BACKGROUND: The middle mesial canal (MMC) represents a complex anatomical variation of mandibular first molars (MFMs). The association between MMC occurrence and anatomical landmarks remains controversial in cone-beam computed tomography (CBCT) studies. MATERIALS AND METHODS: CBCT imaging data and data regarding age, sex, tooth position, the distance between the mesiobuccal (MB) and mesiolingual (ML) orifices, and the presence of radix entomolaris were collected. When MMCs were present, root canal morphology was classified according to the Ahmed classification system. The data were evaluated using the t-test and chi-square test. RESULTS: The incidence of MMCs in MFMs was 8.12%, of which confluent MMCs were the most common. The incidence of MMCs was significantly lower in patients aged ≥ 40 years than in patients aged < 40 years (p < 0.05). The incidence of MMCs was not related to sex or the presence of radix entomolaris but was related to tooth position. Specifically, the incidence was slightly higher in the left MFM than in the right MFM (p < 0.05). On the pulp chamber floor, as the distance between the MB and ML orifices decreased, the incidence of MMCs increased (p < 0.05). CONCLUSIONS: General dental practitioners should carefully examine anatomical landmarks of MFMs (particularly the pulp chambers) to help predict the presence of MMCs. Understanding these anatomical landmarks may help general dental practitioners to avoid missing MMCs and to prevent the excessive cutting of dental structures during clinical practice.
Han et al. (Thu,) studied this question.