Effect of water-aging on the antimicrobial activities of an ORMOSIL-containing orthodontic acrylic resin

Abstract

Quaternary ammonium methacryloxy silicate (QAMS), an organically modified silicate (ORMOSIL) functionalized with polymerizable methacrylate groups and an antimicrobial agent with a long lipophilic alkyl chain quaternary ammonium group, was synthesized through a silane-based sol-gel route. By dissolving QAMS in methyl methacrylate monomer, this ORMOSIL molecule was incorporated into an auto-polymerizing, powder/liquid orthodontic acrylic resin system, yielding QAMS-containing poly(methyl methacrylate). The QAMS-containing acrylic resin showed a predominant contact-killing effect on Streptococcus mutans (ATCC 35668) and Actinomyces naeslundii (ATCC 12104) biofilms, while inhibiting adhesion of Candida albicans (ATCC 90028) on the acrylic surface. The antimicrobial activities of QAMS-containing acrylic resin were maintained after a 3month water-aging period. Bromophenol blue assay showed minimal leaching of quaternary ammonium species when an appropriate amount of QAMS (<4wt.%) was incorporated into the acrylic resin. The results suggest that QAMS is predominantly co-polymerized with the poly(methyl methacrylate) network, and only a minuscule amount of free QAMS molecules is present within the polymer network after water-aging. Acrylic resin with persistent antimicrobial activities represents a promising method for preventing bacteria- and fungus-induced stomatitis, an infectious disease commonly associated with the wearing of removable orthodontic appliances.

Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Figures

Fig. 1

Percentage of live bacteria within the biovolume-of-interest (i.e. the volume of biofilm from the base to the 24th µm of a z-stack), and within the contact-surface biomass (i.e. within 2 µm from disk surface) of biofilms that were grown on acrylic resin disks from the control (0 wt.% QAMS) and four experimental groups (0.4–6 wt.% QAMS). (A, B) S. mutans biofilms. (C, D) A. naeslundii biofilms. For each parameter (upper case letters for baseline and lower case letters for 3 months), groups with the same letters are not statistically significant (p > 0.05). For comparisons between baseline and 3 months, groups connected with a horizontal bar are not statistically significant (p > 0.05).

Fig. 2

Representative live/dead stained S. mutans biofilms grown on the surfaces of 3 month water-aged acrylic disks with varied QAMS concentrations. Green: live bacteria; red: dead bacteria. Left column represents 3-D plots of the 24 µm thick biovolume-of-interest from each biofilm. Right column represents the biomass of live and dead bacteria as a function of biofilm level (Z step = 2 µm).

Fig. 3

Representative live/dead stained A. naeslundii biofilms grown on the surfaces of 3 month water-aged acrylic disks with varied QAMS concentrations. Green: live bacteria; red: dead bacteria. Left column represents 3-D plots of the 24 µm thick biovolume-of-interest from each biofilm. Right column represents the biomass of live and dead bacteria as a function of biofilm level.

Fig. 4

Representative merged images showing 2-D biomasses of C. albicans that adhered and grew on surfaces of 3 month water-aged acrylic resin disks containing: (A) 0 wt.% QAMS, (B) 0.4 wt.% QAMS, (C) 2 wt.% QAMS, (D) 4 wt.% QAMS, (E) 6 wt.% QAMS. For all images, bar = 100 µm. (F) Percentage distributions of live fungi within the 2-D biomass on the surfaces of acrylic disks with varied QAMS concentrations. Data obtained from the baseline and 3 month water-aged specimens were included in the statistical analysis. For each parameter (upper case letters for baseline and lower case letters for 3 months), groups with the same letters are not statistically significant (p > 0.05). For comparisons between baseline and 3 months, groups connected with a bar are not statistically significant (p > 0.05).

Fig. 5

Colony forming unit (CFU) cell viability counts and XTT cell metabolism assays of microorganisms grown on orthodontic acrylic resin disks from the control (0 wt.% QAMS) and four experimental groups (0.4–6 wt.% QAMS). (A, D) S. mutans biofilms. (B, E) A. naeslundii biofilms. (C, F) C. albicans. For each parameter (upper case letters for baseline and lower case letters for 3 months), groups with the same letters are not statistically significant (p > 0.05; note – only groups that are not significantly different are labeled). For comparisons between baseline and 3 months, groups connected with a bar are not statistically significant (p > 0.05).

Fig. 6

Leaching of quaternary ammonium moieties from QAMS-containing acrylic disks (bromophenol blue assay). (A) Baseline and 3 month aging in deionized water. (B) Aging in the absence of porcine liver esterase in phosphate-buffered saline (PBS) for 2 weeks. Note that the scales of the y-axis in the two charts are different. For each parameter (upper case letters for baseline and lower case letters for 3 months in (A) and upper case letters for no esterase and lower case letters for with esterase in (B)), groups with the same letters are not statistically significant (p > 0.05; note: only groups that are not significantly different are labeled). For comparisons between baseline and 3 months, groups connected with a bar are not statistically significant (p > 0.05).