title: Cyclic fatigue of ProFile rotary instruments after prolonged clinical use.
abstract: OBJECTIVE
  The purpose of the present study was to evaluate resistance to cyclic fatigue of new and used ProFile Ni-Ti rotary instruments.
  
  
  METHODS
  Used instruments were operated in 10 clinical cases using passive instrumentation and a crown-down preparation technique. Cyclic fatigue testing of new and used engine-driven instruments was then performed with a specific device which allowed the instruments to rotate freely inside a stainless steel artificial canal, whilst maintaining conditions close to the clinical situation. Instruments were rotated until fracture occurred and time to fracture was visually recorded with a chronometer.
  
  
  RESULTS
  A significant reduction of rotation time to breakage (life span) was noted between new and used instruments. In all sizes new instruments were significantly more resistant than used ones (two-sample t-test, P < 0.01). No instrument underwent intracanal failure during clinical use.
  
  
  CONCLUSIONS
  Prolonged clinical use of Ni-Ti engine-driven instruments significantly reduced their cyclic fatigue resistance. Nevertheless, each rotary instrument was successfully operated in up to 10 clinical cases without any intracanal failure.
authors.affiliation: Department of Periodontics-Endodontics, Faculty of Dentistry, University of La Sapienza, Rome, Italy. ggambarini@tin.it
authors.forename: G
authors.initials: G
authors.lastname: Gambarini
mesh_terms: D003755:Dental High-Speed Technique; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004868:Equipment Failure; D017743:Equipment Reuse; D006801:Humans; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium