A panoramic radiograph shows a well-defined radiopacity where the mandibular second premolar should be. There is no root resorption, no radiolucent rim, and the lesion is not attached to any tooth. What is the most likely diagnosis?

Correct answer: C. Idiopathic osteosclerosis

• A. A cementoblastoma is by definition FUSED TO A ROOT and is surrounded by a radiolucent rim, with root resorption of the involved tooth. The stem explicitly excludes all three features.
• B. Osteosarcoma produces an ill-defined lesion with a sunburst periosteal reaction and symmetrical widening of the periodontal ligament space — an aggressive appearance quite unlike this.
• C. CORRECT. A dense, well-defined radiopacity with NO radiolucent rim, NO root resorption and NO attachment to a tooth is a bone island — idiopathic osteosclerosis, also called dense bone island or enostosis. It is a developmental variant, entirely asymptomatic, requires no treatment, and needs only periodic radiographic observation.
• D. An ameloblastoma is a RADIOLUCENT lesion, typically multilocular with a soap-bubble pattern, and characteristically causes root resorption and cortical expansion.

Note: The three discriminating features for radiopaque jaw lesions: is it attached to a root? (cementoblastoma yes, osteosclerosis no); is there a radiolucent rim? (cementoblastoma yes, osteosclerosis no); is there root resorption? (cementoblastoma yes, osteosclerosis no). Also distinguish CONDENSING OSTEITIS, which is inflammatory sclerosis at the apex of a NON-VITAL tooth — vitality testing separates it from osteosclerosis.