Materials Flashcards
1
Q
what is MTA? What is it used for
A
MTA is biodentine and is biocompatible and has very good outcomes. This can help dentine bridge formations. This is used as a liner for pulp exposures that is then topped with a permanent restoration.
2
Q
what should a root canal filling materials characteristics be?
A
radiopaque non-toxic inert biocompatible long shelf life easily introduced into the canal
3
Q
what type of materials can be used as root fillers
A
resin based
Zinc Eugenol
CaOH
4
Q
what material do we use for inter visit medication and why
A
non-setting CaOH with barium
pH > 12 so very few bacteria can survive in this presence over 4 weeks
radio-opaque so we can see on radiograph if it is filling canal
5
Q
how does Ca(OH)2 act against bacteria
A
Damages bacterial cytoplasmic membranes Denatures proteins Damages DNA Inactivates bacterial enzymes results in the destruction of phospholipids and the breakdown of lipopolysaccharides
6
Q
when do we use setting and non-setting calcium hydroxide
A
setting : as a direct pulp cap
non-setting: inter visit dressing medication
7
Q
what brand of non-setting calcium hydroxide do we use
A
hypo-cal
8
Q
what is mixed with Calcium hydroxide to make it radio-opaque
A
barium
9
Q
why is it important that no Hypo-cal exits the canal apex
A
causes sterile burn and will be degraded by the periodontal tissue
10
Q
what are some components of filler material e.g. odontopaste for RCT
A
broad spectrum antibiotic to attack bacteria
anti-inflammatory to reduce inflammation and pain
calcium hydroxide
11
Q
what are the properties of metal, glass, ceramics and polymers
A
metals are malleable, strong, shiny, conductors,
ceramics/glasses are brittle, strong, not conductors - hard manufacture
polymers are strong, flexible, heat changing, dont conduct, not birttle, easy manufacture
12
Q
what are direct restorative materials and what are the properties of a good direct material
A
materials that can be applied in 1 session command set quick easy cheap aesthetic restore function
13
Q
what are indirect dental materials
A
multi-step production that can be removable or non-removable
veneers, dentures, crowns, bridges
14
Q
explain pre-market testing
A
ensuring materials fit to safety guidelines by FDA and other organisations
in-vitro to test toxicity and genoticity
in vivo to test against tissue and organs
15
Q
who are the FDA
A
food and drug administration that test safety of materials/foods/drugs
16
Q
what is the CE mark
A
certified to be sold and safe in the EEA European economic area
everything must have this symbol or risk of being fined and jailed
17
Q
what are some allergenic metals
A
nickel 25%
palladium 24%
cobalt 15%
18
Q
what is the likelihood of patient reaction to material allergen compared to reactions to cosmetics
A
dental material is less than 0.1%
cosmetics 10%
19
Q
what material is used for primary impressions - adv/disadv
A
alginate
elastic so can come out of mouth easily
cheap
adaptable with ratio
quickly becomes unstable if not cast
allergies
20
Q
if we use hotter water, how does this affect alginate
A
faster setting
21
Q
how do we mix ZnOE
A
1:1 ratio of red and white paste
22
Q
what is stress
A
the force per cross sectional area put on a material
force / m^2 = (M)Pa m^-2
23
Q
what is strain
A
Strain is the fractional change in the dimensions caused by the force
change in length / original length
24
Q
why is stress an important consideration in restoration
A
stress is force per cross sectional area if our restoration has 1 small high point all force will be put on this small area increasing the stress causing fracture and causing PRF
25
what is resilience and where would it be on a stress/strain graph
resilience is the total energy a material can absorb before undergoing inelastic deformation
area under STRAIGHT line
26
what is toughness and where is this on a graph of strain and stress
amount of energy a material can absorb before fracture
| area under whole graph
27
what is another name for elastic area
resilience
28
is ultimate tensile strenght of fracture strenght higher
UTS
29
what is the elastic limit
amount of energy a material can absorb and still go back to original state
30
how is fatigue measured (2)
fatigue life - number of uses until failure
| fatigue fatigue limit/strength - amount of stress until failure of set number of cycles
31
what is hardness
ability to withstand surface indentation under compressive force
32
why must dental materials be HARD and have high fatigue
hardness is ability to withstand surface indentation from compressive force
indentations would reflect light and be anaesthetic
very high fatigue as they are used many times under high stress
33
what is thermal conductivity and thermal diffusivity
TC: rate of flow from cold to hot
TD: ratio of energy heating up material to energy passes through (to pulp = bad)
34
why do we want low thermal expansion (and what has high?) in restorations
when we drink hot drinks, we don't want materials to expand as this puts stress on enamel leading to fractures
metals are bad for this
35
what are 2 important necessities of dental materials involving thermal expansion
low as possible
| matching adjacent materials
36
are most setting/curing procedures endothermic or exothermic?
