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Abstract : This study evaluated the danger zone (D.Z.) in mesial roots of mandibular molars and the correlation between the sex of the patient and the dentin thickness at the danger zone area. And evaluated anatomical references of the D.Z. and some anatomical landmarks, including tooth/root length, inter-canal orifices distance, and the influence of the age and sex of the patient on the dentin thickness at the danger zone area. A total of 301 randomly selected CBCTs were included in this cross-sectional study. Two experienced endodontists assessed the images. The MR length of each specimen was recorded from the cementoenamel junction of M.F.M.s to the apex, using CBCT axial planes, and categorized according to the length of teeth as follows: Short root (9-12mm), medium root (12.1-15 mm), long root (15.1-19mm). Then, the minimum dentin thickness of the distal wall of the ML and M.B. canal was evaluated in the axial view of the CBCT images in sections 3 mm below the furcation. Additionally, the distance between mesiobuccal (M.B.) and mesiolingual (ML) canal orifices of all specimens was recorded at the lowest level of the cementoenamel junction on the buccal aspect of the crown and calculated as the linear distance between the central axe of each orifice, in millimeters. The sample comprised 301 subjects, 118 males (39.2%) and 183 females (60.8%), distributed into five age groups. The Shapiro-Wilk (W) goodness-of-fit test showed non-significant deviation from normality for most of the sample in relation to sexes, so the data were analyzed using parametric tests. There was no significant correlation between root length and the danger zone; there was no significant difference in inter-orifice distance between males and females, but there was a significant difference between the age groups (p value= 0.000). The length of tooth/root and inter-orifice distance of mesial roots of mandibular molars might be predictive factors for the dentin thickness of the D.Z.