title: Safety of the factory preset rotation angle of reciprocating instruments.
abstract: BACKGROUND
  This study aimed to investigate the torsional resistance of 2 reciprocating nickel-titanium instruments (Reciproc [VDW, Munich, Germany] and WaveOne [Dentsply Maillefer, Ballaigues, Switzerland]) operated at the maximum rotating angle in a proprietary motor.
  
  
  METHODS
  With the file tip secured at various levels (3, 4, or 5 mm) of Reciproc R25 and WaveOne Primary, the distortion angles and torsional loads were monitored during counterclockwise movement at 2 rpm until fracture (n = 10 at each level) for a load-distortion graph. The rotation angles and loads at the beginning point of the plateau, the ultimate torsional strength, final fracture angle, and toughness were determined. The data were analyzed using 1-way analysis of variance and the Tukey post hoc test at α = .05. The lateral longitudinal aspect and the fracture cross-section of each specimen were examined by scanning electron microscopy after the test.
  
  
  RESULTS
  The rotation angle at the beginning point of the plateau was significantly greater for a binding site farther away from the tip of the instrument for both systems (P < .05), and all were greater than 170° (preset in the dedicated motor from manufacturer). The ultimate strength and toughness also increased significantly at levels farther away from the instrument tip (P < .05). All specimens showed typical topographic features of torsional fracture, including the circular abrasion marks and fibrous dimples near the rotation center after the test.
  
  
  CONCLUSIONS
  It was determined that the 2 brands of reciprocating files are safe when operated at the rotational angle in the proprietary motor.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea.
authors.forename: Jin-Woon
authors.initials: JW
authors.lastname: Kim
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: Area of Endodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Gary Shun-Pan
authors.initials: GS
authors.lastname: Cheung
authors.affiliation: Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, Memphis, Tennessee.
authors.forename: Antheunis
authors.initials: A
authors.lastname: Versluis
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea.
authors.forename: Sang-Won
authors.initials: SW
authors.lastname: Kwak
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
authors.forename: Hyeon-Cheol
authors.initials: HC
authors.lastname: Kim
mesh_terms: D003722:Dental Alloys / Q000737:chemistry; D004867:Equipment Design; D004868:Equipment Failure; D004869:Equipment Safety; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Distortion; Reciproc; WaveOne; reciprocating nickel-titanium file; torsional resistance