Synthesis of new antibacterial quaternary ammonium monomer for incorporation into CaP nanocomposite

Abstract

Objectives Composites are the principal material for tooth cavity restorations due to their esthetics and direct-filling capabilities. However, composites accumulate biofilms in vivo, and secondary caries due to biofilm acids is the main cause of restoration failure. The objectives of this study were to: (1) synthesize new antibacterial monomers; and (2) develop nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) and antibacterial monomer. Methods Two new antibacterial monomers were synthesized: dimethylaminohexane methacrylate (DMAHM) with a carbon chain length of 6, and dimethylaminododecyl methacrylate (DMADDM) with a chain length of 12. A spray-drying technique was used to make NACP. DMADDM was incorporated into NACP nanocomposite at mass fractions of 0%, 0.75%, 1.5%, 2.25% and 3%. A flexural test was used to measure composite strength and elastic modulus. A dental plaque microcosm biofilm model with human saliva as inoculum was used to measure viability, metabolic activity, and lactic acid production of biofilms on composites. Results The new DMAHM was more potent than a previous quaternary ammonium dimethacrylate (QADM). DMADDM was much more strongly antibacterial than DMAHM. The new DMADDM-NACP nanocomposite had strength similar to that of composite control (p > 0.1). At 3% DMADDM in the composite, the metabolic activity of adherent biofilms was reduced to 5% of that on composite control. Lactic acid production by biofilms on composite containing 3% DMADDM was reduced to only 1% of that on composite control. Biofilm colony-forming unit (CFU) counts on composite with 3% DMADDM were reduced by 2-3 orders of magnitude. Significance New antibacterial monomers were synthesized, and the carbon chain length had a strong effect on antibacterial efficacy. The new DMADDM-NACP nanocomposite possessed potent anti-biofilm activity without compromising load-bearing properties, and is promising for antibacterial and remineralizing dental restorations to inhibit secondary caries.

Novel self-etch adhesive with antibacterial and protein-repellent functions to prevent enamel demineralization

“…QAMs were shown to be promising for dental applications including incorporation into composites and bonding agents, and materials containing QAMs had strong antibacterial properties 14,18,23,27) . The mode of antibacterial action of QAMs was related to quaternary ammonium causing bacteria lysis by binding to cell membranes, leading to cytoplasmic leakage 14) .…”

“…The cured disks were soaked in 200 mL of water and stirred with a magnetic bar at 100 rpm for 1 h to remove any uncured monomers as in previous studies 35,36) ; this was to ensure that the subsequent antibacterial effect came from the polymerized resin and not from the leaching of uncured monomers. The samples were then sterilized with ethylene oxide (Anprolene AN 74i, Andersen, Haw River, NC, USA) and de-gassed for 3 days following the manufacturer's instructions 18,27) . A micro bicinchoninic acid (BCA) method was applied to measure protein adsorption 23,24) .…”

“…The bactericidal efficacy increased with increasing the alkyl chain lengths (CL) of the ammonium groups 17) . Recent studies developed a series of QAMs having CL ranging from 3 to 18 18) . Among these QAMs, dimethylaminohexadecyl methacrylate (DMAHDM) with CL of 16 exhibited the strongest bactericidal efficacy 18) .…”

“…Recent studies developed a series of QAMs having CL ranging from 3 to 18 18) . Among these QAMs, dimethylaminohexadecyl methacrylate (DMAHDM) with CL of 16 exhibited the strongest bactericidal efficacy 18) . When salivary proteins separate the antibacterial material surface from the overlaying biofilm, the contact-inhibition efficacy of QAMs was reduced 14) .…”

Microstructural Features of Current Resin Composite Materials

“…Several direct restorative materials are in fact conducive of biofilm colonization, and therefore, antimicrobial composites have also been proposed [76,77]. The most common approaches are based either on charged sites within the monomer (e.g., quaternary alkylammonium functionalities) [76,78], or the addition of triclosan monomer units [77] or Irgasan-containing delivery beads [79]. While general mechanical properties and polymerization efficiency remain unaltered in comparison to conventional counterparts, the biological activity and substantivity of such materials remain to be elucidated.…”