title: Effect of autoclave sterilization on the cyclic fatigue resistance of thermally treated Nickel-Titanium instruments.
abstract: OBJECTIVE
  To compare the cyclic fatigue resistance of HyFlex CM, Twisted Files (TF), K3XF, Race, and K3, and evaluate the effect of autoclave sterilization on the cyclic fatigue resistance of these instruments both before and after the files were cycled.
  
  
  METHODS
  Five types of NiTi instruments with similar size 30, .06 taper were selected: HyFlex CM, TF, K3XF, Race and K3. Files were tested in a simulated canal with a curvature of 60° and a radius of 3 mm. The number of cycles to failure of each instrument was determined to evaluate cyclic fatigue resistance. Each type of instruments was randomly divided into four experimental groups: group 1 (n = 20), unsterilized instruments; group 2 (n = 20), pre-sterilized instruments subjected to 10 cycles of autoclave sterilization; group 3 (n = 20), instruments tested were sterilized at 25%, 50% and 75% of the mean cycles to failure as determined in group 1, and then cycled to failure; group 4 (n = 20), instruments cycled in the same manner as group 3 but without sterilization. The fracture surfaces of instruments were examined by scanning electron microscopy (SEM).
  
  
  RESULTS
  HyFlex CM, TF and K3XF had significantly higher cyclic fatigue resistance than Race and K3 in the unsterilized group 1 (P < 0.05). Autoclave sterilization significantly increased the MCF of HyFlex CM and K3XF (P < 0.05) both before and after the files were cycled. SEM examination revealed a typical pattern of cyclic fatigue fracture in all instruments.
  
  
  CONCLUSIONS
  HyFlex CM, TF and K3XF instruments composed of new thermal-treated alloy were more resistant to fatigue failure than Race and K3. Autoclaving extended the cyclic fatigue life of HyFlex CM and K3XF.
authors.affiliation: Department of Operative Dentistry and Endodontics, School and Hospital of Stomatology, Wuhan University, Wuhan, China.
authors.forename: D
authors.initials: D
authors.lastname: Zhao
authors.affiliation: Division of Endodontics, Department of Oral Biological & Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, BC, Canada.|Department of Materials Engineering, The University of British Columbia, Vancouver, BC, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Department of Operative Dentistry and Endodontics, School and Hospital of Stomatology, Wuhan University, Wuhan, China. phs301@vip.163.com.
authors.forename: B
authors.initials: B
authors.lastname: Peng
authors.affiliation: Division of Endodontics, Department of Oral Biological & Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, BC, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Haapasalo
mesh_terms: D003762:Dental Instruments; D004867:Equipment Design; D004868:Equipment Failure; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D013242:Sterilization; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: NiTi instrument; autoclave sterilization; cyclic fatigue; thermal treated