Association between C-shaped Root Canal Configuration in Mandibular Second Molars and Radicular Grooves in Mandibular First Premolars: A CBCT-based Study in a Western Chinese Population

C-shaped root canal configurations (CSRCs) in mandibular second molars (MSMs) and radicular grooves (RGs) in mandibular first premolars (MFPs) are anatomical variations that may affect endodontic procedures. However, their relationship within the same individual remains unclear. This study investigated the association between CSRCs and RGs using cone-beam computed tomography (CBCT) in a Western Chinese population.

This retrospective CBCT study enrolled 1,637 participants (682 males and 955 females), and a total of 3,274 MSMs and 3,274 MFPs were assessed. RGs in MFPs were evaluated using the Arizona State University Dental Anthropology Scoring System, whereas CSRCs in MSMs were classified according to the Fan et al. classification system (C1-C5). Examiner reliability was assessed using the Cohen's kappa and weighted kappa coefficients. The prevalence, configuration, and bilateral symmetry of CSRCs and the prevalence, configuration, anatomical location, severity, and bilateral symmetry of RGs were assessed. Cohen's kappa, weighted Cohen's kappa, and McNemar's test were used to assess agreement and bilateral symmetry. The association between CSRCs and RGs was examined using chi-square tests, Cramer's V, and univariable and multivariable binary logistic regression analyses. The multivariable model was adjusted for age group and gender, and a separate multivariable binary logistic regression model was performed to evaluate the associations of age group and gender with the co-occurrence of CSRCs and RGs. Statistical significance was set at P < .05.

At the patient level, CSRCs in MSMs were identified in 46.0% of participants, with C3 being the most prevalent configuration. RGs in MFPs were identified in 38.2% of participants; the mesial surface was the most frequently affected location, and Arizona State University Dental Anthropology Scoring System Grade 3 was the most common groove-positive grade. CSRCs and RGs demonstrated high bilateral symmetry, occurring symmetrically in 86.6% and 88.9% of participants, respectively. Both anatomical variations co-occurred in 21.6% of participants. CSRC presence was significantly associated with RG presence [χ²(1) = 46.087, P < .001], with a weak effect size (Cramer's V = 0.168). After adjustment for gender and age groups, patients with CSRCs had approximately 2.1 times the odds of exhibiting RGs compared with patients without CSRCs (adjusted odds ratio = 2.092, 95% confidence interval: 1.700-2.574, P < .001). Females had higher odds of exhibiting both anatomical variations, whereas participants aged 51-65 years had lower odds of co-occurrence than those aged 13-30 years.

CSRCs in MSMs were significantly associated with RGs in MFPs. Although the underlying developmental relationship requires further investigation, the presence of a CSRC may provide useful adjunctive clinical information during the endodontic assessment.