Dental Amalgam Composition — MFDS Part 1 MCQ

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ModerateDental MaterialsDental Amalgam CompositionMFDS Part 1

During the setting of conventional low-copper dental amalgam, which element in the alloy powder reacts with mercury to form the soft, corrosion-prone gamma-2 phase?

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Correct answer: D — Tin

Tin is correct. In conventional low-copper amalgam, tin released from the alloy powder combines with mercury to form the gamma-2 tin-mercury phase, approximately Sn7-8Hg. This phase is soft and particularly susceptible to corrosion. Silver combines with mercury principally to form the stronger gamma-1 phase. In high-copper amalgam, copper preferentially combines with tin to form the eta phase, Cu6Sn5, thereby reducing or eliminating gamma-2. Zinc functions mainly as a deoxidiser during alloy manufacture. Mercury is required to form gamma-2, but it is not the alloy-powder element requested by the repaired stem.

Reference: Beech DR. High copper alloys for dental amalgam. International Dental Journal. 1982;32(3):240-251. https://pubmed.ncbi.nlm.nih.gov/6958652/