Composite

Question 1

What is the composition of composite?

Answer 1

• 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

Question 2

What does BISGMA stand for?

Answer 2

Bisphenol A glycidyl methacrylate

Question 3

How is composite classified?

Answer 3

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

Question 4

Give an overview of the properties of composite?

Answer 4

• 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

Question 5

What are the advantages of composite?

Answer 5

• wear resistance and compressive strength matches tooth substance
• command set
• good aesthetics
• bonded to tooth - more conservative of tooth tissue

Question 6

What are the disadvantages of composite?

Answer 6

• polymerisation shrinkage
• moisture control essential
• can be brittle in thin sections
• depth of cure only 2mm
• technique of placement can be difficult to master

Question 7

What techniques do we use to overcome polymerisation shrinkage?

Answer 7

• keep operator field as dry as possible (hydrophobic, will shrink away from water)
• place in oblique increments