Abstract
This multinational cone-beam computed tomography (CBCT) study evaluated the root canal morphology of mandibular first premolars (M1Ps) from 21 countries and compared how well the Ahmed and Vertucci classification systems represented these patterns. A total of bilateral mandibular first premolars from eligible CBCT scans were assessed using both systems, and the data were analyzed with a hierarchical probabilistic approach to account for population and imaging-related variation. Across the overall dataset, a simple single-canal configuration was the dominant pattern, and this remained the most common finding in all populations despite limited but structured variation in less frequent subclasses. The Ahmed system classified all observed configurations, whereas the Vertucci system left approximately 10.2% of cases without an equivalent category. In addition, Ahmed preserved more anatomical detail, while Vertucci compressed several distinct configurations into broader groups. Demographic and imaging-related factors had modest effects, with voxel size showing the clearest technical influence on the detection of more complex patterns. Overall, M1P morphology showed a stable global pattern with secondary heterogeneity, and the Ahmed system provided a more complete and informative representation for CBCT-based morphology assessment across diverse populations.