title: Impact of heat treatments on the fatigue resistance of different rotary nickel-titanium instruments.
abstract: BACKGROUND
  The aim of this study was to assess the influence of M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK) and controlled memory technologies on the fatigue resistance of rotary nickel-titanium (NiTi) files by comparing files made using these 2 technologies with conventional NiTi files.
  
  
  METHODS
  Files with a similar cross-sectional design and diameter were chosen for the study: new 30/.06 files of the EndoWave (EW; J. Morita Corp, Osaka, Japan), HyFlex (HF; Coltene/Whaledent, Inc, Cuyahoga Falls, OH), ProFile Vortex (PV; Dentsply Tulsa Dental Specialties, Tulsa, OK), and Typhoon (TYP; Clinician's Choice Dental Products, New Milford, CT) systems together with ProTaper Universal F2 instruments (PTU F2; Dentsply Maillefer, Ballaigues, Switzerland). The compositions and transformation temperatures of the instruments were analyzed using x-ray energy-dispersive spectroscopy and differential scanning calorimetry, whereas the mean file diameter values at 3 mm from the tip (D3) were measured using image analysis software. The average number of cycles to failure was determined using a fatigue test device.
  
  
  RESULTS
  X-ray energy-dispersive spectroscopy analysis showed that, on average, all the instruments exhibited the same chemical composition, namely, 51% Ni-49% Ti. The PV, TYP, and HF files exhibited increased transformation temperatures. The PTU F2, PV, and TYP files had similar D3 values, which were less than those of the EW and HF files. The average number of cycles to failure values were 150% higher for the TYP files compared with the PV files and 390% higher for the HF files compared with the EW files.
  
  
  CONCLUSIONS
  M-Wire and controlled memory technologies increase the fatigue resistance of rotary NiTi files.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Lígia Carolina Moreira
authors.initials: LC
authors.lastname: Braga
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Ana Cristina
authors.initials: AC
authors.lastname: Faria Silva
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil. Electronic address: vbuono@demet.ufmg.br.
authors.forename: Vicente Tadeu Lopes
authors.initials: VT
authors.lastname: Buono
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Maria Guiomar
authors.initials: MG
authors.lastname: de Azevedo Bahia
mesh_terms: D002152:Calorimetry, Differential Scanning; D003722:Dental Alloys / Q000032:analysis / Q000737:chemistry*; D004867:Equipment Design; D004868:Equipment Failure; D006358:Hot Temperature; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008422:Materials Testing; D008669:Metallurgy; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000032:analysis / Q000737:chemistry*; D010087:Oxides / Q000032:analysis; D010781:Photography / Q000379:methods; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000032:analysis / Q000737:chemistry*; D044366:Transition Temperature
chemical_list: D003722:Dental Alloys; D010087:Oxides; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D009532:Nickel; D014025:Titanium
keywords: Controlled memory; M-Wire; fatigue resistance; heat treatment; nickel-titanium endodontic instruments; transformation temperatures