AIM:To compare the generation and distribution of root microcracks during the root canal prepara-tion with 3 kinds of Ni-Ti instruments. METHODS:64 extracted mandibular incisors were selected and randomly as-signed to 4 groups(n＝16). The incisors was left unprepared as the controls,in the remaining 3 groups were instru-mented with the ProTaper Universal(PTU),Twisted Files(TF)and Mtwosystem(MT)respectively up to size #25. Then the roots were sectioned horizontally at 3,6 and 9 mm from the apex and evaluated under a microscope. The gen-eration and distribution of root microcracks were observed and analyzed by using tchi-square test. RESULTS:In the group of control,PTU,TF and MT microcracks were observed in 0,11,3 and 10 of the tooth canals(PTU vs MT, P＞0.05;TF vs PTU or MT,P＜0.05). There no difference among the 4 sides at the section of 3 mm from the apex (P＞0.05),and microcracks of the buccolingual side were more than those of mesiodistal side at 6 mm and 9 mm sec-tions(P＜0.05). CONCLUSION:The Twisted File causes fewer root microcracks than the ProTaper Universal file and Mtwo file during the root canal preparation.In the root apical segment,the microcracks are evenly distributed,and in the middle and upper segments,cracks on the buccolingual sides are mor than on the mesiodistal sides.%目的:比较3种镍钛器械预备根管后牙根微裂的发生和分布情况.方法:收集符合标准的离体下颌切牙64个,随机分为4组(n＝16).对照组不进行根管预备,实验组分别用ProTaper Universal(PTU)、Twisted Files(TF)和Mtwo(MT)进行根管预备至 #25;预备完成后,分别于距根尖3、6、9 mm处垂直于牙体长轴将样本切开,体视显微镜下观察并记录各横断面上牙根微裂的发生和分布情况.结果:根管预备后,对照组无牙根微裂发生.牙根微裂发生率PUT组(68.7%)与MT组(62.5%)无显著差异(P＞0.05);PTU组和MT组分别与TF组(18.75%)比较,P＜0.05;牙根微裂在3 mm截面处各区的分布无差异(P＞0.05),在6、9 mm处均为唇、舌侧区多于近、远中区(P＜0.05).结论:TF预备根管后发生牙根微裂的风险明显小于PTU和MT.牙根微裂在根尖段分布均匀,根中上段主要分布在唇侧和舌侧.
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