Which root of the maxillary first molar may not be anesthetized with a PSA nerve block?

Which root of the maxillary first molar may not be anesthetized with a PSA nerve block?

• A. Mesiobuccal root
• B. Distobuccal root
• C. Palatal root
• D. All roots

Answer: (A)

The main idea is that nerve supply to the maxillary molars can vary between individuals, so a PSA nerve block doesn’t always cover every root of the first maxillary molar. The posterior superior alveolar nerves that a PSA block targets typically anesthetize the distobuccal and other roots, but the mesiobuccal root is often supplied by the middle superior alveolar nerve. Since the PSA block does not reliably block the MSA, the mesiobuccal root may not become fully anesthetized. If the MSA is present, it takes care of the mesiobuccal root independently of the PSA, so that root can be spared by PSA anesthesia; if the MSA is absent, the PSA block may anesthetize it. In practice, to ensure complete anesthesia of the mesiobuccal root, you might need an additional injection targeting the MSA or a targeted local infiltration.

The main idea is that nerve supply to the maxillary molars can vary between individuals, so a PSA nerve block doesn’t always cover every root of the first maxillary molar. The posterior superior alveolar nerves that a PSA block targets typically anesthetize the distobuccal and other roots, but the mesiobuccal root is often supplied by the middle superior alveolar nerve. Since the PSA block does not reliably block the MSA, the mesiobuccal root may not become fully anesthetized. If the MSA is present, it takes care of the mesiobuccal root independently of the PSA, so that root can be spared by PSA anesthesia; if the MSA is absent, the PSA block may anesthetize it. In practice, to ensure complete anesthesia of the mesiobuccal root, you might need an additional injection targeting the MSA or a targeted local infiltration.