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Dental Materials > Exam 1 review > Flashcards

Exam 1 review Flashcards

1
Q

Characteristics of graph 1

A

Stiff

Ductile

Strong

Tough

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2
Q

Characteristics of graph 2

A

Stiff

Brittle

Strong

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3
Q

Characteristics of graph 3

A

Stiff

Ductile

Weak

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4
Q

Characteristics of graph 4

A

Stiff

Brittle

Weak

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5
Q

Characteristics of graph 5

A

Flexible

Ductile

Strong

Resilient

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6
Q

Characteristics of graph 6

A

Flexible

Brittle

Strong

Resilient

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7
Q

Characteristics of graph 7

A

Flexible

Ductile

Weak

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8
Q

Characteristics of graph 8

A

Flexible

Brittle

Weak

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9
Q

In the phase diagram there are ACB and ADB lines.

Above the ACB line is all ___.

Below the ADB line is all ___.

Between the lines is a mix of both - this area has a ____.

A

liquid

solid

melting range

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10
Q

Au and Cu are soluble in each other at any combination. When mixed together they form a ____.

A

solid solution

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11
Q

At certain concentrations of metals mixed together you may get an ____ solution. These solutions impart higher ____ and ____ to alloys.

A

ordered

hardness and strength

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12
Q

___ is used as a binder in materials commonly employed in the casting of dental gold alloys and is generally not heated above 700 C.

A

Gypsum

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13
Q

A binder is used to form a coherent ___ mass and to provide ___ for the investment.

A

solid

strength

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14
Q

___ is a binder used for gold.

___ are binders used for high temp alloys.

A

Calcium sulfate hemihydrate

Phosphate, Ethyl Silicate

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15
Q

A semicircular groove placed across one side of a block is considered a ___.

A

stress raiser

Stress is constant over most of the plane but would rise suddenly near the groove reaching a max at the edge of the groove.

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16
Q

Why can polymers absorb water?

A

Because of weak secondary bonds in polymers, water molecules are able to penetrate between polymer chains

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17
Q

___ alloys occur when 2 metals are soluble as liquids but nearly insoluble as solids.

A

Eutectic

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18
Q

The pure eutectic has a ____ that is lower than either of the pure components.

A

melting point (not a range)

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19
Q

What are the causes (environmental factors) of poor dimensional stability?

A

Syneresis

Imbibition

Evaporation

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20
Q

___ is fluid loss during setting squeezing water from between polysaccharide or alginate chains >> Shrinkage >> Distortion of cast

A

Syneresis

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21
Q

___ alginate powder is the most accurate way to dispense it.

A

Weighing

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22
Q

Where will a porcelain-metal bond most likely fail?

A

In the porcelain body

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23
Q

Why must the coefficient of thermal expansion (CTE) be compatible between porcelain and metal?

A

The materials will have a different contraction rate while cooling. The cooling metal should contract causing the brittle porcelain to become more densely packed and thus more sturdy.

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24
Q

What materials have the highest degree of thermal expansion?

A

Waxes

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25
Q

What is the composition of a High Noble metal?

A
  • 60% Noble metal
  • 40% Gold (Au)
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26
Q

What is the composition of a Noble metal?

A
  • 25% Noble metal
  • no specific gold stipulation
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27
Q

What is the composition of predominantly base metal?

A
  • Noble metal less than 25%
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28
Q

What is the highest point of the stress/strain graph?

A

Ultimate Strength

In most dental alloys and ceramics, the U.S. and the Fs (fracture strength) will be very close

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29
Q

Which is higher on the stress/strain graph (and subsequently numerically), yield strength or proportional limit.

A

Yield strength is higher because materials begin to function in a plastic manner. (limited permanent strain HAS occurred)

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30
Q

Minute scratches on the surface of materials behave like sharp notches which are ________

A

Stress raisers

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31
Q

When stress suddenly rises near a “groove”, reaching a max at the edge of the groove is called _______?

This is a phenomenon that occurs around any irregularity in a material.

A

Stress raiser

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32
Q

What is higher a stress raiser or the average stress in the body?

A

The stress raiser. It can be several times higher. The amount of increased stress depend on the shape of the stress raiser.

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33
Q

Why do materials fail at stresses far below their expected strength?

