  6. In-vitro performance of CAD/CAM-fabricated implant-supported temporary crowns.

    Science.gov (United States)

    Rosentritt, Martin; Raab, Philipp; Hahnel, Sebastian; Stöckle, Matthias; Preis, Verena

    2017-11-01

    The aim of this study was to investigate the in-vitro performance and fracture resistance of a temporary computer-aided designed and computer-aided manufactured polymethylmethacrylate (CAD/CAM-PMMA) material as implant or tooth-supported single crown with respect to the clinical procedure (permanently bonded/temporarily cemented). Sixty-four crowns were fabricated on implants or human molar teeth simulating (a) labside procedure on prefabricated titanium-bonding base ([TiBase] implant crown bonded in laboratory, screwed chairside), (b) labside procedure ([LAB] standard abutment and implant crown bonded in laboratory, screwed chairside), (c) chairside procedure ([CHAIR] implant crown bonded to abutment), and (d) reference ([TOOTH] crowns luted on prepared human teeth). Crowns were made of a CAD/CAM-PMMA temporary material (TelioCAD, Ivoclar-Vivadent). For investigating the influence of fixation, half of the crowns were permanently (P) or temporarily (T) bonded. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). All restorations survived TCML without visible failures. Fracture results varied between 3034.3 (Tooth-P) and 1602.9 N (Tooth-T) [TOOTH], 1510.5 (TiBase-P) and 963.6 N (TiBase-T) [TiBase], 2691.1 (LAB-P) and 2064.5 N (LAB-T) [LAB], and 1609.4 (Chair-P) and 1253.0 N (Chair-T) [CHAIR]. Tested groups showed significantly (p CAD/CAM crowns showed no different in-vitro performance but provided different fracture results that depended on cementation, screw channel, and type of abutment. All bonded and screwed PMMA crowns were in a range where clinical application seems not restricted.

  7. 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.

  8. Through-space electronic communication of zinc phthalocyanine with substituted [60]Fullerene bearing O2Nxaza-crown macrocyclic ligands

    Science.gov (United States)

    Ghanbari, Bahram; Shahhoseini, Leila; Mahlooji, Niloofar; Gholamnezhad, Parisa; Taheri Rizi, Zahra

    2017-01-01

    Two new macrocyclic ligands containing 17- and 19-membered O2N3-donor aza-crowns anchored to [60]Fullerene were synthesized and characterized by employing HPLC, electrospray ionization mass (ESI-MS), 1H and 13C NMR, UV-vis, IR spectroscopies, as well as powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) in solid state. TGA measurements revealed that upon linking each of these macrocycle rings to [60]Fullerene, the decomposition point measured for [60]Fullerene moiety was increased, indicating on the promoted stability of [60]Fullerene backbone during binding to these macrocyclic ligands. Moreover, the ground state non-covalent interactions of [60]Fullerene derivatives of O2Nx (x = 2, and 3) aza-crown macrocyclic ligands namely, L1-L4 with zinc phthalocyanine (ZnPc) were also investigated by UV-vis absorption, steady state and time resolved fluorescence spectrophotometry in N-methyl-2-pyrrolidone (NMP). The calculation of Stern-Volmer constants (KSV) indicated on existence of an efficient quenching mechanism comprising of the excited singlet state of ZnPc in the presence of L1-L4. The observation of an appropriate correlation between decrease in fluorescence intensity and lifetime parameters led us to propose the occurrence of a static mechanism for the fluorescence quenching of ZnPc in the presence of L1-L3. The binding constants (KBH) of L1-L4/ZnPc were also determined applying the fluorescence quenching experiments. Meanwhile, the incompatibility of both KSV and KBH values found for L4 was also described in terms of structural features using DFT calculations using the B3LYP functional and 6-31G* basis set.

  9. In vitro fracture load of monolithic lithium disilicate ceramic molar crowns with different wall thicknesses.

    Science.gov (United States)

    Seydler, Bodo; Rues, Stefan; Müller, Denise; Schmitter, Marc

    2014-05-01

    The objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns. Forty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (d = 0.5, 1.0, and 1.5 mm; n = 16 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000 cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2 million cycles, Willytec CS3, SD Mechatronik, F max = 108 N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0. Crowns with d = 1.0 and 1.5 mm wall thickness did not crack during artificial aging whereas two of the crowns with d = 0.5 mm wall thickness did. The loads to failure (F u) of the crowns without aging (with aging) were 470.2 ± 80.3 N (369.2 ± 117.8 N) for d = 0.5 mm, 801.4 ± 123.1 N (889.1 ± 154.6 N) for d = 1.0 mm, and 1107.6 ± 131.3 N (980.8 ± 115.3 N) for d = 1.5 mm. For aged crowns with d = 0.5 mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with d = 1.0 mm and d = 1.5 mm wall thickness were not significant. Fracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (F u crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances F u > 600 N. The wall thickness of posterior lithium disilicate

  10. A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice.

    Science.gov (United States)

    Ortorp, Anders; Kihl, Maria Lind; Carlsson, Gunnar E

    2009-09-01

    All-ceramic crowns have become increasingly used also in the posterior regions, but there are only few studies documenting the clinical outcome of these restorations. The aim was therefore to present the 3-year outcome of zirconia (NobelProcera) single crowns. All patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The patient records were scrutinized for data on the restorations and the supporting teeth. Information was available for 161 patients and 204 crowns. At the 3-year recall appointments, a sample of 18 patients with 25 crowns was clinically examined and interviewed regarding patient satisfaction. Most crowns (78%) were placed on premolars and molars. The clinical outcome of the crowns was favourable. No zirconia core fractured and no caries was observed on the abutment teeth. Some types of complication were recorded for 32 (16%) crowns or abutment teeth. The most severe complications, in total 12 restorations (6%), were recorded as failures: abutment tooth was extracted (5), remake of crown due to lost retention (4), veneer fracture (2) and persistent pain (1). The CDA criteria for 25 crowns were rated favourably, and patient satisfaction with the zirconia crowns was in general high. The porcelain-veneered zirconia crowns (NobelProcera) showed good clinical results, were well accepted by the patients, and only few complications were reported over the 3-year follow-up period.

  11. Simulated western spruce budworm defoliation reduces torching and crowning potential: A sensitivity analysis using a physics-based fire model

    Science.gov (United States)

    Gregory M. Cohn; Russell A. Parsons; Emily K. Heyerdahl; Daniel G. Gavin; Aquila Flower

    2014-01-01

    The widespread, native defoliator western spruce budworm (Choristoneura occidentalis Freeman) reduces canopy fuels, which might affect the potential for surface fires to torch (ignite the crowns of individual trees) or crown (spread between tree crowns). However, the effects of defoliation on fire behaviour are poorly understood. We used a physics-based fire model to...

  12. 33 CFR 165.T01-0176 - Regulated Navigation Area; Lake Champlain Bridge Construction, Crown Point, New York and Chimney...

    Science.gov (United States)

    2010-07-01

    ... Champlain Bridge Construction, Crown Point, New York and Chimney Point, Vermont. 165.T01-0176 Section 165...; Lake Champlain Bridge Construction, Crown Point, New York and Chimney Point, Vermont. (a) Description... and south of the Lake Champlain Bridge construction zone at Crown Point, New York and Chimney Point...

  13. Enzymatic synthesizing of phytosterol oleic esters.

    Science.gov (United States)

    Pan, Xinxin; Chen, Biqiang; Wang, Juan; Zhang, Xinzhi; Zhul, Biyun; Tan, Tianwei

    2012-09-01

    A method of synthesizing the phytosterol esters from oleic acid and sterols was studied, using immobilized lipase Candida sp. 99-125 as catalyst. Molar ratio (oleic acid/phytosterols), temperature, reaction period, organic solvents, catalyst, and silica-gel drier were optimized, and the result showed that 93.4% of the sterols had been esterified under the optimal synthetic condition: the molar ratio of oleic acid/phytosterol is 1:1 in 10 mL iso-octane, immobilized lipase (w, 140% of the sterols), incubated in an orbital shaker (200 rpm) at a temperature of 45 °C for 24 h. The immobilized lipase could be reused for at least 13 times with limited loss of esterification activity. The conversion still maintained up to 86.6%. Hence, this developed process for synthesizing phytosterol esters could be considered as simple and low-energy consumption compared to existing chemical processes.

  14. Difference-Equation-Based Digital Frequency Synthesizer

    Directory of Open Access Journals (Sweden)

    Lu-Ting Ko

    2012-01-01

    Full Text Available This paper presents a novel algorithm and architecture for digital frequency synthesis (DFS. It is based on a simple difference equation. Simulation results show that the proposed DFS algorithm is preferable to the conventional phase-locked-loop frequency synthesizer and the direct digital frequency synthesizer in terms of the spurious-free dynamic range (SFDR and the peak-signal-to-noise ratio (PSNR. Specifically, the results of SFDR and PSNR are more than 186.91 dBc and 127.74 dB, respectively. Moreover, an efficient DFS architecture for VLSI implementation is also proposed, which has the advantage of saving hardware cost and power consumption.

  15. Syntheses and studies of organosilicon compounds

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Ren [Iowa State Univ., Ames, IA (United States)

    1999-02-12

    The syntheses of polycarbosilanes and polysilanes as silicon carbide ceramic precursors have been active research areas in the Barton Research Group. In this thesis, the work is focused on the preparation of polycarbosilanes and polysilanes as stoichiometric silicon carbide precursor polymers. The syntheses of the precursor polymers are discussed and the conversions of these precursors to silicon carbide via pyrolysis are reported. The XRD pattern and elemental analyses of the resulting silicon carbide ceramics are presented. Silicon monoxide is an important intermediate in the production of silicon metal. The existence of silicon monoxide in gap phase has been widely accepted. In the second part of this thesis, the generation of gaseous silicon monoxide in four different reactors and the reactions of gaseous silicon monoxide towards organic compounds are discussed.

  16. Biological activities of synthesized silver nanoparticles from ...

    Indian Academy of Sciences (India)

    ical scavenging activity was measured by the salicylic acid method [16]. The synthesized AgNPs solution at different concentrations (10 to 80 μg ml. −1. ) was dissolved in 1 ml of distilled water. One millilitre of AgNPs mixed with 1 ml of. 9 mM salicylic acid, 1 ml of 9 mM ferrous sulphate and 1ml of 9 mM hydrogen peroxide.

  17. Spurious in PLL-DDS frequency synthesizers

    Czech Academy of Sciences Publication Activity Database

    Kroupa, Věnceslav František; Štursa, Jarmil

    2002-01-01

    Roč. 2, č. 1 (2002), s. 48-51 ISSN 1335-8243. [Digital Signal Processing and Multimedia Communications DSP-MCOM 2001 /5./. Košice, 27.11.2001-29.11.2001] R&D Projects: GA ČR GA102/00/0958 Institutional research plan: CEZ:AV0Z2067918 Keywords : frequency synthesizers * phase locked loops * direct digital synthesis Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  18. Total syntheses of (-)-haemanthidine, (+)-pretazettine, and (+)-tazettine.

    Science.gov (United States)

    Baldwin, S W; Debenham, J S

    2000-01-27

    [structures: see text] The total syntheses of the amaryllidaceae alkaloids haemanthidine, pretazettine, and tazettine as optically pure enantiomers are reported. Using D-mannose as the starting material, the critical relative stereochemical relationships are established with an intramolecular nitrone-alkene cycloaddition reaction. The synthetic route leads successively to (-)-haemanthidine and then to (+)-pretazettine and (+)-tazettine, taking advantage of the well-established complex relationships among these three alkaloids.

  19. Magnesioferrite synthesized from magnesian-magnetites

    Directory of Open Access Journals (Sweden)

    Marcelo Hidemassa Anami

    2014-02-01

    Full Text Available Magnesioferrite is an important mineral due to its use in different scientific fields and by the fact that the soil through the action of weathering, can be a source of nutrients essential for plant development by the fact that in the soil. Its use in pure form or associated with other minerals is only possible through the synthesis in laboratory conditions. This study aimed to synthesize magnesioferrite and hematite from magnesian-magnetite by a co-precipitation procedure. The methodology used is an adaptation of the method of synthesis of pure magnetite, partially replacing the soluble salts of iron with soluble magnesium salts in the proportion of 30.0 mol% of Fe for Mg. The characterization of the synthetic minerals used x-rays diffraction, total chemical analysis and mass specific magnetic susceptibility. The results showed that besides the magnesian-magnetite an unprecedented muskoxita was synthesized, which upon annealing was converted to magnesioferrite and hematite and in the proportion of 93.1% and 6.9% respectively. The isomorphous substitution of Fe for Mg enhanced the thermal stability of the ferrimagnetic mineral synthesized.

