A well-defined radiopaque lesion made of multiple small tooth-like structures ('denticles') is found on a panoramic radiograph of an adolescent and is blocking eruption of a permanent tooth. The most likely diagnosis is:

A compound odontoma is a hamartoma of dental tissues forming multiple small discrete tooth-like structures (denticles), appears radiopaque with a radiolucent rim, and is a common cause of failed eruption. It is the most common odontogenic tumor.Other options: Ameloblastoma is radiolucent/multilocular; a dentigerous cyst is radiolucent around a crown; cemento-osseous dysplasia occurs in tooth-bearing areas of adults.Key exam takeaway: Radiopaque mass of little teeth in a young patient blocking eruption = compound odontoma (a complex odontoma is a disorganized radiopaque mass).