National Dental Assisting Examining Board (NDAEB) Practice Exam

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Alginate impression material is classified as which type of hydrocolloid?

Reversible
Irreversible
Thermal
Elastic

The correct answer is: Irreversible

Alginate impression material is classified as an irreversible hydrocolloid because, once it has set, it cannot be returned to its original liquid state. This transformation occurs through a chemical reaction that solidifies the alginate into a gel-like structure, allowing it to take accurate impressions of teeth and oral tissues. This irreversible characteristic makes alginate particularly useful in various dental applications, including taking preliminary impressions for study models and custom trays. In contrast, reversible hydrocolloids, such as agar, can change from a gel back to a liquid state with heat and then regain their gel form upon cooling. Thermal refers to a process influenced by temperature but does not specifically designate whether a material is irreversible or not. Elastic simply describes the property of a material to return to its original shape, which doesn't classify alginate correctly as either reversible or irreversible. Thus, defining alginate as an irreversible hydrocolloid is accurate and key to understanding its role and limitations in dental practices.