Impression Materials — Detailed Properties
- Addition silicone (PVS) — most accurate and dimensionally stable; no by-product (a hydrogen scavenger is added); hydrophobic (improved with surfactants). Material of choice for precise work.
- Condensation silicone — releases ethanol by-product → shrinks on storage.
- Polysulfide — long set, high tear strength, messy; releases water by-product.
- Polyether — very accurate, hydrophilic, stiff; absorbs water (store dry).
- Alginate — irreversible hydrocolloid; snap set; subject to syneresis/imbibition so pour promptly.
Concepts
Dimensional stability, detail reproduction, tear strength, and hydrophilicity drive material selection.
Exam Tips ⭐
PVS = most accurate, no by-product; condensation silicone = alcohol by-product; polyether = hydrophilic + stiff.
📝 Practice MCQs — Impression Materials — Detailed Properties
Q1. Which impression material has essentially no reaction by-product?
A. Condensation silicone
B. Addition silicone (PVS)
C. Polysulfide
D. Alginate
Show Answer
✅ Answer: B
Addition silicone has no significant by-product (with a hydrogen scavenger).
Q2. Polyether impression material should be stored:
A. In water
B. Dry (it absorbs water)
C. In disinfectant soak
D. Frozen
Show Answer
✅ Answer: B
Polyether is hydrophilic and imbibes water, so store dry.
Q3. Alginate must be poured promptly because of:
A. High cost
B. Syneresis and imbibition (dimensional change)
C. Toxicity
D. Color change
Show Answer
✅ Answer: B
Water loss/gain (syneresis/imbibition) distorts alginate over time.
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Related Topics
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