If the MSA nerve is missing, anesthesia from an MSA approach is provided by branches of which nerve?

• A. Infraorbital nerve
• B. Anterior superior alveolar nerve
• C. Glossopharyngeal nerve
• D. Inferior alveolar nerve

Answer: (B)

When the middle superior alveolar nerve isn’t present, the area that would normally be anesthetized by it still can be numbed because its sensory fibers are supplied by branches of another nerve. The anterior superior alveolar nerve, a branch that comes from the infraorbital nerve, provides the alveolar innervation to the maxillary teeth in that region. So an MSA approach ends up blocking the fibers of the anterior superior alveolar nerve, which takes over the function for those premolars and related buccal gingiva. The other nerves listed don’t innervate this maxillary premolar region in the same way: the glossopharyngeal nerve isn’t involved with the teeth, the inferior alveolar nerve serves the mandible, and while the infraorbital nerve is the parent trunk, the actual sensory contribution for this region in the absence of MSA comes from the anterior superior alveolar nerve.