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Dental Materials > midterm > Flashcards

midterm Flashcards

1
Q

what are the 3 main classes of materials

A

metals
ceramics
polymers

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2
Q

mechanical properties of metals

A

Hard

Ductile – able to be deformed without losing toughness

Strong

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3
Q

bonding properties of metals

A

Metallic elements have 1-3 electrons in their outer shell which are loosely bound to the nucleus and interact with other electrons from various metals in the alloy to get them together

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4
Q

Almost exclusively crystalline in structure – forms grains

A

microstructure of metals

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5
Q

In __, no phase ever represents a pure metallic element

A

metal alloys

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6
Q

Mixture of two or more metallic elements

May be a homogenous mixture or exist in more than one phase

A

alloy

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7
Q

thermal properties of metals

A

high processing temperatures

thermal conductors

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8
Q

what happens when you heat up metals

A

it will start to look like like polymer, stretch out

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9
Q

in metals, Electrons have free mobility so they are ___ and

___ conductive.

A

thermally and electrically conductive

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10
Q

bend without breaking

A

Ductility

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11
Q

mechanical properties of ceramic

A

hard
brittle(shatters)
strong

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12
Q

bonding of ceramic

A

ionic and covalent bonds

semicrystalline or polycrystalline

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13
Q

thermal properties of ceramic

A

melt at high temp

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14
Q

mixture of metallic and nonmetallic elements

A

ceramics

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15
Q

most common ceramics

A

SiO2 – silicon dioxide
Al2O3 – aluminum oxide
K2O – potassium oxide

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16
Q

mechanical properties of polymer

A

soft
ductile (tough - bends)
weak

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17
Q

bonding of polymers

A

covalent bonds

high MW

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18
Q

long polymer chains (nonmetallic) - drive strength and properties from entanglement

A

polymers

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19
Q

use free radical concept to make __

A

polymers

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20
Q

polymers use free radical concept, what does that consist of

*polymerization

A

activation
initiation
propagation
termination

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21
Q

what factors contribute to metal mechanical properties

A 
high processing temps
indirect placement (exception is amalgam)
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22
Q

what factors contribute to ceramic mechanical properties

A

high processing temps

indirect placement (exception is cements)

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23
Q

what factors contribute to polymers mechanical properties

A

lower processing temps
direct placement (exceptions are indirect composites)
impressions, temporary crowns, restorations

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24
Q

polymerization can be initiated by (3 things)

A

light
heat
chemical mixing

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25
Q

explain the 1st step in polymerization process

A

activation - an initiator molecule is activated by either light, heat, or chemical mixing to form free radicals

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26
Q

explain 2nd step in polymerization process

A

initiation- free radicals combine with monomer units present in the polymer mixture - attachment of the free radicals opens up the double bond present on the monomer, creating a new free radical

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27
Q

explain the 3rd step in polymerization process

A

propagation - the constantly forming monomer free radicals continue to bind with other monomers, which become free radicals and bond to other nearby monomers, thus growing the polymer chain

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28
Q

as the polymer chain grows in in the propagation phase of polymerization what happens to the volume of the polymer mix

A

the volume of the polymer mix decreases and begins to shrink (molecules are bound instead of floating free)

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29
Q

last and 4th step in polymerization process

A

termination - a floating free radical bonds to the free radical end of the polymer chain, creating a double bond and capping off the chain

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30
Q

what is the difference between a linear polymer and crosslinked polymer?

A

linear polymer - no long chain branches so can not become tangled

crosslinked polymer - have long chain branches, become tangled and are therefore mechanicall stronger

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31
Q

Form from monomethacrylates – only one free radical end

Tangled spaghetti – long, intertwined strands

A

linear polymer

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32
Q

Form from dimethacylates – short chain with two free radical ends
“Fishing Net” – many branched chains that form crosslinks and form a network

A

branched/crosslinked polymer

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33
Q

define a composite

A

physical mixture of metals, ceramics, polymers (all 3)

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34
Q

what is the goal of composites

A

goal is the achieve some intermediate properties between the materials

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35
Q

what is the rule of mixtures and which material is it relating to

A

relating to composites

Knowing phases present in structures of materials and
interfacial interactions it is possible to predict the overall properties of the
combination

