A biopsy is planned on the lower lip. Anaesthesia is required for all of the following nerves EXCEPT:

Correct answer: C. The facial nerve (CN VII)

• A. The incisive nerve is the intrabony continuation of the IAN supplying the anterior teeth and adjacent labial tissue, and is anaesthetised alongside the mental nerve.
• B. The inferior alveolar nerve is the parent trunk from which both of the above arise; a block anaesthetises the whole distribution.
• C. CORRECT as the exception. The FACIAL NERVE is purely MOTOR to the muscles of facial expression in this region. It carries no sensation from the lip, so blocking it achieves nothing for the biopsy — and blocking it would produce an unwanted marginal mandibular palsy with a drooping lip.
• D. The mental nerve is the terminal sensory branch supplying the skin and mucosa of the lower lip and chin. It is the principal target.

Note: The sensory/motor split is the whole point: V3 carries sensation from the lower face, VII drives its movement. A patient who cannot feel the lip but can still smile has had a correct block. A patient whose lip droops has had the anaesthetic placed too far posteriorly, near the parotid.