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The purpose of this study was to determine root canal cross-sectional shapes (RCCSSs) of human permanent teeth using new cone-beam computed tomographic (CBCT) software. RCCSS was determined on CBCT scans of 1400 teeth (422 patients) as follows: (1) circular, (2) conical/pyramidal, (3) oval/long oval, (4) flat/ribbonlike, (5) 8 shaped, (6) C shaped, (7) calcified, (8) trapezoidal, (9) drop shaped, and (10) other shapes. Root canal shapes were evaluated in the coronal and middle thirds, 2 mm below their beginning, and in the apical third, 1 and 2 mm short of the apical foramen. Categoric variables were described as frequencies and percentages and analyzed using the chi-square test. The level of significance was set at P =.05. Maxillary anterior teeth and maxillary first and second premolars had a circular RCCSS at 1 and 2 mm from the apical foramen in more than 45% of the cases. The most frequent RCCSS in the buccal canal of maxillary first premolars at 1 mm from the apical foramen was circular (71%) followed by flat/ribbonlike (10%) and oval/long oval (6%). In mesiobuccal roots of maxillary and mandibular first molars at 1 mm from the apical foramen, the circular shape was found in 52% and 49%, respectively. The RCCSSs in human permanent teeth are variable according to the tooth group and root thirds. The highest frequency of the circular-shaped canal at 1 and 2 mm from the apical foramen was found in maxillary central incisors and mandibular first and second premolars. Oval-shaped canals were detected in practically all tooth groups and root thirds. [ABSTRACT FROM AUTHOR]