Methods: Scotchbond Multi-Purpose (SBMP) served as the parent bonding agent. DMADM and NAg were incorporated into the primer and adhesive. A dental plaque microcosm biofilm model was used to investigate biofilm metabolic activity, colony-forming unit (CFU) counts, and lactic acid production (n=6). Dentin shear bond strengths were measured (n=10).
Results: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the new DMADM (6.10 µg/mL and 12.21 µg/mL, respectively) were orders of magnitude lower than those of a previously-synthesized quaternary ammonium dimethacrylates (QADM) (1.25×104 µg/mL and 2.5×104 µg/mL, respectively). The bacteria inhibition zones of un-cured primer containing DMADM was much larger than that of QADM (p<0.05). Cured primer/adhesive samples containing DMADM and NAg greatly reduced biofilm metabolic activity (p<0.05). Combining DMADM with NAg in primer/adhesive resulted in less CFU than using DMADM alone, including total microorganism, total streptococci and mutans streptococci (p<0.05). Lactic acid production by biofilms was reduced by 20-fold via DMADM and NAg (0.52±0.18 mmol/L), compared to commercial bonding agent control (18.49±2.61 mmol/L). Biofilms on control disks had primarily live bacteria. In contrast, substantial increases in dead bacteria occurred when DMADM, or DMADM+NAg, were incorporated into primer/adhesive. Incorporation of the new DMADM and NAg into primer and adhesive did not adversely affect the dentin bond strength (p>0.1).
Conclusions: Novel antibacterial primer and adhesive containing the new monomer DMADM are promising to combat residual bacteria in the tooth cavity and the invading bacteria at tooth-restoration margins to inhibit caries. In addition, DMADM and NAg are promising for incorporation into a wide range of dental adhesive systems and restoratives.