title: Cyclic fatigue testing and metallographic analysis of nickel-titanium rotary instruments.
abstract: BACKGROUND
  The aim of this study was to compare cyclic fatigue resistance of four nickel-titanium rotary systems and to evaluate their surface, fractographic, and matrix morphology.
  
  
  METHODS
  Four models of endodontic rotary files (EasyShape [Komet/Gebr. Brasseler, Lemgo, Germany], ProTaper [Dentsply Maillefer, Ballaigues, Switzerland], NRT [MANI Inc, Toshigi-Ken, Japan], and AlphaKite [Komet/Gebr. Brasseler]) were subjected to fatigue testing in artificial canals with angle of curvature of 45° and 60° and a radius of curvature of 5 mm until fracture occurred. Nickel-titanium (NiTi) alloy properties were investigated by light microscopy, environmental scanning electron microscopy (ESEM), and energy dispersive x-ray spectrophotometry (EDS). ESEM analysis was conducted on new files to examine surface characteristics and on fractured samples to identify the crack origin and the fractographic features.
  
  
  RESULTS
  Analysis of variance testing revealed significant differences (P < .001) among the groups. NRT files had the highest fatigue resistance followed by AlphaKite, EasyShape, and ProTaper. All the new files presented surface imperfections. Fractographic analysis found the crack initiation to originate at the level of surface irregularities. Optical microscope inspection of the NiTi alloy matrix disclosed different-sized nonmetallic inclusions among models. EDS analysis of these inclusions showed that they were composed of carbon and oxygen in addition to nickel and titanium. Under light microscopy, austenitic grains appeared larger near the handle and smaller near the tip in all instruments.
  
  
  CONCLUSIONS
  NRT files presented the longest fatigue life. All samples showed surface irregularities and nonmetallic inclusions. Austenitic grains were smaller near the tip than near the handle. The angle of curvature was confirmed to influence the fatigue life of NiTi instruments.
authors.affiliation: Department of Dental Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy. chiara.pirani4@unibo.it
authors.forename: Chiara
authors.initials: C
authors.lastname: Pirani
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Cirulli
authors.forename: Stefano
authors.initials: S
authors.lastname: Chersoni
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Micele
authors.forename: Oddone
authors.initials: O
authors.lastname: Ruggeri
authors.forename: Carlo
authors.initials: C
authors.lastname: Prati
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D003799:Dental Stress Analysis; D004867:Equipment Design; D004868:Equipment Failure; D008422:Materials Testing; D008669:Metallurgy; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium