Dental Impression Materials Overview
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Questions and Answers

What is a significant disadvantage of using irreversible hydrocolloid materials for impressions?

  • Exhibits some permanent deformations (correct)
  • Requires custom trays for cooling
  • Forms an irreversible gel
  • Can only be used with plastic casts

    • Which characteristic of polysulfide polymer elastomeric materials makes them a cost-effective option?

  • Rapid setting time
  • High elastic properties
  • Easy pouring
  • Least expensive elastomer (correct)

    • What disadvantage is specific to the use of reversible hydrocolloid materials during the impression process?

  • Cannot be reused
  • Requires specific equipment for heating and cooling (correct)
  • Cools too quickly
  • High cost compared to other materials

    • How do condensation silicones differ from polysulfide polymer in terms of composition?

    <p>Made of dimethylsiloxane with reactive -OH groups</p> Signup and view all the answers

    What must be done immediately after taking an impression with elastomeric materials such as polysulfide?

    <p>Pour within an hour</p> Signup and view all the answers

    What is one major disadvantage of condensation silicone impression materials?

    <p>Poor wetting capabilities</p> Signup and view all the answers

    Which of the following characteristics does addition silicone have compared to condensation silicone?

    <p>Better dimensional stability</p> Signup and view all the answers

    Why must teeth and gingival sulci be free of moisture when using condensation silicone?

    <p>To avoid poor adhesion of light body</p> Signup and view all the answers

    What is a crucial step to avoid air bubbles when pouring casts from condensation silicone impressions?

    <p>Application of surfactant</p> Signup and view all the answers

    What characteristic of addition silicone helps improve the overall user experience during manipulation?

    <p>Short setting time</p> Signup and view all the answers

    Study Notes

    Impression Materials

    • Inelastic Impression Materials: Less common now, prone to breakage during removal, suitable for edentulous cases (minimal undercuts). Examples include Plaster of Paris (type I gypsum) and impression compounds.

    Elastic Impression Materials

    • Reversible Hydrocolloids: Agar hydrocolloid (seaweed-based). Changes from gel to sol at high temperatures (90°C), and sol to gel at low temperatures (below 50°C).

      • Advantages: Hydrophilic, low cost, reusable, no custom tray needed.
      • Disadvantages: Requires heating/cooling equipment, poor tear strength, low stability (must be poured rapidly).

    • Irreversible Hydrocolloids: Alginate impressions form an irreversible gel when mixed with water. Comes in various setting speeds.

      • Advantages: Rapid setting, hydrophilic, easy technique, low cost.
      • Disadvantages: Only suitable for stone casts, less detailed than other materials, some permanent deformation.

    • Elastomeric Materials: More modern and versatile.

      • Polysulfides: Oldest elastomeric type, two-part paste system (base & catalyst), available in different viscosities (light, regular, heavy), brown color, requires lead peroxides for polymerization.
        • Advantages: High tear strength, high elasticity, easy removal, easy pouring, better stability than hydrocolloids (still needs fast pouring).
        • Disadvantages: Slight contraction during polymerization (custom tray helps), long setting time (10 minutes), affected by humidity/temperature, patient dislike (color/odor), messy, staining potential.
      • Condensation Silicones: Two-part base and catalyst, dimethylsiloxane with reactive -OH groups, higher molecular weight = heavier consistency, available as putty, heavy body, light body.
        • Advantages: Short setting time (6-8 minutes), less affected by high temperatures, odorless.
        • Disadvantages: Hydrophobic (poor wetting), needs moisture-free impressions, needs surfactant before pouring to avoid air bubbles, putty contamination can prevent light-body adherence, potential dimensional instability over time if water/alcohol is lost.
      • Addition Silicones (Polyvinyl Siloxane): Similar to condensation silicones but more stable (no water/alcohol byproducts), after setting, more rigid than polysulfides. Available in various consistencies (putty, heavy body, regular body, light body).
        • Advantages: Dimensionally stable (some up to a week), pleasant to use, short setting time, automix available, less material waste, better mixing, fewer air bubbles.
        • Disadvantages: Hydrophobic nature, hydrophilic materials can absorb water, setting inhibited by latex gloves (dithiocarbamates), some release H₂ gas during polymerization (air bubbles in cast - wait 1 hour before pouring).

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    Description

    Explore the different types of dental impression materials, focusing on inelastic and elastic categories. This quiz covers key concepts about reversible hydrocolloids, irreversible hydrocolloids, and their advantages and disadvantages. Test your knowledge on how these materials impact dental practices.

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