National Dental Assisting Examining Board (NDAEB) Practice Exam

What type of impression materials does alginate belong to?

1. Reversible hydrocolloid

2. Irreversible hydrocolloid

3. Silicone elastomers

4. Agar impression materials

The correct answer is: Irreversible hydrocolloid

Alginate is classified as an irreversible hydrocolloid impression material. This classification is due to its chemical properties and the way it sets after mixing. When alginate is combined with water, it forms a gel-like substance that captures the details of the oral structures effectively. Once it sets, it cannot return to its original liquid state, which is a defining feature of irreversible hydrocolloids. The setting process involves a chemical reaction that results in a permanent gel, creating an accurate and reliable impression for various dental procedures, such as creating study models or fabricating dental appliances. This characteristic distinguishes alginate from reversible hydrocolloids, which can be reheated and transformed back into a liquid state. Understanding the nature of alginate as an irreversible hydrocolloid is critical for dental assistants, as it directly influences how impressions should be handled and the types of procedures for which alginate is suitable.