When bacteria enter your tooth through deep cavities, cracks or flawed fillings, your tooth can become abscessed. An abscessed tooth is a tooth with an infection in the pulp. If pulp becomes infected, it needs to be removed(ROOT CANAL TREATMENT). An abscessed tooth may cause pain and/or swelling. Your dentist may notice the infection from a dental X-ray or from other changes with the tooth. If left untreated, an abscessed tooth can cause serious health problems.