Question

Which of the following structures may not be anesthetized by the PSA nerve block?

a. MB root of max third molar
b. MB root of max second molar
c. MB root of max first molar
d. all of the above

Answer 1

The MB root of the maxillary first molar is often not anesthetized by the PSA nerve block because it is typically innervated by the Middle Superior Alveolar (MSA) nerve.

Step-by-step explanation:

The structure that may not be anesthetized by the Posterior Superior Alveolar (PSA) nerve block is c. the MB root of the maxillary first molar.

The PSA nerve block commonly anesthetizes the pulp, buccal periodontium, and buccal mucosa of the maxillary third molar, second molar, and the palatal and distobuccal roots of the maxillary first molar. However, it typically does not anesthetize the mesiobuccal (MB) root of the maxillary first molar, hence the correct answer is 'MB root of max first molar.' This limitation is due to the innervation pattern whereby the MB root of the maxillary first molar is usually supplied by the Middle Superior Alveolar (MSA) nerve, a branch of the maxillary nerve, rather than the PSA nerve.