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Impression Materials — Properties

Prosthodontics • NEET MDS Study Guide • AI-Generated Notes

⭐ High-Yield Facts for Exam

  • Accuracy: PVS > Polyether > Condensation silicone > Polysulfide.
  • Alginate = irreversible hydrocolloid; pour promptly.
  • Agar = reversible hydrocolloid.
  • Polyether = hydrophilic but stiff.
  • Condensation silicone releases alcohol → shrinkage.

Impression Materials

Hydrocolloids

  • Alginate — irreversible hydrocolloid; cheap, hydrophilic, single use; for study models and primary impressions. Pour promptly (dimensional change with imbibition/syneresis).
  • Agar — reversible hydrocolloid (sol-gel by temperature).

Elastomers (accuracy ranking)

From least to most accurate/dimensionally stable: Polysulfide < Condensation silicone < Polyether < Addition silicone (PVS).

  • Addition silicone (PVS) — most accurate, excellent dimensional stability, no significant by-product (hydrogen if no scavenger). The material of choice for fixed prostheses.
  • Polyether — very accurate and hydrophilic (good in moisture) but stiff and absorbs water on storage.
  • Condensation silicone — releases alcohol by-product → shrinkage on storage.
  • Polysulfide — long setting, messy, good tear strength.

Exam Tips ⭐

Most accurate = addition silicone (PVS). Polyether = stiff + hydrophilic. Alginate = irreversible hydrocolloid, pour soon.

📝 Practice MCQs — Impression Materials — Properties

Q1. The most accurate elastomeric impression material is:
A. Polysulfide
B. Condensation silicone
C. Polyether
D. Addition silicone (PVS)
Show Answer
✅ Answer: D
PVS (addition silicone) has the best accuracy and dimensional stability.
Q2. Alginate is classified as a:
A. Reversible hydrocolloid
B. Irreversible hydrocolloid
C. Elastomer
D. Rigid material
Show Answer
✅ Answer: B
Alginate is an irreversible hydrocolloid.
Q3. Which elastomer is hydrophilic and very stiff?
A. Polysulfide
B. Polyether
C. Condensation silicone
D. Addition silicone
Show Answer
✅ Answer: B
Polyether is hydrophilic and rigid.
Q4. Condensation silicone shrinks on storage because it releases:
A. Water
B. Alcohol (ethanol)
C. Hydrogen
D. Oxygen
Show Answer
✅ Answer: B
Condensation silicone releases ethanol by-product, causing shrinkage.
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