Periapical periodontitis

Periapical periodontitis or apical periodontitis (AP) is an acute or chronic inflammatory lesion around the apex of a tooth root, most commonly caused by bacterial invasion of the pulp of the tooth. It is a likely outcome of untreated dental caries (tooth decay), and in such cases it can be considered a sequela in the natural history of tooth decay, irreversible pulpitis and pulpal necrosis. Other causes can include occlusal trauma due to 'high spots' after restoration work, extrusion from the tooth of root filling material, or bacterial invasion and infection from the gums. Periapical periodontitis may develop into a periapical abscess, where a collection of pus forms at the end of the root, the consequence of spread of infection from the tooth pulp (odontogenic infection), or into a periapical cyst, where an epithelial lined, fluid-filled structure forms.

Etymologically, the name refers to inflammation (Latin, -itis) around (peri- ) the root tip or apex (-apical) of the tooth (-odont-). Periradicular periodontitis is an alternative term.