Influence of misfit direction and abutment type on torque loss and fracture strength of implant-supported fixed dental prostheses

Abstract

PURPOSE. This study aimed to evaluate the effects of fatigue and misfit on the reverse torque, load-bearing capacity, and failure modes of cemented and screwretained two-implant-supported fixed dental prostheses (FDPs). MATERIALS AND METHODS. Eighty CAD-CAM zirconia frameworks with porcelain veneering were assigned to three groups based on engaging (E) and non-engaging (N) abutment configurations: N-N, N-E, and E-E. Misfit scenarios included a control cast and 100 µm horizontal or vertical misfits. Frameworks were mounted on implants as screw-retained or cement-retained 3-unit FDPs, forming seven test groups and one control group (n = 10). Reverse torque was measured before and after thermomechanical cycling, followed by maximum failure load (Fmax) testing and failure mode analysis. Fmax was evaluated using two-way ANOVA, and reverse torque using mixed-effects ANOVA accounting for engagement, misfit, and implant position (α = 0.05). RESULTS. No significant differences in Fmax were observed across zirconia specimen groups or engagement configurations under various misfit conditions (P >. 05). Engagement configuration did not significantly impact fracture strength or reverse torque (P =. 421). A significant difference was found in the horizontal misfit group compared to controls (P