|CT scan through head showing a right periapical cyst|
|Classification and external resources|
The periapical cyst (also termed radicular cyst or dental cyst) is the most common odontogenic cyst. It is caused by pulpal necrosis secondary to dental caries or trauma. The cyst lining is derived from the epithelial cell rests of Malassez. Usually, the periapical cyst is asymptomatic, but a secondary infection can cause pain. On radiographs, it appears a radiolucency (dark area) around the apex of a tooth's root.
Signs and symptoms
Expansion of the cyst causes erosion of the floor of the maxillary sinus. As soon as it enters the maxillary antrum, the expansion starts to occur a little faster because there is space available for expansion. There is no pain in teeth at percussion (tapping on teeth), since the pulp is dead due to infection . This is virtually diagnostic of pulpal infection.
Radiographically, it is virtually impossible to differentiate granuloma from a cyst. If the lesion is large it is more likely to be a cyst, but can be differtiated as there is pain on tapping in granuloma but no pain is there in cyst. Radiographically, both granulomas and cysts appear radiolucent.
Dental cysts are usually caused due to root infection involving tooth decay. The resulting pulpal necrosis causes a release of toxins at the apex of the tooth leading to periapical inflammation. This inflammation leads to the formation of reactive inflammatory (scar) tissue called periapical granuloma; further necrosis and damage stimulates the Malassez epithelial rests found in the periodontal ligament, resulting in the formation of a cyst that may be infected or sterile. (The epithelium undergoes necrosis and the granuloma becomes a cyst.) These lesions can grow large because they apply pressure over the bone, causing resorption. The toxins released by the breakdown of granulation tissue are one of the common causes of bone resorption. Such cysts are not true neoplasms.
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