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Questions and Answers
Which type of gypsum is classified as dental stone with high strength and high expansion?
Which type of gypsum is classified as dental stone with high strength and high expansion?
Type II gypsum is used primarily for taking impressions.
Type II gypsum is used primarily for taking impressions.
False
What is produced during closed calcination?
What is produced during closed calcination?
α-hemihydrate
Type ___ Gypsum is classified as the Plaster Model or Plaster of Paris.
Type ___ Gypsum is classified as the Plaster Model or Plaster of Paris.
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What measurement tool is used to assess the initial setting time of gypsum?
What measurement tool is used to assess the initial setting time of gypsum?
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Match the following types of gypsum with their primary uses:
Match the following types of gypsum with their primary uses:
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Type IV gypsum has loosely packed crystals.
Type IV gypsum has loosely packed crystals.
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What shape are the crystals in α-hemihydrate gypsum?
What shape are the crystals in α-hemihydrate gypsum?
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The correct pressure used during closed calcination is ___ PSI.
The correct pressure used during closed calcination is ___ PSI.
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What is the maximum temperature that can be reached during the final setting of gypsum?
What is the maximum temperature that can be reached during the final setting of gypsum?
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The initial setting time (I.S.T) is measured from the start of mixing until the second increase of temperature.
The initial setting time (I.S.T) is measured from the start of mixing until the second increase of temperature.
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What is the recommended soaking time for gypsum in water before mixing?
What is the recommended soaking time for gypsum in water before mixing?
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The time available to use a workable mix is known as ________ time.
The time available to use a workable mix is known as ________ time.
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Match the terminologies with their definitions:
Match the terminologies with their definitions:
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What is the main purpose of setting time in dental materials?
What is the main purpose of setting time in dental materials?
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How long does mechanical mixing generally take to complete?
How long does mechanical mixing generally take to complete?
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Final setting time is typically 20 minutes for gypsum products.
Final setting time is typically 20 minutes for gypsum products.
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A lower water-powder ratio tends to result in shorter mixing times and greater setting expansion.
A lower water-powder ratio tends to result in shorter mixing times and greater setting expansion.
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What is the significance of knowing the final setting time (F.S.T)?
What is the significance of knowing the final setting time (F.S.T)?
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What effect does increasing the amount of spatulation have on setting time?
What effect does increasing the amount of spatulation have on setting time?
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Hand spatulation generally requires at least ________ to obtain a smooth mix.
Hand spatulation generally requires at least ________ to obtain a smooth mix.
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The ideal W/P ratio for high-strength dental stone is typically between __________.
The ideal W/P ratio for high-strength dental stone is typically between __________.
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What is the significance of knowing the initial setting time (I.S.T)?
What is the significance of knowing the initial setting time (I.S.T)?
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Which of the following factors affects setting expansion?
Which of the following factors affects setting expansion?
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Chemical modifiers tend to increase setting expansion in dental materials.
Chemical modifiers tend to increase setting expansion in dental materials.
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List one chemical modifier that can be used in dental materials.
List one chemical modifier that can be used in dental materials.
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Setting expansion is usually measured through a __________ test.
Setting expansion is usually measured through a __________ test.
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Match the type of material with its water-powder ratio:
Match the type of material with its water-powder ratio:
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The setting expansion for die stone is 0% to 0.10%.
The setting expansion for die stone is 0% to 0.10%.
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What is the effect of accelerators on the setting time of gypsum products?
What is the effect of accelerators on the setting time of gypsum products?
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Retarders create a surface coating of crystals that makes gypsum less soluble to water.
Retarders create a surface coating of crystals that makes gypsum less soluble to water.
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What is the primary result of the interaction and entanglement of gypsum crystals?
What is the primary result of the interaction and entanglement of gypsum crystals?
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The best accelerator for gypsum products is __________ at concentrations greater than 2%.
The best accelerator for gypsum products is __________ at concentrations greater than 2%.
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Match the following materials with their corresponding compressive strength (MPA):
Match the following materials with their corresponding compressive strength (MPA):
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What happens to the setting expansion when the concentration of NaCl increases?
What happens to the setting expansion when the concentration of NaCl increases?
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The dry strength of gypsum is twice the wet strength after 24 hours.
The dry strength of gypsum is twice the wet strength after 24 hours.
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What should be done to prolong the shelf-life of gypsum products?
