MB2 mainly refers to the second root canal on the proximal mesiobuccal side of the maxillary molar, the one near the buccal side is called the proximal mesiobuccal, and the buccal root canal near the lingual side is called the proximal mesiobuccal second root canal, which is also called MB2 . Generally, the incidence of MB2 can reach about 70%-80% in China, and the second root canal on the proximal mesiobuccal side is slightly thicker and easier to find in young patients. However, in older patients, the calcification may be more severe and difficult to find, requiring microscopic ultrasound-assisted exploration. Most of the reasons for root canal failure may be missed root canals, so if you encounter a maxillary molar, make an effort to find if there is MB2, and the success rate of root canal treatment will be much higher if you find MB2.