midterm Flashcards
1
Q
what are the 3 main classes of materials
A
metals
ceramics
polymers
2
Q
mechanical properties of metals
A
Hard
Ductile – able to be deformed without losing toughness
Strong
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
4
Q
Almost exclusively crystalline in structure – forms grains
A
microstructure of metals
5
Q
In __, no phase ever represents a pure metallic element
A
metal alloys
6
Q
Mixture of two or more metallic elements
May be a homogenous mixture or exist in more than one phase
A
alloy
7
Q
thermal properties of metals
A
high processing temperatures
thermal conductors
8
Q
what happens when you heat up metals
A
it will start to look like like polymer, stretch out
9
Q
in metals, Electrons have free mobility so they are ___ and
___ conductive.
A
thermally and electrically conductive
10
Q
bend without breaking
A
Ductility
11
Q
mechanical properties of ceramic
A
hard
brittle(shatters)
strong
12
Q
bonding of ceramic
A
ionic and covalent bonds
semicrystalline or polycrystalline
13
Q
thermal properties of ceramic
A
melt at high temp
14
Q
mixture of metallic and nonmetallic elements
A
ceramics
15
Q
most common ceramics
A
SiO2 – silicon dioxide
Al2O3 – aluminum oxide
K2O – potassium oxide
16
Q
mechanical properties of polymer
A
soft
ductile (tough - bends)
weak
17
Q
bonding of polymers
A
covalent bonds
high MW
18
Q
long polymer chains (nonmetallic) - drive strength and properties from entanglement
A
polymers
19
Q
use free radical concept to make __
A
polymers
20
Q
polymers use free radical concept, what does that consist of
*polymerization
A
activation
initiation
propagation
termination
21
Q
what factors contribute to metal mechanical properties
A
high processing temps indirect placement (exception is amalgam)
22
Q
what factors contribute to ceramic mechanical properties
A
high processing temps
indirect placement (exception is cements)
23
Q
what factors contribute to polymers mechanical properties
A
lower processing temps
direct placement (exceptions are indirect composites)
impressions, temporary crowns, restorations
24
Q
polymerization can be initiated by (3 things)
A
light
heat
chemical mixing
25
explain the 1st step in polymerization process
activation - an initiator molecule is activated by either light, heat, or chemical mixing to form free radicals
26
explain 2nd step in polymerization process
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
27
explain the 3rd step in polymerization process
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
28
as the polymer chain grows in in the propagation phase of polymerization what happens to the volume of the polymer mix
the volume of the polymer mix decreases and begins to shrink (molecules are bound instead of floating free)
29
last and 4th step in polymerization process
termination - a floating free radical bonds to the free radical end of the polymer chain, creating a double bond and capping off the chain
30
what is the difference between a linear polymer and crosslinked polymer?
linear polymer - no long chain branches so can not become tangled
crosslinked polymer - have long chain branches, become tangled and are therefore mechanicall stronger
31
Form from monomethacrylates – only one free radical end
Tangled spaghetti – long, intertwined strands
linear polymer
32
Form from dimethacylates – short chain with two free radical ends
“Fishing Net” – many branched chains that form crosslinks and form a network
branched/crosslinked polymer
33
define a composite
physical mixture of metals, ceramics, polymers (all 3)
34
what is the goal of composites
goal is the achieve some intermediate properties between the materials
35
what is the rule of mixtures and which material is it relating to
relating to composites
Knowing phases present in structures of materials and
interfacial interactions it is possible to predict the overall properties of the
combination
36
how do fillers affect the final properties of composites
as filler volume increases; material strength, modulus of elasticity/stiffness, viscosity increase, and shrinkage during curing deceases
as filler size increases; surface roughness increases
37
Rate of change of a material’s size upon heating or cooling
Measured in ppm/degree C
thermal expansion coefficient
38
```
thermal expansion coefficient of;
tooth
amalgam
composite
metals
polymers
```
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
39
dispersed phase of mixture; low flow properties, high strength
glass fillers
40
matrix phase of mixture; highly flowable, low strength
monomer resin
41
fillers are chemically bonded to resin phase by _ to improve properties
silane coupling agents
42
__ 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
dentin and enamel
43
chemical implication of heat flow represents
represents the amount of heat flow over time toward the pulp through the restoration
44
__can withstand small temperature changes for short periods of time without damage
pulp
45