What should be done to prolong the shelf-life of gypsum products?
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A higher water-to-powder (W/P) ratio generally results in __________ setting expansion.
A higher water-to-powder (W/P) ratio generally results in __________ setting expansion.
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Which of the following is a commonly used retarder for gypsum products?
Which of the following is a commonly used retarder for gypsum products?
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What happens to the strength of a cast when the water/powder (w/p) ratio increases?
What happens to the strength of a cast when the water/powder (w/p) ratio increases?
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Dry strength of a cast is less than wet strength.
Dry strength of a cast is less than wet strength.
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What should be used for disinfecting casts according to the guidelines?
What should be used for disinfecting casts according to the guidelines?
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The __________ strength of a cast is twice that of the wet strength.
The __________ strength of a cast is twice that of the wet strength.
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Match the following properties of a good cast with their descriptions:
Match the following properties of a good cast with their descriptions:
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What is the effect of adding both accelerators and retarders to gypsum products?
What is the effect of adding both accelerators and retarders to gypsum products?
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Study Notes
Types of Gypsum Products
- Large crystals viewed microscopically appear spongy and irregular in shape.
- Type IV Gypsum: High-strength dental stone suitable for detailed dental work.
- Type V Gypsum: High-strength dental stone with high expansion, ideal for investment models.
Calcination Process
- Closed calcination occurs in an autoclave at 16 PSI and 120° to 130°C.
- This process produces α-hemihydrate, characterized by smaller, regularly shaped crystalline particles.
ADA Classification of Gypsum Products
- Type 1: Impression plaster, used for taking impressions.
- Type 2: Plaster of Paris, used for making study casts and records.
- Type 3: Dental stone, stronger than plaster, used as a working cast that can withstand applied forces.
- Type 4: Die stone, known for high strength and lower expansion.
- Type 5: Dental stone, high strength and high expansion, used as an investment model.
Instruments for Measuring Setting Times
- Vicat needle measures initial setting time (1/4 lb).
- Gillmore needle measures final setting time (1/4 lb for initial and 1 lb for final setting).
Exothermic Setting Reaction
- Maximum temperature reached during final hardening can hit 30°C at the center.
- Temperature increase duration depends on material bulk and thermal properties.
Mixing and Setting Times
- Gypsum powder should initially soak in water for 20 seconds.
- Mechanical mixing is ideal for 20-30 seconds while hand spatulation should require about one minute.
- Initial setting time is tracked from mixing until semi-hard stage (7-13 minutes).
- Final setting time is observed until the temperature decreases a second time (approximately 20 minutes).
Importance of Initial and Final Setting Times
- Initial Setting Time (I.S.T) allows for trimming excess plaster or stone.
- Final Setting Time (F.S.T) prevents premature separation of the cast, avoiding breakage.
Water-Powder Ratio (W/P Ratio)
- Affects compressive strength and setting expansion; less ratio means longer mixing time and greater setting expansion.
- Varying W/P ratios lead to different compressive strengths across types, with dental stone having the highest strength.
Practical Factors Influencing Setting
- High hygroscopic setting expansion corresponds to gypsum immersion in water.
- Accelerators (e.g., potassium sulfate) speed up setting, while retarders (e.g., borax) slow it down.
Strength Measurement
- Strength and hardness are determined by the crystal interaction and entanglement.
- Measured in terms of compressive strength, laboratory plaster stands at 27.5 MPA and dental stone at 62 MPA.
Care of Gypsum Products
- Store in airtight containers to prevent deterioration.
- Shake the container before use and utilize dry spoons to avoid moisture contamination.
Properties of an Ideal Cast
- Should exhibit high strength to reduce the chance of fracture.
- Must have a hard surface to prevent scratches during carving.
- Accurate measurement and stability are imperative to control setting expansion.
- Should be compatible with impression materials to avoid toxic reactions.
Disinfecting Solutions for Casts
- Follow manufacturer's guidelines or immerse in a 1:10 dilution of sodium hypochlorite for 30 minutes.
- Non-disinfected models can be aseptically wrapped and sterilized using ethylene oxide in clinical settings.
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Description
Explore the fascinating world of gypsum and its various forms in dental applications. This quiz covers large crystals, pores, and the specific types of gypsum used for high strength and expansion in dental stones. Test your knowledge on the closed calcination process and its significance in creating dental materials.
