Paralysis of the mental nerve is one of the principal complications of surgery of the mandibular canal and mental foramen region. The position of mental foramen can be clearly depicted on CT scans. The mental foramen is bilaterally located at the mandibular premolar region and appears as a dimple on the bone surface. However, several reports have described an accessory mental foramen (AMF). We examined CT pictures taken from patients with implants for missing mandibular teeth to detect variations of the AMF. The results were follows: 1) AMFs were present in 28 patients (24.6 %). 2) Unilateral AMFs were found in 24 patients, and bilateral AMFs in 4 patients. 3) Among patients with unilateral AMFs, 21 had AMFs with one foramen, and 3 had AMFs with two foramens. Among patients with bilateral AMFs, 2 patients had one foramen on each side, and 2 had two foramens on one side. 4) The position of AMF relative to that of the mental foramen was as follows: 18 foramens were superior mesial, 8 were superior distal, 6 were inferior mesial, and 5 were inferior distal.
These results suggest that one quarter of patients with missing mandibular teeth may have AMFs around the mental foramen.