A

Stress raisers allow stresses to reach the theoretical strength of the material at a relatively low stress. When the theoretical strength is exceeded at the tip of the notch the bonds break at the tip. The adjacent bonds are not the tip of the notch (and become the point of greatest stress concentration). Therefore, the crack will propagate through the material until the crack/fracture will move completely thorughtout the material.

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34
Q

What desired effect does Sodium Phosphate have when preparing an Alginate mixture?

A

Retarder. It’s a real thing.

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35
Q

What is syneresis?

A

Fluid loss during setting, squeezing water from between polysaccharide or alginate chains

36
Q

What effect does syneresis have on a cast, and what should be done to avoid this effect?

A

Shrinkage –> Distortion

Pour impression ASAP! Do it now!

37
Q

What is Imbibition?
What does it cause?
What should you avoid?

A

Uptake of water in the GEL state

Expansion

Don’t soak in water, rinse, or spray with disinfectant

38
Q

How do you counteract the undesired effects of evaporation on alginate?

What will you get if you don’t address it?

A

Retard dimensional changes - wrap in wet paper towel and pour ASAP

Shrinkage. We all get it, but it can be avoided.

39
Q

True or False: A high # of low MW molecules and a low # of high MW molecules may have the same average MW AND properties

A

FALSE

Same avg MW, but DIFFERENT properties

40
Q

Some polymers, when heated, soften the material by breaking weak physical bonds, allowing the chains to slide past one another. When cooled, the bonds reform and the material hardens again. This property is called ___________.

A

Thermoplastic

41
Q

Covently-bonded, cross linked polymers that do not soften on heating are termed:

A

Thermoset

42
Q

Addition Polymerization:

Stage 1: ______ Stage

This stage creates _______, which attack double bonds of monomer molecules

A

Initiation

Free-Radicals

43
Q

What role does sodium phosphate have in the composition of alginate?

A

retarder

44
Q

What are the 3 environmental factors that give alginate poor dimensional stability?

A

syneresis, imbibition, evaporation

45
Q

______ is fluid loss during setting, squeezing water from between polysaccharide or alginate chains. = shrinkage

A

syneresis

46
Q

_____ is the uptake of water in gel

A

Imbibition

47
Q

_____ is water loss due to environmental conditions

A

Evaporation

48
Q

A ____ # of low mw molecules - a ____ # of high mw molecules, may have the same average mw but different properties

A

high, low

49
Q

What is a thrermoplastic material?

A

When heated weak physical bonds break and the chains can slide past one another, result in a soft material. On cooling the bongs reform and the material hardens. Materials that under go this softening and hardening are thermoplastic.

50
Q

What is the key feature of a thermoset polymer?

A

Cross inked polymers DO NOT soften on heating

51
Q

What are the three stages of polymerization?

A

initiation, propagation, termination

52
Q

What happens in the initiation stage of polymerization?

A

Free radicals are created which go and attack the double bonds of monomer molecules. Unshared electrons move to the end of the monomer thus activating the monomer molecules.

53
Q

What happens in the propagation stage of polymerization?

A

Activated monomers attack double bonds of another monomer. More monomers are added to the free radical, and the chains grow in length.

54
Q

What happens during the termination stage of polymerization?

A

Materials like hydroquinone, eugenol, or large amounts of oxygen inhibit polymerization by reacting with the free radicals. Decreases rate of initiation/ increases termination.

55
Q

What is the setting reaction for Gypsum?

A

CaSO4 * 1/2 H2O + 1 1/2 H2O —> CaSO4 * 2H2O + Heat

56
Q

What is the definition of setting rxns we don’t need to know just recognize?

A

Nucleated recrystallization, characterized by a continuous solution of hemihydrate, diffusion of calcium and sulfate ions to nucleation centers, and precipitation of microscopic gypsum crystals

57
Q

Which phase is responsible for co-efficient expansion?

A

Leucite phase

58
Q

What makes up the pigments added to porcelain?

A

Metallic oxides Titanium oxide = yellow-brown manganese oxide = brown iron oxide = brown cobalt oxide = bluecopper/chromium oxide = greennickel oxide = brown lanthanide oxides = fluorescence

59
Q

What is the process of sintering?

A

Crown is dried at the door of the oven where it is heated under vacuum. Porcelain particles join together by flow on contact as a result of surface energy.

