The Study On The Self-produced Method Of Silver Nanoparticles In Dental Resin Materials

Silver nanopartical, which is known to exhibit a strong toxicity to a wide range of micro-organisms, is expected to be used in developing a novel bactericidal dental resin composites. Coupling photoinitiated free radical polymerization of dimethacrylates with in situ silver ion reduction is a simplified procedure, less by-products and better dispersion of silver nanoparticals. However, all of these research haven’t given the the exact mechanism of the reduction of Ag ions. They just believe in the concurrent reduction of Ag ions and polymerization of dimethacrylate based polymers. In our previous study, we repeat the synthetic of silver nanoparticles in resin materials. Saddly, the particles we got is too large to use and we can not control the size. Besides, we found silver mirror reaction in the mixture of organic silver salt and amine solution. Maybe the silver salt solution can produce silver nanoparticles without the radical from polymeration. It is neccesary to clarify the mechanism of silver reduction and choose the best source of silver salt and dissolving agents to control the size of silver nanoparticles, making sure a better dispersion and proper size distribution in resin materials, without affecting its polymeration、mechanical and chemical properties.Objective:The aim of this study was to systhesize AgNPs by dissolving silver 2-ethylhexanoate or silver benzoate in 2-(Dimethylamino)ethyl methacrylate (DMAEMA) or 2-(tert-Butylamino)ethyl methacrylate (TBAEMA), and to explore the mechanism of silver reduction to guide the AgNPs modification of light-curing resin composite. To evaluate silver particles, the silver mirror reaction was checked along time; the size and dispersion was assessed; the mechanism of silver reduction was explored and verified.Methods:0.2wt% camphorquinone (CQ) and 0.8% ethyl-4-N,N-dimethalaminobenzoate (EDMAB) was dissolved in a 50:50 Bis-GMA and TEGDMA resin mixture. Silver 2-ethylhexanoate was dissolved in 2-(tert-Butylamino)ethyl methacrylate (TBAEMA) and then added to the resin mixture at 0.08wt%. A drop of the overnight silver salt resin mixture was clamped by two pieces of polyester films and light-cured for 40s.After gold spraying, the resin film was observed by a Field Emission Scanning Electron Microscope (FE-SEM), the analyzed by an Energy Dispersive Spetrometer (EDS) incorporated in the FE-TEM.8wt% silver 2-ethylhexanoate or silver benzoate was dissolved in 2-(Dimethylamino)ethyl methacrylate (DMAEMA) or 2-(tert-Butylamino)ethyl methacrylate (TBAEMA). After ultrasonic vibration for 1 min, these solutions were kept in room temperatue with common fluorescent lamp irradiating and observed the color change and silver mirror reaction continually.The partical size in the solutions were measured by laser particle sizer in period of 20min-.40min and 60min, each repeated three times.UV/Vis spetra from 200 to 800nm were taken using the control (pure DMAEMA and TBAEMA) as blank to measure all the solution in 1h and 20h.0.5g silver 2-ethylhexanoate or silver benzoate was dissolved in 1g DMAEMA or TBAEMA. All the solutions were detected by fourier transform infrared spectroscopy(FT-IR) to contrast important chemical groups with pure DMAEMA or TBAEMA.Statistical analysis was performed using SPSS 18 statistical software. The size of each group was analyzed through three-way ANOVA followed by comparison of means with Tukey’s test were applied in order to compare the size of all the groups (p<0.05).Results:The bright particles in the resin film observed by FE-SEM were proved to be AgNPs with the analysis of EDS. The size of those particles was about 0.82 u m.The color of silver 2-ethylhexanoate/DMAEMA and silver 2-ethylhexanoate/TBAEMA turned from light yellow to deep along with time. The color of silver 2-ethylhexanoate/DMAEMA changed fastest, which turned to light gray in 5min. The color of silver 2-ethylhexanoate/TBAEMA stayed steady. Silver benzoate/DMAEMA seem colorless, then it turned yellow and its color was the deepest in all the groups at a later stage. Silver benzoate/TBAEMA was removed as silver benzoate was insoluble in TBAEMA. The situation was same for silver 2-ethylhexanoate/ethanol and silver benzoate/ethanol. There was silver mirror reaction in all the groups, but at different speed. Silver 2-ethylhexanoate/DMAEMA was fastest and its silver mirror was gray-yellow. The second is silver benzoate/DMAEMA, which is grayish black. Then came silver 2-ethylhexanoate/TBAEMA for shiny silver. The control groups also turned silver mirror.The particle size of silver 2-ethylhexanoate/DMAEMA and silver benzoate/DMAEMA increased with time and the particle size of the latter was larger than 100nm at all the time periods. The particle size of silver 2-ethylhexanoate/TBAEMA was stable, almost unchanged from 20min to 60min.All the three groups showed a peak centered around 320nm for AgNPs.20h later, the peak absorbance of two DMAEMA salt solution increased, suggesting the continual reaction of salt solution and the increasing concentrations of AgNPs. But for silver 2-ethylhexanoate/TBAEMA, the peak absorbance didn’t change much.Fourier transform infrared spectroscopy confirms characteristic peaks of C=C and-NH-unchanged before and after dissolving organ silver salt in TBAEMAConclusions:1. We can synthesizing silver particles "in situ" in light-cured resin materials.2.There is silver mirror and silver nanoparticles insilver 2-ethylhexanoate/DMAEMA, silver benzoate/DMAEMA and silver 2-ethylhexanoate/TBAEMA.3. As silver soluent, TBAEMA is more stable than DMAEMA, and the size of silver nanoparticles in TBAEMA is smaller.4. DMAEMA may has the ability to reduce organ silver salt to silver. But for the deeper color and unstability, DMAEMA may not be suitable for clinical use.5. Without free radical from polymerization process, we can get silver nanoparticles in organ salt solutions.