exothermic
37
what are some ideal properties of primary impression material
high dimensional stability -stay the same dimensions over time
non-toxic
no major thermal expansion
unique low viscosity to flow into sulci but also high viscosity to record details and compress
38
which of silicone, alginate, ZnOE and polyethers can be used for undercut impressions and why
```
silicone
alginate
polyethers
NOT ZNOE
all elastic apart from ZnOE
```
39
how many types of plaster are there
5
40
what colour/name are the different plasters and what are their uses (1-4)
1 + 2 = white, dental plaster for diagnostic models e.i. making secondary special tray
3 = yellow, model dental stone = opposing models during dentures
4 = die stone = very accurate and low expansion for bridges and crowns
41
as we go from plaster II to plaster III what changes
ratio of plaster to water
hardness increases
expansion decreases
compressive strenght increases
42
for model casting during denture making, what types of plaster of paris do we use, in what ratio and with how much water
II (plaster) and III (stone) in 1:1 ratio
| mix this powder: water as 1:2.5
43
what metals are used in dentistry
gold - crowns
amalgam - restoration
stainless steel - braces
titanium - implants
44
what is a 'transition' of a material
re-organisation of the atoms
45
why are metals shiny and malleable
shiny because sea of delocalised electrons can absorb light, get excited and then release photons
malleable as the ions are all positives don't repel each other so come move into one another. Ionic lattices cannot do this
46
what are ceramics
Inorganic, non-metallic compounds, usually crystalline in nature
47
what are ceramics
Inorganic, non-metallic compounds, usually crystalline in nature
brittle, hard materials with high melting points
48
what does amorphous mean
atoms/crystals are not arranged in a regular way
49
what is glass
supercooled, non-crystalline, amorphus transparent solids
| brittle
50
what are glass ceramics and why are they useful in dentistry
glass structures with inorganic additions that when slowly heated, form crystals
glass + opaque inorganic makes the material translucent
similar to enamel so good for composite and also reduced shatter as energy from fracture has to reflect off of crystals and loose energy
51
what is a mucostatic material
a material that has the viscosity to flow and not displace the soft tissues
low viscosity
52
what is a mucocompressive material
high viscosity - will not flow until we compress it against the tissues
53
what type of material are alginate and ZnOE
alginate is mucocompressive, flexible hydrocolloid
| ZnOE is a mucostatic rigid material
54
what affects dimensional accuracy of impression materials
shrinkage and expansion of the material
55
what is rheology
study of the flow of materials
56
what graph shows us if something is a (non-) Newtonian material
shear stress against shear rate graph
57
what is a Newtonian fluid
a fluid that doesn't change viscosity under shear stress
| shear stress directly proportional to shear rate
58
what is a non-newtonian fluid
a fluid that changes viscosity under shear pressure
| shear pressure is not directly proportional to shear rate
59
what two types of newtonian fluid are there
shear thickening - thicken under stress e.i. piutty
| shear thinning - ketchup
60
what impression material is shear thinning
silicone impression material
61
why is wettability important for impression materials
means that all of the surfaces will be recorded and we will have less voids
62
what is TEC and what is a high TEC
thermal expansion co-efficient
| high TEC means that the material expands a lot under heat
63
why is dental wax bad for impressions
very high TEC so would have poor dimensional accuracy
64
what are plasticisers
materials that we add very small amounts of that have large structural/functional affects
65
why is ZnOE good for impressions
good dimensional accuracy
low TEC
stable on storage
good surface accuracy
66
why may ZnOE not be good for impressions
it is mucostatic so cannot be used for deep undercuts
67
what is plaster of paris
gypsum
| calcium sulphate dihydrate
68
what chemicals cals are added to plaster and why (for making of models)
potassium sulphate to reduce expansion but this accelerates setting time
Borax decellerates setting time to counteract potassium sulphate
added because plaster expands 0.3-0.6% which is dimensionally noticable
69
how much does plain plaster expand and how can we change this
0.3-0.6%
| addition of potassium sulphate and borax
70
what are some rigid materials for impressions
ZnOE
plaster
impression compo
dental waxes
71
what is C factor
the stress put on adhesive surfaces from shrinkage of composite polymers
depends on how many surfaces in contact with
72
how do we reduce C factor when placing composite
place in small, wedged increments to reduce the number of surfaces each placement is in contact with
73
how far can light cure through composite resin
2 mm
74
what are the classes of C factor and their ratios
```
Class I = 5 bonded : 1 unbonded = 5
Class II = 4 bonded : 2 unbonded = 2
Class III = 3 bonded : 3 unbonded = 1
Class IV = 2 bonded : 4 unbonded = 0.5
Class V = 1 bonded : 5 unbonded = 0.2
```
75
if a filling material was shear thinning, how could we make it fill voids?
use sonic vibrations
76
what are bulk fill composites
polymer resins that we can place in upto 4mm thickness wedges and still light cure effectivly
reduced polymer shrinkage
77
what are the three phases and components of composite resins
organic phase - resin matrix
dispersed phase - inorganic filler
interfacial phase - coupling agent
78
what is the function of the organic matrix in composites
forms the polymer backbone and provides tensile strength
79
what is the function of the inorganic filler material of composite resins
improves mechanical properties like wear and compressive strength
redcues shrinkage
80
what is the function of the coupling agent in composite resins
the bind the organic phase matrix tot he dispersed phase
81
what is the most common monomer used for the organic matrix of composites
methacrylates
| big- GMA
82
why might multiple methacrylate's be used in the organic phase of a composite
alter physical properties like viscosity
83
why do we not used chemical cured resin composites
not controlled by operator
| more time pressure and leads to worsened fillings
84
how are light cure resins initiated and what is the name for this process
photoinitiated addition free radical polymerisation
free radical vinyl polymerisation
Camphoroquinone at 470nm wvl
85
how does free radical vinyl polymerisation work
470nm light forms free radicals
high energy chemical group
seek out vinyl double bond of methacrylate and break the bond
internal energy released which opens another methacrylate bond - bond together
86
how do coupling agents work
coat the surface of filler particles
improve adhesive surface
create stronger bonds between filler and matrix with a hydrophillic (organic) end and hydrophobic (inorganic) end
87
what are some disadvantages of using silanes for filler
loose potency over time
age in storage
sensative to water
88
what have we used for fillers for the past 50 years
silanes
89
why can we not let a composite resin get wet whilst un-cured
water break the silane bonds
silane is the coupling agent
breaks adhesion of matrix and filler
looses integrity
90
what do we find in the organic phase of resins
methacrylate monomer
initiator
inhibitor
pigments
91
why are macrofilled filler particles not good
large 10-50micrometer particles
scatter light --> very opaque
high wear rate
high polymerisation shrinkage
92
why is hybrid filler better than microfilled
allows more packing and more particles
| less polymerisation shrinkage
93
why is micro filled better than hybrid filler
worse aesthetics
| large particles reflect light and make it more opaque
94
why is it hard to disperse nanoparticles and not allow them to conglomurate?
