Synthesis and characterization of dimethacrylates containing quaternary ammonium functionalities for dental applications

Abstract

Objectives: The widespread incidence of recurrent caries highlights the need for improved dental restorative materials. The objective of this study was to synthesize low viscosity ionic dimethacrylate monomers (IDMAs) that contain quaternary ammoniums groups (antimicrobial functionalities) and are compatible with existing dental dimethacrylate-based monomers. Such monomers have the potential to copolymerize with other methacrylate monomers and produce antibacterial polymers.

Methods: Two monomers (IDMA-1 and IDMA-2) were synthesized using the Menschutkin reaction and incorporated at 0-30% (by mass) into a 1:1 (by mass) bisphenol A glycerolate dimethacrylate (BisGMA):triethylene glycol dimethacrylate (TEGDMA) resin. Resin viscosity was quantified using rheology, and polymer degree of conversion (DC) and surface charge density were measured using Fourier transform infrared spectroscopy (FTIR) and fluorescein binding, respectively. Effects of IDMA-1 on initial attachment of Streptococcus mutans and on viability and metabolic activity (via reductase enzymes) of RAW 264.7 macrophage-like cells were quantified.

Results: IDMA-1 and IDMA-2 were prepared and characterized. IDMA-1 was miscible with BisGMA:TEGDMA and slightly increased the resin viscosity and DC. As expected, polymeric surface charge density increased with increasing IDMA-1. Incorporation of 10% IDMA-1 into BisGMA:TEGDMA reduced bacterial colonization without affecting viability or metabolic activity of mammalian cells. Increasing IDMA-1 up to 30% had no additional effect on bacterial coverage, but ≥20% IDMA-1 significantly reduced macrophage density, viability, and metabolic activity. Leachables from polymers containing IDMA-1 were not cytotoxic.

Significance: The Menschutkin reaction provides a facile, convenient means to synthesize new monomers with quaternary ammonium groups for dental and medical applications.

Figure 1

Reaction scheme for the synthesis of low viscosity ionic dimethacrylates containing quaternary ammonium functionalities: (A) IDMA-1, (B) IDMA-2.

Figure 2

FTIR spectra of reactants and products for low viscosity ionic dimethacrylate monomers (A) IDMA-1 and (B) IDMA-2.

Figure 3

Effect of IDMA-1 incorporation on (A) resin viscosity and (B) DC. Each error bar represents one standard deviation. The data points represent the average values, and the lines are the best linear fit of the data.

Figure 4

S. mutans evaluation at 4 h. (A) Images of S. mutans cultured on polymer disks containing increasing amounts of IDMA-1. Scale bars = 10 μm. (B) Individual object area as a function of IDMA-1 concentration. (C) Object density normalized to density on 0 % IDMA-1 disks (control). (D) Fraction of surface covered normalized to 0 % IDMA-1 disks. * P-value < 0.05 as compared to 0 % IDMA-1. Each error bar represents one standard deviation and serves as the estimate of standard uncertainty.

Figure 5

RAW 264.7 viability at 24 h. (A) Images of viability staining. (B) Cell density as a function of IDMA-1 concentration. (C) Viable cell fraction as a function of IDMA-1. * P-value < 0.05 compared to 0 % IDMA-1. ** P-value < 0.05 compared to both 0 % and 10 % IDMA-1. Each error bar represents one standard deviation and serves as the estimate of standard uncertainty.

Figure 6

MTT assay results for RAW 264.7 macrophages at 24 h. (A) MTT activity for cells cultured directly on the polymer disks (disk cells). ** P-value < 0.05 compared to 0 % IDMA-1 and 10 % IDMA-1. (B) MTT activity for cells cultured in the same well as the polymer disks but growing on the TCPS well plate (TCPS cells). No significant differences were present for TCPS cells (p-value > 0.05). Each error bar represents one standard deviation and serves as the estimate of standard uncertainty.