title: Cyclic fatigue behavior of nickel-titanium dental rotary files in clinical simulated root canals.
abstract: OBJECTIVE
  Dental rotary instruments can be applied in multiple conditions of canals, but unpredictable fatigue fracture may happen. This study evaluated the fatigue lives of two batches of nickel-titanium (NiTi) dental rotary files operating in clinically simulated root canals.
  
  
  METHODS
  Single-step cyclic fatigue tests were carried out to assess the performance of two batches of NiTi files (ProTaper and ProFile) in nine combinations of simulated canals (cylinder radii 5 mm, 7.5 mm, and 10 mm, and insertion angles 20°, 40°, and 60°). Two-step cyclic fatigue tests were carried out in simulated root canals with the same radius by using the following two sets of insertion angles: (20°, 40°), (20°, 60°), (40°, 20°), and (60°, 20°). Fracture surfaces were observed by scanning electron microscopy.
  
  
  RESULTS
  The single-step cyclic fatigue results showed that cyclic fatigue lives of the files decreased with increasing insertion angles or decreasing cylinder radius. The ProFile #25 .04 file was more fatigue resistant than the ProTaper F2 file. In two-step cyclic fatigue tests, the total fatigue lives were usually more than 100% when the files operated at a lower strain and then at a higher strain. By scanning electron microscopy, a larger area of fatigue striation corresponded to a longer fatigue life.
  
  
  CONCLUSIONS
  Cyclic fatigue life can be influenced by the strains and geometries of files. The fatigue life was prolonged when the files operated at a lower strain and then at a higher strain. However, the fatigue life was shortened if the loading sequence was reversed.
authors.affiliation: Graduate Institute of Clinical Dentistry, School of Dentistry and National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Chih-Wen
authors.initials: CW
authors.lastname: Chi
authors.affiliation: Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Chun-Chieh
authors.initials: CC
authors.lastname: Li
authors.affiliation: Graduate Institute of Clinical Dentistry, School of Dentistry and National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Chun-Pin
authors.initials: CP
authors.lastname: Lin
authors.affiliation: Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan. Electronic address: csshin@ntu.edu.tw.
authors.forename: Chow-Shing
authors.initials: CS
authors.lastname: Shin
mesh_terms: D003799:Dental Stress Analysis; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: cyclic fatigue life; nickel–titanium endodontic instrument; two-step fatigue test