PVS Hydrogen Gas Release — NDEB AFK MCQ

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ModerateDental MaterialsPVS Hydrogen Gas ReleaseNDEB AFK

An elastomeric impression material that releases hydrogen gas during setting and must be poured after a 30-minute delay to avoid surface bubbles is which of the following?

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Correct answer: A — Polyvinyl siloxane (addition silicone)

Addition silicone (PVS) releases small amounts of hydrogen gas as a byproduct of the platinum-catalysed polymerisation reaction (residual hydride groups react with moisture). If the impression is poured immediately, gas bubbles on the surface of the stone cast create pitting. A delay of approximately 30 minutes (or up to 1 hour for some products) before pouring allows the hydrogen to dissipate. Many modern PVS formulations contain platinum or palladium scavengers that absorb the hydrogen, allowing immediate pouring.

Reference: Anusavice – Phillips' Science of Dental Materials, 13th ed., 2022