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Dental Materials > Final Exam > Flashcards

Final Exam Flashcards

1
Q

What are the three main classes of materials?

A

Metals, Ceramics, and Polymers

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2
Q

Describe the mechanical properties of metals

A

Hard, Ductile, Strong

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3
Q

Describe the mechanical properties of ceramics

A

Hard, Brittle, Strong

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4
Q

Describe the mechanical properties of polymers

A

Soft, Ductile, Weak

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5
Q

Describe the bonding of metals

A

1-3 loosely bound electrons that have free mobility.

This contributes to thermal and electrical conductivity as well as the ability to be ductile.

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6
Q

Describe the bonding of ceramics

A

Form ionic and covalent bonds. The ions are not mobile.

Covalent > Ionic > Metallic

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7
Q

Describe the bonding of polymers

A

Form covalent bonds and have high molecular weight.

Long molecules primarily of non-metallic elements entangle (spaghetti) which contributes to strength and properties.

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8
Q

Describe the thermal properties of metals

A

High processing temperatures.

Act as thermal conductors.

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9
Q

Describe the thermal properties of ceramics

A

High processing temperatures

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10
Q

Describe the thermal properties of polymers

A

Low processing temperatures.

Used as direct processing materials

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11
Q

Metals:

  1. Typically used for ___ placement
  2. ___ processing temperatures
  3. Exception: ___
A
  1. Indirect
  2. High
  3. Amalgam
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12
Q

Ceramics:

  1. Typically used for ___ placement
  2. ___ processing temperatures
  3. Exception: ___
A
  1. Indirect
  2. High
  3. Cements
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13
Q

Polymers:

  1. Typically used for ___ placement
  2. ___ processing temperatures
  3. Exception: ___
A
  1. Direct
  2. Low
  3. Indirect Composites
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14
Q

Name the 4 steps of polymerization

A
  1. Activation
  2. Initiation
  3. Propagation
  4. Termination
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15
Q

Explain the activation step of polymerization

A

An initiator molecule is activated by either light, heat, or chemical mixing to form free radicals.

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16
Q

Explain the initiation step of polymerization

A

Free radicals combine with monomer unites. This opens up the double bond on the monomer to create a new free radical.

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17
Q

Explain the propagation step of polymerization

A

Monomer free radicals bind to grow the polymer chain.

As this happens, the polymer volume decreases and shrinks.

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18
Q

Explain the termination step of polymerization

A

A floating free radical bonds to the free radical end of the chain.

This creates a double bond and caps off the chain.

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19
Q

What do linear polymers form from?

A

Monomethacrylates

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20
Q

What is significant about monomethacrylates?

A

They only have one free radical end

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21
Q

What do linear polymers resemble when intertwined?

A

Tangled spaghetti

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22
Q

What do branched polymers form from?

A

Dimethacrylates

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23
Q

What is significant about dimethacrylates?

A

Short chain with two free radical ends

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24
Q

What do branched polymers resemble when intertwined?

A

Fishing Net

They have many branched chains that form crosslinks

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25
Q

What can polymerization be initiated by?

A

Light, heat, and chemical mixing

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26
Q

Define a composite

A

Physical mixtures of metals, ceramics, and/or polymers

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27
Q

What is the goal of a composite

A

To achieve some intermediate properties between two material types

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28
Q

What is the rule of mixtures?

A

By knowing the phases present in the structure of any material and interfacial interactions, it is possible to predict the overall properties fairly well

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29
Q

What happens to the final properties if you increase filler volume?

A
  1. Material strength increases
  2. Modulus of elasticity (stiffness) increases
  3. Viscosity increases
  4. Shrinkage during curing decreases
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30
Q

What happens to the final properties if you increase the filler size?

A

Surface roughness increases

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31
Q

What is the point of using fillers?

A

They are chemically bonded to resin phase to improve properties

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32
Q

What is the thermal expansion coefficient?

What is the general trend for the materials?

A

Rate of change of a material’s size upon heating or cooling.

It is measured in ppm/°C

Ceramics < Metals < Polymers

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33
Q

Do metals need a base?

A

Yes. They require thermal insulator like bases because metals are thermal conductors

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34
Q

Do composites need a base?

A

No. They have low thermal conductivity, so they do not need a base

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35
Q

Teeth are considered ___ due to high mineral content. Because of this, the pulp requires __ during a restoration

A

Insulators

Protection

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36
Q

Describe thermal conductivity

A

Rate of heat conduction

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37
Q

Describe thermal diffusivity

A

Conductivity/Time

The amount of heat flow over time toward the pulp through the restoration

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38
Q

How is color defined?

