Critical Bending Moment of 4 Implant-Abutment Interface Designs

Clinical overload leading to excessive bending moment has been reported as a major cause of implant prosthetic component failure.  Critical Bending Moment (CBM) has been defined as the bending moment at which applied non-axial load overcomes screw joint preload, causing loss of contact between mating surfaces of implant screw joint components.  At this point, all external load will be instantaneously taken up by the screw shank, rapidly leading to screw failure. Objectives: This study investigated the CBM of 4 different systems' regular diameter fixture-abutment interfaces, measured at 80%, 100% and 120% of manufacturers' recommended torque levels. Methods: Strain-gauged abutments were loaded vertically (L) at distance x mm from fixture-abutment interfaces and microstrain (με) dynamically logged using a HP VEE Pro 6.2 program, with a Series B HP 75000 VXI multimeter and HP E1357 FET multiplexers, to determine gap-opening. Sample size for each system was 5 and measurements of CBM repeated 5 times. Results: Critical Bending Moment, Ncm (SD)

(*superscript letters indicate statistical subsets)

Two-way ANOVA showed significant differences (P<0.5) in CBM between implant systems (F=290.591) and torque levels (F=414.437).  Subsequent multiple one-way ANOVA and Tukey HSD post hoc tests confirmed that significant differences existed between all applied torque levels for each implant system except Lifecore system.  Conclusions: CBM in most implant systems was correlated to applied torque levels.  To ensure screw joint integrity under functional loading, manufacturers' recommended torque levels should be followed. This study was supported by NUS Research Grant R-224-000-010-112