From 340 CBCT included in this study, 65 patients (19.1%) found a C-shaped root canals in the mandibular first premolars, 13 patients (3.8%) - C-shaped root canals in mandibular second premolars, 34 (10%) patients - in the mandibular second molars. Patients with C-shaped root canals in the mandibular first premolars 10,77% found C-shaped root canals in the mandibular second premolars. This is 2,8 times higher than the incidence C-shaped canals in the mandibular second premolars (3,85%) patients in the sample. C-shaped root canals in the mandibular second molars in 20,6% of patients were combined with the C-shaped root canals first mandibular premolars. It is 2 times larger than those in the sample (10%). The combination of C-shaped root canals in the first mandibular premolars and mandibular second premolars with mandibular incisors and canines with two canals not exceed their prevalence in the sample.