title: The effects of loading on the preload and dimensions of the abutment screw for a 3-unit cantilever-fixed prosthesis design.
abstract: OBJECTIVE
  The purpose of this study was to use an in vitro model system to compare the effects on the screw torque and screw dimensions within 2 commercially available implant systems from occlusal loading on a cantilevered-fixed partial denture.
  
  
  METHODS
  Cantilevered implant-supported 3-unit prostheses with 2 premolar abutments and 1 premolar pontic (7.3 mm in length) were made on resin casts containing 2 implant analogs for 2 implant systems: BioLok Silhouette Tapered Implant System (Birmingham, AL) and Zimmer Tapered Screw-Vent Implant System (Carlsbad, CA) with 10 samples in each group. Each sample was loaded with either of 2 protocols: (1) a load of 50 N on the cantilevered pontic unit and (2) a loading of 150 N on all 3 units. The outcome measures were (1) changes in residual torque of the abutment screws and (2) changes in screw dimension.
  
  
  RESULTS
  The BioLok Silhouette Tapered Implant group demonstrated slight but statistically significant torque loss 18.8% to 28.5% in both abutment screws for both protocols, P ≤ 0.05, without any changes in screw dimension. In the Zimmer Tapered Screw-Vent Implant group, there was a significant elongation of the abutment screws and a markedly significant 44.4%, (P ≤ 0.01) loss in torque in the mesial screw and a 28.5%, (P ≤ 0.05) loss in torque in the distal screw when the cantilever alone was loaded.
  
  
  CONCLUSIONS
  Differences in screw design influence the maintenance of preload and distortion of the shank. The influence of the interface design, namely an internal hex of 1 mm versus an external hex did not influence the preload. Cantilevered prostheses can cause loss of torque and dimensional changes in abutment screws.
authors.affiliation: Restorative Dentistry, University of California at San Francisco, San Francisco, CA, USA.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Setia
authors.forename: Hoda
authors.initials: H
authors.lastname: Yousef
authors.forename: David
authors.initials: D
authors.lastname: Ehrenberg
authors.forename: Allyn
authors.initials: A
authors.lastname: Luke
authors.forename: Saul
authors.initials: S
authors.lastname: Weiner
mesh_terms: D002484:Cementation / Q000379:methods; D003442:Crowns; D059605:Dental Implant-Abutment Design; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis / Q000295:instrumentation; D003779:Denture Design; D003830:Denture, Partial, Fixed; D004548:Elasticity; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008422:Materials Testing; D018715:Microscopy, Video; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque