Final answer:
The most likely condition for the client's symptoms with a positive vitalometer test and a radiopaque area is calcified pulp, although the vitalometer result could suggest other conditions such as a periapical abscess or pulpal necrosis.
Step-by-step explanation:
The most likely condition responsible for the client's symptoms, given a positive vitalometer test indication of nonvital pulp and the presence of a radiopaque area at the apex of the distal root, is calcified pulp. When the pulp becomes calcified, it can lead to pulp stones which could cause intermittent sensitivity like that reported by the client. A calcified pulp can present with a radiopaque area on radiographs, consistent with what is described. However, because the vitalometer indicates nonvital pulp, the tooth should not respond to the test. There may be some confusion in the question; if the response to the vitalometer is truly positive, alternative conditions such as a minimally symptomatic periapical abscess or pulpal necrosis with secondary calcification could be possible.