title: Effect of washers on reverse torque displacement of dental implant gold retaining screws.
abstract: BACKGROUND
  Gold screw loosening is a frequent problem that affects dental implants.
  
  
  OBJECTIVE
  This study determined the effect of spring washers on gold screw displacements during applied removal torque in dental implants.
  
  
  METHODS
  A 3-unit fixed partial denture was cast in semiprecious alloy and fixed to 2 dental implants with gold-retaining screws. Implants were embedded in acrylic resin and restrained from movement. A miniature load sensor was attached to a torque controller handpiece to accurately measure the time and torque needed to completely loosen the gold screws. Rotational displacements were calculated for 4 experimental setups, involving washers placed on (a) both, (b) the mesial, (c) the distal, and (d) no implants. Screw displacement data were compared between implants in all 4 combinations by means of paired t tests.
  
  
  RESULTS
  Gold screws with underlying conical spring washers underwent on average up to 35% (14.1 microm) more rotational displacement during applied removal torque than those without washers.
  
  
  CONCLUSIONS
  Inclusion of a conical spring washer significantly increased the amount of rotational displacement needed to completely loosen an implant gold retaining screw.
authors.affiliation: Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, MN 55455, USA. korio001@tc.umn.edu
authors.forename: T W
authors.initials: TW
authors.lastname: Korioth
authors.forename: A C
authors.initials: AC
authors.lastname: Cardoso
authors.forename: A
authors.initials: A
authors.lastname: Versluis
mesh_terms: D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D003781:Denture Retention / Q000295:instrumentation*; D003830:Denture, Partial, Fixed; D006047:Gold Alloys; D006801:Humans; D019415:Torque
chemical_list: D006047:Gold Alloys