A

In a 3D coordinate system

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39
Q

Define Hue

A

Wavelength
“Color” (ROYGBIV)

  • Left to right
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40
Q

Define Value

A

Intensity
Brightness

  • Top to bottom
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41
Q

Define Chroma

A

Purity
Density or Concentration

  • Inside to Outside
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42
Q

Define metamerism

A

2 objects appear the same under one light source but different under another.

Due to different spectral characteristics

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43
Q

What does the contact angle measure?

A

How a liquid interacts with a solid

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44
Q

Good wetting = ___ contact angle

A

Low (close to 0)

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45
Q

Poor wetting = ___ contact angle

A

High (close to 180)

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46
Q

Hydrophobicity and Hydrophilicity can help determine:

A

The wetting properties of a material

The hydrophobic part is the part that polymerizes

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47
Q

Hydrophilic Primers:

  1. Allows for?
  2. Mixed with?
  3. Viscosity?
A
  1. Allows for penetration into areas with water AND attachment to composite
  2. Solvent (alcohol, acetone)
  3. Very low viscosity
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48
Q

T/F: Molecules can either be hydrophilic or hydrophobic, but not both.

A

False. They can have both hydrophilic and hydrophobic components.

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49
Q

What are 4 things that surface wetting is important for?

A
  1. Anytime 2 different materials come into contact
  2. Impression materials
  3. Adhesives
  4. Bacterial Adhesion
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50
Q

Disposal Issues with Mercury

A

Ends up in the water systems

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51
Q

Patient issues with Amalgams

A

Poor esthetics

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52
Q

Operator issues with Amalgams

A

Brittle, sensitive

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53
Q

Define creep

A

The tendency of a solid material to deform permanently over time under low constant stresses

  • Result from accumulated strain from long-term stresses (chewing, biting, grinding)
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54
Q

Is amalgam ductile or brittle?

A

Brittle

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55
Q

What can improve corrosion resistance of amalgam?

A

Zinc - it will also make the material more brittle

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56
Q

What can minimize corrosion?

A

Polishing

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57
Q

What is the major reaction phase in both low and high-copper amalgams

A

Gamma 1

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58
Q

What does not form with high copper amalgams?

A

Gamma 2

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59
Q

What is the strongest microstructural phase in dental amalgams?

A

Incompletely consumed starting alloy particles (Gamma 1)

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60
Q

What is the weakest microstructural phase in dental amalgams?

A

Gamma 2 in low-copper amalgams (high corrosion prone)

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61
Q

What causes contraction during amalgam setting?

A

The absorption of Hg.

The final absorption of mercury by remaining amalgam allow particles also causes contraction.

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62
Q

What causes expansion during amalgam setting?

A

The formation and growth of the gamma phases

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63
Q

Lathe-cut has more:

A

Condensation resistance

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64
Q

Spherical has:

A

Better mechanical properties and is cut with less mercury.

65
Q

What phases are formed in the first step of the setting reaction?

A

Both Gamma 1 and 2

66
Q

What happens in the second step of the setting reactions?

A

Disappearance of Gamma 2 and formation of n’ (Eta prime)

67
Q

What does heat treatment of an alloy do?

A

Relieves stresses in alloy particles and provides control of setting time. Eliminates compositional nonuniformity in ingot before cutting.

68
Q

3 types of corrosion in metals

A

Active, Passive, Immune

69
Q

4 types of active corrosion

A
  1. Electrochemical (Galvanic)
  2. Structure Selective
  3. Crevice
  4. Stress
70
Q

Electrochemical (Galvanic) Corrosion

A

Electron transfer to allow for oxidation of a metal. (ex: gold next to amalgam)

71
Q

Structure selective corrosion

A

Two phases (cathode and anode) that go through redox corrosion (amalgam)

72
Q

Crevice corrosion

A

Crack in the structure

73
Q

What is important about passive corrosion?

A

Produces a film that prevents further corrosion (implants)

74
Q

What metals are immune to corrosion?

A

Noble metals (gold)

75
Q

Describe corrosion of ceramics

A

Covalent bonds are broken down by water

76
Q

Describe corrosion of polymers

A

Absorption of water leads to hydrolytic degredation

77
Q

What is a hazard of degredation?

Major concern for amalgams?

Major concern for composites?

A

Byproducts can be toxic.

Mercury is of concern for amalgams.

