A well-defined radiolucency is seen in an edentulous area where a tooth was extracted five years ago. The patient is asymptomatic. What is the MOST likely diagnosis?

Correct answer: D. Residual cyst

• A. A central giant cell granuloma is typically multilocular and occurs anterior to the first molar in younger patients.
• B. A dentigerous cyst is by definition attached to the crown of an UNERUPTED tooth — impossible in an edentulous site.
• C. A traumatic bone cyst occurs in young patients with teeth present, scalloping between the roots.
• D. Correct. A RESIDUAL CYST is a radicular (inflammatory) cyst that was left behind when the offending tooth was extracted and the cyst lining was not curetted out. It persists as a well-defined, corticated radiolucency in an EDENTULOUS site, is usually asymptomatic, and is discovered incidentally on radiographs taken years later — often during denture or implant planning. Treatment is enucleation.