Accessory Apical Foramina in Mandibular Second Molars with Mesial and Distal Root Canal Systems: An Ex Vivo Micro-CT Morphometric Study

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• Picked for Anatomy (paper of the day, 19 October 2026): Accessory apical foramina in mandibular second molars

Abstract

Background: The apical anatomy of mandibular second molars may include accessory foramina not adequately represented by classifications of the main root canal configuration. This ex vivo micro-computed tomographic study evaluated the frequency, number, and two-dimensional perimeter of accessory apical foramina associated with independent mesial and distal canal systems. Methods: Sixty-four extracted mandibular second molars were selected, including teeth with completely separate roots and teeth with partial external root fusion, provided that the mesial and distal canal systems remained independent and terminated in distinct main foramina. Mesial systems were stratified by Vertucci configuration as Type I (n = 21), Type II (n = 21), and Type IV (n = 22), whereas all distal systems were Type I. Specimens were scanned at an isotropic voxel size of 10.98 μm. Accessory apical foramina were defined as openings distinct from the main apical foramen or foramina that were continuous with the canal system and communicated with the external root surface. Mesial and distal systems were compared using paired analyses. Results: Accessory apical foramina were detected in 42/64 mesial systems (65.6%) and 21/64 distal systems (32.8%). Their frequency was significantly higher in mesial systems. Overall, 152 accessory foramina were identified in mesial systems and 66 in distal systems, with significantly higher paired counts mesially (p = 0.0002). Among the 15 teeth presenting accessory apical foramina in both the mesial and distal canal systems, the mean number of accessory foramina was similar between the two systems, whereas distal accessory foramina had a larger mean two-dimensional perimeter. Mesial Vertucci configuration was not significantly associated with their presence or number. Conclusions: Accessory apical foramina occurred frequently, particularly in mesial canal systems. Main canal configuration did not fully represent apical foraminal complexity, emphasizing the importance of cleaning, disinfection, and obturation of the entire apical canal system. Because the sample was deliberately stratified by mesial canal configuration, the reported frequencies characterize the selected sample and should not be interpreted as population prevalence estimates.

Abstract as published, via PubMed.