Bisphenol A is a concern for composites as it is estrogen like.

78
Q

Name the 4 regions of the stress-strain curve

A
  1. Elastic limit
  2. Proportional limit
  3. Ultimate strength
  4. Elastic modulus
79
Q

What is the elastic limit?

A

If a stress is put on an object and released before it exceeds the elastic limit, said material will return to the original shape

80
Q

What is the proportional limit?

A

The point where stress and strain are directly proportional. Up to this point the curve is a straight line.

81
Q

What is ultimate strength?

A

Where the material breaks; peak of the curve

82
Q

What is the elastic modulus?

A

How stiff the material is; between the start of a curve and the proportional limit. Greater slope means greater stiffness.

83
Q

Curves with a high elastic modulus tend to be…

A

Resistant to stress but cannot bear a lot of strain. Will break (ex. glass)

84
Q

Curves with a low elastic modulus will..

A

Strain greatly under a low amount of stress. (ex. red vine/polymer)

85
Q

Curves with a medium elastic modulus can..

A

Withstand a lot of stress and can strain to support more stress (like a tootsie roll or metal)

86
Q

Define modulus

A

(Resilience)

The energy absorbed before deformation occurs

87
Q

Define toughness

A

The energy absorbed before failure or fracture occurs

88
Q

How can heat effect mechanical properties?

A

It can change the setting time of a material

89
Q

Define fatigue

A

Multiple cycles of low stress

90
Q

Define fracture toughness

A

Ability of a cracked material to resist fracture

91
Q

Define cyclic stresses

A

Over time, many cycles of small amounts of deformation occur until failure occurs at low stress

92
Q

Because teeth are not completely rigid, they can have ___

A

Abfractions

93
Q

What is an abfraction?

A

Mechanical loss of tooth structure near the gum line

94
Q

Explain Buccal-Lingual Stability

A

Cusps work as an entity when undergoing B-L forces. Have a high stability.

95
Q

How can a cavity prep lead to B-L instability and cusp fracture?

A

When a cavity prep takes out the central groove the cusps become separate entities and now cannot resist B-L stress as well. Subject to fracture.

96
Q

In general terms, how is each material processed?

A

Metals - melted together
Ceramics - fused together
Polymers - polymerization

97
Q

What factors contribute to each materials mechanical properties?

A

Bonding, Microstructure

98
Q

When you make an amalgam, will you have a single phase or multiple phases? What does this do to the properties?

A

Multiple phases. Some of them have the same and others have different properties.

This is why you have corrosion

99
Q

What is the effect of alloying on amalgam?

A

Improves properties and corrosion

100
Q

___ and ___ are useful in alloying

A

Copper and Zinc

101
Q

Components of composite resin

A

Resin system, filler, bonding agent, visible light initiator

102
Q

What is the role of the resin system

A

Helps with processing and handling

103
Q

What is the role of the filler?

A

Helps modulus and wear resistance

104
Q

What is the role of the bonding agent?

A

Bonds filler to the resin system

105
Q

What are the trade-offs that occur in properties?

A

Inorganic - allows for wear resistance and strength but is poor for processing and is brittle

Polymer - has poor resistance but is tough and good for processing

106
Q

Explain crosslinking

A

Allows for a stronger, one unit matrix to be formed as opposed to multiple linear but independent units to be present - decreasing strength

107
Q

How does crosslinking control properties?

A

A greater crosslink density leads to a greater strength; however, shrinkage is a worry

108
Q

T/F: There is only one size of filler

A

False. Different filler sizes exist

109
Q

How does the filler size control properties?

A

More crosslinking = higher modulus

Smaller filler leads to better wear properties for polishing and finishing. Also better mechanical properties.

110
Q

What does a coupling agent do?

A

Coats the surface of the filler and binds it to the resin matrix. This moves groups to the surface to allow for curing (forms covalent bonds and improves properties)

111
Q

Define polymerization shrinkage

A

Results from density change of monomer to polymer

112
Q

What are clinical consequences of shrinkage?

A

Causes stress on the tooth, leads to microleaks and secondary caries

113
Q

2 components of glass-ionomer cement

A

Acid polymer in aqueous solution

Basic glass

114
Q

How are glass-ionomer cements cured? How is this different from composites?

A

They are cured by an acid-base reaction. They form salt bridges instead of covalent bonds.

115
Q

Glass-ionomer cements are a ___ based restorative

A

Water

116
Q

What do glass-ionomer cements release?

