Douglas Fabris1, Júlio C M Souza2, Filipe S Silva3, Márcio Fredel1, Michael Gasik4, Bruno Henriques5. 1. Ceramic and Composite Materials Research Group (CERMAT), Federal University of Santa Catarina (UFSC), Campus Trindade, Florianópolis, SC, Brazil. 2. CMEMS-UMinho, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal; School of Dentistry (DODT), Post-Graduation Program in Dentistry (PPGO), Federal University of Santa Catarina, Campus Trindade, 88040-900, Florianópolis, SC, Brazil. 3. CMEMS-UMinho, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal. 4. Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University Foundation, 00076 Aalto, Espoo, Finland. 5. Ceramic and Composite Materials Research Group (CERMAT), Federal University of Santa Catarina (UFSC), Campus Trindade, Florianópolis, SC, Brazil; CMEMS-UMinho, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal; School of Dentistry (DODT), Post-Graduation Program in Dentistry (PPGO), Federal University of Santa Catarina, Campus Trindade, 88040-900, Florianópolis, SC, Brazil. Electronic address: brunohenriques@dem.uminho.pt.
Abstract
OBJECTIVES: Thermal cycling is widely used to simulate the aging of restorative materials corresponding to the changes of temperature in the oral cavity. However, test parameters present in literature vary considerably, which prevents comparison between different reports. The aim of this work is to assess the influence of the specimens' geometry and materials on the thermal stresses developed during thermal cycling tests. MATERIALS AND METHODS: Finite elements method was used to simulate the conditions of thermal cycling tests for three different sample geometries: a three-points bending test sample, a cylinder rod and more complex shape of a restoration crown. Two different restorative systems were considered: all-ceramic (zirconia coupled with porcelain) and metal-ceramic (CoCrMo alloy coupled with porcelain). The stress state of each sample was evaluated throughout the test cycle. RESULTS: The results show that the sample geometry has great influence on the stress state, with difference of up to 230% in the maximum stress between samples of the same composition. The location of maximum stress also changed from the interface between materials to the external wall. CONCLUSIONS: Maximum absolute stress values were found to vary between 2 and 4MPa, which might not be critical even for ceramics. During multi-cycle testing these stresses would cause different fatigue in various locations. The zirconia-based specimens and zirconia-based restoration (crown) exhibited the most similar stress states. Thus it might be recommended to use these geometries for fast screening of the materials for this type of restorations. CLINICAL SIGNIFICANCE: The selection of specimens' geometry and materials should be carefully considered when aging conditions close to clinical ones want to be simulated.
OBJECTIVES: Thermal cycling is widely used to simulate the aging of restorative materials corresponding to the changes of temperature in the oral cavity. However, test parameters present in literature vary considerably, which prevents comparison between different reports. The aim of this work is to assess the influence of the specimens' geometry and materials on the thermal stresses developed during thermal cycling tests. MATERIALS AND METHODS: Finite elements method was used to simulate the conditions of thermal cycling tests for three different sample geometries: a three-points bending test sample, a cylinder rod and more complex shape of a restoration crown. Two different restorative systems were considered: all-ceramic (zirconia coupled with porcelain) and metal-ceramic (CoCrMo alloy coupled with porcelain). The stress state of each sample was evaluated throughout the test cycle. RESULTS: The results show that the sample geometry has great influence on the stress state, with difference of up to 230% in the maximum stress between samples of the same composition. The location of maximum stress also changed from the interface between materials to the external wall. CONCLUSIONS: Maximum absolute stress values were found to vary between 2 and 4MPa, which might not be critical even for ceramics. During multi-cycle testing these stresses would cause different fatigue in various locations. The zirconia-based specimens and zirconia-based restoration (crown) exhibited the most similar stress states. Thus it might be recommended to use these geometries for fast screening of the materials for this type of restorations. CLINICAL SIGNIFICANCE: The selection of specimens' geometry and materials should be carefully considered when aging conditions close to clinical ones want to be simulated.