A periapical (root-tip) abscess is a pocket of infection at the base of a tooth's root. The tooth becomes abscessed after the pulp (nerve) of the tooth becomes infected. A periapical abscess is usually caused by deep decay or an accident (trauma to the tooth involving nerve damage). A periapically abscessed tooth will require either Root Canal Therapy or an Extraction. In some cases an antibiotic will also be prescribed.