If a radiograph shows a radiolucent area with diffuse margins beneath or adjacent to a restoration, what is the most likely diagnosis?

• A. Recurrent caries
• B. Primary proximal caries
• C. Normal restoration adaptation
• D. Fracture line

Answer: (A)

When a radiograph shows a radiolucent area with diffuse, poorly defined margins beneath or right next to a restoration, it points to recurrent (secondary) caries. This pattern reflects demineralization that has developed at the tooth-restoration interface due to microleakage and bacteria persisting under the restoration. The radiolucency often extends beneath the margin and appears fuzzy because the decay is actively progressing under the seal.

This differs from primary proximal caries, which starts on a previously untouched surface at the contact area and tends to show a more typical proximal lesion away from restorations. Normal restoration adaptation would not present as a creeping radiolucency under the restoration; if anything, any gap would be minimal and not show a diffuse area of decay. A fracture line would appear as a distinct, narrow radiolucent crack through the tooth structure, often following a straight or curved path, rather than a diffuse, ill-defined area beneath a restoration.

So the presence of a diffuse radiolucent region beneath or adjacent to a restoration most strongly suggests recurrent caries needing evaluation and likely restoration replacement.