  20. A clinical study evaluating success of 2 commercially available preveneered primary molar stainless steel crowns.

    Science.gov (United States)

    Leith, Rona; O'Connell, Anne C

    2011-01-01

    To evaluate the success of posterior NuSmile(®) and Kinder™Krown and to determine the level of parental satisfaction with this treatment option. Forty-eight crowns were placed in 18 children with a mean age of 5 years. A split mouth design was used. Each participant randomly received each crown type on 2 or 4 pair matched molars. Two trained operators completed all treatments. Two additional trained and calibrated clinicians blindly re-evaluated crowns according to specified variables. A visual analogue scale was used to determine parental satisfaction. Examiner reliability was determined by Cohen's kappa scores and results were analysed statistically using Fisher's exact test. All crowns were retained after 12 months with no statistical difference in the clinical and radiographic success of posterior NuSmile(®) and Kinder™Krowns. Overall success was high with 81% of facings intact and 83% free of gingival inflammation after 12 months. Radiographically, 81% were successful. Veneer facing wear was significantly more likely to occur with opposing crowns (P=.02). Parental satisfaction was excellent with a mean score of 9.3 out of 10. These crowns combine the durability of conventional stainless steel crowns with improved esthetics and are proposed as a suitable alternative where esthetic demand is increased.

  1. A retrospective analysis of 102 zirconia single crowns with knife-edge margins.

    Science.gov (United States)

    Poggio, Carlo E; Dosoli, Riccardo; Ercoli, Carlo

    2012-05-01

    Clinical reports of feldspathic porcelain veneered-zirconia crowns placed on teeth with knife-edge marginal finish lines have recently been presented but with data available for only a limited number of crowns in the anterior maxilla. This retrospective study evaluated the clinical success and survival of feldspathic porcelain veneered-zirconia crowns fabricated with knife-edge margins in a private practice. One hundred and two teeth (51 anterior, 51 posterior) were prepared with knife-edge margins and restored with feldspathic porcelain veneered-zirconia crowns. The modified California Dental Association (CDA) criteria were used to clinically evaluate subjects recalled between May and December 2010. Data were analyzed with descriptive statistics. The mean follow-up time was 20.9 months (SD, 13.6; range, 10-72). One tooth had to be extracted because of an endodontic problem not related with the restoration, 2 crowns had minor chipping of the veneering porcelain, while no crowns exhibited fracture of the zirconia core. In this retrospective evaluation, feldspathic porcelain veneered-zirconia crowns with knife-edge margins provided clinical performance similar to that reported with other margin designs. Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

  2. 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.

  3. 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)

  4. Microleakage of composite resin and amalgam core material under complete cast crowns.

    Science.gov (United States)

    Larson, T D; Jensen, J R

    1980-07-01

    Ninety extracted human teeth were used to compare the microleakage of composite resin over, amalgam core, and regular crown preparations under a complete cast gold crown cemented with zinc phosphate cement as determined by 2% fluorescein dye solution. Specimens were compared with and without aging after cementation in a thermal bath by cycling some of them between 4 degrees C and 60 degrees C in a 2% fluorescein dye bath and others in a similar bath held at 37 degrees C. Fluorescein dye (under ultraviolet light) demonstrated microleakage of the specimens between the crown-tooth interface and the core-tooth interface. There were no significant differences in the microleakage due to aging. The specimens held at 37 degrees C in the fluorescein dye bath showed no significant differences between the core preparations and the regular crown preparations. However, when specimens were thermally cycled between 4 degrees C and 60 degrees C, there were significant differences. With thermal cycling, the regular crown preparations were better able to resist microleakage at the crown-tooth interface than either the composite resin core or the amalgam core preparations. The results of this investigation seem to indicate a need for further evaluation of core build-ups under cemented complete gold crowns.

  5. A comparison of marginal fit between press-fabricated and CAD/CAM lithium disilicate crowns.

    Science.gov (United States)

    Carlile, Richard S; Owens, Wade H; Greenwood, William J; Guevara, Peter H

    2018-01-01

    The purpose of this study was to compare the marginal fit of press-fabricated lithium disilicate crowns with that of computer-aided design/computer-aided manufacturing (CAD/CAM) lithium disilicate crowns to determine if the fabrication method has an influence on marginal fit. The marginal fit of 25 pressed and 25 CAD/CAM crowns was measured using the replica technique. The sites measured were the mesial, distal, facial, and lingual margins. A microscope at 10× magnification was used to obtain the measurements. Each site was measured 4 times, and intraclass correlation coefficients were used to assess measurement errors. An unpaired t test was used to evaluate the differences between the 2 groups. Mean marginal gap measurements were greater for CAD/CAM crowns than for pressed crowns at all sites. Only the difference in mean gap at the facial margin was statistically significant (P < 0.001). Press-fabricated lithium disilicate crowns provided a better marginal fit than those fabricated by CAD/CAM, but both fabrication methods provided crowns with a clinically acceptable marginal fit.

  6. The general properties of water - nitrobenzene - crown - bis-1,2-dicarbollylcobaltate extraction systems

    International Nuclear Information System (INIS)

    Vanura, P.

    2003-01-01

    The extraction and stability constants in the system water - nitrobenzene have been collected and general rules valid for water - nitrobenzene - crown - bis-1,2-dicarbollylcobaltate extraction system have been found. The main principles are size compatibility of ion diameter and crown cavity diameters, the flexibility of crown, the basicity of crown and the steric factor of both the ligand and the extracted ion. The extraction in the system water - mineral acid or salt polyoxyethylene compound - bis-1,2-dicarbollylcobaltate - nitrobenzene is more complicated than can be expected from usually used ion diameter - crown cavity diameter compatibility principle. The other important factors are the basicity and the deformability of crown, steric aspect and the angles of bonds of extracted ion. The binuclear 'sandwich' complexes with H + ion and Sr 2+ or Ba 2+ ions have been proved for dibenzo-18-crown-6 (DB18C6). On the other hand, only SrL 2 and BaL 2 (L = 15C5) complexes are formed in nitrobenzene saturated with water. The addition of polyoxyethylene compound usually increases the distribution ratio of alkali earth metal ions and the selectivity of its mutual separation. (authors)

  7. 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.

  8. 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.

  9. Early complications and short-term failures of zirconia single crowns and partial fixed dental prostheses.

    Science.gov (United States)

    Pihlaja, Juha; Näpänkangas, Ritva; Raustia, Aune

    2014-10-01

    Ceramic single crowns fabricated from newer materials, especially zirconia, have shown relatively high survival rates. However, early reversible complications may increase the risk of an irreversible failure later. The purpose of the study was to evaluate the early complications and short-term failures of zirconia single crowns and partial fixed dental prostheses (FDPs) made by predoctoral dental students. Data were collected from the patient records. Altogether, 264 zirconia single crowns and 120 FDPs (342 abutments and 190 pontics) were fabricated for 173 patients between 2007 and 2010. Early complications were recorded during the prosthetic treatment phase, and short-term failures were recorded during the first year in use. The most frequent early complications were localized gingival irritation (1.9% of single crowns and 2.5% of FDP) and postoperative tooth sensitivity (0.4% of single crowns and 3.3% of FDPs). Pulp exposure during preparation was recorded in 3 abutment teeth of the FDPs. The most frequent short-term failure was chipping of the veneering porcelain (0.8% for single crowns, 0.8% for FDPs). One crown lost cementation because of poor retention (0.4%), and 2 FDPs failed because of framework fractures (1.7%). The most frequent early complications were localized gingival irritation and postoperative tooth sensitivity, and the most frequent short-term failure was chipping of the veneering porcelain. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  10. Biomechanical three-dimensional finite element analysis of monolithic zirconia crown with different cement type

    Science.gov (United States)

    2015-01-01

    PURPOSE The objective of this study was to evaluate the influence of various cement types on the stress distribution in monolithic zirconia crowns under maximum bite force using the finite element analysis. MATERIALS AND METHODS The models of the prepared #46 crown (deep chamfer margin) were scanned and solid models composed of the monolithic zirconia crown, cement layer, and prepared tooth were produced using the computer-aided design technology and were subsequently translated into 3-dimensional finite element models. Four models were prepared according to different cement types (zinc phosphate, polycarboxylate, glass ionomer, and resin). A load of 700 N was applied vertically on the crowns (8 loading points). Maximum principal stress was determined. RESULTS Zinc phosphate cement had a greater stress concentration in the cement layer, while polycarboxylate cement had a greater stress concentration on the distal surface of the monolithic zirconia crown and abutment tooth. Resin cement and glass ionomer cement showed similar patterns, but resin cement showed a lower stress distribution on the lingual and mesial surface of the cement layer. CONCLUSION The test results indicate that the use of different luting agents that have various elastic moduli has an impact on the stress distribution of the monolithic zirconia crowns, cement layers, and abutment tooth. Resin cement is recommended for the luting agent of the monolithic zirconia crowns. PMID:26816578

  11. Marginal Aaccuracy of Ceromer Crowns and Effect of Relining on the Fitness

    Directory of Open Access Journals (Sweden)

    F. Gerami-Panah

    2004-06-01

    Full Text Available Statement of Problem: Targis restorations provide good esthetic and clinical success;however, improving marginal accuracy requires further investigations.Purpose: The aim of this was to study evaluate the effect of relining on the marginal accuracy of ceromer crowns.Material and Methods: One ivorine maxillary central incisor was prepared for Targis crown. 10 acrylic models were duplicated from ivorine teeth. The specimens were randomly divided in to two groups. In the first group Targis crowns were made according to manufacturer's instructions. In the second group (relined group after construction of Targis crown they were relined by Targis base. All of the specimens were luted with resin cement, embedded in epoxy resin and sectioned buccollingually and mesiodistally.Marginal and internal gap were assessed by image analysis system.Results: The mean marginal opening in labial and lingual margin of Targis crowns were 37.14±6.2 and 35.7±6.2 and in relined group it was 72.1±11 and 56±12μm respectively.Statistical analysis showed significant difference between two groups (P< 0.05.Conclusion: Considering limitations of this study, marginal opening and internal adaptation of the Targis crowns were in acceptable range for clinical application, however relining didn’t improve the fitness of crowns.

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

    Science.gov (United States)

    Cardoso, Mayra; Torres, Marcelo Ferreira; Rego, Mariana Ribeiro de Moraes; Santiago, Luiz Carlos

    2008-01-01

    Marginal discrepancies may lead to cement washout and marginal leakage, damaging periodontal and pulp tissues or causing premature loss of the restoration. This study evaluated the influence of application site of provisional cement on the marginal adaptation of provisional crowns. 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. Mean values of marginal opening obtained for each group were: CAO: 145 microm; CA: 67 microm; CM: 46 microm; TM: 34 microm. CA, CM and TM presented significantly lower marginal openings than CAO (pcrown with provisional cement, including the occlusal surface, provided greater marginal discrepancies when compared to the other methods evaluated.

  13. 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

  14. 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.

  15. [Comparative study of microleakage by using different finished lines in selective laser melting metal crowns].

    Science.gov (United States)

    Peng, Yan; Zhong, Qun; Wu, Xue-Ying; Weng, Jia-Wei

    2016-12-01

    To evaluate microleakage of SLM Co -Cr alloy metal crown with two types finished line (chamfer and shoulder), compared with conventional fabrication of Co -Cr alloy metal crowns. Thirty healthy non-carious human molars were selected and randomly assigned to 3 groups, 10 in each. Teeth in group A and C received a chamfer finish line preparation, whereas teeth in group C received a shoulder finish line. Conventional Co -Cr alloy metal crowns were fabricated for group A when SLM metal crowns were made for group B and group C. Glass ionomer was applied for bonding. After 5000 thermocycles ranging from 5degrees centigrade to 55degrees centigrade,all the specimens were evaluated by dye penetration and then microleakage was examined under light microscope. The data were analyzed statistically with SPSS 20.0 software package. Microleakage in group A was significantly higher than the other two groups, group B and group C showed no significant difference in microleakage while microleakage in group B was higher than that in group C. Microleakage of SLM metal crowns was significantly less than that of conventional Co-Cr alloy metal crowns; chamfer finish line designs was recommended for SLM metal crowns in consideration of reducing microleakage and protecting tooth.

  16. Clinical performance of two different CAD/CAM-fabricated ceramic crowns: 2-Year results.

    Science.gov (United States)

    Seydler, Bodo; Schmitter, Marc

    2015-08-01

    Recently, technical problems, especially chipping, have been reported for ceramic restorations; as a result, ceramic crowns produced entirely by computer-aided design and computer-aided manufacture (CAD/CAM) have become popular because the incidence of chipping is less. The purpose of this study was to report on 2-year results for 2 different types of CAD/CAM ceramic crowns placed in adult patients in a dental practice. Sixty participants who required a crown for a first or second molar were randomly assigned to 1 of 2 groups. Crowns in the veneered zirconia (VZ) group were made of zirconia frameworks veneered with CAD/CAM-produced lithium disilicate ceramic; the other group's crowns were made of monolithic lithium disilicate (MLD) ceramic. Each crown was reviewed after 2 weeks, 1 year, and 2 years by using modified the US Public Health Service (USPHS) criteria. Statistical analysis was performed by using the log-rank test, nonparametric tests, and Kaplan-Meier survival analysis. All 60 participants were recalled after 1 and 2 years. In the VZ group, 2 endodontic complications occurred, and deterioration of periodontal health was observed for 3 participants. In the MLD group, 2 endodontic complications occurred within 2 years. In both of the groups, no caries or marginal discoloration was observed. No technical complications, for example, cracks, chipping, or fractures, were detected after 2 years. The shape and appearance of all crowns were assessed positively by the examining dentist. The log-rank test showed no significant differences in respect to technical or biologic complications (P=.324). For both types of single-crown restoration, no technical failures occurred. The number of biological complications did not differ significantly between the types of crowns. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  17. 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. © 2014 John Wiley & Sons Ltd.

