Impression Materials — MFDS Part 1 MCQ

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ModerateDental MaterialsImpression MaterialsMFDS Part 1

An elastomeric dental impression material sets by cross-linking hydroxyl-terminated polydimethylsiloxane with an alkyl silicate, releasing ethanol as a by-product. Which impression material is described?

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Correct answer: E — C-silicone

Explanation lettering: C = shown as A · E = shown as C · A = shown as E

The correct answer is **A, C-silicone**, also known as condensation silicone. It sets by condensation polymerisation, with cross-linking of hydroxyl-terminated polydimethylsiloxane and release of ethanol. Evaporation of this volatile by-product contributes to continued shrinkage, so the impression should be cast promptly. Polyvinyl siloxane is an addition silicone and does not normally release a volatile reaction by-product, giving it greater dimensional stability. Polyether sets by cationic ring-opening polymerisation rather than condensation polymerisation. Alginate sets through an irreversible sol-to-gel reaction involving calcium alginate formation, whereas agar undergoes a reversible, temperature-dependent physical gelation process.

Reference: Fakoori M, Hesaraki S, Nezafati N, Ghiass M. Evaluation of condensation silicone dental impression materials modified with diatomaceous Earth and zinc oxide fillers. Scientific Reports. 2025; Figure 1 setting-mechanism description. https://pubmed.ncbi.nlm.nih.gov/40652075/