Which material is used to delay the expansion of amalgam?

Zinc is used to delay the expansion of amalgam because it acts as a scavenger that controls the reaction of water with the alloy constituents during the setting process. When amalgam is mixed with the mercury, the addition of zinc helps prevent the formation of gas that could lead to expansion and ultimately, a failure of the restoration. This property is particularly beneficial when the amalgam is exposed to moisture, which could initiate unwanted expansion and compromise the integrity of the filling. The inclusion of zinc in dental amalgam formulations contributes to enhanced stability and longevity of the dental repair.

Other materials listed, such as silver, copper, and tin, while important components of amalgam, do not serve the specific role of managing expansion caused by moisture. Silver is primarily included for strength and corrosion resistance, copper enhances the strength and reduces corrosion, and tin contributes to the workability and expansion properties but does not specifically address the dampening of expansion as zinc does.