title: Influence of glide path on the screw-in effect and torque of nickel-titanium rotary files in simulated resin root canals.
abstract: OBJECTIVE
  The purpose of this study was to investigate the screw-in effect and torque generation depending on the size of glide path during root canal preparation.
  
  
  METHODS
  Forty Endo-Training Blocks (REF A 0177, Dentsply Maillefer) were used. They were divided into 4 groups. For groups 1, 2, 3, and 4, the glide path was established with ISO #13 Path File (Dentsply Maillefer), #15 NiTi K-file NITIFLEX (Dentsply Maillefer), modified #16 Path File (equivalent to #18), and #20 NiTi K-file NITIFLEX, respectively. The screw-in force and resultant torque were measured using a custom-made experimental apparatus while canals were instrumented with ProTaper S1 (Dentsply Maillefer) at a constant speed of 300 rpm with an automated pecking motion. A statistical analysis was performed using one-way analysis of variance and the Duncan post hoc comparison test.
  
  
  RESULTS
  Group 4 showed lowest screw-in effect (2.796 ± 0.134) among the groups (p < 0.05). Torque was inversely proportional to the glide path of each group. In #20 glide path group, the screw-in effect and torque decreased at the last 1 mm from the apical terminus. However, in the other groups, the decrease of the screw-in effect and torque did not occur in the last 1 mm from the apical terminus.
  
  
  CONCLUSIONS
  The establishment of a larger glide path before NiTi rotary instrumentation appears to be appropriate for safely shaping the canal. It is recommended to establish #20 glide path with NiTi file when using ProTaper NiTi rotary instruments system safely.
authors: Department of Conservative Dentistry, Kyungpook National University School of Dentistry, Daegu, Korea.
authors: Jung-Hong
authors: JH
authors: Ha
authors: Sang-Shin
authors: SS
authors: Park
keywords: Glide path; Nickel-titanium file; ProTaper; Screw-in effect; Simulated resin root canal; Torque