Tooth #12 has an occlusomesial amalgam restoration and the tooth has darkened over several years. Most likely cause?

Correct answer: C. Corrosion products from the amalgam staining the surrounding dentin

• A. Recurrent caries would present with a radiolucency beneath the restoration and soft, catchy dentin on probing — a localized finding rather than diffuse greying.
• B. Pulpal necrosis darkens the entire crown uniformly from within, including areas remote from the restoration, and the tooth would not respond to vitality testing.
• C. CORRECT. Tin and silver corrosion products migrate from the amalgam into the dentinal tubules over time, producing a diffuse blue-grey discolouration of the surrounding tooth structure that shows through the enamel. This is a benign, expected finding around long-standing amalgams.
• D. Extrinsic stain sits on the enamel surface, is removed by prophylaxis, and does not concentrate around a specific restoration.

Note: Distinguishing the two things you actually care about: corrosion staining is diffuse, grey-blue, radiographically silent, and needs no treatment. Recurrent caries is localized, produces a radiolucency, and needs restoration. Amalgam 'tattoo' in soft tissue is the same pigment deposited in mucosa.