The morphology of the mesiobuccal (MB) root of maxillary molars commonly presents 2 main root canals, named MB1 and MB2, and a high incidence of fine anatomical structures including intercanal communications, loops, accessory canals and apical ramifications, resulting in a very complex canal system. The orifice of the MB2 is usually located either mesial to or in the sub pulpal groove within 3.5 mm palatally and 2 mm mesially from MB1, often hidden under the shelf of the dentine wall or calcifications in a small groove. In the literature, percentage frequency of MB2 canal in maxillary molars has ranged from 10 to 95%, depending not only on the method used in the study, such as sectioning, dye injection, radiography, scanning electron microscopy, or micro-CT, but also on ethnic and demographic factors related to the studied population, which may include geographic region, age and gender. Consequently, it can be missed in routine clinical practice, especially without using magnification or special lighting equipment. This inability to recognize its presence and to adequately treat it have been considered the major cause of failure in root canal therapy of maxillary molars. Clinicians, therefore, must be aware of MB2 prevalence and adopt procedural steps to locate and prepare it properly.
More information about this topic can be found in this SYSTEMATIC REVIEW
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