A dental abscess is a localized collection of pus associated with a tooth. The most common type of dental abscess is a periapical abscess, and the second most common is a periodontal abscess. In a periapical abscess, usually the origin is a bacterial infection that has accumulated in the soft, often dead, pulp of the tooth. This can be caused by tooth decay, broken teeth or extensive periodontal disease (or combinations of these factors). A failed root canal treatment may also create a similar abscess. A dental abscess is a type of odontogenic infection, although commonly the latter term is applied to an infection which has spread outside the local region around the causative tooth. Classification
The main types of dental abscess are:

Periapical abscess: The result of a chronic, localized infection located at the tip, or apex, of the root of a tooth. Periodontal abscess: begins in a periodontal pocket (see: periodontal abscess)
Gingival abscess: involving only the gum tissue, without affecting either the tooth or the periodontal ligament (see: periodontal abscess)
Pericoronal abscess: involving the soft tissues surrounding the crown of a tooth (see: Pericoronitis)
Combined periodontic-endodontic abscess: a situation in which a periapical abscess and a periodontal abscess have combined (see: Combined periodontic-endodontic lesions). Signs and symptoms
The pain is continuous and may be described as extreme, growing, sharp, shooting, or throbbing. Putting pressure or warmth on the tooth may induce extreme pain. The area may be sensitive to touch and possibly swollen as well.
Treatment typically lasts at least 12 months.Although studies have not yet identified an optimal regimen or confirmed that any therapeutic regimen produces sustained clinical benefit for patients with disseminated MAC, the Task Force concluded that the available information indicated the need for treatment of disseminated MAC. The Public Health Service, therefore, recommends that regimens be based on the following principles:
Treatment regimens outside a clinical trial should include at least two agents. Every regimen should contain either azithromycin or clarithromycin; many experts prefer ethambutol as a second drug. Many clinicians have added one or more of the following as second, third, or fourth agents: clofazimine, rifabutin, rifampin, ciprofloxacin, and in some situations amikacin. Isoniazid and pyrazinamide are not effective for the therapy of MAC. Therapy should continue for the lifetime of the patient if the clinical and microbiologic improvement is observed.Clinical manifestations of disseminated MAC—such as fever, weight loss, and night sweats—should be monitored several times during the initial weeks of therapy. The microbiologic response, as assessed by blood culture every 4 weeks during initial therapy, can also be helpful in interpreting the efficacy of a therapeutic regimen. Most patients who ultimately respond show substantial clinical improvement in the first 4–6 weeks of therapy. Elimination of the organism from blood cultures may take somewhat longer, often requiring 4–12 weeks. HIV-infected children
HIV-infected children less than 12 years of age also develop disseminated MAC. Some age adjustment is necessary when clinicians interpret CD4+ T-lymphocyte counts in children less than 2 years of age.