An old patient has a zirconia crown on tooth #18 and has caries extending below the gingiva. What is the treatment of choice?

Correct answer: D. Silver diamine fluoride (SDF)

• A. Desensitizers address sensitivity — they do not arrest active carious lesions.
• B. Fluoride varnish has preventive and remineralizing effects but is not as powerful as SDF for ARRESTING active subgingival caries under an existing restoration.
• C. Active caries require intervention — observing without treatment allows continued progression.
• D. For an ELDERLY patient with subgingival caries under an existing zirconia crown, SILVER DIAMINE FLUORIDE (SDF) is the most appropriate conservative treatment choice. SDF: (1) arrests active caries without requiring crown removal or invasive preparation, (2) is ideal for elderly patients with complex medical histories and poor tolerance for extensive treatment, (3) penetrates under existing restorations to arrest cervical/root caries. The tradeoff is permanent black staining — acceptable in elderly patients prioritizing function over esthetics.