National Dental Assisting Examining Board (NDAEB) Practice Exam

Which impression material exhibits the lowest permanent deformation?

1. Alginate

2. Polyether

3. Reversible hydrocolloid

4. Silicone

The correct answer is: Polyether

Polyether impression material is recognized for its excellent dimensional stability and low permanent deformation. This characteristic makes polyether particularly valuable in dental applications where precise reproduction of details is critical. Unlike some other materials that can undergo changes in shape or dimensions after being set, polyether maintains its form well over time, thereby ensuring that the impressions remain true to the original preparation. Polyether is also known for its high tear strength and is hydrophilic, which enhances its performance in moist environments. This level of stability and low permanent deformation means that when impressions are taken with polyether, they can be re-used over a period without significant alterations affecting the accuracy of the dental work. In contrast, alginate is subject to considerable permanent deformation due to its hydrocolloid nature, which can lead to inaccuracies if the impressions are not cast promptly. Reversible hydrocolloid can also exhibit changes in dimension after setting, especially if not handled correctly. Silicone, while also a stable choice, may not offer the same level of dimensional accuracy as polyether in all situations. Hence, polyether stands out as the material with the lowest permanent deformation among the options provided.