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36
Q

how do fillers affect the final properties of composites

A

as filler volume increases; material strength, modulus of elasticity/stiffness, viscosity increase, and shrinkage during curing deceases

as filler size increases; surface roughness increases

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37
Q

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

Measured in ppm/degree C

A

thermal expansion coefficient

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38
Q 
thermal expansion coefficient of;
tooth
amalgam
composite   
metals
polymers
A

tooth - 9-11

amalgam - 25

composite - 28-35

metals - 10-30

polymers - 30-600

*ideally want something close to the tooth coefficient of thermal expansion

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39
Q

dispersed phase of mixture; low flow properties, high strength

A

glass fillers

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40
Q

matrix phase of mixture; highly flowable, low strength

A

monomer resin

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41
Q

fillers are chemically bonded to resin phase by _ to improve properties

A

silane coupling agents

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42
Q

__ and __ are thermal insulators due to their high mineral content ,replacement of tooth structure by a restoration requires protection of the pulp from rapid increases or decreases in temperature

A

dentin and enamel

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43
Q

chemical implication of heat flow represents

A

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

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44
Q

__can withstand small temperature changes for short periods of time without damage

A

pulp

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45
Q

pulp dissipates heat via

A

blood circulation

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46
Q

have a high thermal conductivity and thus require an insulator to protect the pulp

A

metals

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47
Q

act as sufficient insulators

A

dental cements

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48
Q

have a low thermal conductivity

A

composite

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49
Q

do metals or composites need liners or bases to provide insulation

A

metals need due to high thermal conductivity

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50
Q

color is defined in a __ system

A

3D coordinate system

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51
Q

two colors look the same under one light but then look different
under another light

A

metamerism

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52
Q

wavelength, color

A

hue

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53
Q

intensity, brightness

A

value

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54
Q

purity, density/concentration

A

chroma

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55
Q

Results from the different spectral characteristics of each object

A

metamerism

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56
Q

mercury issues with amalgams for patients, provider/operator, and disposal

A

patients - color, mercury, can have an allergic skin reaction

operator - controlling the substance and removing the wet surface

disposal - due to toxic material, wastewater pollution with Hg is an issue

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57
Q

_ is a desirable characteristic for materials trying to mimic enamel

A

Translucency

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58
Q

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

A

creep (amalgam does this)

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59
Q

Results from accumulated strain from long-term stresses (like chewing, biting, or grinding)

A

creep

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60
Q

Mechanical Properties of Amalgam;
__ under normal loading
Poor _

A

brittle under normal loading

Poor edge strength

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61
Q

how long does it take for amalgam to reach full strength

A

1 week, but not much difference from strength after 24 hours

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62
Q

mechanical property of amalgam; __ strength is greater than __ strength

A

Compressive strength»tensile strength

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63
Q

what happens to amalgam when there is excessive mercury

A

more expansion and less strength (bad)

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64
Q

turn black over time, but still protects tooth

A

corrosion of amalgam

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65
Q

spontaneous destructive oxidation of metals

A

corrosion

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66
Q

all metals except 3 corrode spontaneously

A

gold
platinum
palladium

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67
Q

The corroding metal acts as an _ and releases metal ions

A

anode

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68
Q

Galvanic Corrosion between Anode and Cathode at

A

interproximal contacts

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69
Q

_ corrosion due to multiple phases with Conducting environment

A

Electrochemical

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70
Q

Corrosion under retained plaque because

A

lower oxygen concentration

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71
Q

_ corrosion from reaction with sulfide ions on Occlusal surface

A

chemical

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72
Q

pits and scratches catch debris and cause corrosion, what can you do to amalgam to limit this

A

minimize with polishing

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73
Q

Silver-mercury (major reaction phase for both low and high

copper amalgam)

A

Phases of and Composition of Amalgam ;

Gamma 1 (γ1)

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74
Q

tin-mercury

A 
Phases of and Composition of Amalgam; 
Gamma 2 (γ2)
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75
Q

chemical composition of amalgam

A

silver - 40-60%

tin - 27-30%

copper - 13-30%

zinc - 1%

and mercury

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76
Q

classification of amalgam; longevity of restoration, low creep values

A

high copper >12%

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77
Q

values of admix version of high copper amalgam

A

1/3 hight copper

2/3 gamma 1(silver-mercury)

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78
Q

classification of amalgam; Facilitates lathe-cut particles, Improves corrosion resistance

A

zinc containing

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79
Q

classification of amalgam; original mix, not used much anymore

A

low copper, high copper is usually used now

80
Q

elements that are useful in alloying

A

copper and zinc are the main ones

then silver, indium, mercury, tin, nobel metals (gold, platinum, palladium)

81
Q

setting reaction, expansion vs contraction (3 things)

