Dental Biomaterials II: Impression Materials

Dental Biomaterials II Overview

• Focuses on materials used in dentistry, including impression materials, casting alloys, and dental waxes.
• Key components include dental base polymers and casting procedures.

Impression Materials

• Definition: Dental impression is a negative replica of teeth and oral soft tissues, used for recording dimensions accurately.
• Types of Impressions:
  • Primary Impression: First impression which does not capture fine details.
  • Secondary Impression: Taken to capture fine details after the primary impression.

Impression Trays

• Tray Types:
  • Stock Tray: Standardized sizes (1, 2, 3), made of metal or plastic, used for primary impressions.
  • Special Tray: Customized on a primary model, made of acrylic or shellac for secondary impressions.

Properties of Ideal Impression Materials

• Ease of manipulation, adequate flow properties, appropriate setting time, good dimensional accuracy, and safety.
• Must be compatible with die and cast materials, have satisfactory odor/taste, be inexpensive, and possess good shelf life.

Classification of Impression Materials

• Classified by:
  • Setting Reaction: Chemical (sets by reaction) vs. physical (sets by temperature change).
  • Elasticity: Rigid (inelastic) materials for areas without undercuts, and elastic (flexible) materials for all cases.

Rigid (Inelastic) Impression Materials

• Limited to non-undercut areas including:
  • Impression compound (thermoplastic).
  • Zinc oxide eugenol impression paste (chemical).
  • Impression plaster (chemical).
  • Impression waxes (physical).

Elastic Impression Materials

• Suitable for both undercut and non-undercut areas:
  • Hydrocolloids: Alginate and agar.
  • Elastomers: Polysulfide, silicone, and polyether rubber.

Impression Compound

• A thermoplastic material that softens with heat (45-55°C) and hardens when cooled.
• Two types:
  • Type I: Low fusing for primary impressions.
  • Type II: High fusing for tray material.
• Packaged in cakes or sticks, available in various colors.

Zinc Oxide Eugenol (ZOE) Impression Material

• Rigid material used primarily for secondary impressions in edentulous patients.
• Comprises two pastes: Base paste (white) and catalyst paste (brown/red).
• Setting involves a chelation reaction, resulting in an irreversible bond.

Properties of ZOE

• Initial setting time is 3-5 minutes, final setting under 10 minutes.
• High dimensional stability with minimal changes during setting (0.1%).
• Requires no separating medium for cast preparation.

Non-Eugenol Paste

• Alternative for patients with eugenol allergies, utilizing orthoethoxy benzoic acid derivatives for saponification reaction.

Impression Plaster

• Rarely used due to rigidity and susceptibility to fracture, mainly for mounting casts or recording occlusal bite registrations.
• Supplied as powder mixed with water.