title: Comparison of cyclic fatigue resistance of used and new RaCe instruments.
abstract: OBJECTIVE
  The aim of this study was to evaluate cyclic fatigue resistance of used and new RaCe rotary nickel-titanium instruments.
  
  
  METHODS
  Forty RaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland) instruments of sizes 30/.06, 30/.02, 25/.04, and 25/.02 were selected and divided into 2 groups: group A = 20 new instruments; group B = 20 used instruments. In group B, each instrument was used for shaping 5 curved molar root canals. Cyclic fatigue testing of new and used instruments was performed using a device that allowed the instruments to rotate freely inside a stainless steel artificial canal. Data were analyzed using t test to determine any statistical significance between used and new instruments of the same file size.
  
  
  RESULTS
  For all sizes, new instruments were more resistant to failure then the used ones (P < .05). A reduction in lifespan was observed ranging from 18% (30/.06) to 51% (25/.02).
  
  
  CONCLUSIONS
  The results showed that clinical use significantly reduced cyclic fatigue resistance of RaCe rotary instruments compared with new ones.
authors.affiliation: Department of Endodontics and Conservative Treatment, Center for Dental Sciences, Gulhane School of Medicine, Ankara, Turkey. cumhuraydin@hotmail.com
authors.forename: Cumhur
authors.initials: C
authors.lastname: Aydin
authors.forename: Ugur
authors.initials: U
authors.lastname: Inan
authors.forename: Yasar M
authors.initials: YM
authors.lastname: Tunca
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003754:Dental High-Speed Equipment; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004868:Equipment Failure; D017743:Equipment Reuse; D006801:Humans; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium