Condensation Silicone Pouring Time — MFDS Part 1 MCQ

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ModerateDental MaterialsCondensation Silicone Pouring TimeMFDS Part 1

Which impression material should be cast promptly because ethanol is formed during setting and its subsequent evaporation contributes to progressive post-set shrinkage?

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Correct answer: A — Condensation silicone

Condensation silicone is the correct answer. Its setting reaction produces ethanol, and continuing evaporation of this volatile by-product causes post-set contraction and loss of dimensional accuracy. The impression should therefore be cast promptly, following the manufacturer's instructions rather than relying on a universal maximum delay. Addition silicone forms no volatile condensation by-product and has substantially better dimensional stability. Polysulphide can also lose accuracy during storage, but its reaction by-product is water rather than ethanol. Polyether does not release ethanol, although water absorption can alter its dimensions. Agar is a reversible hydrocolloid whose instability results principally from syneresis and imbibition, not alcohol evaporation.

Reference: Braden M. Dimensional stability of condensation silicone rubbers. Biomaterials. 1992;13(5):333-336. https://pubmed.ncbi.nlm.nih.gov/1600035/