上颌第二恒磨牙近中颊根第二根管的离体牙研究

目的研究上颌第二恒磨牙近中颊根第二根管（MB2）的发生情况，为提高上颌第二恒磨牙根管治疗的成功率提供解剖学基础。方法于山东地区收集离体上颌第二恒磨牙118颗，采用斜方型开髓洞型开髓，利用小号C型锉探查并疏通根管，记录MB2的发现率及扩通率；拍摄X线牙片，记录近中颊根的根管数目、形态和类型；在根管显微镜下观察并应用数显卡尺测量近中颊根主根管和MB2根管口之间的距离，确定根管口的位置；记录近中颊根的根尖孔数目，并测量解剖根尖孔至解剖根尖的距离。结果118颗上颌第二恒磨牙中，有58颗发现MB2，发现率为49.15%；其中48颗牙齿的MB2被扩通，扩通率为82.76%。108颗3根牙中，近中颊根的根管形态为Ⅰ型者有50颗，占46.30%；Ⅱ型及Ⅲ型者分别为14和34颗，占12.96%和31.48%。近中颊根主根管口与MB2根管口的平均距离为1.26 mm；近中颊根解剖根尖孔至解剖根尖的距离平均值为1.13 mm。结论山东地区上颌第二恒磨牙MB2的发现率较高，临床治疗中采用改良的斜方型开髓孔有利于发现MB2，用X线片确定工作长度时需要结合临床综合判断根尖孔的位置。

In vitro study of the secondary mesiobuccal canal of the maxillary second molar

Objective To get some anatomical knowledge about the second mesiobuccal canal（MB2） of the maxillary second molar of Shandong region by studying the teeth in vitro. The anatomical knowledge may help us to improve the successful rate of root canal therapy of the maxillary molar. Methods 118 maxillary second molars were collected from the different region in Shandong province. Oblique square of pulp opening form was used, then root canals were detected and got through by C-type file. The rate of MB2 detection and getting through was recorded. By taken X-ray, the numbers, the morphologies and classifications of the root canal systems of these molars were recorded. Then the distance between mesiobuccal canal（MB） and MB2 was observed and measured by endodontic operating microscope and digital measurement. At last, we observed the apical foramen from the surfaces of these teeth, and try to analysis the differences between apical foramen and the end points of the roots. Results The rate of MB2 detection was 49.15%, among them 82.76% could be got through by files. 108 molars had three roots, among them, for the mesiobuccal root canal system, 46.30% were Ⅰ root canal system, while Ⅱ and Ⅲ systems were 12.96% and 31.48%, respectively. The distance between MB and MB2 was 1.26 mm averaged. The distance between anatomical apical holes and the end points of roots was 1.13 mm averaged. Conclusion MB2 can be detected in most of maxillary second molars in Shandong region. The dentists should try to detect MB2 in the root canal therapy, and should judge work length by clinical behavior and apical locator rather than by X-ray alone.