[Study of strengthening and stress distribution of porcelain jacket crowns constructed with twin foil technique. 2nd report].

McLean and Sced have reported (J Dent Res, 56: 1067-1069, 1977) a procedure for a reinforcement of the porcelain jacket crown, which improved the resistance to a fracture as a result of inhibiting the propagation of cracks into brittle materials, so called the twin foil technique. The purpose of this study is to evaluate the clinical application of this technique. The FEM analysis revealed that the same magnitude of surface tensile stress and no difference of the stress pattern were observed between porcelain jacket crowns constructed with a conventional and the twin foil technique. As the internal tensile stress concentrated in a platinum matrix of the twin foil technique, the stress distribution in a core layer reduced to about 20-35% compared to that of the conventional technique. This is explained by the mechanical and chemical bonds between a platinum matrix and a core porcelain and also by extreme high young's ratio of platinum. We can assume the similar finding from the fractography of the conventional porcelain jacket crown. But contrary above results, no significant differences of the strength were observed in both the presence and the absence of a platinum matrix in the fracture test. From the fact describe above, we may conclude that the tin coated platinum matrix contributes slightly to the strengthening of the porcelain jacket crown.