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