Clinical aspects: Composites Flashcards
What is composite made up of?
- Matrix
- Fillers
- Coupling agents
- Initiators and accelerators
- Pigments
What is composite made up of?
A resin matrix
Name the steps required to make composite
- Resin matrix
- Filler particles
- Coupling agent
- Optical modifiers/ pigments
What is the resin matrix in compsite made up of?
Bis GMA
UDMA
TEGDMA
HEMA
Which material in resin matrix make it viscous?
The viscous monomers:
Bis GMA and UDMA
What is composite called if it just made up of resin?
Unfilled resin
Why cant composite just be made up of resin?
As it absorbs water
It stains and discolours
It isn’t wear resistant
What do we add to the resin matrix to make it more resistant ?
Filler particles
What are filler particles made up of?
Silica particles
Quartz
Glass (Ba, Sr and Zr)
What would composite be called if it was only made up of filler and resin?
Filled resin
What are composites usually classified by?
Their filler size eg micro filled or nano filled
What does the filler size determine?
Determines the surface smoothness
What is the general relationship between filler sze and composite surface?
Larger the particle size the rougher the surface
If you increase the filer CONTENT how does that change the properties of composite
- Increase in hardness/ strength
- Increase in abrasion resistant
- Handling changes
- Aesthetics change
What is the general relationship between filer content and resin content?
As filler content increases the resin content decreases
What problem do filler particles and the resin matrix have?
They don’t mix as flller is inorganic and resin is organic
What do we add to composite to help aid the mixing of filler and resin?
Coupling agent
What is coupling agent?
It is organosilane (a bifunctional molecule)
How does the coupling agent work?
- The silicane bonds to the hydroxyl group of the filler particles
- Methacrylate end of the agent polymerises with resin
So the agent brings together resin and composite
What do we add to our composite mixer of resin, filler and coupling agent to make it more aesthetic?
Optical modifiers/ pigments
What does the optical modifier/ pigment provide?
Provides translucency and opacity
What are optical modifiers/ pigments made of?
Metal oxides:
Titanium dioxide
Aluminium oxide
Name the 3 materials that make up the basic composition of composite?
- Resin matrix
- Filler particles
- Silane coupling agents
Name the most common type of composite we use in clinic
- Light activated composite
What type of reaction occurs in light activates composite?
Free radical reaction
What do we need to add to light activated materials?
Add something to stop it from activating in the bottle or direct exposure to light
Name some chemicals we add to light activated composite
- Photo inhibitor (camphorquinone)
- Amine accelerator (Diethyl-amino-ethyl-methacrylate)
- Polymerisation inhibitor ( Hydroquinone)
Why so we add a polymerisation inhibitor to light activated composite?
It prevents setting during storage
Name some light sources we can use to activate light activated composite
- Blue light emiiting diode
- Plasma arch light
- Argon laser
- Halogen light
Why can we only use certain light sources when setting light activated composite?
As you need an ideal wavelength to start the free radical reaction
Name some composites that have been classified by filler size
- Macro-filled
- Small particles
- Hybrid
- Micro filled
- Nano hybrid
- Nano filled
How big is the filler in macro filled composite and what is the filler loads?
8-12 micro metres
75-80%
How big is the filler in small particle composite and what is the filler loads?
1-8 micro metres
70-85%
How big is the filler in hybrid composite and what is the filler loads?
0.4-1 micrometre
70-75%
How big is the filler in micro filled composite and what is the filler loads?
0.04-0.4 micro metres
50-60%
How big is the filler in nano hybrid composite and what is the filler loads?
0.02-2.5 micro metre
70-75%
How big is the filler in nano filled composite and what is the filler loads?
Culsters of 0.06-1.4 micro metres (5-20nm)
70-75%
What are the short coming of light cured composite?
- Polymerisation shrinkage
- It is technique sensitive
- It is highly affected by moisture
- It doesn’t bond to the tooth on its own
What does composite need to be able to bind to the tooth?
A bonding agent
By what reaction does polymerisation shrinkage occur?
Addition polymerisation
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Why is polymerisation shrinkage bad?
As it leads to the development of gaps
Why is it a problem if gaps develop following composite placement?
Leads to :
- secondary caries
- Staining
- Sensitivity
- Build up of food in the gaps
- Harder to clean
How can we achieve moisture control when placing a composite fillign?
- Cotton wool rolls
2. Rubber dam
What is important to note before placing a rubber dam?
Make sure the patient has good gingival health
Where can moisture control not be achieved?
Subgingival restorations
