Questions and Answers
What is the function of an impression material?
To accurately record the dimensions of oral tissues and their spatial relationships.
What is an impression referred to?
What is a model or cast?
A positive reproduction of tissues obtained by pouring dental stone or other suitable material into an impression.
Which of the following is NOT a property of an ideal impression material?
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The type of impression made to construct a study cast for diagnosis is called a ______.
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Which type of impression is used for the fabrication of a prosthesis?
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Match the types of impression materials with their classification:
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Which statement correctly describes thermoplastic impression materials?
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Thermoset impression materials harden as a result of temperature changes.
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Study Notes
Impression Materials Overview
- Impression materials accurately record dimensions of oral tissues and their spatial relationships.
- Impression creates a negative reproduction of tissues; the resulting model or cast is a positive reproduction.
- Die cast specifically refers to the positive reproduction of a prepared tooth form.
Properties of Ideal Impression Materials
- Easy manipulation and cost-effective.
- Adequate flow properties and appropriate setting time.
- Sufficient mechanical strength to avoid tearing and permanent deformation.
- Excellent dimensional accuracy and acceptability to patients.
- Non-toxic and non-irritating, compatible with die or cast materials.
- Good keeping qualities, ensuring no deterioration and extended shelf-life.
Types of Impressions
- Preliminary impressions: Initial impressions for study casts used in diagnosis and custom tray fabrication.
- Secondary/Final/Wash impressions: Corrective impressions for creating master or working casts for prosthesis fabrication.
Classification of Impression Materials
- By use: In restorative dentistry, prosthodontics, and orthodontics; specific materials may vary per application.
- By hardening mechanism:
- Thermoplastic materials: Set due to temperature changes, e.g., modeling compound, agar, waxes.
- Thermoset materials: Harden through chemical reactions, e.g., dental gypsum, alginate, rubber impression materials, zinc oxide eugenol pastes.
Types According to Dr. McCracken
- Rigid materials: Harden during removal, used in non-undercut or edentulous areas, such as modeling compound and impression plaster.
- Elastic materials: Flexible upon removal, suitable for areas with undercuts, including alginate and agar.
Types of Impression Materials
- Inelastomeric Materials: Zinc oxide eugenol pastes and impression compound.
- Aqueous materials: Hydrocolloids like agar (reversible) and alginate (irreversible).
- Nonaqueous materials: Elastomers/rubber bases including polysulfides, condensation silicones, polyethers, and additional silicones (polyvinyl siloxanes).
Impression Trays
- Stock trays: Non-perforated for modeling compound; perforated for better retention and pressure release.
- Individual trays: Custom-made trays specific to each patient, often made of acrylic or shellac.
- Water-cooled trays: Designed specifically for agar impression materials.
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Description
This quiz focuses on dental impression materials and their functions in recording the dimensions and spatial relationships of oral tissues. It covers the process of making impressions and the significance of obtaining accurate replicas for dental applications.
