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 loosening. Purpose. This in vitro stud! considered an antirotation resistance form with an increased moment arm length as a strategy to increase the net affect of 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) notches placed equidistant around thr periphery!: and (c) Estheticone abutments (1 mm). Crown castings of 2% gold-palladium-based alloy were made using plas tic and resin patterns molded to fit inside a quarter-inch socket wrench. For testing, each specimen consisted of a 15-mm endosseous threaded implant analog, its abutment (20 N force) and crown casting(10 N force) screened together and securely clamped in a vise. A clockwise shear (rotational) force nas applied using a manual torque driver and the torque recorded to failure 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) (standard implant external hex) demonstrated that the smallest moment arm required a significantly smaller dislodging force (21.3 N.cm). Conclusion, These findings suggest that the addition of an,antirotation resistance form increased the length of the moment arm, thereby increasing the effect of preload and reducing the problem of screw loosening..