1
Q
What is the composition of composite?
A
- resin matrix: (treacle like) methacrylate monomers (BISGMA/urethane dimethacrylate) with diluent monomer to reduce viscosity e.g. TEGMA
- filler: particles of silica based glass and barium oxide for radiopacity (gives strength)
- silane coupling agent - allows resin and filler to bond together
- activator: camphorquinone (light cured composite)
- pigments to give shades
2
Q
What does BISGMA stand for?
A
Bisphenol A glycidyl methacrylate
3
Q
How is composite classified?
A
By filler particle size:
Conventional/macro-filled (large particles)
Micro/nano-filled (small particles)
Hybrid - mixture of both, used anterior and posterior
High resin = less strong, more translucent, more vital appearance
High filler = strong, more wear resistant, shrinks less, more opaque, difficult to polish
4
Q
Give an overview of the properties of composite?
A
- non-adhesive material - requires adhesive bonding
- hydrophobic and photophilic
- undergoes polymerisation shrinkage
- cured in small increments upto 2mm
- hypersensitivity to components of composite e.g. HEMA
5
Q
What are the advantages of composite?
A
- wear resistance and compressive strength matches tooth substance
- command set
- good aesthetics
- bonded to tooth - more conservative of tooth tissue
6
Q
What are the disadvantages of composite?
A
- polymerisation shrinkage
- moisture control essential
- can be brittle in thin sections
- depth of cure only 2mm
- technique of placement can be difficult to master
7
Q
What techniques do we use to overcome polymerisation shrinkage?
A
- keep operator field as dry as possible (hydrophobic, will shrink away from water)
- place in oblique increments
