Abstract: Objective: To investigate the radicular grooves and root canal morphology in mandibular first premolars that exhibit a C-shaped root using cone-beam computed tomography (CBCT). Methods: CBCT images of 65 patients (130 mandibular first premolars) with C-shaped roots from a sample of 600 patients were selected. The location, number of the radicular grooves, configuration, and symmetry of bilateral canal classification were analyzed. Results: The occurrence rate of C-shaped roots canal was 8.9%. All of 107 C-shaped root had radicular grooves, most of which (89.7%) were located at the mesiolingual surface of the root as a single groove. 93 of the grooves (86.9%) located in the middle third, followed by the apical third (12.1%). The incidence of type C3 of root canal systems at the deepest part of the radicular grooves was 71.0%, while 64.6% of C-shaped mandibular first premolar had bilateral canal symmetry. Conclusion: The mandibular first premolars have a high prevalence of canal variation such as C-type canal system. Understanding the anatomic features of the radicular grooves and the internal root canal system is essential for successful endodontic treatment.

Key words: mandibular first premolar, cone-beam computed tomography, C-shaped canal, radicular groove