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Effect of washers on reverse torque displacement of dental implant gold retaining screws
T W Korioth1, A C Cardoso, A Versluis
1Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, MN 55455, USA. korio001@tc.umn.edu
Statement Of The Problem:
Gold screw loosening is a frequent problem that affects dental implants.
Purpose:
This study determined the effect of spring washers on gold screw displacements during applied removal torque in dental implants.
Material And 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.
Conclusion:
Inclusion of a conical spring washer significantly increased the amount of rotational displacement needed to completely loosen an implant gold retaining screw.
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