Epithelium at the apex of a nonvital tooth……………………….. ………………..form a true epithelium lined cyst. stimulatIon by inflammatio n inflammatory response ……… keratinocyte growth factor by periodontal stroma cells, ………increased proliferation of normally quiescent epithelium in the area. source of the epithelium usually a rest of Malassez crevicular epithelium sinus lining epithelial lining of fistulous tracts.

the reported frequency ……. 7% to 54% of periapical radiolucencies. With strict criteria ………the prevalence of periapical cysts ………. 15%. desquamation of epithelium into the lumen………… protein content………. Fluid enters the lumen …………… Most periapical cysts grow slowly and do not attain a large size. Typically…….no symptoms unless …. an acute inflammatory exacerbation. if the cyst reaches a large size….. swelling and mild sensitivity may be noted.

The radiographic pattern is identical to that of a periapical granuloma. a loss of the lamina dura along the adjacent root a rounded radiolucency encircles the affected tooth apex Root resorption is common

Significant growth is possible, neither the size nor the shape of the lesion can be considered a definitive diagnostic criterion.

Histopathologic Features The cyst is lined by stratified squamous epithelium

hyperplasia exocytosis spongiosis

On occasion, the lining epithelium may demonstrate linear or arch- shaped calcifications known as Rushton bodies

The lumen……. will be filled with fluid and cellular debris

Dystrophic calcification, cholesterol clefts with multinucleated giant cells, red blood cells, and areas of hemosiderin pigmentation may be in the lumen, wall, or both