A

Initial contraction when alloy is absorbing mercury

Expansion from formation and growth of y1 and y2

Final absorption of mercury again causes contraction

82
Q

setting reaction; machined from cast ingot

A

lathe-cut

83
Q

setting reaction;
Molten alloy blown through nozzle

Wetted with less mer cury than lathe - cut

Less condensation resistance

A

spherical

84
Q

setting rxns; _ and _ have varying particle

sixes to optimize condensation

A

spherical and lathe-cut

85
Q

phases formed in setting rxn;

__+__= reaction phase

A

starting alloy + mercury = rxn phase

setting reaction

y1 and y2 for initially (step 1)

y2 disappears (step 2, low copper)

86
Q

heat treatment of alloy (3 things)

A

Eliminates compositional nonuniformity that exist in both lathe-cut and
spherical

Relieves stress in alloy particles

Allows companies to control setting times of materials

87
Q

surface properties;

compositing put into tooth

A

hydrophobic

88
Q

surface properties; tooth surface is

A

hydrophillic

89
Q

Hydrophilic primer allow penetrations into areas with water which
allows for the attachment of the

A

composite

90
Q

hydrophilic chemicals wet _ surfaces

A

hydrophilic

  • same goes with hydrophobic, like goes with like
91
Q

Molecules can have both _ and _ components

A

hydrophobic and hydrophilic

92
Q

Measures how a liquid interacts with a solid

A

contact angle

93
Q

The angle a force by the jaw is applied to a tooth or composite

A

contact angle

94
Q

types of metal corrosion (4)

A

Galvanic Corrosion

Structure Selective Corrosion

Crevice Corrosion

Stress Corrosion

95
Q

which material degraded by hydrolysis

A

ceramics and polymers

96
Q

degradation of material;
dissolution of oxides created by H-bonds

acids, and fluoride treatments dissolve

A

ceramics

97
Q

degradation of material; absorb water into self which causes dimensional changes
water, enzymes, and bacteria

A

polymers

98
Q

Degradation products are related to toxicity – what might be absorbed by the
body over time and cause harm?

A

mercury and plastics

99
Q

axis of stress-strain curve

A

y axis = stress

x= strain

100
Q

before failure or fracture occurs

A

toughness

101
Q

before deformation occurs

A

resilience

102
Q

Tendency to deform along an axis with opposing

forces- stress and strain

A

modulus

103
Q

understand how heat can effect mechanical properties

A

Decrease strength because material becomes more pliable and easily
manipulated

104
Q

understand creep

A

Solid material moves slowly/deforms permanently under mechanical
stress (long term)

Deform over time with low constant stress

Impressions want to be taken out quickly to retain the best impression
without deformation

105
Q

the ability of a material containing a crack to resist

further fracture

A

fracture toughness

106
Q

single cycle (force) overload

A

crack (biting on a popcorn cornel

107
Q

Fatigue: slow cracks propagating over time (soft foods)

A

cyclic stresses

108
Q

teeth are not completely Rigid can lead to

A

abfractions

109
Q

Simply how the teeth articulate with each other creating an ideal
environment for mastication

A

buccal-lingual stability

110
Q

how __ lead to buccal-lingual instability and cusp fracture

A

cavity preps

111
Q

how/why cavity preps lead to buccal-lingual instability and cusp fracture

A

taking out cavity removes tooth structure thus weakening the rest of the remaining tooth and puts more stress on the remaining structure

112
Q

components of composite resins

A

resin system: allow for relatively easy processing

filler

bonding agent

visible light initiator

113
Q

in composite resin;
resin helps __

filler helps __

coupling agent __

A

resin helps processing and handling

filler helps modulus and wear resistance

role of coupling agent - bonding between filler and matrix

114
Q

composite is a Hybrid material of organic phase __ and inorganic __ phase

A

organic phase resin and inorganic filler phase

115
Q

component of composite resin that increases viscosity

A

resin

116
Q

decreases flowability and

increase viscosity improving mechanical properties

A

filler

117
Q

The linking of polymers within resin, Can alter density with number and degree

A

crosslinking

118
Q

how does crosslinking control properties

A

increases strength

Cross-linked groups need to be bonded together for this process to be
effective in increasing strength

119
Q

Silica or zirconia based inorganics

A

fillers

120
Q

what makes up 50-80wt% of composite

A

fillers

121
Q

fillers have a surface _ group(s)