vander waals forces are very important at nanoscale
| they come together and form globules of nano-particles
95
why is it not very important that nanoparticles increase wear of composite fillers
hybrid composites dont fail because of wear
| no need to improve it
96
how does oxygen affect placement of composites and how do we counteract this
oxygen inhibits polymerisation
top layer is partially polymerised and weak - opaque
use finishing burrs to remove top oxidised layer
97
where are polymers used and which polymers
methacrylate polymers used for composites
poly methyl methacrylate acrylic used in denture
rubber dam
mixing bowls
protective eyewear
PPE
98
what are some advantages of PMMA
```
relatively cheap
easy to mix
translucent and aesthetic
good strength
good rigidity
```
99
what are the 3 classes of polymer with their subclasses
structural:
- linerar
- cyclic
- brnahced
- cross branched
molecular:
- thermosetting
- thermoplastic
- elastomers
source:
- natural
- synthetic
- addition
- condensation
100
what bonds are formed between monomers of polymers
very strong intramolecular covalent bonds
101
how does chain length affect strength of polymer
increased length = increased strength
102
how do side groups affect polymer strength
allow for intermolecular forces e.g. hydrogen bonding
| increases strength
103
are branched or unbranched polymers more strong
unbranched straight polymer chains
pack together better increasing density and more crystalline
stronger
104
compare the structure of amorphous and crystalline polymers
amorphous have random structure
| crystalline polymers have small domains of structured crystalline ordering with aligned chains of polymer
105
what are thermoplastics and relate to structure
type of polymer
become flowable and shape able when heated and set on cooling
due to straight, unbranched chains with minimal cross linkage
106
what are thermosetting polymers and relate to structure
polymers that when heated, set and form strong irreversible covalent cross links
become hard and non-malleable
107
what are elastomers
stretchy polymers that can be stretched and return to original shape
108
what is Tg, explain and what does this depend on
glass transition temperature
temperature below the boiling point where polymer becomes more flowable
lower Tg comes with weaker/lack of secondayr bonds/cross links
109
what are the 4 steps of polymerisation
activation
initiation
propagation
termination
110
what three methods of polymerisation activation re there
heat
chemical (amides)
or light
111
what is a free radical
atom with unpaired electron, very reactive
112
what is initiation of polymerisation
where the free radical is formed
113
what is propagation of polymerisation
free radical attacks double (vinyl) bond
of monomer
forms a new larger radical (monomer) that attacks and bonds to another monomer
114
what si the common initiator for heat and chemical cure polymers
Benzoyl Peroxide
115
what is the initiator for light cured resins
Camphoroquinone
116
what is condensation polymerisation
reaction of two monomers makes a larger molecule and release a small molecule e.g. water
117
what small molecule is released in silicone condensation polymerisation
methanol
118
what are miscible liquids
mix well
| form a homogeneous mixture when mixed
119
what is a homogeneous liquid
all molecules in uniform structure
120
what are co-polymers
polymers with more than 1 monomer to enhance porperties
121
what is a blend
where monomers are mixed prior to setting/moudling
122
what is youngs modulus
elastic modulus
| gradient of stress/strain graph
123
what is a composite
combination of materials in which the products' properties are superior to both individual properties
124
what is a resin composite
highly crosslinked resin polymer
reinforced by dispersion of silica/filler
bound together by the coupling agent
125
what does the addition of a plasticizer to a polymer do? two affects on properties
reduces bonding between chains
reduces Tg - glass transition temp
reduces elastic modulus - steepness of stress/strain curve
126
What are some advantages and disadvantages of MTA
Non toxic
Non resorbable
Biocompatible
Minimal marginal leakage
Long setting time
127
what is adhesion
forces that bind two dissimilar materials together
128
what are some unwanted clinical adhesions
adhesion of bacteria to pellicle
129
what distance between objects must there be to be classed as 'adhesion'
less than 0.0007 micrometers
130
explain the difference between solid/solid and solid/liquid contact
solid liquid contact is intimate as liquid can flow to 0.0007micrometers close
solid solid contact is not intimate because at microscopic level, there is roughness and lack of contact
131
what mechanical property alters an adhesives ability to cover a substrate
wettability
132
what is required for good wettability
imbalance between surface energy of solid (greater than)
| and surface tension of liquid
133
what is surface energy of a solid
imbalance of energy of the surface level of atoms of a solid
134
if the surface energy of a solid is lower than the surface tension of a liqud, how does this affect wettability
poor wettability
| good wettability = surface energy > surface tension
135
if a liquid is poured on a solid and it forms little watter droplets, what is causing this
poor wettability
| surface tension of liquid > surface energy of solid
136
how do we measure wettability
measure the angle the water droplet forms with the surface
if lower angle, more wettability
if larger angle, more hydrophobic
137
what types of physical bonding can we have in adhesion and why is it important
weak reversible bonds
weak Vander Waals forces
non-permanent dipole dipole interactions
hydrogen bonding
not good for adhesion of materials but can be a precursor for chemical bonding
138
what are the three main types of adhesion important for dental materials
chemical bonding - ionic/covalent/metallic
micromechanical interlocking
entanglement
139
what is micromechanical interlocking
where the surface has microscopic undercuts
| adhesive flows into these undercuts and then sets becoming harder, locking into undercuts
140
what is molecular entanglement
material with a highly porous surface and add a monomer that is absorbed into the porosities and then when cured, crosslinks form and embed the two materials together forming a hybrid layer.
141
what is the conditioner of dentine bonding
phosphoric acid etch 35%
142
what is a 'conditioner' for adhesion
a chemical that alters surface of a material making it more susceptible for adhesion
143
is methacrylate or acrylate more reactive? why?
