Which vital structure lies immediately distal and lingual to tooth #30 and is at risk during periosteal elevation of a lingual flap?

Correct answer: C. The lingual nerve

• A. The nerve to mylohyoid branches from the inferior alveolar nerve before it enters the mandibular foramen and runs in the mylohyoid groove. It is chiefly motor and lies well inferior to the surgical field.
• B. The long buccal nerve lies on the BUCCAL aspect, supplying buccal mucosa and gingiva. A lingual approach does not endanger it.
• C. CORRECT. The LINGUAL NERVE runs in the soft tissue immediately against the lingual plate in the third molar region, and in a substantial minority of people it lies AT OR ABOVE the crest of the lingual plate and directly against the periosteum. That anatomic variation is exactly why raising a lingual flap or slipping an elevator lingually puts it at risk. Injury causes numbness or altered sensation of the ipsilateral anterior two-thirds of the tongue, the floor of mouth and the lingual gingiva, and loss of taste on that side.
• D. The inferior alveolar nerve runs WITHIN the mandibular canal, inferior to the roots. It is at risk from root proximity during the extraction itself and from bur or elevator penetration into the canal, but not from elevating the lingual periosteum.

Note: Lingual nerve injury is less common than IAN injury but recovers less well, because the nerve lies in soft tissue with no bony canal to guide regeneration. Protecting it means keeping instruments on bone and avoiding lingual flap retraction where possible.