Apical periodontitis

Apical periodontitis is an inflammatory lesion in the periodontal tissues that is caused mostly by bacterial elements derived from the infected root canal system of teeth (Core concept 7.1). In non-treated teeth apical periodontitis represents a defensive response to a primary infection in a necrotic pulp. Apical periodontitis may also develop due to a secondary infection subsequent to endodontic treatment procedures. Post-treatment apical periodontitis is most commonly due to either unsuccessful control of primary root canal infection by endodontic treatment measures, or infection or reinfection of the root canal system due to inadequate obturation and/or inadequate coronal seal that allowed bacterial leakage to take place. Inadvertent extrusion of certain medicaments and root filling materials into the periapical tissue compartment may also cause tissue toxic effects as well as precipitate foreign body reactions (Chapter 12). In this chapter the focus will be on apical periodontitis associated with non-endodontically treated teeth affected by root canal infection. It will be described in terms of biological function, pathogenesis and clinical as well as histological presentation. The nature of apical periodontitis