Implant Retaining Screws: Effect of Using Gold/Titanium on Preload

An implant supported prostheses relies on the integrity of the screw joint to ensure predictable long term outcomes. Incorrect preloads on  retaining screws can result in either loosening or fracture of the screw. The aim of this study was to compare the preload in the dental implant body–abutment complex using either gold or titanium retaining screws and to assess the changes in preload generation after repeated torque applications.

Methods:  The in vitro test consisted of an anchored implant body, and a cylindrical transmucosal abutment which was attached with either a gold or a titanium retaining screw. Torques of 20Ncm, 32Ncm and 40Ncm were applied to the retaining screws to investigate the preload generated in both metals as well as the effect of applying torque beyond the manufacturers’ recommended 32Ncm.

Results: Gold retaining screws achieved consistently higher  preload values than titanium retaining screws. Gold retaining screws have a higher modulus of elasticity and the metal being “softer” than titanium results in higher preload values being generated for them. Preload values were not significantly different from the first to the tenth torque cycle. Titanium screws showed more consistent preload values, albeit lower than those of gold retaining screws. However, owing to possible galling of the internal thread of the implant body by titanium screws, gold screws remain the retaining screw of choice.  After ten torque cycles were applied to each screw there was an insignificant change in preload generated in both titanium and gold screws. This study was therefore inconclusive with regards to maintenance protocols.

Conclusions: Gold retaining screws generated better preload values than titanium, and the implant complex was more stable when torqued beyond the manufacturers’ recommendations of 32 Ncm. Further investigation into repeated torque application is required, to determine ideal maintenance protocols.