Protein-repellent and antibacterial dental composite to inhibit biofilms and caries

Abstract

Objectives: Biofilm acids contribute to secondary caries, which is a main reason for dental restoration failures. The objectives of this study were to: (1) develop a protein-repellent and antibacterial composite, and (2) investigate the effects of combining 2-methacryloyloxyethyl phosphorylcholine (MPC) with quaternary ammonium dimethylaminohexadecyl methacrylate (DMAHDM) on composite mechanical properties and biofilm response for the first time.

Methods: MPC, DMAHDM and glass particles were mixed into a dental resin composite. Mechanical properties were measured in three-point flexure. Protein adsorption onto the composites was measured by a micro bicinchoninic acid method. A human saliva microcosm model was used to grow biofilms on composites. Colony-forming unit (CFU) counts, live/dead assay, metabolic activity, and lactic acid production of biofilms were determined.

Results: Incorporation of 3% MPC and 1.5% DMAHDM into composite achieved protein-repellent and antibacterial capabilities without compromising the mechanical properties. Composite with 3% MPC+1.5% DMAHDM had protein adsorption that was 1/10 that of a commercial composite (p<0.05). The composite with 3% MPC+1.5% DMAHDM had much greater reduction in biofilm growth than using MPC or DMAHDM alone (p<0.05). Biofilm CFU counts on composite with 3% MPC+1.5% DMAHDM were more than three orders of magnitude lower than that of commercial control.

Conclusions: Dental composite with a combination of strong protein-repellent and antibacterial capabilities was developed for the first time. Composite containing MPC and DMAHDM greatly reduced biofilm growth and lactic acid production, without compromising mechanical properties of the composite.

Clinical significance: Novel composite with MPC and DMAHDM greatly reduced biofilm activity and is promising to inhibit secondary caries. The dual agents of MPC plus DMAHDM may have wide applicability to other dental materials.

Keywords: Antibacterial property; Caries inhibition; Human saliva microcosm biofilm; Mechanical property; Protein repellent; Resin composite.

Figure 1

Mechanical properties of composites: (A) Flexural strength, and (B) elastic modulus (mean ± sd; n = 6). The composite with 3% MPC + 1.5% DMAHDM had strength and elastic modulus similar to those of a commercial control (p > 0.1). Bars with dissimilar letters indicate values that are significantly different from each other (p < 0.05).

Figure 2

Protein adsorption onto composite surfaces (mean ± sd; n = 6). The composite with 3% MPC, and the composite with 3% MPC + 1.5% DMAHDM, both had much less protein adsorption, which was about 1/10 that of commercial control composite (p < 0.05). Bars with dissimilar letters indicate values that are significantly different from each other (p < 0.05).

Figure 3

Representative live/dead staining images of biofilms adherent on composite disks cultured for 2 days: (A) Commercial control composite, (B) control composite with 0% MPC + 0% DMAHDM, (C) composite with 3% MPC, (D) composite with 1.5% DMAHDM, (E) composite with 3% MPC + 1.5% DMAHDM. (F) area fraction of green staining of live bacteria coverage on composite surface (mean ± sd; n = 6). The live bacteria were stained green, and the dead bacteria were stained red. When live and dead bacteria were in close proximity or on the top of each other, the staining had yellow or orange colors. The composite with 3% MPC + 1.5% DMAHDM had greatly decreased bacterial adhesion, and the biofilms consisted of primarily dead bacteria. Dissimilar letters in (E) indicate values that are significantly different from each other (p < 0.05).

Figure 4

Biofilm viability on composite disks cultured for 2 days: (A) metabolic activity, and (B) lactic acid production (mean ± sd; n = 6). Biofilms on the composite with 3% MPC + 1.5% DMAHDM had metabolic activity that was about 5% that on commercial control (p < 0.05). Lactic acid production by the biofilms on the composite with 3% MPC + 1.5% DMAHDM was about 7% that on the commercial control (p < 0.05). In each plot, values with dissimilar letters are significantly different from each other (p < 0.05).

Figure 5

Biofilm CFU counts on composite disks cultured for 2 days: (A) total microorganisms, (B) total streptococci, and (C) mutans streptococci (mean ± sd; n = 6). All three CFU counts on the composite with 3% MPC + 1.5% DMAHDM were more than 3 orders of magnitude lower than those on commercial control. In each plot, values with dissimilar letters are significantly different from each other (p < 0.05).