不同型号不锈钢根管锉的循环疲劳性能

Cyclic fatigue performance of different types of stainless steel root canal files

背景:根管器械折断是一种比较常见的口腔临床并发症,因此,研究不同型号不锈钢根管锉的循环疲劳性能,具有重要的临床意义。目的:探讨根管弯曲角度及根管器械横截面积变化对不锈钢根管器械循环疲劳性能的影响。方法:选取25#、30#、35#不锈钢K锉(长25 mm,锥度相同)各30支,每种型号随机分为3组,共9组,这9组分别置于弯曲角度为45°,60°,90°的自制人工模拟弯曲根管中,用16∶1减速手机(350 r/min)驱动不锈钢K锉。记录每组器械折断所需时间,将时间转换为转数,采用扫描电镜分析折断K锉断口的显微结构,收集循环疲劳性能实验中折断的器械,电子游标卡尺测量断尖长度。结果与结论:(1)在弯曲角度相同的情况下,随着器械横截面积的增大,器械折断所旋转的周期数明显减少(P<0.05)。在型号相同、横截面积相同的情况下,随着根管弯曲角度的增加,器械折断所旋转的周期数明显减少(P<0.05),器械的循环疲劳性能明显下降;(2)各组不锈钢锉的断口均为韧性断口,断口表面可见一些大小不等的圆形或椭圆形韧窝并存在微观空洞,韧窝间可见延晶断裂的脆性断面。随着根管弯曲角度增大,韧窝直径逐渐增大。在30#、35#不锈钢K锉断口形貌中,随模拟根管弯曲角度增加,脆性断面有逐渐增加的趋势;(3)对于25#不锈钢K型锉,随着根管弯曲角度的增加,器械折断的断尖长度逐渐减小,但变化不明显(P>0.05)。对于#30,#35不锈钢K型锉,随着根管弯曲角度的增加,器械折断的断尖长度逐渐减小(P<0.05),其中#35-60°组与#35-90°组变化呈下降趋势但变化不明显(P=0.095)。在根管弯曲角度相同的情况下,随着不锈钢器械型号的增加,器械折断的断尖长度变化没有规律;(4)结果表明,不锈钢K型根管锉在长度和锥度相同的条件下,横截面积越大根管器械的循环疲劳性能越低,器械越容易折断;相同型号的不锈钢K型锉,随着根管弯曲角度增大,折断位置越靠近根尖部位,即断尖长度越短,断针取出越困难。

BACKGROUND： Root canal files fracture is a kind of common oral clinical complications. Therefore, it is of clinical importance to study the cyclic fatigue of different types of stainless steel root canal files.OBJECTIVE： To explore the effect of the bending angle and cross-sectional area of root canal instruments on cyclic fatigue of stainless steel files.METHODS： Thirty 25# stainless steel K files （25 mm in length） were selected, the same to 30# and 35#. And these three kinds of files were respectively randomized into three groups （n=10 per subgroup）. In the nine subgroups, the files were placed into self-made root canals at the bending angle of 45°, 60°, 90°, and driven by a 16：1 reducer （350 r/min）.Fracture time in each subgroup was recorded and converted into the number of rotations. The microstructure of the fracture end of the files was observed under scanning electron microscope. Fractured files were collected and the crack tip length was measured by an electronic caliper.RESULTS AND CONCLUSION： At the same bending angle, the number of rotations resulting in file fracture was significantly reduced with the increasing of the cross-sectional area of the files （P 0.05）. For 30# and 35# files, the crack tip length was significantly shortened with the increasing of the bending angle of the root canals （P 〈 0.05）. But there were no significant changes in the 35#-60° and 35#-90° groups （P=0.095）. At the same bending angle, there were no regular changes in the crack tip length in the different types of files. In conclusion, with the increasing of the cross-sectional area, the cyclic fatigue performance of the files with the same length and taper is reduced and the files become easy to be fractured; with the increasing of the bending angle of the root canals, the files with the same types are apt to be fractured near the root tip, indicating the shorter length of the crack tip indicates the more difficulty in the removal of the broken files.