Visco-elastic deformation of dental porcelain and porcelain-metal compatibility.

A computer simulation using a visco-elastic stress analysis was conducted to clarify the effect of the heating rate on deformation temperature of dental porcelain during firing. In this simulation, the following temperature-dependent factors were incorporated: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling/heating rate dependencies of both the glass-transition temperature and the temperature distribution in the slab were also included. Thermal expansion curves of porcelain with an applied load at various heating rates were computed. Effects of the applied stress and the heating rate on the deformation temperature of porcelain were revealed. The results suggest that the temperature where the incompatibility stress develops in the porcelain-fused-to-metal strips during cooling can be estimated closely from the deformation point of the heating curve of the porcelain with an applied stress of about 1.2 approximately 3.1 MPa. A method for measuring temperature dependence of viscosity as represented by an Arrhenius equation is proposed.