title: Do NiTi instruments show defects before separation? Defects caused by torsional fatigue in hand and rotary nickel-titanium (NiTi) instruments which lead to failure during clinical use.
abstract: OBJECTIVE
  Visual and microscopic evaluation of defects caused by torsional fatigue in hand and rotary nickel titanium (NiTi) instruments.
  
  
  METHODS
  Ninety-six NiTi greater taper instruments which were routinely used for root canal treatment only in anterior teeth were selected for the study. The files taken include ProTaper for hand use, ProTaper Rotary files and Endowave rotary files. After every use, the files were observed visually and microscopically (Stereomicroscope at 10×) to evaluate the defects caused by torsional fatigue. Scoring was given according to a new classification formulated which gives an indication of the severity of the defect or damage.
  
  
  METHODS
  Data was statistically analyzed using KruskallWallis and Mann-Whitney U test.
  
  
  RESULTS
  Number of files showing defects were more under stereomicroscope than visual examination. But, the difference in the evaluation methods was not statistically significant. The different types of defects observed were bent instrument, straightening/stretching of twist contour and partial reverse twisting. Endowave files showed maximum number of defects followed by ProTaper for hand use and least in ProTaper Rotary.
  
  
  CONCLUSIONS
  Visible defects due to torsional fatigue do occur in NiTi instruments after clinical use. Both visual and microscopic examinations were efficient in detecting defects caused due to torsional fatigue. This study emphasizes that all files should be observed for any visible defects before and after every instrumentation cycle to minimize the risk of instrument separation and failure of endodontic therapy.
authors: Department of Conservative Dentistry and Endodontics, KLR's Lenora Institute of Dental Sciences, Rajahmundry, Andhra Pradesh, India. murali_chnv@yahoomail.com
authors: N V Murali Krishna
authors: NV
authors: Chakka
authors: P
authors: P
authors: Ratnakar
authors: Sanjib
authors: S
authors: Das
authors: Anandamy
authors: A
authors: Bagchi
authors: Sudhir
authors: S
authors: Sudhir
authors: Lavanya
authors: L
authors: Anumula
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D004867:Equipment Design; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D017276:Friction; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium