Research Article Evaluation of Root Canal Morphology of Mandibular First and Second Premolars Using Cone Beam Computed Tomography in a Defined Group of Dental Patients in Iran Neda Hajihassani, 1 Neda Roohi, 1 Karim Madadi, 2 Mahin Bakhshi, 3 and Maryam Tofangchiha 4 1 Department of Endodontics, Dental School, Qazvin University of Medical Sciences, Qazvin, Iran 2 Private Practice, First Floor, No. 1, 7th Ave, Shohada Blvd, P.O. Box 3175745116, Fardis, Kara, Alborz Province, Iran 3 Department of Oral Medicine, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran 4 Department of Oral and Maxillofacial Radiology, Dental School, Qazvin University of Medical Sciences, Qazvin, Iran Correspondence should be addressed to Maryam Tofangchiha; mt tofangchiha@yahoo.com Received 13 May 2017; Revised 15 August 2017; Accepted 5 September 2017; Published 16 November 2017 Academic Editor: Cornelis F. Sier Copyright © 2017 Neda Hajihassani et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Successful dental root canal treatments require a complete knowledge of dental anatomy and root canal morphology. Materials and Methods. One hundred and forty-five cone beam computed tomography (CBCT) images were used to assess the anatomy and morphology of mandibular premolars based on Vertucci’s classifications in a defined group of dental patients in Iran. e number of roots and root canals, root canal morphology, root and canal shape (curvature), existence of C-shaped canal, and influence of sex on each of these were evaluated. A chi-squared test was used for statistical analysis. Results. e mandibular first and second premolars had a single root in 95.97% and 100% cases, respectively. In the mandibular first premolars, 62.2% were of type I, 0.8% type II, 10.9% type III, 0.8% type IV, 20.3% type V, 4.2% type VI, and 0.8% type VII; in the second premolars, 78% of canals were of type I, 3% type II, 11% type III, 7% type V, and 1% type VI. C-shaped canals did not exist in either of the premolars. e most prevalent root and canal shape was straight. e most prevalent root curvature was a distal curvature in both premolars (71.4% and 74% of first and second premolars, resp.). e most prevalent canal curvature was lingual and buccal for the first premolars (7.6% each) and distal for the second premolars (11%). No significant difference was found between men and women in nearly all of the above ( > 0.05). Conclusion. e results suggest that there is a need to conduct further evaluations on finding root and canal variations among more populations to gain better knowledge prior to root canal treatment. 1. Introduction Nowadays, with the evolution of contemporary dentistry, endodontic treatment has become an important and effective method for maintaining and preserving dental health. Lack of knowledge of the internal anatomy of teeth and dental pulp is the second-most-important cause of treatment failures aſter wrong diagnosis and treatment planning [1]. us, an understanding of the internal anatomy of teeth is essential for better debridement and obturation of canals and, therefore, a better prognosis of the treatment. e root canal system has a complex anatomy. It varies not only between different teeth but also in one particular tooth between different persons. Root canal anatomy does not usually reveal a single uniform tapered canal; extra canals, anastomosis, and other irregularities exist [2]. Mandibular premolars have one of the most complex anatomies. Treatment failures and posttreatment flare-ups have been reported in these teeth, thus indicating the exis- tence of too much variation in their morphology [1, 3]. ere have been several studies evaluating the morphology of mandibular premolars’ root canal systems [4–8]. Hindawi Scientifica Volume 2017, Article ID 1504341, 7 pages https://doi.org/10.1155/2017/1504341