Dental Impression Materials: Types, Composition & Properties

Impression Materials

Impression materials are biomaterials that are used for faithful and accurate reproduction of negative hard and soft structures of the oral cavity.

Classification

Classification: rigid and elastic.

Rigid Materials

Rigid: paste and zinc oxide (without eugenol) biomaterials are those that, when subjected to pressure, are permanently deformed and after removal do not recover their original shape. They are used in non-retentive areas of the oral cavity.

Elastic Materials

Elastic: hydrocolloids (reversible and irreversible) and elastomers (mercaptan, silicone, vinyl, polyesters) are materials that deform elastically under pressure and, after removal of pressure, are able to regain their original form. They are used in retentive/undercut areas.

Impression Compounds

Impression compounds are thermoplastic, resinous materials that are rigid at room temperature and are used to make impressions in non-retentive oral areas.

Synonyms: model compounds, modeling clay, Godiva, modeling.

Commercial Presentation

Commercial presentation: tablets, sticks or pencils, short cylinders, cones.

Chemical Composition

Chemical composition: natural or synthetic thermoplastic resin 10% (compound base); beeswax 7% (filler, viscosity); stearic acid 7% (lubricant and plasticizer); coloring agent (color).

Manipulation Technique

Manipulation technique:

• Dry heat (burner): the material is flamed to re-blend the surface layers while massaging.
• Humid heat (hot water): using a container with hot water to soften the material.

Softening Temperatures

Softening temperature:

• 50 °C — intense green-gray
• 53.3 °C — brown or red-ivory
• 55.5 °C
• 56.1–56.6 °C — black

Setting Physical Reaction

Setting physical reaction (by change in temperature): rigid state → with heat becomes plastic → on cooling returns to rigid state.

Properties

Properties: It has high viscosity, which makes it mucocompressive but prevents reproduction of fine details. Flow (runoff) should not exceed 6% when cooled from 83 °C to 45 °C. Short working time. Hardens when cooled. Completely free of irritants or toxic substances. Low thermal conductivity. Thermal expansion up to 0.43% from 25 °C to 40 °C. Contraction approximately 0.3%. Does not suffer dimensional changes on removal from the mouth. The surface should look smooth, shiny and plastic. Once hardened, it may be cut and carved.

Factors Affecting Flow

Factors affecting runoff: temperature, pressure, amount of packing.