Which material is least likely to be affected by water post-impression?

Polyvinyl silicone, also known as addition silicone, is least likely to be affected by water after an impression is taken. This type of material has excellent hydrophobic properties which mean that it does not absorb water and maintains dimensional stability even in moist conditions. This is critical for ensuring that the impressions do not distort after being taken, which is essential for accurate impressions in dental procedures.

In contrast, other materials listed, such as polyether and agar, are more hydrophilic and can absorb water, potentially leading to dimensional changes. Condensation silicone can also be affected by humidity and moisture, as it can undergo changes due to moisture and may lose its dimensional accuracy. Therefore, the resistance of polyvinyl silicone to water makes it the most stable and reliable choice for impressions, especially in environments where moisture is a concern. This property is essential for achieving precise and reproducible results in dental work.