AIM: To evaluate the injury of ProTaper rotary and hand instruments used in preparation ofrnmoderately curved root canals in vitro. METHODS: Six sets of ProTaper nickel-titanium rotary instruments and hand instruments were used respectively to prepare the moderately curved mesial buccal canals of mandibular first molars. After each canal preparation, the instruments were examined under a stereomicroscope by an inspector who was blind to the groups. Fracture of equipments and release of threads were recorded. After 5, 10 and 20 times of canal preparation, S1, Fl files without deformation were selected and the surfaces and cutting edges were observed under scanning electron microscope (SEM). RESULTS: SX, S1, F1 and F3 files were easy to fracture. The fracture position was 3 -4 mm from the tip. Cracks and damages could be easily observed on ProTaper nickel-titanium rotary instruments after 15 times of preparation, while they could be observed after 20 times on the hands instruments. More severe damage was frand on Pro-Taper nickel-titanium rotary instruments when used for the same times. CONCLUSION: ProTaper rotary instruments can be used for less than 15 canals, while hands instruments for 20 canals when used for moderately curved canals.%目的:评估机用和手用ProTaper镍钛器械预备中度弯曲根管后的损伤情况,为临床安全使用ProTaper镍钛器械提供理论指导.方法:使用机用和手用ProTaper镍钛器械各6套预备中度弯曲的下颌第一磨牙近中颊根.每预备1个根管后,在立体显微镜下观察并记录器械分离和螺纹松解情况.预备完成后,分别以扫描电镜观察全新、预备5次、15次和20次的SX和F1表面,观察其表面和切割刃的磨损情况.结果:预备中度弯曲根管时,SX、S1、F1、F3易发生器械分离,断裂位置一般位于距离锉尖3～4 mm处.机用ProTaper器械在使用15次后,可观察到明显的裂纹和损伤,手用ProTaper器械在使用20次后,可观察到明显的微裂纹和切割刃的损伤.使用相同的次数,机用ProTaper镍钛锉的损伤比手用ProTaper镍钛锉严重.结论:推荐机用ProTaper镍钛锉可以安全使用15次,手用ProTaper镍钛锉可以安全使用20次,每次使用后,应重点观察SX、F1和F3的锉尖位置,以便及早发现安全隐患,防止镍钛锉断裂.
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