Abstract : Purpose : The aim of this study was to assess the root and root canal morphology of mandibular premolars in a Japanese population using dental cone-beam computed tomography (CBCT).

 Materials and methods : We analyzed the CBCT images of 286 first premolars and 280 second premolars from 145 patients. The following parameters were evaluated on CBCT : (1) number of roots and root canals ; (2) the classification of root canal configuration according to Vertucci’s criteria.

 Results : The majority of the first and second mandibular premolars had one root (98.3% of the first premolars and 100.0% of the second premolars) ; in addition, two roots were identified in 1.7% of the first premolars. The most prevalent root canal frequency was as follows : one canal (77.0%), two canals (19.2%), and three canals (1.8%) for single-rooted first mandibular premolars ; one canal (98.2%) and two canals (1.4%) for second premolars. The most predominant root canal morphologies for single-rooted first mandibular premolars were Vertucci’s type I (78.6%), followed by type V (14.6%), type III (5.0%), and type VIII (1.8%) configurations ; the most predominant root canal morphologies for second mandibular premolars were type I (98.6%) and type V (1.4%) configurations.

 Conclusion : First mandibular premolars exhibited high variability and complexity in their canal system. On the contrary, the root and root canal configurations of second mandibular premolars showed a lower degree of variability compared with first mandibular premolars.