A

hydroxyl group

122
Q

Higher filler loading results in a

A

higher modulus

123
Q

smaller/larger fillers are better and why

A

smaller are better because matches tooth structure better because teeth are nanocomposites

have better wear properties

allow for better polishing and finishing

better mechanical properties are expected

124
Q

0.5 to 3.0um particles

Can be loaded at 77-88wt% in composite

A

micron (fine) filler

125
Q

0.04 to 0.2um particles

Lower modulus but increased surface area so has a good wear
resistance

Tendency to aggregate

38wt% - maximum loading percentage

A

nano (microfine) filler

126
Q

Adds methacrylate groups that can bond with polymer chains to surface of
filler

A

coupling agent

127
Q

coupling agents form very strong bonds between _ and _

A

filler and resin

128
Q

Results from density change of monomer to polymer

A

shrinkage

129
Q

2 clinical consequences of shrinkage

A

Causes stress on tooth structure - composite fracture

Can cause microleaks and lead to secondary caries

130
Q

__ portion of composite will shrink upon polymerization.

A

Resin (Matrix)

131
Q

fillers reduce __

A

water sorption

132
Q

water sorption promotes

A

hydrolysis

133
Q

_ degrades matrix and matrix-filler bonding

A

water sorption

134
Q

components of glass ionomer cements

A

acidic polymer in aqueous solution(polyacid)

basic glass (aluminafluorisilicate glass, shock cooled and ground up)

water

modifiers (tartaric acid)

135
Q

glass-ionomer cement curing

A

cured by acid-base rxn

polyacid reacts with basic glass

salt bridges form from polyacid to glass

once set, Fluoride will be released

*still not well understood process

136
Q

how does curing of glass-ionomers differ from composite curing?

cross bridge?
based restorative?
releases?

A

Cross bridges between polymers vs salt bridges between poly acids and
basic glass

Water based restorative

Releases fluoride so helps tooth strength

137
Q

Understand similarities and differences between adhesives and composites:___ are based on the composite resin chemistry

A

Adhesives

138
Q

Understand similarities and differences between adhesives and composites: adhesives contain __ groups to promote bonding

A

acidic

139
Q

Understand similarities and differences between adhesives and composites: __ are visibly light cured

A

Dimethacrylates

140
Q

0-10% filler for __

__ are 70-80% filler

A

adhesives

composites

141
Q

Hydrophilic modifiers promote

A

bonding

142
Q

Tooth structure (enamel and dentin) is __, composites are __ and adhesive layers are both hydrophilic and hydrophobic.

A

Tooth structure is hydrophilic

composites are hydrophobic

143
Q

how to remove smear layer

A

etching with acid

144
Q

smear layer consists of __ and __

A

ground collagen and HA

145
Q

Failure between composite and adhesive (poor adhesive)

A

adhesive failure

146
Q

failure in the adhesive section only

A

cohesive failure

147
Q

failure in the dentin portion only

A

structural failure

148
Q

how do sealants differ from composites

A

same materials, however composites have 70-80% filler, while sealants have 0-10% filler

sealants are a preventative material

low viscosity (flowable)

bonding (mostly mechanical, etching, not for longevity

149
Q

Atmospheric layer of the sealant does not solidify well due to __ in the environment attaching to the free radicals and thus terminating the __

A

oxygen in the enviroment

polymerization.

150
Q

_are a BisGMA-TEGDMA system with no filler

A

sealants

151
Q

Oxygen interferes with Radical Polymerization

Surface is often uncured

This causes a problem with sealants because they are so thin

A

oxygen inhibition layer

152
Q

used to bind restorations to the tooth

A

cements

153
Q

requirements for cements

A

low viscosity
good mechanical properties
25um thickness

154
Q

How viscosity and handling properties of cement are modified;

- ratio

powered =

restoration ratio?

_ ratio increases working and setting time (takes longer to dry)

A

Powder to Liquid Ratio

Powered = Filler – More Filler More Viscosity More Modulus

Restoration: 2.7:1

Low ratio increase working and setting time (takes longer to dry)

155
Q

different types of cements

A

resin and glass-ionomers

156
Q

type of cement; water based, one component system,

A

resin cements

157
Q

type of cement; viscosity and strength controlled by filler loading (powder to liquid ratio);
orthodontic bonding needs?

