A localized accumulation of pus in a cavity caused by tissue breakdown as a result of infection or foreign materials. It is a tissue defence reaction to prevent the spread of infection to other parts of the body. An abscess may be described as acute when there has been a rapid onset frequently associated with pain, or chronic when it has developed over a longer period of time and is usually painless. A gingival abscess (gumboil) is associated with the free gingival margin (see gingiva) of a tooth. These are frequently caused by foreign bodies, or food impaction: they may be associated with a non-vital primary tooth and be asymptomatic. A periapical abscess is associated with the root apex of a tooth and the surrounding bone and is a sequel of pulpal infection. A lateral periodontal abscess involves the periodontal attachment tissues and usually arises from an established periodontal pocket. It may occur because of an increase in virulent organisms, a compromised immune response, or reduced drainage from the periodontal pocket. The last may occur following root debridement with superficial tissue healing and residual infection in the periodontal pocket. A pericoronal abscess is related to the flap of gum (operculum) overlying a partially erupted tooth, most commonly the third molar. Treatment is by establishing drainage and addressing the cause.