Cone-beam computed tomography study of incidence of distolingual root and distance from distolingual canal to buccal cortical bone of mandibular first molars in a Korean population.

The purpose of this study was to investigate the incidence of separate distolingual (DL) root and separate DL canal in 1 distal root and to measure the distance from distobuccal (DB) and DL canal to buccal cortical bone of mandibular first molars in a Korean population by using cone-beam computed tomography images.Screening identified 1400 subjects with bilateral permanent mandibular first molars for inclusion in this investigation. The incidences of separate DL root (distal 2 roots with 1 canal for each root, 2 roots 2 canals [2R2C]) and separate DL canal in 1 distal root (distal 1 root with 2 separate canals, 1 root 2 canals [1R2C]) were investigated. The distances from DL canal to buccal cortical bone and from DB canal to buccal cortical bone were measured.The incidence of 2R2C was 26.6% (373 of 1400) on the right side and 19.0% (266 of 1400) on the left side, with a statistically significant difference (P < .001). The incidence of 1R2C was 3.5% (49 of 1400) on the right side and 4.5% (63 of 1400) on the left side. Mean distance from DB canal to buccal cortical bone was 3.37 mm in 2R2C (n = 639) and 4.17 mm in 1R2C (n = 112). Mean distance from DL canal to buccal cortical bone was 8.63 mm in 2R2C and 7.19 mm in 1R2C. Statistical difference was detected between 2R2C and 1R2C for both DB and DL canals (P < .001 and P < .001, respectively).Separate DL root is common in the mandibular first molar in a Korean population. Knowledge of the occurrence of DL root and buccal bone thickness can improve the success rate of endodontic microsurgery.