title: Failure of ProTaper rotary Ni-Ti instruments used by undergraduate students.
abstract: OBJECTIVE
  To evaluate the effect of number of uses, angle and radius of curvature and type of instrument on the fracture of ProTaper rotary instruments when used by undergraduate students.
  
  
  METHODS
  Three hundred and seventy-six molars, with a total of 1114 root canals, extracted were instrumented by undergraduate students using ProTaper instruments according to the manufacturer´s recommendations. When fracture occurred, data were collected concerning the number of uses, type of instrument, level of fracture, angle and radius of curvature. ANOVA test were used to determine the influence of type of instrument in the incidence of instrument fracture. Logistic regression model was used to determine the influence of number of uses, angle and radius of curvature in the incidence of instrument fracture. Significance was set at p< 0.05.
  
  
  RESULTS
  A total of 37 Ni-Ti rotary instruments fractured during the treatment. Fracture occurred in 9.84% (37/376) of the teeth treated and 3.32% of the canals prepared with Ni-Ti rotary instruments (37/1114). A decrease in the radius of curvature of the canal significantly increased the likelihood of fracture (p=0.0001). Instrument fracture significantly increased as the number of uses increased (p=0.0037). No significant differences were found between the 6 types of ProTaper instruments (p=0.8). A reduction in the angle of curvature did not produce a significant decrease in the incidence of instrument separation (p=0.08).
  
  
  CONCLUSIONS
  The results of this study imply that instrument fracture is linked to radius of curvature and number of uses. Key words:Fracture, ProTaper ®, root canal preparation, undergraduate students.
authors.affiliation: DDS. Professor of Endodontics. Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Marc
authors.initials: M
authors.lastname: García-Font
authors.affiliation: DDS, PhD. Professor of Endodontics. Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Duran-Sindreu
authors.affiliation: DDS. Professor of Endodontics. Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Morello-Castro
authors.affiliation: DDS, PhD. Professor of Endodontics. Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Mercade-Bellido
authors.affiliation: DDS, PhD. Professor of Endodontics. Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Rufino
authors.initials: R
authors.lastname: Bueno-Martínez
authors.affiliation: DDS, PhD. Professor of Endodontics and Head of Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Universitat Internacional de Catalunya, Barcelona, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Roig-Cayón