title: Influence of torque control motors and the operator's proficiency on ProTaper failures.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the influence of 2 electric torque control motors and operator experience with a specific nickel-titanium rotary instrumentation technique on the incidence of deformation and separation of instruments.
  
  
  METHODS
  ProTaper (PT) nickel-titanium rotary instruments were used at 300 rpm. In the first part of the study, electric high torque control (group 1) and low torque control (group 2) motors were compared. In the second part of the study, 3 operators with varying experience (groups 3, 4, and 5) were also compared. Twenty sets of PT instruments and 100 canals of extracted human molars were used in each group. Each set of PT instruments was used in up to 5 canals and sterilized before each case. For irrigation, 2.5% NaOCl was used. The number of deformed and separated instruments among the groups (within each part of the study) was statistically analyzed for significance with pair-wise comparisons by using the Fisher exact test (alpha =.05).
  
  
  RESULTS
  In part 1, instrument deformation and separation did not occur in groups 1 and 2. In part 2, 25 and 12 instruments were deformed and separated, respectively, with the least experienced operator. Instrument deformation and separation did not occur with the most experienced operator. The Fisher exact test revealed a significant difference between groups 3 and 4 with respect to instrument deformation (P =.0296). In addition, the Fisher exact test revealed that the incidence of instrument deformation was statistically different between groups 3 and 5 (P <.0001) and groups 4 and 5 (P =.0018). The incidence of instrument separation was significantly higher in group 5 than in groups 3 and 4 (P =.001).
  
  
  CONCLUSIONS
  Preclinical training in the use of the PT technique at 300 rpm is crucial to prevent instrument separation and reduce the incidence of instrument deformation. The use of an electric high torque control motor is safe with the experienced operator.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, University of Toronto, Ontario, Canada. g.yared@utoronto.ca
authors.forename: Ghassan
authors.initials: G
authors.lastname: Yared
authors.forename: Fadia
authors.initials: F
authors.lastname: Bou Dagher
authors.forename: Kiran
authors.initials: K
authors.lastname: Kulkarni
mesh_terms: D002983:Clinical Competence; D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D004202:Disinfectants / Q000737:chemistry; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D016555:Matched-Pair Analysis; D008963:Molar; D009532:Nickel / Q000737:chemistry; D012388:Root Canal Irrigants / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D012973:Sodium Hypochlorite / Q000737:chemistry; D013242:Sterilization; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D003722:Dental Alloys; D004202:Disinfectants; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite