Antibacterial-remineralizing Nanocomposite Inhibit Root-caries Pathogen Biofilms and Protect Root-dentin Hardness

Objectives: The world population continues to age. Seniors have a higher incidence of root caries. The objectives of this study were to: (1) develop a bioactive composite with antibacterial and calcium (Ca) and phosphate (P) ion-releasing capabilities via dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); (2) establish a biofilm model of root caries pathogens of Streptococcus mutans, Lactobacillus acidophilus, and Candida albicans, and determine root dentin demineralization and hardness at the restoration margins under root pathogen multi-species biofilms for the first time.
Methods: Five groups were tested: (1) Heliomolar nanocomposite (Commercial control); (2) Experimental composite control (0% NACP, 0% DMAHDM); (3) Remineralizing composite (30% NACP); (4) Antibacterial composite (3% DMAHDM). (5) Remineralizing and antibacterial composite (NACP+DMAHDM). Colony-forming units (CFU), lactic acid and polysaccharide of biofilms were evaluated (n=6). Ca-P ions releases were measured. Demineralization of bovine root-dentin with restorations was induced via multi-species biofilms, and root-dentin hardness was measured.
Results: Adding DMAHDM and NACP into composite did not compromise the mechanical properties (P>0.05). Biofilm lactic acid, polysaccharides and CFU were greatly reduced via DMAHDM (P<0.05). Ca-P ion releases of NACP and DMAHDM+NACP composites were substantially increased at cariogenic low pH. With multi-species biofilm acid attack, root-dentin hardness (GPa) decreased to 0.12±0.03 for Commercial control, and 0.11±0.03 for Experimental control. Root-dentin hardness was 0.20±0.04 for NACP group, 0.21±0.04 for DMAHDM group, and 0.30±0.03 for NACP+DMAHDM group (P<0.05). For root-dentin cross-sectional hardness, NACP+DMAHDM group produced the greatest hardness, approximately 2-fold those of control groups (P<0.05).
Conclusions: The novel DMAHDM+NACP nanocomposite had strong antibacterial effects and Ca-P ion releases. When tested in a root cavity model, DMAHDM+NACP nanocomposite substantially reduced root dentin demineralization and protected dentin hardness around restorations under biofilm acids. Therefore, this novel bioactive composite is promising to inhibit root caries.