Antimicrobial Oligomeric Additives for Dental Adhesives and Composites

Objectives: Composite restorations have been shown to be compromised by secondary caries formation. One quaternary ammonium-containing monomer (QAT), dimethylaminohexadecyl methacrylate (DMAHDM) has shown antimicrobial properties, but at high concentrations, may compromise mechanical properties. The aim of this study is to overcome this issue by tethering QATs to a thiourethane-based oligomer, known to increase toughness in composites.
Methods: One thiourethane oligomer was synthesized as previously described. The pendant thiol content was determined with iodometric titration. DMAHDM was reacted in a 0.1 mol equivalence of SH, confirmed through NMR/IR spectroscopy. 5wt% of DMAHDM:TU was solubilized BisEMA:UDMA:TEGDMA (50:30:20 wt%, BUT), made polymerizable with camphorquinone/amine. Resin discs were photoactivated at 109 mW/cm2 for 2 minutes each side, then roughness and polymerization conversion (by near-IR) were determined. S. mutans biofilm viability (luciferase assay) and biomass (crystal violet assay) were assessed. Data were analyzed with one-way ANOVA/Tukey’s test (alpha=5%).
Results: Data for biofilm viability and biomass are shown in the Table (arbitrary units; same superscript indicates statistical similarity). At the QAT concentration used for the TU:DMAHDM synthesis, the oligomer was not easily dissolved in the resin matrix. BUT:TU:DMAHDM led to no reduction in the biofilm viability (p=0.0728) or biomass (p=0.2803) compared to the controls for both planktonic and biofilm-bound bacteria.
Conclusions: The high QAT concentration on the TU oligomer impaired solubility in the resin matrix. The resulting increased roughness of the surface masked any potential differences in antimicrobial effect. Future studies will include synthesis of TU oligomers with lower QAT content, which should improve its dispersion in the resin matrix and allow for higher concentration of QAT in the material overall.