methacrylate less reactive
| extra methyl group makes the reactive atoms less available
144
what is a 'sealer' in adhesives
component that flow into porosities and sets forming a seal with the base material through molecular entanglement and micromechanical interlocking
145
how does acid etch work
removes smear layer
demineralizes the surface layer of dentine/enamel exposing collagen for molecular entanglement
(if in dentine) opens up dentinal tubules, mechanical interlocking
4 micrometre demineralized layer
146
what is a primer/coupling agent in an adhesive
a molecule in the adhesive that links the (hydrophilic) surface to the (hydrophobic) filling material e.i. composite
147
what is HO - CH3 - CH3 - Methacrylate
hydroxyl ethyl methacrylate
| HEMA
148
why are spacers important in composite resins
avoid repulsion of hydrophobic and hydrophilic ends
149
is dentine hydrophilic or hydrophobic and why
hydrophilic - mainly composed of organic material
150
is enamel hydrophilic or hydrophobic
hydrophobic
| mainly composed of in-organic material
151
how might a hydroxy group be advantageous in a resin for dentine bonding
dentine contains collagen and hydroxyapatite
hydroxy group can form chemical bonds with amino acids in collagen
can also form bonds with hydroxy groups of hydroxyapatite
152
what methacrylate resin contains a hydroxy group
HEMA - hydroxy ethyl methacrylate
153
which part of a resin adhesive binds to the composite
methacrylate group - hydrophobic
154
which part of a resin adhesive binds to dentine
hydroxy/reactive/hydrophilic end (not the methacrylate side)
155
what is the structure of a primer/coupling agent within resin adhesives
bifunctional monomer containing a hydrophilic and hydrophobic head
156
what are two characteristics of a resin sealant
contains methacrylate groups
| light curable
157
why is dentine less reliable for adhesion than enamel
more dynamic
more organic and hydrophilic
smear layer
problems with shrinkage and wettability due to wet surface
158
how much do polymer composites shrink by
2-3%
159
what causes polymerisation shrinkage
as monomer forms chemical bonds
wander vaals spaces become bonds
molecules become more compact taking up less space and contract
160
why is polymerisation shrinkage bad for composite restorations
puts contractional stress on cavity walls
| may separate from cavity walls allowing microleakage and secondary caries
161
why do we dry a composite bond (2)
evaporate solvent
| disperse evenly over surface
162
what happens if we dry dentine too much (2)
collagen forms a thick dense layer that the primer cannot penetrate
fibrils and dentinal tubules collapse preventing entrance of adhesive agent
may pull odontoblasts up dentinal tubules, killing the odontoblasts and causing sclerosis
163
what 3 stages to composite adhesion are there
etch
prime
seal
164
what does 'moh's scale determine
hardness
165
describe the inorganic structure of enamel
hexagonal hydroxyapatite crystals rods 6 micrometres in diameter
perpendicular to tooth surface
166
why must an area being restored by composite resin be kept relatively dry
resin is very hydrophobic
saliva/wet is very hydrophilic
repel each other and not allow good adhesion and wettability
Microleakage
167
what percentage phosphoric acid do we use in acid etch
35%
168
when restoring enamel with composite, what 3 things do we do before bonding
patient selection - decide if surfaces can be kept dry or not and decide weather to use resin or GIC
enamel prophylaxis - cleaning pellicle and bacteria/salivary proteins that would reduce the bonding strength
acid etch
169
what are ideal properties of composite resins
aesthetic - translucent, colour adaptable
non-toxic
stable in state and colour
form a good seal and transition with tooth structure
dont reuqire lots of cavity prep like amalgam
170
why is composite better than amalgam
doesn't contain mercury - better for pt and environment
adhesive to tooth structure, less microleakage
tooth coloured and aesthetic
less mechanical pre - no need to remove sound tooth for undercut
171
how long do composites roughly last
~10 years
172
how much is 1 capsule of composite resin
£2
173
what are some disadvantages of composite resins
polymer shrinkage leads to contractive stress and microleakage
not bind directly to surface, need bond, technique sensitive
174
what are inhibitors important for in composite resins
prevent curing of polymer to improve shelf life
175
why is amalgam better than composite and when do we use it
more wear strength to resist tooth grinding
less shrinkage
less dependant on dry surfaces
more useful for posterior restorations and cusp replacements
176
why might we not be able to control moisture for a restoration
age
cavity very close to gingival margin
unable to place rubber dam or isolation
177
what is the minimum thickness of amalgam, what happens if we go thinner
1.5-2mm
| very brittle in thin sections
178
is composite or amalgam cheaper
amalgam
179
when should we colour match composite to teeth and why
before any procedure
dehydration may alter shade
blue rubber dam may reflect on shade
180
what are resin tags
resin filled tubules
181
what
182
what is a solution
homogeneous mixture consisting of a single phase
| particles smaller than 10^-7cm
183
what is colloid
colloid is a heterogeneous mixture of two phases, where the two phases are not readily differentiated.
particle size between 10^-7cm and 10^-5cm
184
what is a suspension
mixture of 2 phases
| particle sizes of more than 10^-5cm
185
what are hydrocolloids
heterogenous group of long chain polymers
| form viscous dispersion or gel when mixed with water
186
what is a sol
hydrocolloid in its viscous form
187
what is a 'gel'
hydrocholloid in its jelly like state
188
what is the transition name from sol to gel
gelation
189
what is the difference between agar and alginate
agar is a reversible hydrocolloid - gelates due to temperature change
alginate is a irreversible hydrocolloid - gelates due to chemical reaction
190
what types of gelation are there
irrerversible - chemical
| reversible - temperature
191
are hydrocolloids inserting in their sol or gel phase
sol
192
what else is found with agar impression material
potassium sulphate and borax to prevent expansion and reduce setting time
193
when is agar impression material used
replicating dentures
194
how do we get from alginic acid to set alginate (2)
alginic acid + sodium ions --> sodium alginate
| sodium alginate + calcium ions --> crosslinks, gel state
195
what two ions are necessary and why for alginate production
alginic acid + Na+ = sodium alginate
sodium alginate + Ca2+ = cross links between COO groups
gel state achieved
196
what derived alginate
alginic acid
197
what chemical reaction occurs for irreversible setting of alginate
Calcium allows cross linkages between alginate polymer chains via COO groups
198
what is Syneresis and where is this relevent in dentistry
oozing of liquid out of gels
| water oozes out of alginate impressions causing shrinkage
199
what is imbition and what is its relevance in dentistry
swelling of gels by the uptake of water
alginate impressions swell through sorption of water
affects shape and accuracy o alginate impressions
200
why does alginate have poor shelf life and dimensional stability
alginate is a hydrocolloid gel
can shrink due to syneresis - loss of water over time
can expand due to imbition - sorption of water
expansion/shrinkage depends on thickness and so different thicknesses expand/shrink at different rates
201
when are polysulphides used and why
for bridge and crown work impressions
| very high accuracy and high dimensional stability
202
what 3 types of elastomer are there
polysulphides
polyethene
silicones
203
what catalyst is required for polymerisation of condensation silicone impression material and what is released
