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SU14 Fixed Restorative > Die and Investment Materials > Flashcards

Die and Investment Materials Flashcards

1
Q 
Which ones undergo shrinkage and which under expansion
elastomeric impression material
die stone
wax pattern
gold alloy
casting investment
A 
elastomeric impression material; shrinkage
die stone; 0.1% expansion
wax pattern; ranging
gold alloy; 2% shrinkage
casting investment; 2% expansion
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2
Q

What is the formula for calcium sulfate dihydrate

A

CaSO4 • 2H20

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3
Q

What is the formula for calcium sulfate hemihydrate

A

CaSO4 • 1/2H20

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4
Q

This calcining procedure has container open to air

A

plaster (β form)

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5
Q

This calcining procedure has closed autoclave under steam pressure

A

stone (α form)

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6
Q

This calcining procedure has boiling calcium chloride solution

A

high-strength stone (α form)

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7
Q

This has the highest porosity and surface area (spongy appearance)

A

plaster

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8
Q

This has a rectangular shape, lower porosity and surface area than plaster particles

A

stone

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9
Q

This has the most uniform shape, lowest porosity and surface area

A

high-strength stone

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10
Q

What is the typical water to powder ratio of plater, stone, and high strength die stone

A

plater; 0.4-0.5
stone; 0.3-0.4
HSDS; 0.2-0.3*

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11
Q

What three things happen during the setting reaction for gypsum products

A

exothermic reaction
reverse of calcining process
end product is gypsum

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12
Q

What is the theoretical minimum water/powder ratio for a balanced setting reaction

A

0.186 (0.19)

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13
Q

Excess water is required for wetting particles and desired viscosity for mix; most for this material and least for this

A

most for plaster

least for high-strength stone

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14
Q

What are common accelerators and retardants

A

accelerator = potassium sulfate
retarder = borax
NaCl; accelerator at low conc. retarder at high

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15
Q

Expansion is caused by what

A

gypsum particles pushing each other apart

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16
Q

This high strength die stone have the lowest setting expansion and contain larger amounts of modifiers to provide this property

A

type IV high-strength die stones

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17
Q

Type V die stones are both what and what, designed for modern casting alloys higher melting point alloys with greater casting shrinkage than traditional high-gold alloys

A

high-strength

high-expansion

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18
Q

Brittle materials have a much higher compressive strength than what

A

tensile srength

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19
Q

In which condition is there much higher strength

A

dry conditions have higher strength compared to wet condition

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20
Q

Strength is related to what

A

the starting W/P ratio used for mixing product, which determines amount of porosity in set material

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21
Q

What happens to the strength if there is a high W/P ratio

A

decreased strength

22
Q

Loss of excess water beyond that required for balanced setting reaction causes what

A

porosity in dry material

23
Q

Porosity acts to what

A

concentrate stress during mechanical testing, leading to material fracture

24
Q

These are termed low-heat investments; used with gold-based casting allows for all-metal restorations

A

gypsum-bonded casting investments

25
Q

These phosphate-bonded investments are used with alloys for metal ceramic restorations and some base metal casting allows for RPD
Also, silicate-bonded investments are used with other base metal casting allows for RPD which have high melting temps

A

high-heat casting investment

26
Q

This provides mold cavity for allow after burnout of wax pattern or plastic pattern; provides compensating expansion for casting shrinkage when alloy cools

A

casting investments

27
Q

What are the three means for investment expansion of mold cavity

A

normal setting expansion; approx. 0.3-0.4%
hygroscopic setting expansion over 2%
thermal expansion; amount depends on burnout temp, 1%

28
Q

What is the composition of gypsum bonded casting investment powder

A

binder is calcium sulfate hemihydrate (stone or α form) 30-45%
refractory is quartz and/or cristobalite; 1/2 to 2/3
chemical modifiers 3% or less

29
Q

Chemical modifiers can do what two things

A

control setting time

reducing atmosphere when casting alloy

30
Q

What is the purpose of the binder component of gypsum bonded investment powder

A

binds components together; provides structural framework at low temps

31
Q

This component of gypsum-bonded investment powder does not participate in the setting reaction, its most important role is to provide thermal expansion during heating in burnout furnace; proves strength of investment at temps above 100°C

A

refractory component

32
Q

Which one has a much higher thermal expansion; cristobalite investment or quartz investment

A

cristobalite

33
Q

Pure gypsum undergoes what over burnout temperature range

A

contraction

34
Q

The presence of stone powder component in investment reduces expansion by about how much

A

1/3

35
Q 
True or False
Fused silica (glass) has much lower thermal expansion than crystalline forms
A

True

36
Q

This causes a large thermal expansion over a narrow temperature rand

A

changes in crystal structure

37
Q

Never heat gypsum bonded investments over what temp

A

700°C

38
Q

Why would you not want to overheat gypsum bonded investments

A

breakdown of calcium sulfate causes sulfur incorporation in casting
results in discoloration and embrittlement

39
Q

Increasing or decreasing the PW ration increases strength an expansion (more powder less water)

A

increasing

40
Q

Why does increasing the PW ration, increase strength and expansion

A

more dense gypsum framework

41
Q

Increasing the amount of what increases setting expansion and strength; it breaks down he forming gypsum framework and weakens structural framework

A

spatulation

42
Q

What are the two components in the two-component system of PBIs (phosphate bonded investments)

A

powder and aqueous solution of stabilized colloidal silica

43
Q

Particles of glasses and other metal oxides provide what in PBIs

A

bulk and help achieve smooth surface finish

44
Q

In the setting reaction for PBIa, the binder component undergoes an acid-base reaction between what

A

ammonium phosphate and magnesia

45
Q

Water produced by the setting reaction of a PBI does what

A

lowers viscosity of mix as spatulation continues

46
Q

To produce higher expansion, manufactures use a combination of what

A

different particle sizes of silica

47
Q

True or False

either water or special liquid provided by manufacturer can be used

A

True

48
Q

What is the “special liquid”

A

some form of silica sol in water; provides higher setting expansion and hygroscope expansion

49
Q

What are three advantages of PBIs

A

high green strength and high fired strength
sufficient setting and thermal expansion
withstand burnout temperatures

50
Q

What are four disadvantages of PBIs

A

when temps excess 1375°C; breakdown
high strength can bauds difficulty in removal
use of additional special liquid results in denser and less porous mold
if bulk powder used instead of remeasured packages, reaction with air may reduce setting expansion

SU14 Fixed Restorative (9 decks)

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