pulp dissipates heat via
blood circulation
46
have a high thermal conductivity and thus require an insulator to protect the pulp
metals
47
act as sufficient insulators
dental cements
48
have a low thermal conductivity
composite
49
do metals or composites need liners or bases to provide insulation
metals need due to high thermal conductivity
50
color is defined in a __ system
3D coordinate system
51
two colors look the same under one light but then look different
under another light
metamerism
52
wavelength, color
hue
53
intensity, brightness
value
54
purity, density/concentration
chroma
55
Results from the different spectral characteristics of each object
metamerism
56
mercury issues with amalgams for patients, provider/operator, and disposal
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
57
_ is a desirable characteristic for materials trying to mimic enamel
Translucency
58
the tendency of a solid material to deform permanently over time under low constant stresses
creep (amalgam does this)
59
Results from accumulated strain from long-term stresses (like chewing, biting, or grinding)
creep
60
Mechanical Properties of Amalgam;
__ under normal loading
Poor _
brittle under normal loading
Poor edge strength
61
how long does it take for amalgam to reach full strength
1 week, but not much difference from strength after 24 hours
62
mechanical property of amalgam; __ strength is greater than __ strength
Compressive strength>>tensile strength
63
what happens to amalgam when there is excessive mercury
more expansion and less strength (bad)
64
turn black over time, but still protects tooth
corrosion of amalgam
65
spontaneous destructive oxidation of metals
corrosion
66
all metals except 3 corrode spontaneously
gold
platinum
palladium
67
The corroding metal acts as an _ and releases metal ions
anode
68
Galvanic Corrosion between Anode and Cathode at
interproximal contacts
69
_ corrosion due to multiple phases with Conducting environment
Electrochemical
70
Corrosion under retained plaque because
lower oxygen concentration
71
_ corrosion from reaction with sulfide ions on Occlusal surface
chemical
72
pits and scratches catch debris and cause corrosion, what can you do to amalgam to limit this
minimize with polishing
73
Silver-mercury (major reaction phase for both low and high
| copper amalgam)
Phases of and Composition of Amalgam ;
Gamma 1 (γ1)
74
tin-mercury
```
Phases of and Composition of Amalgam;
Gamma 2 (γ2)
```
75
chemical composition of amalgam
silver - 40-60%
tin - 27-30%
copper - 13-30%
zinc - 1%
and mercury
76
classification of amalgam; longevity of restoration, low creep values
high copper >12%
77
values of admix version of high copper amalgam
1/3 hight copper
| 2/3 gamma 1(silver-mercury)
78
classification of amalgam; Facilitates lathe-cut particles, Improves corrosion resistance
zinc containing
79
classification of amalgam; original mix, not used much anymore
low copper, high copper is usually used now
80
elements that are useful in alloying
copper and zinc are the main ones
then silver, indium, mercury, tin, nobel metals (gold, platinum, palladium)
81
setting reaction, expansion vs contraction (3 things)
Initial contraction when alloy is absorbing mercury
Expansion from formation and growth of y1 and y2
Final absorption of mercury again causes contraction
82
setting reaction; machined from cast ingot
lathe-cut
83
setting reaction;
Molten alloy blown through nozzle
Wetted with less mer cury than lathe - cut
Less condensation resistance
spherical
84
setting rxns; _ and _ have varying particle
| sixes to optimize condensation
spherical and lathe-cut
85
phases formed in setting rxn;
| __+__= reaction phase
starting alloy + mercury = rxn phase
setting reaction
y1 and y2 for initially (step 1)
y2 disappears (step 2, low copper)
86
heat treatment of alloy (3 things)
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
surface properties;
| compositing put into tooth
hydrophobic
88
surface properties; tooth surface is
hydrophillic
89
Hydrophilic primer allow penetrations into areas with water which
allows for the attachment of the
composite
90
hydrophilic chemicals wet _ surfaces
hydrophilic
* same goes with hydrophobic, like goes with like
91
Molecules can have both _ and _ components
hydrophobic and hydrophilic
92
Measures how a liquid interacts with a solid
contact angle
93
The angle a force by the jaw is applied to a tooth or composite
contact angle
94
types of metal corrosion (4)
Galvanic Corrosion
Structure Selective Corrosion
Crevice Corrosion
Stress Corrosion
95
which material degraded by hydrolysis
ceramics and polymers
96
degradation of material;
dissolution of oxides created by H-bonds
acids, and fluoride treatments dissolve
ceramics
97
degradation of material; absorb water into self which causes dimensional changes
water, enzymes, and bacteria
polymers
98
Degradation products are related to toxicity – what might be absorbed by the
body over time and cause harm?