60
Q

What will happen to ceramic metal bonds if oxide layer is too thick?

A

Fracture through the oxide layer. If that doesn’t make sense Ceramics slide 30

61
Q

What are the two phases in porcelains?

A

Vitreous (glass) phase: properties of typical glass, brittleness, non-directional fracture pattern, translucency, high surface tension as a liquid.Crystalline (mineral/leucite) phase: high thermal expansion, content (10-20%) controls the CTE of the porcelain contributes strength.

62
Q

Addition Polymerization:

Stage 2: ______ Stage

______ ______ ______ attack double bonds of other monomer molecules.

Chains grow in length

A

Propogation Stage

Activated Monomer Molecules

63
Q

Addition Polymerization:

Stage 3: ______ Stage

Materials like hydropuinone, eugenol or oxygen will inhibit or retard polymerization by reacting with _______.

A

Termination

Free-Radicals

64
Q

_________ the rate of polymerization: Decreases the degree of polymerization or molecular weight.

A

Decreasing

65
Q

What reaction is this?

A

Gypsum Setting Reaction

66
Q

What is this monstrous paragraph defining?

Nucleated recrystallization, characterized by a continuous solution of hemihydrate, diffusion of calcium and sulfate ions to nucleation centers, and precipitation of microscopic gympsum crystals. This is caused by DIFFERENCE IN SOLUBILITY of the two forms. Dihydrate is less soluble than hemihydrate.

A

Definition of the Gypsum Setting Reaction

67
Q

Shattered mix of molten glass and leucite forms FRIT. After frit is formed, what pigmented materials can be added to produce various shades?

A

Metallic Oxides

68
Q

_________ phase controls the CTE of the porcelain and contributes strength. It constitutes _____% of the overall content.

A

Crystalline (mineral/leucite)

10-20%

69
Q

During sintering, the crown is heated under vacuum, and the ________ particles join together by ___ __ ____ as a result of surface energy

A

porcelain

flow on contact

70
Q

2 phases of feldspathic dental porcelain:

A

Vitreous (glass) phase

Crystalline (mineral/leucite) phase

71
Q

Which phase of feldspathic dental porcelain is responsible for high thermal co-efficient expansion?

A

Crystalline (mineral/leucite) phase

72
Q

What process takes place when a crown is fired/heated under vacuum?

What is this first firing called?

A

Sintering

Biscuit Bake (It’s really the “Bisque” firing… I took ceramics in undergrad, so I can basically make pots with my bare hands. Like in “Ghost”. But cooler.)

73
Q

In Ceramic-metal bonding, the _____ layer fractures the most, when it is too _____.

A

Oxide

Thick

74
Q

In _____ bonding, the highest strength of ceramic-metal specimens fracture in the porcelain layer.

A

Proper bonding

75
Q

What is the result of increasing the W/P ratio.

A

Decreased setting and thermal expansion

Decreased strength

Increased porosity

76
Q

What is the result of decreasing the W/P ratio?

A

Denser cast

Hardens quicker

77
Q

Thick mixes (___ W/P ratio) hardens more quickly because of ____ concentrated in smaller volume.

A

low

nucleation centers

78
Q

What are the refractory and binding components of investor material? What do they do for the investor material?

A

Refractory - Silicon Dioxide (provides expansion to compensate for gold shrinkage)

Binding - Gypsum (provides strength)

79
Q

What makes a material brittle?

A

inability to deform and redistribute stress. They cannot get atomic center materials to slide past one another.

80
Q

How do you get a finer grain size in alloys?

A
  • rapid cooling
  • add very fine, high melting metal or oxide powder
81
Q

___ is resistance to fracture

A

Toughness

82
Q

___ is resistance to permanent deformation

A

Resilience

83
Q

Which is more likely to fracture, long grains or fine grains? Why?

A

Large grains are more likely to fracture because they cannot slide well.

Fine grains have increased YS, Ductility, US, UTS and elongation.

84
Q

___ occurs when 2 metals are soluble as liquids but nearly insoluble as solids.

A

Eutectic Alloys

85
Q

____ is causing a plastic deformation by hammering, drawing, cold forging, cold rolling or bending. Produces many dislocations that can not slip easily through each other as the lattice becomes more distorted.

A

Cold working

Dental Materials (5 decks)

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