title: Comparative evaluation of cyclic fatigue resistance of D-RaCe and ProTaper retreatment instruments in curved artificial canals.
abstract: OBJECTIVE
  To compare the cyclic fatigue resistance of D-RaCe and ProTaper rotary nickel-titanium (NiTi) retreatment files when used in curved artificial canals.
  
  
  METHODS
  A total of 120 new D-RaCe DR2 and ProTaper D3 retreatment files were tested in stainless steel artificial canals having 45° and 60° angles of curvature. Thirty instruments of each of the file systems were tested in both angles of curvature (n = 30). The retreatment instruments were rotated until fracture to calculate the number of cycles to failure. The length of each fractured fragment was recorded. Data were analysed by independent sample t-test. Fractured surfaces of the instruments were analysed by scanning electron microscopy.
  
  
  RESULTS
  In the canal with 45° angle of curvature, no significant difference was observed between the retreatment systems (P > 0.05); on the other hand, in the canal with 60° angle of curvature, D-RaCe DR2 instruments had greater cyclic fatigue resistance than ProTaper D3 (P < 0.05). No difference was observed between the retreatment instruments regarding the lengths of fractured fragments (P > 0.05). The fracture surfaces of the instruments had morphologic characteristics of ductile fracture.
  
  
  CONCLUSIONS
  D-RaCe DR2 instrument exhibited greater cyclic fatigue resistance than ProTaper D3 only in root canals with 60° angle of curvature.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: H S
authors.initials: HS
authors.lastname: Topçuoğlu
authors.affiliation: Department of Pedodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: G
authors.initials: G
authors.lastname: Topçuoğlu
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey.
authors.forename: A
authors.initials: A
authors.lastname: Aktı
mesh_terms: D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000601:surgery; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006801:Humans; D008855:Microscopy, Electron, Scanning; D018915:Root Canal Preparation / Q000295:instrumentation*
keywords: cyclic fatigue; nickel-titanium; retreatment