Impression Materials In Dentistry

Comparing Types Of Dental Impression Materials

Enumerate various impression materials used in dentistry. 
Answer:

Enumeration of Various Impression Materials Used in Dentistry:

1. Rigid impression materials

• Impression plaster
• Impression compound
• Zinc oxide eugenol impression paste
• Impression waxes

2. Elastic impression materials

• Hydrocolloids
  • Agar, i.e. reversible hydrocolloid
  • Alginate, i.e. irreversible hydrocolloid
•  Elastomeric impression materials
  • Polysulphide
  • Condensation polymerizing silicones
  • Addition polymerizing silicones
  • Polyether

Impression Materials In Dentistry

Classify compare elastic impression materials.
Answer:

Elastic Impression Materials:

• Hydrocolloids or aqueous elastic impression material
  • Agar, i.e. reversible hydrocolloid
  • Alginate, i.e. irreversible hydrocolloid
• Elastomeric impression materials or non-aqueous elastic impression materials
  • Polysulphide
  • Condensation polymerizing silicones
  • Addition polymerizing silicones
  • Polyether

Comparison of Elastomeric Impression Materials:

Impression Compound

• Type I—Impression compound.
• Type II—Tray compound.

Properties of Elastomeric Impression Materials

• Fusion Temperature: When the impression compound is heated in a water bath, it softens at 39°C, on continued heating above 43.5°C material start to soften and flow to a plastic mass which is manipulated. All impressions should be made above this temperature.
• Thermal Properties:
• It has low thermal conductivity and is a poor conductor of heat.
• The coefficient of thermal expansion is high due to the presence of resin and wax. Linear contraction from mouth to room temperature is 0.3%.
• Flow: During impression making good flw is necessary. Soft material flows in tissue contour. As the impression compound hardens its flow is stopped.

Applications of impression compound

• For type I:
  • Making a primary impression in the edentulous mouth.
  • For the impression of full crown preparation where gingival tissues should be displaced.
  • In border molding.
• For type II:
  • For checking undercut in inlay preparation.
  • For making special tray.

Advantages of impression compound

• Material can be reused a number of times if an error occurs.
• If any portion remains inaccurate, it should be remade without making a complete impression.
• By filming the surface of impression material accuracy can be improved.
• The material got its own body to support itself mainly in peripheral portion.
• The material should not collapse completely if tray is unable to support it.

Disadvantages of impression compound

• Due to high viscosity details recorded are fewer.
• While taking impressions soft tissues get compressed.
• Dental impression Compound has poor dimensional stability due to which it gets distorted.
• If undercuts are present it is difficult to remove.
• Dental impression Compound  gets overextended mainly in peripheries.