Efeito da espessura oclusal do cimento e da sua união à cerâmica na resistência à fratura de coroas CAD/CAM: método de elementos finitos e testes monotônicos
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Data
2010-10-04
Autores
May, Liliana Gressler [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste estudo avaliou-se a influência da espessura oclusal do cimento e de sua união à cerâmica na resistência à fratura de coroas CAD/CAM. O software COMSOL Multiphysics® foi utilizado para análise de elementos finitos (AEF) em modelos axi-simétricos bidimensionais de coroas de cerâmica vítrea estilizadas, com espessura oclusal de 1,5 mm, cimentadas à troqueis de material análogo à dentina quanto ao módulo elástico e potencial de união à resina composta (NEMA G-10 International Paper, USA). Variou-se as espessuras oclusais de cimento resinoso de 50 a 500 μm. Uma carga de 500 N foi aplicada com um pistão de extremidade circular plana (2 mm de diâmetro) sobre as coroas. A contração de polimerização do cimento foi simulada através de contração térmica. O contato entre cimento e cerâmica foi configurado para “união” e “ausência de união”. O contato cimento-troquel foi sempre do tipo “união”. As tensões dadas pela AEF foram utilizadas para o cálculo de cargas para fratura, levando-se em conta os efeitos deletérios da usinagem e do condicionamento ácido relatados na literatura. As coroas (Mark II, Vita Zhanfabrik, Germany) foram usinadas (CEREC InLab, Sirona, Germany), condicionadas e cimentadas (Multilink Automix, Ivoclar, Lietchstein) à troqueis de NEMA G-10 (n=6). Para a produção de corpos-de-prova na condição “ausência de união”, aplicou-se uma fina película de poli(dimetilsiloxano) 30,000 cSt na superfície interna das coroas. As coroas foram submetidas à carregamento de 5N/s, com pistão de NEMA G-10, de extremidade plana e 2 mm de diâmetro. As fraturas radiais foram detectadas por sensor acústico. A magnitude das tensões resultantes da contração de polimerização dependeram da condição de união à cerâmica e da espessura oclusal de cimento. As cargas médias para fratura (N) de coroas com “união” ao cimento foram...
In this study the influence of the occlusal cement thickness and its bonding to ceramic on the stresses and failure-loads of CAD/CAM crowns were evaluated. The software used for finite element analysis (FEA) was COMSOL Multiphysics®. Bi-dimensional axially symmetric models simulated stylized feldspathic crowns (1.5 mm occlusal thickness) with resin cement layers of 50 μm, 100 μm, 300 μm and 500 μm on dentin analog (NEMA G-10, International Paper, USA) under 500 N loading (2 mm diameter piston). Polymerization shrinkage of the cement layer was simulated as thermal contraction. Ceramic-cement interface was either bonded or not; cement-dentin was always bonded. Stress data were used for load-to-fracture predictions, using literature strengths accounting for milling and acid etching. Mark II® (Vita Zahnfabrik) crowns were milled (Cerec InLab®, Sirona), etched and cemented (Multilink Automix®, Ivoclar) to dentin analogs (NEMA G-10) (n=6). Non-bonding was achieved by applying a thin layer of 30,000 cSt poly(dimethylsiloxane) on the internal surface of the crowns. Crowns were loaded (5N/s) beneath a 2mm flat G-10 piston and radial cracks were detected acoustically. Stress magnitude resulting after cement shrinkage and loading depended on the bonding condition and on the cement thickness. Average failure loads (N) of bonded crowns were: 673.5 N for 50μm-cement thickness and 300.6 N for 500 μm. For non-bonded crowns, failure loads were 308,3 N, for 50 μm cement thickness and 233,3 N, for 500 μm. Bonded crowns presented failure loads at least two times higher than non-bonded, for 50 μm cement thickness, both experimentally and by FEA-based predictions. The benefit of bonding was lost when the cement was thicker than 500 μm. The resistance to fracture decreased with the cement thickness. Calculated loads based on FEA stresses and experimental data were comparable for the evaluate... (Complete abstract click electronic access below)
In this study the influence of the occlusal cement thickness and its bonding to ceramic on the stresses and failure-loads of CAD/CAM crowns were evaluated. The software used for finite element analysis (FEA) was COMSOL Multiphysics®. Bi-dimensional axially symmetric models simulated stylized feldspathic crowns (1.5 mm occlusal thickness) with resin cement layers of 50 μm, 100 μm, 300 μm and 500 μm on dentin analog (NEMA G-10, International Paper, USA) under 500 N loading (2 mm diameter piston). Polymerization shrinkage of the cement layer was simulated as thermal contraction. Ceramic-cement interface was either bonded or not; cement-dentin was always bonded. Stress data were used for load-to-fracture predictions, using literature strengths accounting for milling and acid etching. Mark II® (Vita Zahnfabrik) crowns were milled (Cerec InLab®, Sirona), etched and cemented (Multilink Automix®, Ivoclar) to dentin analogs (NEMA G-10) (n=6). Non-bonding was achieved by applying a thin layer of 30,000 cSt poly(dimethylsiloxane) on the internal surface of the crowns. Crowns were loaded (5N/s) beneath a 2mm flat G-10 piston and radial cracks were detected acoustically. Stress magnitude resulting after cement shrinkage and loading depended on the bonding condition and on the cement thickness. Average failure loads (N) of bonded crowns were: 673.5 N for 50μm-cement thickness and 300.6 N for 500 μm. For non-bonded crowns, failure loads were 308,3 N, for 50 μm cement thickness and 233,3 N, for 500 μm. Bonded crowns presented failure loads at least two times higher than non-bonded, for 50 μm cement thickness, both experimentally and by FEA-based predictions. The benefit of bonding was lost when the cement was thicker than 500 μm. The resistance to fracture decreased with the cement thickness. Calculated loads based on FEA stresses and experimental data were comparable for the evaluate... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Resistência à tração, Cimentos de resina, Carga para fratura, Análise de elementos finitos, Testes monotônicos, Resin cement, Ceramics, Finite element analysis
Como citar
MAY, Liliana Gressler. Efeito da espessura oclusal do cimento e da sua união à cerâmica na resistência à fratura de coroas CAD/CAM: método de elementos finitos e testes monotônicos. 2010. 171f. Tese (doutorado) – Universidade Estadual Paulista , Faculdade de Odontologia de São Jose dos Campos, 2010.