title: Effect of root canal curvature on the failure incidence of ProFile rotary Ni-Ti endodontic instruments.
abstract: OBJECTIVE
  To investigate the effect of root canal curvature on the failure incidence and fracture mechanism of ProFile rotary Ni-Ti endodontic instruments.
  
  
  METHODS
  Three hundred mesial root canals of mandibular molars were instrumented using the ProFile system in a crown-down technique up to size 25 0.06 taper. Root canals were classified according to the angle and radius of curvature to: straight (group A: 0 + 10°, radius 0 mm), moderately curved (group B: 30 ± 10°, radius 2 ± 1 mm) and severely curved (group C: 60 ± 10°, radius 2 ± 1 mm). After each use, instruments were cleaned ultrasonically and autoclaved. Instruments that prepared 20 root canals, fractured or were plastically deformed without fracture were retrieved and substituted. Kaplan-Meier estimator was used for survival analysis and post hoc test for determination of significant differences (a=0.05). All fractured instruments were subjected to fractographic analysis under SEM, and all used instruments were viewed under the metallographic microscope.
  
  
  RESULTS
  Regardless of the size of instrument, fracture and overall failure were significantly more frequent (P<0.05) in group C. SEM examination of the fracture surfaces revealed mainly the characteristic pattern of ductile failure, whereas examination under the metallographic microscope revealed no sign of cracks.
  
  
  CONCLUSIONS
  The abruptness of root canal curvature negatively affected the failure rate of ProFile rotary Ni-Ti instruments. The fractographic results confirmed that failure of Ni-Ti files was caused by a single overload during chemomechanical preparation.
authors.affiliation: Department of Endodontics, School of Dentistry, University of Thessaloniki, Thessaloniki, Greece. elkosti@dent.auth.gr
authors.forename: E
authors.initials: E
authors.lastname: Kosti
authors.forename: S
authors.initials: S
authors.lastname: Zinelis
authors.forename: I
authors.initials: I
authors.lastname: Molyvdas
authors.forename: T
authors.initials: T
authors.lastname: Lambrianidis
mesh_terms: D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D004203:Disinfection / Q000379:methods; D004868:Equipment Failure / Q000706:statistics & numerical data; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D008669:Metallurgy / Q000295:instrumentation; D008853:Microscopy / Q000295:instrumentation; D008855:Microscopy, Electron, Scanning; D008963:Molar / Q000033:anatomy & histology; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D013242:Sterilization / Q000379:methods; D013314:Stress, Mechanical; D013499:Surface Properties; D016019:Survival Analysis; D014025:Titanium / Q000737:chemistry; D014465:Ultrasonics
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium