title: Measurements of Repeated Tightening and Loosening Torque of Seven Different Implant/Abutment Connection Designs and Their Modifications: An In Vitro Study.
abstract: OBJECTIVE
  Repeated tightening and loosening of the abutment screw may alter its mechanical and physical properties affecting the optimal torque and ultimate reliability of an implant/abutment connection. The purpose of this study was to evaluate the effect of repeated tightening and loosening of implant/abutment screws on the loosening torque of implant/abutment connections of commercially available implant systems.
  
  
  METHODS
  Seven different implant/abutment connections and their modifications were tested. The screws of each system were tightened according to the manufacturer's specifications. After 20 minutes the screws were loosened. This procedure was repeated ten times, and the differences between the 1st and 10th cycle were expressed as a percentage change RTq(%) and correlated with initial torque, the number of threads, the length of shank, and thread surface area employing Spearman's analysis.
  
  
  RESULTS
  All systems showed significant differences in residual torque (RTq) value (p < 0.05) between the 1st and 10th cycle except groups 6 and 11 (p > 0.05). All connections but group 3 (p = 1.000) showed a significant change from the initial torque (ITq) to the RTq values. The first successive RTq values increased in two connection groups 1 and 2. The remaining connections showed reduced RTq values ranging from -1.2 % (group 5) to -23.5% (group 6). The RTq values declined gradually with every repeated tightening in groups 1, 2, 3, 8, 9, 11, 12. In group 2, after the tenth tightening the RTq was still above the ITq value. Only length of shank demonstrated a correlation with the RTq(%) change over the successive tightening loosening cycles (p < 0.05).
  
  
  CONCLUSIONS
  Repeated tightening and loosening of implant/abutment screws caused varying torque level changes among the different systems. These observations can probably be attributed to connection design.
  
  
  CONCLUSIONS
  Limiting the number of tightening/loosening cycles in clinical and laboratory procedures is advisable for most of the implant systems tested.
authors.affiliation: Boston University, Goldman School of Dental Medicine.
authors.forename: Alena
authors.initials: A
authors.lastname: Butkevica
authors.affiliation: Boston University, Goldman School of Dental Medicine.
authors.forename: Dan
authors.initials: D
authors.lastname: Nathanson
authors.affiliation: Boston University, Goldman School of Dental Medicine.
authors.forename: Richard
authors.initials: R
authors.lastname: Pober
authors.affiliation: Boston University, Goldman School of Dental Medicine.
authors.forename: Herman
authors.initials: H
authors.lastname: Strating
mesh_terms: D000044:Dental Abutments; D059605:Dental Implant-Abutment Design / Q000009:adverse effects / Q000379:methods; D015921:Dental Implants; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D019415:Torque
chemical_list: D015921:Dental Implants
keywords: Dental implants; connecting screw loosening; implant-abutment connection design