Stress distribution in photoelastic models of transverse sections of porcelain-fused-to-gold crowns and preparations.

The literature related to stress distribution in porcelain-fused-to-gold restorations and the supporting structures has been reviewed by Craig, El-Ebrashi. and Peyton.1 They used two-dimensional composite photoelastic models to study the stress distribution in labial-lingual and mesial-distal sections of a central incisor that contained a porcelainfused-to-gold or a porcelain crown restoration. The stress distribution was measured as a function of geometric design, position, and magnitude of loading. The various portions of the photoelastic models were constructed of various plastics so that the ratio of the elastic moduli was almost the same as that for porcelain, gold alloy, and human dentin. They found that the porcelain-togold joint near the shoulder should be 300 from the horizontal and that porcelain supported by gold alloy was superior to a porcelain jacket crown. They established that the bulk of gold in the gingival region reduced the state of stress and that the porcelain-to-gold joint on the lingual shoulder should be as far as possible from the usual site of loading. They also found that com-