Which phase of dental amalgam alloy is most prone to corrosion during clinical service?

The phase of dental amalgam alloy that is most prone to corrosion during clinical service is the Gamma-2 (Sn-Hg) phase.

Dental amalgam is composed of several phases formed after the setting reaction between the silver-tin alloy powder and mercury.
These phases include:
- Gamma (Ag-Sn) phase: This is the original alloy phase responsible for the strength of amalgam.
- Gamma-1 (Ag-Hg) phase: This phase forms after mercury reacts with silver, providing strength and corrosion resistance.
- Gamma-2 (Sn-Hg) phase: This phase results from the reaction between tin and mercury.
- Copper phase: Present in high-copper amalgams to improve properties such as strength and corrosion resistance.

- Among these, the Gamma-2 (Sn-Hg) phase is the least corrosion-resistant and is most prone to degradation in the oral environment.
- This susceptibility to corrosion leads to a breakdown of the amalgam and can result in marginal breakdown, discoloration, and the release of corrosion products.
- The presence of high copper content alloys reduces or eliminates the Gamma-2 phase, which significantly improves the longevity and biocompatibility of dental amalgam restorations.

Key Points:
- Gamma-2 phase (Sn-Hg) is highly prone to corrosion.
- Corrosion of this phase weakens the restoration.
- High copper amalgams reduce Gamma-2 phase formation.
- Improving corrosion resistance enhances clinical longevity of amalgam.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition, Chapter on Dental Amalgam, Pages 150-155