A patient experiences pain and some gingival swelling in the anterior segment of the mandible. The mandibular lateral incisor has a shallow restoration, is tender to percussion and gives a positive response to an electric pulp test. There is some mobility. What is the most likely diagnosis?

Periodontal abscess.

Reversible pulpitis.

Symptomatic irreversible pulpitis.

Acute apical abscess (acute periradicular abscess).