ABSTRACT
This study aims to evaluate the root canal system and its curvature and the relationship between the root concavity and the dentin thickness of danger zone in the mandibular first molar using the cone beam CT method. A sum of 101 fresh extracted mandibular first molar were gathered and scanned by CBCT [planmeca romexis 3D] machine. The root canal configuration was evaluated according to Vertucci's classification. Then, the canal curvature was evaluated according to schneider's method in clinical and proximal views. Finally, the relationship between the root concavity and the dentin thickness of danger zone was evaluated using the Pearson correlation coefficient. The most common canal configuration of the mesial roots was vertucci type IV [49.5%], followed by type II [46.5%]. Root canal configuration of the distal root revealed type I in 50.5% and type II in 29.7%. The average angles in proximal dimension for MB, ML, DB and DL canals were 18.80, 18.77, 8.22 and 16.86, respectively. These values in clinical dimension were 22.50, 21.90, 13.83 and 12.04, respectively. No meaningful relationship was found between the dentin thickness and the root concavity of danger zone. The clinician's awareness of the anatomy of the root canal system and the canal curvatures and the internal and external anatomy of the root is helpful and necessary in diagnosis and treatment of the endodontic cases