Composite Resin
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what are the applications of direct filling materials?
new dental caries, abrasion/erosion, failed restoration/secondary caries, trauma
what are the ideal properties of direct filling materials?
strength, rigidity, hardness, bonding to tooth, thermal properties, aesthetics, handling/viscosity, smooth surface finish, low setting shrinkage, radiopaque, anticariogenic, biocompatible
what is composite resin composed of?
filler particles, resin, camphorquinone, low weight dimethacrylates, silane coupling agent
what are the different types of filler particles?
microfine silica, quartz, borosilicate glass, lithium aluminium silicate, barium aluminium silicate
what are the monomers used in the resin?
BIS-GMA or urethane dimethacrylates
what are the key characteristics of a monomer?
difunctional molecule, undergoes free radical addition polymerisation
what is camphorquinone
photoinitiator
how is camphorquinone activated?
blue light
what does cahmphorquinone do?
produces free radical molecules which initiate free radical addition polymerisation of bis-GMA leading to changes in resin properties. This causes a degree of conversion of resin
what do low weight dimethacrylates do?
adjust viscosity and reactivity
what is a silane coupling agent used for?
to preferentially bond to glass and also bond to resin
where does the silane coupling agent sit?
around the perimeter of the filler particles
when is composite used?
where aesthetics are important, class 3,4,5 restorations, labial veneers, inlays and onlays, luting cements
how are composite resins classified?
filler type, curing method, area of use (anterior/posterior/universal), handling characteristics (syringable, flowable)
what is the effect of adding filler particles?
improved mechanical properties, lower thermal expansion, lower polymerisation shrinkage, less heat of polymerisation, improved aesthetics, some radiopaque
what are the different types of composite curing?
self curing, UV activation, light curing (blue light)
how is self curing composite activated?
benzoyl peroxide and aromatic tertiary amine come together which causes free radicals to break C=C bonds causing polymerisation
how is light curing composite activated?
camphorquinone is activated by blue light which causes free radicals to break resin C=C bonds causing polymerisation
what are the advantages of light curing systems?
extended working time, less finishing, immediate finishing, less waste, higher filler levels, less porosity
what is the consequence of most of the blue light being absorbed close to the surface of the composite resin?
composite resin nearest the surface sets the most readily and becomes hard
what is the ISO 4049
the cure test where you cure a cylinder of composite resin then scrape away the unpolymerisation layer at the bottom and measure the length of it - depth of cure defined as half of this length
what is the hardness ratio?
another way of assessing depth of cure where hardness is assessed at various depths of the resin and each value is compared to the surface
what is depth of cure defined as?
depth at which material hardness is about 80% that of the cured surface
what is the typical depth of cure?
2mm