title: [Fracture of ProTaper rotary instrument with analysis on influential factors].
abstract: OBJECTIVE
  To evaluate the fracture of ProTaper rotary instrument clinically, and analyze the influential factors.
  
  
  METHODS
  A total of 432 patients who underwent root canal therapy were selected from our endodontic clinic between September 2008 and September 2009. ProTaper rotary instrument was used to achieve root canal preparation, the number and size of fracture instruments, the position of treated tooth were recorded. The data was analyzed by SPSS17.0 software package for Fisher's exact test.
  
  
  RESULTS
  There were a total of 27 fractured ProTaper rotary instruments, with a fracture rate of 10%. Twenty-one fractured instruments were fatigue fracture and 6 were torsion fracture. Statistical analysis indicated that SX, S1, F1 were more likely to fracture than other sizes. Vast majority of instrument fracture occurred in molar root canals. The fracture rate was significantly increased after the number of prepared canal exceeded 20 times.
  
  
  CONCLUSIONS
  From this study,we conclude that ProTaper rotary instrument is more likely to fracture when preparing molar canals, instruments of particular size (SX S1 FI) with higher fracture rate should be used with great care in clinic. The times of using each ProTaper file should be less than 20 in consideration of safety. Supported by Natural Science Foundation of Shandong Province (Grant No.Y2006C48).
authors.affiliation: Department of Endodontics,Dental School of Shandong University, Shandong Provincial Key Laboratory of Oral Biomedicine. Jinan 250012, Shandong Province, China. marvin2322@126.com
authors.forename: Hong-wei
authors.initials: HW
authors.lastname: Ma
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
authors.forename: Li-li
authors.initials: LL
authors.lastname: Wang
mesh_terms: D003722:Dental Alloys; D004868:Equipment Failure; D006801:Humans; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation; D012390:Root Canal Therapy; D014025:Titanium
chemical_list: D003722:Dental Alloys; D009532:Nickel; D014025:Titanium