Preload, Coefficient of Friction, and Thread Friction in an Implant-Abutment-Screw Complex

Purpose: To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. Materials and Methods: In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Results: Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. Conclusion: These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.