Influence of the coefficient of thermal expansion on the stress distribution in ceramic veneers after thermal simulation

The aim of the study was to evaluate the stress distribution in the ceramic veneers in a full prosthetic crown with different framework after the sintering and cooling cycle through the thermal analysis by three-dimensional finite element analysis. Using images from a computerized microtomography of a central incisor, an anterior crown was constructed. The models were composed of 2mm thickness ceramics (feldspathic ceramics) and 0.4mm thickness frameworks(zirconia, alumina, lithium-disilicate, or metal). Ansys Workbench finite element software was used for analysis and mesh generation through a 5% convergence. The thermal loading was performed in 2 stages simulating the heating and cooling of the ceramic veneer sintering cycle: stage 1 - 403 to 750 degrees C; stage 2 - from 750 to 25 degrees C. The von Mises equivalent strain(σvM) was used for the quantitative and qualitative evaluation of the framework. The maximum (σmax) and minimum (σmin) stresses were used to evaluate the ceramic veneer and zirconia, alumina, and lithium-disilicate frameworks. The highest values of compressive stress (294,58 MPa) were found in the ceramic veneer in the models with alumina framework, followed by models with zirconia (253,65 MPa), palladium silver (239,74 MPa), and lithium disilicate (205,43MPa). The tensile stresses followed the same behavior presenting the highest values in the alumina prostheses (Al: 93,977 MPa, Zr: 76,358 MPa, Ps:68,193 MPa and Ld: 56,573 MPa). The ceramic framework alumina and zirconia cause a higher stress concentration in the ceramic veneers. The stress concentration in the ceramic veneers was affected not only by the coefficient of thermal expansion but also for the mechanical properties of the framework materials.