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Dental Materials > Final > Flashcards

Final Flashcards

1
Q

What are the three main classes of materials?

A

metals, ceramics, polymers

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2
Q

What are the mechanical properties of metals?

A

Hard, ductile, strong

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3
Q

What type of structure do metals have?

A

crystalline, forms grains

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4
Q

What is an alloy?

A

mix of 2 or more metallic elements, can be homogenous or multi-phase, stronger but less ductile

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5
Q

What type of bonds do metals form?

A

Metallic bonds

1-3 electrons in outer shell held loosely to nucleus

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6
Q

What results from metal electrons being able to move freely?

A

thermal/electrical conductivity and ductility

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7
Q

T or F: metals act as thermal conductors

A

true

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8
Q

What are the mechanical properties of ceramics?

A

hard, brittle, strong

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9
Q

What is the composition of ceramics?

A

a mixture of metal and non metal elements

metal oxides are most common in dentistry

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10
Q

What type of bonds do ceramics form?

A

ionic or covalent

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11
Q

Relative bond strengths

A

Covalent > ionic > metallic

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12
Q

What are the mechanical properties of polymers?

A

soft, ductile, weak

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13
Q

What type of bonds do polymers form?

A

covalent bonds

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14
Q

What is the composition of polymers?

A

long molecules of non metallic elements, “cooked spaghetti”

entanglement gives strength and properties

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15
Q

What temperatures are required for processing of metals, ceramics, and polymers?

A

high, high, low

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16
Q

Steps of polymerization

A

activation, initiation, propagation, and termination

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17
Q

Activation

A

step 1: initiator molecule is activated by light, heat, or mixing to form free radicals

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18
Q

Initiation

A

step 2: free radicals combine with monomer units in polymer mixture, attachment of free radical opens up double bond on monomer, creating new free radical

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19
Q

Propagation

A

step 3: constantly forming monomer free radicals continue to bind with other monomers, polymer chain grows

volume of polymer mix decreases and shrinks as chain grows

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20
Q

Termination

A

step 4: floating free radical bonds to free radical end of the polymer chain creating double bond and capping off chain

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21
Q

Linear polymers

A

form from monomethacrylates, only one free radical end, “tangled spaghetti”

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22
Q

Crosslinked polymers

A

form from dimethacrylates, short chain with two free radical ends, “fishing net”, network is formed

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23
Q

What is composite?

A

a physical mixture of metals, ceramics, and polymers

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24
Q

What is the rule of mixing for composites?

A

want composite properties to be as similar to tooth structure as possible

can predict properties fairly well by knowing phases present

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25
Q

Dispersed phase

A

glass filler: low flow, high strength

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26
Q

Matrix phase

A

monomer resin: high flow, low strength

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27
Q

What impact does more filler volume have on final properties?

A

increase strength, modulus, toughness, and viscosity, decrease shrinkage

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28
Q

What impact does smaller filler size have on final properties?

A

smoother surface

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29
Q

What is the thermal expansion coefficient?

A

rate of change of a material’s size upon heating/cooling (in ppm/decree C)

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30
Q

Chemical implications of heat flow

A

thermal conductivity and diffusivity

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31
Q

Are dentin and enamel thermal insulators or conductors?

A

insulators, because high mineral content

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32
Q

Do lines have to be used with metals? composites?

A

yes, no

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33
Q

How is color defined?

A

3D coordinate system

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34
Q

What are the components of the color system?

A

hue, value, chroma

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35
Q

What is metamerism?

A

when 2 objects appear the same color under one light, but different under another because of special characteristics

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36
Q

What issues does mercury in amalgam cause?

A

disposal, pt issues, operator issues

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37
Q

What is creep?

A

a solid material deforming permanently over time under low constant stress

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38
Q

What metals are immune to corrosion?

A

noble metals: gold, platinum, palladium, titanium?

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39
Q

What are the two types of corrosion?

A

active: destruction of metal
passive: produces film on surface preventing further corrosion

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40
Q

What elements are used in alloying of amalgam?

A

copper and zinc

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41
Q

What is the effect of alloying on amalgam?

A

amalgam becomes stronger, but less ductile (differently sized atoms prevent sliding)

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42
Q

What are the phases of amalgam?

A

gamma 1, gamma 2

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43
Q

What is the chemical composition of the gamma phases?

A

Ag3Sn

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44
Q

What type of chemicals wet hydrophilic surfaces?

A

hydrophilic chemicals

45
Q

What is a contact angle?

A

angle between tangent to liquid droplet and surface

46
Q

What does a large contact angle indicate?

A

poor wetting (droplet NOT spread out)

47
Q

What are the types of active corrosion in metals?

A

galvanic, structure selected, crevice corrosion, stress corrosion

48
Q

What is the degradation process for ceramics?

A

hydrolysis via chemical dissolution

49
Q

What is the degradation process for polymers?

A

hydrolysis via 1. absorption of water into polymers 2. hydrolytic degradation and release of polymer components

50
Q

What are some concerns about degradation problems

A

sensitivity and toxicity

51
Q

What does a steeper modulus on a stress-strain curve indicate?

A

stiffer material

52
Q

What are the characteristics on a stress strain curve of a stiff and brittle material?

A

steep modulus, small plastic region

53
Q

What are the characteristics on a stress strain curve of a stiff and ductile material?

A

steep modulus, large plastic region

54
Q

What are the characteristics on a stress strain curve of a flexible and ductile material?

A

loe modulus, plastic region continues past ultimate strength

*can reach deformation without failing

55
Q

How does heat effect mechanical properties?

A

materials become more flexible and less tough

56
Q

What is fatigue?

