High-Copper Amalgam γ₂ Elimination — NDEB AFK MCQ

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HardDental MaterialsHigh-Copper Amalgam γ₂ EliminationNDEB AFK

In dental amalgam composition, the high-copper amalgam alloy was developed primarily to eliminate which phase that was associated with corrosion and marginal breakdown?

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Correct answer: B — Gamma-2 (γ₂) phase — Sn₇Hg

High-copper amalgam alloys (>12% Cu, e.g., Dispersalloy, Tytin) were developed to eliminate the gamma-2 (γ₂, Sn₇Hg) phase, which was the weakest and most corrosion-prone phase in conventional (low-copper) amalgam. In high-copper amalgams, excess copper reacts preferentially with tin to form Cu₆Sn₅ (eta prime, η'), preventing formation of the γ₂ phase. This results in improved corrosion resistance, marginal integrity, compressive strength, and clinical longevity compared to conventional amalgam.

Reference: Anusavice – Phillips' Science of Dental Materials, 13th ed., 2022