Impression Materials Quick Key

A comprehensive set of vocabulary flashcards covering the classification, rankings, facts, and techniques of dental impression materials.

Rigid (Non-elastic) Materials

A category of impression materials that includes Impression Compound, ZOE, and Impression Plaster.

Agar

A reversible elastic hydrocolloid that sets by a temperature change (cooling).

Alginate

An irreversible elastic hydrocolloid that is the least accurate elastic material and must be poured immediately.

Elastomers

A group of impression materials including Polysulphide, Polyether, Addition Silicone ($PVS$), and Condensation Silicone.

Primary Impression Materials

Includes Alginate ($A$), Compound ($C$), and Putty Elastomers ($P$).

Secondary (Final) Impression Materials

Includes ZOE (light body) and light body elastomers.

Dimensional Stability Ranking

$$PVS > \text{Polyether} > \text{Condensation Silicone} > \text{Polysulphide}$$

Accuracy Ranking

$$PVS > \text{Polyether} > \text{Polysulphide} > \text{Alginate}$$

Tear Strength Ranking

$$\text{Polysulphide} > \text{Polyether} > \text{Silicone}$$

Hydrophilicity Ranking

$$\text{Polyether} > \text{Addition Silicone} > \text{Condensation Silicone}$$

Flexibility Ranking

$$\text{Polysulphide} > \text{Silicone} > \text{Polyether}$$

Working Time Ranking

Polysulphide has the longest; Polyether has the shortest.

Addition Silicone ($PVS$)

The gold standard for crowns and bridges with the best dimensional stability and least shrinkage; inhibited by sulfur from latex gloves or rubber dams.

$H_2$ gas release

A phenomenon in $PVS$ that occurs if poured too early, leading to pinholes in the cast.

Polyether

The most hydrophilic and most rigid elastomer; inherently hydrophilic due to its aziridine ring. Should be avoided in patients with epoxy resin allergy.

Polysulphide

The elastomer with the highest tear strength and longest working time; it has an unpleasant smell and produces a water (alcohol) by-product during setting.

Condensation Silicone

A hydrophobic elastomer that produces ethyl alcohol as a byproduct, resulting in significant shrinkage; must be poured immediately.

Syneresis

The loss of $H_2O$ leading to shrinkage, commonly seen in Alginate.

Imbibition

The gain of $H_2O$ leading to expansion, commonly seen in Alginate.

Alginate Reactor and Retarder

Contains $Ca^{2+}$ sulphate as a reactor and $Na$ phosphate as a retarder.

Potassium Sulphate in Alginate

Acts as a gypsum hardener for a better cast surface.

ZOE

A mucostatic, rigid, and dimensionally stable material used for complete denture final wash impressions; free eugenol can cause burning or stinging.

Impression Compound

A thermoplastic, rigid, mucocompressive material. Type I is for final impressions and Type II is for border molding (green stick).

Impression Compound Pour Time

Must be poured within $1\text{ hour}$ to minimize distortion from internal stress relaxation.

Mucostatic Technique

An impression technique where no pressure is applied and tissues are at rest; uses ZOE or Impression Plaster.

Mucocompressive Technique

An impression technique that applies definite pressure to simulate functional load; uses Compound, Waxes, or Soft liners.