Composite Flashcards
What is the ideal properties of composite
mechanical (strength, rigidity, hardness) bonding to tooth/compatible with bonding systems thermal properties aesthetics radiopaque handling/viscosity anticariogenic smooth surface finish/polishable low setting shrinkage biocompatible
what are the 2 key components of composite resin
glass filler particles
resin material
what is the key feature of the filler particles and resin
they are the opposite of each other
resin is soft while the filler is hard
what are the 5 components of composite
filler particles resin camphorquinone low weight dimethacrylates silane coupling agent
what are the filler particles
they are made of glass - they are what allow the composite resin to be hard
what are examples of glass filler particles
- Microfine silica
- Quartz
- Borosilicate glass
- Lithium aluminum silicate
- Barium aluminum silicate
what is hybrid composite
most common
has a little bit of the larger particles and a little bit of the microfine particles
The small particles fill the spaces between the large ones
what does more filler mean for the material
it is harder
what is the monomers used for resin
BIS-GMA
urethane methacrylate
what is BIS-GMA
reaction product of bisphenol-A and glycidyl methacrylate
what are the key characteristics of the resin monomer
it is a difunctional molecule and it is essential for the crosslinking required for the polymerization as it has C=C and it undergoes free radical addition polymerization
what is camphorquinone
activated by blue light to produce free radical molecules
imitates free radical addition polymerization of BIS-GMA
changes the resin properties to make it stronger
is all the monomer reacted?
no the degree of conversion of resin is only 35-80%
what is the function of the low weight dimethacrylates
they are added to adjust viscosity and reactivity
It improves the material to adjust its properties as if you cure without it then it sets too quickly and does not give us enough working time.
what is an example of a low weight dimethacrylates
TEGDMA
what is a silane coupling agent
it allows a bond between the filler particle and resin
why do the filler particle and resin not bond without the silane coupling agent
Normally water will adhere to glass filler particles preventing resin from bonding to the glass surface.
what is an example of a silane
methacryloxypropyltrimemethoxysilane
how does methacryloxypropyltrimethoxysilane work (silane coupling agent)
the methoxy groups hydrolyse to hydroxy group by reacting with the absorbed water or -OH groups on the filler
what are the different uses of composite
- It is often used where aesthetics is important
- Class III, IV, & V permanent restorations
- Class II – limited occlusal wear
- Labial veneers
- Inlays, onlays – indirect techniques
- Cores
- Modified forms as luting cements (some dual cured)
how is composite classified
filler type
curing method
area of use
handling
what type of composite is used for anterior teeth
microfilled or sub micron hybrid
what type of composite is used for posterior teeth
heavy filled
what type of composite is universal
sub micron hybrid
how can composite be classified based on its handling
can be condensable
syringable
flowable
what is condensable composite
‘amalgam feeling’ – it is more viscous and is used for packing the cavity in a similar way to amalgam. Has a greater porosity.
what is syringable composite
good adaption, less porosities, easy to apply
what is flowable composite
lower filler content, more shrinkage, difficult to apply, place for them with fibre ribbons.
how can composite be classed on curing method
light cured
self cured
what would happen if we stuck to only one size of filer particle
if we only used a large filler particle we would run out of space and we would not be able to fill up the volume but if we put more of the smaller ones then we can get more filler particles per unit volume than if we restricted ourselves to the larger one
what are the advantages of adding more filler particles
• Improved mechanical properties
o Strength
o Hardness
o Rigidity
• Improved aesthetics – it is the glass that reflects the light and is what is responsible for the tooth like appearance
• Increased abrasion resistance – the filler particles make it less easy to break the surface of the composite surface
• Lower thermal expansion (still not perfect)
• Lower polymerization shrinkage (still a problem)
• Less heat of polymerization (but not negligible)
• Some radiopaque
what are the different types of curing
self curing (two pastes) UV activation (obsolete, one paste) light curing (blue light 440 nm, one paste)
what is direct curing
cured in the mouth
what is indirect curing/post curing
cured outside the mouth
what happens in self curing
Consists of benzoyl peroxide + aromatic tertiary amine which react to create the free radicals and start the polymerization reaction
what happens in light curing
Blue light source activates the camphorquinone to create free radicals which breaks the resin C=C and start the polymerization reaction
how did the halogen light cure work
was a box which had an ordinary halogen white light and a filter which would only allow the blue light to pass through.
what is the peak of the halogen LCU
500nm - out of the camphorquinone absorption range
what is the peak of the LED LCU
460 nm
what is the peak of the camphorquinone absorption
460 nm
why is LED better than halogen
Ideally the light source should focus on the optimum wave light.
LED is efficient as there is an overlap but its peak is the same as camphorquinone but for the old style halogen LCU it’s peak is well beyond that of camphorquinone showing that it is not as efficient as the LED for curing the composite.
what are the advantages of light curing systems
- Extended working time as it is on demand set
- Less finishing
- Immediate finishing
- Less waste
- High filler levels (not mixing two pastes)
- Less porosity (not mixing two pastes) – porosity is not a good thing as it is more vulnerable to fracture
where is most of the blue light absorbed
close to the surface and this means that the composite resin nearest the surface sets the most readily and becomes hard as there is more polymerization at the surface and the molecules are harder and heavier
what is sufficient polymerization
where the hardness of the material is half of that of the surface – this is typically around 2mm and this is why we use increments when building a restoration
what does an increment greater than 2mm result in
underpolymerised base
leads to early failure
what do bulk fill composites claim
cure depth of up to 6mm
how do bulk fill composites claim to cure up to 6 mm
they have lucerin initiator as well as camphorquinone
what is the optical absorption spectrum of lucerin
UV
means we need to use poly wave curing light technology
what are the variables that mean that the lab tests are not representative of the clinical situation
- Can curing light be positioned the same as in a lab test?
- Can optical rod be placed adjacent to tooth/composite
- Does all blue light illuminate material?
- Will composite polymerize (cure) fully?
- What impact does ‘stray’ blue light have on tissue
what are the potential problems of light curing
light/material mismatch premature polymerization from dental lights optimistic depth of cure values recommended setting times too short polymerisation shrinkage
what are the safety issues of light curing for patients
when you polymerase the reaction is an exothermic one - potential pulp damage
divergent light beam
modern devices are brighter/more intense
illumination of patient’s soft tissue causing thermal trauma
what is the temperature for potentially irreversible traumatization to the dental pulp
5.5 degrees
what is the danger of light curing to clinical staff
ocular damage
