Which caries type appears radiolucent with diffuse margins beneath or adjacent to a restoration?

• A. Recurrent or residual
• B. Occlusal
• C. Proximal
• D. Root surface

Answer: (A)

Recurrent or residual caries is the best match. When decay is at or just beneath the edge of an existing restoration, microleakage at the tooth–restoration interface allows bacteria to invade again, producing a radiolucent area that lies along the restoration margin. The borders are typically diffuse or poorly defined because the demineralization is spreading irregularly under and adjacent to the restoration, rather than forming a neat, localized lesion.

Other caries types have different radiographic patterns and locations: occlusal caries show on the chewing surface and fissure areas; proximal caries appear between teeth at the contact area; root surface caries occur on exposed root surfaces near the cementoenamel junction.