Resin Composites Flashcards
in the 1950’s/1960’s what were used?
silicates
silicates were the earliest what?
tooth coloured material
silicates are the product of?
an acid base reaction of aluminasilicate glass, phosphoric acid
properties of silicates?
release F
moisture sensitive
erosion prone
brittle
what were used in the 1960’s/1980’s?
acrylics
where were acrylics derived from?
denture making products
what form did acrylics come in?
what type of set were they?
powder to liquid
chem set = limited working time
what were acrylics powder component?
polymethylmethacrylate pmma beads under 50nanometres
liquid portion of acrylics?
what was the chem activator?
methyl methacrylate monomer
chem activator = tertirary amine
acrylic setting reaction is?
free radical addition polymerisation
stages of a free radical addition polymerization of methyl methacrylate?
activation
initiation
propogation
termination
what happens at the termination stage?
chain attaches to impurity/free radical or further growing chain
what is the mechanism of polymerization?
free radical addition
material contracts on?
reaction is?
what gives poor colour stability?
must use correct?
polymerization
exothermic
tertiary amine not all used up
powder:liquid
compared to silicates, acrylics are less? exhibit?
less prone to erosion, soluble, acidic, britlle
exhibit lower thermal diffusivity
acrylics match?
do not use long term if?
setting reaction is?
residual mma causes?
tooth shade
if amine present
exothermic
pulp irritancy
acrylics interact with?
contract what % by volume?
low?
poor?
eugenol
6%
low hardness
poor abrasion resistance
in 1951 Knock and Glenn?
introduced inert filler particles to reduce shrinkage = also weakened the material
in 1963 Bowens composite had?
BISGMA resin matrix
coupling agent and filler particles
what is a resin composite?
a combination of 2 different chemical materials with distinct interface separating the components and properties which could not have been achieved alone.
early composites retained?
later became?
acrylics free radical addition polymerization - 2 pastes mixed together = reduced working time and incorporated porosities
later = light cured
resin matrix includes?
methacrylate/dimethycrylate monomers e.g BISGMA
includes monomers e.g TEGMA
inhibitors
what does TEGMA allow?
controls viscosity
facilitates manufacturers filler addition
easier clinical handling
what does the viscosity of the matrix polymer do?
reduces mobility of unreacted monomers
what do unreacted monomers allow?
space for chairside repair
what does the C to C double bond take part in?
take part in free radical polymerisation
in new products based on silaranes, ring opening occurs, producing what?
expansion that offsets shrinkage
still an overall contraction
types of silaranes?
siloxanes - hydrophobicity
oxiranes - ring opening polymerisation
how are they cationic cured?
camphorquinone - photosensitiser iodium salt electron donor - decomposes iodium salt to an acidic cation ring opening polymerisation less shrinkage
what kind of fillers can be used?
quartz
silica
glasses - aluminasilicate, borosilicate, barium oxide
what kinds of coupling agents?
6-methacryloxypropylthimethaxyslane = gamma silane
difunctional - methacrylate characteristics - silane interacts and bonds with glass
good wetting = 1g->412m2
if you increase the % of filler what happens to surface hardness?
increased surface hardness
if you increase the % of filler what happens to the setting contraction?
decrease in % volume setting contraction
if you increase the % of filler what happens to the thermal expansion?
decreased thermal expansion
In what forms composites be activated chemically?
powder/liquid mixed
paste/liquid mixed
encapsulated
early light set composite was?
composite light set today was?
early - UV
today - camphorquinone - protects eyes, sets a little under operating light
how does camphorquinone cause setting?
yields the necessary free radicals to start polymerisation
becomes excited at 460-480nm (visible blue light)
most readily generated by quartz halogen lights
how does shrinkage occur?
resins are susceptible to shrinkage on polymerisation
may be modified methacrylate or a chemical that on setting expands due to ring opening mechanism - e.g oxirane = expansion in resin volumes offsets to a degree the shrinkage
what aspect of the filler controls the properties?
type
concentration
particle size/distribution
resin and filler are useless without a?
coupling agent
what does a coupling agent do?
transfers stresses generated under loading from rigid/brtille filler to more flexible and ductile polymer matrix
what does the filler act as?
a shock absorber
how are composites classified?
by mode of activation
filler particle size/distribution
conventional composite particle size? by weight?
1-50micrometre
60-80% by weight
microfilled composite?
0.01-0.1um
30-60% by weight
hybrid?
mean = 0.04um hybrid 75% 1 8% 2 total = 83-90 by weight
nanocomposites?
particles less than 1um
handling classifications?
packable - highly viscous, packaging = challenge
flowable - more fluid less filler
intended clinical application
ISO 4049 type 1? type 2?
1 - cavities including occlusal surfaces
2 - all other polymer based filling and restorative material
for a material to be on the market what must it conform with?
ISO 4049
what happens to the viscosity of composite on leaving the tube?
increases
what kind of set does composite have?
exothermic
where does the setting contraction go towards?
not towards light source
thermal properties of composite?
mismatch tooth for thermal expansion
= risks marginal prelocation
thermal diffusivity matches dentine
if chemically activated what is the working time like?
less working time
extended working time if activated how?
light activated
gradual set from outer to inner
distance light from surface and use incremental curing
physical properties of composite are reduced with what?
porosities
what is considered to be more important than compressive strength?
tensile and flexural strength
what is tribology?
composite changes with function/loss of resin rich outer layer
thermal properties of composite are proportional to what?
filler content
if filler is increased what happens to the coefficient of heat expansion?
increase
mechanical properties of composite are dependent on?
filler content and type
efficiency of coulping
degree of porosity
increased porosity and reduced coupling, what happens to the strength?
reduced strength with porosity
reduced strength with coupling by 30%
increased porosity and reduced coupling, what happens to the amount of fatigue composite can take?
reduced fatigue with porosity
reduced fatigue with coupling by 30%
why may composite stain?
resin matrix can take up fluids e.g wine
what creates a picture frame stain?
marginal deterioration
