Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 1 4 2004 12 15 43 47 K. Ashofteh Yazdi A. Jafari 2015 10 03 Statement of Problem: Knowledge of internal anatomy of tooth plays an important role in a successful endodontics treatment. For a proper endodontic treatment, it is not only important to know the form of normal anatomy of tooth’s interior but one must also be acquainted with the possible diverse forms. Purpose: A thorough understanding of the internal anatomy of human mandibular incisors (central and lateral). Materials and Methods: A total of 205 central and lateral mandibular incisors that had healthy roots were selected and put in 10% formalin solution. After cleaning the samples with the help of brushes and other devices, they were kept in 5% sodium hypochlorite solution. Finally the roots were cleaned and the samples were prepared for next stages. Three methods were used, coloring (fushin1%, radiography (buccolingual and proximal sides), and cross-sectioning (cervical- middle-apical). Results: The result indicated that: - 88%of the teeth had a single canal and one apical foramen; - 8% of the teeth had a single canal and two apical foramena; - 3.5% of the teeth had two canals and one apical foramen; - 0.5% of the teeth had two canals and two apical foramena; Conclusion:A thorough understanding of the pulp morphology is essential for successful treatment of root canal. Therefore, a dentist should always be on the watch for the existence of two canals or a two-branched canal while working on the mandibular incisor teeth. it is essential to have the necessary precision in finding the second canal. https://fid.tums.ac.ir/index.php/fid/article/view/39 https://fid.tums.ac.ir/index.php/fid/article/download/39/39