A retained third molar is surrounded by a well-defined unilocular radiolucency enveloping the crown. Which of the following is a legitimate differential diagnosis alongside dentigerous cyst?

Correct answer: C. Unicystic ameloblastoma

• A. Fibrous dysplasia is a mixed to ground-glass radiopaque lesion with an ill-defined blending border — not a corticated pericoronal radiolucency.
• B. A traumatic (simple) bone cyst scallops BETWEEN the roots of erupted teeth and does not envelop an impacted crown.
• C. Correct. UNICYSTIC AMELOBLASTOMA is the great mimic of a dentigerous cyst. It arises from odontogenic epithelium but behaves and appears cystic: a unilocular corticated radiolucency surrounding the crown of an IMPACTED THIRD MOLAR in a young patient. It cannot be distinguished radiographically — only histopathology after enucleation reveals the ameloblastic epithelial lining, which is why every pericoronal radiolucency must be submitted for histological examination.
• D. PCOD occurs at the apices of vital ANTERIOR mandibular teeth and evolves from radiolucent to mixed to radiopaque.