| In recent years, dental resin materials have been widely used in prosthodontic treatments. However, a major shortcoming of these materials is that they accumulate more biofilms and plaques in vivo, compared with other restorative materials. Therefore resin restorations are challenged by micro-organisms in the oral environment, and the antimicrobial modification of dental resin materials is a solution to this problem. With a broad antimicrobial spectrum, high biological security, as well as no drug resistance, silver nanoparticles (AgNPs) gradually become an excellent candidate of antimicrobial agent for the modification. Among those methods incorporating AgNPs into dental resin materals, physical admixture is limited by some problems such as complicated procedures, the use of toxic reagents and non-uniform dispersion, meanwhile the in-situ systhesis of AgNPs in resin matrix provides a new idea for research considering its simplified procedures, less by-products and better dispersion.Objective:The aim of this study was to systhesize AgNPs in situ in light-curing (LC) bisphenol A glycidyl methacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA)-based resin to obtain antimicrobial modification. To evaluate this novel LC resin, the dispersion of AgNPs in the polymer and the Ag+release in deionized water were checked, preliminary antimicrobial efficiency against Candida albicans was assessed using a biofilm model, the physical and mechanical properties such as chromatic changes and Knoop microhardness of the nanocomposite specimens were analyzed.Methods:0.2wt%camphorquinone (CQ) and0.8wt%ethyl-4-N,N-dimethylaminobenzoate (EDMAB) was dissolved in a1:1Bis-GMA/TEGDMA resin mixture. Silver2-ethylhexanoate was dissolved into2-(tert-butylamino) ethyl mathacrylate (TBAEMA) and then added to the LC resin mixture at different concentrations (0,0.02,0.04,0.06,0.08,0.1,0.12,0.16,0.2wt%). The blend was poured into a mold (12mm diameter×1mm thick) between two pieces of polyester films (0.05mm thick) and light-cured for40s on each side.After gold coating,5specimens from0,0.06,0.08,0.1,0.12wt%groups were observed by a Field Emission Scanning Electron Microscope (FE-SEM), then the disks were analyzed by an Energy Dispersive Spectrometer (EDS) incorporated in the FE-SEM.After ultrasonic cleaning for5min, specimens from each group were separately immersed in12ml of sterile deionized water and kept at37℃(n=6). At certain intervals (1day,3day,1week,2weeks),3ml of the water was extracted and its UV/Vis absorption was measured at233nm wavelength to analyze the Ag+release of the novel LC resin.The sterilized specimens were placed in24-well plates and incubated with fresh suspension of Candida albicans, then the metabolic activity analysis of Candida albicans biofilms formed on the surface was performed by XTT reduction assay and the reduction rates were calculated to assess the antimicrobial activity of AgNPs/resin composite.The cured specimens before/after water storage was detected by a chromameter (ShadeEye NCC Ⅱ). The L*, a*, b*values were determined and the color difference values△E*were calculated to characterize the chromatic changes of those different concentration groups and those specimens before/after water storage.The Knoop microhardness of cured specimens before/after water storage was measured using a microhardness indenter under a load of0.245N for15s (n=5). Five indentations were made randomly on the surface of each specimens, the arithmetic mean was considered as the Knoop microhardness value.Results:The bright particles in the specimens observed by FE-SEM were proved to be AgNPs with the analysis of EDS. The size of those particles was ranged from30nm to50nm, and a homogeneous dispersion of AgNPs was visible in the Bis-GMA/TEGDMA resin matrix. However, there were also some large agglomerates ranging from200nm to500nm in the specimens. With the increase of silver2-ethylhexanoate, more agglomerates were observed.In Ag+release study, due to the disturbance of photo initiator and resin monomer dissolved in the deionized water, no valid data was obtained at233nm wavelength. It indicated that another method had to be developed.In the XTT reduction assay, the metabolic activity in the Candida albicans biofilms adherent on thesurface of AgNPs/resin composite disks was inhibited. With the increase of silver2-ethylhexanoate concentration, the metabolic activity decreased. In the0.2wt%group, the reduction rate of Candida albicans biofilms activity was (55.47±2.12)%.Before deionized water storage, the color of the resin changed from amber to taupe as the silver2-ethylhexanoate concentration increased, the AgNPs clusters were found in the disks from0.12,0.16,0.2wt%groups. After immersing in deionized water for7days, the specimens turned even darker and no cluster was visible. The mean color difference values△E*between0,0.02,0.04wt%groups and the control group were acceptable in clinical conditions, meanwhile the color difference values of other groups were not.The Knoop microhardness values ranged from22MPa to27MPa in groups before water storage and they demonstrated no statistically significant differences compared with the control group (P>0.05). After water storage for7days, the Knoop microhardness values of each group decreased to16-19MPa and there was also no statistically significant differences between the experimental groups and the control. Conclusions:This study demonstrated a chemical in-situ synthesis process that generates AgNPs in the LC Bis-GMA/TEGDMA resin matrix. The experimental AgNPs/resin composite preliminaryly showed inhibition effect against Candida albicans biofilms. The incorporation of AgNPs might have an impact on the color stability, meanwhile the Knoop microhardness of the AgNPs/resin composite was not significantly affected by AgNPs. |
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