title: [Comparison on the shaping ability of three different instruments in preparing curved molar canals].
abstract: OBJECTIVE
  To study the changes of root canal curvatures and apical transportation index when the curved root canals were prepared by hand-use ProTaper, stainless steel K-files or nickel-titanium K-files.
  
  
  METHODS
  Forty-five extracted molars, with the degree of root canal curvature from twenty to forty, were divided into fifteen sections in curvature sequence. After that, three canals of each section were randomly distributed to three different instrumentation groups. One group of them was prepared by hand-use ProTaper with crown-down technique. The other two groups were instrumented by stainless steel or nickel titanium K-files with modified step-back technique to working length. The standard digital radiographs were taken to record the profiles of root canals and the positions of the tips of the instruments. The change of curvature degree between pre- and post-instrumentation and the apical transportation indexes (ATI) among three groups were analyzed respectively using SAS statistical software.
  
  
  RESULTS
  The change of curvature degree between pre- and post-instumentation for stainless steel K-files group was largest, and the ATI of stainless steel K-files group was significantly greater than that for nickel titanium K-files group (P < 0.05). The canals prepared by hand-use ProTaper was smallest in the change of curvature and ATI among the three groups (P < 0.01).
  
  
  CONCLUSIONS
  When preparing curved molar canals, hand-use ProTaper with crown down technique can obtain better shaping effect and higher efficiency.
authors.affiliation: Dept. of Oral Medicine, The Ninth People's Hospital, School of Stomatology, Shanghai Second Medical Un and thersity, Shanghai 200011, China.
authors.forename: Ya-qin
authors.initials: YQ
authors.lastname: Zhu
authors.forename: Ying-xin
authors.initials: YX
authors.lastname: Gu
authors.forename: Rong
authors.initials: R
authors.lastname: Du
mesh_terms: D003762:Dental Instruments; D003786:Dental Pulp Cavity; D008963:Molar; D009532:Nickel; D018915:Root Canal Preparation; D012390:Root Canal Therapy; D013193:Stainless Steel; D014025:Titanium
chemical_list: C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D014025:Titanium