Chi Chih-Wen, Lai Eddie Hsiang-Hua, Liu Chao-Yuan, Lin Chun-Pin, Shin Chow-Shing
Graduate Institute of Clinical Dentistry, School of Dentistry and National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan.
J Dent Sci. 2017 Mar;12(1):21-26. doi: 10.1016/j.jds.2016.06.001. Epub 2016 Aug 10.
BACKGROUND/PURPOSE: Heat pretreatment can improve the cyclic fatigue life of nickel-titanium (NiTi) instruments. This study evaluated the effects of two different heat treatments on the cyclic fatigue resistance and cutting efficiency of ProTaper Universal F2 files.
The files were divided into three groups: no treatment (control), heat treatment at 400°C (HT400) and heat treatment at 600°C (HT600). The phase transformation of the files was evaluated by differential scanning calorimetry. In cyclic fatigue tests, the differences in file performance in four simulated canals among the three groups were assessed. The cutting efficiency was tested at four cutting portions (3 mm, 6 mm, 9 mm, and 12 mm) from the tip of the file.
Differential scanning calorimetry showed a prolonged phase transformation of the files only after 600°C treatment. At 3 mm cutting portion, 400°C heat-treated files had significantly better cutting ability than those in the control group. However, the files in the HT600 group had significantly lower cutting efficiency than those in the other two groups at the four tested positions. In the cyclic fatigue test, fatigue lives of the files after 400°C and 600°C treatment were prolonged from 2.1 to 2.8 times and from 1.7 to 5.5 times, respectively.
Although 600°C treatment increased resistance to cyclic fatigue, it reduced the cutting efficiency of the files. The 400°C treatment maintained the cutting ability and prolonged the cyclic fatigue life of the files. Therefore, for clinical use of ProTaper Universal F2 files, 400°C pretreatment is a better choice than 600°C pretreatment.
背景/目的：热预处理可提高镍钛（NiTi）器械的循环疲劳寿命。本研究评估了两种不同热处理对ProTaper Universal F2锉的循环抗疲劳性和切削效率的影响。
将锉分为三组：未处理（对照组）、400°C热处理（HT400）和600°C热处理（HT600）。通过差示扫描量热法评估锉的相变。在循环疲劳试验中，评估三组在四条模拟根管中锉性能的差异。在距锉尖四个切削部位（3mm、6mm、9mm和12mm）测试切削效率。
差示扫描量热法显示仅在600°C处理后锉的相变延长。在3mm切削部位，400°C热处理的锉比对照组具有显著更好的切削能力。然而，在四个测试位置，HT600组的锉切削效率明显低于其他两组。在循环疲劳试验中，400°C和600°C处理后锉的疲劳寿命分别从2.1倍延长至2.8倍和从1.7倍延长至5.5倍。
虽然600°C处理增加了对循环疲劳的抗性，但降低了锉的切削效率。400°C处理保持了锉的切削能力并延长了其循环疲劳寿命。因此，对于ProTaper Universal F2锉的临床应用，400°C预处理比600°C预处理是更好的选择。
