Introduction: Precise anatomical information about periapical region is important to perform apical surgery. Especially in case of mandibular first molar which has radix entomolaris(RE), caution is required to surgeon because of anatomical limitations to approach the lesion. In this study Korean mandibular first molars which have RE were investigated. 3D position and curve direction were analyzed by using cone-beam computed tomography(CBCT) images. The purpose of this study is to provide 3D positional information which is needed when surgical approach is performed to DL root of RE.Methods: Mandibular CBCT images of 139 adults who took the images in Seoul National University Dental Hospital on June, July and August, 2014 were examined. 72 mandibular first molars which have DL root were selected among 278 teeth. Distance from distolingual(DL) root tip to mandibular canal, buccal cortical bone, lingual cortical bone and adjacent distobuccal(DB) root tip and curve direction of DL root were measured.Results: The average distance to mandibular canal was 8.50mm in male and 6.90mm in female. The average distance to buccal cortical bone was 10.20mm in male and 9.74mm in female. The average distance to lingual cortical bone was 4.31mm in male and 3.75mm in female. The average distance to adjacent DB root tip was 6.96mm in male and 6.33mm in female. Among 72 teeth, 40 had distobuccal curve direction, 3 had distolingual curve direction, 25 had mesiobuccal curve direction, 4 had mesiolingual curve direction. Conclusions: In case of male, the average distance from DL root tip was generally farther than female. The nearest anatomical structure from DL root tip was lingual cortical bone and DB root tip, mandibular canal and buccal cortical bone were next. Most of RE had buccal curve direction. The result from this study provide useful information which is needed when surgical approach is performed to DL root of RE.
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