title: Effect of environment on fatigue failure of controlled memory wire nickel-titanium rotary instruments.
abstract: BACKGROUND
  This study examined the fatigue behavior of 2 types of nickel-titanium (NiTi) instruments made from a novel controlled memory NiTi wire (CM wire) under various environment conditions.
  
  
  METHODS
  Three conventional superelastic NiTi instruments of ProFile (Dentsply Maillefer, Ballaigues, Switzerland), Typhoon (Clinician's Choice Dental Products, New Milford, CT), and DS-SS0250425NEYY (Clinician's Choice Dental Products) and 2 new CM wire instruments of Typhoon CM and DS-SS0250425NEYY CM were subjected to rotational bending at the curvature of 35° in air, deionized water, 17% EDTA, or deionized water after immersion in 6% sodium hypochlorite for 25 minutes, and the number of revolutions of fracture (N(f)) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. The crack-initiation sites and the percentage of dimple area to the whole fracture cross-section were noted.
  
  
  RESULTS
  Two new CM Wire instruments yielded an improvement of >4 to 9 times in N(f) than conventional NiTi files with the same design under various environments (P < .05). The fatigue life of 3 conventional superelastic NiTi instruments was similar under various environments, whereas the N(f) of 2 new CM Wire instruments was significantly longer in liquid media than in air (P < .05). The vast majority of CM instruments showed multiple crack origins, whereas most instruments made from conventional NiTi wire had one crack origin. The values of the area fraction occupied by the dimple region were significantly smaller on CM NiTi instruments than in conventional NiTi instruments under various environments (P < .05).
  
  
  CONCLUSIONS
  Within the limitations of this study, the type of NiTi metal alloy (CM files vs conventional superelastic NiTi files) influences the cyclic fatigue resistance under various environments. The fatigue life of CM instruments is longer in liquid media than in air.
authors.affiliation: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, British Columbia, 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: D000388:Air; D055598:Chemical Phenomena; D003722:Dental Alloys / Q000737:chemistry* / Q000145:classification; D004492:Edetic Acid / Q000737:chemistry; D004548:Elasticity; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry* / Q000145:classification; D018583:Pliability; D012388:Root Canal Irrigants / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D012973:Sodium Hypochlorite / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry* / Q000145:classification; D014867:Water / Q000737:chemistry
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; D014867:Water; C040654:titanium nickelide; D009532:Nickel; D004492:Edetic Acid; D014025:Titanium; D012973:Sodium Hypochlorite