Final answer:
A Pulp vitality test is most useful in differentiating between an acute apical abscess and an acute periodontal abscess as it determines the health of the dental pulp.
Step-by-step explanation:
The best test for differentiating between an acute apical abscess and an acute periodontal abscess is E. Pulp vitality test. An acute apical abscess is typically a result of pulp infection, which can eventually lead to necrosis of the pulp, whereas an acute periodontal abscess originates from an infection in the periodontal ligaments and usually does not affect the pulp. Therefore, a pulp vitality test, which assesses the health of the dental pulp, can help determine whether the pulp is still alive (which would be more consistent with a periodontal abscess) or if it has died (consistent with an apical abscess). Other tests such as palpation, radiographs, anesthetic tests, and percussion tests can provide additional information but are less definitive in differentiating between these two types of abscesses.