What is syneresis in the context of alginate impressions?

Syneresis refers to the process where a gel, such as an alginate impression, contracts and expels some of its liquid component, typically water. In the context of alginate impressions, this phenomenon can lead to a loss of water and subsequent shrinkage of the impression material.

As alginate sets, it forms a gel that is initially stable. However, over time, due to environmental conditions or the inherent properties of the material, some of the water trapped within the gel matrix can escape. This results in a reduction in volume, or shrinkage, which can potentially distort the impression and negatively impact the accuracy of the dental cast produced from it.

With this understanding, the other options do not accurately capture the essence of syneresis. While absorption of water and a chemical reaction with calcium sulfate are relevant processes within the context of dental materials, they do not define syneresis. Mixing with powder is simply part of the preparation of the alginate but does not relate to the changes the gel undergoes over time after setting.