National Dental Assisting Examining Board (NDAEB) Practice Exam

What happens to alginate impressions if they are left out in the air?

1. They harden

2. They become sticky

3. They retain moisture

4. They emit odor

The correct answer is: They harden

When alginate impressions are left exposed to air, they undergo a process called desiccation, which leads to them hardening. Alginate is a hydrophilic material, meaning it has an affinity for water, but when it is exposed to air, it loses moisture. This loss of moisture causes the impression material to become rigid and hard, which compromises the detail and accuracy of the impression. Therefore, the correct understanding of how alginate behaves when left out is that it hardens due to the evaporation of water content. The other possible outcomes, while they may describe surface changes or properties of materials in a different context, do not accurately reflect the primary physical change that occurs when alginate is improperly stored in air.