title: Geometric analysis of root canals prepared by single twisted file in three different operation modes.
abstract: OBJECTIVE
  The aim of this study was to evaluate and compare the effects of a single twisted file (TF) instrument in three different operation modes on the preparation of curved root canals in human molars and to explore a new possible method in canal shaping in the clinic setting.
  
  
  METHODS
  A total of 105 selected root canals with an angle of curvature ranging from 20° to 35° were divided into the following three groups with 35 samples each according to the different operation mode in canal preparation: "continuous rotation-500" (CR, 500 rpm), reciprocating movement-300 (RM-300 rpm) and CR-300 rpm. Root canals were prepared by single file (a size 25/0.06 TF). The pre- and post-instrumented images of the sections were scanned using a cone-beam computed tomography scanner to measure the root transportation and centering ratio. The data were evaluated at 1.5 mm, 3.0 mm and 6.0 mm positions from the apex. The significance level was set at P < 0.05.
  
  
  RESULTS
  The results showed a statistically significant difference in root transportation that was only found in cross-sections 3.0 mm from the anatomic apex between group "CR-500" and group "CR-300." In addition, a significant difference in centering ratio was found between group "RM-300" and group "CR-300." There was no significant difference in the two indices among the three groups at cross-sections 1.5 mm and 6 mm from the apex.
  
  
  CONCLUSIONS
  Under the three conditions of this study, the continuous rotation mode has better shaping ability in root canal preparation than the RM mode when used with a TF single file (size 25/0.06).
authors.affiliation: Department of General Dentistry, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Xing-Chen
authors.initials: XC
authors.lastname: Wu
authors.affiliation: Department of General Dentistry, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Ya-Qin
authors.initials: YQ
authors.lastname: Zhu
keywords: Centering ratio; nickel-titanium instrument; root canal preparation; root canal transportation; twisted file