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Sp 15- Fixed Restorative Final > Brantley: Die and Investment Materials > Flashcards

Brantley: Die and Investment Materials Flashcards

1
Q

When working with elastomeric impression material for preparation of cast gold restorations, _______ is possible due to polymerization reaction.

A

Shrinkage

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2
Q

The die stone will provide approximately ____% expansion, whereas the casting investment will provide up to approximately _____% expansion to compensate for shrinkage of polymerization reaction.

A

die stone: 0.1%

investment: 2%

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3
Q

Which has higher expansion, the die stone or the casting investment?

A

The investment

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4
Q

Why is it important that the investment expands?

A

To compensate for shrinkage from polymerization of elastomeric impression material.
We want expansion=shrinkage

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5
Q

What is calcining?

A

Thermal treatment process in the absence or limited supply of air or oxygen applied to solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction.
AKA: HEATING PROCESS

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6
Q

What is the starting mineral in the calcining process for Gypsum Products?

A

Calcium Sulfate Dihydrate

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7
Q

The starting mineral in the calcining process for Gypsum is calcium sulfate dihydrate. What is the product?

A

Calcium Sulfate Hemihydrate

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8
Q

BOARDS: Calcining procedures for Gypsum products give products in which two forms? Which is associated with stone and which is associated with plaster?

A

Alpha and Beta products
Alpha: stone and high-strength stone
Beta: Plaster

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9
Q

BOARDS: Gypsum products that result from the calcining process will be either alpha form or beta form. Describe the various calcining procedures that would result in 1. Plaster 2. Stone 3. High-strength Stone

A
  1. Plaster: Beta form: container open to air
  2. Stone: alpha form: closed autoclave under steam pressure
  3. High strength stone: alpha form: boiling calcium chloride solution
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10
Q

Which has higher porosity, plaster or stone?

A

Plaster

spongy appearance: highest porosity and surface area

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11
Q

Which has lower surface area, plaster or stone?

A

Stone

lower porosity and surface area than plaster

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12
Q

How does particle morphology influence porosity and surface area?

A

Stone

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13
Q

During mixing, is it better to have a high or low water-to-powder ratio?

A

low: You want MORE POWDER
plaster = 0.4 to 0.5
stone = 0.3 to 0.4
HS stone = 0.2 to 0.3

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14
Q

BOARDS: What is the setting reaction for Gypsum products?

A

CaSO40.5H20 + 1.5H20–> CaSO42H20

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15
Q

The setting reaction for Gypsum products is an _______ reaction and is the same for all Gypsum products.

A

Exothermic

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16
Q

Whether using plaster or stone, the starting product is calcium sulfate dihydrate and the end product is always _______.

A

Gypsum

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17
Q

What is the theoretical minimum water to powder ratio for Gypsum?

A

0.19

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18
Q

Excess water is required for _____ particles and reaching the desired ______ for mixing.

A

Wetting

viscosity

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19
Q

The highest amount of excess water (mixing/viscosity/wetting) is needed for which Gypsum product?

A

Plaster

least for High-strength stone

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20
Q

What does the “theoretical contraction during setting” refer to?

A

During the setting reaction, the specific volume is lower for products than for reactant. However, a setting EXPANSION actually occurs due to gypsum particles pushing each other apart.

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21
Q

BOARDS: What is the difference between an accelerator and a retarder for setting of Gypsum products?

A

Accelerator: reduce the setting time
Retarder: Increase the setting time

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22
Q

BOARDS: During setting of Gypsum products, NaCl is a/an ______ at low concentrations and a/an _______ at high concentrations

A

Accelerator

Retarder

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23
Q

BOARDS: What is a common accelerator in the setting of Gypsum products?

A

Potassium Sulfate

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24
Q

BOARDS: What is a common retarder in the setting of Gypsum products?

A

Borax

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25
Q

What is the difference in expansion for a setting reaction in air versus a hygroscopic setting condition?

A

In air, there is much less porosity and expansion compared to a hygroscopic setting.
Hygroscopic: crystal growth > radial spikes push crystals apart> water enters> more expansion > water leaves > porosity

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26
Q

Two important types of Die Stones are Type ___ and Type ____.

A

IV

V

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27
Q

Type IV die stone has high ______, the lowest setting _____, and contain larger amounts of _______.

A

strength
expansion
modifiers

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28
Q

What do modifiers do for gypsum products?

A

They CHANGE THE SHAPE of crystals and therefore allow for higher strength and lower setting expansion.

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29
Q

Type V die stone is both high ____ and high _____. Type V stone is designed for modern casting alloys and high melting point alloys that have greater shrinkage than traditional high-gold.

A

strength

expansion

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30
Q

Gypsum products are _____ materials with much higher ____ strength than ______ strength.

A

Brittle
compressive
Tensile

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31
Q

Describe the mechanical properties of Gypsum in regards to strength.

A

Compressive Strength > Tensile Strength

Failure = crack propagation at defects or pores

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32
Q

How do Gypsum products typically fail?

A

Gypsum is brittle.

At pores and defects there is CRACK PROPAGATION that results in failure

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33
Q

_____ stress acts to close cracks, whereas _____ stress will open cracks in Gypsum.

A

Compressive

Tensile

34
Q

True or False: Gypsum has much higher strength in wet conditions compared to dry.

A

False: Wet= weaker, Dry = Stronger

35
Q

Strength of Gypsum is a result of the starting ratio between ____ and ____ in the mixing of product.

A

water
powder
(higher W/P results in decreased strength)

36
Q

What is the result of a high W/P ratio?

A

Porosity

Decreased Strength

37
Q

What is the result of a high P/W ratio?

A

Increased Strength

Less porosity

38
Q

For all types of Gypsum products,is the setting expansion greater in air or in water?

A

Water (Hygroscopic)

39
Q

Loss of excess water beyond that required for a balanced setting reaction causes ______ in dry material.

40
Q

Porosity acts to concentrate stress during mechanical testing, leading to ______.

A

Material fracture

41
Q

Gypsum-Bonded casting investments are termed ____- heat investments.

42
Q

Low-Heat Investments (Gypsum-Bonded) are used with gold-based casting alloys for what type of restorations?

43
Q

_______-Bonded and _______-Bonded casting investments are termed high-heat investments.

A

Phosphate

Silicate

44
Q

High-heat investments are used with alloys for _______ restorations and some base metal casting alloys for removable partial denture frameworks.

A

metal-ceramic

45
Q

Phosphate and Silicate are ____-heat investments. Gold is _____-heat.

46
Q

All metal restorations use ____-heat investments. Metal-ceramic restorations and removable partial dentures use _____-heat investments.

A

All metal: Low-heat
Metal Ceramin: High-heat
Partials: High-heat

47
Q

What are the two roles of casting investments?

A
  1. Provide mold cavity for alloy after burnout of wax pattern
  2. Provide compensating expansion for casting shrinkage when alloy cools
48
Q

How does the investment counteract the casting?

A 
investment = expansion
casting = shrinkage
49
Q

What are the three means for investment expansion of the mold cavity?

A
  1. Normal setting expansion: approximately 0.3-0.4%
  2. Hygroscopic setting expansion: approximately 2%
  3. Thermal expansion: amount depends on burnout ~1%
50
Q

Which means of investment provides the greatest expansion?

A

Hygroscopic (water bath)

51
Q

What is the “binder” and approximately what percent of Gypsum stone is binder?

A

Binder: calcium sulfate hemihydrate

30-45%

52
Q

Approximately how much of Gypsum stone is made up by the refractory? What two types of refractory are common?

A

1/2 to 2/3!!!

quartz and/or cristobalite

53
Q

Which elements make up the greatest proportion in Gypsum powder?

A

Refractory

quartz or cristobalite

54
Q

Which elements compose the smallest proportion of Gypsum powder?

A

Chemical modifiers

55
Q

What two roles do chemical modifiers play in Gypsum?

A
  1. Control of setting time by changing crystal shape

2. Reduce atmosphere when casting alloy

56
Q

What is the “binder component” in the powder?

A

Gypsum (calcium sulfate dihydrate)

57
Q

What does the binder do?

A

It binds components together and provides structural framework at low temperatures

58
Q

True or False: The refractory component participates in the setting reaction.

59
Q

What is the most important role of the refractory component?

A

To provide thermal expansion during the heating in burnout furnace
(also provides strength of investment at temperatures above 100 degrees celsius)

60
Q

Match the letters to numbers:

a. binder b. refractory
1. strength 2. thermal expansion 3. setting

A

a. 3

b. 1, 2

61
Q

Why would pure gypsum make a terrible investment?

A

It shrinks when heated (contraction over burnout temperature range)

62
Q

Which has a higher thermal expansion, cristobalite or quartz? (refractory elements)

A

Cristobalite

63
Q

Why is glassy quartz not a very good investment?

A

it expands very little

64
Q

_______ exists as three forms and is important in thermal expansion (refractory).

A

Silicon Dioxide

65
Q

What are the three forms of silicon dioxide (commonly two forms are used)?

A

Cristobalite
Quartz
tridymite

66
Q

True or false: Fused silica (glass) has a much lower thermal expansion than the crystalline form.

67
Q

Rate of expansion is much greater for _____ than quartz.

A

Cristobalite

68
Q

What is the concern with low-heat techniques for burnout? What is an example?

A

Concern is an incomplete burnout of the wax pattern

Hygroscopic expansion investment

69
Q

What is an example of high-heat techniques for burnout and what is the concern with this method?

A

Thermal Expansion Investment

Caution about overheating the investment and causing decomposition

70
Q

Why must you never heat gypsum-bonded investments to temperatures over 700 degrees?

A

The breakdown of calcium surface causes sulfur incorporation in the casting, results in discoloration (black) and embrittlement.

71
Q

Increased expansion and strength is due to a more dense gypsum ________ resulting from a/an ______ powder to water ratio.

A

Framework

Increased

72
Q

Increasing the amount of spatulation (mixing) ________ setting expansion and strength.

73
Q

What is the problem with overspatulation of gypsum material?

A

It will break up the forming gypsum framework and makes it weaker.

74
Q

_____-bonded investments are the most common type in modern dental laboratories.

75
Q

For phosphate-bonded investments, which component makes up about 80% of the mass?

A

Refractory (quartz or cirstobalite)

76
Q

What provides bulk and helps to achieve a smooth surface finish in phosphate-bonded investments?

A

Particles of glasses and other metal oxides

77
Q

How do manufacturers produce higher expansion for phosphate-bonded investments?

A

By using a combination of different particle sizes of silica

78
Q

What is “special liquid”?

A

Its a solution of water and silica solute that is used in place of pure water during the mixing of powder. Special liquid:

  1. provides higher setting expansion and hygroscopic expansion
  2. increases strength of phosphate-bonded investment
79
Q

Does speical liquid increase or decrease expansion?

A

Increases expansion

80
Q

An advantage of PBIs is that they can withstand burnout temperatures up to __ and temperatures up to ____ for a short period of time; allow for fabrication of porcelain veneers.

A

900 degrees

1000 degrees

81
Q

Use of special liquid in PBIs results in dense and less porous molds that may cause incomplete castings, why?

A

There is not adequate release of trapped gases when molten metal enters the mold

Sp 15- Fixed Restorative Final (10 decks)

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