Dental Materials: Impression Waxes

Impression Materials

Impression Waxes

• Considered one of the first impression materials in dentistry.
• Characteristics: cheap, clean, user-friendly.
• Available in various consistencies: soft, medium, hard, and extra hard.
• Described as rigid, muco-static, hydrophobic, and reversible; softens with heat and hardens upon cooling (thermoplastic).
• Composed of low melting paraffin and beeswax in a 3:1 ratio.
• High coefficient of thermal expansion leads to distortion when removed from undercuts.
• Not commonly used for complete impressions due to weak mechanical properties.
• Solid at mouth temperature but moldable when heated to tolerable levels for oral tissues.
• Formats include sticks, strips, and tubes.
• Key types include:
  • Corrective Impression Wax: Used to register soft tissue details over original impressions.
  • Bite-Registration Wax: For accurately articulating opposing arches, now often replaced by silicone and polyether materials.

Impression Compound

• One of the oldest dental impression materials.
• Classified as inelastic (rigid), hydrophobic, mucocompressive, and reversible thermoplastic.
• Primarily employed for making primary impressions of edentulous mouths.
• Alternative names include dental compound, model compound, and model plastic.
• Presentation: available as cakes, sticks, and cones.
• Setting reaction involves no chemical change; softens with heat and hardens upon cooling.

Composition

• General composition includes:
  • Natural or synthetic resin for cohesion and flowance.
  • Waxes (40%): provides thermoplasticity and flow.
  • Stearic acid, shellac, gutta-percha (3%): assists in consistency.
  • Diatomaceous earth, French chalk, or talc (50%): contributes to thermoplasticity.
• Utilizes low thermal conductivity; requires thorough heating, ideally in a water bath.
• Can be reused for the same patient if errors occur; inaccurate portions can be remade without duplicating the entire impression.

Advantages of Impression Compound

• Compatible with model materials; does not require a separating medium before pouring plaster.
• Reusable and adaptable, allowing for corrections.
• No need for a special tray.
• Effective for techniques needing a tight peripheral seal.
• Can be combined with other materials.
• Cost-effective.

Drawbacks of Impression Compound

• Rigid once set, leading to distortion; not suitable for undercut areas.
• Acts as a muco-compressive material, potentially displacing soft tissue.
• Fails to reproduce fine surface detail owing to high viscosity and low flow.