Resin-based composites Flashcards
What is a composite?
- A material made out of synthetic organic and inorganic resins.
What is the difference between an organic and inorganic resin?
An inorganic resin does not have carbon in it
What are the properties of composite?
- Has more than 1 distinct phase
- Well matched to natural tooth appearance in shade and translucency
- Strong and durable
- Technique sensitive
What are the uses of composite?
- Anterior and posterior fillings and build ups
- Repair of old restorations (composites, amalgams)
- Indirect composites - used for crowns, veneers, inlays
- Can be put on top of amalgam and also old composites
What is the composition of composite?
- Filler particles
- Resin
- A coupling agent
What are the filler particles and properties of these particles in composite?
Silica (glass) = 70-85%
- Lack of filler means resin will wear easily and exhibit high shrinkage.
- Hybrid filler - some large and small particles gives the advantage of a macrofilled and microfilled filler = good mechanical strength and easier to polish.
What is the resin component of composite and its properties?
Resin = continuous phase (what filler sits in and goes continually from one side to another)
UDMA (urethane dimethacrylate) OR Bis-GMA (main resin).
Diesters with 2 polymerisable groups
Triethylene glycol dimethacrylate (TEGDMA - dilute resin) makes resin easier to handle.
2 resins used to achieve the correct viscosity which is easier to handle.
What is the coupling agent and its use?
Usually a silane
Forms a covalent babe with the filler particles and resin. Without this, material would be brittle.
Resin - hydrophobic
Filler - hydrophilic
What are the other components of composite?
- Heavy metal glasses (strontium/barium oxide for radiopacity)
- Camphorquinone - polymerisation photoinitiator. Activated by blue light.
- Hydroquinone - inhibits premature polymerisation to allow for an acceptable shelf life.
How does composite set?
- Exposure to light 460-480nm (blue light)
- Camphorquinone released free radicals
- Free radicals initiate polymerisation of resin monomers
- Resin polymerises and hardens, setting fillers in place (command cure)
- 20-40s
What are the features of a Quartz tungsten halogen system?
- White light with blue filter - inefficient
- Lose brightness and need testing with a radiometer
- If they lose too much light, composite does not set properly.
What are the features of an LED system?
- Emit light over a narrow wavelength
- No deterioration, either works or does not work
What are the advantages of composite?
- Command cure
- Good aesthetics
- Good mechanical properties
- Can be made to adhere to teeth
- Micro-mechanical retention
What are the limitation of composite?
- Adhesion process complex and prone to error - Not suitable in instances where moisture control is an issue (elderly/young)
- More time consuming than some materials
- More expensive due to cost and time
- Polymerisation inhibited by oxygen so placed in layers
- Top layer stays uncured due to O2 exposure. Should be set with plastic matrix to inhibit O2 and allow light.
- Resin = high setting shrinkage - reduced by a higher amount of filler (~3%)
- High coefficient of thermal expansion - add as much filler as possible
- Resultant net coefficient not too different from teeth.
What is polymerisation effected by?
- Depth of cure
- Time of curing
- Distance from light to material
- Intensity of light
- Shade - More pigment (DoC)
- Filler content - larger filler particles mean that light bounces back.
