Composite 1 Flashcards
What clinical cases can direct filling materials be applied in?
- new dental caries
- abrasion / erosion
- failed restoration/secondary caries
- trauma
What are the components of composite resin?
- Filler particles
- Resin
- Camphorquinone
- Low weight dimethacrylates
- Silane coupling agent
What are the types of filler particles?
types of glass
– microfine silica
– quartz
– borosilicate glass
– lithium aluminium silicate
– barium aluminium silicate
What are the types of resin?
Monomers used:-
– BIS-GMA - reaction product of bisphenol-A and glycidyl methacrylate
– urethane dimethacrylates
What are the key characteristics of resin monomers?
- bifunctional molecule
(C=C bonds – facilitate crosslinking)
– undergoes free radical addition polymerisation
What are properties of camphorquinone and why is it added?
– activated by blue light
– produces radical molecules
– these initiate free radical addition polymerisation of BIS-GMA
– leading to changes in resin properties
(ie increased molecular weight, so increased viscosity, and strength)
Why are low weight dimethacrylates (e.g TEDGDMA) added?
added to adjust viscosity & reactivity
Why is a silane coupling agent added?
– normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
– a coupling agent is used to preferentially bond to glass and also bond to resin
What are the classifications of composite?
- Curing method
– light cured - self cured
- Filler type:
– microfilled - submicron hybrid
- heavily filled
- Handling characteristics
– condensable
– syringeable
– flowable
What are the 3 steps of composite development?
- filler particles
- curing (activation)
- particle /resin bonding
What is the advantageous effect of adding filler particles?
- improved mechanical properties
– strength, rigidity, hardness, abrasion resistance etc - lower thermal expansion (still not perfect)
- lower polymerisation shrinkage (still a problem)
- less heat of polymerisation (BUT not negligible)
- improved aesthetics
- some radiopaque
What are the ways composite can be cured?
- self curing (two pastes)
- Light curing (blue light 440nm, one paste)
How is composite actived in the curing process of self curing and light curing?
self curing = benzoyl peroxide + aromatic tertiary amine
light curing = camphorquinone + blue light
=
free radicals are formed (polymerisation)
What are the two lights used for light curing?
halogen
LED
What are the advantages of a light curing system?
- extended working time
– on-demand set, triggered when light activated - less finishing
- immediate finishing
- less waste
- higher filler levels (not mixing two pastes)
- less porosity (not mixing two pastes)
What layer of composite sets best/first in light curing?
Most of blue light is absorbed close to the surface.
Composite resin nearest the surface sets the most readily and becomes hard.
What is used to signify the depth of cure? (system)
- Surface hardness profile is accepted as more realistic
- Instrumentation used to create indentations on surface, that are quantified
- And then sub-surface measurements related to this
- DoC is defined as depth at which material HARDNESS is about 80% that of the cured surface
What is the depth of cure and what is it used to assess?
Depth of cure
– the depth to which the composite resin polymerises sufficiently
it’s HARDNESS is about 80% (to 90%) of the cured surface (D = 0mm)
typically 2mm
indicates increment thickness to use when building a restoration
using increment > 2mm results in UNDER-POLYMERISED base “soggy bottom” poor bonding to tooth….early failure !
What layer thickness should be used for hybrid composites?
2mm
What are bulk fill composites?
why are they used
Has lucerin initiator as well as camphorquinone
UV and blue light needed to polymerise (cure) material fully
produce a deeper DOC resulting in less time wasted
What layer thickness is recommended for bulk fill composites?
4-6mm
What are the problems that can occur with light curing?
- light / material mismatch - overexpose
- premature polymerisation from dental lights - avoid exposure
- optimistic “depth of cure” values (small increments)
- recommended setting times too short
- polymerisation shrinkage
What are the safety concerns for light curing?
thermal trauma from heat generation (exothermic reaction)
ocular damage from intense light sources,
