DM L1 Composites pt 1 Flashcards
what is a composite
2 or more materials put together with each contributing to overall properties
name 5 uses of composites
restorative filling materials fissure sealants indirect restorations endo post + cores luting agents
what are the 3 main phases/components of dental composites
organic matrix
inorganic filler
coupling agents
what is the organic matrix phase of the dental composites
plastic monomer/resin material that polymerises (sets/cures) to form continuous phase
where binding the filler particles (via coupling agent)
hydrophobic
what is the inorganic filler phase of the dental composites
enhances material’s mechanic properties
reinforcing particles and/or fibres dispersed in the matrix
what is the coupling agent phase of the dental composites
bonding agent promotes adhesion between filler + resin matrix
hydrophilic end - chemically bonds to inorganic filler
what is the organic matrix made of
monomers - chemically active components of composite - polymerises
-> glassy polymer in set state
how do monomers form polymers in the organic matrix
monomer - viscous fluid, polymerises -> rigid polymeric material
free radical, addition polymerisation reaction
what monomer does organic matrix contain
Bis-GMA = Bowens’ monomer
made from bisphenol A + glycidal methacrylate
2 metha
crylate groups , ends
what is and why is another monomer used instead of Bis GMA in the organic matrix stage
Bis GMA = viscous monomer
so UDMA = urethane dimethacrylate used
UDMA less viscous than Bis GMA but still viscous
except UDMA, what is alternate monomer can be used in the organic matrix
Ethoxylated Bisphenol A derivative
2 methacrylate undergo polymerisation - break C=C
what does characteristics of monomers in organic matrix mean + how is it solved
Bis GMA - super viscous
UDMA - little less viscous
high viscous - monomers unworkable + add filler viscous increases more
diluent monomers (viscosity controllers added) = gylcol dimethacrylates
why dimethacrylates used in composites
low molecular weight of MMA (methyl methacrylate ) + low molar vol –> high vol shrinkage after polymerisation
high mole weight + low vol of Bis GMA –> lower vol shrinkage after polymerisation
what happens to Bis GMA, UDMA + diluents when they polymerise
all have 2 sets of C=C double bonds
all polymerise + contribute to overall shrinkage of material when set
what other 7 additives does organic matrix contain
- hydroquinone = stabilises free radicals, prevents initiation inhibitor -> increases shelf life
- Activator/initiator system for Room temp cure = DHPT/Benzoyl peroxide
- Light cure = DHPT/Camphorquinone
o Fillers
o Pigments e.g. iron oxide
o UV stabilisers
o Optical brighteners
what are 6 advantages of using fillers in composites
Advantages:
o Reduce setting shrinkage ∴ more filler-↓monomer/resin required
o Reduce coefficient of thermal expansion - closer to tooth tissue
o Enhance modulus and strength (compressive), hardness
o May provide radio-opacity e.g. quartz, fused silica, radio-opaque glass
o Control of aesthetics e.g. translucency, fluorescence, colour
o higher filler amounts, mech properties of composite increases
what is important wheen choosing filler for composite
refractive index of filler + resin must closely match - avoid scattering light
–>otherwise full depth of cure not achieved on light curing the resin
end result = translucent material
what must the filler be treated with and why is particle size of filler important
silane treated
o Single filler insufficient- many types used
o Avg particle size and particle size distribution = determines amt of incorporated filler
o Fillers have an effect on surface finish; i.e. smaller particles = smoother finish)
what are 3 types of fillers
conventional/Macro
hybrid/blended or small particle hybrid
microfine/ microfillers
what was 1st type of macro used in fillers and why is it not used much nowadays
>1µm - 1 st used = ground quartz - Good strength BUT Poor finish of composite - dull appearance ∵ protruding particles from resin surface
what eg of microfillers used in fillers and why were they good + why bad
colloidal silica
increased viscosity to an already
viscous resin (more diluent had to be added)
- Can b e polished; v smooth surface finish
- V Large s.a. in contact with resin ∴ difficult to
obtain high filler loading ∴ mechanical props inferior
- CANNOT be used in post cavities
what was the 2 stage process of microfillers
micro-filled composite polymerised - then ground into tiny particles
tiny particles put in another organic matrix to fill resin matrix
increases filler loading
what are hybrid composites
contain large filler particles + small amount of colloidal silica
small particle hybrid comps -achieves high polished surfaces
packing density increases - as 2 diff sizes used as fillers
what are 4 advantages of hybrid fillers + 1 disadvantage
- Favourable physical, mech and opt properties
- great wear resistance (compared to macrofilled)
- Surface morphology: superior to ; Conventional
- Radiopacity possible
Disadvantages: - ↑ surface roughness with time; resin wears
