Dynamic Fatigue Performance of Implant-abutment Assembles with Different Torque Values

Objectives: To evaluate the effect of dynamic fatigue loading on the reverse torque value of dental implant system with different tightening torque value in vitro. Methods: Thirty bone level implant assembles (Zimmer Dental, Carlsbad, CA, USA) were randomly assigned to three tightening groups (less than recommended torque, 24Ncm; recommended torque, 30Ncm; and more than recommended torque, 36Ncm). Each group consisted of 10 implants. Five implant assembles from each group were unscrewed after 3 hours, reverse torque values were recorded. The remaining specimens were subjected to fatigue test according to ISO14081:2007 guidelines. A compressive cyclic sine wave load between 30N and 300N at a loading frequency of 15Hz was applied for 5×10⁶cycles. Residual reverse torque values were recorded after fatigue testing. Scanning electron microscope (SEM) micrographs were obtained from the fractured implant. Results: Implant assembles tested under fatigue loading presented torque loss. A statistical significant difference (p<0.05) was found between unloaded and loaded groups. In the 24Ncm tightening group, all the implant and abutment screw fractured at the first outer thread of implant after loading, SEM observation showed fatigue crack propagation at the fractured surface. Conclusions: Within the limitations of this in vitro study, the following conclusions could be drawn. Fatigue load decreased the reverse torque value of abutment screw. Insufficient torque may lead to poor fatigue performance of dental implant systems, and abutment screw should be tightened to the torque recommended by the manufacturer to prevent mechanical complications.