Dental Impression Techniques
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Questions and Answers

What should be done first when preparing the mixture?

  • Mix water with the powder until creamy
  • Place water into the rubber bowl (correct)
  • Allow the mixture to set immediately
  • Add the powder directly into the patient's mouth

    • What is the purpose of mixing the powder with water?

  • To ensure the mixture is fluffy
  • To form a creamy mixture (correct)
  • To increase the volume of the powder
  • To create a solid form

    • What tool is used to mix the water and powder?

  • A blender
  • A whisk
  • A spoon
  • A spatula (correct)

    • How should the mixture be applied after it is prepared?

    <p>Filled into a tray and seated into the mouth</p> Signup and view all the answers

    What happens after the tray is placed in the patient's mouth?

    <p>It is allowed to set</p> Signup and view all the answers

    What is a consequence of storing substances in hot water for an extended period?

    <p>It can lead to leaching of important constituents.</p> Signup and view all the answers

    What materials are commonly used for final impressions in complete denture work?

    <p>Zinc-oxide eugenol and impression plaster</p> Signup and view all the answers

    What is the recommended thickness for the acrylic tray used with the material?

    <p>1.5 mm</p> Signup and view all the answers

    What happens when a compound is overheated in hot water?

    <p>It becomes sticky and difficult to handle.</p> Signup and view all the answers

    Which type of tray is utilized for taking impressions of partially edentulous ridges?

    <p>Stock tray</p> Signup and view all the answers

    Which impression materials are mentioned for use in stock trays?

    <p>Hydrocolloids and elastomers</p> Signup and view all the answers

    Which important constituent is mentioned as being affected by leaching in hot water?

    <p>Stearic acid</p> Signup and view all the answers

    What is the percentage of dimensional changes during the setting of the material?

    <p>0.06%</p> Signup and view all the answers

    What characteristic is NOT applicable to the type of stock tray used for taking impressions?

    <p>Custom-fit for individual mouths</p> Signup and view all the answers

    What practice can help maintain the quality of a compound when using hot water?

    <p>Minimizing the time the compound spends in hot water.</p> Signup and view all the answers

    Which of the following statements about the dimensional stability of the material is true?

    <p>It maintains minimal dimensional changes during setting.</p> Signup and view all the answers

    When taking a final impression for complete dentures, which of the following is typically used?

    <p>Zinc-oxide eugenol or impression plaster</p> Signup and view all the answers

    What type of tray is recommended for optimal use of the material?

    <p>Acrylic tray</p> Signup and view all the answers

    To prevent the compound from becoming difficult to handle, what should be avoided?

    <p>Overheating it during storage.</p> Signup and view all the answers

    How is the dimensional stability of the material quantitatively expressed during setting?

    <p>0.06%</p> Signup and view all the answers

    How long is the mixing process supposed to last?

    <p>60 seconds</p> Signup and view all the answers

    What tool is used to combine the strips during the mixing process?

    <p>Spatula</p> Signup and view all the answers

    At what point are the strips combined together?

    <p>From the 1st sweep of spatula</p> Signup and view all the answers

    What is the next step after mixing the strips for about 60 seconds?

    <p>Fill the mixture into a special tray</p> Signup and view all the answers

    How many strips are mentioned to be combined during the mixing process?

    <p>Two strips</p> Signup and view all the answers

    What is the primary role of resinous balsam in the mentioned mixture?

    <p>To improve flow and mixing properties</p> Signup and view all the answers

    What does the chemical reaction of ZnO and eugenol produce?

    <p>Zinc eugenolate and unreacted ZnO</p> Signup and view all the answers

    What is included in the set material after the reaction?

    <p>An amorphous zinc eugenolate matrix</p> Signup and view all the answers

    What is the percentage of the coloring agent used in the mixture?

    <p>5%</p> Signup and view all the answers

    What does the unreacted ZnO represent in the set material?

    <p>A byproduct with no functional role</p> Signup and view all the answers

    Study Notes

    Impression Materials

    • A dental impression is a negative record of the tissues in the mouth. It is used to create a positive reproduction of the teeth and surrounding structures.
    • A positive reproduction is made by pouring a suitable material (like dental stone) into the impression, allowing it to harden.
    • A single tooth reproduction is called a die, while several teeth or a whole arch is called a cast or model.
    • Impression material is placed in a tray, which can be a stock tray or a special tray.

