title: Operator-induced compressive axial forces during implant gold screw fastening.
abstract: BACKGROUND
  The gold screw of an implant is put under tension during fastening. An increase in operator-induced compressive axial force during fastening may diminish screw tension, lower the friction between the screw threads, and allow for increased tightening torque.
  
  
  OBJECTIVE
  This study was undertaken to assess and compare the compressive axial forces and torques placed simultaneously on implant gold screws by persons with varying degrees of expertise.
  
  
  METHODS
  A calibrated electric torque driver was used to fasten implant gold screws. Three groups of operators with various levels of implant experience (faculty [F; n = 4], prosthodontic residents [R; n = 4], and undergraduate dental students [S; n = 6]) were asked to repeatedly tighten and loosen a new gold abutment screw into a standard 3.75-mm diameter Branemark abutment. Compressive axial forces during torquing were assessed over the tightening time by means of a miniature load cell adapted to the electric torque driver. Each operator repeated the experiment 3 times after calibration. Within operator and between operator reliability were evaluated.
  
  
  RESULTS
  Loosening compressive axial forces were always higher than tightening compressive axial forces, and peak torque was less on loosening than tightening. Faculty placed a smaller range of forces on the screws (mean = 3.29 N, SD +/- 1.45 N) than did the residents (mean = 2.74 N, SD +/- 1.96) or the students (mean = 3.01 N, SD +/- 2.54).
  
  
  CONCLUSIONS
  The clinical experience of operators seems to influence their application of compressive axial force during gold screw tightening. Less torque during unfastening of gold screws seems to be related to increased axial loading.
authors.affiliation: School of Dentistry and Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis 55455, USA. pesun001@tc.umn.edu
authors.forename: I J
authors.initials: IJ
authors.lastname: Pesun
authors.forename: M E
authors.initials: ME
authors.lastname: Brosky
authors.forename: T W
authors.initials: TW
authors.lastname: Korioth
authors.forename: J
authors.initials: J
authors.lastname: Hodges
authors.forename: B J
authors.initials: BJ
authors.lastname: Devoe
mesh_terms: D000704:Analysis of Variance; D002138:Calibration; D000044:Dental Abutments; D003758:Dental Implantation, Endosseous / Q000295:instrumentation / Q000379:methods*; D015921:Dental Implants; D017267:Dental Prosthesis Design; D005179:Faculty, Dental; D017276:Friction; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007396:Internship and Residency; D015588:Observer Variation; D011476:Prosthodontics / Q000193:education; D013314:Stress, Mechanical; D013335:Students, Dental; D019415:Torque; D016474:Weight-Bearing
chemical_list: D015921:Dental Implants; D006047:Gold Alloys