title: Influence of curvature location along an artificial canal on cyclic fatigue of a rotary nickel-titanium endodontic instrument.
abstract: OBJECTIVE
  This study evaluated the effects of curvature location along an artificial canal on cyclic fatigue (CF) of an Mtwo rotary instrument, verifying the number of cycles to fatigue fracture (NCF) and morphologic characteristics of the fractured instruments.
  
  
  METHODS
  CF testing of instruments was performed in artificial canals with curvature radii of 10 mm and arc lengths of 11 mm. Mtwo rotary instruments size 40, 0.04 taper were used in 2 groups (n = 10): group A, curvature positioned on middle part; group B, apical curvature. All instruments were rotated until fracture. The number of cycles to failure was registered. Data were analyzed by independent sample t test. Fractured surfaces and the helical shafts of the instruments were analyzed by scanning electron microscopy.
  
  
  RESULTS
  NCF for groups A and B had significant statistic differences (P < .05). The highest values were found in the group where the curvature was positioned on the apical part of the canal. No plastic deformation was observed on the helical shafts.
  
  
  CONCLUSIONS
  The number of cycles to fracture of the Mtwo instruments increased when the arc was changed from the middle to the apical part of the canal. The morphologic characteristics of the fractured surfaces were of the ductile type.
authors: Department of Endodontics, Faculty of Dentistry, Estácio de Sá University, Rio de Janeiro, Brazil.
authors: Hélio Pereira
authors: HP
authors: Lopes
authors: Wanderson Miguel Maia
authors: WM
authors: Chiesa
authors: Norbi Rodrigues
authors: NR
authors: Correia
authors: Núbia Carvalho
authors: NC
authors: de Souza Navegante
authors: Carlos Nelson
authors: CN
authors: Elias
authors: Edson Jorge Lima
authors: EJ
authors: Moreira
authors: Bianca Esther Cabral
authors: BE
authors: Chiesa
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D003799:Dental Stress Analysis; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D008422:Materials Testing; D008953:Models, Anatomic; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium