Which of the following mechanical failures is MOST associated with poor condensation of an amalgam restoration?

Correct answer: B. Marginal breakdown and post-operative sensitivity from microleakage

• A. DELAYED EXPANSION is a specific phenomenon of ZINC-containing LOW-COPPER amalgam contaminated by MOISTURE during condensation. Zinc reacts with water to liberate hydrogen gas, which expands the restoration days to weeks later, causing pain and protrusion. It is a moisture-contamination problem, not a condensation-force problem, and it does not occur with modern zinc-free high-copper alloys.
• B. CORRECT. Adequate CONDENSATION serves two purposes: it expresses excess mercury toward the surface (to be carved away) and it eliminates VOIDS and porosity. Poor condensation leaves internal porosity, a high residual mercury content and, most importantly, an incompletely adapted MARGIN — producing microleakage, post-operative sensitivity, marginal breakdown and recurrent caries. Marginal integrity is the single most important determinant of amalgam longevity.
• C. Discolouration of adjacent tooth structure results from corrosion products and amalgam ions diffusing into dentin over time — an aesthetic issue unrelated to condensation technique.
• D. CREEP is a property of the ALLOY itself. Low-copper conventional amalgams contain the gamma-2 phase, which creeps under load and causes marginal deterioration. High-copper amalgams eliminate gamma-2 and have very low creep.

Note: Condensation principles: use a small condenser first to reach the internal line angles, condense in small increments with firm pressure directed at the margins and into retention features, overfill before carving, and complete condensation within the working time before crystallisation advances.