The radiographic appearance of an occlusal lesion that has progressed into the dentin is best described as which of the following?

• A. A diffuse radiolucent shadow
• B. A sharp radiopaque outline
• C. A circular radiolucent lesion
• D. A narrow radiopaque line along the enamel

Answer: (A)

When a carious lesion has reached dentin, the radiographic appearance becomes a diffuse radiolucent shadow because dentin is less mineralized and its tubular structure allows the decay to spread irregularly beyond the enamel surface. The enamel may still look intact at the surface, but the underlying dentin shows demineralization that appears darker on the image as a broad, ill-defined area rather than a sharply outlined or circular lesion. This diffuse radiolucency reflects the progressive loss of mineral content in dentin and the way caries extend laterally within dentin.