Antibacterial activity of dental composites containing quaternary ammonium polyethylenimine nanoparticles against Streptococcus mutans
Introduction
Composite resin materials are widely used in the dental clinic for replacement of hard tissues [1]. Although the mechanical properties and wear resistance of these materials have been improved substantially [2], their antibacterial properties are still limited [3], [4]. These resin-based materials accumulate more dental plaque than other restorative materials both in vitro [5], [6], and in vivo [7], [8], [9], which may result in secondary caries [10]. A number of reports described experiments in which composite resins were impregnated with antibacterial agents such as antibiotics, silver ions, iodine and quaternary ammonium compounds, and these agents were gradually released [11], [12], [13], [14]. However, release of antibacterial agents into the surrounding milieu at various releasing rates had several disadvantages: a decrease in the mechanical properties of the carrier material over time, short-term effectiveness, and possible toxicity if the release is not properly controlled [15], [16], [17], [18]. As compared with conventional antibacterial agents of low molecular weight, the advantages of polymeric antibacterial agents are that they are non-volatile, chemically stable, can be chemically bound within the polymer carrier via active groups for improved integration in the composite, and are difficult to penetrate through the skin. It has been reported that polycations exhibit antibacterial properties, i.e. interact with and disrupt bacterial cell membranes [19]. A number of polymers with antibacterial properties were developed for this purpose, including soluble and insoluble pyridinium-type polymers involved in surface coating [20], [21], [22]. Several reports have described incorporation of a methacryloyloxydodecyl pyridinium bromide (MDPB) monomer in composite resins that showed no release of the incorporated monomer but still exhibited antibacterial properties [23], [24]. The hypothesis tested in this study was that the insoluble crosslinked quaternary ammonium polyethylenimine (PEI) nanoparticles in composite resin restorative materials have a stable and long-lasting antibacterial effect against oral bacteria, Streptococcus mutans. Furthermore, the addition of a small amount (1% w/w) of nanoparticles to the composite should not affect the flexural strength of the commercial materials. The mechanical properties of the new composites were close to those of the original composite possessing strong antibacterial activity upon contact that lasted for at least 1 month.
Section snippets
PEI nanoparticle preparation
An aqueous solution of PEI was lyophilized to dryness before use. PEI (18.65 g, 0.434 mol) of 1,000,000—6,00,000 Da dissolved in 186 ml of absolute ethanol was crosslinked with 8.7 mmol dibromopentane (PEI monomer/dibromopantane mole ratio: 1:0.02) at reflux conditions for 24 h. The generated HBr was neutralized with 1 g of sodium hydroxide under the same conditions for an additional 24 h. The resulting residue was purified from NaBr by gravitational filtration and dried under reduced pressure to yield
Quaternary ammonium PEI nanoparticles
Nanoparticles with N-octyl, N,N-dimethyl ammonium groups were prepared from PEI by crosslinking with 1,5-dibromopentane, followed by alkylation with bromooctane and quaternarization with methyl iodide. Nanoparticles of less than 100 nm were obtained reproducibly using this method. The data analysis for the nanoparticles used in this study is summarized in Table 1. The IR, NMR and elemental analysis indicate significant content of quaternary ammonium groups in the particles.
Direct contact test
The average optical
Discussion
Antimicrobial surfaces have been a major challenge, particularly in dentistry where bacterial biofilms tend to accumulate and propagate on solid surfaces. One way to address this problem is to engineer materials with antibacterial properties. Antibacterial properties can be achieved by modifying the composite resins polymers. In this study, this was achieved by incorporating quaternary ammonium insoluble nanoparticles in dental commercial composite resins. In vitro results showed that these
Conclusions
The nanoparticles in this study were made from crosslinked poly(ethyleneimine) (PEI) that underwent quaternarization with octyl groups, followed by methylation to form quaternary amines. Antimicrobial tests using S. mutants showed that these PEI nanoparticles when incorporated in dental composite resins at low concentration (1%) exhibited a strong antibacterial effect against the tested bacteria. Composite resin materials incorporated with PEI nanoparticles maintained antibacterial properties
Acknowledgments
This study was conducted in part at the Ronald Goldstein Research Center, Faculty of Dentistry, Hadassah-Hebrew University.
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Affiliated with the Alex Gross Center for Drug Design and Synthesis and the David R. Bloom Center for Pharmaceutical Research at the Hebrew University, Lionel Jacobson Chair in Medicinal Chemistry.