title: Incidence of apical root cracks and apical dentinal detachments after canal preparation with hand and rotary files at different instrumentation lengths.
abstract: BACKGROUND
  The aim of this study was to compare the incidence of apical root cracks and dentinal detachments after canal preparation with hand and rotary files at different instrumentation lengths.
  
  
  METHODS
  Two hundred forty mandibular incisors were mounted in resin blocks with simulated periodontal ligaments, and the apex was exposed. The root canals were instrumented with rotary and hand files, namely K3, ProTaper, and nickel-titanium Flex K files to the major apical foramen (AF), short AF, or beyond AF. Digital images of the apical surface of every tooth were taken during the apical enlargement at each file change. Development of dentinal defects was determined by comparing these images with the baseline image. Multinomial logistic regression test was performed to identify influencing factors.
  
  
  RESULTS
  Apical crack developed in 1 of 80 teeth (1.3%) with hand files and 31 of 160 teeth (19.4%) with rotary files. Apical dentinal detachment developed in 2 of 80 teeth (2.5%) with hand files and 35 of 160 teeth (21.9%) with rotary files. Instrumentation with rotary files terminated 2 mm short of AF and did not cause any cracks. Significantly less cracks and detachments occurred when instrumentation with rotary files was terminated short of AF, as compared with that terminated at or beyond AF (P < .05). The AF deviated from the anatomic apex in 128 of 240 teeth (53%). Significantly more apical dentinal detachments appeared in teeth with a deviated AF (P = .033).
  
  
  CONCLUSIONS
  Rotary instruments caused more dentinal defects than hand instruments; instrumentation short of AF reduced the risk of dentinal defects.
authors.affiliation: Department of Endodontics, Capital Medical University School of Stomatology, Beijing, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Liu
authors.forename: Anjali
authors.initials: A
authors.lastname: Kaiwar
authors.forename: Hagay
authors.initials: H
authors.lastname: Shemesh
authors.forename: Paul R
authors.initials: PR
authors.lastname: Wesselink
authors.forename: Benxiang
authors.initials: B
authors.lastname: Hou
authors.forename: Min-Kai
authors.initials: MK
authors.lastname: Wu
mesh_terms: D004396:Coloring Agents; D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000293:injuries*; D003804:Dentin / Q000293:injuries*; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007180:Incisor / Q000293:injuries; D008334:Mandible / Q000473:pathology; D008422:Materials Testing; D008751:Methylene Blue; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation*; D012399:Rotation; D014025:Titanium / Q000737:chemistry; D019227:Tooth Apex / Q000293:injuries*; D019415:Torque
chemical_list: D004396:Coloring Agents; D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D008751:Methylene Blue