Thermal stress analysis by finite elements of a metal-ceramic dental bridge during the cooling phase of a glaze treatment.

In the present paper, a computational finite element analysis (FEA) was developed by using the COMSOL Multiphysics® software to evaluate the thermal accumulated stress on a 3-unit dental ceramic pressed over metal (POM) bridge, at different cooling rates during the glaze treatment. The cooling rates are related to the free opening of the furnace at 800 °C (extreme case) and the restricted opening when the restoration reaches 450 °C (slow case). The thermal expansion coefficients of the materials and the glass transition point of the ceramic were measured experimentally using a dilatometer test. The FEA was performed based on the ceramic temperature profile, which was determined experimentally by using thermocouples type K. When the dental ceramic reaches its transition temperature (Tg) at 510 °C, maximum principal stress at the grooves from the occlusal surface of the pontic are reported as 140 MPa for the slow and 400 MPa for the fast cooling rate. Additionally, it is demonstrated that stresses can be reduced by using low Young's modulus metals and with small differences in the material's thermal expansion coefficient (CTE).