Al Marhubi, S; (2017) Monomer conversion and colour of antibacterial, remineralising dental composites. Doctoral thesis (D.Dent), UCL (University College London).

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Abstract

The aim of this research was to develop a composite dental material that has a higher monomer conversion by replacing the commonly used bulk monomer Bisphenol A-glycidyl methacrylate (BisGMA) with Urethane Dimethacrylate (UDMA) and by replacing Triethylene Glycol Dimethacrylate (TEGDMA) with a more biocompatible and larger diluent monomer Poly-Propylene Glycol Dimethacrylate (PPGDMA). The study assesses the effect of including an adhesion promoting monomer 4- Methacryloyloxyethyl trimellitate anhydride (4META), and different levels of initiator Camphorquinone (CQ) and polymerisable activator2-Dimethyl amino ethyl methacrylate (DMAEMA) on conversion, colour and clarity of composite monomers. The change in mass and volume and the final water sorption were evaluated for active composite materials that contained reminerelising monocalcium phosphate monohydrate (MCPM) and antibacterial, polylysine (PLS) and the colour change effect was assessed following immersion of the active composite discs in different solutions. Methods: Composite monomers were prepared by mixing UDMA and either PPGDMA or TEGDMA at a 3:1 ratio. CQ & DMAEMA were added at 0.5, 0.75 or 1 wt%. All monomers contained the adhesion promoting monomer 4META at 5 wt% intially). A standard 7-μm glass was used at powder/liquid ratio (PLR) of 4. UV-spectrometry was used to assess the colour and clarity of the monomers. FTIR (infrared) was employed to determine monomer conversion (MC) with 40s light exposure at 1 mm depth. With the elimination of the activator DMAEMA, clear UDMA/PPGDMA monomers that also contained 3 wt% 4META were used with hybrid glass, MCPM and PLS to contract composite discs that were used to check mass and volume changes at 37 Co. The effect of extrinsic discolouration of the experimented MCPM and PLS containing composites was also evaluated visually and using a colour measuring instrument (spectroshade). Values of colour change were recorded in the form of ΔE and the change was compared to a commercial material Z250. Results: Composites prepared with PPGDMA had approximately 20% higher conversion. DMAEMA resulted in increased clarity of the monomers by enhancing dissolution of 4META as demonstrated by UV spectrometry. The addition of DMAEMA had no significant effect on MC of monomers containing PPGDMA but increased MC in those containing TEGDMA. CQ concentration enhanced colour. Maximum conversion was obtained with 0.75 wt% CQ in UDMA/PPGDMA, 3 wt% 4META composites. Active composites with PLR 3 and 5 wt% of PLS resulted in the highest percentage in mass change with more than 4%. Higher volume changes were obtained with formulations of PLR 4 and 5 wt% PLS. There was no significant difference on effect of extrinsic discolouration of composite discs when visually assessed, however, using the Spectroshade it was clear that composites with PLR 5 were discoloured the most. Conclusions: Monomer conversion can be improved by changing the monomer content of dental composites. This will result in a reduction of leaching of unreacted monomers into the oral cavity and therefore improve biocompatibility. Composites containing PPGDMA had a better monomer conversion compared to those with TEGDMA. In this research, the main intrinsic factor that affected the colour of the monomer was the concentration of CQ whereas the effect of extrinsic discolouration can be attributed to PLR.

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