AIM To evaluate, using micro-CT, the remaining dentine thickness after preparation of the mesiobuccal (MB), mesiolingual (ML) and middle mesial (MM) canals of mandibular first molars with the ProTaper Next rotary system. METHODOLOGY Eleven mesial roots of mandibular first molars having three independent canals from the furcation level up to at least 5 mm towards the apical direction were selected. Preparation of MM canals was performed in two steps using ProTaper Next X2 (step 1) and X3 (step 2) instruments, whilst MB and ML canals were prepared in a single step up to X3 instruments. The roots were scanned (pixel size of 10 µm) before and after each step, and the dentine volume was calculated. Postoperative models of the roots were coregistered with their preoperative dataset and colour-coded cross-sections of the roots were used to measure the smallest dentine thickness surrounding each canal at 1.0-mm intervals from the furcation level up to 5 mm in the apical direction, in both mesial and distal aspects of the roots. Changes in the remaining wall thickness between mesial canals were analysed with repeated-measures anova and post hoc Tukey test. Significance level was set at 5%. RESULTS Mean percentage reduction of dentine volume after steps 1 and 2 was 4.66% and 5.16%, respectively. Overall, pre- and postoperative dentine thickness of the MM canal walls, in both mesial and distal aspects of the root, were significantly thinner than those of MB and ML canals (P < 0.05). No significant difference was observed when comparing dentine thickness in the mesial and distal directions of MM canal after preparation step 1 (0.88 ± 0.18 mm and 0.73 ± 0.26 mm, respectively) or 2 (0.83 ± 0.17 mm and 0.67 ± 0.26 mm, respectively) (P > 0.05). Dentine thickness values less than 0.5 mm were observed mostly towards the distal aspect of the MM canal. Mesial roots were not associated with strip perforations after canal preparation procedures. CONCLUSIONS A significant decrease in the thickness of canal walls at all levels evaluated in the mesial roots of mandibular molars suggests that files with small tapers should be used in preference to instruments with large tapers to prepare mesial canals in mandibular molars.

中文翻译：

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旋转器械制备的下颌磨牙中膜中段牙本质厚度的评估：一项微CT研究。

目的使用微型CT评估使用ProTaper Next旋转系统制备下颌第一磨牙的中颊（MB），舌中（ML）和中颌（MM）管后的剩余牙本质厚度。方法学选择下颌第一磨牙的11个近中牙根，从分叉水平到根尖方向至少5 mm具有三个独立的根管。使用ProTaper Next X2（第1步）和X3（第2步）器械分两步进行MM根管的准备，而MB和ML根管直至X3根器械均一步一步制备。在每个步骤之前和之后扫描牙根（像素大小为10 µm），并计算牙本质的体积。将根部的术后模型与其术前数据集进行配准，并使用颜色编码的根部横截面测量距根尖分叉处直至根部5 mm处每根根管的最小牙本质厚度，其间隔为1.0 mm。在根部的内侧和外侧。使用重复测量的方差分析和事后图基测试分析中耳道之间剩余壁厚的变化。显着性水平设定为5％。结果步骤1和步骤2后，牙本质体积平均减少百分比分别为4.66％和5.16％。总体而言，MM根管的根部和远端方面，术前和术后牙本质壁的厚度均显着小于MB和ML根管的厚度（P <0.05）。在准备步骤1（分别为0.88±0.18 mm和0.73±0.26 mm）或2（分别为0.83±0.17 mm和0.67±0.26 mm）之后，比较MM管的近中和远端方向上的牙本质厚度没有观察到显着差异（P＞ 0.05）。观察到的牙本质厚度值通常小于MM根管的远端，小于0.5 mm。根管预备后，中根与条状穿孔无关。结论在下颌磨牙的牙根中，在所有水平评估的管壁厚度均显着降低，这表明应使用小锥度的锉刀，而不是大锥度的器械来准备下颌磨牙的中管。分别为26毫米）或2（分别为0.83±0.17毫米和0.67±0.26毫米）（P> 0.05）。观察到的牙本质厚度值通常小于MM根管的远端，小于0.5 mm。根管预备后，中根与条状穿孔无关。结论在下颌磨牙的牙根中，在所有水平评估的管壁厚度均显着降低，这表明应使用小锥度的锉刀，而不是大锥度的器械来准备下颌磨牙的中管。分别为26毫米）或2（分别为0.83±0.17毫米和0.67±0.26毫米）（P> 0.05）。观察到的牙本质厚度值通常小于MM根管的远端，小于0.5 mm。根管预备后，中根与条状穿孔无关。结论在下颌磨牙的牙根中，在所有水平评估的管壁厚度均显着降低，这表明应使用小锥度的锉刀，而不是大锥度的器械来准备下颌磨牙的中管。