INTRODUCTION: Commercial resin-based composites are mainly composed of dimethacrylate-based monomers, such as triethyleneglycol dimethacrylate (TEGDMA), inorganic fillers and a coupling agent. Cured resinbased composites have no antibacterial effect against oral bacteria [1] and half of all fillings replaced are because of new caries [2]. Chitosan is a natural carbohydrate polymer derived from the deacetylation of chitin. Chitosan has been shown to have an inhibitor effect on the adherence of oral bacteria onto human tooth surfaces [3]. Chitosan has a polycationic carbohydrate structure with three reactive functional groups. The positive charged amino groups are suggested to be the cause of chitosan’s antimicrobial activity. Functionalization of chitosan with methacrylate groups allows for copolymerization with the resin in dental materials. This means that chitosan can be incorporated in resin-based composites in order to produce material with antibacterial activity. The aim of the present study was to study the antibacterial effects of modified chitosan, adding functional methacrylate groups.

METHODS: Low molecular chitosan, MW 150 kDa, ca 80 % deacetylation, was modified with methacrylate groups using a method of FloresRamirez [4]. The product was examined for its ability to inhibit planktonic growth and formation on biofilm for Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli. Planktonic growth after 18 h was examined for different concentrations of chitosan in growth medium, by counting of colony forming units (CFU). Biofilm, on polystyrene or composite discs, was allowed to form, 18 h for S. epidermidis and 24 h for E. coli. Total mass of biofilms were investigated by measuring optical density (OD) at 530 nm after staining with 0.1% solution of safranin. Chitosan is insoluble in most solvents, but is soluble in dilute organic acids and all experiments were therefore done at a pH 5.9.

RESULTS: Chitosan demonstrated to inhibit planktonic growth and biofilm formation depending on the concentration of chitosan in the medium. The results of the two test models suggest that chitosan has a higher antibacterial activity against S. epidermidis than against E. coli. Chitosan could be modified with a methacrylate functionality, but the modified chitosan had poor solubility and had low antibacterial effect compared to natural chitosan.

DISCUSSION & CONCLUSIONS: Modified chitosan was prepared and incorporated into resinbased composites during polymerization. However, no antibacterial effect on the formation of biofilm was observed. This could be explained by blocking of antibacterial amino groups during modification. The study continues with improvements of the chitosan modification.

Antibacterial effects of native and methacrylate modified chitosan
Dragland IS, Knarvang T, Kopperud HBM.
Eur Cells Mater 2013; 26. Suppl 2: 2. ISSN 1473-2262.