Influence of heat treatment on color and flexibility of nickel-titanium endodontic instruments

ABSTRACT Objective The aim of this study was to evaluate and compare the effect of heat treatment at different temperatures on the color and flexibility of nickel-titanium endodontic instruments. Methods Thirty-six nickel-titanium K-file endodontic instruments were divided into six groups and submitted to heat treatment at several temperatures between 450ºC and 750ºC. The color was visually observed. Cantilever-bending tests were performed to measure the flexibility of the instruments. The data were statistically evaluated by one-way analysis of variance and Tukey post hoc comparisons. Results It was observed that the color becomes darker as the heating temperature increases. The flexibility is significantly higher after the heat treatment (P < 0.05). Instruments treated at 650ºC and 750ºC had higher flexibility than those treated at lower temperatures (450ºC, 500ºC and 550ºC) (P < 0.05). Conclusion Heat treatment has a significant effect on the surface color and flexibility of nickel-titanium endodontic instruments. The highest flexibility was observed in instruments heated at 650ºC and 750ºC.

摘要
目的 本研究旨在评估并对比不同温度热处理对镍钛K型根管器械（nickel-titanium K-file endodontic instruments）色泽与柔韧性的影响。
方法 将36支镍钛K型根管器械分为6组，于450℃至750℃的多个温度梯度下实施热处理。采用目视法评估器械色泽；通过悬臂梁弯曲试验测定器械柔韧性。采用单因素方差分析与Tukey事后多重比较对数据进行统计学分析。
结果 结果显示，随着热处理温度升高，器械色泽逐渐加深。经热处理后，器械柔韧性显著提升（P < 0.05）。经650℃与750℃热处理的器械，其柔韧性显著高于450℃、500℃及550℃热处理组（P < 0.05）。
结论 热处理对镍钛根管器械的表面色泽与柔韧性具有显著影响。经650℃与750℃热处理的器械柔韧性最高。