An in vitro analysis of implant screw torque loss with external hex and internal connection implant systems.

Purpose: The purpose of this study was to examine, in a controlled environment, effects of connection design upon screw stability. Implant fixtures have 2 types of connections to the abutment: internal connection and external hex. Four implant systems were tested: Bio-Lok (external hex; Bio-Lok International, Inc., Deerfield Beach, FL); Zimmer (internal connection; Zimmer Dental, Carlsbad, CA); Nobel Biocare (external hex; Nobel Biocare USA, Inc., Yorba Linda, CA); and Astra Tech (internal connection; Astra Tech Inc., Waltham, MA).

Materials And Methods: Ten samples of each system, including base, implant, abutment, and molar crown, were loaded to 200 N for 1 x 10(6) cycles. Screws were tightened to manufacturers' recommendations,and torque audits done at 2.5 x 10(5), 5 x 10(5), 7.5 x 10(5), and 1 x 10(6) cycles.

Results: The Bio-Lok samples lost an average of 10% of the original torque values, the Astra Tech group lost almost all of the torque and loosened, while the Zimmer and Nobel Biocare samples lost an average of 50% of the torque but did not loosen (P
Conclusions: It may be concluded from this study that although internal connections are clinically favored, this study did not show any advantage relative to screw loosening. However, screw design may be a significant factor in loosening of the joint.