Abstract: Objective    To compare the centering ability of three different nickel-titanium（Ni-Ti）rotary instruments in preparing resin simulated curved root canals. Methods    Thirty resin simulated curved root canals were divided into three groups（n = 10）and prepared by ProTaper Universal（Group A），ProTaper Gold（Group B）and M3-Pro（Group C）. Preparation time was recorded. Photos of pre- and post-instrumentation morphology were taken by SLE camera in the same place and overlapped by Adobe Photoshop CS5. Then，ten observation points were determined at 1 mm to 10 mm from the apical foramen to analyze centering ability of these 3 instruments. Results    None of the groups experienced instrument separation. Group B demonstrated the least preparation time，while Group A displayed the longest preparation time（P < 0.05）. No significant difference was found concerning canal curvature among the three groups（P > 0.05）. In the apical area，Group A showed a lower centering ability than the other two groups（P < 0.05）. Group C presented a better centering ability than Group A and Group B at the curved section（P < 0.05）. There was no significant difference among the three groups at the straight part（P > 0.05）. Conclusion    The three nickel-titanium instruments all can maintain the original canal curvature well. ProTaper Gold presents the least time in preparing the canal. ProTaper Gold and M3-Pro show a better centering ability compared with ProTaper Universal，which is more suitable in preparing curved root canals.

Key words: centering ability, apical transportation, nickel-titanium instrument

摘要： 目的    比较3种机用镍钛器械预备树脂模拟弯曲根管的中心定位能力。方法    将30个树脂模拟弯曲根管分成3组，分别使用机用镍钛器械ProTaper Universal（A组）、 ProTaper Gold（B组）、M3-Pro（C组）进行根管预备，记录预备时间。使用相机在同一位置拍摄预备前后根管形态图片，应用Adobe Photoshop CS5 软件将预备前后图像叠加，距离根尖孔每1 mm取1个观测点（共10个），对3种器械的中心定位能力进行比较分析。结果    整个实验过程中没有发生器械分离。B组预备时间最短，A组最长（P < 0.05）。预备前后根管弯曲度变化在3组之间的差异无统计学意义（P > 0.05）。在根尖区，A组中心定位能力较差（P < 0.05）；在弯曲点附近，C组的中心定位能力优于其余2组（P < 0.05）；在冠方，3组间差异无统计学意义（P > 0.05）。结论    3种器械均能维持根管原始形态，ProTaper Gold的预备时间最短；与ProTaper Universal相比，ProTaper Gold和M3-Pro具有更好的中心定位能力，更适合弯曲根管的预备。

关键词: 中心定位能力, 根尖偏移, 镍钛器械