Restorative & Materials · single question
A picture of an amalgam done 5 years ago shows a dull look. Why?
Show answer and explanation
Correct answer: A. Corrosion (due to the gamma-2 phase)
- A. The dull, tarnished appearance of an older amalgam restoration is due to CORROSION of the GAMMA-2 PHASE (Sn7-8Hg — tin-mercury compound). The gamma-2 phase is the weakest and most corrosion-prone component of conventional amalgam. Over time, gamma-2 corrodes in the oral environment, causing the amalgam to appear dark, dull, and pitted. Modern high-copper amalgams minimize gamma-2 formation, reducing corrosion.
- B. While poor initial polishing can affect esthetics, the progressive dulling of amalgam over time is primarily due to corrosion of the gamma-2 phase, not polishing failure.
- C. Creep and flow cause amalgam to overhang at margins (marginal breakdown) — not the overall dull appearance, which is corrosion-related.
- D. Mercury vaporization does occur at low levels but does not cause the dull appearance — corrosion of the tin-mercury phase is responsible.
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