Dental Problems

Dental Composite Resins -Constituents, Variations and Limitations

Dental composite resins are used for the tooth restoration. They are used for preventing caries and closing the tooth cavity. In this article, there is a brief discussion on the constituents, variations and limitations of dental composite resins. Let us examine them.

Constituents of dental composite resins

The chemistry and setting reaction of a composite resin is very complex so there are a number of different chemicals and materials incorporated, each with a specific function and the proportion is likely to vary from one manufacturer to another.

  • An organic resin component that forms the matrix, for example BisGMA.
  • Inorganic filler: These are of two types.
    • A. Macro fillers with the particle size of 5 -30 mm, for example glass, ceramic, quartz, glass, etc.
    • B. Micro fillers with the particle size of about 0.04mm for example amorphous silica.
  • Coupling agent applied to the particles to unite the filler to the resin silane.
  • Initiator system to activate the setting mechanism
  • Stabilisers (inhibitors)
  • Pigments (coloring agents)

Variations in composite resin

Based upon the forgoing information there have been further variation developed in the composite resin range based largely upon the filler particles and their size distribution.

Flowable:

The term flowable has been developed to indicate a composite resin which is relatively simple to place into a cavity in contrast to the standard hybrid materials which can be rather stiff and possibly a bit sticky.

Such a flowable material is mainly used in the case of a deciduous tooth. The flowablity of the composite resin is improved by reducing the filler content.

Packable:

Another term has been introduced to differentiate a material from a standard hybrid composite resin and that is the term packable. The difference is achieved by varying the particle size and size distribution though the water uptake and the wear factor will remain standard and acceptable.

The main difference will be in the feel of the material when being placed into the cavity. The material will be less likely to stick to the packing instrument and be withdrawn from the cavity during placement.
Chemically activated systems:

These materials are marketed as two paste or powder or liquid systems. One part will contain an initiator, benzoyl peroxide and the other part contains a tertiary aromatic amine accelerator and combination of two parts will yield free radicals. These radicals initiate polymerization of the resin.

Visible light activated systems:

Single paste, visible light activated composite resin systems contain a two component initiator system, comprising a diketone and a tertiary amine. The photosensitive diketone usually 0.2 -0.7% camphoroquinone absorbs the radiant energy of wavelength approximately 47nm.

At the approximate stage of excitation, the diketone combines with an amine to form a complex that breaks down to release free radicals than then initiate polymerization of the resin.

Other systems:

Dual activated composites have both a light activated and a chemically activated initiation system and are packaged as two pastes. The light activation mechanism is used to initiate polymerization and the chemical activation is relied upon to continue and complete the setting reaction.

Limitations of composite resin

  • Both the resin and the fillers used are anhydrous and completely inert. However, some of the minor constituents such as HEMA are identified as allergens and pose a potential risk. It has been shown to be identifiable in the pulp tissue in certain circumstances and care should be exercised in its use.
  • Any unreacted polymer chains might be an irritant to the pulp and may further cause post-insertion sensitivity.
  • The tissue cells may respond less favorably to composite resin than they do to glass ionomer and it has been postulated that incomplete cure of the resin is the prime cause of this.

The above article discusses briefly about the constituents and variations of

dental composite resins

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