A 19-year-old woman has noted swelling in the back of her mouth for 2 months. On dental examination, she has an area of swelling in the location of the left third molar. Dental radiographs show a radiolucent unilocular, well-circumscribed cyst surrounding the crown of the unerupted third mandibular molar. The lesion is excised, and on microscopic examination, the cyst is lined by stratified squamous epithelium and surrounded by a chronic inflammatory infiltrate. What is the most likely diagnosis?

A dentigerous cyst typically occurs in young persons when teeth are erupting, particularly molars. It is benign and does not recur following complete excision. Dentigerous cysts originate around the crown of an unerupted tooth, typically the third molar, and are lined by a thin, nonkeratinizing layer of squamous epithelium; they contain a dense chronic inflammatory infiltrate in the stroma. An odontogenic keratocyst that arises from rests of odontogenic epithelium within the jaw and is benign, but can recur if inadequately excised. Ameloblastoma and odontoma are tumors arising from odontogenic epithelium. Odontoma, the most common odontogenic tumor, shows extensive deposition of enamel and dentin. Periapical cysts/granulomas are inflammatory lesions that develop at the apex of teeth as complications of long-standing pulpitis.