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.
Similarly, in a periodontal abscess pus most likely discharges via the periodontal pocket, whereas a periapical abscess generally drains via a parulis nearer to the apex of the involved tooth. If the tooth has pre-existing periodontal disease, with pockets and loss of alveolar bone height, it is more likely to be a periodontal abscess; whereas if the tooth has relatively healthy periodontal condition, it is more likely to be a periapical abscess. In periodontal abscesses, the swelling usually precedes the pain, and in periapical abscesses, the pain usually precedes the swelling. A history of toothache with sensitivity to hot and cold suggests previous pulpitis, and indicates that a periapical abscess is more likely. If the tooth gives normal results on pulp sensibility testing, is free of dental caries and has no large restorations; it is more likely to be a periodontal abscess. A dental radiograph is of little help in the early stages of a dental abscess, but later usually the position of the abscess, and hence indication of endodontal/periodontal etiology can be determined. If there is a sinus, a gutta percha point is sometimes inserted before the x-ray in the hope that it will point to the origin of the infection. Generally, periodontal abscesses will be more tender to lateral percussion than to vertical, and periapical abscesses will be more tender to apical percussion. Treatment
Successful treatment of a dental abscess centers on the reduction and elimination of the offending organisms.