Immobilization of Antibacterial Monomer onto Dentin Substrate by Non-thermal Plasma

Objectives: The antibacterial effects of quaternary ammonium methacrylates (QAMs) included in adhesives are not sustainable due to their no/little interactions with dentin substrate. Non-thermal atmospheric plasma (NTAP) brush has been regarded as a predominate technique for surface modification/functionalization. In this first of its kind study, the use of NTAP on immobilization of dimethylaminohexadecyl methacrylate (DMAHDM), a typical QAM, onto dentin bonding substrate, and resulting antibacterial activity against Streptococcus mutans were investigated
Methods: Mid-coronal human dentin was sectioned into 4 X 2 X 0.7 mm slices and a bonding substrate with several-micron-demineralized layer was created by using 0.5 mol/L EDTA solution for 30 min. 5 or 30 wt% DMAHDM was applied onto demineralized dentin substrate with or without plasma exposure (10 W, 30 s). SEM and FTIR spectroscopy were employed to verify the immobilization/grafting of DMAHDM onto the substrate. Antibacterial activity of the resulting substrate was assessed by using tests on colony-forming unit (CFU) and confocal scanning laser microscopy (CSLM). Effects of saliva pellicle treatment and aging process on the DMAHDM immobilized-substrate were also evaluated.
Results: The SEM and FITR results demonstrated that plasma-treatment could induce DMAHDM immobilization onto dentin substrate, which was further verified via quantitative IR spectral analysis (i.e. 2925 cm^-1/1635 cm^-1, 1455 cm^-1/1635 cm^-1, DMAHDM/collagen ratios). Comparing with non-plasma-treated, the plasma-treated dentin bonding substrate, with CFU 4 log lower, exhibited much stronger inhibitory effects, which were minimally affected by saliva or aging.
Conclusions: The DMAHDM-immobilized dentin substrate showed effective and sustained antibacterial characteristics