Impression Compound — MFDS Part 1 MCQ
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Correct answer: B — Thermoplastic, non-elastic impression material
Impression compound is a thermoplastic, non-elastic impression material. Heating softens it so that it can be moulded; cooling causes physical hardening without a chemical setting reaction. This process is reversible because the material can be softened again by reheating. Once cooled, it is rigid and therefore should not be withdrawn through significant undercuts. Elastomers remain elastic after setting. Alginate is an irreversible hydrocolloid, whereas agar is a reversible hydrocolloid. A thermosetting material hardens through an irreversible chemical reaction rather than reversible temperature-dependent softening. Impression compound is commonly associated with preliminary edentulous impressions and border moulding, but it is not generally classified as a wash material.
Reference: Gupta R, Brizuela M. Dental Impression Materials. StatPearls, 2026 edition. https://pubmed.ncbi.nlm.nih.gov/34662010/