C23 Identify four factors that are responsible for marginal deterioration of amalgams.
Marginal deterioration of amalgam restorations are mainly caused by the following four factors.
1. Improper marginal preparation
Poorly supported enamel may fracture. These fractures may result in a crevice formation adjacent to the amalgam margin.
2. Improper carving and finishing
If amalgam flash is left around the margin, the flash may fracture and chip.
3. Excess mercury
Excess mercury results in a weaker amalgam containing more gamma-2. In fact, if too much mercury is present in a high copper amalgam, even this amalgam may contain some gamma-2 phase.
4. Use of gamma-2 containing amalgams
Low copper containing amalgams contain gamma-2. Gamma-2 corrodes over time and as a result of loss of this phase the margins become more porous and fracture prone.
5. Amalgam expansion
An amalgam that expands will protrude. When the amalgam has protruded, the margins will not be supported by the enamel, and the likelihood of marginal chipping will increase.