Stress distribution in porcelain-fused-to-gold crowns and preparations constructed with photoelastic plastics.

Extensive restorations of single anterior teeth are accomplished by using porcelain jacket crowns or porcelain enamel or plastic veneer restorations supported by an alloy restoration that is luted to the tooth. The porcelain jacket crown has the advantage that less tooth tissue must be removed, but the material is brittle and lacks impact strength. Studies by McLean",2 have shown that these restorations can be improved considerably by the use of alumina-reinforced porcelain and he estimates an 80% improvement in the flexural strength of these materials. Porcelain-fused-to-metal restorations increased in popularity as a result of the development of low-fusing porcelain enamels with coefficients of thermal expansion similar to those of the supporting metal. The development of higher melting gold alloys that did not decrease in hardness with repeated firing also was an important advance.3 The bond strength developed between porcelain enamels and gold alloys has received considerable attention,4-6 and although there is some question regarding whether it is a van der Waals bond or a