A

weakening of a material caused by repeatedly applied loads

57
Q

What is fracture toughness?

A

a measure of a material’s resistance to crack propagation (ability of cracked material to resist fracture)

58
Q

T or F: teeth are completely rigid

A

false, leads to abfractions

59
Q

Why is buccal lingual stability important?

A

so B and L cusps can all withstand biting chewing forces

60
Q

How do preps lead to B L instability?

A

an overextended prep, or unequally extended prep can lead to cusp fracture

61
Q

What are the components of composite resin?

A
  1. resin (organic phase)

2. filler (inorganic phase)

62
Q

What is the role of resin in composite resin?

A

helps processing and handling

63
Q

What is the role of filler in resin composite?

A

helps modulus and wear resistance

64
Q

What happens to composite resin when resin amount is increased?

A

increases toughness, flowability, decreases wear resistance

65
Q

What happens to composite resin when filler volume is increased?

A

higher modulus (stiffer)

66
Q

What is cross linking?

A

inducing polymerization of resin, forms bonds between polymer chains and resin

67
Q

What results from smaller filler sizes?

A

better material, lower modulus but more surface area = better wear resistance

68
Q

What does a coupling agent do?

A

adds methacrylate groups that can bond with polymer chains to surface of filler, forms very strong bonds between filler and resin

69
Q

What causes polymerization shrinkage?

A

resin portion shrinks upon polymerization because density change from monomer to polymer

70
Q

What is a result of shrinkage?

A

stress of tooth, microleaks leading to secondary caries

71
Q

What are the components of glass ionomer cements?

A

acidic polymer (polycarboxylate cement) in aqueous solution and basic glass

72
Q

How are glass ionomers cured?

A

acid/base rxn, salt bridges for cross linkages

73
Q

GI is a _____ restorative

A

water based

74
Q

GI release of fluoride

A

from toothpaste, releases daily, more so in early life span of GI

75
Q

What type of modifiers promote bonding?

A

hydrophilic

76
Q

How are adhesives similar to composites?

A

based on composite resin chemistry, hydrophilic AND hydrophobic

77
Q

How do sealants differ from composites?

A

only contain 0-10% filler, not intended for longevity, bonding is mostly mechanical

78
Q

What is the oxygen inhibition layer?

A

the top layer of sealant that doesn’t solidify well because of O2 in environment, needs to be wiped off

79
Q

What are the two major classes of impression materials?

A

hydrocolloid (includes alginate and ager-ager) and elastomers (viscoelastic)

80
Q

What are the ideal properties of impression materials?

A

low cost, long shelf life, biocompatible, pleasant to pt, dimensionally stable, good handling properties

81
Q

Alginates are _____ based

A

water

82
Q

What type of crosslinkages occur in alginates?

A

calcium

83
Q

What are advantages of alginate being water based?

A

surface energy allows for good wetting of tooth and gypsum

84
Q

What are disadvantages of alginate being water based?

A

bad dimensional stability (water loss and gain), limitied detail reproduction, low tear resistance

85
Q

Polysiloxanes are hydro____

A

phobic

86
Q

What are the consequences of taking impressions with polysiloxanes?

A

because hydrophobic, can repour, excellent accuracy, expensive, difficult to vary setting time, good dimensional stability

87
Q

How are polysiloxanes crosslinked?

A

via hydrosilation rxn

88
Q

What is the role of surfactants?

A

can make silicone hydrophilic, improve detail registration and transfer

89
Q

Polyethers are hydro_____

A

phobic

90
Q

Do polysiloxanes or polyethers have better surface characteristics?

A

polyethers

91
Q

How is gypsum cured?

A

water

92
Q

What is the hydration-dehydration sequence?

A

gypsum is first the dihydrate form of calcium sulfate, then dehydrated to calcium sulfate hemihydrate (calcination)

93
Q

What are the properties of gypsum dependent upon?

A

density and crystal structure (interlocking contributes to strength)

94
Q

Is dental stone or plaster used for models?

A

stone

plaster is weaker because of irregularly shaped particles

95
Q

What causes the difference in composition between denture bases and provisionals?

A

filler, leads to differences in mechanical characteristics

96
Q

How is denture base usually cured?

A

visible light

97
Q

How are provisionals usually cured?

A

chemically

TRIM and JET are more workable than TRIAD

98
Q

Are mouthguards thermoplastic or thermoset?

A

thermoplastic

99
Q

What controls properties of mouthguards?

A

copolymer (Poly Vinyl Acetate-co-Ethylene)

100
Q

What is the role and function of cements?

A

to bind restorations or appliances to tooth structure

101
Q

What are the requirements for cements?

A

low viscosity (but good mech properties), 25 um thick

102
Q

How is viscosity and handling properties of cements modified?

A 
powder to liquid ratio (lower ratio = increased setting and working time)
filler loading (more filler = higher viscosity)
103
Q

What are the different types of cements?

A

resin cements, GIs

104
Q

What is the function of bases and liners?

A

to protect pulp and minimize post op sensitivity (thermal and chem barrier, control inflammation and fluid movement)

105
Q

What does calcium hydroxide do as a base?

A

cap pulp, acts as insulator, stimulates repairative dentin

106
Q

What does ZOE do?

A

dulls pulpal pain, expands when set to seal exposure, CANNOT put composite on ZOE because limits polymerization

107
Q

What are the requirements of waxes?

A

melt at lower materials, carvable, able to be burned off, dimensionally stable

108
Q

What are waxes?

A

lower molecular weight materials in between polymers and organic liquids

Dental Materials (1 decks)

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