ABSTRACT
<p><b>OBJECTIVE</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>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.</p>