Interpretation of Cone-Beam Computed Tomography Scans of Mesio-buccal Roots of Maxillary Molars: Developmental and Technological Considerations

Abstract

Maxillary molars have usually three roots. The palatal and disto-buccal roots have a roughly round cross section with a single root canal. The third root, the mesio-buccal root has commonly an oval cross section and often has two canals. One canal is larger and located in the buccal part of the root, referred to as MB1 canal and another, which has usually a smaller diameter and is located in the more palatal part of the root is referred to as MB2 canal. Failure of endodontic treatment of maxillary molars is often related to the second MB2 root canal that was not recognized and not treated, thus containing necrotic tissue and bacteria. When considering the developmental pattern of the mesio-buccal root, it is rather predictable that if the root has an oval cross-section it is most likely to have an MB2 canal. Oval cross section may be best demonstrated in an axial view of a Cone-Beam Computerized Tomographic (CBCT) scan of the tooth. Yet, such scan may often have no evidence of the presence of MB2 canal. When voxel size of the CBCT scan is considered, absence of an MB2 canal in the scan may mean that its diameter may be smaller than can be detected in a clinical CBCT image. MB2 canals with a diameter of 100 µm cannot be expected to be seen even in a high resolution clinical CBCT scan, yet failing to find and treat them may lead to failure of the endodontic treatment of maxillary molars. Thus, when an oval cross section is detected in the MB root, the operator should use all his skills to find and treat the “invisible” MB2 canal.