title: The incidence of root microcracks caused by 3 different single-file systems versus the ProTaper system.
abstract: BACKGROUND
  The aim of this study was to compare the incidence of root cracks observed at the apical root surface and/or in the canal wall after canal instrumentation with 3 single-file systems and the ProTaper system (Dentsply Maillefer, Ballaigues, Switzerland).
  
  
  METHODS
  One hundred mandibular incisors were selected. Twenty control teeth were coronally flared with Gates-Glidden drills (Dentsply Maillefer). No further preparation was made. The other 80 teeth were mounted in resin blocks with simulated periodontal ligaments, and the apex was exposed. They were divided into 4 experimental groups (n = 20); the root canals were first coronally flared with Gates-Glidden drills and then instrumented to the full working length with the ProTaper, OneShape (Micro-Mega, Besancon, France), Reciproc (VDW, Munich, Germany), or the Self-Adjusting File (ReDent-Nova, Ra'anana, Israel). The apical root surface and horizontal sections 2, 4, and 6 mm from the apex were observed under a microscope. The presence of cracks was noted. The chi-square test was performed to compare the appearance of cracked roots between the experimental groups.
  
  
  RESULTS
  No cracks were found in the control teeth and teeth instrumented with the Self-Adjusting File. Cracks were found in 10 of 20 (50%), 7 of 20 (35%), and 1 of 20 (5%) teeth after canal instrumentation with the ProTaper, OneShape, and Reciproc files, respectively. The difference between the experimental groups was statistically significant (P < .001).
  
  
  CONCLUSIONS
  Nickel-titanium instruments may cause cracks on the apical root surface or in the canal wall; the Self-Adjusting File and Reciproc files caused less cracks than the ProTaper and OneShape files.
authors.affiliation: Department of Endodontics, Capital Medical University School of Stomatology, Beijing, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Liu
authors.forename: Ben Xiang
authors.initials: BX
authors.lastname: Hou
authors.forename: Paul R
authors.initials: PR
authors.lastname: Wesselink
authors.forename: Min-Kai
authors.initials: MK
authors.lastname: Wu
authors.forename: Hagay
authors.initials: H
authors.lastname: Shemesh
mesh_terms: D003722:Dental Alloys / Q000737:chemistry; D003786:Dental Pulp Cavity / Q000293:injuries*; D003804:Dentin / Q000293:injuries; D004867:Equipment Design; D006801:Humans; D007180:Incisor / Q000293:injuries; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation*; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D014025:Titanium / Q000737:chemistry; D019227:Tooth Apex / Q000293:injuries*; D014092:Tooth Root / Q000293:injuries
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium; D012973:Sodium Hypochlorite
keywords: Root crack; single-file system