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DENT MAT LEC PRELIMS > Chapter 4: Gypsum > Flashcards

Chapter 4: Gypsum Flashcards

1
Q

The process of heating a solid material to drive off volatile chemically combined components such as water and carbon dioxide.

A

Calcination

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2
Q

A reproduction of the shape and surface of a structure made in an impression of the surface.

A

Cast

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3
Q

The beta form of calcium sulfate hemihydrate.

A

Dental Plaster (Plaster of Paris)

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4
Q

The alpha form of calcium sulfate hemihydrate

A

Dental Stone

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5
Q

A reproduction of a prepared tooth made from a gypsum product, epoxy resin, a metal, or a refractory material.

A

Die

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6
Q

Calcium sulfate dihydrate

A

Gypsum

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7
Q

A refractory material consisting of silica and gypsum as a binder used to produce a mold for the metal casting process.

A

Gypsum-Based Investment

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8
Q

The expansion that occurs when gypsum or a gypsum-bonded investment sets while immersed in water (usually heated to approximately 38 °C [100 °F]).

A

Hygroscopic Setting Expansion

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9
Q

A positive likeness of an object.

A

Model

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10
Q

The expansion that occurs when gypsum or a gypsum-bonded investment sets in ambient air.

A

Normal Setting Expansion

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11
Q

Formed when calcium sulfate is mixed with water

A

Gypsum

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12
Q

Main ingredient of gypsum

A

Calcium sulfate

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13
Q

Gypsum is produced as a by-product of?

A

Flue Gas Desulfurization

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14
Q

What is the appearance of gypsum?

A

White to milky yellowish, a compact mass in nature

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15
Q

Uses of gypsum

A
  1. Occasionally used for intraoral to make impression
  2. Auxiliary Materials
  3. Gypsum-Based Investment
  4. Ancient Egypt Pyramids
  5. Others (Building construction, Soil conditioning, Food additives, Pharmaceuticals, Medical devices, and dental applications.)
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16
Q

This material is used for edentulous patients

A

Plaster Impression

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17
Q

What type of gypsum is used for construction of onlays and inlayrs

A

Type IV (Dental Stone, High Strength Type, or Die Stone)

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18
Q

What materials are used for embedding plaster, dentures, and cast?

A

Dental flask and pressor

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19
Q

Gypsum is added to silica as a binder for what purpose?

A

For dental casting investments

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20
Q

Gypsum is used as a _________ for dental laboratory operations involved in the production of dental prostheses.

A

Auxiliary Materials

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21
Q

When a gypsum product is mixed with refractory fillers, such as different crystalline forms of silica, it becomes more heat resistant, which makes it useful to form molds for the casting of molten metal in an anatomic form for dental restorations.

A

Gypsum-Based Investment

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22
Q

What is the role of gypsum when it comes to the ancient Egypt pyramids?

A

A mixture of plaster (a gypsum product) was used in joining the stone blocks of ancient Egypt’s pyramid

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23
Q

Gypsum is also known as

A

calcium sulfate dihydrate (CaSO4*2H2O)

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24
Q

The process of heating a solid material to drive off volatile chemically combined components such as water and carbon dioxide

A

Calcination

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25
Q

The products of calcining gypsum

A
  1. α-hemihydrate
  2. β-hemihydrate
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26
Q

Gypsum is ground and subjected to temperatures of _______ to _______ in open containers to drive off part of the water of crystallization.

A

110°C to 130°C (230°F to 266°F)

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26
Q

The principal constituent of gypsum-based products

A

Calcium Sulfate Hemihydrate (CaSO4 * 1/2H2O)

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26
Q

The β-hemihydrate of gypsum

A

Dental Plaster (Plaster of Paris)

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27
Q

What are the different gypsum products?

A
  1. Dental Plaster (Plaster of Paris)
  2. Dental Stone
  3. Improved Alpha Hemihydrate or Die Stone
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27
Q

The shape of β-hemihydrate or Dental Plaster

A

Fibrous aggregate of fine crystals with capillary pores (“spongy” and irregular shape)

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28
Q

The temperature needed to heat gypsum in an open under dry calcination to produce dental plaster

A

110°C to 130°C

29
Q

As the temperature is further raised, dental plaster becomes

29
Q

What is the shape of the dental stone

A

Rods and prisms (Prismatic and more regular)

30
Q

Dental Stone is heated between the temperature of

A

120°C to 130°C

31
Q

Dental stone is heated under the pressure of

A

17 psi for 5-7 hours

32
Q

Dental Stone is a _______ hemihydrate

A

crytalline

33
Q

What is the shape of the Improved Alpha Hemihydrate or Die Stone

A

Cube shaped (more prismatic, more regular, more densely packed)

34
Q

To produce improved alpha hemihydrate or die stone, it must undergo the process of

A
  • Boiling gypsum in 30% aqueous solution of calcium chloride at 100°C
  • Washing the powder with hot water to remove residual calcium chloride or sodium succinate
35
Q

Why do gypsum products have different w/p ratios?

