Bactericidal dental nanocomposites containing 1,2,3-triazolium-functionalized POSS additive prepared through thiol-ene click polymerization

- Use of azide-alkyne click reaction to generate triazolium functional POSS.
- Use of thiol-ene/methacrylate polymerization to prepare dental materials with low shrinkage strain.
- Lower deterioration of mechanical strength under wet condition by proper selection of biocidal additive.
- Preparation of dental materials with improved bactericidal activity against Streptococcus mutans.

ObjectiveDeterioration of mechanical strength for the dental composite containing ionic bactericidal compounds restricts the widespread utilization of this class of useful materials. This problem is originated from the reduction of the intermolecular interaction of polymeric network due to plasticization effect of absorbed water molecules penetrated between the chain segments. The main goal of this study is the synthesis of the highly efficient bactericidal additive with low hydrophilicity and consequently the least adverse effect on the final mechanical strength of the dental composite.MethodsThe bactericidal 1, 2, 3-triazolium functional groups were chemically anchored on the surface of hydrophobic POSS nanoparticles (Triazolium-POSS) and incorporated into a dental restorative system composed of a ternary thiol-allyl ether-methacrylate resin and glass fillers. A similar system was also prepared, in which the POSS additive was replaced with quaternized dimethyl aminoethyl methacrylate monomer (DMAEMA-BC). The chemical structure of POSS derivatives was evaluated by 1HNMR and FTIR spectra. The water uptake of dental composites was evaluated at days 1 and 14 after immersion into water. The bactericidal activity of composite specimens against Streptococcus mutans (ATCC 35668) was determined based on ASTM E 2180 - 07. The flexural properties of samples were investigated through three-point bending assay and the shrinkage-strain of photo-cured resins was measured using the bonded-disk technique. The degree of conversion (DC %) of methacrylate functions was followed by FTIR spectroscopy. MTT assay was performed to investigate the cytocompatibility of samples.ResultsRegardless of the partial increase in water uptake for Triazolium-POSS-containing sample, this parameter was much favor than the composite made from DMAEMA-BC. Therefore, the lower decline in flexural properties was recorded under the wet condition for the former system. Incorporation of Triazolium-POSS had no significant effect on shrinkage strain and cytocompatibility of composite specimen, meanwhile, a higher degree of conversion of methacrylate functional groups was recorded. The Triazolium-POSS-containing nano composite showed significantly higher bactericidal activity against Streptococcus mutans than another studied model system.SignificanceThe new derivative of bactericidal POSS nanoparticles decorated with 1, 2, 3-Triazolium moieties is a highly efficient bactericidal compound. If Triazolium-POSS is incorporated into a proper dental resin formulation, it can provide a strong bactericidal activity for dental materials; in the meantime, it leads to minimum deterioration of their mechanical strength due to its low water uptake.

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