  18. Performance of Monolithic and Veneered Zirconia Crowns After Endodontic Treatment and Different Repair Strategies.

    Science.gov (United States)

    Scioscia, A; Helfers, A; Soliman, S; Krastl, G; Zitzmann, N U

    To investigate failure loads of monolithic and veneered all-ceramic crowns after root canal treatment and to analyze marginal integrity of repair fillings. Seventy-two human molars were restored with monolithic (Zr-All) or veneered (Zr-Ven) zirconia crowns. Molars were assigned to six groups (n=12 per group) depending on restoration material, access type (no access cavity [control] or endodontic treatment [test]), and type of filling (one-step [1-st] or two-step [2-st]). For type of filling, molars were treated using a self-etch universal adhesive and cavities were either filled with layered composite (1-st) or filled until the crown material was reached, which was additionally conditioned and then filled (2-st). Scanning electron microscopic analysis of the restoration margins was performed before and after thermomechanical loading (TML), and the percentage of continuous margins was assessed. Crowns were then loaded to failure. Preparation of the access cavity required more time in monolithic (445 s) than in veneered crowns (342 s). Loads to failure were higher in control groups (Zr-All: 5814 N; Zr-Ven: 2133 N) and higher in monolithic test (2985 N) than in veneered test crowns (889 N). In monolithic crowns, 1-st had lower fracture loads than 2-st fillings (2149 N vs 3821 N). Continuous margins of 66% to 71% were achieved, which deteriorated after TML by 39% to 40% in Zr-All, by 34% in Zr-Ven-1-st, and by 24% in Zr-Ven-2-st. Endodontic access and adhesive restorations resulted in reduced fracture load in monolithic and veneered zirconia crowns. Two-step fillings provided higher fracture loads in Zr-All and better marginal quality in Zr-Ven crowns.

  19. 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.

  20. Chair-side generated posterior monolithic lithium disilicate crowns: clinical survival after 6 years.

    Science.gov (United States)

    Rauch, Angelika; Reich, Sven; Schierz, Oliver

    2017-07-01

    The objective of this prospective clinical study was to evaluate the clinical performance of chair-side generated monolithic lithium disilicate crowns after 72 months. Forty-one posterior full contour crowns made of lithium disilicate ceramic were inserted in 34 patients with a chair-side CAD/CAM technique. One crown per patient was randomly selected for evaluation at baseline, 6, 12, 24, 36, 48, 60 and 72 months according to the modified US Public Health Service criteria. After a mean examination time of 73.2 months (SD ± 1.7 months), 25 crowns were available for re-examination. Within the observation period, three failures occurred due to one crown fracture after 2.9 years, an abutment fracture after 6.0 years, and one severe endodontic problem after 6.1 years. One lithium disilicate crown showed a loss of retention after 2 years but could be reinserted. There were two events of caries below the crown margin, one after 24 and another one after 48 months. Both teeth received cervical adhesive composite fillings. Two abutment teeth changed their sensibility perception from positive to negative within the first 13 months. The failure-free rate was 87.6%, and the complication-free rate was 70.1% after 6 years according to the Kaplan-Meier analysis. Due to the fact that there was only one severe technical complication and the severe biological complications were in a normal range, the clinical performance of monolithic lithium disilicate crowns in the posterior region was completely satisfying. The chair-side application of monolithic lithium disilicate crowns can be recommended.

  1. Cementing an Implant Crown: A Novel Measurement System Using Computational Fluid Dynamics Approach.

    Science.gov (United States)

    Wadhwani, Chandur; Goodwin, Sabine; Chung, Kwok-Hung

    2016-02-01

    Cementing restorations to implants is a widely used clinical procedure. Little is known about the dynamics of this process. Using a systems approach and advanced computing software modeling this can be investigated virtually. These models require validation against real-life models. The study aims to consider the system effect of a crown, abutment, and cement flow under different conditions and comparing real physical models to virtual computer simulations. A physical model of implant abutments and crowns provided three groups according to abutment screw access modification (n = 9): open (OA), closed (CA), and internal vented (IVA) abutment groups. Crowns were cemented using standardized amounts and site application. Proportion of cement retained within the crown-abutment system was recorded and compared. Differences among groups were identified using analysis of variance (ANOVA) with Tukey's post hoc test (α ≤ 0.05). Three-dimensional multiphysics numerical stimulation software (STAR-CCM+, CD-adapco) with computational fluid dynamics (CFD) approach was applied to a virtual model system of a scanned abutment and crown system. Three-dimensional real-time model simulations of cement and air displacement were produced, evaluating cement application site, speed of crown seating, and abutment modifications. Statistically significant differences in cement retained within the system (p  OA > OCA abutment groups. The CFD virtual simulations followed this trend. Site application and speed of seating also affected cement extrusion and cement marginal infill. Fast crown seating and occlusal cement site application produced air incorporation at the margins. The CFD approach provides a convenient way to evaluate crown-cement-implant abutment systems with respect to cement flow. Preliminary evaluation indicates that the results achieved follow those of a physical actual cement-retained crown-implant abutment study. © 2014 Wiley Periodicals, Inc.

  2. 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.

  3. Retention of CAD/CAM resin composite crowns following different bonding protocols.

    Science.gov (United States)

    Nejat, Amir H; Lee, Jinwhan; Shah, Shreya; Lin, Chee Paul; Kulkarni, Prajakta; Chavali, Ramakiran; Lawson, Nathaniel C

    2018-04-01

    To evaluate the effect of different surface treatments and primers with a CAD/CAM resin composite block on its crown retention. 120 human molars were prepared with a 24° total convergence angle, 1.5 mm height, and axial walls in dentin. Surface area was measured by digital microscopy. Crowns were machined from CAD/CAM resin composite blocks. Teeth were randomly allocated to 12 groups (n= 10) based on possible combinations of three surface treatments: [Control, Alumina air abrasion (50-µm Al₂O₃ at 0.28 MPa) ]; 5% hydrofluoric acid etch (20-second scrub); silane application (with or without Kerr Silane primer); and adhesive application (with or without Optibond XTR Adhesive). Optibond XTR Adhesive was applied to the tooth preparations and crowns were bonded with MaxCem Elite cement. Crowns were fatigued for 100,000 cycles at 100 N in water and debonded in tension (1 mm/minute). Crown retention strength (maximum load/surface area) values were analyzed using a three-way ANOVA with Tukey's post-hoc tests (α= 0.05). Surface treatment, silane and adhesive applications independently affect retention force (P 0.05). Alumina airborne abrasion surface treatment, silane and adhesive applications all improve retention strength. Therefore, CAD/CAM resin composite crowns can withstand debonding while undergoing mechanical fatigue. Although all forms of surface treatment and primer application improve bond strength, the highest mean retention strength values were recorded when the crowns were alumina particle abraded and coated with adhesive (with or without silane). In order to improve the bonding of resin composite crowns, application of alumina airborne particle abrasion and a coat of adhesive (proceeded by an optional coat of silane) is recommended. If hydrofluoric acid is utilized, the crowns should be treated with a coat of silane followed by adhesive application. Copyright©American Journal of Dentistry.

  4. 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).

  5. Reliability of Reduced-thickness and Thinly Veneered Lithium Disilicate Crowns

    OpenAIRE

    Silva, N.R.F.A.; Bonfante, E.A.; Martins, L.M.; Valverde, G.B.; Thompson, V.P.; Ferencz, J.L.; Coelho, P.G.

    2012-01-01

    The present investigation hypothesized that the reliability of reduced-thickness monolithic lithium disilicate crowns is high relative to that of veneered zirconia (Y-TZP) and comparable with that of metal ceramic (MCR) systems. CAD/CAM first mandibular molar full-crown preparations were produced with uniform thicknesses of either 1.0-mm or 2.0-mm occlusal and axial reduction, then replicated in composite for standard crown dies. Monolithic 1.0-mm (MON) and 2.0-mm CAD/CAM lithium disilicate c...

  6. Distribution and prevalence of crown rot pathogens affecting wheat crops in southern Chile

    OpenAIRE

    Ernesto Moya-Elizondo; Nolberto Arismendi; María Paz Castro; Herman Doussoulin

    2015-01-01

    Crown rot pathogens are associated with higher losses for wheat crop farmers, but information about the distribution and prevalence of these pathogens in Chile is inadequate. Distribution and prevalence of wheat (Triticum aestivum L.) crown rot pathogens were examined in a survey of 48 commercial fields from December 2011 to February 2012 in southern Chile. These fields were located between Collipulli (37°56'00" S; 72°26'39" W) and Purranque (40°50'30" S; 73°22'03" W). Severity of crown rot d...

  7. Effect of surface topography of implant abutments on retention of cemented single-tooth crowns.

    Science.gov (United States)

    de Campos, Tomie Nakakuki; Adachi, Lena Katekawa; Miashiro, Karen; Yoshida, Hideki; Shinkai, Rosemary Sadami; Neto, Pedro Tortamano; Frigerio, Maria Luiza Moreira Arantes

    2010-08-01

    This study investigated whether surface topography affects the retentive strength of cemented full crowns, comparing the effects of standard machined, sandblasted, and grooved implant abutments. Five metallic crowns per abutment type were cast and cemented with zinc phosphate. After 24 hours, the specimens were submitted to a tensile test. The retentive strength of the cemented crowns was affected by abutment surface topography. The sandblasted and grooved surface groups had approximately 2.4 times greater mean uniaxial retentive strength than the machined surface group (P < .001). The retentive strength of the sandblasted and grooved abutments was similar, despite marked differences in surface profiles and roughness parameters.

  8. Possible applications of crown-ethers to metal extraction using liquid membrane technology - a literature survey

    International Nuclear Information System (INIS)

    Dozol, M.

    1990-01-01

    Ether-crowns, discovered in 1967 by J.C. PEDERSEN, exhibit attractive complexive and extractive properties, enhanced in various fields, such as analytical chemistry, chemical synthesis, field of biology, or extractive chemistry. The investigations carried out on these macrocyclic compounds are continually increasing, as show in international literature. Among the focus of interest, the applications to metal extraction are extensively studied with crown compounds present in liquid phase or impregnated on supports (membranes or resins). The goal of this paper is to describe the application of crown-ethers to metal extraction, using liquid membrane processes. 69 refs

  9. Effect of a fluoride varnish on the margin leakage and retention of luted provisional crowns.

    Science.gov (United States)

    Lewinstein, Israel; Fuhrer, Nitzan; Ganor, Yehuda

    2003-01-01

    Provisional crowns cemented with provisional luting agents are susceptible to washout, margin leakage, and secondary caries when placed for a prolonged period. This study was conducted to determine the effect of combining a varnish containing 2.26% NaF with 2 provisional luting agents on the margin leakage and retention of provisional crowns. Acrylic resin provisional crowns were fabricated for 8 shoulder-prepared molars. The eight provisional (N=24) crowns were luted individually with Temp-Bond (TB), Freegenol (FG), or Duraphat (DU). Specimens were thermocycled 500 times (5 degrees and 60 degrees C) with a 1-minute dwell time, stored in 100% relative humidity at 37 degrees C for 6 days, and then immersed in a 0.5% Gentian violet solution for 24 hours. Seven days after cementation, a removal test of the crowns (shear retention test) was conducted with a universal testing machine at a crosshead speed of 5 mm/min. Retention was determined as the maximum recorded force needed for crown dislodgment. DU varnish was applied to the inner surface of the dislodged crowns with no removal of the cement layer TB, FG (N=16). The crowns were relined with a 0.5-mm layer of acrylic resin and luted with a combination of luting agent and DU (TB, FG) N=16. No luting agent (NC) served as the control (N=8). Results were analyzed with the Wilcoxon matched-pairs signed-ranks test. Leakage at the margins was assessed with a 4-level dye penetration scale, and statistical differences were identified with a chi(2) test. All hypothesis testing was conducted at the 95% level of confidence. The mean 7-day retention forces were as follows: 44.5 N (Temp-Bond), 51.6 N (Freegenol), and 35.9 N (Duraphat). There were no significant differences among these values. Duraphat combined with Freegenol decreased the retention of provisional crowns, but Duraphat combined with Temp-Bond increased the retention of provisional crowns by 69-145%. Duraphat alone and in combination with both provisional luting

  10. Esthetic and endodontic management of a deep crown-root fracture of a maxillary central incisor.

    Science.gov (United States)

    Tsurumachi, Tamotsu; Matsumoto, Sakurako; Kobayashi, Yoshimi; Ohara, Kinuyo; Suzuki, Yusuke; Ogiso, Bunnai

    2012-01-01

    Treatment of trauma to anterior teeth should aim at preserving the affected teeth so as to restore function and esthetic appearance. Recently, patients have come to expect adequate esthetics immediately after trauma. In the present case, a deep crown-root fracture compromised the pulp and extended subgingivally on the palatal aspect. After using the fractured fragment as a provisional crown, the patient received conventional root canal treatment, which provided immediately satisfactory esthetic results and reliable short-term restoration of the crown-root fractured tooth. Rehabilitation of the fractured central incisor was performed with a post-core-supported prosthetic restoration.

