Dental Problems

Properties of Composite Resins

tooth-5Composite resins are the materials that are used for the tooth restoration. They have the ability to restore aesthetics and to maintain and develop adhesion in the oral environment. In this article, there is a brief discussion on the properties of composite resins. Read on to know more.

  • Polymerization:

    • The actual chemistry of the setting reaction is reasonably complex but is typical of all resin polymerization.
    • In the activated composite resin, there is a uniform chemical reaction which takes place throughout the whole material.
    • Whereas, in the light activated composite resin systems, the depth to which activation will occur is dependent on a number of factors. It is important to note that much of the composite resin which is initially not activated by the light system at the curing time will remain unset.
    • In both the systems, a significant proportion of the methacrylate groups remain unreacted even after some hours.
    • The quantity of the unreacted methacrylate groups will be influenced by the concentration of the different monomers.
    • Most of the setting chemical reaction and even the consequent contraction will take place during the light activation just within a first few seconds and the latter reaction will be completed within two days.
  • Solubility and water sorption:

    • Water sorption is very higher in micro filled resins and also for hybrid and for macrofilled resins.
    • A minimum amount of water sorption is essential to a newly placed composite resin because it will bring about a degree of expansion and help to counteract setting reaction.
    • Variation in the solubility and water sorption of different composite resins is associated with its amount and type of monomers and diluents.
    • The degree of polymerization will also have a bearing so that, if the curing time is reduced by 25% there will be a 2 fold increase in sorption and a4 to 6 fold increase in solubility.
    • Both the long term durability of the restoration and its color stability will be seriously affected by inadequate polymerization.
    • Rapid thermal changes may also cause break down of the silane coating and in micro filled composites. The bond between the prepolymeroized particles and the matrix is a potential site for hydrolytic failure.
  • Polymerization contraction:

    • The resin matrix in a composite resin is highly subject to a setting contraction whether it is light activated or auto cured.
    • The risks and problems are less in the restoration of deciduous teeth as the caries are relatively small and it is therefore somewhat easier to get the penetration of light activation through a relatively shorter distance to the restoration base.
    • As the material sets first in proximity to the activator light the contraction will be towards the light, thus tending to pull the resin away from the cavity walls and floor.
    • With chemically activates composites the contraction develops more slowly and evenly with a tendency to draw towards the center of the restoration.
    • The polymerization contraction with either material has a substantial impact on adaption to dentin, marginal adaption and marginal seal.
    • In a large cavity with weakened cusps there is a tendency for cusp deformation leading to post-restoration sensitivity and even fracture at the base of a cusp.
  • Wear:

    • Clinical wear of composite resin remains the main weakness in its use as the restoration on the load bearing surfaces.
    • Regardless of the material, clinical wear is associated with a roughening of the surface of the restoration, due in part to scratching of microfilled composites and partly due to loss of particles and frictional contact in the case of macro filled composited.
    • The slightly greater resistance to wear of a heavily filled micro filled composite to consistent with the greater resistance to sliding wear shown by this material.
    • Therefore it is desirable to use the most heavily filled material available regardless of possible difficulty in clinical building.

The above article discusses briefly about the properties of composite resin.

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