tin Sn catalyst
| 3 molecules of ethanol
204
what catalyst is reuqired for addition silicone impression material polymerisation
platinum Pt
205
what do surfactants do to the physical properties of fluids
increase wettability
206
when are elastomers used and why
bridge, crown, implant, overdenture work
| very high surface accuracy
207
which is the best elastomer for impressions and why
polyethene's
| most hydrophilic so cover wet surfaces best
208
what is the structure of metals
crystalline structure of regular arranged cations with a sea of electrons
209
how many crystalline structures for metals are there and which are most relevant to dentistry
7
Face centred cubic
body centred cubic
210
if FCC or BCC more dense and why
FCC as this gets 4 ions per square unit whereas BCC gets 2 ions per square unit
211
metals are polycrystalline. What does this menas
made up of many small crystals
| when freezing they expand to meet each other and form a grade boundary
212
how are grain boundaries form in solid metals
metals are polycrystalline
when liquid there are many small crystals
when solidifying, crystals grow
when they meet other crystals, grain boundaries are formed
213
what is the implication of grain boundaries
grain boundaries are very high energy
| when etching metals, the high energy grains will etch more
214
is a stronger metal one with small or large grains and why
small
| fractures are reflected at each grain
215
what is an alloy
mixture of metal and another type of atom - usually metal
216
what type of mixed structures can we get from alloys
interstitial solid solution
substitutional solid solution
intermetallic compound
217
explain interstitial solid solution
solute atom < solvent atom
solute added and fit into spaces between ions
disrupting regular lattice making less malleable as layers cannot freely slide over each other
solid solution means will fully dissolve in each other and fully mix together
218
explain a substitutional solid solution
metal ions swapped for other metallic ions of similar diameter (within 15%), valency and same crystalline structure
Cold and copper are an example
219
what is a solid solution
mixture of metals that fully dissolve in one another and mix completely
220
describe an intermetallic compound
combination of 2 or more metals that form a regular structure with a discrete composition or stoichiometric ratio
221
what type of alloy is amalgam
intermetallic compound
222
what are the 3 criteria of a substitutional solid solution
similar atomic diameter within 15% difference
same valency
same crystalline structure
223
what is a phase
homogeneous physically distinct part of a system that is separated from other parts by a definite physical boundary
224
what does a phase diagram show
gradual crystallisation of alloys
| shows break points of where crystallisation starts and ends, depending on composition of metals in alloy
225
where do we find the solidus and liquidus line and what do they show
on phase diagram
liquidous line shows break point of crystallisation initiation from liquid to solid/liquid
solidus lie shows break point for completed crystallisation from solid/liquid to solid
226
when is a eutectic phase diagram used
metals are partially soluble in each other
227
what is the eutectic point of an alloy
point of composition at which on decrease in temperature there would be an immediate change from liquid to solid at a lower melting point than both constituents
forming a homogeneous laminar structure of the two metals
228
what metals are in amalgam in descendnig order of %
```
silver
tin
copper
zinc
mercury
```
229
what two types of amalgam can we get
conventional amalgam
| High copper amalgam
230
what rough percent's of metals are in conventional amalgam
```
silver ~65-75%
tin ~25%
copper ~6%
zinc ~2%
mercury ~ remainder
```
231
in low copper amalgam, what percent is mercury
~50%
232
how do we find the gamma phase on an amalgam phase diagram
3rd pure phase along
233
what is the gamma phase made up of and what type of alloy is this
silver and tin - Ag3Sn
| similar size but different valency and structure so intermetallic compound
234
what is the formula for gamma phase
Ag3Sn
| silver 3 tin
235
what types of particle can be in amalgam and what implications of this
lathe cut - fine lathe cut set faster with higher surface area
spherical cut - easier to work with and shape
mixture - alters setting time for learners
236
what is the gamma equations for conventional amalgam with state symbols
gamma (s) + Hg (l) --> gamma (s) + gamma 1 (s) + gamma 2(s)
237
what is the word equation of gamma gamma 1 and gamma 2
gamma = silver tin alloy
gamma I = silver mercury
gamma II = tin mercury
238
how much more silver/tin is there than tin/silver and why
3 times more silver than tin
| gamma phase is Ag3Sn
239
out of gamma, gamma 1 and gamma II which will be least prevelent and why
gamma II tin mercury
limiting factor is tin
Gamma is Ag3Sn
3 times less tin than silver
240
how many phases does amalgam contain
3
gamma - Ag3Sn
gamma I - Ag2Hg3
gamma II - Sn7-8Hg
241
what is gamma I phase
Ag2Hg3
242
what is gamma II phase
Sn7-8Hg
243
why might we get a tooth fracture after amalgam restoration
residual caries
unsupported enamel or thin enamel
weak enamel tissue e.g. hypophosphotasia
244
which part of amalgams is most likely to fracture
isthmus
| transition between occlusal and proximal surface
245
what is the leading cause of restoration failure
secondary caries
246
what will the prognosis of an amalgam restoration be if the amalgam is not mixed well and why
poor due to secondary caries
| poor condensation and excess mercury formation leading to microleakage
247
why might we get gross amalgam fractures
placing amalgam too thinly
| if there is not sufficient undercut/retention, restoration will fall out
248
why do we avoid sharp internal angles
these create high stress areas, should be rounded
249
what amalgam specific characteristics of cavity prep and placement are there
grooves and undercut for retention
90 degree Cavo surface angles so no thin placement
minimum depth of 2mm
good mixing to provide good condensation and no excess mercury
250
what is marginal breakdown and why does it occur
breakdown of tissue/restoration at margin between tooth and restoration
occurs if there is a poor Cavo-surface angle
251
what are some causes of marginal breakdown (4)
poor Cavo surface angle (not 90 degrees)
underfilling/overfilling leading to pressure points
creep/corrosion
Marginal expansion
252
what is marginal expansion amalgam and what does it lead to
when in close contact to moisture
Zn from amalgam reacts forming ZnO and hydrogen forming gas bubbles
expanding amalgam putting pressure on dentine and pulp
causes voids and leads to weakness and fracture
253
what is creep and how does it affect dentistry
the slow movement or deformation of metal when under constant mechanical stress
creep on amalgam fillings causes marginal breakdown
254
what is corrosion
electrochemical degradation of metals over time caused by a difference in electrochemical charge
255
why is high copper amalgam used
reduces unfavourable gamma 2 phase - Sn7-8Hg
| gamma 2 phase responsible for creep and corrosion
256
which treaty does mercury containing amalgam concern
minimata
257
who cannot have amalgam fillings
children under 15
| breastfeeding or pregnant women
258
what are advantages of amalgam
Relatively cheap (but increasing)
Relatively non-technique sensitive
Can work in moist conditions however still better in dry conditions
Strong
Durable
Long shelf life
No need for adhesive, no biocompatibility problems
259
what are disadvantages of amalgam
Not environmentally friendly with the minamata treaty
Toxic mercury inside, even though safe when set, is still a concern. The most significant mercury release is upon placement and removal of amalgam.