    Classification of Impressions

    • Preliminary impressions
    • Final impressions
    • Bite registrations

    Impression Trays

    • Quadrant tray: Covers half of the arch.
    • Section tray: Covers the anterior portion of the arch.
    • Full arch tray: Covers the entire arch.
    • Perforated tray: Has holes to hold the impression material in place.
    • Smooth tray: The interior is coated with adhesive to hold the impression material.

    Requirements of an Ideal Impression Material

    • Accurate reproduction of surface details, depending on low viscosity for soft tissue prevention of displacement.
    • Compatibility with moisture and saliva (hydrophilic).
    • Dimensional accuracy and stability, depending on the type of tray and material shrinkage.
    • Permanent set and storage stability.
    • Freedom from toxic or irritant constituents.
    • Easy manipulation, appropriate setting time, and adequate strength.
    • Compatibility with cast and die material.
    • Easy disinfection.

    Key Properties

    • Accuracy: Ability to replicate intraoral surface details.
    • Dimensional stability: Ability to maintain its size over time.
    • Tear resistance: Ability to resist tearing.

    Classification of Impression Materials (According to Elasticity)

    • Elastic materials: Return to their original shape after removal from the mouth. They can engage undercuts and are used in partially and fully edentulous patients.
    • Rigid materials: Do not return to their original shape. They cannot engage undercuts and are used for edentulous patients only.

    Classification of Impression Materials (According to Setting Reaction)

    • Physical reaction (reversible, thermoplastic): Softens when heated and hardens when cooled (e.g., impression compound, agar, wax).
    • Chemical reaction (irreversible): Chemical changes occur during setting (e.g., impression plaster, zinc oxide eugenol, alginate, polysulfide, silicones, polyether).

    Classification of Impression Materials (According to Reaction with Saliva)

    • Hydrophilic: Compatible with moisture and saliva, completely absorbing it.
    • Hydrophobic: Does not absorb saliva; saliva will repel off the surface.

    Classification of Impression Materials (According to Viscosity Before Setting)

    • Mucostatic: Does not compress tissue during setting.
    • Mucocompressive: Compresses tissue during setting (more viscous).
    • Pseudo-plastic: Viscous materials that become fluid under low stress.

    Methods of Making Impressions

    • Stock tray with pressure: Primary impressions for complete dentures using impression compound.
    • Resin custom tray without pressure: Final impressions for complete dentures using Zinc oxide-eugenol or impression plaster.
    • Stock tray (rim-lock, perforated or adhesive): Partially edentulous impressions using hydrocolloids or elastomers.
    • Custom Resin trays: Crown and bridge impressions or partial dentures, using regular or heavy/light body elastomers.

    Impression Plaster

    • Presentation: Powder mixed with water (w/p=0.6).
    • Composition:Calcium sulfate beta hemihydrate, potassium sulfate, borax, pigments (like alizarin).

    Starch in Impression Plaster

    • Added for easier separation of the cast from the impression.
    • Hot water softens the starch grains for easy separation.

    Zinc Oxide-Eugenol

    • Reaction of zinc oxide and eugenol creates a hard mass, with mechanical and medical properties (used in certain dental fields).
    • Various types (I and II), with different setting times.

    Impression Materials: Advantages and Disadvantages

    • Advantages:*
    • High accuracy for soft tissue impressions
    • Good surface detail reproduction
    • Inexpensive
    • Disadvantages:*
    • Messy material
    • Variable setting time (dependent on temperature and humidity)
    • Non-elastic, susceptible to fracture in undercuts
    • Eugenol is irritating to soft tissues.

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    Dental Materials Lecture 3 PDF

    Description

    This quiz covers essential techniques in dental impression making, focusing on the preparation and application of mixtures for final impressions in complete denture work. It addresses materials, tools used, and the effects of temperature on dental compounds. Test your knowledge on the important steps and considerations in this crucial dental procedure.

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