A

Fluoride

117
Q

What is the role of an adhesive?

A

It contains acid groups to promote bonding of the composite to the hydrophilic tooth surface.

118
Q

What promotes bonding?

A

Hydrophilic modifiers

119
Q

Are both hydrophilic and hydrophobic characteristics needed for bonding?

A

Yes

120
Q

How are sealants different from composites?

A

They’re designed to flow into pits and are attached through mechanical means rather than chemical; usually lack a filler

121
Q

What is the oxygen inhibition layer?

A

Oxygen interferes with radical polymerization at the surface leaving a thin layer often uncured; more of a problem for thin layers like sealants

122
Q

What is hydrocolloid impression material?

A

Alginate (not as accurate)

123
Q

What is elastomers impression material?

A

Polysulfide (good surface detail)

124
Q

Ideal properties for impression materials

A
  1. Low cost
  2. Long shelf life,
  3. Biocompatible
  4. Pleasant to patient
  5. Dimensionally stable
  6. Good handling properties
125
Q

Alginates are ___ based

A

Water

126
Q

Alginates are ___ crosslinked

A

Calcium

127
Q

Advantages of alginates being water based

A
  1. Economical
  2. Easy to use
  3. Quick setting
  4. Fair taste
  5. Hydrophilic
128
Q

Disadvantages of alginates being water based

A
  1. Dimensional instability
  2. Low tear resistance
  3. Limited detail reproduction
  4. Single pour only
  5. Quick pouring required
129
Q

What is dimensional instability

A

Undergoes shrinkage or expansion upon loss or gain of water

130
Q

Polysiloxanes are ____

A

Hydrophobic

131
Q

Because Polysiloxanes are hydrophobic, there are ___ for taking ____

A

Consequences for taking impressions

132
Q

Polysiloxanes are crosslinked by ____ reaction

A

Hydrosilation

133
Q

Polysiloxanes have good ___ ____

A

Dimensional stability

134
Q

What is the role of surfactants?

A

Can turn this hydrophobic material into a hydrophilic one

135
Q

Polyethers are ___

A

Hydrophobic

136
Q

Although polyethers are ___, they have better ____ ____

A

Hydrophobic

Surface characteristics

137
Q

Polyethers have good ___ ___

A

Dimensional stability

138
Q

Gypsum is ___ cured

A

Water

139
Q

Explain the dehydration-hydration sequence

A

Mineral gypsum is heated and dehydrated resulting in a model plaster and water.
When mixed with water, it is rehydrated.

140
Q

What are gypsum properties dependent on?

A

Density and crystal structure.

141
Q

Dental stone is used for ___ not ____

A

Models not plaster

142
Q

Where are there differences in composition for denture base and provisionals?

A

Dentures need to be able to last longer. Provisionals are temporary.

143
Q

Denture base is normally ___

A

VLC

144
Q

___ are normally chemically cured

A

Provisionals

145
Q

Mouthguards are ____ not ___

A

Thermoplastic not Thermoset

146
Q

_____ controls the properties of a mouthguard

A

Copolymer

147
Q

Cements are used to…

A

Bind restorations of appliances to tooth structure

148
Q

What do cements require?

A

Low viscosity with good mechanical properties.

149
Q

How are viscosity and handling properties modified in cements?

A

Powder to liquid ratio balances the mechanical properties and viscosity

More filler - more viscosity and modulus
Low powder - increases working and setting time

150
Q

Two types of cements

A

Resin and Glass Ionomers

151
Q

Resin cements have a ___ component system

A

1

152
Q

Glass ionomers have a ___ component system

A

2

153
Q

Function of bases

A

Used to provide thermal protection for the pulp and mechanical support for the restoration

154
Q

Function of liners

A

Used to protect the dentin from residual reactants that can diffuse out of the restoration or fluids that may leak in from the oral cavity; near pulp exposure.

155
Q

Explain pulp capping

A

Near or direct pulp exposure. Use Calcium hydroxide to initiate the formation of reparative dentin (odontoblast formation)

156
Q

What does ZOE stand for and what is it used for

A

Zinc oxide and eugenol. It is used as a sedative restoration for pain reduction.

Inhibits polymerization - can’t use with composite.

157
Q

What are 4 requirements for wax?

A
  1. Should melt at lower temperatures
  2. Able to be carved
  3. Able to burn off
  4. Dimensionally stable.
158
Q

____ molecular weight materials in between polymers and ___ ___

A

Lower

Organic liquids

Dental Materials (1 decks)

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