title: Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments.
abstract: BACKGROUND
  Recently introduced into the market are shape memory nickel-titanium (NiTi) rotary files. The objective of this study was to investigate the torsion and bending properties of shape memory files (CM Wire, HyFlex CM, and Phoenix Flex) and compare them with conventional (ProFile ISO and K3) and M-Wire (GT Series X and ProFile Vortex) NiTi files.
  
  
  METHODS
  Sizes 20, 30, and 40 (n = 12/size/taper) of 0.02 taper CM Wire, Phoenix Flex, K3, and ProFile ISO and 0.04 taper HyFlex CM, ProFile ISO, GT Series X, and Vortex were tested in torsion and bending per ISO 3630-1 guidelines by using a torsiometer. All data were statistically analyzed by analysis of variance and the Tukey-Kramer test (P = .05) to determine any significant differences between the files.
  
  
  RESULTS
  Significant interactions were present among factors of size and file. Variability in maximum torque values was noted among the shape memory files brands, sometimes exhibiting the greatest or least torque depending on brand, size, and taper. In general, the shape memory files showed a high angle of rotation before fracture but were not statistically different from some of the other files. However, the shape memory files were more flexible, as evidenced by significantly lower bending moments (P < .008).
  
  
  CONCLUSIONS
  Shape memory files show greater flexibility compared with several other NiTi rotary file brands.
authors.affiliation: Department of General Dental Sciences-Dental Biomaterials, Marquette University School of Dentistry, Milwaukee, Wisconsin 53233, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Ninan
authors.forename: David W
authors.initials: DW
authors.lastname: Berzins
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D004548:Elasticity; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry*; D019415:Torque; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium