Restor Dent Endod.  2012 Nov;37(4):215-219.

Influence of glide path on the screw-in effect and torque of nickel-titanium rotary files in simulated resin root canals

• Ha JH
• Park SS

Abstract

OBJECTIVES
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.
MATERIALS AND 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.

Keyword

Glide path; Nickel-titanium file; ProTaper; Screw-in effect; Simulated resin root canal; Torque

MeSH Terms

Dental Pulp Cavity
Polymethyl Methacrylate
Torque
Polymethyl Methacrylate

Figure

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  Figure 1 Custom-made device. (a) A simulated root canal was mounted on a tension/compression sensor by using a mounting jig. The generated signals by simulated canals were recorded; (b) ProTaper S1 instrument was synchronized with a torque sensor. The generated torque signals in mA were amplified and transferred to a computer; (c) The pecking distance was controlled by a control panel.

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  Figure 2 The typical strip-chart recording the screw-in effect (solid line) and torque (dotted line) during preparation. (a) Group 1: #13 glide path; (b) Group 2: #15 glide path; (c) Group 3: #18 glide path; (d) Group 4: #20 glide path. At the moment the screw-in occurred, the torque value suddenly increased. After that, the torque value returned to the baseline. In most groups, the screw-in effect and torque increased as the file approached apical foramen. Exceptionally in group 4, the screw-in effect and torque decreased within 1 mm from the apical foramen (Asterisk).

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