A

Because of their difference in shape and in the compactness of their crystals. The more irregular in shape and porous in character, the more water required for the powder to be mixed and poured.

36
Q

Time from adding the powder to the water until mixing is completed.

A

Mixing Time

37
Q

Two types of Mixing and their time allotment

A
  1. Mechanical Mixing - 20-30 seconds
  2. Hand Spatulation - Atleast 1 minute
38
Q

From the start of the mixing to the point where the consistency is no longer acceptable for the product’s intended purpose

A

Working Time

39
Q

General working time

40
Q

Differentiate initial setting time and final setting time

A

Initial setting time
- When the mix loses it surface gloss and gains strength but no measurable compressive strength and cast cannot be safely removed from the impression.

Final setting time
- The elapsed time at which a heavier Gillmore needle leaves only a barely perceptible mark on the surface.
- Needle: 453.6 g, 1.06 mm tip

41
Q

How to check for setting time?

A
  1. Loss of Gloss - 9 minutes
  2. Initial Set - 13 minutes
  3. Final Set (Vicat Needle Test and Gillmore Needle Set) - 30 minutes
42
Q

Factors affecting the setting time

A
  1. Impurities
  2. Fineness
  3. Water or W/P Ratio
  4. Mixing
  5. Temperature
  6. Addition of Chemical Modifiers
43
Q

High W/P Ratio = ____ Setting

44
Q

Finer particles = ______ Setting

45
Q

Addition of particle residues from incomplete calcination will ______ the setting time.

46
Q

Increase in the W/P Ratio = ______

A

Decrease in the strength and decrease in the setting expansion

47
Q

The longer and the more rapidly the gypsum product is mixed, the _____ is the setting time.

48
Q

Higher temperature = _______ setting time

49
Q

If the plaster-water mixture exceeds 50°C, _________ occurs.

A

gradual retardation

50
Q

Chemical Modifiers

A
  1. Accelerators
  2. Retarders
51
Q

Differentiate accelerators and retarders

A

Accelerators
- Accelerates the setting reaction
- Lower ang concentration na kailangan compared sa retarders

Retarders
- Delays setting time

52
Q

Example of accelerators

A
  1. Potassium Sulfate - most commonly used
  2. Sodium Chloride
53
Q

Differentiate the two types of setting expansion

A

Hygroscopic Setting Expansion
- The expansion that occurs when gypsum is immersed in water and is heated to approximately 38°C.

Normal Setting Expansion
- The expansion of gypsum when set in ambient air.

Mas malaki expansion sa water.

54
Q

The strength of gypsum products is generally expressed in terms of

A

Compressive Strength

55
Q

Differentiate wet and dry strength

A

Wet strength has a presence of excess water which weakens the product.

Dry strength has no excess water and may be two or more times as high as the wet strength.

56
Q

This is the equivalent of drying in air for 24 hours

A

Microwave irradiation for 1 minute

57
Q

What happens when you overmix the product?

A

The product’s strength decreases

58
Q

What happens when mixing time is increased

A

The strength increases

59
Q

What happens when W/P ratio is increased?

A

Porosity is increased, Dry strength is decreased

60
Q

The incorporation of accelerators and retarders results in

A

Wet and Dry Strength Decrease

61
Q

Types of Gypsum Products

A
  1. Type I (Impression Plaster)
  2. Type II (Dental Plaster)
  3. Type III (Dental Stone)
  4. Type IV (Dental Stone, High Strength/Die Stone)
  5. Type V (Dental Stone, High Strength, High Expansion)
62
Q

Setting time of Type I Gypsum

A

4-5 minutes

63
Q

Type II Gypsum uses

A
  • To make study casts
  • To mount cast in articulator
  • To fill flasks in complete denture construction
64
Q

Setting time and hardness of Type III Gypsum

A

Setting Time: 45-60 minutes
Hardness: 82 in Rockwell Hardness Test

65
Q

Uses of Type III Gypsum

A
  • To make cast impressions for denture production
  • For indirect wax pattern of indirect restorations
66
Q

Hardness of Type IV Gypsum

A

92 in Rockwell Hardness Test

67
Q

Uses of Type IV Gypsum

A
  • For carving wax patterns for construction of inlays and onlays
68
Q

Use of Type V Gypsum

A
  • For the construction of removable partial dentures and fixed partial dentures
69
Q

Use of Type V Gypsum

A
  • For the construction of removable partial dentures and fixed partial dentures
70
Q

W/P Ratio for the different types of gypsum

A
  1. Type I - 0.60 ml
  2. Type II - 0.50 ml
  3. Type III - 0.30 ml
  4. Type IV - 0.24 ml
  5. Type V - 0.18 ml
71
Q

Bowl and Spatula requirements

A

Bowl
- Parabolic, Smooth, Abrasion Resistant

Spatula
- Convenient Handle, Stiff Blade

DENT MAT LEC PRELIMS (4 decks)

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