title: An in vitro analysis of implant screw torque loss with external hex and internal connection implant systems.
abstract: OBJECTIVE
  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).
  
  
  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 <or= 0.05).
  
  
  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.
authors.affiliation: Department of Restorative Dentistry, New Jersey Dental School, Newark, NJ 07101, USA.
authors.forename: Jack
authors.initials: J
authors.lastname: Piermatti
authors.forename: Hoda
authors.initials: H
authors.lastname: Yousef
authors.forename: Allyn
authors.initials: A
authors.lastname: Luke
authors.forename: Richard
authors.initials: R
authors.lastname: Mahevich
authors.forename: Saul
authors.initials: S
authors.lastname: Weiner
mesh_terms: D003442:Crowns; D000044:Dental Abutments; D015921:Dental Implants; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D006801:Humans; D008422:Materials Testing; D013499:Surface Properties; D019415:Torque
chemical_list: D015921:Dental Implants