Physicochemical, Mechanical, and Antimicrobial Properties of Novel Dental Polymers Containing Quaternary Ammonium and Trimethoxysilyl Functionalities

Abstract

The aims of this study were to evaluate the physicochemical and mechanical properties, antimicrobial (AM) functionality, and cytotoxic potential of novel dental polymers containing quaternary ammonium and trimethoxysilyl functionalities (e.g., N-(2-(methacryloyloxy)ethyl)-N,N-dimethyl-3-(trimethoxysilyl)propan-1-aminium iodide (AM_sil1) and N-(2-(methacryloyloxy)ethyl)-N,N-dimethyl-11-(trimethoxysilyl)undecan-1-aminium bromide (AM_sil2)). AM_sil1 or AM_sil2 were incorporated into light-cured (camphorquinone + ethyl-4-N,N-dimethylamino benzoate) urethane dimethacrylate (UDMA)/polyethylene glycol-extended UDMA/ethyl 2-(hydroxymethyl)acrylate (EHMA) resins (hereafter, UPE resin) at 10 or 20 mass %. Cytotoxic potential was assessed by measuring viability and metabolic activity of immortalized mouse connective tissue and human gingival fibroblasts in direct contact with monomers. AM_sil-UPE resins were evaluated for wettability by contact angle measurements and degree of vinyl conversion (DVC) by near infra-red spectroscopy analyses. Mechanical property evaluations entailed flexural strength (FS) and elastic modulus (E) testing of copolymer specimens. The AM properties were assessed using Streptococcus mutans (planktonic and biofilm forms) and Porphyromonas gingivalis biofilm. Neither AM_sil exhibited significant toxicity in direct contact with cells at biologically relevant concentrations. Addition of AM_sils made the UPE resin more hydrophilic. DVC values for the AM_sil-UPE copolymers were 2%-31% lower than that attained in the UPE resin control. The mechanical properties (FS and E) of AM_sil-UPE specimens were reduced (11%-57%) compared to the control. Compared to UPE resin, AM_sil1-UPE and AM_sil2-UPE (10% mass) copolymers reduced S. mutans biofilm 4.7- and 1.7-fold, respectively (p ≤ 0.005). Although not statistically different, P. gingivalis biofilm biomass on AM_sil1-UPE and AM AM_sil2-UPE copolymer disks were lower (71% and 85%, respectively) than that observed with a commercial AM dental material. In conclusion, the AM function of new monomers is not inundated by their toxicity towards cells. Despite the reduction in mechanical properties of the AM_sil-UPE copolymers, AM_sil2 is a good candidate for incorporation into multifunctional composites due to the favorable overall hydrophilicity of the resins and the satisfactory DVC values attained upon light polymerization of AM_sil-containing UDMA/PEG-U/EHMA copolymers.

Keywords: antimicrobial effect; biofilms; cytotoxicity; dental resins; mechanical properties; physicochemical properties; quaternary ammonium methacrylates.

Figure 1

Skeletal structural formulas of AM_sil1 (a) and AM_sil2 (b) monomers.

Figure 2

Percent control value of viability (a) and metabolic activity (b) of CCL1 cells exposed to 2-fold serial dilutions of AM_sil1 (≤8.34 mmol/L) for 24 or 72 h. Data represent mean ± standard error for five independent replicates tested in triplicate.

Figure 3

Percent control value of viability of human gingival fibroblast (HGF) cells exposed to 2-fold serial dilutions of AM_sil1 (≤8.34 mmol/L) for (a) 24 h or (b) 72 h. Data represent mean ± standard error for five independent replicates tested in triplicate.

Figure 4

Percent control value of viability of CCL1 cells exposed to 2-fold serial dilutions of AM_sil2 (≤7.28 mmol/L) for 24 or 72 h. Data represent mean ± SEM for five independent replicates tested in triplicate. * indicates p ≤ 0.05 when compared to concentrations ≤ 0.91 mmol/L within the same time period. + indicates p ≤ 0.05 when compared to 0.455, 0.228, or 0.114 mmol/L concentrations within same time period.

Figure 5

Percent control value of viability of HGF cells exposed to 2-fold serial dilutions of AM_sil2 (≤7.28 mmol/L) for 24 h or 72 h. Data represent mean ± SEM for five independent replicates tested in triplicate. + indicates p ≤ 0.05 when compared to concentrations ≤ 0.455 mmol/L within same time period. * indicates p ≤ 0.05 when compared to concentrations ≤ 0.91 mmol/L within same time period. ^ indicates p ≤ 0.05 when compared to concentrations ≤ 0.114 mmol/L within same time period. $ indicates p ≤ 0.05 when compared to concentrations ≤ 0.228 mmol/L within same time period.

Figure 6

The contact angle (CA) values of AM_sil–UPE and UPE control indicative of the changes in resin’s overall hydrophilicity/hydrophobicity upon introduction of AM_sil monomers at 10 and 20 mass % relative to UPE. Shown are mean values + standard deviation of four repetitive measurements in each experimental group.

Figure 7

The values for degree of vinyl conversion (DVC) attained 24 h post-cure in AM_sil–UPE copolymers compared to no-AM UPE control. Shown are mean values + standard deviation of three repetitive measurements.

Figure 8

(a) Flexural strength and (b) tensile elasticity of AM_sil–UPE copolymers in comparison with the UPE control. Indicated are mean values + standard deviation of three specimens.

Figure 9

Streptococcus mutans biofilm growth inhibition by the experimental AM_sils–UPE (10 mass %) copolymers compared to UPE control resin. Bar height indicates mean + standard deviation of 5 specimens/group.

Figure 10

Porphyromonas gingivalis biofilm growth inhibition by the experimental AM_sils–UPE (10 mass %) copolymers compared to UPE control resin. Bar height indicates mean + standard deviation of 5 specimens/group.