  11. [Three-dimensional data fusion method for tooth crown and root based on curvature continuity algorithm].

    Science.gov (United States)

    Zhao, Y J; Liu, Y; Sun, Y C; Wang, Y

    2017-08-18

    To explore a three-dimensional (3D) data fusion and integration method of optical scanning tooth crowns and cone beam CT (CBCT) reconstructing tooth roots for their natural transition in the 3D profile. One mild dental crowding case was chosen from orthodontics clinics with full denture. The CBCT data were acquired to reconstruct the dental model with tooth roots by Mimics 17.0 medical imaging software, and the optical impression was taken to obtain the dentition model with high precision physiological contour of crowns by Smart Optics dental scanner. The two models were doing 3D registration based on their common part of the crowns' shape in Geomagic Studio 2012 reverse engineering software. The model coordinate system was established by defining the occlusal plane. crown-gingiva boundary was extracted from optical scanning model manually, then crown-root boundary was generated by offsetting and projecting crown-gingiva boundary to the root model. After trimming the crown and root models, the 3D fusion model with physiological contour crown and nature root was formed by curvature continuity filling algorithm finally. In the study, 10 patients with dentition mild crowded from the oral clinics were followed up with this method to obtain 3D crown and root fusion models, and 10 high qualification doctors were invited to do subjective evaluation of these fusion models. This study based on commercial software platform, preliminarily realized the 3D data fusion and integration method of optical scanning tooth crowns and CBCT tooth roots with a curvature continuous shape transition. The 10 patients' 3D crown and root fusion models were constructed successfully by the method, and the average score of the doctors' subjective evaluation for these 10 models was 8.6 points (0-10 points). which meant that all the fusion models could basically meet the need of the oral clinics, and also showed the method in our study was feasible and efficient in orthodontics study and clinics

  12. Evaluation of various Crown ethers for the supercritical fluid extraction of uranium from nitric acid medium

    International Nuclear Information System (INIS)

    Kumar, Pradeep; Rao, Ankita; Ramakumar, K.L.

    2009-01-01

    Various crowns have been evaluated for supercritical fluid extraction of uranium from nitric acid medium employing HPFOA as counter ion. Uranium extraction efficiency was found to be influenced by cavity size of crown ether and nature of substituents. Complexation tendency of UO 2 2+ increases with increasing cavity size of crown ether. Electron withdrawing substituents decreased the extraction efficiency which could be attributed to decrease in the basicity of four oxygen atoms and hence their bonding ability. Whereas electron donating substituents increased the efficiency due to increases in basicity of oxygen atoms and hence in increase in bonding ability. (author)

  13. Long-term survival of repaired amalgams, recemented crowns and gold castings.

    Science.gov (United States)

    Smales, Roger J; Hawthorne, Warwick S

    2004-01-01

    This retrospective longitudinal study compared the long-term survival rate of repaired versus replaced amalgam restorations and recemented crowns and gold castings versus non-recemented similar restorations. Private general dental practitioners treated adult subjects at three city practices. No significant survival differences were found between the repaired and replaced amalgams at five years, although the repaired amalgams showed higher failure rates by 10 years (p=0.37). However, there were significantly higher failures by five years for recemented crowns (pamalgams had survival rates of approximately 37 +/- 15 (SEr) percent, recemented crowns 28 +/- 15 (SEr) percent and recemented gold castings 42 +/- 17 (SEr) percent.

  14. [Repair and revision 4. Cracked tooth and crown fractures: diagnostics and treatment].

    Science.gov (United States)

    Willemsen, W L; van der Meer, W J

    2001-05-01

    Trauma to the teeth can result in the formation of cracks in the crown or root of the tooth. The location and the extent of these cracks determine the proper treatment choice. This treatment is oriented towards saving pulp vitality and/or tooth integrity. In this paper the diagnosis of these cracks is described as well as the desired treatment. These are discussed relative to the location of the cracks, namely in the clinical crown of the tooth, resulting in enamel infraction, cracked tooth and crown fractures, and in the root of the tooth, resulting in a vertical or horizontal root fracture.

  15. Crown Prince Frederick of Prussia: Suez and syphilis. Un canard dévoilé.

    Science.gov (United States)

    Laurenson, R D

    1995-06-01

    Frederick III (Crown Prince of Prussia, and Emperor of Germany) died of cancer of the larynx in 1888. In Drame Imperial (1888) journalist Jean de Bonnefon asserted that the disease was not cancer but syphilis which the Crown Prince acquired in 1869 in Suez. What de Bonnefon wrote about the prince does not coincide with the prince's itinerary published in the London Times. This discrepancy is examined and the reason for de Bonefon's claim is considered. The report that Crown Prince Frederick of Prussia caught syphilis in Suez is a canard.

  16. 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; Nothdurft, 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.

  17. 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 ...

  18. Management of complicated crown-root fracture in central incisors using intentional replantation with 180° rotation: A case report

    Directory of Open Access Journals (Sweden)

    Reyhaneh Faghihian

    2017-01-01

    Full Text Available Introduction: Complicated crown-root fractures are rare and their treatment is complex. Numerous methods such as crown lengthening and orthodontic or surgical extrusion have been described for the treatment of crown-root fracture. The aim of this study was to report managing complicated crown-root fracture using intentional replantation with 180° rotation. Case report: This case report demonstrates successful management of complicated crown-root fracture in central incisor of a 10-year-old boy using intentional replantation with 180° rotation. Discussion: At 18-month follow-up, the replanted tooth revealed normal function with no obvious resorption.

  19. Marginal adaptation of ceramic crowns: a systematic review.

    Science.gov (United States)

    Contrepois, Mathieu; Soenen, Arnaud; Bartala, Michel; Laviole, Odile

    2013-12-01

    After the development of a variety of ceramic restorative systems over the past 20 years, the fabrication of fixed dental prostheses has undergone considerable change. Esthetics and resistance to fracture are two of the main determinants of the success of a restoration; the third is marginal adaptation. Therefore, a systematic review of the literature dedicated to the marginal accuracy of ceramic systems is indicated. This study reviewed the current scientific literature that pertains to the marginal fit of ceramic crowns fabricated with different systems and investigated the factors that influence marginal adaptation. An electronic search was completed by using the PubMed and Scopus databases with the following combination of key words: (discrepancy or fit or gaps or adaptation) and (disilicate or ceramic) and (copings or crowns). The search was limited to English-language peer-reviewed articles published before April 15, 2012. Titles and abstracts were read to identify articles that fulfilled the inclusion criteria designed for this review. Of 469 studies identified, 54 satisfied the selection criteria and were included in this review. All were published between 1994 and 2012. A total of 17 ceramic systems were tested in 48 in vitro and 6 in vivo studies. Of all the marginal gaps measured, 94.9% were in the range of clinical acceptability. Study heterogeneity made it impossible to conduct a proper meta-analysis of research findings and to compare and rank the various systems in terms of marginal fit. Four parameters were found to influence marginal adaptation: finish line configuration, value of the predefined cementing space, veneering process, and cementation. The systems evaluated in the selected articles generally provide a clinically acceptable marginal fit. The current state of research does not allow for a proper comparison of the various systems in terms of marginal fit. The use of computer x-ray microtomography is recommended for further research on

  20. Survival of ceramic computer-aided design/manufacturing crowns bonded to preparations with reduced macroretention geometry.

    Science.gov (United States)

    Bindl, Andreas; Richter, Björn; Mörmann, Werner H

    2005-01-01

    Adhesive cementation reduces the need for macroretentive preparation for crowns. This study investigated the survival and clinical rating of monolithic computer-aided design/manufacturing (CAD/CAM) ceramic crowns bonded to preparations with reduced macroretention, hypothesizing that adhesion would compensate for reduced retention geometry. Two-hundred eight posterior CAD/CAM-generated crowns from feldspar block ceramic were adhesively bonded in 136 patients in three preparation groups: classic (100% stump height, n = 70); reduced (reduced stump height or irregular stump, n = 52); and endo (absent stump but pulp chamber retention cavity, n = 86). Crowns were examined at baseline and after 55 +/- 15 months using modified USPHS criteria. Plaque and bleeding of gingiva around the crowns were assessed. Cumulative Kaplan-Meier survival of crowns on premolars/molars was: classic = 97.0%/94.6%; reduced = 92.9%/92.1%; and endo = 68.8%/87.1%, confirming the hypothesis for classic, reduced, and endo molars as well as for classic and reduced premolars. A significant difference was found between classic and endo premolar crowns, rejecting the hypothesis for endo preparation on premolars. Plaque and bleeding indices were significantly lower for crowned teeth than for controls. The survival of classic and reduced crowns was rated adequate for premolars and molars. Endo preparation appeared acceptable for molar crowns but inadequate for premolar crowns.

  1. Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling.

    Science.gov (United States)

    Syrek, Andreas; Reich, Gunnar; Ranftl, Dieter; Klein, Christoph; Cerny, Barbara; Brodesser, Jutta

    2010-07-01

    The aim of the present study was to compare the fit of all-ceramic crowns fabricated from intraoral digital impressions with the fit of all-ceramic crowns fabricated from silicone impressions. Twenty patients agreed to take part in the study to receive two Lava crowns each for the same preparation. One crown was fabricated from intraoral scans using the Lava Chairside Oral Scanner (Lava C.O.S.), and the other crown from a two-step silicone impression. Prior to cementation the fit of both crowns was clinically evaluated by two calibrated and blinded examiners; the marginal fit was also scored from replicas. Data from the replica scores were analysed by Anderson-Darling test, Levene's test and Mann-Whitney test. All tests were performed with alpha-level of 0.05. Median marginal gap in the conventional impression group was 71microm (Q1:45microm; Q3:98microm), and in the digital impression group 49microm (Q1:32microm; Q3:65microm). Mann-Whitney test revealed a significant difference between the groups (pdigitally fabricated crowns. 1. Crowns from intraoral scans revealed significantly better marginal fit than crowns from silicone impressions. 2. Marginal discrepancies in both groups were within the limits of clinical acceptability. 3. Crowns from intraoral scans tended to show better interproximal contact area quality. 4. Crowns from both groups performed equally well with regard to occlusion. Copyright 2010 Elsevier Ltd. All rights reserved.

  2. Biocompatibility of poly allylamine synthesized by plasma

    International Nuclear Information System (INIS)

    Colin, E.; Enriquez, M.A.; Olayo, M.G.; Cruz, G.J.; Morales, J.; Olayo, R.

    2007-01-01

    A study of the electric and hydrophilic properties of poly allylamine (PAI) synthesized by plasma whose structure contains N-H, C-H, C-O and O-H bonds is presented, that promote the biocompatibility with the human body. To study the PAI hydrolytic affinity, solutions of salt concentration similar to those of the human body were used. The results indicate that the solutions modify the charge balance in the surfaces reducing the hydrophobicity in the poly allylamine whose contact angle oscillates among 10 and 16 degrees and the liquid-solid surface tension between 4 and 8 dina/cm. (Author)

  3. Syntheses and electronic structures of decamethylmanganocenes

    International Nuclear Information System (INIS)

    Robbins, J.L.; Edelstein, N.M.; Cooper, S.R.; Smart, J.C.

    1979-01-01

    The syntheses of [(C 5 (CH 3 ) 5 ) 2 Mn]PF 6 , (C 5 (CH 3 ) 5 ) 2 Mn, and Na[(C 5 (CH 3 ) 5 ) 2 Mn] are described. Magnetic susceptibility, infrared, electrochemical, NMR, and reactivity studies suggest the formulation of these complexes as low-spin 16-, 17-, and 18-electron planar metallocenes. EPR spectra of the neutral complex are consistent with the 2 E/sub 2g/ configuration determined for other low-spin 17-electron metallocenes. 1 figure, 3 tables

  4. CNN based texture synthesize with Semantic segment

    OpenAIRE

    Liang, Xianye; Zhuo, Bocheng; Li, Peijie; He, Liangju

    2016-01-01

    Deep learning algorithm display powerful ability in Computer Vision area, in recent year, the CNN has been applied to solve problems in the subarea of Image-generating, which has been widely applied in areas such as photo editing, image design, computer animation, real-time rendering for large scale of scenes and for visual effects in movies. However in the texture synthesize procedure. The state-of-art CNN can not capture the spatial location of texture in image, lead to significant distorti...

  5. Fracture resistance of metal- and galvano-ceramic crowns cemented with different luting cements: in vitro comparative study.

    Science.gov (United States)

    Ghazy, Mohamed H; Madina, Manal M Abo

    2006-01-01

    This study aimed to compare the fracture resistance of galvano-ceramic crowns with metal-ceramic crowns cemented to natural premolar teeth with different luting cements. Sixty intact maxillary premolars were prepared to receive full-coverage crown restorations and were divided into 2 equal groups (n = 30): galvano-ceramic crowns and metal-ceramic crowns. Each group was further subdivided into 3 equal subgroups (n = 10) according to the luting cement used: zinc-phosphate, glass-ionomer, or adhesive-resin cement. The specimens were then compressively loaded until failure in a universal testing machine. The metal-ceramic crowns exhibited higher resistance to fracture compared to galvano-ceramic crowns, but both exceeded the normal documented values of occlusal masticatory forces.

