Effect of an antirotation resistance form on screw loosening for single implant-supported crowns

Statement of problem. The gold screw of the single tooth implant-supported restoration has frequently been reported to exhibit the problem of screw lo osening. Purpose. This in vitro stud! considered an antirotation resistance form wit h an increased moment arm length as a strategy to increase the net affect o f the retaining screw preload. Material and methods. Three groups examined included (a) standard abutments (3 mm), (b) modified standard abutments(3 mm) with 1 milled (1 x 1 mm) not ches placed equidistant around thr periphery!: and (c) Estheticone abutment s (1 mm). Crown castings of 2% gold-palladium-based alloy were made using p las tic and resin patterns molded to fit inside a quarter-inch socket wrenc h. For testing, each specimen consisted of a 15-mm endosseous threaded impl ant analog, its abutment (20 N force) and crown casting(10 N force) screene d together and securely clamped in a vise. A clockwise shear (rotational) f orce nas applied using a manual torque driver and the torque recorded to fa ilure of thr gold screw or loosening of the abutment screw. Results. Analysis revealed that the dislodging force for groups (b) and. (c ) was similar (69.6 and 71.0 N.cm cm, respectively), whereas group (a) (sta ndard implant external hex) demonstrated that the smallest moment arm requi red a significantly smaller dislodging force (21.3 N.cm). Conclusion, These findings suggest that the addition of an,antirotation res istance form increased the length of the moment arm, thereby increasing the effect of preload and reducing the problem of screw loosening..