Analysis of loss of torque in dental implants containing gold washers between implant and screw head

This paper analyzes a novel solution of a dental prosthesis containing a gold washer between the implant and the screw head (made of a titanium alloy, Ti-6Al-4V), and compares its mechanical behavior under variable loading with those observed in two other solutions commonly used in dentistry, one of them having the implant, the abutment and the screw made of a titanium alloy, and the other one having a screw made of pure gold (the implant and the abutment being made of the same titanium alloy). The analysis has consisted in the measurement of the torque loss in the three types of prostheses after the application of a given number of variable loading cycles following ISO protocol 14 801. The investigation has been completed with the scanning electron microscopy (SEM) analysis of the different components after testing.The torque loss in this new solution is very similar to that obtained in the prosthesis containing a gold screw, and 30.7 % lower than that obtained in the prosthesis whose components are all made of a titanium alloy. This behavior can be accounted for by the lower friction between gold and titanium (when compared to titanium-titanium friction), which causes a higher preload in the screw. Also, the SEM analysis has revealed greater damage in Ti-Ti contacts than in Au-Ti contacts, and significant material transfer between the gold washer and the titanium alloy screw. The solution including a gold alloy washer combines low torque loss, as observed in the prosthesis with the gold screw, with the good mechanical (tensile) properties of the solution with the titanium alloy screw, which allows repairs in vivo to be performed more easily.