title: Effect from Rotational Speed on Torsional Resistance of the Nickel-titanium Instruments.
abstract: BACKGROUND
  The purpose of this study was to evaluate differences in torsional resistance using up-regulated speed of rotational spindle.
  
  
  METHODS
  Three NiTi rotary instrument systems were selected in this study: K3XF (SybronEndo, Glendora, CA), BLX (B&L Biotech, Ansan, Korea), and OneShape (MicroMega, Besançon, France). The tip size and taper for all files were #25 and 0.06. Experimental groups (n = 10/group) were assigned to 2-, 60-, 350-, and 600-rpm groups by the rotational speed of spindle. Forty new files were used for each test. The file tip of 5-mm length was secured between brass plates. While keeping the file straight, it was rotated clockwise at a constant rotational speed until fracture occurred. The parameters of torsional resistance, torsional load (Ncm), and distortion angle (°) were measured using an AEndoS-k (DMJ System, Busan, Korea), and the toughness until fracture was computed from these data. The 1-way analysis of variance test was used to analyze the torsional resistance at a significance level of 95%. All fractured fragments were observed under a scanning electron microscope to evaluate the topographic features of the fractured surfaces.
  
  
  RESULTS
  No significant difference in torsional resistance was found among groups when they were compared for ultimate strength at the maximum torque, fracture angle, and toughness. Scanning electron microscopic examination of the fractured cross-sectional surfaces revealed typical features of torsional fractures, concentric abrasion marks, and fibrous dimples from the torsional center.
  
  
  CONCLUSIONS
  Under the conditions of the study, the torsional resistances of the rotary instruments were not affected by the rotational speed.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors.forename: Jung-Hong
authors.initials: JH
authors.lastname: Ha
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea.
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Kwak
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors.forename: Sung Kyo
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Department of Endodontics, New York University College of Dentistry, New York, New York.
authors.forename: Asgeir
authors.initials: A
authors.lastname: Sigurdsson
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
authors.forename: Hyeon-Cheol
authors.initials: HC
authors.lastname: Kim
mesh_terms: D004868:Equipment Failure; D008422:Materials Testing; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: D009532:Nickel; D014025:Titanium
keywords: Instrument fracture; nickel-titanium rotary file; rotational speed; test methods; torsional resistance