Objective This study aimed to evaluate the incidence of middle mesial canals (MMCs) in mandibular first molar in Haikou and analyse the related factors. Methods The cone-beam computed tomography images of 1 964 mandibular first molars from 1 032 patients from January 2018 to December 2020 were retrospectively analysed. The morphological characteristics of mesial root canals were observed, and the incidence of MMCs was analysed. The age, sex, ethnicity, living environment, tooth position, distance between mesial buccal (MB) and mesial lingual (ML) root canal orifi-ces and existence of root canal isthmus (RCIs) were collected and recorded. Logistic regression analysis was performed on the related factors of MMCS. Results The incidence of MMCs in mandibular first molars was 22.3% in Haikou, and the additional type (3-2) was the most common type of MMCs, accounting for 63.8%. The incidence of RCIS was 50.5%. Multivariate logistic analysis showed that patients ≤40 years old (OR=2.667, 95%CI: 1.185-6.004), city residence (OR=1.456, 95%CI: 1.036-2.048), accompanied by RCIs (OR=3.808, 95%CI: 1.353-10.718), distance between MB-ML root canal orifices<3 mm (OR=3.374, 95%CI: 1.168-9.741) were independent risk factors for MMCs in mandibular first molars. Conclusion The incidence of MMCs in mandibular first molars in Haikou is relatively high, and the independent risk factors for MMCS were ≤40 years old, city residence, accompanied by RCIs and distance between MB-ML root canal orifices<3 mm.
