Agar vs Alginate — MFDS Part 1 MCQ
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Correct answer: A — Its sol–gel transition is thermally reversible
Agar is a reversible hydrocolloid: heating converts the gel to a sol, and cooling returns it to a gel without a setting chemical reaction. Alginate, by contrast, forms an irreversible calcium alginate gel and cannot be reliquefied after setting, so B describes alginate. Agar can reproduce fine surface detail, making C incorrect. Alginate is generally cheaper and simpler to manipulate, so D does not distinguish agar. Conventional agar techniques require a hydrocolloid conditioning unit and a water-cooled impression tray; therefore E is also false.
Reference: Wilhelm MW, Andres CJ, Brown DT, Munoz CA. A comparison of three methods for preparing reversible hydrocolloid duplicating material. Journal of Prosthetic Dentistry. 1995;74(6):557–562. https://pubmed.ncbi.nlm.nih.gov/29262138/