Why teeth associated with inflammatory periapical lesions can have a vital response

It is a general conception that teeth having an inflammatory periapical lesion are nonvital and the associated periapical lesions are not innervated. However, structurally intact and functioning nerve fibers have been shown to be present in the periapical lesion and/or the associated pulp. Therefore, when a patient presents with an endodontically involved tooth associated with a periapical lesion and experiences pain during canal instrumentation, the need for local anesthesia is apparent.