Materials Flashcards
what is MTA? What is it used for
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.
what should a root canal filling materials characteristics be?
radiopaque non-toxic inert biocompatible long shelf life easily introduced into the canal
what type of materials can be used as root fillers
resin based
Zinc Eugenol
CaOH
what material do we use for inter visit medication and why
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
how does Ca(OH)2 act against bacteria
Damages bacterial cytoplasmic membranes Denatures proteins Damages DNA Inactivates bacterial enzymes results in the destruction of phospholipids and the breakdown of lipopolysaccharides
when do we use setting and non-setting calcium hydroxide
setting : as a direct pulp cap
non-setting: inter visit dressing medication
what brand of non-setting calcium hydroxide do we use
hypo-cal
what is mixed with Calcium hydroxide to make it radio-opaque
barium
why is it important that no Hypo-cal exits the canal apex
causes sterile burn and will be degraded by the periodontal tissue
what are some components of filler material e.g. odontopaste for RCT
broad spectrum antibiotic to attack bacteria
anti-inflammatory to reduce inflammation and pain
calcium hydroxide
what are the properties of metal, glass, ceramics and polymers
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
what are direct restorative materials and what are the properties of a good direct material
materials that can be applied in 1 session command set quick easy cheap aesthetic restore function
what are indirect dental materials
multi-step production that can be removable or non-removable
veneers, dentures, crowns, bridges
explain pre-market testing
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
who are the FDA
food and drug administration that test safety of materials/foods/drugs
what is the CE mark
certified to be sold and safe in the EEA European economic area
everything must have this symbol or risk of being fined and jailed
what are some allergenic metals
nickel 25%
palladium 24%
cobalt 15%
what is the likelihood of patient reaction to material allergen compared to reactions to cosmetics
dental material is less than 0.1%
cosmetics 10%
what material is used for primary impressions - adv/disadv
alginate
elastic so can come out of mouth easily
cheap
adaptable with ratio
quickly becomes unstable if not cast
allergies
if we use hotter water, how does this affect alginate
faster setting
how do we mix ZnOE
1:1 ratio of red and white paste
what is stress
the force per cross sectional area put on a material
force / m^2 = (M)Pa m^-2
what is strain
Strain is the fractional change in the dimensions caused by the force
change in length / original length
why is stress an important consideration in restoration
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
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
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
what is another name for elastic area
resilience
is ultimate tensile strenght of fracture strenght higher
UTS
what is the elastic limit
amount of energy a material can absorb and still go back to original state
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
what is hardness
ability to withstand surface indentation under compressive force
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
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)
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
what are 2 important necessities of dental materials involving thermal expansion
low as possible
matching adjacent materials
are most setting/curing procedures endothermic or exothermic?
exothermic
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
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
how many types of plaster are there
5
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
as we go from plaster II to plaster III what changes
ratio of plaster to water
hardness increases
expansion decreases
compressive strenght increases
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
what metals are used in dentistry
gold - crowns
amalgam - restoration
stainless steel - braces
titanium - implants
what is a ‘transition’ of a material
re-organisation of the atoms
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
what are ceramics
Inorganic, non-metallic compounds, usually crystalline in nature
what are ceramics
Inorganic, non-metallic compounds, usually crystalline in nature
brittle, hard materials with high melting points
what does amorphous mean
atoms/crystals are not arranged in a regular way
what is glass
supercooled, non-crystalline, amorphus transparent solids
brittle
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
what is a mucostatic material
a material that has the viscosity to flow and not displace the soft tissues
low viscosity
what is a mucocompressive material
high viscosity - will not flow until we compress it against the tissues
what type of material are alginate and ZnOE
alginate is mucocompressive, flexible hydrocolloid
ZnOE is a mucostatic rigid material
what affects dimensional accuracy of impression materials
shrinkage and expansion of the material
what is rheology
study of the flow of materials
what graph shows us if something is a (non-) Newtonian material
shear stress against shear rate graph
what is a Newtonian fluid
a fluid that doesn’t change viscosity under shear stress
shear stress directly proportional to shear rate
what is a non-newtonian fluid
a fluid that changes viscosity under shear pressure
shear pressure is not directly proportional to shear rate
what two types of newtonian fluid are there
shear thickening - thicken under stress e.i. piutty
shear thinning - ketchup
what impression material is shear thinning
silicone impression material
why is wettability important for impression materials
means that all of the surfaces will be recorded and we will have less voids
what is TEC and what is a high TEC
thermal expansion co-efficient
high TEC means that the material expands a lot under heat
why is dental wax bad for impressions
very high TEC so would have poor dimensional accuracy
what are plasticisers
materials that we add very small amounts of that have large structural/functional affects
why is ZnOE good for impressions
good dimensional accuracy
low TEC
stable on storage
good surface accuracy
why may ZnOE not be good for impressions
it is mucostatic so cannot be used for deep undercuts
what is plaster of paris
gypsum
calcium sulphate dihydrate
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
how much does plain plaster expand and how can we change this
0.3-0.6%
addition of potassium sulphate and borax
what are some rigid materials for impressions
ZnOE
plaster
impression compo
dental waxes
what is C factor
the stress put on adhesive surfaces from shrinkage of composite polymers
depends on how many surfaces in contact with
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
how far can light cure through composite resin
2 mm
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
if a filling material was shear thinning, how could we make it fill voids?
