title: Fatigue testing of controlled memory wire nickel-titanium rotary instruments.
abstract: BACKGROUND
  To improve the fracture resistance of nickel-titanium (NiTi) files, manufacturers have introduced new alloys to manufacture NiTi files and developed new manufacturing processes. This study was aimed to examine the fatigue behavior of NiTi instruments from a novel controlled memory NiTi wire (CM Wire).
  
  
  METHODS
  Instruments of ProFile, Typhoon (TYP), Typhoon CM (TYP CM), DS-SS0250425NEYY (NEYY), and DS-SS0250425NEYY CM (NEYY CM) (DS Dental, Johnson City, TN) all size 25/.04 were subjected to rotational bending at the curvature of 35° and 45° in air at the temperature of 23° ± 2°C, and the number of revolutions to fracture (N(f)) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. The crack-initiation sites, the percentage of dimple area to the whole fracture cross-section, and the surface strain amplitude (ε(a)) were noted.
  
  
  RESULTS
  The new alloy yielded an improvement of over three to eight times in N(f) of CM files than that of conventional NiTi files (P < .05). The vast majority of CM instruments (50%-92%) showed multiple crack origins, whereas most instruments made from conventional NiTi wire (58%-100%) had one crack origin. The values of the fraction area occupied by the dimple region were significantly smaller on CM NiTi instruments compared with conventional NiTi instruments (P < .01). The square (NEYY CM) versus the triangular (TYP CM) configuration showed a significantly different lifetime on CM wire at both curvatures (P < .01).
  
  
  CONCLUSIONS
  The material property had a substantial impact on fatigue lifetime. Instruments made from CM Wire had a significantly higher N(f) and lower surface strain amplitude than the conventional NiTi wire files with identical design.
authors.affiliation: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada.
authors.forename: Ya
authors.initials: Y
authors.lastname: Shen
authors.forename: Wei
authors.initials: W
authors.lastname: Qian
authors.forename: Houman
authors.initials: H
authors.lastname: Abtin
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.forename: Markus
authors.initials: M
authors.lastname: Haapasalo
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004867:Equipment Design; D004868:Equipment Failure; D008422:Materials Testing; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D013314:Stress, Mechanical; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium