Protein-repellent and antibacterial functions of a calcium phosphate rechargeable nanocomposite.

Objectives: We recently developed a new rechargeable composite with nanoparticles of amorphous calcium phosphate (NACP) having long-term calcium (Ca) and phosphate (P) ion release; however, this composite was not antibacterial. The objectives of this study were to: (1) incorporate dimethylaminohexadecyl methacrylate (DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine (MPC) into rechargeable NACP composite, and (2) investigate mechanical properties, protein adsorption and biofilm response of composite, and the pH of biofilm medium.

Methods: MPC, DMAHDM and NACP were mixed into a resin of ethoxylated bisphenol A dimethacrylate (EBPADMA) and pyromellitic glycerol dimethacrylate (PMGDM). Protein adsorption was measured using a micro bicinchoninic acid method. A human saliva microcosm biofilm model was used to grow biofilms on composites. Colony-forming units (CFU), live/dead assay, metabolic activity, and biofilm culture medium pH were determined. The tests used n=6.

Results: The composite with 3% MPC had protein adsorption an order of magnitude less than that of a commercial composite (p<0.05). Control composites were fully covered by live bacteria. Live bacteria were reduced via MPC; 3% MPC+3% DMAHDM had the least live bacteria (p<0.05). The composite with 3% MPC+3% DMAHDM inhibited biofilm growth and viability, reducing biofilm CFU by 3 log compared to commercial control composite (p<0.05), while having a flexural strength similar to that of the commercial composite (p>0.1). The composite containing 3% MPC+3% DMAHDM with biofilm culture maintained a pH above 6.5, while the commercial composite had a cariogenic pH of 4.2 in biofilm culture medium.

Conclusions: The new protein-repellent and antibacterial NACP rechargeable composite substantially reduced biofilm growth, yielding a much higher pH than a commercial composite.

Clinical Significance: This novel bioactive nanocomposite is promising to protect tooth structures from biofilm acids and caries. The method of using NACP, MPC and DMAHDM may be applicable to other dental materials to reduce plaque buildup and secondary caries.