Abstract: Objective Distolingual root canal length and curvature in mandibular first molars were measured by CBCT in order to provide theoretical guidance and basis for clinical treatment. Methods The cone-beam computed tomography (CBCT) images of 292 three-rooted mandibular first molars were three-dimensionally reconstructed into the models, and the root canal measurement was used to measure the length and curvature of the distolingual root. Results The mean root canal lengths (from orifice to root apex) of the DL roots were 8.57±1.46mm. The average canal length of DL roots was 6.61±1.38mm for Type I, 8.55±1.34mm for Type II, and 9.02±1.31mm for Type III. These lengths differed significantly by DL root type (p<0.05), and the mean length of the Type I DL roots was the shortest among the 3 types. The degrees of primary canal curvatures of DL roots were measured by the Schneider method. The mean degrees of curvature of DL root canal was 9.71±10.42°in buccolingual view (clinical view, CV), whereas the average curvature of DL root canal was 28.55±11.22°in mesiodistal view (proximal view, PV). Statistical analysis showed that the curvature of DL roots in PV was significantly (p<0.05) greater than that in CV. Conclusion To understand and get familiar with the characteristics of the length and curvature of the distolingual root of the first mandibular molars is helpful to improve the success rate of root canal treatment.

Key words: Key words: distolingual root, mandibular first molar, CBCT