National Dental Assisting Examining Board (NDAEB) Practice Exam

What type of impression material is typically used to take a preliminary impression?

1. Polyether

2. Irreversible Hydrocolloid

3. Silicone

4. Wax

The correct answer is: Irreversible Hydrocolloid

The type of impression material most commonly used for taking a preliminary impression is irreversible hydrocolloid. This material is known for its ability to capture details of the oral structures effectively while being cost-effective and easy to manipulate. Irreversible hydrocolloid, also known as alginate, is preferred for preliminary impressions because it is hydrophilic, allowing it to capture accurate detail from the wet environment of the mouth. Additionally, it sets quickly, making it particularly suitable for initial impressions where speed and ease of use are important. The material expands slightly upon setting, which helps it release from the dental structures without damaging the impression. Because it is flexible after setting, it can be removed from the mouth without distorting the impression as long as it’s handled properly. In contrast, while other materials listed have their specific uses, they are generally not as suitable for preliminary impressions. Polyether, for instance, is used for more detailed, accurate final impressions due to its superior dimensional stability but can be less comfortable for patients. Silicone materials can also offer high detail but are primarily used for final impressions or specific situations where higher accuracy is required. Wax is sometimes used in bite registrations or for specific custom trays, but it does not capture the fine details needed for a