mercury and plastics
99
axis of stress-strain curve
y axis = stress
x= strain
100
before failure or fracture occurs
toughness
101
before deformation occurs
resilience
102
Tendency to deform along an axis with opposing
| forces- stress and strain
modulus
103
understand how heat can effect mechanical properties
Decrease strength because material becomes more pliable and easily
manipulated
104
understand creep
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
the ability of a material containing a crack to resist
| further fracture
fracture toughness
106
single cycle (force) overload
crack (biting on a popcorn cornel
107
Fatigue: slow cracks propagating over time (soft foods)
cyclic stresses
108
teeth are not completely Rigid can lead to
abfractions
109
Simply how the teeth articulate with each other creating an ideal
environment for mastication
buccal-lingual stability
110
how __ lead to buccal-lingual instability and cusp fracture
cavity preps
111
how/why cavity preps lead to buccal-lingual instability and cusp fracture
taking out cavity removes tooth structure thus weakening the rest of the remaining tooth and puts more stress on the remaining structure
112
components of composite resins
resin system: allow for relatively easy processing
filler
bonding agent
visible light initiator
113
in composite resin;
resin helps __
filler helps __
coupling agent __
resin helps processing and handling
filler helps modulus and wear resistance
role of coupling agent - bonding between filler and matrix
114
composite is a Hybrid material of organic phase __ and inorganic __ phase
organic phase resin and inorganic filler phase
115
component of composite resin that increases viscosity
resin
116
decreases flowability and
| increase viscosity improving mechanical properties
filler
117
The linking of polymers within resin, Can alter density with number and degree
crosslinking
118
how does crosslinking control properties
increases strength
Cross-linked groups need to be bonded together for this process to be
effective in increasing strength
119
Silica or zirconia based inorganics
fillers
120
what makes up 50-80wt% of composite
fillers
121
fillers have a surface _ group(s)
hydroxyl group
122
Higher filler loading results in a
higher modulus
123
smaller/larger fillers are better and why
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
0.5 to 3.0um particles
Can be loaded at 77-88wt% in composite
micron (fine) filler
125
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
nano (microfine) filler
126
Adds methacrylate groups that can bond with polymer chains to surface of
filler
coupling agent
127
coupling agents form very strong bonds between _ and _
filler and resin
128
Results from density change of monomer to polymer
shrinkage
129
2 clinical consequences of shrinkage
Causes stress on tooth structure - composite fracture
Can cause microleaks and lead to secondary caries
130
__ portion of composite will shrink upon polymerization.
Resin (Matrix)
131
fillers reduce __
water sorption
132
water sorption promotes
hydrolysis
133
_ degrades matrix and matrix-filler bonding
water sorption
134
components of glass ionomer cements
acidic polymer in aqueous solution(polyacid)
basic glass (aluminafluorisilicate glass, shock cooled and ground up)
water
modifiers (tartaric acid)
135
glass-ionomer cement curing
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
how does curing of glass-ionomers differ from composite curing?
cross bridge?
based restorative?
releases?
Cross bridges between polymers vs salt bridges between poly acids and
basic glass
Water based restorative
Releases fluoride so helps tooth strength
137
Understand similarities and differences between adhesives and composites:___ are based on the composite resin chemistry
Adhesives
138
Understand similarities and differences between adhesives and composites: adhesives contain __ groups to promote bonding
acidic
139
Understand similarities and differences between adhesives and composites: __ are visibly light cured
Dimethacrylates
140
0-10% filler for __
__ are 70-80% filler
adhesives
composites
141
Hydrophilic modifiers promote
bonding
142
Tooth structure (enamel and dentin) is __, composites are __ and adhesive layers are both hydrophilic and hydrophobic.
