Jung-Hong Ha1, Sang Won Kwak2, Asgeir Sigurdsson3, Seok Woo Chang4, Sung Kyo Kim1, Hyeon-Cheol Kim5. 1. Department of Conservative Dentistry, School of Dentistry, IHBR, Kyungpook National University, Daegu, Korea. 2. Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea. 3. Department of Endodontics, New York University College of Dentistry, New York, New York. 4. Department of Conservative Dentistry, School of Dentistry, Kyung Hee University, Seoul, Korea. 5. Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
Abstract
INTRODUCTION: The aim of this study was to evaluate the effect of different pecking depth on the stress generated by the screw-in forces of a rotating endodontic file in simulated canals. METHODS: Twenty simulated resin blocks with a J-shaped curvature were used. Twenty OneG files (MicroMega, Besançon, France) were assigned for a screw-in test depending on the pecking depth in 2 groups (n = 10). The files were operated at 300 rpm, and the up and down speed was controlled at 1 mm/s stroke velocity and a 10-millisecond dwell time using a customized device. The distances (pecking depth) for the pecking motion were 2 mm or 4 mm for each group; "6 mm forward and 4 mm backward" and "6 mm forward and 2 mm backward" movements were applied, respectively, for the 2 pecking groups. During the operation, the positive and negative apical loads were recorded at a rate of 50 Hz using customized software attached to the device. The maximum negative apical load (screw-in force [SF]) was recorded, and the total energy during pecking motion until the file reached the working length (cumulative screw-in forces [CSFs]) was computed. The data were analyzed using an independent t test at a significance level of 95%. RESULTS: No significant difference in SF was found between the 2 groups of pecking depths. However, the longer pecking depth (4-mm group) showed a significantly larger CSF compared with the shorter pecking depth group (P < .05). CONCLUSIONS: The shorter pecking depth may generate lower overall stresses for the root dentin as well as the instrument.
INTRODUCTION: The aim of this study was to evaluate the effect of different pecking depth on the stress generated by the screw-in forces of a rotating endodontic file in simulated canals. METHODS: Twenty simulated resin blocks with a J-shaped curvature were used. Twenty OneG files (MicroMega, Besançon, France) were assigned for a screw-in test depending on the pecking depth in 2 groups (n = 10). The files were operated at 300 rpm, and the up and down speed was controlled at 1 mm/s stroke velocity and a 10-millisecond dwell time using a customized device. The distances (pecking depth) for the pecking motion were 2 mm or 4 mm for each group; "6 mm forward and 4 mm backward" and "6 mm forward and 2 mm backward" movements were applied, respectively, for the 2 pecking groups. During the operation, the positive and negative apical loads were recorded at a rate of 50 Hz using customized software attached to the device. The maximum negative apical load (screw-in force [SF]) was recorded, and the total energy during pecking motion until the file reached the working length (cumulative screw-in forces [CSFs]) was computed. The data were analyzed using an independent t test at a significance level of 95%. RESULTS: No significant difference in SF was found between the 2 groups of pecking depths. However, the longer pecking depth (4-mm group) showed a significantly larger CSF compared with the shorter pecking depth group (P < .05). CONCLUSIONS: The shorter pecking depth may generate lower overall stresses for the root dentin as well as the instrument.