Change of mechanical properties of Ni-Ti rotary instruments through heat treatment

众所周知，镍钛旋转器械的机械性能受到热处理的强烈影响。研究了热处理工艺对镍钛旋转器械弯曲性能、成形性能和疲劳性能的影响。钛锉分别在400 ℃（400组）、450 ℃（450组）和500 ℃（500组）下热处理30分钟。未热处理的样本用作对照。采用单轴弯曲试验评价了热处理引起的弹性和超弹性变形范围内的试件柔韧性变化。制作弯曲根管模型。记录准备过程中器械变形和断裂。将术前和术后图像叠加。确定从顶端6 mm的弯曲的内侧和外侧去除的树脂量。以250 rpm的速率进行旋转弯曲试验，直至断裂。在距尖端2 mm处，将每个样本水平偏转至1。0或1。所有样本均在每个偏转下进行测试。在弯曲试验中，在弹性范围内，对照组和500组的载荷值高于400组和450组（P<0. 05）。05）。在超弹性范围内，对照组的弯曲载荷在所有组中最高（p<0. 05）。05）。在成形能力方面，对照组根尖部的根管向弯曲外侧移动的程度高于热处理组（p<0. 05）。05）。在旋转弯曲试验中，与对照组相比，第450组和第500组在1以下显示出更高的NCF。0和1。5 mm偏转，而400组仅在1. 5 mm偏转（p<0. 05）。结论：热处理可以提高锉的柔韧性和疲劳寿命，使其更有效地预备根管。

It is known that the mechanical behavior of Ni-Ti rotary instruments is strongly affected by heat treatment. The aim of this study was to investigate the effect of heat treatment on bending properties, shaping abilities and fatigue properties of Ni-Ti rotary instruments.Raw Ni. Ti files were heat-treated for 30 minutes at 400(group 400), 450(group 450) and 500(group 500) degrees centigrade. Non heat-treated specimens were used as control. A cantilever-bending test was used to evaluate changes in specimen flexibility both elastic and superelastic deformation range caused by heat treatment. Curved canal models were prepared. Deformed and fractured instruments during preparation were recorded. Pre-and post operative images were superimposed. The amounts of resin removed from both the inner and outer sides of the curvature in the apical 6 mm were determined. The rotational bending test was performed at a rate of 250 rpm until fracture. At 2 mm from the tip, each specimen was deflected horizontally to 1. 0 or 1. 5 mm. All specimens were tested under each deflection. The number of cycles until fracture(NCF) was counted.In the cantilever-bending test, load values of the control group and group 500 were higher than those of groups 400 and 450 at the elastic range(P<0. 05). At the superelastic range, the bending load of the control group was the highest amongst all groups(p<0. 05). Regarding shaping ability, in the control group, root canals at the apex were transported more to the outer side of the curvature compared with those of all heat-treated groups(p<0. 05). In the rotational bending test, as compared to the control group, Groups 450 and 500 showed a higher NCF under 1. 0 and 1. 5 mm deflection, whereas Group 400 showed a higher NCF only under 1. 5 mm deflection(p<0. 05).In conclusion, heat treatment of files might improve their flexibility and fatigue life, making them more effective for preparation of cured canals.