title: Influence of different manufacturing methods on the cyclic fatigue of rotary nickel-titanium endodontic instruments.
abstract: BACKGROUND
  The aim of this study was to evaluate, by static and dynamic cyclic fatigue tests, the number of cycles to fracture (NCF) 2 types of rotary NiTi instruments: Twisted File (SybronEndo, Orange, CA), which is manufactured by a proprietary twisting process, and RaCe files (FKG Dentaire, La Chaux-de-Fonds, Switzerland), which are manufactured by grinding.
  
  
  METHODS
  Twenty Twisted Files (TFs) and 20 RaCe files #25/.006 taper instruments were allowed to rotate freely in an artificial curved canal at 310 rpm in a static or a dynamic model until fracture occurred.
  
  
  RESULTS
  Measurements of the fractured fragments showed that fracture occurred at the point of maximum flexure in the midpoint of the curved segment. The NCF was significantly lower for RaCe instruments compared with TFs. The NCF was also lower for instruments subjected to the static test compared with the dynamic model in both groups. Scanning electron microscopic analysis revealed ductile morphologic characteristics on the fractured surfaces of all instruments and no plastic deformation in their helical shafts.
  
  
  CONCLUSIONS
  Rotary NiTi endodontic instruments manufactured by twisting present greater resistance to cyclic fatigue compared with instruments manufactured by grinding. The fracture mode observed in all instruments was of the ductile type.
authors: Department of Endodontics, São Leopoldo Mandic, Dental Research Center, Campinas, São Paulo, Brazil.
authors: Renata C V
authors: RC
authors: Rodrigues
authors: Hélio P
authors: HP
authors: Lopes
authors: Carlos N
authors: CN
authors: Elias
authors: Georgiana
authors: G
authors: Amaral
authors: Victor T L
authors: VT
authors: Vieira
authors: Alexandre S
authors: AS
authors: De Martin
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004867:Equipment Design; D004868:Equipment Failure; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium