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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
The products of calcining gypsum
1. α-hemihydrate 2. β-hemihydrate
26
Gypsum is ground and subjected to temperatures of _______ to _______ in open containers to drive off part of the water of crystallization.
110°C to 130°C (230°F to 266°F)
26
The principal constituent of gypsum-based products
Calcium Sulfate Hemihydrate (CaSO4 * 1/2H2O)
26
The β-hemihydrate of gypsum
Dental Plaster (Plaster of Paris)
27
What are the different gypsum products?
1. Dental Plaster (Plaster of Paris) 2. Dental Stone 3. Improved Alpha Hemihydrate or Die Stone
27
The shape of β-hemihydrate or Dental Plaster
Fibrous aggregate of fine crystals with capillary pores (“spongy” and irregular shape)
28
The temperature needed to heat gypsum in an open under dry calcination to produce dental plaster
110°C to 130°C
29
As the temperature is further raised, dental plaster becomes
anhydrite
29
What is the shape of the dental stone
Rods and prisms (Prismatic and more regular)
30
Dental Stone is heated between the temperature of
120°C to 130°C
31
Dental stone is heated under the pressure of
17 psi for 5-7 hours
32
Dental Stone is a _______ hemihydrate
crytalline
33
What is the shape of the Improved Alpha Hemihydrate or Die Stone
Cube shaped (more prismatic, more regular, more densely packed)
34
To produce improved alpha hemihydrate or die stone, it must undergo the process of
- 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
Why do gypsum products have different w/p ratios?
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
Time from adding the powder to the water until mixing is completed.
Mixing Time
37
Two types of Mixing and their time allotment
1. Mechanical Mixing - 20-30 seconds 2. Hand Spatulation - Atleast 1 minute
38
From the start of the mixing to the point where the consistency is no longer acceptable for the product's intended purpose
Working Time
39
General working time
3 minutes
40
Differentiate initial setting time and final setting time
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
How to check for setting time?
1. Loss of Gloss - 9 minutes 2. Initial Set - 13 minutes 3. Final Set (Vicat Needle Test and Gillmore Needle Set) - 30 minutes
42
Factors affecting the setting time
1. Impurities 2. Fineness 3. Water or W/P Ratio 4. Mixing 5. Temperature 6. Addition of Chemical Modifiers
43
High W/P Ratio = ____ Setting
Longer
44
Finer particles = ______ Setting
Faster
45
Addition of particle residues from incomplete calcination will ______ the setting time.
Shorten
46
Increase in the W/P Ratio = ______
Decrease in the strength and decrease in the setting expansion
47
The longer and the more rapidly the gypsum product is mixed, the _____ is the setting time.
shorter
48
Higher temperature = _______ setting time
longer
49
If the plaster-water mixture exceeds 50°C, _________ occurs.
gradual retardation
50
Chemical Modifiers
1. Accelerators 2. Retarders
51
Differentiate accelerators and retarders
Accelerators - Accelerates the setting reaction - Lower ang concentration na kailangan compared sa retarders Retarders - Delays setting time
52
Example of accelerators
1. Potassium Sulfate - most commonly used 2. Sodium Chloride
53
Differentiate the two types of setting expansion
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
The strength of gypsum products is generally expressed in terms of
Compressive Strength
55
Differentiate wet and dry strength
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
This is the equivalent of drying in air for 24 hours
Microwave irradiation for 1 minute
57
What happens when you overmix the product?
The product's strength decreases
58
What happens when mixing time is increased
The strength increases
59
What happens when W/P ratio is increased?
Porosity is increased, Dry strength is decreased
60
The incorporation of accelerators and retarders results in
Wet and Dry Strength Decrease
61
Types of Gypsum Products
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
Setting time of Type I Gypsum
4-5 minutes
63
Type II Gypsum uses
- To make study casts - To mount cast in articulator - To fill flasks in complete denture construction
64
Setting time and hardness of Type III Gypsum
Setting Time: 45-60 minutes Hardness: 82 in Rockwell Hardness Test
65
Uses of Type III Gypsum
- To make cast impressions for denture production - For indirect wax pattern of indirect restorations
66
Hardness of Type IV Gypsum
92 in Rockwell Hardness Test
67
Uses of Type IV Gypsum
- For carving wax patterns for construction of inlays and onlays
68
Use of Type V Gypsum
- For the construction of removable partial dentures and fixed partial dentures
69
Use of Type V Gypsum
- For the construction of removable partial dentures and fixed partial dentures
70
W/P Ratio for the different types of gypsum
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
Bowl and Spatula requirements
Bowl - Parabolic, Smooth, Abrasion Resistant Spatula - Convenient Handle, Stiff Blade

DENT MAT LEC PRELIMS (4 decks)

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