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

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

Answer: (C)

Focus on caries that develop at the tooth–restoration interface. When a restoration doesn’t seal perfectly, bacteria can infiltrate along that margin and under the restoration. In radiographs, this shows up as a radiolucent area right beneath or beside the restoration, and the borders tend to be diffuse or poorly defined because the decay spreads irregularly under the seal rather than leaving a sharp, clearly demarcated edge. This pattern is what points to recurrent or residual caries—the decay that reappears beneath or adjacent to an existing restoration after placement or as it progresses under it. In contrast, occlusal caries shows on chewing surfaces, proximal caries along the contact area, and root caries at the root surface, each with their characteristic appearances.