Which dental material is primarily responsible for the expansion of amalgam?

Zinc plays a significant role in the expansion behavior of amalgam restorations. When amalgam is mixed, various metals such as silver, tin, copper, and zinc are incorporated. While silver and tin are critical for strength and corrosion resistance, zinc is particularly known for its ability to enhance the expansion of the material.

One of the key characteristics of zinc in amalgam is its tendency to absorb moisture, which can lead to a chemical reaction that results in the formation of hydrogen gas. This gas can cause the amalgam to expand slightly as it sets, which is especially beneficial in compensating for shrinkage that may occur during the hardening process. As such, the inclusion of zinc in the formulation helps to ensure that the amalgam adapts well to the cavity preparation, providing a good seal and reducing the risk of marginal gaps over time.

In contrast, the other metals—silver, copper, and tin—while essential to the amalgam's overall physical properties, do not predominantly influence the expansion that zinc does. Silver contributes to strength and durability, copper aids in improving corrosion resistance and preventing the formation of harmful gamma-2 phase, and tin is mainly involved in controlling the flow and viscosity of the amalgam.