A well-defined corticated radiolucency associated with an unerupted lower third molar includes all of the following in the differential diagnosis EXCEPT:

Correct answer: D. Ameloblastoma (NOT in the DDx for a simple pericoronal lucency — requires more aggressive features)

• A. OKC frequently occurs in the posterior mandible, often pericoronal, and must be considered.
• B. Primordial cyst (now considered a subset of OKC) develops from the dental organ before tooth formation — included in the DDx.
• C. Dentigerous cyst is the MOST COMMON cyst associated with the crown of an unerupted tooth — must be in the DDx.
• D. Correct. For a WELL-DEFINED, CORTICATED radiolucency around the crown of an unerupted tooth, the DDx includes: dentigerous cyst (most common), OKC, and unicystic ameloblastoma. However, AMELOBLASTOMA in its typical form is NOT expected — it usually presents as a multilocular radiolucency with cortical expansion, not a simple well-defined pericoronal lucency. Recall sources indicate ameloblastoma is the exception here.