Residual cysts develop from incomplete removal of radicular cysts. Radicular cysts are also known as periapical cysts. Residual cysts may develop months or years after tooth extraction. Radicular cysts develop within periapical granulomas. These lesions form in response to chronically inflamed granulation tissue at the apex of a devitalized tooth. The incidence of granuloma cystification is unknown, but is related to the length of retention of the retained, untreated tooth with pulpal necrosis. Residual cysts are most commonly found in the maxilla, although they may be seen in either jaw. They are usually first detected as asymptomatic, incidental findings on routine dental radiographic surveys. These lesions usually appear radiographically as unilocular round or ovoid radiolucencies circumscribed by a thin radiopaque border. Cortical expansion is rare. Treatment consists of removal by local debridement to prevent expansion of these potentially destructive lesions. While most residual cysts are less than 1.5cm, they have the capacity to enlarge and destroy extensive segments of the maxilla or mandible. Their recurrence after thorough curettage is rare and complete bone repair is common after treatment.
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