  6. 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)

  7. Effect of bioagents and resistance inducers on grapevine crown gall

    Directory of Open Access Journals (Sweden)

    E. Biondi

    2010-01-01

    Full Text Available Bioagents and chemicals were applied to one-year old grafted vines (Ancelotta/420A in glasshouse and field experiments set up at the Vivai Cooperativi Rauscedo (VCR, Pordenone, Italy. In the glasshouse, holes were drilled in vines on the rootstock and the holes were charged with suspensions of different strains of Pseudomonas spp., and with the biofungicides BS-F4 and Serenade, both based on Bacillus subtilis, before inoculation with a vitopine Agrobacterium vitis strain. The growth retardant Regalis and the resistance inducer Bion were applied to the vines two weeks before inoculation with the pathogen. Six months after inoculation, disease incidence was lowest when BS-F4 had been applied. In the field trial, the vines were wounded by making a cut in the crown, after which they were dipped into the antagonist suspensions just before inoculation with the pathogen. In the two weeks before inoculation, the root systems of the vines were dipped into Regalis and Bion solutions at 7 day intervals. Only these resistance inducers and BS-F4 significantly reduced disease severity. The results indicate that a potential for defence against A. vitis may exist even in susceptible grapevine cultivars, and that this potential can be activated by diverse elicitors.

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

    International Nuclear Information System (INIS)

    Pontes, F.H.D.; Taguchi, S.P.; Machado, J.P.B.; Santos, C.

    2009-01-01

    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. Crown ethers and phase transfer catalysis in polymer science

    CERN Document Server

    Carraher, Charles

    1984-01-01

    Phase transfer catalysis or interfacial catalysis is a syn­ thetic technique involving transport of an organic or inorganic salt from a solid or aqueous phase into an organic liquid where reaction with an organic-soluble substrate takes place. Over the past 15 years there has been an enormous amount of effort invested in the development of this technique in organic synthe­ sis. Several books and numerous review articles have appeared summarizing applications in which low molecular weight catalysts are employed. These generally include either crown ethers or onium salts of various kinds. While the term phase transfer catalysis is relatively new, the concept of using a phasetrans­ fer agent (PTA) is much older~ Both Schnell and Morgan employed such catalysts in synthesis of polymeric species in the early 1950's. Present developments are really extensions of these early applications. It has only been within the last several years that the use of phase transfer processes have been employed in polymer synthesis...

  10. Extraction chromatographic studies on a strontium selective crown ether

    International Nuclear Information System (INIS)

    Pathak, P.N.; Mohapatra, P.K.; Kulkarni, M.J.; Manchanda, V.K.

    1998-08-01

    Selective adsorption of radiostrontium from nitric acid medium on a chromatographic resin material consisting of di-t-butyl cyclohexano 18 crown 6/n-octanol sorbed onto amberlite XAD-7 (particle size: 100-150μm) has been carried out. The column capacity is evaluated as ∼ 21 mg of Sr per gram of the resin material. The separation of radiostrontium from several metal ions present in environmental and biological samples viz. Li, Na, K, Mg, Ca, Al, Fe, Co, Ni, Zn and Cd has been achieved. A promising separation method for 90 Y from 90 Sr- 90 Y mixture has also been developed. Nitric acid concentration has no observable effect on the elution profile of 90 Y as the entire amount of the loaded 90 Y activity can be eluted by 1.5 ml of the acid in a wide concentration range (0. 1 - 10 M). Half-life of the eluted 90 Y sample is calculated as 63.75 ± 0.40 hours by following the decay profile. Repeated elutions using 1.5 ml of 3 M HNO 3 after loading 200 μCi of 90 Sr - 90 Y revealed that the product with ∼ 98% radiochemical purity could be obtained up to the 12th run beyond which the contamination due to 90 Sr increased significantly. (author)

  11. From song dialects to speciation in white-crowned sparrows.

    Science.gov (United States)

    Toews, David P L

    2017-06-01

    The behavioural signals used in mate selection are a key component in the evolution of premating isolating barriers and, subsequently, the formation of new species. The importance of mating signals has a long tradition of study in songbirds, where many species differ in their song characteristics. In oscine songbirds, individual birds usually learn their songs from a tutor. Mistakes during learning can help generate geographic dialects, akin to those within human language groups. In songbirds, dialect differences can often be substantial and there is an intuitive connection between the evolution of song amongst populations at a small scale, and the more substantive song differences between bird species and presumably used in species recognition. However, studies investigating the concordance between putative genetic and behavioural boundaries have generated mixed results. In many cases, this is possibly a function of the poor resolving power of the genetic markers employed. In this issue of Molecular Ecology, Lipshutz et al. () combine genomic markers with a robust behavioural assay to address the importance of song variation amongst white-crowned sparrow (Zonotrichia leucophrys) subspecies. © 2017 John Wiley & Sons Ltd.

  12. The Role of the British Crown on Security Issues

    Directory of Open Access Journals (Sweden)

    Behar Selimi

    2016-07-01

    Full Text Available United Kingdom is a limited parliamentary monarchy, in which state sovereignty is exercised jointly by two basic political institutions: Royal Crown and Parliament. The credit for a successful political co-governance of these institutions, which are simultaneously bearers of popular sovereignty, are usually addressed to the Queen's lack of executive power to exercise power alone and hence all the restraint in the race for primate of governance. It goes even further considering that the Queen is quite weak and has only ceremonial functions, which do not disturb the Parliament. However, a careful researcher may notice that the Queen continues to affect the British Government in general and in particular on defence issues. Declassification of communication between Prince Charles and the Government in 2013, pointed out a continuing impact of the Queen and her son on many political issues, including those of defence and security. Since Britain has no codified constitution in a single document, it is not easy to determine the real power and competences of the Queen. It is even more difficult, because customary law and precedent prevail. Therefore, the real definition of the role of the Queen in general in the British Government, can be done by studying the culture, structure and constitutional practice. On their basis I will try to determine the real impact of the Queen in matters of defence and security, whether through her prerogatives in relation to the Government and Parliament, or through moral and informal influence in relation to the Prime Minister and particular ministers.

  13. Eocene diversification of crown group rails (Aves: Gruiformes: Rallidae.

    Directory of Open Access Journals (Sweden)

    Juan C García-R

    Full Text Available Central to our understanding of the timing of bird evolution is debate about an apparent conflict between fossil and molecular data. A deep age for higher level taxa within Neoaves is evident from molecular analyses but much remains to be learned about the age of diversification in modern bird families and their evolutionary ecology. In order to better understand the timing and pattern of diversification within the family Rallidae we used a relaxed molecular clock, fossil calibrations, and complete mitochondrial genomes from a range of rallid species analysed in a Bayesian framework. The estimated time of origin of Rallidae is Eocene, about 40.5 Mya, with evidence of intrafamiliar diversification from the Late Eocene to the Miocene. This timing is older than previously suggested for crown group Rallidae, but fossil calibrations, extent of taxon sampling and substantial sequence data give it credence. We note that fossils of Eocene age tentatively assigned to Rallidae are consistent with our findings. Compared to available studies of other bird lineages, the rail clade is old and supports an inference of deep ancestry of ground-dwelling habits among Neoaves.

  14. Color stability of provisional crown and fixed partial denture resins.

    Science.gov (United States)

    Haselton, Debra R; Diaz-Arnold, Ana M; Dawson, Deborah V

    2005-01-01

    Provisional resins are used extensively during fixed prosthodontic treatment and exhibit varying degrees of color change/discoloration over time. Data are needed to help predict color stability of provisional resins. The purpose of this in vitro study was to measure the color change of 12 provisional prosthodontic materials after immersion in artificial saliva and artificial saliva-coffee solutions for 1, 2, and 4 weeks. Twelve provisional materials were studied. Methacrylates consisted of Alike, Jet, Temporary Bridge Resin, Unifast, and Zeta CC. Bis-acryl resins included Instatemp, Integrity, Luxatemp, Protemp Garant, Provipont, Provitec, and Temphase. Ten specimens (25.4 mm x 25.4 mm x 2.4 mm) of each material were fabricated. Five specimens were stored at 37 degrees C in artificial saliva and 5 were stored in a solution of artificial saliva (400 cc) and coffee (800 cc). Baseline color was measured using a colorimeter. Further color measurements were made after 1, 2, and 4 weeks of immersion. CIE L *a *b * values were recorded and color differences (DeltaE) between baseline and each storage interval were calculated using a 2-way ANOVA with Bonferroni adjustment for multiple comparisons in conjunction with an overall alpha=.05. Results indicated the presence of strong interaction between material and storage solution regardless of the aspect of color considered (Pprovisional crown and fixed partial denture resins demonstrated varying tendency to discolor over a range of time periods when immersed in artificial saliva and artificial saliva-coffee solutions.

  15. 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.

  16. The effects of crown venting or pre-cementing of CAD/CAM-constructed all-ceramic crowns luted on YTZ implants on marginal cement excess.

    Science.gov (United States)

    Zaugg, Lucia K; Zehnder, Isabella; Rohr, Nadja; Fischer, Jens; Zitzmann, Nicola U

    2018-01-01

    The purpose of this study was to analyze the cement excess produced when cementing CAD/CAM-fabricated lithium disilicate (L) or zirconium dioxide (Z) crowns using adhesive cement (A) or resin-modified glass ionomer cement (B). Three different cementation techniques were applied: palatal venting (PV), pre-cementation with custom analogs (CA), and conventional standard procedure (SP). Seventy-two crowns (36 each material) were assigned to 12 experimental groups depending on the restoration material (L, Z), type of cement (A, B), and cementation technique (PV, CA, SP). Weight measurements were taken during cementation, and the amounts of excess cement, cement retained in crown, and relative excess cement were calculated and statistically analyzed. A significant direct relation between the amounts of cement applied and excess cement was observed in groups CA and SP. Vented crowns showed least amounts of marginal excess cement (0.8 ± 0.3 μl) followed by CA (4.2 ± 1.1 μl) and SP (8.8 ± 2.5 μl; p cement (95%CI: 28.4, 35.7) was produced than in the SP group (p cement (A) than of glass ionomer cement (B) were retained in crowns. Using crown venting was the most effective measure to reduce the amount of marginal excess cement, followed using a pre-cementation device. To keep the marginal excess cement of one-piece zirconia implants to a minimum, both techniques should be considered for clinical application. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  17. Comparative Evaluation of Enhancing Retention of Dislodged Crowns Using Preparation Modifications and Luting Cements: An In-Vitro Study

    Science.gov (United States)

    Amarnath, G S; Pandey, Apurva; Prasad, Hari Ananth; Hilal, Mohammed

    2015-01-01

    Background: Complete cast crowns are good alternatives and have best longevity for the restoration of damaged posterior teeth. Occasionally, a crown with clinically acceptable margins, preparation design, and occlusion becomes loose. Providers often debate whether such a crown can be successfully recemented with any degree of confidence that it will not be dislodged under normal masticatory function. It has been documented that resistance form increases by placing grooves opposing each other in a crown and tooth; cements also have a role to play in retention of crowns. To determine whether the addition of horizontal groove in the internal surface of the crown and/or tooth preparation will increase retention of the crowns, without remaking them and achieving better retention with cements. Materials and Methods: A total of 80 extracted human mandibular molars were taken and standard preparation was done. After the crowns were ready, the groove was made in the internal surface of the crown and on the tooth, which were cemented with glass ionomer cement and resin cement. The tensile force needed to dislodge the crowns and teeth after cementation was found out. Result: The mean tensile force needed to dislodge the crown and tooth combination was highest for the group in which crown had a groove without any groove on the tooth and cemented using resin cement (252.60N). Conclusion: It can be concluded from the study that it is best to recement a crown and tooth combination using resin cement where the crown has a groove, and the tooth has no groove. PMID:26464539

  18. [Computer aided design and manufacture of the porcelain fused to metal crown].

    Science.gov (United States)

    Nie, Xin; Cheng, Xiaosheng; Dai, Ning; Yu, Qing; Hao, Guodong; Sun, Quanping

    2009-04-01

    In order to satisfy the current demand for fast and high-quality prosthodontics, we have carried out a research in the fabrication process of the porcelain fused to metal crown on molar with CAD/CAM technology. Firstly, we get the data of the surface mesh on preparation teeth through a 3D-optical grating measuring system. Then, we reconstruct the 3D-model crown with the computer-aided design software which was developed by ourselves. Finally, with the 3D-model data, we produce a metallic crown on a high-speed CNC carving machine. The result has proved that the metallic crown can match the preparation teeth ideally. The fabrication process is reliable and efficient, and the restoration is precise and steady in quality.

  19. A guide to minimally invasive crown lengthening and tooth preparation for rehabilitating pink and white aesthetics.

    Science.gov (United States)

    Al-Harbi, F; Ahmad, I

    2018-02-23

    The rehabilitation of anterior dental aesthetics involves a multitude of disciplines, each with its own methodologies for achieving a predefined goal. The literature is awash with different techniques for a given predicament, based on both scientific credence, as well as empirical clinical judgements. An example is crown lengthening for correcting uneven gingival zeniths, increasing clinical crown lengths, and therefore, reducing the amount of maxillary gingival display that detracts from pleasing pink aesthetics. Many procedures have been advocated for rectifying gingival anomalies depending on prevailing clinical scenarios and aetiology. This paper presents a minimally invasive technique for crown lengthening for short clinical crowns concurrent with excessive maxillary gingival display, which is expedient, maintaining the inter-proximal papilla, mitigating morbidity, reducing post-operative inflammation, and increasing patient comfort. In addition, with a similar ethos, a minimally invasive tooth preparation approach is presented for achieving optimal white aesthetics.

