A patient experiences numbness of the lower lip and chin after a dental block. Which block is most likely responsible?

• A. Inferior alveolar nerve block
• B. Posterior superior alveolar block
• C. Infraorbital nerve block
• D. Buccal nerve block

Answer: (A)

Numbness of the lower lip and chin points to anesthesia of the nerve that provides sensation to the lower jaw area and also gives off a branch to the chin and lower lip. The inferior alveolar nerve block directly anesthetizes the inferior alveolar nerve as it enters the mandibular canal, and its mental nerve branch exits at the mental foramen to supply the skin of the chin and the lower lip. When this block is deposited, both the teeth on that side and those soft-tissue areas commonly go numb, including the lower lip and chin.

The other blocks target areas that do not involve the chin and lower lip in the same way: a posterior superior alveolar block affects maxillary molars and surrounding buccal tissue; an infraorbital block affects the midface including the upper lip; a buccal nerve block anesthesia is limited to the buccal mucosa near the molars. That combination makes the observed numbness most consistent with the inferior alveolar nerve block.