The PSA innervates the 1st, 2nd, and 3rd maxillary molars, but may not innervate which root?

The PSA innervates the 1st, 2nd, and 3rd maxillary molars, but may not innervate which root?

• A. The mesiobuccal root of the maxillary 1st molar
• B. The distobuccal root of the maxillary 2nd molar
• C. The palatal root of the maxillary 2nd molar
• D. The mesial root of the maxillary 3rd molar

Answer: (A)

A key idea here is that the posterior superior alveolar nerve (PSA) supplies the molar region, but its distribution can vary because a separate branch, the middle superior alveolar nerve (MSAN), may be present. When MSAN exists, it often provides innervation to the mesiobuccal root of the maxillary first molar. In that scenario, that particular root receives sensation from MSAN rather than the PSA, so the PSA may not innervate it. The other roots—the distobuccal root of the second molar, the palatal root of the second molar, and the mesial root of the maxillary third molar—are more consistently supplied by PSA or by other adjacent nerves, so they’re less likely to be spared by PSA innervation. Thus, the mesiobuccal root of the maxillary first molar is the root that PSA may not innervate.

A key idea here is that the posterior superior alveolar nerve (PSA) supplies the molar region, but its distribution can vary because a separate branch, the middle superior alveolar nerve (MSAN), may be present. When MSAN exists, it often provides innervation to the mesiobuccal root of the maxillary first molar. In that scenario, that particular root receives sensation from MSAN rather than the PSA, so the PSA may not innervate it. The other roots—the distobuccal root of the second molar, the palatal root of the second molar, and the mesial root of the maxillary third molar—are more consistently supplied by PSA or by other adjacent nerves, so they’re less likely to be spared by PSA innervation. Thus, the mesiobuccal root of the maxillary first molar is the root that PSA may not innervate.