Apical anatomy of primary molar root canals: a micro-Ct study

To investigate, using micro-computed tomography (micro-CT), the apical anatomy of mandibular second primary molar roots in Egyptian children, with emphasis on the spatial relationship between the apical foramen and the anatomic apex, and the morphology and dimensions of the root canal at the apical foramen level.

Fifty extracted human mandibular second primary molars (150 canals: 50 distal, 50 mesiobuccal, 50 mesiolingual) with complete root length and minimal resorption were scanned using high-resolution micro-CT (15.24 μm voxel size). The distance between the apical foramen and the apex, canal major diameter, and roundness at the foramen level were measured using CTAn software. Descriptive statistics were calculated, and exploratory canal-type comparisons were performed using one-way ANOVA followed by Tukey post-hoc tests. (α = 0.05).

The apical foramen did not coincide with the anatomic apex in any canal. The mean apex-to-foramen distance was 0.57 ± 0.44 mm. Mean apical canal diameter was 0.63 ± 0.24 mm and mean roundness was 0.48 ± 0.17, indicating predominantly oval canal shapes. The overall comparison suggested variation in apex-to-foramen distance among canal types (p = 0.040), but post-hoc comparisons did not confirm statistically significant pairwise differences between individual canal types. Distal canals exhibited significantly larger diameters than both mesial canals (p < 0.05), whereas the difference between mesiobuccal and mesiolingual canals was not significant. Roundness did not differ significantly among canal types (p = 0.079).

In Egyptian children, the apical foramen of mandibular second primary molar is consistently offset from the anatomic apex. The distal canals demonstrated the largest major canal diameter at the apical foramen level.

Because the apical foramen rarely coincides with the apex and complete mechanical enlargement to the true apical diameter is often clinically unrealistic, pediatric endodontic treatment should prioritize accurate working-length determination (e.g., electronic apex locators) and combine conservative shaping with effective chemical disinfection to optimize apical cleaning while preserving root integrity.