Course of the mandibular incisive canal and its impact on harvesting symphysis bone grafts

Purpose To characterize the anatomic course of the mandibular incisive canal to define parameters for harvesting autogenous bone from the symphysis of the mandible. Materials and Methods A series of osteotomies were completed between the mental foramina in the anterior mandibles of 19 cadavers. Methylene blue dye was used to help identify the incisive canal. From the canal, distances to key adjacent landmarks were measured with a Boley gauge to 0.1 mm. Measurements included distances from the mandibular incisive canal to the buccal cortex, the lingual cortex, the inferior border of the mandible, the apices of the teeth, and the buccal cementoenamel junction (CEJ) of the teeth. Results The canal decreased in diameter from lateral to medial. It tended to be closer to the buccal cortical bone than to the lingual cortex (P <.001) and was, at times, directly abutting the buccal cortex (average distance to buccal cortex, 3.5 mm). The canal maintained a relatively constant distance from the apices of the teeth (approximately 7 to 8 mm), coursing inferiorly under the longer canines bilaterally. The canal became increasingly difficult to identify toward the midline, likely dispersing into microscopic tributaries. Conclusions The authors suggest several modifications to the standard surgical approach to the symphysis area during the harvest of bone grafts. When the goal is to avoid the mandibular incisive canal, osteotomies should not exceed a depth of 4 mm, should be at least 5 mm anterior to the mental foramen, and 9 mm below the root apices (or 23 mm below the lowest facial CEJ) and should maintain the contour of the mandible's inferior border. Alternatively, some degree of canal compromise can be accepted and larger grafts can be obtained by increasing the depth of the harvest in the horizontal dimension or decreasing the distance from the osteotomy to the root apices (or the CEJ) in the vertical dimension.