title: The influence of abutment screw tightening on screw joint configuration.
abstract: BACKGROUND
  Limiting abutment-to-implant hexagonal discrepancies and rotational movement of the abutment around the implant to less than 5 degrees would result in a more stable screw joint. However, the exact relationship after abutment screw tightening is unknown, as is the effect of a counter-torque device in limiting abutment movement during screw tightening.
  
  
  OBJECTIVE
  This study examined the orientation of the abutment hexagon to the implant hexagon after tightening of the abutment screw for several abutment systems with and without the use of a counter-torque device.
  
  
  METHODS
  Thirty conical self-tapping implants (3.75 x 10.0 mm) and 10 wide-platform Brånemark System implants (5.0 x 10.0 mm), along with 10 abutment specimens from the CeraOne, Estheticone, Procera, and AuraAdapt systems, were selected for this investigation. The implants were placed in a holding device prior to tightening of the abutments. When the tightening torque recommended for each abutment system was reached with the use of a torque controller, each implant abutment specimen was removed from the holding device and embedded in a hard resin medium. The specimens were sectioned in a horizontal direction at the level of the hexagons and cleansed of debris prior to examination. The hexagon orientations were assessed as the degree and direction of rotation of the abutment hexagon around the implant hexagon.
  
  
  RESULTS
  The range of the maximum degrees of rotation for all 4 abutment groups tightened with or without the counter-torque device was slightly more than 3.53 degrees. The absolute degrees of rotation for all 4 abutment groups were less than 1.50 degrees with or without the use of the counter-torque device.
  
  
  CONCLUSIONS
  The hexagon-to-hexagon orientation measured as rotational fit on all abutment systems was below the 5 degrees suggested as optimal for screw joint stability. The absolute degrees of rotation for all 4 abutment groups were less than 1.50 degrees regardless of whether the counter-torque device was used.
authors.affiliation: Department of Restorative Dentistry, Division of Prosthodontics, School of Dentistry, University of Colorado, Denver Health Sciences Center, 80262, USA. Lisa.Lang@uchsc.edu
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Lang
authors.forename: Rui-Feng
authors.initials: RF
authors.lastname: Wang
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: May
mesh_terms: D000044:Dental Abutments; D015921:Dental Implants; D017267:Dental Prosthesis Design; D006801:Humans; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque
chemical_list: D015921:Dental Implants