Sabet Yazdan, Shahsiah Samira, Yazdizadeh Mohammad, Baghamorady Sana, Jafarzadeh Mansour
Department of Endodontics, Faculty of Dentistry, Lorestan University of Medical Sciences, Lorestan, Iran.
Department of Endodontics, Faculty of Dentistry, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
Dent Res J (Isfahan). 2020 Aug 14;17(4):300-305. eCollection 2020 Jul-Aug.
Cryogenic methods have been used to increase the wear, abrasion, corrosion resistance and to improve the strength of metals. The aim of this study was to evaluate the effect of cryogenic treatment on the cyclic fatigue resistance of rotary nickel-titanium (NiTi) instruments.
In this study, 20 Hyflex (Coltene, Altstätten, Switzerland) nickel-titanium instruments, size 25, 0.06 taper, were randomly divided into two groups as follows: untreated NiTi rotary files (Group A) and cryotreated NiTi rotary files (Group B). The instruments of Group A were completely immersed in a cryocan containing liquid nitrogen (-196°C) for 24 h. After 24 h, the instruments were removed from the bath and were allowed to return to room temperature gradually. All files were used (at a speed of 500 rpm and a torque of 2.5 Ncm) in an artificial canal with a 60° curvature until fracture. Time to failure was recorded with a stopwatch in seconds and subsequently converted to number of cycles to fracture (NCF). Groups were compared using the independent-samples -test. The level of statistical significance was set at 0.05.
Mean NFCs in Group A and B were 1576 and 1395, respectively. However, statistical analysis showed that there was no significant difference between the groups ( = 0.2).
Deep cryotherapy of NiTi endodontic files cannot improve the cyclic fatigue resistance of HyFlex files, but further studies are required to evaluate these cryogenically treated NiTi files clinically.
低温处理方法已被用于提高金属的耐磨性、抗磨性、耐腐蚀性并增强其强度。本研究的目的是评估低温处理对旋转镍钛（NiTi）器械循环疲劳抗力的影响。
在本研究中，将20支型号为25、锥度为0.06的Hyflex（瑞士科尔tene公司，阿尔特施泰滕）镍钛器械随机分为两组：未处理的NiTi旋转锉（A组）和低温处理的NiTi旋转锉（B组）。A组器械完全浸入装有液氮（-196°C）的低温罐中24小时。24小时后，将器械从浴中取出，使其逐渐恢复到室温。所有锉均在曲率为60°的人工根管中以500转/分钟的速度和2.5牛厘米的扭矩使用，直至折断。用秒表记录折断时间，随后换算为折断循环次数（NCF）。采用独立样本t检验对两组进行比较。统计学显著性水平设定为0.05。
A组和B组的平均NCF分别为1576和1395。然而，统计分析表明两组之间无显著差异（P = 0.2）。
NiTi根管锉的深度冷冻疗法不能提高HyFlex锉的循环疲劳抗力，但需要进一步研究以临床评估这些经过低温处理的NiTi锉。
