Restorative & Materials · single question
What is the function of zinc in a dental amalgam alloy?
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Correct answer: C. It acts as a deoxidiser, scavenging oxygen during manufacture
- A. Zinc does not increase setting expansion under normal conditions — its notorious expansion effect occurs only in the presence of moisture contamination.
- B. It is not a setting accelerator.
- C. CORRECT. Zinc is a DEOXIDISER or scavenger. During melting and manufacture of the alloy it preferentially combines with oxygen, preventing the formation of oxides of silver, tin and copper that would otherwise contaminate the alloy and impair its properties. The benefit accrues at manufacture; zinc plays no direct part in the clinical setting reaction.
- D. Zinc has no aesthetic function in a silver-coloured restoration.
Note: Alloys are classified as zinc-containing (more than 0.01% zinc) or zinc-free. The distinction matters for one reason only: delayed expansion on moisture contamination.
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