Which complication is most commonly associated with untreated periapical periodontitis?

Periapical periodontitis is inflammation at the apex of a tooth, most commonly due to pulpal necrosis and bacterial invasion of the periapical tissues. If untreated, the most common complication is spread of infection along fascial planes, resulting in cellulitis or abscess formation. Depending on the affected tooth and its relationship to muscle attachments and fascial spaces, infection can spread to: the vestibular/buccal space, sublingual or submandibular space, parapharyngeal or retropharyngeal spaces (with risk of airway compromise — Ludwig's angina), or the orbital space (maxillary teeth). Systemic complications (sepsis, bacteremia, cavernous sinus thrombosis) are rare but life-threatening.