Consideration of the forces during pecking motion with NiTi Files

Objectives: The purpose of this study was to consider forces during pecking motion using NiTi rotary files in preparation of the curved canals. Methods: Fifteen transparent plastic blocks #V040245 (VDW, Munich, Germany) which had the curvature of 30 degrees were prepared by five dentists with 21mm Flexmaster basic kit (VDW, Munich, Germany) installed in E-Master (VDW, Munich, Germany). The working times except root canal cleaning and exchanging of instruments were measured and totaled. The forces were measured at 100 ms intervals with digital force gauge FGC-1B (SIMPO, Kyoto, Japan) and recorded with pressure measurement software NCS-162 (Nihonkaikeisoku, Toyama, Japan). The data were analyzed by Student's t-test. Results: The total working times were different according to each dentist. The shortest total working time for preparation was 80 seconds and the longest one was 153 seconds. The working times were longer along with increasing of pecking frequency. The pecking frequency in a dentist was constant though the file type changed. The total pecking frequencies in each file were 40-65 in maximum and 2-3 in minimum. The intervals of pecking motion were different in each dentist, therefore the numbers of pecking motions per one second were 0.24 to 2.41, and the duration of them were 0.4 to 4.6 seconds per one stroke. The pulling forces in pecking motions were greater than pushing action. The maximum forces were -730 grams during pulling and 479 gram during pushing, and the minimum forces were -198 grams and 122 grams. The outside transportations of the canal wall were observed more along with increasing of the pecking frequency. Conclusions: This study indicated that the pecking motions were different according to dentists and the times and forces of pecking motion influenced the outside transportations in using NiTi rotary files.