title: Crack initiation on the apical root surface caused by three different nickel-titanium rotary files at different working lengths.
abstract: BACKGROUND
  The aim of this study was to compare the effects of three brands of nickel-titanium (NiTi) rotary files with different designs on the initiation of apical root cracks when working short, at, and beyond the apical foramen.
  
  
  METHODS
  One-hundred eight teeth with straight single canals were selected and mounted on resin blocks with simulated periodontal ligaments, and the apex was exposed. The teeth were divided into 9 groups of 12 teeth according to the NiTi rotary file type used (Profile [Dentsply Maillefer, Ballaigues, Switzerland], K3 [SybronEndo, West Collins, CA], and EndoWave [FKG Dentaire, La-Chaux-de-Fonds, Switzerland]) and working length (at CL, 1 mm short of [CL - 1 mm], and 1 mm beyond [CL + 1 mm] the apical foramen). Digital images of the apical surface of every tooth were taken during the apical enlargement sequence at each file change. These images were compared with the baseline image, and the presence of a crack was noted.
  
  
  RESULTS
  Significantly less cracks were observed in the CL - 1 mm group than in the CL and CL + 1 mm groups. No significant difference was found between the file types used.
  
  
  CONCLUSIONS
  Working 1 mm short of the apical foramen caused less cracks on the apical surface. In addition, more cracks were observed when using larger file sizes. Instrumentation with NiTi rotary files could potentially cause cracks on the apical root surface.
authors.affiliation: Pulp Biology and Endodontics, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. c.adorno.endo@tmd.ac.jp
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Adorno
authors.forename: Takatomo
authors.initials: T
authors.lastname: Yoshioka
authors.forename: Hideaki
authors.initials: H
authors.lastname: Suda
mesh_terms: D003722:Dental Alloys; D003786:Dental Pulp Cavity / Q000293:injuries*; D003804:Dentin / Q000293:injuries; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007180:Incisor / Q000293:injuries; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D013499:Surface Properties; D014025:Titanium; D019227:Tooth Apex / Q000293:injuries*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium