Gypsum Crystals and Types
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Questions and Answers

What type of gypsum product is used primarily for taking impressions?

  • Type 1: Impression/Soluble Plaster (correct)
  • Type 2: Plaster Model/Plaster of Paris
  • Type 3: Dental Stone
  • Type IV: Die Stone

    • Type V Gypsum has lower strength than Type IV Gypsum.

    False

    What is produced when calcination is performed in an autoclave at 16 PSI and 120° to 130°C?

    α-hemihydrate or Dental Stone

    Type IV gypsum is also known as __________.

    <p>Die Stone</p> Signup and view all the answers

    Match the following types of gypsum products with their characteristics:

    <p>Type 1 = Used to take impression Type 2 = Used to make study cast/Model Type 3 = Stronger than Plaster of Paris Type 4 = High strength, lower expansion</p> Signup and view all the answers

    What happens to the setting time when water is added in excess?

    <p>Setting time increases</p> Signup and view all the answers

    Adding more water to the plaster mixture will lead to a thicker consistency.

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

    What chemical reaction occurs during the setting of gypsum?

    <p>H2O + CaSO4⋅1⁄2 H2O ----- CaSO4⋅2H2O + HEAT</p> Signup and view all the answers

    Gypsum products experience greater setting expansion when allowed to expand in _____ during normal setting.

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

    Match the types of plaster with their correct setting time percentage:

    <p>Type I: Impression Plaster = 0.13% Type II: Model Plaster = 0.3% Type III: Dental Stone = 0.15-0.2% Type IV: Die Stone = 0.08% Type V: High Strength, High Expansion Dental Stone = 0.3%</p> Signup and view all the answers

    What is the effect of temperature above 50°C on gypsum setting reaction?

    <p>Acts as a retarder</p> Signup and view all the answers

    Finer particles of gypsum will dissolve more quickly and lead to faster setting.

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

    What is the recommended mixing time for gypsum products?

    <p>2 minutes</p> Signup and view all the answers

    What effect does a higher concentration of NaCl have on the setting expansion of gypsum products?

    <p>It decreases expansion</p> Signup and view all the answers

    Borax is classified as an accelerator for gypsum products.

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

    What is the primary effect of temperature on the setting time of gypsum products?

    <p>It slows down the setting time.</p> Signup and view all the answers

    A good accelerator for gypsum products is __________ at concentrations greater than 2%.

    <p>K2 SO4</p> Signup and view all the answers

    Match the following types of gypsum products with their compressive strength:

    <p>Laboratory plaster = 27.5 MPA Dental Stone = 62 MPA Die Stone = 79 MPA</p> Signup and view all the answers

    Which of the following is NOT a care instruction for gypsum products?

    <p>Use a wet spoon when getting powder</p> Signup and view all the answers

    The dry strength of gypsum is half of the wet strength after 24 hours.

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

    The interaction and entanglement of crystals contribute to the strength and __________ of gypsum products.

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

    What is the measurement of the Initial Setting Time (I.S.T) for gypsum products?

    <p>7-13 minutes</p> Signup and view all the answers

    The Final Setting Time (F.S.T) for gypsum products is 20 minutes.

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

    What should gypsum be soaked in before mixing?

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

    The Gillmore needle is used to measure __________.

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

    How long should mechanical mixing of gypsum last?

    <p>20-30 seconds</p> Signup and view all the answers

    The maximum temperature during the exothermic setting reaction can reach 30°C.

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

    What is the effect of increasing the water/powder (W/P) ratio on the strength of a cast?

    <p>Decreases strength and increases porosity</p> Signup and view all the answers

    What is the purpose of monitoring the temperature of gypsum during the setting process?

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

    Working Time (W.T) allows the user to maintain __________ consistency.

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

    Overmixing the material will improve the strength of the cast.

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

    Match the terms with their respective definitions:

    <p>Mixing Time (MT) = Duration for adding powder to water Working Time (WT) = Time to maintain a workable mix Initial Setting Time (I.S.T) = Time until semi-hard stage is reached Final Setting Time (F.S.T) = Time until cast can be separated</p> Signup and view all the answers

    What is the recommended immersion method for disinfecting casts?

    <p>Immersion in a 1:10 dilution of sodium hypochlorite solution for 30 minutes.</p> Signup and view all the answers

    What is the adequate working time for a gypsum mix?

    <p>3 minutes</p> Signup and view all the answers

    A good cast should be __________ with the impression material to prevent any adverse reaction.

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

    Match the following properties of a good cast with their descriptions:

    <p>High strength = Reduces the chance of fracture Hard surface = No scratches during carving Stable measurement = Controlled setting expansion Smooth surface = Free of bubbles</p> Signup and view all the answers

    Study Notes

    Forms of Gypsum

    • Two principal forms: Type IV Gypsum (Dental Stone) - High Strength and Type V Gypsum (Dental Stone) - High Strength and High Expansion.

    Closed Calcination Process

    • Conducted in an autoclave at 16 PSI, 120° to 130°C.
    • Produces α-hemihydrate (Dental Stone) with smaller, regularly shaped crystalline rods or prisms.

    ADA Classification of Gypsum Products

    • Type 1: Impression/Soluble Plaster - Used for taking impressions.
    • Type 2: Plaster Model/Plaster of Paris - Used for study casts/models.
    • Type 3: Dental Stone (Class 1) - Stronger than plaster; used for working casts.
    • Type 4: Die Stone - High strength, low expansion.
    • Type 5: High Strength High Expansion Dental Stone - For investment models.

    Measurement Tools

    • Vicat Needle: Measures initial setting time (1/4 lb).
    • Gillmore Needle: Measures final setting time (1/4 lb for initial; 1 lb for final).

    Uses of Gypsum Products

    • Ceramics and medical casts for broken bones.
    • Stabilization of articulation between upper and lower casts.

    Key Terminology

    • Mixing Time (MT): Duration for mixing gypsum powder with water.
    • Working Time (WT): Time available to use a mix before it becomes unworkable.
    • Setting Time (ST): Time to reach a semi-hard state after mixing.

    Exothermic Setting Reaction

    • Final hardening increases temperature, can reach 30°C.
    • Temperature rise is affected by the amount of material used.

    Setting Expansion Types

    • Normal Setting Expansion: Expansion when allowed in the air.
    • Hygroscopic Setting Expansion: Expansion when set immersed in water.

    Accelerators and Retarders

    • Accelerators: Remove crystal surface coating, making them soluble to water; examples include K2SO4.
    • Retarders: Create crystal coating to slow down setting time; examples include borax and higher concentrations of salt.

    Chemical Reaction of Setting

    • Water + Calcium Sulfate Hemihydrate → Calcium Sulfate Dihydrate + Heat.

    Strength and Hardness

    • Strength results from crystal interaction; measured in compressive strength:
      • Laboratory plaster = 27.5 MPa/4000 PSI.
      • Dental Stone = 62 MPa/9000 PSI.
      • Die Stone = 79 MPa/11,500 PSI.

    Care of Gypsum Products

    • Store in airtight containers to extend shelf-life.
    • Use a dry scoop for powder; adhere to the correct water/powder ratio.

    Properties of a Good Cast

    • High strength to reduce fracture chances.
    • Hard surface to prevent scratches during carving.
    • Stable setting expansion; compatible with impression material.
    • Good color contrast; smooth, free of bubbles.

    Disinfecting Solution for Casts

    • Follow manufacturer’s instructions or use a 1:10 dilution of sodium hypochlorite for immersion (30 minutes).
    • Non-disinfected impressions can be aseptically wrapped and sterilized in ethylene oxide.

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    Gypsum Products Notes PDF

    Description

    Explore the fascinating world of gypsum crystals and their various forms, including Type IV and Type V gypsum for dental applications. This quiz will cover the properties, heating processes, and the structural characteristics of these minerals. Test your knowledge on how different gypsum types are utilized in dentistry.

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