Impression Materials in Dentistry: Types, Properties, and Applications

Impression Materials

Die: A reproduction of a prepared tooth made from a gypsum product, epoxy resin, a metal, or refractory material.

Cast: A dimensionally accurate reproduction of a part or parts of the oral cavity or ex- tra oral facial structures produced in a durable hard material.

Model: A positive full-scale replica of teeth, soft tissues, and restored structures used as a diagnostic aid for the construction of orthodontic and prosthetic appliances.

Impression Materials In Dentistry Types, Properties, And Applications

Polymerization: A chemical reaction that transforms small molecules into large polymer chains.

Syneresis: Expression of fluid into the surface of the gel structure.

Imbibition: Process of water sorption.

Read And Learn More: Basic Dental Materials Notes

Classification by elasticity and use

A review of impression materials

A review of impression materials

Polysulphides: Also known as

First dental elastomers
Rubber-base impression materials Vulcanizing impression materials
Mercaptan impression materials
Thiokol
- Contains lead dioxide polymer that gives polysulfide its characteristic brown color.
- The polymerization reaction is exothermic in nature.
- It has a long setting time of 8 to 12 minutes. it has an unpleasant odor and color. both of these properties cause patients discomfort heat and moisture accelerate the setting time.
- It is messy and stains clothes.
- Shows the highest permanent deformation. if maximal accuracy is to
- be maintained, the cast should be poured within the first 30 minutes.
- Shows high polymerization shrinkage due to loss of the by-product (water).
- Polymerization shrinkage and permanent deformation can be minimized by taking a minimum quantity of impression material and by using the custom acrylic tray.
- Shows the highest tear strength.
- Hydrophobic in nature. So the impression area should be dried before making an impression.
- Shows high flexibility and so the material can be released from undercut areas with minimum stress.
- Causes the lowest cell death count & so biocompatibility is good.
- Polysulphides are the only impression materials that can be elec- troplated.

Condensation silicones:

Also known as room temperature (RTV) silicones.
Highest curing shrinkage due to evaporation of ethyl alcohol byproduct. to avoid this, cast should be poured within the first 30 minutes.
Less permanent deformation than polysulphides.
Pleasant color and odor.
Low tear strength.
Hydrophobic in nature.
Flexibility is high when compared with polysulphides. So, the impression can be removed from undercuts without distortion. Has a limited shelf life because of oxidation of the tin component.
Handling latex globes is contraindicated.

Addition silicones (pseudoplastic impression materials):

Also known as polyvinyl siloxane or vinyl poly siloxane im- precision materials.
No volatile by-product.
Lowest curing shrinkage and lowest permanent deformation with best dimensional stability. So casts can be poured after several hours.
Extremely hydrophobic.
Shows the least setting time of all the elastomeric impression materials.
Handling with latex gloves is not indicated because the sulfur present in the natural latex gloves inhibits the settings of the addition of silicone impression materials.
Shows good shelf life than condensation silicones.
Hydrophobic in nature.
Vinyl impression materials can be disinfected by immersing in 10% hypochlorite or 2% glutaraldehyde solutions.
Sometimes hydrogen may be evolved and may cause pinpoint voids in stone casts.

Polyether:

First elastomer is to be developed primarily to function as an impression material. All the other materials were adapted for other uses.
Stiffest of all elastomeric impression materials. So extremely difficult to remove from undercut areas because of the high modulus of elasticity.
High tear strength next to polysulphides.
Dimensionally more stable. The casts can be poured immediately or after several hours, or after several days. Pouring up the im- precision and removing the cast several times does not alter the dimensional stability of the polyether.
Shows the highest cell toxicity and so the biocompatibility is not good.
Hydrophilic in nature. (Note: Agar and alginate are also hydrophilic).

Impression Compound (ADA – 3)

Applications: For making a primary impression, individual teeth impression

Impression Compound (ADA - 3)