Synthesis and characterization of novel polymerizable bis-quaternary ammonium dimethacrylate monomers with antibacterial activity as an efficient adhesive system for dental restoration

This paper focuses on the analysis and synthesis of two new gemini or bis-quaternary ammonium dimethacrylate compounds (bis-QAC) with different spacer lengths (DMBB and DMBH) for the first time. These innovative quaternary ammonium-based resin monomers can be employed as effective dental adhesives, due to their antibacterial properties against the Streptococcus mutans bacteria (bacteria in dental plaque). In this research, this blend of monomers is incorporated into a commercial adhesive (1wt% bis-QAC and 99wt% Tetric N-Bond). The chemical structures and thermal behavior of all prepared compounds are confirmed by FTIR, H-1-NMR, C-13-NMR and TGA/DTG. Moreover, mechanical properties, degree of conversion (monomer to polymer) and cell cytotoxicity of the samples containing an antibacterial agent are compared to commercial adhesives. Finally, experimental results illustrate that the minimum inhibitory concentration of adhesives with new bis-QAC is significantly lower than samples without an antimicrobial monomer. Moreover, the mixture of gemini QAC with adhesive does not demonstrate any adverse effect on the degree of conversion and bond strength of the experimental adhesive. Furthermore, specimens of DMBH indicate a higher antibacterial characteristic, despite the reduction in the cell viability.