The mental foramen is an oval opening on the external surface of the mandibular body, typically located below the second premolar or between the premolars, approximately at the mid-height of the body. It transmits the mental nerve (terminal sensory branch of the inferior alveolar nerve), the mental artery, and the mental vein. The mental nerve provides cutaneous sensation to the lower lip, chin, and buccal gingiva of the anterior teeth.
The mental foramen is the critical landmark in anterior mandibular dental procedures: implant placement, root resection, and bony surgery of the premolar region must avoid the foramen to prevent mental nerve injury. The inferior alveolar nerve forms an anterior loop before turning posterior to exit the mental foramen, and this loop may extend further anteriorly than expected, placing it at risk during implant placement. Mental block anaesthesia for the lower lip and chin is performed by depositing local anaesthetic at the foramen.
Implant placement too posteriorly in the mental foramen zone risks trauma to the anterior loop of the inferior alveolar nerve before it exits as the mental nerve, causing lower lip and chin numbness; preoperative CBCT assessment of the foramen position and anterior loop length is essential for implant planning in the premolar region.
The mental foramen can be mistaken for a periapical lesion on periapical dental radiograph when the beam angle aligns the foramen superimposed on a tooth root; clinical correlation with absence of periapical symptoms and a positive pulp vitality test distinguishes normal anatomy from pathology.