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

    DEFF Research Database (Denmark)

    Pedersen, Jan

    The scientific progress of our understanding of the interaction between coastal structures and the sea has greatly improved in the recent years. The present state of knowledge includes structural and financial optimization of the structures based on reliability evaluations. The first requirement ....... The stability of crown wall structures has also been investigated and a new methodology for the evaluation of the geodynamic response of the foundation is presented....... 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...... 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...

  1. A Simple Chairside Technique of Removing Crown and Fixed Partial Denture Restorations

    Directory of Open Access Journals (Sweden)

    Abhinav Gupta

    2014-03-01

    Full Text Available Retrieving failed cemented crowns and fixed partial dentures with minimum discomfort to the patient has always been a clinical concern. This article describes a technique which will allow easy and predictable removal of these restorations.

  2. Crown ethers as synergistic agents in the solvent extraction of trivalent lanthanides with 8-hydroxyquinoline

    Directory of Open Access Journals (Sweden)

    M. ATANASSOVA

    2008-01-01

    Full Text Available The liquid extraction of the 13 lanthanides with mixtures of 8-hydroxyquinoline (HQ and crown ethers (S dibenzo-18-crown-6 (DB18C6 and dibenzo-24-crown-8 (DB24C8 in 1,2-dichloroethane as a diluent from chloride medium at constant ionic strength μ = 0.1 was investigated. The composition of the extracted species was established as LnQ3 with HQ alone and as LnQ3·S in the presence of a crown ether. The values of the equilibrium constants were calculated. The addition of DB18C6 to the metal chelate system improved the extraction efficiency, while a weak synergistic enhancement was found when the metals were extracted with mixtures of HQ–DB24C8. The parameters of the extraction process were determined and the separation factors between two adjacent lanthanides(III were calculated.

  3. SYNTHESIS, COMPLEXATION BEHAVIOR AND REACTIONS OF THIA-CROWN ETHERS INCORPORATING PROPAN-2-ONE UNITS

    NARCIS (Netherlands)

    KELLOGG, RM; VANBOLHUIS, F

    1991-01-01

    Thia-crown ethers containing ketone functionality derived from 1,3-dichloroacetone have been prepared in 70-80% yields; the crystal structures of one free macrocycle and two Ag1 complexes have been determined.

  4. Biogenic synthesized nanoparticles and their applications

    International Nuclear Information System (INIS)

    Singh, Abhijeet; Sharma, Madan Mohan

    2016-01-01

    In the present scenario, there are growing concerns over the potential impacts of bioengineered nanoparticles in the health sector. However, our understanding of how bioengineered nanoparticles may affect organisms within natural ecosystems, lags far behind our rapidly increasing ability to engineer novel nanoparticles. To date, research on the biological impacts of bioengineered nanoparticles has primarily consisted of controlled lab studies of model organisms with single species in culture media. Here, we described a cost effective and environment friendly technique for green synthesis of silver nanoparticles. Silver nanoparticles were successfully synthesized from 1 mM AgNO 3 via a green synthesis process using leaf extract as reducing as well as capping agent. Nanoparticles were characterized with the help of UV–vis absorption spectroscopy, X-ray diffraction and TEM analysis which revealed the size of nanoparticles of 30-40 nm size. Further the nanoparticles synthesized by green route are found highly toxic against pathogenic bacteria and plant pathogenic fungi viz. Escherichia coli, Pseudomonas syringae and Sclerotiniasclerotiorum. The most important outcome of this work will be the development of value-added products and protection of human health from pathogens viz., bacteria, virus, fungi etc.

  5. Squid Giant Axons Synthesize NF Proteins.

    Science.gov (United States)

    Crispino, Marianna; Chun, Jong Tai; Giuditta, Antonio

    2018-04-01

    Squid giant axon has been an excellent model system for studying fundamental topics in neurobiology such as neuronal signaling. It has been also useful in addressing the questions of local protein synthesis in the axons. Incubation of isolated squid giant axons with [ 35 S]methionine followed by immunoprecipitation with a rabbit antibody against all squid neurofilament (NF) proteins demonstrates the local synthesis of a major 180 kDa NF protein and of several NF proteins of lower molecular weights. Their identification as NF proteins is based on their absence in the preimmune precipitates. Immunoprecipitates washed with more stringent buffers confirmed these results. Our data are at variance with a recent study based on the same experimental procedure that failed to visualize the local synthesis of NF proteins by the giant axon and thereby suggested their exclusive derivation from nerve cell bodies (as reported by Gainer et al. in Cell Mol Neurobiol 37:475-486, 2017). By reviewing the pertinent literature, we confute the claims that mRNA translation is absent in mature axons because of a putative translation block and that most proteins of mature axons are synthesized in the surrounding glial cells. Given the intrinsic axonal capacity to synthesize proteins, we stress the glial derivation of axonal and presynaptic RNAs and the related proposal that these neuronal domains are endowed with largely independent gene expression systems (as reported by Giuditta et al. in Physiol Rev 88:515-555, 2008).

  6. Recent Advances in Chemoenzymatic Peptide Syntheses

    Directory of Open Access Journals (Sweden)

    Kenjiro Yazawa

    2014-09-01

    Full Text Available Chemoenzymatic peptide synthesis is the hydrolase-catalyzed stereoselective formation of peptide bonds. It is a clean and mild procedure, unlike conventional chemical synthesis, which involves complicated and laborious protection-deprotection procedures and harsh reaction conditions. The chemoenzymatic approach has been utilized for several decades because determining the optimal conditions for conventional synthesis is often time-consuming. The synthesis of poly- and oligopeptides comprising various amino acids longer than a dipeptide continues to pose a challenge owing to the lack of knowledge about enzymatic mechanisms and owing to difficulty in optimizing the pH, temperature, and other reaction conditions. These drawbacks limit the applications of the chemoenzymatic approach. Recently, a variety of enzymes and substrates produced using recombinant techniques, substrate mimetics, and optimal reaction conditions (e.g., frozen aqueous media and ionic liquids have broadened the scope of chemoenzymatic peptide syntheses. In this review, we highlight the recent advances in the chemoenzymatic syntheses of various peptides and their use in developing new materials and biomedical applications.

  7. Biogenic synthesized nanoparticles and their applications

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Abhijeet, E-mail: abhijeet.singh@jaipur.manipal.edu; Sharma, Madan Mohan [Manipal University Jaipur (India)

    2016-05-06

    In the present scenario, there are growing concerns over the potential impacts of bioengineered nanoparticles in the health sector. However, our understanding of how bioengineered nanoparticles may affect organisms within natural ecosystems, lags far behind our rapidly increasing ability to engineer novel nanoparticles. To date, research on the biological impacts of bioengineered nanoparticles has primarily consisted of controlled lab studies of model organisms with single species in culture media. Here, we described a cost effective and environment friendly technique for green synthesis of silver nanoparticles. Silver nanoparticles were successfully synthesized from 1 mM AgNO{sub 3} via a green synthesis process using leaf extract as reducing as well as capping agent. Nanoparticles were characterized with the help of UV–vis absorption spectroscopy, X-ray diffraction and TEM analysis which revealed the size of nanoparticles of 30-40 nm size. Further the nanoparticles synthesized by green route are found highly toxic against pathogenic bacteria and plant pathogenic fungi viz. Escherichia coli, Pseudomonas syringae and Sclerotiniasclerotiorum. The most important outcome of this work will be the development of value-added products and protection of human health from pathogens viz., bacteria, virus, fungi etc.

  8. The clinical success of zirconia-based crowns: a systematic review.

    Science.gov (United States)

    Larsson, Christel; Wennerberg, Ann

    2014-01-01

    This review aimed to evaluate the documented clinical success of zirconia based crowns in clinical trials. Electronic databases were searched for original studies reporting on the clinical performance of tooth- or implant-supported zirconia-based crowns, including PubMed, Cochrane Library, and Science Direct. The electronic search was complemented by manual searches of the bibliographies of all retrieved full-text articles and reviews as well as a hand search of the following journals: International Journal of Prosthodontics, Journal of Oral Rehabilitation, International Journal of Oral & Maxillofacial Implants, and Clinical Oral Implants Research. The search yielded 3,216 titles. Based on preestablished criteria, 42 full-text articles were obtained. While 16 studies fulfilled the inclusion criteria, only 3 randomized controlled trials were reported. Seven studies reported on tooth-supported and 4 on implant-supported crowns, and 5 studies reported on both types of support. Ten studies on tooth-supported and 7 on implant supported crowns provided sufficient material for statistical analysis. Life table analysis revealed cumulative 5-year survival rates of 95.9% for tooth-supported and 97.1% for implant-supported crowns. For implant-supported crowns, the most common reasons for failure were technical (veneering material fractures). For tooth-supported crowns, technical (veneering material fractures, loss of retention) and biologic (endodontic/ periodontic) reasons for failure were equally common. The most common complications for implant-supported crowns were veneering material fractures and bleeding on probing. For tooth-supported crowns, the most common complications were loss of retention, endodontic treatment, veneering material fractures, and bleeding on probing. The results suggest that the success rate of tooth-supported and implant-supported zirconia-based crowns is adequate, similar, and comparable to that of conventional porcelain-fused-to-metal crowns

  9. A 2-year Retrospective Clinical study of Enamic Crowns Performed in a Private Practice Setting.

    Science.gov (United States)

    Chirumamilla, Geetika; Goldstein, Cary E; Lawson, Nathaniel C

    2016-07-01

    To evaluate the clinical performance and survival of Enamic crowns placed in a prosthodontic dental practice. Thirty-five patients and 45 crowns were included in the study. At 1-year recall appointments, the restorations were examined for survival. At the 2-year recall appointment, all restorations were clinically evaluated by an independent evaluator for CDA clinical criteria. Kaplan-Meier method and a log-rank test were used to compare the survival of the restorations placed with resin and resin-modified glass ionomer (RMGI) cements. Out of the 45 crowns that were followed, 2 were lost to follow-up by 1 year and 7 were lost to follow-up by 2 years. Severe complications were observed in 2 teeth by the 2-year follow-up and were recorded as failures due to recurrent decay, and an internal crack in the abutment tooth. There was no difference between the survival probability for crowns cemented with resin cement (96.8%) and with RMGI cements (92.9%) (p = 0.42), however, 1 out of the 14 crowns cemented with RMGI cement debonded. The crowns were evaluated according the CDA criteria with over 90% alfa scores for all categories aside from surface texture (86% alfa). The estimated 2-year survival of Enamic crowns is >90%. Based on the preliminary 2-year results achieved in a clinical practice, Enamic is a suitable material for full-coverage single-unit crowns. Further studies are necessary to evaluate the long term success. (J Esthet Restor Dent 28:231-237, 2016). © 2016 Wiley Periodicals, Inc.

  10. The clinical and radiographic success of bonded resin composite strip crowns for primary incisors.

    Science.gov (United States)

    Kupietzky, Ari; Waggoner, William F; Galea, Jon

    2003-01-01

    The aim of this study was to examine the clinical and radiographic success of the treatment of maxillary anterior primary incisors with composite resin strip crowns placed in a private practice setting. This was a retrospective, clinical study of patients who had strip crowns (SC) placed on maxillary primary incisors, returned for at least 1, 6-month recall examination, and whose parents consented to participate in the study. Radiographic and photographic examinations were used for evaluation. Two evaluators rated the images independently. When ratings were not in agreement, the 2 examiners reviewed the photograph or radiograph together and reached a consensus rating. One hundred twelve restorations placed in 40 children were evaluated. The evaluations were performed after the crowns had been in place for an average of 18 months. None of the restorations were totally lost, and only 12% were rated as having lost some resin material, resulting in an 88% overall retention rate. There was no difference in restoration success if the crowns were placed 4 at a time, or if fewer crowns were placed in a single sitting; the failure rates were comparable. Teeth that had pulpal treatment were judged to have far more significant color match discrepancies than those teeth without pulpal treatment. Ninety-one percent of the teeth demonstrated healthy pulps. Eight percent had some pulpal changes but did not require immediate attention. Only 1 tooth showed radiographic evidence of pulpal necrosis. Only 11 teeth had pulpal treatment, but of these, 10 demonstrated clinical success. Composite resin strip crowns for restoring primary incisors with large or multisurface caries performed well. Color match of these crowns with adjacent teeth may be significantly reduced when placed upon teeth that have undergone pulpectomy treatment and have been obturated with an iodoform paste. However, based upon the results of this study, the strip crown may provide an esthetic and durable restoration

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

    OpenAIRE

    Mitov, Gergo; 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 f...

