Review the clinical photograph. A premolar with an occlusomesial amalgam shows greyish-black discoloration of the adjacent tooth structure. What is the most likely cause?

Correct answer: A. Corrosion of the amalgam with diffusion of metallic products into dentin

• A. CORRECT. AMALGAM CORROSION releases tin, silver, and mercury sulfides and oxides, which diffuse along the dentinal tubules and stain the surrounding dentin a characteristic grey-black. It shows as a diffuse dark halo through translucent enamel around and beneath the restoration margin, is not soft to explorer pressure, and is essentially always present to some degree around older amalgams. It is an esthetic issue, not an indication for replacement by itself.
• B. Extrinsic stain from coffee, tea, or tobacco is superficial, removable by prophylaxis, and would not be confined to the tooth structure adjacent to a metallic restoration.
• C. Pulpal necrosis discolors the ENTIRE crown uniformly from within, not a localized zone adjacent to one restoration.
• D. Recurrent caries produces a SOFT, cavitated, typically brown lesion with a detectable marginal gap or ditch, and usually a radiographic radiolucency beneath the restoration.