title: Microstructure alterations of rotary files after multiple simulated operative procedures.
abstract: OBJECTIVE
  to assess morphological alterations of ProTaper rotary NiTi files before and after continuous use by scanning electron microscopy (SEM).
  
  
  METHODS
  30 root canals were chosen with an angle between 15 and 30 degrees . Before starting to prepare the canals the files were observed microscopically using a scanning electronic microscope. The ProTaper sequence recommended by the manufacturer was used, with NaOCl as irrigant. The instruments were sterilised after every three canals were shaped. The instruments were observed with the same microscope after shaping each canal, until 30 root canals were shaped. The criteria used for checking the instruments were: blunt cutting edges, disruption of cutting edge, microfractures, fatigue cracks, metal flash, dentine remains.
  
  
  RESULTS
  Many microscopic defects were found such as: cutting edge breaks (up to 70%); fatigue cracks, between 33 and 100%. No microfractures were found. An S1 and an SX file were fractured.
  
  
  CONCLUSIONS
  ProTaper instruments are quite reliable if used following usual requirements.
authors.affiliation: Department of Stomatology, Universitat de València, Valencia, Spain.
authors.forename: Arlinda
authors.initials: A
authors.lastname: Luzi
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Forner
authors.forename: Amelia
authors.initials: A
authors.lastname: Almenar
authors.forename: Carmen
authors.initials: C
authors.lastname: Llena
mesh_terms: D019544:Equipment Failure Analysis; D006801:Humans; D008855:Microscopy, Electron, Scanning; D008963:Molar; D012390:Root Canal Therapy / Q000295:instrumentation*