Cone beam CT-based measurement of the accessory mental foramina in the Chinese Han population

Anatomical data of accessory mental foramina (AMFs) were investigated in a Chinese Han population using cone beam CT (CBCT). A retrospective analysis was performed on 527 selected sets of CBCT images. The average frequency and diameter of AMFs, the diameter of the ipsilateral mental foramen (MF), and the center distance and relative position between the AMFs and MF were measured and calculated by three professional dentists. Among the 527 patients, AMFs were identified in 36 cases (frequency 6.83%), of which 68.75% of AMFs were larger than 1 mm. The mean diameters of the AMFs and the ipsilateral MF were 1.32±0.61 mm and 3.26±0.90 mm, respectively. The average distance from the AMFs to the alveolar ridge crest (ARC) was 15.05±3.50 mm, and the average distance to the mandibular plane was 15.87±3.64 mm. The positions of the AMFs relative to the MF varied widely. The AMFs were mostly positioned distal-inferior to the ipsilateral MF and under the mandibular second premolars. Nutrient foramina around the MFs were distinguished from AMFs. The reference plane for measuring AMFs was suggested to be the mandibular plane to increase the repeatability and accuracy of the experiment. Standard planes were proposed to determine the relative position between AMFs and the MFs. Based on our results, we propose that for implant surgeries, the safety region of 2 mm above the MFs should be reevaluated. CBCT examination is recommended before the operation to identify important anatomical structures around the MF region and their variations and set the safety distance on an individual basis.