Objective: This study investigated safe area for orthodontic anchorage device (OAD; including plate type) placement in the mandible, focusing on mandibular canal.
Methods: We used cone-beam computed tomographic images of 35 patients to determine the distance from alveolar crest to mandibular canal (DMC) and the shortest distance from buccal and lingual cortex to mandibular canal (attaining distance: AD) in the areas between premolars (premolar area), between second premolar and first molar (middle area), and between first and second molars (molar area).
Results: DMCs in each area were 16.6, 18.9, and 16.6 mm, respectively, and were similar in adults and adolescents. In case AD was 8 mm, the heights on buccal and lingual sides of the areas were 9.0 and 16.6 mm, 13.7 and 14.7 mm, and 15.3 and 12.0 mm, respectively. On lingual side, AD tended to be shorter in adolescents than in adults. The heights on buccal and lingual sides in case AD was 6 mm were 11.2 and 19.8 mm, respectively, in premolar area and 18.5 and 16.8 mm in middle area. In molar area, this height on lingual side was 13.8 mm, while AD in all patients was greater than 6 mm on buccal side.
Conclusions: Risk of proximity to the mandibular canal should be considered at above heights or greater when an OAD 8 mm in length is placed. Careful attention is needed for placements on lingual side in adolescents. By reducing the OAD length to 6 mm, placement safety increases in all areas except premolar area, especially on buccal side.