Unaesthetic and may feel wrong
Media reports of unsafety
Limited to posterior
Non adhesive so we have to prepare more cavity and therefor lose more tooth
Minimum thickness of 2mm
260
why is a 90 degree cavosurface angle important in amalgam restorations
prevents fracture of thin amalgam and protects enamel prisms
261
which part of the body does mercury affect
acts as a neurotoxin, cumulative affect
| hard to remove from body
262
why is amalgam bad for the environment
small amounts released as waste
works its way up the food chain to large fish e.g. tuna
ingested and cumulative affect on e.g. pregnant women
263
when is amalgam hopefully going to be phased out and what treaty lead to this
2030
| Minamata treaty
264
other than mercury, what other aspects of amalgam are hazardous to the body
silver
tin
zinc
265
what are the relative tensile strengths of gamma, gamma I and gamma II
Gamma strongest
Gamma I next strongest
Gamma II weakest
266
what is an admix alloy
mixture of lathe cut and spherical particles
267
how do we get an admix alloy in amalgam
```
admix = spherical and lathe cut
silver tin (gamma) is cut from an ingot = lathe cut
silver copper (in Cu rich amalgam) is spherical
mixture of this with Hg leads to an admix
```
268
what is the copper rich amalgam reaction
gamma + AgCu + Hg --> gamma + gamma I + Cu6Sn5
| Ag3Sn + AgCu + Hg --> Ag3Sn + Ag2Hg3 + Cu6Sn5
269
what copper tin compounds cna be formed depending on starting AgCu somposition
Cu6Sn5 or Cu3Sn
270
how much copper is in copper rich amalgam
>12%
271
are gamma, gamma I and gamma II cathodic or anodic
gamma and gamma I are cathodic
| gamma II is anodic
272
why does gamma II make conventional amalgam more corrosive and susceptible to creep and how do we solve this
is is very anodic (compared to cathodic gamma and gamma I)
large difference in electrocurrent = susceptible to corrosion
use high copper amalgam to remove gamma II phase = less corrosive
273
what are some advantages of high copper amalgam over conventional - explain each
more resistant to corrosion = Cu6Sn5 less anodic than gamma II
higher tensile strength = Cu6Sn5 stronger than Gamma II
easier to finish and compact = Cu6Sn5 is spherical making it easier to finish
lower mercury content = less mercury components, less risk
274
compare lathe cut and spherical particles
lathe cut are made from cutting an ingot of alloy
spherical are made by atomisation of molten alloy
lathe cut require more mercury
lathe cut are harder to condense and require a broader condensation point
spherical have a smoother, better finish after burnishing
lathe cut have less undercut and stronger contact points
275
what is one advantage of lathe cut and 1 advantage of spherical particles
lathe cut - stronger proximal contacts
| spherical - less mercury, smoother finish, easier to compress, mslaler compresive point
276
give some side affects of mercury poisoning
respiratory failure
memory loss
hypertension
277
give 4 examples of when mercury is released in dentistry
leaky amalgam capsule
spillage when mixing
when finishing dental amalgam restorations
when removing dental amalgam restorations
278
what is a liner material, where are they placed
applied in a thin layer, usually less than 0.5 mm thick, to seal the dentine.
They are placed in the deepest aspect of the cavity, close to the pulp.
They are usually calcium hydroxide but can also be calcium silicate cements (MTA and Biodentine) which are biocompatible and promote remineralization.
279
compare MTA to calcium hydroxide for a liner
MTA is biocompatible and is stronger so allows thicker layers
280
what functions do CaOH have as a liner
very high alkaline pH 11 - stimulates pulp to lay down dentine to separate pulp from restoration
stimulates remineralisation as it contains calcium
antimicrobial to prevent reinfection
281
what are disadvntages of CaOH as a liner
soluble
| mechanically weak
282
compare liners and bases
liners placed in thinner sections closer to pulp - simulate tertiary dentine
bases placed in thicker sections above liners to replace dentine
liners are biocompatible (calcium), bases are not (polymer e.g. GIC)
liners are weaker, bases are stronger
283
how does GIC set
acid base reaction between 2 phases mixed in an amalgamator
284
Give some advantages and disadvantages of GIC
contains calcium, fluoride and phosphate --> remineralisation
non-toxic
non-biocompatible
low solubility so can be used in high salivary situations
strong good for bases
Bulk fill
No polymerisation shrinkage
Not as hard as composite
Not as aesthetic as composite
285
compare Fuji 9 and Fuji 2 GIC
Fuji 9 is self setting by acid base reaction, 6 minutes, time pressure
Fuji 2 is RM-GIC so dual setting - contains camphorquinone for light set
286
when is ZnOE used as a base and why is it usually avoided
only for temporary base quick and cheap
soluble and weak
risk of pulpal necrosis
inhibition of composite resin polymerisation
287
when would we apply a liner
with a very small pinpoint pulp exposure
rarely for carious exposure as presence of bacteria = RCT
mechanical exposure
after 2 days of expsoure = very poor prognosis
could use liner as a IPC to stimulate tertiary dentine
288
what are some ideal base material properties
safe, nontoxic and biocompatible
provide thermal insulation
provide good seal with tooth and definitive restoration material
tooth coloured so no staining or shadowing
289
what are benefits of having a base rather than just a definitive restoration
seal dentine = reduced microleakage = less postoperative sensitivity with reduced risk of pulpal inflammation.
Thermal insulation = less sensitivity to hot or cold.
Mechanical protection = resistance to packing or elimination of undercuts = better supported restoration and further pulpal protection.
Stimulation of new tertiary dentine to further protect the pulp due to calcium and phosphate
290
what types of base are there
```
base varnish
GIC
RM-GIC
ZnOE
CaOH cement
```
291
explain the use and function of cavity varnish
very thin layer of 'base' material to underlie a definitive restoration
Natural or synthetic polymer resins dissolved in a solvent and applied to the cavity floor with brush or cotton.
