title: Deformation and fracture of K3 rotary nickel-titanium endodontic instruments after clinical use.
abstract: OBJECTIVE
  The aim was to evaluate the incidence and type of defects that occurred with K3 rotary nickel-titanium instruments during routine clinical use.
  
  
  METHODS
  A total of 2397 K3 (G-PACKS, SybronEndo, West Collins, Orange, CA, USA) instruments were collected from a graduate endodontic clinic over 21 months. All the instruments were limited to a maximum use of 30 canal preparations. The collected instruments were measured by a digital caliper to determine whether any fractures had occurred and then were visually inspected for deformation and fracture under a stereomicroscope. The surfaces of fractured instruments were further evaluated under a scanning electron microscope. Data were analysed using chi-square test and Kruskal-Wallis test.
  
  
  RESULTS
  The incidence of instrument defect was 5.63%, consisting of 3.59% fractures and 2.05% deformations. The defect rates of 0.04 and 0.06 files were statistically higher than the other taper groups (P < 0.003) except for 0.08 files (P > 0.05). For the fractured instruments, 63.95% failed from flexural fatigue, whilst 36.05% failed from torsion.
  
  
  CONCLUSIONS
  Flexural fracture was the major mode of fracture for instruments with larger taper. A routine check for instrument integrity particularly for 0.04 and 0.06 files at high magnification is recommended after each clinical use.
authors.affiliation: Department of Endodontic and Operative Dentistry, Tianjin Stomatological Hospital, Tianjin, China.|State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China.
authors.forename: S M
authors.initials: SM
authors.lastname: Shen
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China.|Department of Oral Biology, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: M
authors.initials: M
authors.lastname: Deng
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China.|Department of Periodontology, Guangdong Provincial Key Laboratory of Stomatology, Guangzhou, China.
authors.forename: P P
authors.initials: PP
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China. chenxinmei61@126.com.|Department of Endodontic and Operative Dentistry, West China Hospital of Stomatology, Chengdu, China. chenxinmei61@126.com.
authors.forename: X M
authors.initials: XM
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China.|Department of Endodontic and Operative Dentistry, West China Hospital of Stomatology, Chengdu, China.
authors.forename: L W
authors.initials: LW
authors.lastname: Zheng
authors.affiliation: Department of Endodontic and Operative Dentistry, West China Hospital of Stomatology, Chengdu, China.
authors.forename: H L
authors.initials: HL
authors.lastname: Li
mesh_terms: D003762:Dental Instruments; D004867:Equipment Design; D004868:Equipment Failure; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation; D013314:Stress, Mechanical; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: K3; instrument failure; nickel-titanium; root canal preparation