Background: The purpose of this study was to evaluate the prevalence of middle mesial canal in mandibular first molars using cone-beam computed tomography (CBCT). Materials and Methods: In this descriptive study, a total of 768 radiographs of mandibular first molars, 384 for males and 384 for females, taken at a private radiology center in Isfahan, were assessed for the presence of middle mesial canal based on the gender of the patients. All samples had been prepared by one CBCT machine. The images were evaluated by endodontists and radiologists. Then, the morphology of first molar mesial root canals was assessed by Vertucci classification, and the obtained results were analyzed by SPSS software using a Chi-square test. The comparison was considered statistically significant at P < 0.05. Results: Twenty-four samples (3.13%) had a middle mesial canal. The prevalence rates of the middle mesial canal in the females and males were found to be 9 and 15 (2.35% vs. 3.92%), respectively, indicating no statistically significant difference (P = 0.21). Of 24 teeth with middle mesial canal, 17 samples (70.8%) were of Type XII and 7 samples (29.2%) were of Type VIII. There was no statistically significant difference between genders with regard to the prevalence of different types of middle mesial canals (P = 0.19). Conclusion: The prevalence of the middle mesial canal was rather low in this study, and it is necessary to detect additional canals in the patients under root canal treatment.

Introduction: Digital and film-based radiography are the most common methods of working length determination. The objective of this study was to compare the accuracy of working length determination of curved canals using digital and film-based radiography. Materials & Methods: This experimental and interventional study, included forty teeth with curved canals conducted at the Dentistry Faculty of Isfahan University of Medical Sciences, in 2018. After access cavity preparation, the direct observation method of the apical tip of the file in the root apex determined the actual working length. Teeth were mounted in acrylic blocks. Canal curvature was calculated based on Schneider’s method using software of indirect digital radiography. Images gathered by E-speed film and digital sensors. A pre-curved file was used to measure the working length of film-based images. In digital radiography, a digital caliper was used to measure the working length with three and six clicks. Data were analyzed by repeated measure analysis, paired t-test, and Intraclass Correlation Coefficient. The Level of significance was set at 0.001. Results: All groups overestimated the actual length although there weren’t any significant differences (p value > 0.05). Paired t-test didn’t show any significant differences between digital and film-based groups (p value > 0.05). Conclusion: Considering several advantages of digital radiography over the film-based method, it is the preferred method for working length determination of curved canals.