Yazdizadeh Mohammad, Skini Masoumeh, Hoseini Goosheh Seyyed Mohsen, Jafarzadeh Mansour, Shamohammadi Milad, Rakhshan Vahid
Department of Endodontics, Dental School, Ahvaz Jundishapur University of Medical Science, Ahvaz, Iran.
Department of Orthodontics, Dental School, Ahvaz Jondishapoor University of Medical Science, Iran.
Iran Endod J. 2017 Spring;12(2):216-219. doi: 10.22037/iej.2017.42.
Cyclic fatigue is the common reason for breakage of rotary instruments. This study was conducted to evaluate the effect of cryogenic treatment (CT) in improving the resistance to cyclic fatigue of endodontic rotary instruments.
In this study, 20 RaCe and 20 Mtwo files were randomly divided into two groups of negative control and CT. CT files were stored in liquid nitrogen at -196C for 24 h, and then were gradually warmed to the room temperature. All files were used (at torques and speeds recommended by their manufacturers) in a simulated canal with a 45 curvature until breakage. The time to fail (TF) was recorded and used to calculate the number of cycle to fail (NCF). Groups were compared using independent-samples t-test.
Mean NCFs were 1248.2±68.1, 1281.6±78.6, 4126.0±179.2, and 4175.4±190.1 cycles, for the Mtwo-control, Mtwo-CT, RaCe-control, and RaCe-CT, respectively. The difference between the controls and their respective CT groups were not significant (>0.3). The difference between the systems was significant.
Deep CT did not improve resistance to cyclic fatigue of the evaluated rotary files.
循环疲劳是旋转器械折断的常见原因。本研究旨在评估低温处理（CT）对提高根管治疗旋转器械抗循环疲劳能力的效果。
在本研究中，将20支RaCe锉和20支Mtwo锉随机分为阴性对照组和低温处理组。低温处理组的锉在-196℃的液氮中保存24小时，然后逐渐升温至室温。所有锉均在曲率为45°的模拟根管中（按照制造商推荐的扭矩和转速）使用，直至折断。记录折断时间（TF），并用于计算折断循环次数（NCF）。采用独立样本t检验对各组进行比较。
Mtwo对照组、Mtwo低温处理组、RaCe对照组和RaCe低温处理组的平均NCF分别为1248.2±68.1、1281.6±78.6、4126.0±179.2和4175.4±190.1次循环。对照组与其各自低温处理组之间的差异不显著（>0.3）。两种系统之间的差异显著。
深度低温处理并未提高所评估旋转锉的抗循环疲劳能力。
