Association Between Middle Mesial Canals and Additional Distal Root Canal Anatomy in Mandibular First Molars: A Cone-Beam Computed Tomography Study in an Iranian Population.

BACKGROUND

A comprehensive understanding of root canal morphology is essential for successful endodontic treatment. Anatomical variations such as middle mesial canals (MMCs), second distal canals, and additional distal roots may complicate canal identification and instrumentation. Although the prevalence of these anatomical features has been investigated in different populations, evidence regarding their potential coexistence within the same tooth remains limited. This study evaluated the prevalence of MMCs and their association with second distal canals and additional distal roots in mandibular first molars using cone-beam computed tomography (CBCT) in an Iranian population.

METHODS

This retrospective cross-sectional study analyzed 200 CBCT examinations obtained from patients referred to the Department of Oral and Maxillofacial Radiology, Tabriz University of Medical Sciences, between 2019 and 2021. The prevalence of MMCs, second distal canals, and additional distal roots was recorded. Associations among anatomical variables were evaluated using chi-square tests and multivariable logistic regression analyses adjusted for age and sex.

RESULTS

MMCs were identified in 26 of 200 mandibular first molars (13.0%), while second distal canals were observed in 64 cases (32.0%). Among teeth with a second distal canal, 15 cases (23.4%) also exhibited an additional distal root. In multivariable analysis, the presence of an MMC was associated with higher odds of a second distal canal (adjusted odds ratio [OR] = 2.62; 95% confidence interval [CI]: 1.11-6.20; p = 0.027). Among teeth with a second distal canal, an association was also observed between MMC presence and additional distal roots (adjusted OR = 6.00; 95% CI: 1.33-27.16; p = 0.020). However, the relatively small number of positive cases, particularly for additional distal roots, resulted in wide CIs and limited the precision of these effect estimates.

CONCLUSIONS

Within the limitations of this retrospective CBCT-based study, MMCs were associated with the presence of additional distal canal anatomy in mandibular first molars. The findings suggest a possible relationship between mesial and distal anatomical complexity; however, the relatively small number of positive cases and wide CIs warrant cautious interpretation. These associations should be considered exploratory rather than definitive and require confirmation in larger, multicenter studies with greater statistical precision.