Chemical Analysis of Dental Adhesives and Their Application with Self-Sealing Composites

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University College London
Background and aims: Conventional resin composite materials typically require preconditioning of the tooth substrate, prior to their application, for reliable adhesion to the dental tissue. To simplify the adhesive process and reduce the potential for error arising from the additional steps, self-adhesive materials were introduced. These still, however, require improvements to overcome limited bonding and cavity sealing ability. The aim of this study was to develop novel methods to evaluate the chemical composition, polymerization and evaporation kinetics of different commercial adhesives. Furthermore, to compare their bonding to that of self-adhesive resin composite formulations. Methods: An FTIR model was used to evaluate the chemical component ratios of 8 commercial adhesive resins. The change in the chemical composition of three of those adhesives was further investigated during the processes of solvent drying and polymerization. Self-adhesive materials were developed by mixing a base monomer (UDMA), a diluent monomer (PPGDMA) and a functional monomer (4-META) with a hybrid filler at a 3:1 powder-to-liquid ratio. The filler included a remineralizing material, monocalcium phosphate monohydrate (MCPM), and an antibacterial material, poly-lysine (PLS) at varying levels. Bond strength and interfacial adaption observed via micro-computed tomography (Micro-CT), scanning electron and confocal microscopy were evaluated. VI Results: The FTIR analysis provided evidence that diverse bonding systems contained various concentrations and compositions of hydrophilic/hydrophobic monomers, functional acidic monomers, solvents, and fillers. In addition, the variable chemical composition of the adhesive systems affected the rate and level of solvent evaporation and degree of conversion. Micro-CT demonstrated that the experimental resin composite with the lowest MCPM and PLS concentration displayed the smallest gap at the interface compared to 3 commercial filling materials. In addition, it was also able to inhibit matrix metalloproteinase activity at the interface as observed under confocal microscopy. Conclusion: The type and concentrations of the monomers and solvents in the adhesives have a significant effect on polymerization and evaporation kinetics. Additionally, adding PLS and MCPM is beneficial in terms of gap reduction at the interface, dentine bonding strength and inhibition of matrix metalloproteinase’s activity.
Resin composite, Dental adhesives