use sonic vibrations
what are bulk fill composites
polymer resins that we can place in upto 4mm thickness wedges and still light cure effectivly
reduced polymer shrinkage
what are the three phases and components of composite resins
organic phase - resin matrix
dispersed phase - inorganic filler
interfacial phase - coupling agent
what is the function of the organic matrix in composites
forms the polymer backbone and provides tensile strength
what is the function of the inorganic filler material of composite resins
improves mechanical properties like wear and compressive strength
redcues shrinkage
what is the function of the coupling agent in composite resins
the bind the organic phase matrix tot he dispersed phase
what is the most common monomer used for the organic matrix of composites
methacrylates
big- GMA
why might multiple methacrylate’s be used in the organic phase of a composite
alter physical properties like viscosity
why do we not used chemical cured resin composites
not controlled by operator
more time pressure and leads to worsened fillings
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
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
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
what are some disadvantages of using silanes for filler
loose potency over time
age in storage
sensative to water
what have we used for fillers for the past 50 years
silanes
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
what do we find in the organic phase of resins
methacrylate monomer
initiator
inhibitor
pigments
why are macrofilled filler particles not good
large 10-50micrometer particles
scatter light –> very opaque
high wear rate
high polymerisation shrinkage
why is hybrid filler better than microfilled
allows more packing and more particles
less polymerisation shrinkage
why is micro filled better than hybrid filler
worse aesthetics
large particles reflect light and make it more opaque
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
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
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
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
what are some advantages of PMMA
relatively cheap easy to mix translucent and aesthetic good strength good rigidity
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
what bonds are formed between monomers of polymers
very strong intramolecular covalent bonds
how does chain length affect strength of polymer
increased length = increased strength
how do side groups affect polymer strength
allow for intermolecular forces e.g. hydrogen bonding
increases strength
are branched or unbranched polymers more strong
unbranched straight polymer chains
pack together better increasing density and more crystalline
stronger
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
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
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
what are elastomers
stretchy polymers that can be stretched and return to original shape
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
what are the 4 steps of polymerisation
activation
initiation
propagation
termination
what three methods of polymerisation activation re there
heat
chemical (amides)
or light
what is a free radical
atom with unpaired electron, very reactive
what is initiation of polymerisation
where the free radical is formed
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
what si the common initiator for heat and chemical cure polymers
Benzoyl Peroxide
what is the initiator for light cured resins
Camphoroquinone
what is condensation polymerisation
reaction of two monomers makes a larger molecule and release a small molecule e.g. water
what small molecule is released in silicone condensation polymerisation
methanol
what are miscible liquids
mix well
form a homogeneous mixture when mixed
what is a homogeneous liquid
all molecules in uniform structure
what are co-polymers
polymers with more than 1 monomer to enhance porperties
what is a blend
where monomers are mixed prior to setting/moudling
what is youngs modulus
elastic modulus
gradient of stress/strain graph
what is a composite
combination of materials in which the products’ properties are superior to both individual properties
what is a resin composite
highly crosslinked resin polymer
reinforced by dispersion of silica/filler
bound together by the coupling agent
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
What are some advantages and disadvantages of MTA
Non toxic
Non resorbable
Biocompatible
Minimal marginal leakage
Long setting time
what is adhesion
forces that bind two dissimilar materials together
what are some unwanted clinical adhesions
adhesion of bacteria to pellicle
what distance between objects must there be to be classed as ‘adhesion’
less than 0.0007 micrometers
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
what mechanical property alters an adhesives ability to cover a substrate
wettability
what is required for good wettability
imbalance between surface energy of solid (greater than)
and surface tension of liquid
what is surface energy of a solid
imbalance of energy of the surface level of atoms of a solid
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
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
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
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
what are the three main types of adhesion important for dental materials
chemical bonding - ionic/covalent/metallic
micromechanical interlocking
entanglement
what is micromechanical interlocking
where the surface has microscopic undercuts
adhesive flows into these undercuts and then sets becoming harder, locking into undercuts
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.
what is the conditioner of dentine bonding
phosphoric acid etch 35%
what is a ‘conditioner’ for adhesion
a chemical that alters surface of a material making it more susceptible for adhesion
is methacrylate or acrylate more reactive? why?
methacrylate less reactive
extra methyl group makes the reactive atoms less available
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