Influence of misfit direction and abutment type on torque loss and fracture strength of implant-supported fixed dental prostheses
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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 screw-retained 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 < .001). Reverse torque values differed between distal (13.5 ± 0.5 Ncm) and mesial implants (18.6 ± 0.5 Ncm) (P = .000), suggesting distal implants may be more prone to preload loss and mechanical issues. CONCLUSION. The engagement configuration of implants did not significantly affect reverse torque, fracture strength, or failure modes of cemented and screw-retained restorations, although horizontal misfit reduced load-bearing capacity.
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 screw-retained 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 < .001). Reverse torque values differed between distal (13.5 ± 0.5 Ncm) and mesial implants (18.6 ± 0.5 Ncm) (P = .000), suggesting distal implants may be more prone to preload loss and mechanical issues. CONCLUSION. The engagement configuration of implants did not significantly affect reverse torque, fracture strength, or failure modes of cemented and screw-retained restorations, although horizontal misfit reduced load-bearing capacity.