The solvent evaporates to leave a thin layer of resin. Process may be repeated.
Acts as a barrier against chemical penetration of tooth tissue and may protect against microleakage and secondary caries
Being so thin, they provide little thermal insulation
292
explain function and properties of CaOH base material
rigid self setting base material
high alkalinity = >11pH = antimicrobial and stimulates pulp to lay down tertiary dentine
low compressive strength but enough to withstand compression of amalgam
slowly soluble in water so can lead to microleakage
293
what are some good properties of GIC for base material
Relatively robust (compressive strength >50 MPa)
adhesive
insoluble
insulating
fluoride releasing
aesthetic (also a direct restorative material).
Provides a strong marginal seal
294
how does a GIC set
acid base reaction
295
compare RM-GIC and GIC
GIC sets with acid base reaction, RM-GIC sets with acid base and photopolymerization
RM-GIC has addition of water miscible monomer (HEMA)
RM-GIC sets by light cure but less useful in wet locations
296
why is composite better than amalgam
```
tooth coloured
bond directly to tooth tissue
can add small bits to existing restoration
can place in increments less than 2mm
no mercury
```
297
where might we use composite material
restoring carious lesion
increase OVD from tooth wear
mask discolouration
fractured anterior tooth
298
what is the most common denture base material and what type of material is it
PMMA poly methyl methacrylate
| thermoplastic polymer
299
what is the initiator for PMMA and how does it work
Benzoyl Peroxide
readily splits in 2 forming 2 sections both with an unpaired electron (free radical)
these molecules attack the double vinyl bond on the methacrylate group causing it to open and bond with another monomer
this now becomes the free radical and repeats until termination
300
what is the point of a cross linking agent for PMMA
creates cross links between PMMA strands
increases tensile strength
increases compressible strength
301
compare hot and cold set PMMA
cold set:
- more porous
- used chairside
- weaker
- more prone to discolouration
- less dense
- used for repairs
302
what properties of an ideal denture material does PMMA not have (4)
strength
toughness
antimicrobial (candida albicans)
low thermal conductivity
303
when would we use flexible denture material
in places of high undercut or abnormal growths e.g. Tori
304
compare the two soft liner materials
Silicone:
- elastic and retain elasticity
- weak bond to PMMA
- poor tear strength
- not resistant to candida albicans
- poor wettability = poor retention
PMMA:
- elastic but goes hard
- good bond to PMMA
- acceptable tear strength
- not resistant to candida albicans but resistant to bacteria
- good wettability
305
what are some ideal properties of soft liners for dentures
```
good bond with denture base
elastic and remain elastic
resistant to bacteria and candida albicans
high tear strength
good wettability
dimensionally stable
```
306
what are the 4 components of GIC
fluoroaluminosilicate glass
polymeric acid (multiple carboxyl groups)
water
tartaric acid.
307
how does GIC set (3)
acid base
Dissolution
Gelation
Hadrening
308
compare composite to GIC
composite is more durable, less brittle, more aesthetic, more soluble, worse in wet conditions, light cured, less susceptible to wear due to smaller filler particles, polymerisation shrinkage, require bond, hydrophobic
GIC is less durable, more brittle, less aesthetic (but still acceptable), insoluble so work well in wet environments, chemical cured acid base, more susceptible to wear due to larger filler particles, no shrinkage or exotherm, no bond required, hydrophilic
309
what is in the liquid and powder phase of GIC Fuji 9 before mixing in an amalgamator
powder: Flouro-aluminosilicate glass, freeze dried polymeric acid and pigments
liquid: distilled water, tartartic acid
310
what are the 3 stages in GIC chemical curing
Dissolution
Gelation
Hardening
311
explain the first step of GIC formation
Dissolution:
-acidic attack of glass surface
-Water is added and this ionises the carboxylic acids to release their protons which then
react with the basic glass.
-Acidic attack of the glass surface liberates some of the glass cations including calcium,
aluminium and trivalent cations.
-The silica is then retained on the surface forming a gel on the glass surface.
312
explain the second stage of GIC setting
Gelation:
- early cross-linking by Ca++
- The cations released from the glass form salt bridges with the Coo- group
- Adjacent carboxylic acid residues become stabilized.
- Aluminium stabilises more than calcium (so higher aluminium = stronger?)
313
explain the final stage of setting GIC
Hardening:
- (substitution of Ca++ by Al+++)
- Acid degraded glass sets in a crosslinked hydrogel matrix.
