Composite Resin Flashcards
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
what does depth of cure indicate?
increment thickness to use when building a restoration
what does using increments greater than 2mm result in?
under-polymerised base so poor bonding to teeth and early failure
what is the depth of cure of hybrid composites?
2mm
what is the depth of cure for bulk-fill composites?
supposedly 6mm
what initiator do bulk fill composites also have apart from camphorquinone?
lucerin initiator
why do bulk fill composites have an extra photo initiator?
as it has different optical absorption spectrum and so UV and blue light are needed to polymerise material fully
what are the potential problems with light curing?
light/material mismatch (overexpose), premature polymerisation from dental lights, optimistic depth of cure values, recommended setting times too short, polymerisation shrinkage
how do you overcome recommended setting times being too short for light curing composites?
use a light curing time >30s
what does polymerisation shrinkage affect?
affects bond to tooth
how do you overcome the polymerisation shrinkage problems with light cured composites?
use small increments and light from different angles
what are the safety concerns for the patient with light cured composites?
exothermic reaction (heat released exceeds that of heat needed for pulpal damage), divergent light beam, modern devices are brighter/more intense and may cause thermal trauma to patients soft tissues
what are the safety concerns of light cured composite for the clinical staff?
occular damage from looking at the light
how do you overcome the risk of occular damage from curing lights?
use safety shields or safety glasses
what is the compressive strength of composite?
300MPa
what is the rigidity of composite?
15GPa so it is rigid with high Young’s modulus
what are the mechanical requirements for a posterior composite?
high strength, high YM, high abrasion resistance
what are the mechanical requirements for a deciduous composite?
strong in thin section, wear = wear of tooth, bonding and microleakage
describe the properties of conventional composite
strong but problems with finishing and staining due to soft resins and hard particles
describe the properties of microfine composites
smaller particles for smoother surface and better aesthetics for longer period but inferior mechanical properties
describe the properties of hybrid composites
improved filler loading and coupling agents which have improvements in mechanical properties
what is hardness?
material surface’s resistance to scratching and resistance to indentation
what is abrasion
removal of surface layers when two surfaces make frictional contact
what does surface roughness affect?
appearance, plaque retention, sensation when in contact with tongue
what factors of the material affect wear?
filler material, particle size distribution, filler loading, resin formulation, coupling agent
what are the clinical factors affecting wear?
cavity size and design, tooth position, occlusion, placement technique, cure efficiency, finishing methods
what is the typical bond strength of composite to enamel and dentine?
40MPa
what is bond strength dependent on?
surface preparation of tissue, composite brand and test method
what are the aims of bonding to the tooth?
reduce microleakage, counteract polymerisation shrinkage, minimise cavity design, stress transfer to tooth
what is the compressive strength of enamel?
262MPa
what is the compressive strength of dentine?
235MPa
what is the thermal conductivity for composite?
low
what is the thermal diffusivity for composite?
low
what is the thermal expansion coefficient for composite?
high which is poor
why should thermal conductivity of composite be low?
to avoid pulpal damage from hot and cold foods/fluids
what is thermal diffusivity?
how readily a material transmits heat when exposed to a short transient stimulus
why should thermal expansion coefficient be equal to the tooth?
to reduce microleakage
what is the thermal expansion coefficient for enamel?
11
what is the thermal expansion coefficient of dentine?
8
what is the thermal expansion coefficient for amalgam?
22-28
what is the thermal expansion coefficient for composite?
25-68
what are the properties of aesthetics?
shade range, translucency, maintenance of properties over lifetime, resistance to staining, surface finish
which type of restorative material is used for high caries risk and frequent attenders?
RMGI
what type of restorative material is used for medium caries risk regular attenders?
compomer
what type of restorative material is used for low caries risk patients?
composite resin
