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.