Tooth structure is hydrophilic
composites are hydrophobic
143
how to remove smear layer
etching with acid
144
smear layer consists of __ and __
ground collagen and HA
145
Failure between composite and adhesive (poor adhesive)
adhesive failure
146
failure in the adhesive section only
cohesive failure
147
failure in the dentin portion only
structural failure
148
how do sealants differ from composites
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
Atmospheric layer of the sealant does not solidify well due to __ in the environment attaching to the free radicals and thus terminating the __
oxygen in the enviroment
polymerization.
150
_are a BisGMA-TEGDMA system with no filler
sealants
151
Oxygen interferes with Radical Polymerization
Surface is often uncured
This causes a problem with sealants because they are so thin
oxygen inhibition layer
152
used to bind restorations to the tooth
cements
153
requirements for cements
low viscosity
good mechanical properties
25um thickness
154
How viscosity and handling properties of cement are modified;
_-_ ratio
powered =
restoration ratio?
_ ratio increases working and setting time (takes longer to dry)
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
different types of cements
resin and glass-ionomers
156
type of cement; water based, one component system,
resin cements
157
type of cement; viscosity and strength controlled by filler loading (powder to liquid ratio);
orthodontic bonding needs?
resin water based cement
orthodontic bonding needs (crowns, bridges, veneers, inlays, onlays)
158
type of cement; water based, powder to liquid ration is 2.7:1
adhere to tooth structure(mineral portion)
glass-ionomers cement
159
```
type of cement;
fluoride release
better than composite for clinical retention
dimensionally stable
biocompatible
```
glass-ionomers
160
disadvantages of glass-ionomers
slow setting, looks bad
161
Used to protect the pulp and minimize post-op sensitivity
Thermal/chemical barrier
Controls pulp inflammation
Controls fluid movement
bases and liners
162
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
liners
163
Provide thermal protection for pulp
Supplement mechanical support of restoration by distribution local stresses
from restoration to underlying dentin
bases
164
stimulates odontoblast formation
pulp capping to prevent pulp from dying
calcium hydroxide
165
pain reduction
| sedative, expands when set and seals
ZOE
166
ZOE can't be used with composite as it inhibits
polymerization
167
requirements of waxes
```
temporary
melt at low temps
carveable
burn off
dimensionally stable
```
168
_ materials in-between polymers and organic liquids
Lower molecular weight
169
major classes of impression materials
hydrocolloid
| elastomers
170
impression material;
Alginate
Making impressions
Irreversible
Lacks some accuracy so not used from crown and bridge
impressions
hydrocolloid
171
_ + _ = solution with colloidal particles in liquid (impression material)
Alginate Acid + Water = solution with colloidal particles in liquid
172
impresision material that Sets via chemical and temperature
hydrocolloid
173
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
hydrocolloid
174
impression material; Higher tear strength
Stable dimensions in storage no synersis or imbibition
Rubber-like polymer
Expensive
elastomers
175
ideal properties of impression material
```
Low cost
Long shelf life
Biocompatibility
Pleasant to patient
Dimensionally stable
Good handling properties
```
176
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
elastomers
177
alginates are __ based and _ crosslinked
water based and calcium crosslinked
178
advantages and disadvantages of alginates being water based
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
Dimensional stability means?
| *alginate
water lose and gain
180
crosslinked by hydrosilation reaction
polysiloxanes
181
polysiloxanes have good _
dimensional stability
182
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
polysiloxanes
183
role of surfactants in polysiloxanes
make the silicone hydrophilic by adding surfactants into silicone backbone
Improve detail registration and transfer
184
Hydrophobic – Consequences for taking impression
polysiloxanes
185
Hydrophobic – but better surface characteristics
Good Dimensional stability
polyethers
186
gypsum is __ cured
water
187
gypsum properties are dependent on __ and _
density and crystal structure
188
gypsum, dental stone used for __ not for __
dental stone used for models not plaster
189
Understand dehydration-hydration sequence of gypsum
___: gypsum + water via heat = plaster
Reverse Reaction =
Calcination
Reverse Reaction = add water it releases heat and goes back to calcium
sulfate
190
mouthguards are __ not thermoset
thermoplastic
191
copolymer controls properties in_
mouthgaurds
192
Not Thermoset: can’t be melted and reformed
mouthgaurds
193
denture base is normally __ cured
visible light cured
194
provisionals are normally __ cured
chemically cured
195
why are there a difference in composition denture base and provisionals
Differences in composition provide differences in mechanical
characteristics of the tray
Fillers – Provide Hardness and Rigidity to the Tray
