Anti-biofilm and Modulating Biofilm Equilibrium via Novel Bonding Agent

Objectives: Dental caries is associated with biofilms and disequilibrium between cariogenic species and commensal residents. This study aimed to develop a novel bonding agent containing dimethylaminohexadecyl methacrylate (DMAHDM) and investigate its dual ability of anti-biofilm and modulating biofilm species equilibrium for the first time.
Methods: DMAHDM was incorporated into Scotchbond Multi-Purpose adhesive and primer at mass% of 0%, 2.5%, 5%, 7.5% and 10%. The highest concentration of 10% was chosen without compromising the mechanical properties. A multispecies biofilm model consisting of Streptococcus mutans, Streptococcus sanguinis and Streptococcus gordonii was used to grow 3-day biofilms on resins. Colony-forming units (CFUs), metabolic activity and live/dead were evaluated to investigate biofilms. Lactic acid and polysaccharide productions were measured to assess biofilm cariogenicity. TaqMan realtime polymerase chain reaction was used to determine each species proportion.
Results: Bonding agents containing DMAHDM possessed a strong anti-biofilm function. Compared to control, biofilm CFUs in DMAHDM groups were reduced by nearly 4 orders of magnitude. Biofilm metabolic activity was the lowest in 10% DMAHDM group (0.11±0.01) OD_540nm/cm², and the highest in control (1.90±0.25) OD_540nm/cm² (p<0.05). Biofilm lactic acid in 10% DMAHDM group (0.99±0.20) mmol/L was substantially lower than control (13.18±1.60) mmol/L (p<0.05). Biofilm polysaccharide production in 10% DMAHDM group was (28.32±8.33) mg/mL, much lower than (271.19±17.25) mg/mL in control (p<0.05). The cariogenic Streptococcus mutans proportion in biofilms on DMAHDM-containing resins was 49% for 2.5% DMAHDM, 22% for 5% DMAHDM, 19% for 7.5% DMAHDM, and 15% for 10% DMAHDM. In contrast, in control biofilm with 0% DMAHDM, the Streptococcus mutans proportion was an overwhelming 90%.
Conclusions: Incorporating DMAHDM into bonding agent yielded potent anti-biofilm properties and modulated biofilm species toward a healthy composition with substantially reduced cariogenic species proportion. These dual functions of DMAHDM suggest that it is a promising agent for dental applications to combat caries.