title: Retentive forces and fatigue resistance of thermoplastic resin clasps.
abstract: OBJECTIVE
  The objective of this study was to evaluate the retentive force of clasps made from three thermoplastic resins and cobalt-chromium (CoCr) alloy by the insertion/removal test simulating 10 years use.
  
  
  METHODS
  On standardized premolar metal crowns 112 clasps were fabricated, including 16 CoCr (1.0 mm thick) clasps and 32 clasps (1.0 or 1.5 mm thick) from each of the following thermoplastic resins: polyetheretherketon (PEEK), polyetherketonketon (PEKK) and polyoxymethylene (POM). Specimens were divided in subgroups with clasp undercuts of 0.25 mm and 0.5 mm, respectively. Each clasp assembly was subjected to an insertion/removal test on its abutment crown for 15,000 cycles. To analyze the retention over the course of insertion/removal test, retention was measured every 1500 cycles. Data were statistically analyzed using 3-way ANOVA (α=0.05).
  
  
  RESULTS
  Resin clasps with 1.5mm thickness showed higher retention (4.9-9.1 N) than clasps with 1.0mm thickness (1.2-3.1 N; P≤0.001). Resin clasps of both dimensions had significantly lower retentive force than CoCr clasps (11.3-16.3 N; P≤0.001). Clasps with 0.25 mm undercut showed significantly less retention than clasps with 0.50 mm (P≤0.001). All clasps exhibited an increase in retentive force during the first period of cycling followed by continuous decrease till the end of the cycling but it was still significantly not different compared to the initial retentive force (P=0.970).
  
  
  CONCLUSIONS
  Thermoplastic resin clasps maintained retention over 15,000 joining and separating cycles with lower retention than CoCr clasps. However, the retention of adequately designed resin clasps might be sufficient for clinical use.
authors: Department of Prosthodontics, Propaedeutics and Dental Materials, Christian-Albrechts University at Kiel, Germany. ftannous@proth.uni-kiel.de
authors: Fahed
authors: F
authors: Tannous
authors: Martin
authors: M
authors: Steiner
authors: Ramez
authors: R
authors: Shahin
authors: Matthias
authors: M
authors: Kern
mesh_terms: D001577:Benzophenones; D002858:Chromium Alloys; D003442:Crowns; D000044:Dental Abutments; D016734:Dental Clasps; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D003799:Dental Stress Analysis; D007659:Ketones; D008422:Materials Testing; D011092:Polyethylene Glycols; D011108:Polymers; D012117:Resins, Synthetic
chemical_list: D001577:Benzophenones; D002858:Chromium Alloys; D007659:Ketones; D011108:Polymers; D012117:Resins, Synthetic; C063834:polyetheretherketone; D011092:Polyethylene Glycols; C010102:delrin