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Tim's Cards > Dental Materials II > Flashcards

Dental Materials II Flashcards

1
Q 
Stress/Strain curve for:
Stiff
Ductile
Strong
Tough
A

2;30

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2
Q

Stress/Strain curve for:
Flexible
Brittle
Weak

A

2;30

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3
Q

How does rapid cooling affect the atomic structure of metals and alloys?

A

Forms more nuclei per unit volume

Decreases grain size

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4
Q

What 2 terms are used for the ability of atomic centers to slide against each other into new positions within the same crystal lattice?

A

Ductility

Malleability

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5
Q

For metals and alloys, what raises yield strength, increases ductility, and raises the ultimate strength?

A

Finer grain size

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6
Q

What is related to plastic deformation and fracture in metals and alloys?

A

Change grain size

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7
Q

A fracture due to a crack opening up on a grain boundary is more likely to occur in…

A

Large grain metals

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8
Q

The mechanism of plastic deformation is called…

A

Dislocation motion

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9
Q

What process causes many plastic deformations by producing dislocations (and increases likelihood of fracture)?

A

Cold Working (wrought)

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10
Q

The phase diagram of metals and alloys reveals…

A

Melting range

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11
Q

What are the 3 possibilities when mixed metals are cooled?

A

Solid Solution - (soluble)
Eutectic - (not soluble)
Intermetallic compound (rxn)

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12
Q

What 2 metals always form a solid solution?

Why?

A

Au and Cu

Soluble

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13
Q

What is special about ordered solutions?

A

They impart greater hardness

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14
Q

When Au and Cu occupy specific positions, it is an…

A

ordered solution

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15
Q

When 2 metals are soluble as liquids, but nearly insoluble as solids, they form…

A

Eutectic alloys

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16
Q

A pure Eutectic has a ______ that is ______ than either of the pure components.

A 
Melting point (not range)
Lower
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17
Q

What % by weight must a noble alloy contain to be considered noble?

A

25%

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18
Q

Carat content of pure gold:

A

24 K

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19
Q

How is fineness measured?

A

out of 1000

75% pure = 750

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20
Q

What 2 effects will adding 10% Cu to Au have?

A

Increase tensile strength
Increase BHN

(what is BHN?)

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21
Q

What 2 factors does the creation of an ordered solution depend on?

A

% metals

Cooling rate

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22
Q

T/F

An ordered solution will increase hardness, decrease elongation, and increase yield strength.

A

True

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23
Q

T/F

The stress at any point in a Ceramic is the same as the average stress

A

True

*if stretched

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24
Q

In ceramics, where will stress rise significantly?

A

around a Stress Raiser

*groove and edge of groove

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25
Q

What allows water molecules to penetrate polymer chains?

A

Weak secondary bonds

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26
Q

What defines high noble?
Noble?
Base metal?

A

60% noble / 40% gold
25% noble
less than 25%

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27
Q

What adds color to ceramics?

A

Metallic Oxides

28
Q

What are the 2 post-manufacture phases of feldspathic dental porcelain?

A

Vitreous (glass)

Crystalline (mineral/leucite)

29
Q

The Vitreous phase of ceramic porcelain is like…

A

Glass

30
Q

The Crystalline phase of ceramic porcelain contributes what 2 things?

A 
Strength
Thermal Expansion (high)
31
Q

What process joins porcelain particles together?

A

Sintering

*Biscuit Bake

32
Q

What often fractures in the Oxide layer of ceramics-metal bonds?

A

Base metals

*layer too thick

33
Q

Where does the fracture take place if proper bonding occurs in ceramic-metal specimens?

A

Porcelain

34
Q

In a ceramic-metal system, the Coeffecient of Thermal Expansion must be ____ for the metal.

A

Higher

*puts ceramic into compression where it is stronger

35
Q

What type of wax will soften when heated?

A

Thermoplastic

36
Q

T/F

Waxes have a low degree of thermal expansion.

A

False

37
Q

What type of stress in waxes usually results from non-uniform heating/cooling?
How can this be relieved?

A

Internal

Release Residual stress by heating

38
Q

4 characteristics of all Waxes:

A

Melting range
Tendency to flow
Residual Stresses
Largest CTE of all dental matls

39
Q

What is the most accurate way to dispense the mixing powder making up aliginate impression materials?

A

Weighing

40
Q

What ingredient in Alignate retards hardening?

A

Sodium phosphate

aka tri-sodium phosphate

41
Q

What can cause the shrinkage and distortion of an aliginate impression due to fluid loss?
(not evaporation)

A

Syneresis

42
Q

T/F

Syneresis is the same as evaporation

A

False

43
Q

What can cause expansion of an Aliginate impression?

A

Imbibition

44
Q

What is Imbibition?

A

The uptake of water in the gel state

45
Q

What can lead to shrinkage of an Aliginate impression and is often due to level of humidity in the room?

A

Evaporation

46
Q

What is the basis for all gypsum used in dentistry?

A

Calcium sulfate hemihydrate

47
Q

The 3 types of material derived from the partial dehydration of gypsum rock (plaster, stone, high strength stone) have what major difference?

A

Manner of driving off water

48
Q

What 3 materials are derived from Mineral Gypsum (dihydrate)?

A

Plaster
Dental stone
High strength stone

49
Q

The gypsum setting reaction is what type?

characterized by what 3 things?

A

Nucleated recrystallization

continuous solution of hemihydrate
diffusion of Ca and sulfate ions to nucleation centers
Precipitation of microscopic gypsum crystals

50
Q

What leads to less porosity and more strength in gypsum products?

A

Less water

51
Q

What leads to more porosity and less strength in gypsum products?

A

More water

52
Q

Why do thick mixes in water/powder of gypsum products harden more quickly?

A

Nucleation centers concentrated

53
Q

T/F

Porosity tends to strengthen gypsum products

A

False

54
Q

What happens if you decrease the water/powder ratio in a gypsum product?

A

Denser cast

55
Q

What does increasing the Water/Powder ratio do to gypsum products?

A

Decrease Strength

56
Q

How is Gypsum used in gold alloy casting?

A

as a Binder

57
Q

What provides expansion to compensate for gold shrinkage?

A

Refractory

a silicone dioxide

58
Q

What are the 2 functions of Binder in Gypsum Bonded Investments?

A

Forms solid mass

Provides strength

59
Q

What is the composition of Binder in Gypsum Bonded Investments for gold?
For high temp alloys?

A

Calcium sulfate hemihydrtate

Phosphate, ethyl silicate

60
Q

What is the low temperature phase for a silica?

High temperature phase?

A

Alpha

Beta

*change between 2 is responsible for most thermal expansion

61
Q

T/F

A Utectic has a melting range and not a melting point

A

False

*Has a Melting Point

62
Q

What is the difference between a Thermoplastic and Thermoset material?

A

Thermoplastic - Softens upon heating

Thermoset - no expansion/contraction on heating
stronger

63
Q

What gives polymers its properties?

A

Molecular weights of make-up

64
Q

What is responsible for the Thermal Expansion of porcelain?

A

Leucite phase

65
Q

What does a refractory component do?

A

controls expansion

66
Q

Does the refractory material have strength?

What holds it together?

A

No

Gypsum binder

67
Q

T/F

Metal should have slightly higher coefficient of thermal expansion than porcelain

A

True

Tim's Cards (140 decks)

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