Resin Based Composites Flashcards
What is an example of the heavy resin?
UDMA: urethane dimethacrylate
BIS-GMA: bisphoenol A glycldyl methacrylate
Which two types of resins are inside composite?
Heavy
Diluant
What is an example of a diluant resin?
TEGMA: triethylene dimethacrylate
MMA: methyl methacrylate
What are the fillers used in composite?
Quartz and silica (sio2)
Quartz is just a differnt structure of silica
What size are the filler particles?
Traditional 10-20 microns
Microfilled 10-50nm
Hybrid (15-20 microns and 10-50 nm)
Nano particles
What is the problem with the traditional filler sizes?
They have a poor surface finish and rough
What is the problem with the microfilmed fillers?
Difficult to get a filler loading of more than 20% so resin is cures and ground up mad filled resin chunks then used as filler for final resin to achieve filler loading of 50%
What is the advantage of the hybrid fillers?
Good compromise and can get small particle hybrids where largely parcules are 0.1-6 mincrons
What is the purpose of the coupling agent?
There is not inherent bonding between the filler and the resin and this without the coupling agent you would get cracks propagating
They form a covalent bond to the filler and resin
What material is used as the coupling agent?
Usually a silane
What is the name of the most common type of coupling agent used?
Gamma MPTS
Gamma methacryloxypropyltrimethoxysilane
What is the purpose of the initiator system in composite?
2 components
Produces free radicals that initiate polymerisation
What is the purpose of hydro quinine?
This is added at 0.5% and used to prevent polymerisation and thus extend the shelf life
T/F composites are radiopque?
T
What makes composite radiopque?
Heavy metal fillers containing barium and strontium salts
How do most composites cure?
Blue light with a wavelength of 460-480nm
What type of compounds are the initiatior and give an example ?
Alpha DI ketone eg Camphoroquinone
Amine
What can inhibit polymerisation?
Oxygen
What are the factors which affect the depth of cure for composites?
Wavelength 460-480nm Time of curing 40s Power of light source Distance from source Oxygen inhibition Filler content Shade of composite
What other types of curing method are there for composites?
Chemically cured
What are the activator and initiator system use in chemically cured composites?
nn dihydroxyl p toludine and benzoyl peroxide
Reaction starts as soon as they are mixed together
What is the typical setting shrinkage for composites?
2-4%
How can we reduce setting shrinkage?
Increase filler loading and use larger monomers
T/F the reaction is for light cured is exothermic?
T
How much rise in temp is there upon setting?
6 degrees
What is the working time and setting time for composite?
Working time is unlimited
Setting time is 40s
What is the effect of increasing filler loadin?
Polymerisation shrinkage is reduced
Coefficient of thermal expansion reduces
How can composite deteriorate?
Wear: worn down by teeth and other material s
Stain: picks up stain at margins of of the surface is rough
Water sorptkon: can cause deterioration of mechanical properties and may occur over months and years
What happens between the spaces of the monomers when they are cured?
The spaces reduce hence polymerisation shrinkage
Where does the shrinkage occur?
Good bond: shrinkage occurs betwen material and tooth at the interface
Poor bond: shrinkage occurs in the bulk which will lead to failure
Which techniques are there to reduce shrinkage?
Incremental building
Pulsed light curing (not sure how effective)
Cure through the enamel which cures the margin first and prevents stress in the bond
Increase filler loading
Cavity design
T/F chemically cured compostes shrink less?
T
Likely because they have
internal pores which can expand to accommodate shrinkage of material
Longer pre gel phase: more chance of the stresses being relieved befor the final shape of the composite is made
What is silorane?
Cyclic monomer derbies from siloxane a and oxiranes
What is the settin shrinkage for siloranes?
Less than 1% since rings open up as length of monomer increase in the polymer form and this less gaps
What is the effect if the siloxane backbone in siloranes?
This is hydrophobic so reduced chance of water sorption
Better colour stability
What is the effect of oxiranes moieties?
This leads to cat ionic polymerisation
T/F the light stability for siloranes of better than normal composite?
T
What are viscous bonding resins?
When the VBR is used it accommodates composite shrinkage and relieve the stress
Eg Virtebond
What is super bond?
Resin bonding system occurs on contact with water eg tissue surface which means where the polymerisation starts is where the bonding occurs at the tissue surface
What can happen with nano sized fillers?
They can clump together acting as a normal filler and not a nano
Aesthetics of the composite are controlled by which composer?
Filler particles
How much is the filler loading in composite?
60-70% filler
Silanes are what kind of compound?
Bifunctional
What happens when the light is shone in the composite?
Some absorbed by pigments and fillers
Some scattered
Some is transmitted
Darker shades mean what?
Absorbed more light therefor has shorter depth of cure
The more fillers mean what?
More likely to be scattered and thus shorter depth of cure
How much intensity f light is needed?
300milliwatts/ sq cm
What do colloid fillers do?
Bounce the light around inside so increase depth of cure
What causes intrinsic staining of composite?
Chemical reaction occurring in the composite and needs to be replaced!
