Composites in Dentistry

Composite is a compound of two or more different constituents with properties that are superior to those of the individual constituent.

COMPOSITION:
a) Resin Matrix
The matrix consists of Bis-phenol Glycidylmethacrylate (Bis-GMA) and Triethylene Glycol Dimethacrylate (TEGDMA). TEGDMA is used as a viscosity controller.

b) Fillers - silica
Addition of fillers increases the strength, hardness, abrasion resistance and decreases the polymerization shrinkage and water sorption.

c) Coupling agent
Organosilane, zirconates or titanates. They bond the filler particles to the resin matrix.

d) Inhibitor - Hydroquinone
Prevents premature polymerization

e) Opacifiers and coloring agents
Titanium dioxide and aluminum oxide are the opacifiers.
The coupling agent between filler particle and the resin is VINYL SILANE.

TYPES:
CHEMICALLY ACTIVATED COMPOSITES:
# Supplied in two pastes

  • Basic Paste - Contains the initiator benzoyl peroxide
  • Accelerator Paste - Contains tertiary amine as activator (N-dimethyl-p-toluidine)
# It is manipulated by mixing the proper proportions on a mixing pad with an agate spatula as metal spatula discolors the material.

# Cavity should be slightly overfilled.
# Shrinkage occurs towards the centre of the material.
LIGHT ACTIVATED COMPOSITES
# Consists of a single paste
Initiator - Camphoroquinone
Activator - diethyl-amino-ethyl-methacrylate or diketone

- They interact when exposed to light at wavelength of 400-500 nm i.e. blue region of the visible light spectrum.

- Ultraviolet light curing is not indicated because of its limited depth of penetration through tooth structure. It also poses a potential health hazard.

- The source of light is a tungsten halogen bulb.

- The tip should be kept as close as possible to the restoration and should be cured in increments.

- Each increment should not be greater than 2 mm and the exposure time should be 40-60 seconds.

- Darker shades require longer exposure time.

- Light emitted may cause retinal damage and can be prevented by using protective eyeglasses.

- Shrinkage occurs towards the light source.

- Cavity preparation for composites is beveled except when margins are in cementum.

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