A A cyst is a benign pathogenic cavity within bone or in soft tissues, formedby a connective tissue wall and lined by epithelium. Periapical cystdevelops from proliferation of the Malassez epithelial rests, which arefound in the periodontal ligament, and often the origin comes from toothinfected leading to pulpal death. Proliferation of the epithelial restsstimulation and connective tissue capsule, accumulation of fluid within thecyst, resorption of the surrounding bone and incomplete compensatoryrepair are the main factors responsible for periapical cyst development.Periapical radiolucency can not be automatically assumed to be a cyst. Insome cases such a cyst of long standing may undergo an acuteexacerbation of the inflammatory process and develop rapidly into anabscess which may then proceed to cellulites or form a draining fistula. Ifleft untreated, both may produce bony destruction and tooth rootresorption. When a cyst reaches a large size it may produce intraoral orfacial asymmetry and even paresthesia due to compression of nerves,occasionally may erode the bone cortical plate or invade the maxillarysinus or the nasal fossae. Successful treatment rates of periapical cysts asmuch as 85-90% have been reported after conventional root canaltreatment with healing of periapical cysts.