title: [Comparison of the incidences of apical root cracks after canal preparation with two nickel-titanium rotary systems: an in vitro study].
abstract: OBJECTIVE
  To compare the incidences of root cracks after canal instrumentation with HyFlex CM system and the ProTaper Universal system.
  
  
  METHODS
  Sixty mandibular incisors were mounted in resin blocks with simulated periodontal ligaments, and the apex was exposed. The control group of 20 teeth was not prepared, and the other 40 teeth were divided into 2 experimental groups (n=20). The 40 root canals of the experimental groups were instrumented using HyFlex CM and ProTaper Universal to the major apical foramen (AF). The horizontal sections 1 mm, 2 mm, and 3 mm from the apex were observed under an optical stereomicroscope at 25×magnification. The presence of cracks was noted.
  
  
  RESULTS
  No cracks were found in the control teeth. Cracks were found in 1 of 20 (5%) teeth in HyFlex CM group, and 17 of 20 (85%) teeth in ProTaper Universal group. The difference between the two experimental groups was statistically significant (P<0.01).
  
  
  CONCLUSIONS
  The HyFlex CM files caused fewer root cracks than the ProTaper Universal files during the root canal instrumentation.
authors: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors: Chen
authors: C
authors: Chen
authors: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors: Yu-hong
authors: YH
authors: Liang
authors: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors: Xue-jun
authors: XJ
authors: Gao
mesh_terms: D001641:Bicuspid; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D007180:Incisor; D008334:Mandible; D009532:Nickel; D018915:Root Canal Preparation; D014025:Titanium; D019227:Tooth Apex; D014092:Tooth Root
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium