Methods: QADM was bis(2-methacryloyloxyethyl) dimethylammonium bromide (ionic dimethacrylate-1). It was synthesized from 2-(N,N-dimethylamino)ethyl methacrylate and 2-bromoethyl methacrylate. NanoAg was synthesized by dissolving Ag 2-ethylhexanoate salt in 2-(tert-butylamino)ethyl methacrylate. Three antibacterial nanocomposites were developed: NanoACP+QADM; NanoACP+NanoAg; NanoACP+QADM+NanoAg. Composite disks were inoculated with Streptococcus mutans. Biofilm viability, metabolic activity, and lactic acid production were measured.
Results: Flexural strength of NanoACP+QADM (53±7 MPa), NanoACP+NanoAg (67±4 MPa), and NanoACP+QADM+NanoAg (54±12 MPa) matched those of commercial control composites (Helimolar: 57±12 MPa; Renamel: 56±8 MPa) (p>0.1). Colony-forming unit (CFU) counts (x106) of biofilms on NanoACP+QADM+NanoAg was (8±1), significantly lower than (120±11) on Helimolar, and (130±11) on Renamel (p<0.05). NanoACP+QADM+NanoAg had lower CFU counts than NanoACP+QADM (55±7) and NanoACP+NanoAg (31±6) (p<0.05). MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that NanoACP+QADM+NanoAg significantly (p<0.05) reduced the metabolic activity of biofilms to (1.4±0.2 A540/cm2), compared to (2.2±0.1 A540/cm2) for Helimolar, and (2.7±0.3 A540/cm2) for Renamel. Lactic acid production of biofilms on NanoACP+QADM+NanoAg was (6.4±0.4 mmol/L), significantly (p<0.05) less than those on commercial composites (Helimolar: 13.2±0.8 mmol/L; Renamel: 16.7±0.6 mmol/L). Lactic acid on NanoACP+QADM+NanoAg (6.4±0.4 mmol/L) was significantly (p<0.05) less than NanoACP+QADM (8.2±0.9 mmol/L) and NanoACP+NanoAg (7.3±0.7 mmol/L) (p<0.05). Therefore, combining QADM with NanoAg into the same composite rendered it more strongly antibacterial than either QADM or NanoAg alone.
Conclusions: The novel NanoACP+QADM+NanoAg nanocomposite was strongly-antibacterial and greatly reduced the CFU counts, metabolic activity, and lactic acid production of S. mutans biofilms, while possessing mechanical properties similar to commercial composites. This nanocomposite is promising to have the double benefits of remineralization and antibacterial capabilities to inhibit dental caries. Supported by NIH R01 DE17974 and DE14190 (HX), and NIDCR-NIST Interagency Agreement Y1-DE-7005-01.
Keywords: Antibacterial nanocomposite, Biofilm and Caries
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