The aim of this study was to evaluate the features of the root canals cross-sectional shape at the coronal, middle, and apical levels using cone beam computed tomography (CBCT) among residents of Moscow region. CBCT images of 560 patients were analysed. The cross-sectional shape was determined in the horizontal plane at the coronal, middle and apical thirds of the root canal on intact teeth. The root canal shape was determined as follows: round, oval, and ribbon-like. The root canals of the maxillary anterior teeth belong to the canals with a constant cross-sectional shape from the coronal to the apex, while for mandibular anterior teeth it might change in the apical area. In premolars, oval shape was found in almost 70.0%, ribbon-like shape in 30.0%. For maxillary molars, a changing shape in the middle and apical thirds was established in the mesio-buccal and disto-buccal canals. In the mandibular molars, the shape of the canals changed in the middle and apical thirds of mesial and distal roots. The high occurrence of oval and ribbon-shaped canals, especially in the apical region, may be a problem in their processing and requires further study. © 2025 Elsevier B.V., All rights reserved.