Mental Nerve Injury — MFDS Part 1 MCQ

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EasyAnatomy (Head & Neck)Mental Nerve InjuryMFDS Part 1

A patient sustains a mandibular body fracture at the level of the second premolar. Afterwards, they have numbness of the ipsilateral lower lip and skin of the chin, but sensation in the mandibular teeth remains normal. Which nerve has most likely been injured?

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Correct answer: C — Mental nerve

The correct answer is C, the mental nerve. It is the terminal sensory branch that emerges from the mental foramen and supplies the ipsilateral lower lip and skin of the chin. Preserved sensation in the mandibular teeth is the key discriminator because the mental nerve does not supply the teeth. Injury to the inferior alveolar nerve proximal to the mental foramen would usually also impair dental sensation. The lingual nerve supplies general sensation to the anterior two-thirds of the tongue and lingual gingiva. The buccal nerve supplies the cheek mucosa and buccal gingiva around the mandibular molars. The mylohyoid nerve is predominantly motor to mylohyoid and the anterior belly of digastric.

Reference: Betz D, Fane K. Mental Nerve Block. StatPearls, updated 2026. https://pubmed.ncbi.nlm.nih.gov/29489259/