title: Effect of repeated closures on opening torque values in seven abutment-implant systems.
abstract: BACKGROUND
  Implant abutment screw joints tend to loosen under clinical conditions. During impression and prosthesis fabrication, repeated clinical closing and opening of abutment screws may cause component wear and decrease frictional fit of the mating parts, resulting in altered resistance to opening and potential for loss of preload in function.
  
  
  OBJECTIVE
  This study recorded changes in opening torque values due to multiple consecutive closures at a constant torque within and between different abutment/implant (A/I) systems.
  
  
  METHODS
  Repeated opening-closing cycles were used to simulate in vitro embedment relaxation and component wear of 7 A/I systems from 5 manufacturers. Screw opening torque values were recorded up to 200 consecutive closures at 20 N/cm.
  
  
  RESULTS
  A progressive decrease in opening torque values was measured in all implant systems. Significant differences were found between A/I systems. Systems with morse tapered and spline connections consistently maintained a higher resistance to opening force. Percentage torque loss ranged from 3% to 20% on immediate opening, and from 4.5% to 36% for average of first 30 opening/closing cycles.
  
  
  CONCLUSIONS
  Repeated opening and closing of implant abutment screws caused progressive loss of torque retention with variations between systems. This was probably due to a decrease in the coefficient of friction between the mating components.
authors.affiliation: The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel-Aviv University, Tel Aviv, Israel. ervinw@post.tau.ac.il
authors.forename: E I
authors.initials: EI
authors.lastname: Weiss
authors.forename: D
authors.initials: D
authors.lastname: Kozak
authors.forename: M D
authors.initials: MD
authors.lastname: Gross
mesh_terms: D000704:Analysis of Variance; D000044:Dental Abutments; D015921:Dental Implants; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D003799:Dental Stress Analysis; D017276:Friction; D006801:Humans; D016014:Linear Models; D018709:Statistics, Nonparametric; D013674:Technology, Dental / Q000379:methods; D019415:Torque
chemical_list: D015921:Dental Implants