Statement of the Problem: To perform a successful endodontic treatment, sufficient knowledge about the number of root canals and their morphology is essential. Missed normal variations may burden this treatment.Purpose: This study aimed to evaluate the presence of the second canal in the roots of mandibular central and lateral incisors in an Iranian population by employing CBCT images.Materials and Method: This cross-sectional study recruited 180 CBCT image of mandible to evaluate the number of roots as well as the number and types of root canals. Data for each sample were collected in a data collection form set and analyzed by chi-square test using SPSS17 software.Results: A total of 681 permanent mandibular incisors were assessed. All samples had one root. Most of the samples (70.3%) had only one canal (type 1 Vertucci classification). The frequency of dual-canal in samples was 29.7%; the prevalence of dual-canal in mandibular lateral teeth (35%) was more than the mandibular central teeth (23.9%, p< 0.05). Following type 1 canal, type 3 (15.7%), type 5 (12.9%), type 4 (0.7%), and type 2 (0.3%) canals had the highest frequencies respectively.Conclusion: Based on this study, presence of a second canal in mandibular lateral teeth (35%) is more common than in mandibular central teeth (23.9 %). The most common canal type observed was type 1 (according to Vertucci classification) followed by type 3.