Hamadan University of Medical Sciences Avicenna Journal of Dental Research 2423-7582 17 2 2025 06 30 How Common Are the Anatomical Anomalies of Mandibular Molars in an Iranian Subpopulation? A Cone-Beam Computed Tomography Assessment 109 117 10.34172/ajdr.2165 EN Shamsodin Heydari https://orcid.org/0009-0001-1602-0618 Behnam Bolhari Foozie Zahedi https://orcid.org/0000-0001-8096-0957 Shima Younespour Journal Article 10.34172/ajdr.2165 2024 11 23 2025 01 20 Background: Information about root canal anatomical variations is important for successful root canal treatment. This study assessed the frequency of common anomalies of permanent mandibular first and second molars using cone-beam computed tomography (CBCT). Methods: In this cross-sectional study, 505 CBCT scans were evaluated by an oral radiologist and an endodontist to determine the presence/absence of the mid-mesial canal, the C-shaped canal configuration and its type, the third root and its type, taurodontism and its percentage, and dilaceration and its degree. To assess intra- and inter-observer agreements, all CBCT scans were evaluated twice at a one-week interval by both observers. The data were analyzed using the kappa coefficient and univariate logistic regression. Results: The kappa values showed acceptable inter-observer (0.780) and intra-observer (0.983) agreements. Of all, 21 teeth (4.17%) had a mid-mesial canal, 20 teeth (3.96%) had a third root, and 38 teeth (7.52%) had a C-shaped canal. The frequency of the third root (P=0.01) and C-shaped canal (P<0.000) in mandibular second molars was significantly higher than that in mandibular first molars (P<0.000). Taurodontism was detected in 6 teeth (1.19%), while root dilaceration was present in 162 teeth (34.23%). Age and gender had no significant association with the presence of a mid-mesial canal, third root, C-shaped canal, or dilaceration (P>0.05). Conclusion: Mandibular first and second molars were not significantly different in the frequency of mid-mesial canal, taurodontism, and dilaceration. Considering the relatively high prevalence of dilaceration and C-shaped canals in the study population, these anatomical variations should be taken into account in root canal treatment.