  12. Clinical outcomes of zirconia-based implant- and tooth-supported single crowns.

    Science.gov (United States)

    Nejatidanesh, Farahnaz; Moradpoor, Hedayat; Savabi, Omid

    2016-01-01

    Zirconia-based restorations have been increasingly used on implant and teeth abutments, but the evidence about clinical outcomes of these restorations is limited. The aim of this study was to assess up to 7-year clinical outcomes of implant- and tooth-supported zirconia-based single crowns. In this retrospective study, 261 patients with 556 single crowns supported by either teeth (324) or implants (232) were examined during 3- to 7-year follow-up (mean observation of 60.70 months for tooth and 59.20 months for implant-supported crowns). California Dental Association (CDA) quality evaluation system was used to evaluate the restorations. Soft tissue status was assessed using plaque and gingival index scores, bleeding on probing, and pocket depth. Patient and professional satisfaction were evaluated by visual analog scale (VAS). The 5-year Kaplan-Meier survival probability was 98.3 and 97.3 for implant- and tooth-supported crowns, respectively. In regard to CDA rating, most of the crowns were ranked as either excellent or acceptable (99.5 %). The recorded failures were replacement of the crown due to porcelain chipping (3), implant failure (1), and teeth extraction (5). Soft tissue parameters were not affected by the restorations compare to control teeth. The VAS was high for both patients and clinicians. Zirconia-based single crowns on both tooth and implant abutments showed promising clinical performance in this up to 7-year follow-up. The zirconia-based single crowns can be used clinically for tooth- and implant-supported restorations.

  13. Adaptation of zirconia crowns created by conventional versus optical impression: in vitro study

    OpenAIRE

    Cetik, Sibel; Bahrami, Babak; Fossoyeux, In?s; Atash, Ramin

    2017-01-01

    PURPOSE The aim of this study was to compare the precision of optical impression (Trios, 3Shape) versus that of conventional impression (Imprint IV, 3M-ESPE) with three different margins (shoulder, chamfer, and knife-edge) on Frasaco teeth. MATERIALS AND METHODS The sample comprised of 60 zirconia half-crowns, divided into six groups according to the type of impression and margin. Scanning electron microscopy enabled us to analyze the gap between the zirconia crowns and the Frasaco teeth, usi...

  14. Modelling Growth of Juvenile Crown-of-Thorns Starfish on the Northern Great Barrier Reef

    OpenAIRE

    Jennifer Wilmes; Samuel Matthews; Daniel Schultz; Vanessa Messmer; Andrew Hoey; Morgan Pratchett

    2016-01-01

    The corallivorous crown-of-thorns starfish (Acanthaster spp.) is a major cause of coral mortality on Indo-Pacific reefs. Despite considerable research into the biology of crown-of-thorns starfish, our understanding of the early post-settlement life stage has been hindered by the small size and cryptic nature of recently settled individuals. Most growth rates are derived from either laboratory studies or field studies conducted in Fiji and Japan. The Great Barrier Reef (GBR) is currently exper...

  15. Genetic variation between Phytophthora cactorum isolates differing in their ability to cause crown rot in strawberry

    OpenAIRE

    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, and New Zealand, were identical in an analysis based on 96 polymorphic bands from seven primer combinations. Leather rot isolates of strawberry could not be distinguished from isolates from other...

  16. Electroplated telescopic retainers with zirconia primary crowns: 3-year results from a randomized clinical trial.

    Science.gov (United States)

    Schwindling, Franz Sebastian; Lehmann, Franziska; Terebesi, Sophia; Corcodel, Nicoleta; Zenthöfer, Andreas; Rammelsberg, Peter; Stober, Thomas

    2017-12-01

    The objective of the study was to investigate the clinical outcome for electroplated telescopic removable dental prostheses (E-RDPs) with zirconia primary crowns. Sixty E-RDPs, with primary crowns manufactured from either cobalt-chromium alloy or zirconia, were fabricated for 56 participants. Electroplating was used to produce gold copings directly on the telescopic primary crowns. These copings were bonded intra-orally to the prosthesis framework. After 36 months, prosthesis survival and number of complications were assessed. Statistical analysis was performed by the use of Kaplan-Meier modeling and the log-rank test. Survival of the E-RDPs, 96.4% after 3 years, was identical in both groups. The need for aftercare was high but not significantly different: technical complications were observed for 37% and 42.9% of the prostheses for the zirconia and cobalt-chromium alloy primary crowns, respectively. Fracture of composite veneer was the most frequent complication (59.1%). The incidence of fractured abutment teeth, decementation, and endodontic problems was 7.9% in the zirconia group and 14% in the control group. The majority of abutment-level complications were treated restoratively. A significant difference was found for maximum probing depth at the abutment teeth: In the zirconia group, it decreased by 0.2 mm, whereas it increased by 0.8 mm in the control group (p = 0.04). After 3 years of observation, survival of zirconia E-RDPs was favorable and comparable with that of established double-crown-retained prostheses. Further studies must clarify whether there are benefits of zirconia primary crowns for periodontal health. Although these results encourage the use of zirconia primary crowns, more research is necessary to reduce the number of complications observed for secondary telescopic crowns, for example, failure of the veneer.

  17. 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.

  18. Distribution and prevalence of crown rot pathogens affecting wheat crops in southern Chile

    Directory of Open Access Journals (Sweden)

    Ernesto Moya-Elizondo

    2015-03-01

    Full Text Available Crown rot pathogens are associated with higher losses for wheat crop farmers, but information about the distribution and prevalence of these pathogens in Chile is inadequate. Distribution and prevalence of wheat (Triticum aestivum L. crown rot pathogens were examined in a survey of 48 commercial fields from December 2011 to February 2012 in southern Chile. These fields were located between Collipulli (37°56'00" S; 72°26'39" W and Purranque (40°50'30" S; 73°22'03" W. Severity of crown rot disease was determined through visual assessment of the first internode of 20 tillers obtained from each field. Incidence of crown rot pathogens per field was determined by plating the 20 tillers on Petri plates with 20% potato dextrose agar amended with lactic acid (aPDA medium. Resulting fungal colonies from monoxenic culture were identified by morphological or molecular-assisted identification. Severity of crown rot varied between 11.3% and 80% for individual fields. Culture plate analysis showed 72.2% of stems were infected with some fungus. Fusarium avenaceum, F. graminearum, and F. culmorum, pathogens associated with Fusarium crown rot disease were isolated from 13.5% of tillers. Gaeumannomyces graminis, causal agent of take-all disease in cereals, was isolated from 11.1% of culms. Phaeosphaeria sp., an endophyte and possibly a non-pathogenic fungus, was isolated from 13.9% of tillers. Pathogenic fungi such as Rhizoctonia spp. and Microdochium nivale, other saprophyte, and several unidentified non-sporulating fungi were isolated at frequencies lower than 3% of the total. Fusarium crown rot and take-all were the most prevalent and distributed crown rot diseases present in wheat crops in southern Chile.

  19. Retention of cast crowns cemented to amalgam and composite resin cores.

    Science.gov (United States)

    Hormati, A A; Denehy, G E

    1981-05-01

    An in vitro study was conducted to determine the tensile bond strength of complete cast gold restorations cemented with zinc phosphate cement on composite resin and amalgam crown cores. The samples were thermocycled and tested at 1-week, 1-month, and 3-month intervals. Results of the study showed that: (1) the amalgam core provides more retention for the cast gold crown than does the composite resin core and (2) the composite resin core provides increasing retention over a longer time period.

  20. Synthesis and Characterization of Benzo-15-Crown-5 Ethers with Appended N2O Schiff Bases

    Directory of Open Access Journals (Sweden)

    Baltazar de Castro

    2003-12-01

    Full Text Available New derivatives of benzo-15-crown-5 with flexible appended N2O unsymmetrical Schiff bases were prepared by a two step procedure which involves: (i preparation of N2O Schiff bases by condensation of hydrazine with salicylaldehyde, 3-methoxysalicylaldehyde or 2-hydroxy-1-naphtaldehyde and (ii reaction of the resulting NH2 functionalized compounds with 4’-formyl-benzo-15-crown-5.

  1. Elimination of a "Gummy Smile" With Crown Lengthening and Lip Repositioning.

    Science.gov (United States)

    Mahn, Douglas H

    2016-01-01

    Excessive gingival display is considered unattractive by many patients. A combination of surgical approaches may be required to correct this problem. Clinical crown lengthening involves recontouring crestal bone levels and moving the gingival margin in an apical direction. Lip repositioning reduces gingival display by limiting upper lip movement when smiling. This article describes a case in which a combination of clinical crown lengthening and lip repositioning was used to correct excessive gingival display when smiling.

  2. Crown-Stump Diameter Model for Parkia biglobosa Benth. Species in Makurdi, Benue State, Nigeria

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    O. Chukwu

    2017-07-01

    Full Text Available The crown of tree is the centre of physiological activity which gives an indication of the potential photosynthetic capacity on a tree. Though, its measurement remains a challenge in forest inventory task. The ability to predict crown diameter from stump diameter provides an effective technique of obtaining its estimate. This helps in detecting the excessive tree felling than actual requirements and wildlife suitability.The main objective of this study was to develop and test crown diameter prediction models for silvicultural management of naturally grown Parkia biglobosa within the University of Agriculture, Makurdi. Nine 100 m x 100 m temporary sample plots were established using simple random sampling method. Crown diameter and stump diameter were measured in all living P. biglobosa trees with stump diameter ≥10.0 cm. Least square method was used to convert the counted stumps into harvested crown dimension. Three linear and three non-linear models using stump diameter as the exploratory variable were developed and evaluated using the adjusted coefficient of determination (Adj.R2, standard error of estimate (SEE, prediction error sum of squares (PRESS and Akaike information criterion (AIC. The crown-stump diameter relationship was best described by the double logarithmic function with .The result showed that Crown diameter estimation was feasible even when the only information available is stump diameter.The resulting equation was tested for validation with independent data obtained from additional plots and was found to be desirable for estimating the crown diameter for Parkia biglobosa in Makurdi, Benue State, Nigeria.

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

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    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.

  4. Influence of resin cement polymerization shrinkage on stresses in porcelain crowns.

    Science.gov (United States)

    May, Liliana G; Kelly, J Robert

    2013-10-01

    The aim of this study was to analyze the influence of polymerization shrinkage of the cement layer on stresses within feldspathic ceramic crowns, using experimentally validated FEA models for (1) increasing occlusal cement thickness; and, (2) bonded versus non-bonded ceramic-cement interfaces. 2-D axial symmetric models simulated stylized feldspathic crowns (1.5mm occlusal thickness) cemented with resin-cement layers of 50-500μm on dentin preparations, being loaded (500N) or not. Ceramic-cement interface was either bonded or not. Cement was bonded to the dentin in all models. Maximum axial shrinkage of 0%, 1%, 2%, 3%, 4% and 4.65% were simulated. The first principal stresses developing in the cementation surface at the center and at the occluso-axial line-angle of the crown were registered. Polymerization shrinkage of the cement increased tensile stresses in the ceramic, especially in loaded non-bonded crowns for thicker cement layers. Stresses in loaded non-bonded crowns increased as much as 87% when cement shrinkage increased from 0% to 4.65% (100-187MPa), for a 500μm-thick cement. Increasing polymerization shrinkage strain raised the tensile stresses, especially at the internal occlusal-axial line-angle, for bonded crowns. Changes in the polymerization shrinkage strain (from 0% to 4.65%) have little effect on the tensile stresses generated at the cementation surface of the ceramic crowns, when the occlusal cement thickness is thin (approx. 50μm for bonded crowns). However, as the cement becomes thicker stresses within the ceramic become significant. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  5. INFLUENCE OF APPLICATION SITE OF PROVISIONAL CEMENT ON THE MARGINAL ADAPTATION OF PROVISIONAL CROWNS

    OpenAIRE

    Cardoso, Mayra; Torres, Marcelo Ferreira; Rego, Mariana Ribeiro de Moraes; Santiago, Luiz Carlos

    2008-01-01

    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 ful...

  6. Cumulative effects of successive restorative procedures on anterior crown flexure: intact versus veneered incisors.

    Science.gov (United States)

    Magne, P; Douglas, W H

    2000-01-01

    When successive restorative procedures (e.g., porcelain veneers, interdental resin composite restorations, and endodontic treatment) are carried out on the same tooth, significant effects on crown flexure can be expected. Dentin-bonded porcelain veneers (experimental group) were assessed in vitro using functional and cyclic thermal loads. They were compared to natural teeth (control group) with respect to 2 parameters: coronal flexure (investigated using experimental strain gauges) and morphology of the tooth-restoration interface (scanning electron microscopic evaluation). For both veneered and natural teeth, crown deformation was recorded at 5 sequential experimental steps: intact tooth (baseline), Class III cavities, Class III resin composite restorations, endodontic treatment, and endodontic restoration (without posts). No significant differences in crown flexure were found between natural and veneered incisors when compared across experimental steps. The main effect for experimental steps was highly significant. When averaged across all specimens (natural and veneered teeth), the endodontic treatment step resulted in the highest crown flexure (1.55x the baseline value). The unrestored Class III cavities and the endodontic restoration were next highest (1.30x and 1.28x the baseline value, respectively). The lowest crown flexures were found after restoration of the Class III cavities (1.13x the baseline value). No measurable microleakage or gaps were detected at the ceramic-resin, resin-enamel, or resin-dentin interfaces (Optibond FL, Kerr). Each subsequent reduction in tooth structure resulted in a substantial increase in crown flexibility, even after restoration. Endodontic procedures were responsible for most of the loss in crown stiffness. Extensive proximal cutting and restorations seemed to minimally affect crown flexure. Porcelain veneers showed perfect biomimetic behavior, because cumulated restoration procedures had the same effect on natural and

  7. Swimming black-crowned night-herons (Nycticorax nycticorax) Kleptoparasitize American coots (Fulica americana)

    DEFF Research Database (Denmark)

    Graves, Gary R.

