8: The tooth-coloured restorative materials II: Compomers

Chapter 8 The tooth-coloured restorative materials II

Compomers

Introduction

Compomers first appeared in the early 1990s in an attempt to combine the potential advantages of fluoride release as seen with the glass ionomer cements, with the many advantages of the resin composites. The aim was therefore to produce a resin composite which exhibited a sustained and effective release of fluoride. Previous attempts to achieve this had involved adding various fluoride salts to conventional resin composite formulations, but this proved to be less than successful. The mechanism of fluoride release relies on water being absorbed by the resin composite which then dissolves fluoride salts such as ytterbium fluoride followed by diffusion of fluoride ions out of the material. However, the nature of the resin composites meant that only the fluoride in the subsurface layers was released by this process because of the difficulty encountered by the fluoride ions in diffusing through the bulk of polymerized resin. Small amounts of fluoride were released initially but this was not sustained in the longer term. Unfortunately, another effect of these additions was to reduce the resin composite’s longevity because of degradation of the methacrylates.

The material finally developed lies closer to the resin-based composites in the continuum of materials than to the glass ionomer cements. It is primarily a resin system and is manufactured without the addition of any water. Instead an additional resin is incorporated which is difunctional.

Composition

The material is essentially a composite in nature, in that it is composed of a resin components and a filler (Table 8.1).

Table 8.1 Components of compomer materials

Component Chemical example Reason for inclusion
Filler Fluoro-alumino-silicate glass Imparts strength
    Source of fluoride ions for use in the secondary reaction
Dimethacrylate monomer Urethane dimethacrylate (UDMA) Primary monomer forming the resin matrix
Difunctional resin TCB resin: the reaction product of butane tetracarboxylic acid and hydroxyethyl methacrylate Cross-linking agent in the primary reaction
    Source of carboxyl groups for secondary reaction with glass
Photo-activator and initiator Camphorquinone Required to effect light polymerization
  Tertiary amine  
Hydrophilic monomers Glycerol dimethacrylate Enhances water diffusion within resin matrix

Setting Reaction

The setting reaction is a two-stage process.

Jan 31, 2015 | Posted by in Dental Materials | Comments Off on 8: The tooth-coloured restorative materials II: Compomers
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