title: Cyclic Fatigue Resistance and Fractographic Analysis of Race and Protaper Rotary NiTi Instruments.
abstract: BACKGROUND
  This study investigated the fatigue and fracture modes of RaCe and ProTaper rotary instruments.
  
  
  METHODS
  Fatigue resistance was evaluated by rotating the files 30° or 60° and with 2 or 5mm radius of curvature. RaCe taper 06 size 25 and ProTaper F1 files (n=40) were used. The number of rotations to failure was analyzed by two-way ANOVA and independent sample t-test. Fracture surfaces were examined under a scanning electron microscope.
  
  
  RESULTS
  Both files exhibited significantly more resistance to fracture when angle severity was reduced and increase in curvature radius (P=0.000). ProTaper demonstrated higher number of cycle of failure (P=0.0029) in one group (r=5mm, 60º). SEM observation revealed fatigue mark/features in 17 specimens, shear characteristics in 37 samples, and tensile overload in 26 samples.
  
  
  CONCLUSIONS
  Radius of curvature was the main factor in torsional and fatigue failures.
authors.affiliation: Department of Endodontics, Dental School, Islamic Azad University of Medical sciences, Tehran, Iran.
authors.forename: Shahram
authors.initials: S
authors.lastname: Azimi
authors.forename: Parisa
authors.initials: P
authors.lastname: Delvari
authors.forename: Hamid Cyrus
authors.initials: HC
authors.lastname: Hajarian
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Saghiri
authors.forename: Kasra
authors.initials: K
authors.lastname: Karamifar
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Lotfi
keywords: Cyclic Fatigue; Fractographic Analysis; Rotary NiTi Instrument; Torsional Failure