Dental Materials: Impression Materials Overview

Impression Materials Overview

• Impression materials register the form and relationship of teeth and oral tissues, creating accurate replicas or molds.
• Used for single teeth, full dentition, or edentulous mouths, producing a negative reproduction (impression) that can be filled with dental stone for a positive cast.
• Final cast is critical for constructing dentures, crowns, fixed dental prostheses, and restorations.

Impression Trays

• Trays carry impression material to the mouth and support it until set.
• Functions of trays include acting as a carrier and providing support for the set impression.

Types of Impression Trays

• Stock Tray (Prefabricated): Available in plastic disposable or metal materials.
• Custom Tray: Made from a model of the patient with acrylic or other resins for a tailored fit.
• Bite Registration Tray: Records occlusal surfaces of both arches, relates upper and lower casts.

Ideal Requirements of Impression Materials

• Safety: Non-toxic and non-irritant.
• Patient Acceptability: Factors include setting time, taste, and consistency.
• Accuracy: Demands high surface reproducibility and dimensional stability.
• Ease of Use: Requires good mixing properties and handling.
• Cost-Effectiveness: Affordable with a long shelf life to reduce redoing impressions.
• Elastic Properties: Ensures easy removal post-setting.
• Disinfection: Must be easily disinfected without compromising accuracy.

Classification of Impression Materials

• Organized based on the ability of the material to be withdrawn over undercuts.

Non-Elastic Impression Materials

• Rigid with little to no elasticity; ideal for cases without undercuts, primarily for edentulous patients.
• Key types include Impression Plaster, Impression Waxes, Impression Compound, and Zinc Oxide Eugenol.

Impression Plaster

• Usage: Mainly for complete denture impressions.
• Advantages: Rapid setting and cost-effective.
• Disadvantages: Complex technique, hard and brittle, unpleasant taste.

Impression Waxes

• Nature: Thermoplastic material that softens with heat and hardens upon cooling.
• Usage: Primary impressions for dentures, bite registration, and correcting minor voids.
• Advantages: Clean, inexpensive, easy to use.
• Disadvantages: Weakness, lack of accuracy, easily distorted.