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Understanding Dental Impression Materials

Apr 22, 2025

Dental Impression Materials and Techniques

Overview

  • Presenter: Dr. M Bustani
  • Topic: Impression materials used in dentistry, focusing on elastomers and their properties.

Impression Materials

Inelastic Materials

  • Impression Compound
  • ZOE (Zinc Oxide Eugenol)
  • Impression Plaster
  • Impression Waxes

Elastic Materials

  • Hydrocolloids
    • Reversible: Achieves a gel state through temperature changes.
    • Irreversible: Chemical reactions set the material, making it irreversible.

Synthetic Elastomers

  • Introduced in the late 1950s to address hydrocolloids' issues:
    • Poor dimensional stability
    • Inadequate tear resistance
  • Types:
    • PolySulphide
    • PolyEther
    • C-Silicone
    • A-Silicone

PolySulphide

  • Also known as rubber base impression material
  • Components: Two pastes (catalyst and base)
  • Reactions: Condensation polymerization, with water as a by-product causing shrinkage
  • Advantages: Long working time, high tear resistance, moderate cost
  • Disadvantages: Long setting time, requires custom tray, messy, bad odor/taste
  • Special Considerations: Should be poured within 1 hour to avoid dimensional instability

PolyEther

  • Created to solve problems associated with PolySulphide
  • Characteristics:
    • Pseudo-plastic/thixotropic: Becomes fluid under pressure
    • Undergoes ring-opening polymerization
  • Advantages: Fast setting, good stability, long shelf life, least hydrophobic
  • Disadvantages: Rigid, bitter taste, absorbs water, high cost
  • Special Considerations: Store dry, pour within 48 hours

Silicones

C-Silicone (Condensation Cure)

  • Produces ethyl alcohol as a by-product, causing shrinkage
  • Advantages: Clean, good working time
  • Disadvantages: High shrinkage, should be poured immediately

A-Silicone (Addition Cure/PVS)

  • Used to address C-Silicone issues
  • Characteristics:
    • No byproduct except for hydrogen gas
    • Superior dimensional stability
  • Advantages: Clean, can be poured repeatedly, stable
  • Disadvantages: Hydrophobic, low tear strength

Impression Techniques

Multiple-Mix Technique

  • Utilizes two viscosities at one time
  • Involves syringe and tray materials

Monophase

  • Single viscosity used in both syringe and tray
  • Ideal for pseudo-plastic materials

Putty-Wash Technique

  • Uses two viscosities in two steps
  • Primarily for C-Silicone
  • Allows for impression repair

Key Takeaways

  • Understand the composition, accuracy, and setting time of each material
  • Consider when and how to use each type for optimal results