Background and Objectives: residual cyst is an odontogenic cyst that develops after a tooth with a radicular cyst is extracted so that all or part of the cyst remain in place. These cysts are known as asymptomatic inflammatory odontogenic cysts and form approximately 2.2%-18% of odontogenic cysts. Methods: A 30 years old man patient, referred to the department of oral medicine of Yazd dental university for evaluation of radiolucent lesion seen in panoramic radiography. Large oval shape unilacular radiolucency with well-circumscribed and corticated borders was seen that extended from the distal of left central tooth to the apex of second premolar on the same side. The canine tooth also appeared to be in sinus space. Conclusion: According to the present study, basically, residual cystic should be considered in differential diagnosis of unilacular radiolucency in edentulous area.

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