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 Brånemark 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 1.0 x 10(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).
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 Brånemark 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 1.0 x 10(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).
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