Observation of the retromolar foramen and canal of the mandible: a CBCT and macroscopic study

The retromolar foramen (RMF) is an anatomical structure on the alveolar surface of the retromolar area. This foramen runs consecutive to the retromolar canal (RMC), which diverges from the mandibular canal. It is important to confirm the RMF and canal locations prior to surgical procedures, such as extraction of an impacted molar and bone harvesting as a donor site for bone graft surgery. This aim of this study was to investigate the RMF in Japanese cadaver mandibles using cone-beam computed tomography (CBCT) images and anatomical observations. Ninety sides of 46 cadaver mandibles were investigated in this study. CBCT images around the retromolar region were acquired for all of the mandibles. The frequency and anteroposterior and buccolingual locations of the RMF were examined on these images. Subsequently, four sides of three mandibles were dissected to confirm the contents of the RMC/RMF. In 24 of 46 (52%) mandibles and 34 of 90 (37%) sides, at least one RMF was observed in the images. In 26 dentate mandibles, 12 (48%) mandibles and 14 (33%) sides presented at least one RMF. The average location of the RMF was 14.4 mm posterior from the distal edge of the second molar. The buccolingual location was 3.0 mm lingual from the mandibular canal. Observations made during the cadaver dissections confirmed that the vessels and nerves diverged from the mandibular canal. The findings suggest that the RMF is not a rare anatomical structure and that practitioners should take this foramen into account in all anesthetic and surgical procedures involving the retromolar area.