A

resin water based cement

orthodontic bonding needs (crowns, bridges, veneers, inlays, onlays)

158
Q

type of cement; water based, powder to liquid ration is 2.7:1

adhere to tooth structure(mineral portion)

A

glass-ionomers cement

159
Q 
type of cement;
fluoride release
better than composite for clinical retention
dimensionally stable
biocompatible
A

glass-ionomers

160
Q

disadvantages of glass-ionomers

A

slow setting, looks bad

161
Q

Used to protect the pulp and minimize post-op sensitivity

Thermal/chemical barrier

Controls pulp inflammation

Controls fluid movement

A

bases and liners

162
Q

Thin material used to protect dentin from residual reactants the diffuse
out of restorations or oral fluids that could penetrate a leaky restoration
Low Viscosity

A

liners

163
Q

Provide thermal protection for pulp

Supplement mechanical support of restoration by distribution local stresses
from restoration to underlying dentin

A

bases

164
Q

stimulates odontoblast formation

pulp capping to prevent pulp from dying

A

calcium hydroxide

165
Q

pain reduction

sedative, expands when set and seals

A

ZOE

166
Q

ZOE can’t be used with composite as it inhibits

A

polymerization

167
Q

requirements of waxes

A 
temporary
melt at low temps
carveable
burn off
dimensionally stable
168
Q

_ materials in-between polymers and organic liquids

A

Lower molecular weight

169
Q

major classes of impression materials

A

hydrocolloid

elastomers

170
Q

impression material;
Alginate

Making impressions

Irreversible

Lacks some accuracy so not used from crown and bridge
impressions

A

hydrocolloid

171
Q

_ + _ = solution with colloidal particles in liquid (impression material)

A

Alginate Acid + Water = solution with colloidal particles in liquid

172
Q

impresision material that Sets via chemical and temperature

A

hydrocolloid

173
Q

Material is elastic and used in stock tray for primary impressions and Final impressions for complete dentures

Setting of the polymeric die material is affected by water content of the alginate

Higher tear strength than agar due to filler content

Use jerk removal to minimize tearing and prevent unwanted deformation

A

hydrocolloid

174
Q

impression material; Higher tear strength
Stable dimensions in storage no synersis or imbibition
Rubber-like polymer
Expensive

A

elastomers

175
Q

ideal properties of impression material

A 
Low cost
Long shelf life
Biocompatibility
Pleasant to patient
Dimensionally stable
Good handling properties
176
Q

Upon placing impression tray with material on teeth (stress application) the material will immediately strain (deform) and on removal of the impression tray with material (stress removal) the material will be permanently strained and no recovery of original shape (thus permanently deformed)

Use rapid snap removal of impression with long axis of teeth to decrease unwanted deformation and prevent tearing

A

elastomers

177
Q

alginates are __ based and _ crosslinked

A

water based and calcium crosslinked

178
Q

advantages and disadvantages of alginates being water based

A

advantage -Use water temp to manipulate setting time – colder water
increases working time, Surface energy,
wets tooth structure and gypsum stone well,
Quick setting
Easy to use, displaces blood/saliva

disadvantages - Undergoes shrinkage or expansion with loss/gain of water

Syneresis: loss of water to surroundings

Imbibition: gain water from surroundings

Limited detail

Low tear resistance

Single pour only

Need to work quickly

Low dimensional stability

179
Q

Dimensional stability means?

*alginate

A

water lose and gain

180
Q

crosslinked by hydrosilation reaction

A

polysiloxanes

181
Q

polysiloxanes have good _

A

dimensional stability

182
Q

Condensation type was the first type introduced
Inherently hydrophobic
Do not wet tooth structure or gypsum well
Good chemical and dimensional stability
More stable than alginate and polysulfides
Can re-pour
Excellent accuracy

A

polysiloxanes

183
Q

role of surfactants in polysiloxanes

A

make the silicone hydrophilic by adding surfactants into silicone backbone
Improve detail registration and transfer

184
Q

Hydrophobic – Consequences for taking impression

A

polysiloxanes

185
Q

Hydrophobic – but better surface characteristics

Good Dimensional stability

A

polyethers

186
Q

gypsum is __ cured

A

water

187
Q

gypsum properties are dependent on __ and _

A

density and crystal structure

188
Q

gypsum, dental stone used for __ not for __

A

dental stone used for models not plaster

189
Q

Understand dehydration-hydration sequence of gypsum

___: gypsum + water via heat = plaster

Reverse Reaction =

A

Calcination

Reverse Reaction = add water it releases heat and goes back to calcium
sulfate

190
Q

mouthguards are __ not thermoset

A

thermoplastic

191
Q

copolymer controls properties in_

A

mouthgaurds

192
Q

Not Thermoset: can’t be melted and reformed

A

mouthgaurds

193
Q

denture base is normally __ cured

A

visible light cured

194
Q

provisionals are normally __ cured

A

chemically cured

195
Q

why are there a difference in composition denture base and provisionals

A

Differences in composition provide differences in mechanical
characteristics of the tray

Fillers – Provide Hardness and Rigidity to the Tray

Dental Materials (1 decks)

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