Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system

Statement of problem. Efforts to reduce the recurrence of abutment screw loosening with single tooth implant-supported restorations have been reported. However, the current knowledge about the role of the implant external hexagon is incomplete. Purpose. This in vitro study investigated the effect of lateral cyclic loading with different load positions on abutment screw loosening of an external hexagon implant system. Material and methods. Fifteen Branemark implant assemblies were divided equally into 3 groups, A, B, and C. Each assembly consisted of a Mark IV implant (4 X 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant, whereas for group B, the same load was applied eccentrically (at a distance of 4 mm) in a loosening direction. A target of 1.0x10(6) cycles (40 months of simulated function) was defined. Group C (control) was left unloaded for the same loading time period as groups A and B. Reverse torque was recorded before and after loading and the difference was calculated. The data were analyzed with 1-way analysis of variance and compared with the Tukey test (alpha=.05). Results. Group A exhibited a significant difference in the reverse torque difference values ([-5.6 to -3.4] +/- 0.86 N(.)cm) compared with groups B ([-1.9 to 0.5] +/- 0.99 N(.)cm) and C ([-0.7 to 0.0] +/- 0.26 N(.)cm) (P<.001). Groups B and C were not significantly different from each other. Conclusion. Within the limitations of this study, reverse torque values of the screw joint were preserved under eccentric lateral loading, as compared with centric loading (P<.001).