- released calcium for remineralization
314
how do GIC adhere to tooth surface
Gelation stage
| calcium ions form bridges between carboxyl groups, other carboxyl groups and calcium in calcium hydroxyapatite of enamel
315
how does GIC aid remineralization
releases flouride
bonds to H+ causing FH formation which can interfere with bacterial metabolism
F- released to form flourapatite to remineralize tooth structure
316
why is GIc better than composite
```
Used in wet areas
Bulk fill
No polymerisation shrinkage
No adhesive needed
Biocompatible
Releases flouride for reminerlaisation
```
317
why is GIC better than composite
no shrinkage or exotherm = less microleakage
no bond required - biocompatible with tooth surface
insoluble so can be used in wet areas
318
when do we use GIC over composite
```
deciduous teeth
wet environment e.g. near gingival margin Class V
Fissure sealants for remineralisation
temporary restorations
Cavity bases
```
319
what are the ideal properties of a filling material
```
aesthetics (composite)
hard and tough (composite)
no shrinkage (GIC)
used in wet environments (GIC)
adhesive to tooth surface (GIC)
safe and non-irritant
```
320
why are resin composites and GIC hard to mix
composite are hydrophobic
| GIC are hydrophilic
321
what is a RM GIC
resin modified glass ionomer cement
GIC mixed with a water miscible monomer (mixed with water but not hydrophilic) -HEMA
photoinitiator
322
why is HEMA a better wetting agent than PMMA
hydroxyethyl methacrylate and polymethylmethacrylate
| hydroxyl group on HEMA makes more hydrophilic allowing more contact with wet surface
323
why is HEMA used rather than PMMA in RM-GIC
HEMa has higher wettability due to OH group making RM-GIC far less hydrophobic than resin composites
324
what should be some similar and dissimilar properties between ideal definitive and temporary restoration
similar:
- good marginal seal
- strong and compressible
- fluoride releasing
- resistant to cold/hot
dissimilar:
- not same colour as teeth, easy to see
- easy to remove
- not too adhesive as this makes hard to remove
325
give advantages and disadvantages of ZnOE as a temporary restoration
```
+white so easy to find and distinguish
+adhesion low so easy to remove
+antimicrobial so further defence
+cheap and easy
+pain relieving
```
- no adhesion
- low surface hardness
- poor compressible strength
- variable marginal leakage
- poor aesthetics
- inhibit composite polymerisation
326
what affect does eugenol have on composite and what implications of this are there
prevents polymerisation
can't use ZnOE as a base if composite is going directly above
use something else
327
give advantages and disadvantages of Zn Oxide/Zinc/Calcium Sulphates as a temporary restoraiton
+absence of eugenol means set on saliva and dont inhibit polymerisation of composite
+cheap
+easy to use
+different colour to tooth
- no adhesion and variable marginal seal
- poor compressible strength
- possible expansion on setting
- poor aesthetics
- no command set
- no antimicrobial factors
- no pain relieving factors
328
what is the best polymer wetting agent and why
HEMA
| hydroxyl group makes less hydrophobic and more polar
329
compare ZnOE and ZnO as a temporary restoration
ZnO has
-no pain relieving factors
-no antimicrobial factors
+no eugenol so doesn't inhibit polymerisation of composites
ZnOE
+pain releiving
+antimicrobrial
-eugenol inhibits polymerisation of composites
330
give advantages and disadvantages of (RM)GIC good for temporary restorations
+adhesive to tooth structure
+good aesthetics but still distinguishable
+release fluoride
+biocompatible
- initial weakness, gets stronger through time via hardening
- more expensive than other options
- harder to remove than other options
331
compare ZnOE and RM-GIC as a temporary material
```
RMGIC:
+command set
+release flouride
-more expensive
-harder to remove
+better aesthetics
-not pain releiving
+biocompatible and adhesive
```
332
when should different temporary filling materials be used
composite is the ideal restorative material
small fractures on incisor: composite
grossly infected carious lesions: GIC (no retention factors)
class V near gingiva: GIC
retention e.g. occlusal: ZnOE
333
what are some properties of dental modelling materials
```
cheap
heat resistant up to 100 degrees
hard and robust
don't react with impression materials, wax, PMMA
resistant to wear
```
334
what 2 characteristics of an 'ideal' model material does plaster of Paris not fit
resistance to wear
| non-reactive : sodium alginate reactions with calcium sulphate in gypsum
335
what is the main component of gypsum/plaster of paris
calcium sulphate beta-hemihydrate
336
what are the three types of gypsum used in the dental school, there similarities and differences
plaster (beta gypsum) - weaker, large porous particles, calcium sulphate beta-hemihydrate, 110-120 degrees
stone (alpha gypsum)- denser, smaller less porous particles, calcium sulphate beta-hemi-hydrate 125 degrees
improved stone - very small dense particles, calcium sulphate beta-hemi-hydrate, added MgCl
337
when do we use plaster over stone and why
denture models as it breaks off easily and has very minimal epxansion 0.2-0.3%
338
what type of gyspum do we use for bridge work (dies)
improved plaster stone
| much stronger and more rigid
339
what type of material is plaster of paris
non-newtonian, more viscous on vibrating
calcium sulphate beta hemi-hydrate
mined from gypsum sedimentary rock
340
why do we heat mined gypsum and what is the reaciton
mined gypsum = clacum sulphate dihydrate
heated = calcium sulphate beta-hemihydrate
= strong rigid
341
what is the process of forming plaster from pure gypsum and why do we get expansion
mined gypsum - calcium sulphate dihydrate
dissolved in water and supersaturated
super heated at different temperatures and pressures
Crystals grow and interlock to form a hard rigid stone substance = calcium sulphate beta-hemihydrate
The friction of the crystals meshing together causes the exotherm and due to slight TEC, expansion
342
why do we get expansion on setting gypsum and how can we reduce this
very slight TEC
when crystals set, friction causes exotherm
causes expansion 0.3-0.6%
reduce by adding retarders to slow setting time and reduce expansion
343
what can we place in-between plaster to stop sticking together
sodium alginate
| vasaline
344
what acts as a gypsum accelerator rand retarder
accelerator: potassium sulphate (reduced expansion)
retarder: borax
345
what can affect the setting time of gypsum
water to powder ratio
temperature and pressure
accelerators/retarders
346
what powder: water ratios do we use for plaster and stone
plaster: 50ml water to 100g gypsum
stone: 20-25ml water to 100g gypsum
347
what causes small pink spots in plaster and why is this added
small amounts of sodium chloride act as a accelerator
348
what affects do sodium chloride have on setting plaster
in large amounts: retardant
| in small amounts: accelerator and cause small pink spots
349
what type of material is Dycal and when is it used
Calcium hydroxide
| pulp liner
350
what type of material is IRM, MTA, Kalzinol
Zinc Oxide Eugenol
liner under amalgam fillings
rot filler for intervisit medication
351
how does setting CaOH act as a liner
causes necrosis of pulp which calcifies and causes a protective layer
antibacterial
stimulates dentine formation
can cause further inflammation and pain
352
compare Calcium Hydroxide, GIC and ZnOE as liners
all antibacterial
CaOH causes tertiary dentine and pulp necrosis and comes in 2 pastes
GIC is adhesive, plugs dentinal tubules, releases fluoride
ZnOE used under amalgam restorations
353
list 5 ceramic/glasses used in dentistry
```
GIC
Gypsum
hydroxyapatite
Porcelain
Silane fillers in composite filling
```
354
what are PMC made out of
stainless steel
355
how long does fuji-9 take to set
2-3 mins by acid base
356
What type of impression material is impression compound
Not elastic
Rigid
For edentolous patients
357
What does tin do in amalgam
Gamma and gamma 2 phase
| Slows down setting time
358
What does zinc do in amalgam
Increase wettability
359
what is the most dimensionally stable elastomer impression material
addition cured silicones
360
what 3 factors alter the spacing needed in secondary impression trays (3)
elastic limit of material
tear strength of material
presence of undercut/extent
