title: Influence of multiple clinical use on fatigue resistance of ProTaper rotary nickel-titanium instruments.
abstract: OBJECTIVE
  To examine the influence of clinical use on the occurrence of deformation and fracture and on the fatigue resistance of ProTaper rotary instruments.
  
  
  METHODS
  Root canal treatments were performed on patients using the ProTaper rotary system. Ten sets of instruments were used by an experienced endodontist, each set in five molars. Another 10 sets of instruments were used by the same operator, each set in eight molars. In addition, 10 sets of instruments were used, each set in five molars, by undergraduate students with no clinical experience with the system. After clinical use, S1, S2, F1 and F2 instruments were analysed for damage by optical and scanning electron microscopy. The used sets, along with a control group of 12 sets of new instruments, were then tested in a bench device for fatigue resistance.
  
  
  RESULTS
  The use of the ProTaper rotary instruments by an experienced endodontist allowed for the cleaning and shaping of the root canal system of up to eight molars without fracture. During the students work, six instruments fractured. Fatigue resistance decreased upon clinical use for all instruments analysed.
  
  
  CONCLUSIONS
  Fatigue resistance of used instruments was reduced, but no significant change was observed amongst the instruments used for shaping the canals of five and eight molars. Operator experience affected the occurrence of fracture and plastic deformation during shaping.
authors.affiliation: Department of Restoration Dentistry, Faculty of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: E P
authors.initials: EP
authors.lastname: Vieira
authors.forename: E C
authors.initials: EC
authors.lastname: França
authors.forename: R C
authors.initials: RC
authors.lastname: Martins
authors.forename: V T L
authors.initials: VT
authors.lastname: Buono
authors.forename: M G A
authors.initials: MG
authors.lastname: Bahia
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D004708:Endodontics / Q000193:education; D004867:Equipment Design; D004868:Equipment Failure; D017743:Equipment Reuse; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013335:Students, Dental; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium