Root and canal morphology of mandibular first premolars with radicular grooves.

To investigate the relation between the radicular groove (RG) and the internal root canal morphology in mandibular first premolars by using micro-computed tomography.A total of 249 extracted mandibular first premolars were collected from a native Chinese population. After scoring the RGs according to the Arizona State University dental anthropology scoring system (ASUDAS), 148 teeth were selected and scanned by using micro-computed tomography. The root canal systems were examined two- and three-dimensionally under the software Mimics 10.01. The depth and angle of the RGs at different levels were measured.The presence of Tomes' root trait (ASU=3-5) was identified in 47/249 of the sample teeth (18.9%). The mean depths of the shallow (ASU=1), moderately deep (ASU=2) and deep grooves (ASU=3) were 0.18, 0.36 and 1.24 mm, and the mean angles were 28.8°, 47.5° and 101.7°, respectively. The incidences of complicated root canal systems were 15.5% (ASU=0), 18.7% (ASU=1), 37.0% (ASU=2) and 90.0% (ASU=3). In nine scanned specimens, accessory canals were found communicating between the main canal and the RG. Invagination canals were observed in four specimens, and C-shaped canals were found in 29 specimens (19.6%).The complexity of root canal systems in mandibular first premolars is determined by the severity of RGs, which can be scored by the ASUDAS. Detecting the incidence of various root canal forms corresponding to each ASUDAS score is useful for calculating the standardized rates from published data of dental anthropology. Understanding the anatomic features of the RG and the internal root canal system is essential for successful dental treatment.