The purposes of this study were to elucidate the anatomic relationship between the dental roots and surrounding tissues and to identify the optimal sites at which to install dental surgical devices including immediate-implant fixtures and alveolar distractors. We made 5 types of measurements on horizontal cross sections obtained at 1-mm intervals from 20 Korean mandibles. The following results were obtained: (1) the mandibular facial plate was thinnest at the canine (0.5-0.7 mm) and became thicker toward the molar region; (2) the thicknesses of the facial and lingual cortical bone in the interdental region increased from anterior to posterior and from coronal to apical aspects; (3) in each section, the buccolingual root was narrower than 4 mm at depths greater than 8 and 9 mm in the central and lateral incisors, respectively, and the maximum mesiodistal root widths were 3.0 and 3.3 mm; (4) the interroot distance increased from anterior to posterior and from coronal to apical aspects; and (5) on the sections of the first and second molars, the diameter of the septal bone ranged from 4.2 to 7.9 mm buccolingually and from 1.3 to 3.3 mm mesiodistally. Achieving successful placements of implant fixtures and bone screws requires an accurate understanding of the anatomic structure at the installation site. The reported anatomic data might facilitate successful treatments and provide crucial information for use when planning and performing placements of dental surgical devices.