More information HERE and HERE Introduction: The morphology of the supernumerary third root (radix) in mandibular first molars was examined by micro–computed tomography (mCT) scanning. Methods: Nineteen permanent mandibular first molars with radix were scanned in amCT device to evaluate their morphology with respect to root length, root curvature direction, location of radix, apical foramen, accessory canals and apical deltas, and distance between canal orifices as well as 2- and 3-dimensional parameters of the canals (number, area, roundness, major/minor diameter, volume, surface area, and structure model index). Quantitative data were analyzed by 1-way analysis of variance and the Tukey test (P<.05). Results: The mean length of the mesial, distal, and radix roots was 20.36 ± 1.73 mm, 20.0 ± 1.83 mm, and 18.09 ± 1.68 mm, respectively. The radix was located distolingually (n= 16), mesiolingually (n= 1), and distobuccally (n= 2). In a proximal view, most radix...