The effect of two marginal designs (chamfer and shoulder) on the fracture resistance of all ceramic restorations, Inceram: An in vitro study

BACKGROUND AND AIM: One of the major problems of all ceramic restorations is their probable fracture against the occlusal force. The aim of the present in vitro study is to compare the effect of two marginal designs (shoulder and chamfer) on the fracture resistance of all ceramic restorations, INCERAM. MATERIALS AND METHODS: On an extracted first maxillary premolar 50 in. chamfer margin (0.7 mm) was prepared. Ten impressions were taken using a polyvinylsiloxane. The impressions were poured with epoxy resin to fabricate dies. The same tooth was retrieved and 50 in. chamfer was converted into 90 in. shoulder (1 mm). Ten impressions were taken and ten more epoxy resin dies were fabricated. Impressions of each epoxy resin die were taken using polyvinylsiloxane impression material and poured with die stone. Alumina cores with 0.5 mm thickness fabricated on the stone dies in a dental laboratory. The alumina cores were then cemented on the epoxy resin dies and underwent a fracture test with a universal testing machine and samples were investigated from the point of view of the origin of the failure. RESULT: The mean value of fracture resistance for the chamfer samples were 610.18 ± 58.79 N and 502.72 ± 105.83 N for the shoulder samples. The Student's t-test revealed a statistically significant difference between groups. CONCLUSION: The result of this study indicates a relationship between the marginal design of the alumina cores and their fracture resistance. A chamfer margin could improve the biomechanical performance of posterior single crown alumina restorations. This may be because of the strong unity in the chamfer margin.