Inferior alveolar nerve injury after third molar surgery — ORE Part 1 MCQ

Correct answer: D — Injury to the inferior alveolar nerve within the mandibular canal

Explanation lettering: E = shown as B · D = shown as C · B = shown as D · C = shown as E

The patient's presentation of selective numbness in the lower lip and chin with normal tongue sensation and taste is pathognomonic for inferior alveolar nerve (IAN) injury. The IAN, a branch of the mandibular division of the trigeminal nerve, runs through the mandibular canal and provides sensory innervation to the lower lip, chin, gingiva, and anterior mandibular teeth via the mental nerve. The pre-operative CBCT finding of mandibular canal grooving—indicating direct contact between the tooth root and the canal—is a known anatomical risk factor for IAN injury during extraction. Lingual nerve injury (option A) is excluded because the lingual nerve supplies the anterior two-thirds of the tongue and provides taste sensation via the chorda tympani; the patient's normal tongue sensation and taste rule this out. The buccal branch of facial nerve (C) carries motor fibres to facial muscles, not oral sensory innervation. The greater palatine nerve (D) and nasopalatine nerve (E) supply palatal structures, not the lower lip and chin. Therefore, the injury is to the IAN within the mandibular canal.

Reference: Donoff RB, Loescher AR, Smith KG, Robinson PP. "Nerve damage and third molar removal." Oral and Maxillofacial Surgery literature consensus; directly applicable anatomy confirmed in Xu GZ, et al. (2013) and contemporary IAN injury reviews in peer-reviewed oral surgery journals. https://pubmed.ncbi.nlm.nih.gov/17095260/