title: Elastic limits in torsion of reciprocating nickel-titanium instruments.
abstract: BACKGROUND
  Reciprocating angle and torsional load at the superelastic limit were investigated for nickel-titanium (NiTi) instruments used with reciprocating movements.
  
  
  METHODS
  Two reciprocating NiTi instruments (Reciproc R25 [VDW, Munich, Germany] and WaveOne Primary [Dentsply Maillefer, Ballaigues, Switzerland]) and ProTaper F2 (Dentsply Maillefer) were tested for 2 torsional conditions using a custom-designed testing device. Rotational angles were applied, and generated torque values were recorded. The first test condition fixed the files at 5 mm and repetitively rotated them with gradually increasing angles up to 250° (n = 10). The second test subjected the files to a single continuous rotation until fracture (n = 10). The superelastic limits of the instruments were determined from their torque-rotation curves. Statistical analysis was performed (Kruskal-Wallis) at a 95% significance level. The tested specimens were examined under a scanning electron microscope.
  
  
  RESULTS
  It was found that the angle at the superelastic limit was higher for R25 and Primary files than the ProTaper file (P < .05). Repetitive torsional loading with a gradually increasing rotational angle reduced the torsional resistance compared with the single rotation motion. At the 5-mm fixation level all files had superelastic limit angles higher than the 170° set in the dedicated reciprocating motor. The scanning electron microscopic analysis showed features of torsional failure.
  
  
  CONCLUSIONS
  Under the conditions of this study, the 170° set angle of dedicated motors for reciprocating file systems is safe at the 5-mm level. Reuse of reciprocating systems, even with the movements within the elastic limit, may cause deterioration of the instruments.
authors: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors: Jung-Hong
authors: JH
authors: Ha
authors: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea.
authors: Seo-Ryeong
authors: SR
authors: Kim
authors: Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, Memphis, Tennessee.
authors: Antheunis
authors: A
authors: Versluis
authors: Area of Endodontics, Faculty of Dentistry, University of Hong Kong, Hong Kong SAR, China.
authors: Gary Shun-Pan
authors: GS
authors: Cheung
authors: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea.
authors: Jin-Woon
authors: JW
authors: Kim
authors: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
authors: Hyeon-Cheol
authors: HC
authors: Kim
mesh_terms: D004869:Equipment Safety; D006801:Humans; D008422:Materials Testing; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Distortion angle; Reciproc; WaveOne; elastic limit; reciprocating nickel-titanium file; torsional resistance