    2015-01-01

    I observed black-crowned night-herons (Nycticorax nycticorax) swimming and kleptoparasitizing American coots (Fulica americana) at an artificial lake in Pinal County, Arizona. This appears to be the first record of interspecific kleptoparasitism by a swimming ardeid.......I observed black-crowned night-herons (Nycticorax nycticorax) swimming and kleptoparasitizing American coots (Fulica americana) at an artificial lake in Pinal County, Arizona. This appears to be the first record of interspecific kleptoparasitism by a swimming ardeid....

  8. Adhesive crowns and fixed partial dentures fabricated of ceromer/FRC: clinical and laboratory procedures.

    Science.gov (United States)

    Krejci, I; Boretti, R; Giezendanner, P; Lutz, F

    1998-05-01

    Ceramic optimized polymer and fiber-reinforced composite materials represent a significant development in prosthetic dentistry. When utilized in conjunction with adhesive luting techniques, exceptionally conservative crown and bridge restorations may be achieved. This article discusses utilization of these materials in inlay and onlay restorations, as well as clinical and laboratory procedures for fabrication, preparation, and seating of adhesive crown and bridge restorations. The initial results of restorations utilizing these innovative materials are presented.

  9. Preliminary age determinations of crown of thorns starfish spicules by accelerator mass spectrometry

    International Nuclear Information System (INIS)

    Sparks, R.J.; Wallace, G.; Lowe, D.C.; Manning, M.R.

    1986-12-01

    The Institute of Nuclear Sciences accelerator mass spectrometry system has been used to determine the ages of a selection of spicules from crown of thorns starfish, collected at the Great Barrier Reef, Queensland. The measurements constitute a pilot study to determine the feasibility of using the technique to establish whether or not there is a periodicity in the invasion of The Great Barrier Reef by Crown of Thorns starfish

  10. Crystallographic studies on complexes of potassium iodide and copper perchlorate with N, Nʹ-dicyclohexylurea tethered to a benzo-12-crown-4

    Science.gov (United States)

    Tripathi, Garima; Ramanathan, Gurunath

    2018-03-01

    The N, N‧-dicyclohexylurea-capped benzo-12-crown-4 (compound 1) has been synthesized. The coordination behaviour of this compound (1) has been studied by crystallizing it with KI (2) and Cu(ClO4)2 (3) salts. The crystallographic studies were performed with all three compounds. The presence of metal ions significantly affects the crystal packing of the compound 1. The crystal lattice of compound 1 was stabilized by Csbnd H⋯π and Cdbnd O⋯Hsbnd N hydrogen bonding. The presence of KI in compound 2 results in a dimer structure in which iodide anion behaves as a bridging ligand. The K+ forms a perching structure with the crown ring. In the compound 3, Cu2+ ion and ligand molecule (1) crystallized independently. They were connected through hydrogen bonding. Interestingly, Cu2+ adopts two different geometries with the coordination number 5 and 6. The centre Cu2+ (Cu1) adopted an octahedral geometry whereas the terminal Cu2+ (Cu2) acquired square pyramidal geometry. The coordination sphere of Cu2+ contains ClO4- anion and water molecules. Cu2+ ion forms a chain structure through ClO4- anion and water molecules involve in hydrogen bonding with the ligand molecule.

  11. Two new 3-D cadmium bromoplumbates: the only example of heterometallic bromoplumbate based on crown [Cd(Pb4O4)Br2] clusters.

    Science.gov (United States)

    Xiao, Hong; Zhou, Jian; Liu, Xing

    2018-04-03

    Two new cadmium bromoplumbates [CdPb2Br2L2]n (1, L = ethylene glycol) and [CdPb6Br6L4]n (2) have been solvothermally synthesized and structurally characterized. 1 contains 1-D neutral heterometallic chains [CdPb2Br2L2]n, which are further connected via weak Pb-Br bonds, resulting in a 3-D network structure. The 3-D framework of 2 is constructed by the interconnection of a 2-D neutral layer [CdPb6Br6L4]nvia weak Pb-Br bonds. The [CdPb6Br6L4]n layer is based on the linkages of dimeric [Pb2Br4] units and heterometallic crown [Cd(Pb4O4)Br2] clusters containing a rare eight-membered [Pb4O4] ring. Although a few heterometallic bromoplumbate clusters have been reported, they usually exhibit molecular moieties. 2 represents the only example of 3-D heterometallic bromoplumbate based on the combination of heterometallic crown [Cd(Pb4O4)Br2] clusters and dimeric [Pb2Br4] units. Their optical properties are studied and density functional theory calculations for 1 and 2 have also been performed.

  12. Complete digital workflow for the production of implant-supported single-unit monolithic crowns.

    Science.gov (United States)

    Joda, Tim; Brägger, Urs

    2014-11-01

    The aim of this case series was to introduce a complete digital workflow for the production of monolithic implant crowns. Six patients were treated with implant-supported crowns made of resin nano ceramic (RNC). Starting with an intraoral optical scan (IOS), and following a CAD/CAM process, the monolithic crowns were bonded either to a novel prefabricated titanium abutment base (group A) or to a CAD/CAM-generated individualized titanium abutment (group B) in premolar or molar sites on a soft tissue level dental implant. Economic analyses included clinical and laboratory steps. An esthetic evaluation was performed to compare the two abutment-crown combinations. None of the digitally constructed RNC crowns required any clinical adaptation. Overall mean work time calculations revealed obvious differences for group A (65.3 min) compared with group B (86.5 min). Esthetic analysis demonstrated a more favorable outcome for the prefabricated bonding bases. Prefabricated or individualized abutments on monolithic RNC crowns using CAD/CAM technology in a model-free workflow seem to provide a feasible and streamlined treatment approach for single-edentulous space rehabilitation in the posterior region. However, RNC as full-contour material has to be considered experimental, and further large-scale clinical investigations with long-term follow-up observation are necessary. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  13. Etiology and Population Genetics of Colletotrichum spp. Causing Crown and Fruit Rot of Strawberry.

    Science.gov (United States)

    Ureña-Padilla, A R; Mackenzie, S J; Bowen, B W; Legard, D E

    2002-11-01

    ABSTRACT Isolates of Colletotrichum spp. from diseased strawberry fruit and crowns were evaluated to determine their genetic diversity and the etiology of the diseases. Isolates were identified to species using polymerase chain reaction primers for a ribosomal internal transcribed spacer region and their pathogenicity was evaluated in bioassays. Isolates were scored for variation at 40 putative genetic loci with random amplified polymorphic DNA and microsatellite markers. Only C. acutatum was recovered from diseased fruit. Nearly all isolates from crowns were C. gloeosporioides. In crown bioassays, only isolates of C. gloeosporioides from strawberry caused collapse and death of plants. A dendrogram generated from the genetic analysis identified several primary lineages. One lineage included isolates of C. acutatum from fruit and was characterized by low diversity. Another lineage included isolates of C. gloeosporioides from crowns and was highly polymorphic. The isolates from strawberry formed distinctive clusters separate from citrus isolates. Evaluation of linkage disequilibrium among polymorphic loci in isolates of C. gloeosporioides from crowns revealed a low level of disequilibrium as would be expected in sexually recombining populations. These results suggest that epidemics of crown rot are caused by Glomerella cingulata (anamorph C. gloeosporioides) and that epidemics of fruit rot are caused by C. acutatum.

  14. 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.

  15. 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.

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

    Science.gov (United States)

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

    2016-02-01

    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. 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. 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. 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.

  17. Assessment of 68 Prosthodontic Crowns in 41 Pet and Working Dogs (2000-2012).

    Science.gov (United States)

    Fink, Lisa; Reiter, Alexander M

    2015-01-01

    A search of the medical and dental records at the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania was conducted to identify dogs that received full or partial prosthodontic crowns over a 13-year period (2000-2012). Forty-one dogs with a total of 68 prosthodontic crowns were identified. Further criteria for acceptance into the study included presence of complete medical records containing adequate information pertaining to the procedures performed, and current follow-up either by telephone, electronic mail, or via in-person examination. Treatment was considered to be successful when the prosthodontic crown was in place and there was no further structural injury to the tooth upon making contact with the client or at the time of death of the dog confirmed by the client. The mean number of days the prosthodontic crowns remained in place without further injury to the tooth was 1,598 (range, 161-4, 464 days [median, 1,414 days], standard deviation 1,093 days). Bond failure between the cement and the tooth or the cement and the prosthodontic crown occurred in 3 cases (4.4%). Fracture of the prosthodontically treated tooth occurred in an additional 7 cases (10.3%). Treatment was classified as successful in 58 cases (85.3%). The results suggest that prosthodontic crown therapy is a successful, practical, and durable treatment option for protection of previously injured teeth in pet and working dogs.

  18. Crystal structure of cis-anti-cis-dicyclohexane-18-crown-6 acetonitrile disolvate

    Directory of Open Access Journals (Sweden)

    Alexander Nazarenko

    2015-07-01

    Full Text Available The title compound (systematic name: cis-anti-cis-2,5,8,15,18,21-hexaoxatricyclo[20.4.0.09,14]hexacosane acetonitrile disolvate, C20H36O6·2CH3CN, crystallizes from an acetonitrile solution of dicyclohexane-18-crown-6 on evaporation. The molecule is arranged around a center of symmetry with half the crown ether molecule and one molecule of acetonitrile symmetry independent. All O—C—C—O torsion angles are gauche while all C—O—C—C angles are trans. The sequence of torsion angles is [(tg+t(tg−t]3; the geometry of oxygen atoms is close to pseudo-D3d with three atoms below and three atoms above the mean plane, with an average deviation of ±0.16 (1 Å from the mean plane. This geometry is identical to that observed in metal ion complexes of dicyclohexane-18-crown-6 but differs significantly from the conformation of a free unsolvated molecule. Each acetonitrile molecule connects to a crown ether molecule via two of its methyl group H atoms (C—H...O. Weaker interactions exist between the third H atom of the acetonitrile methyl group and an O atom of a neighbouring crown ether molecule (C—H...O; and between the N atom of the acetonitrile molecule and a H atom of another neighbouring crown ether molecule. All these intermolecular interactions create a three-dimensional network stabilizing the disolvate.

  19. Effect of Luting Cement Space on the Strain Response of Gold Crowns Under Static Compressive Loading.

    Science.gov (United States)

    Asbia, S; Ibbetson, R; Reuben, B

    2015-03-01

    The aim the work was to investigate the effect of varying degrees of luting cement thickness on the strain of the cemented gold alloy crowns under compression. Five dies with their corresponding crowns were fabricated using a lost wax technique. Three gold crowns for each die were fabricated under the control of specific die spacer layers to provide a space of 40 µm (10 layers of die-spacer thickness) and 80 µm (20 layers of die-spacer thickness). The crowns were subsequently cemented using zinc phosphate cement. The crowns were subjected to gradual static compressive loading between 10N to 250N (Newton) and the strain measured simultaneously. The results were statistically analysed using Independent t-test for the different die-spacer thickness at the 95% confidence interval (p = 0.05). It was found that a significant relationship in the three thicknesses. It was concluded that the absence of die-spacer significantly reduced strain response, whereas a very little change in the strain recorded as the die spacer layers has increased. Clinically, decreasing the number of die-spacer layers is advantageous as it provides a lower strain response under static compressive loading that would improve the longevity of the cemented full crowns inside the patient's mouth.

  20. Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate.

    Science.gov (United States)

    Gomes, Rafael Soares; Souza, Caroline Mathias Carvalho de; Bergamo, Edmara Tatiely Pedroso; Bordin, Dimorvan; Del Bel Cury, Altair Antoninha

    2017-01-01

    In this study, marginal and internal misfit and fracture load with and without thermal-mechanical aging (TMA) of monolithic ZLS and lithium disilicate (LDS) crowns were evaluated. Crowns were milled using a computer-aided design/computer-aided manufacturing system. Marginal gaps (MGs), absolute marginal discrepancy (AMD), axial gaps, and occlusal gaps were measured by X-ray microtomography (n=8). For fracture load testing, crowns were cemented in a universal abutment, and divided into four groups: ZLS without TMA, ZLS with TMA, LDS without TMA, and LDS with TMA (n=10). TMA groups were subjected to 10,000 thermal cycles (5-55°C) and 1,000,000 mechanical cycles (200 N, 3.8 Hz). All groups were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 1 mm/min until failure. Student's t-test was used to examine misfit, two-way analysis of variance was used to analyze fracture load, and Pearson's correlation coefficients for misfit and fracture load were calculated (α=0.05). The materials were analyzed according to Weibull distribution, with 95% confidence intervals. Average MG (pcrowns. TMA did not affect the fracture load of either material. However, fracture loads of ZLS crowns were lower than those of LDS crowns (pcrowns had lower fracture load values and greater marginal misfit than did LDS crowns, although these values were within acceptable limits.