Effect of Metal Design on Fracture Resistance of Implant-supported Crowns

Objective: This study evaluated the fracture resistance of different metal substructure designs for implant-supported porcelain-fused-to-metal (PFM) crowns. Methods: A total of eighteen PFM crowns were fabricated using different metal substructure designs (Group A: minimum thickness required, Group B: conventional, and Group C: wrinkled design) and were conventionally cemented on implant abutment analogs. The specimens were subjected to cyclic loading with 200 N at 2 Hz for300,000 times before fracture resistance testing using compression load on the buccal functional cusp. One-way ANOVA and Tukey's test for multiple comparisons were performed to test for differences in fracture resistance values among groups. Results: The mean fracture resistance value of group A, B and C was 1089.07±266.07 N, 2314.07±384.26 N, and 1848.57±118.58 N respectively. There were statistically significant differences found for the fracture resistance comparison between Group B and C (p < 0.05) and highly significant differences were found when Group A was compared with Group B or C (p < 0.01). Conclusions: The results show that the conventional design has the maximum fracture resistance, and the over-thickness of the porcelain layer has lower fracture resistance strength. As regards the wrinkled design, the present experiment did not respond to the ideal result of this design. Therefore the theory that the wrinkled design can provide better support needs further corroboration.