Photocurable epoxy-polyol matrices for use in dental composites I

There is a need for low shrinkage visible-light cure resins to replace the dimethacrylate polymers used in dental composites. Cycloaliphatic epoxy resins formulated with polyol network extenders have been considered as potential candidates to address this need. This paper presents basic materials characterisation to underpin the selection of epoxy-polyol matrices cured with cationic onium/camphorquinone initiators. The study investigates the effect of choice of polyol and the ratio of epoxy groups to polyol groups in the matrix (R). The limitations of some analytical methods are also discussed. Epoxy-polyols are shown to have significant advantages over dimethacrylates for dental as they exhibit: lower polymer shrinkage, no oxygen inhibition layer, higher strength, equivalent hardness and acceptable glass transition temperatures (by DMA). However, the mass increase of the epoxy-polyols materials in water at 37 degrees C is almost double that of the conventional dimethacrylate matrices and cracking was observed in some samples during hydration. It is demonstrated that this can be avoided by careful selection of the formulation parameters. The paper concludes that R should be selected to lie between the limits of 4 and 8 to ensure the matrix has a balance of acceptable properties. The reduction of the water-uptake of epoxy-polyol matrices remains an important target and will be addressed through further research. (C) 2000 Elsevier Science Ltd. All rights reserved.