预弯操作对不同机用镍钛器械的抗疲劳强度和弯曲根管形态的影响初探

Effect of precurved operation on fatigue strength of different NiTi instruments and curved root canal morphology

目的:研究预弯操作对不同代镍钛器械的抗疲劳强度的影响,以及在根管预备过程中对弯曲根管形态的影响。方法:选择Hyflex CM(HCM)、Protaper Universal(PTU)S1、PTU S2、Protaper Next(PTN)X1、Mtwo 10/.04、Mtwo 15/.05共6种型号机用旋转镍钛器械作为研究对象,每种器械分别被分为预弯组和非预弯组(n=10)。采用自制模拟人牙弯曲根管不锈钢块和固定机用镍钛马达对所有研究对象进行疲劳测试,通过高清数码摄像机记录每个测试样本从旋转开始到器械断裂的全过程,计算出各组镍钛器械断裂时的旋转时间和旋转圈数;选取48个弯曲度为20°~60°的牙根作为研究模型,随机平均分配到PTU S2、PTN X1(15/.04)、Mtwo(15/.05)的各预弯组和非预弯组(n=8),利用Micro CT对预备前、后的根管形态进行扫描记录,计算并分析各测量点的根管偏移量。结果:旋转疲劳测量结果显示,对于HCM、PTU、Mtwo机用镍钛器械,两组间的抗旋转疲劳强度无差异(P>0.05),但对于PTN机用镍钛器械,预弯操作会明显降低样本的疲劳断裂时间和圈数,两组间抗旋转疲劳强度有差异(P<0.05)。两组控制记忆镍钛器械HCM的抗旋转疲劳强度都明显高于其余三种镍钛器械(P<0.05);对预备后根管偏移量的测量结果显示,对于Mtwo、PTU、PTN三种机用镍钛器械,各自预弯组与非预弯组间根管预备后偏移量无差异(P>0.05)。结论:PTN抗疲劳强度受预弯影响相对较大,避免预弯操作;Mtwo和PTU抗疲劳强度受预弯影响相对较小,可适当进行预弯操作,而HCM抗疲劳强度是比较适用于使用预弯技术的机用镍钛器械。将尖端直径<0.15 mm的机用镍钛器械预弯后发生永久形变,并进行弯曲根管预备时,发生根管偏移的概率较小。

Objective:To study the fatigue strength of different generations of precurved NiTi instruments,and the shaping ability of precurved instruments in the curved canals.Methods:Six kinds of NiTi rotary instruments were divided respectively into precurved group and non-precurved group(n=10):Hyflex CM(HCM),Protaper Universal(PTU)S1,S2,Protaper Next(PTN)X1,Mtwo 10/.04,15/.05.Fatigue tests were carried out by using stainless steel blocks simulating curved canals.The whole process was recorded through a high-definition digital camera.The rotation time and the number of revolutions of each group were calculated.48 curved root canals of permanent teeth with angles of curvature ranging from 20-60°were randomly distributed to each group of PTUS2、PTNX1(15/.04)and Mtwo(15/.05)(n=8).Micro CT was used to scan and record the root canal morphology.Root canal transportation of each measuring point was calculated.Results:The results of rotational fatigue measurement showed that there was no significant difference in the anti-fatigue strength between precurved group and non-precurved group of Mtwo,PTU and HCM instruments(P>0.05).However,the difference of two groups of PTN was statistically significant(P<0.05).In general,the anti-fatigue strength of HCM is significantly higher than that of the other three NiTi instruments in not only precurved group but also non-precurved group(P<0.05).The results of root canal deviation showed that there was no significant difference between precurved group and non-precurved group after preparation for Mtwo,PTU and PTN(P>0.05).Conclusions:The risk of fracture of precurved PTN in root canal preparation is so high that avoiding precurved operation is recommended.The fatigue strength of Mtwo and PTU is relatively less affected by precurved operation,so that it can be properly performed.HCM fatigue strength is recommended for precurved technology.In clinical practice,NiTi instruments with tip diameter less than 0.15 mm may permanently deformed after precurved operation,and root canal deviation may be of a low probability.