抄録
Porcelain-fused-to-metal (PFM) restorations may develop cracks during processing or in-mouth service if the relative physico-mechanical properties of the porcelain and alloy are highly mismatched. The precise conditions when it might occur are not known. Many processing and property variations can affect the stresses developed throughout a porcelain-alloy system. To understand this, a computer simulation of stress in a PFM strip was conducted. The simulation considers cooling from temperatures higher than the porcelain sag point. The following temperature-dependent factors were incorporated : the elastic modulus, shear viscosity (porcelain), and coefficient of thermal expansion. Cooling rates during tempering of porcelain were measured. The cooling rate dependencies of the glass transition temperature and temperature distribution during cooling were also included in the simulation. The results suggest that tempering with a high cooling rate make up for compressive residual stress in body porcelain and the high curvature of the composite beam.
