A panoramic radiograph shows a well-defined radiopacity in an edentulous mandibular premolar region. There is no root resorption, no associated tooth, and no surrounding radiolucent rim. What is the MOST likely diagnosis?

Correct answer: B. Idiopathic osteosclerosis (dense bone island)

• A. OSTEOSARCOMA produces an ill-defined lesion with a sunburst periosteal reaction and symmetrical WIDENING of the periodontal ligament space — an aggressive, rapidly changing picture.
• B. CORRECT. IDIOPATHIC OSTEOSCLEROSIS is a localized area of increased bone density of unknown cause, most common in the mandibular premolar-molar region. Defining features, all present here: NO associated tooth or inflammatory source, NO radiolucent rim, NO expansion, NO root resorption, and NO symptoms. It is a developmental variant of normal requiring only documentation and periodic observation.
• C. A CEMENTOBLASTOMA is by definition FUSED TO A ROOT, has a radiolucent rim, causes root resorption, and is often painful — the stem explicitly excludes an associated tooth.
• D. AMELOBLASTOMA is a RADIOLUCENT, often multilocular expansile lesion, not a radiopacity.

Note: The radiopacity checklist: is it attached to a tooth? Is there a rim? Is the tooth vital? Is there expansion? Those four answers narrow the differential immediately.