The porpoise of the study was to evaluate the antibacterial effect of silver nanoparticles (Ag-NPs) versus chlorhexidine (CHX) against Streptococcus mutans and Lactobacillus casei. Three different reducing agents were used for the synthesis and characterization of Ag-NPs: sodium borohydride (NaBH 4), a chemical method, and Heterotheca inuloides (Hi) and Camellia sinensis (Cs), two eco-friendly methods. The synthesized substance was deposited on deciduous teeth. Its behavior in dental tissues was evaluated through an energy dispersive X-ray spectroscopy (EDS) analysis, using a scanning electron microscope (SEM). The characterization of Ag-NPs in terms of shape, size, and polydispersity was performed through spectrophotometry of ultraviolet-visible light analysis (UV-vis), as well as by transmission electron microscopy. Isolation and culture of strains S. mutans and L. casei were done to perform the microbiological analysis. In Petri dishes, paper discs containing different concentrations of Ag-NPs (synthesized by Hi, and by Cs) were deposited and tested along with paper discs containing CHX. Their antibacterial effect against both bacteria was evaluated by the inhibition zones test. By means of UV-Vis and TEM analysis, it was possible to observe that Heterotheca inuloides produced smaller and more stable nanoparticles, also in greater quantities (17.5 nm), when compared to Camellia sinensis. EDS analysis through SEM showed a 6.25 average absorption of silver in dental tissues. The microbiological analysis revealed a greater zone of inhibition when the test bacteria were in contact with 20 μl of Ag-NPs, synthesized by Hi, being statistically significant (p < 0.05), compared to the growth inhibition zones produced by Cs, and CHX against both strains. We can conclude that eco-friendly methods produced Ag-NPs with an important antibacterial effect in both strains.

Two bionanocomposites based on suture threads, silk-silver nanoparticles (Ag NPs) and catgut-Ag NPs, were prepared through a green chemistry methodology using Chenopodium ambrosioides (Mexican Epazote) as reducing agent. UV-Vis spectrophotometry (UV-Vis), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), were used for their characterization. UV-Vis confirmed the synthesis of silver nanoparticles. Micrographs showed polydisperse, mostly spherical, Ag NPs attached to both suture threads. The bionanocomposites antimicrobial properties were evaluated through cultures and inhibition zones tests. The Chenopodium ambrosioides-assisted synthesized bionanocomposites have proved antibacterial effect against S. aureus and E. coli in both sutures (silk and catgut) and could be potentially useful for oral or periodontal surgery. There was no significant difference statistically in inhibition of Staphylococcus aureus versus Escherichia coli.

This work demonstrates an efficient, low-cost and environmentally friendly synthetic method of Ag/Cu bimetallic nanoparticles (NPs), which allows taking advantage of renewable resources, using Ricinus Communis leaf extract as bioreducing and passivating agent. By varying the metal salt precursors of AgNO 3 and CuSO 4 .5H 2 O concentrations, the stable bimetallic NPs were obtained. The Ag/Cu bimetallic NPs were characterised using ultraviolet-visible absorption spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), X-ray dispersive energy spectroscopy (EDS), and scanning and transmission electron microscopy (SEM and TEM). In all cases, the particles size is less than 100 nm. The 10:90 Ag/Cu system has the best control of morphology (spheroid) and size in range of 10-25 nm ( ¯= X 18 nm, σ=9). Selected area electron diffraction patterns (SAED) are in concordance with JCPDF cards for silver and copper face-centered cubic (fcc) crystal structures. Microbiological susceptibility was tested by disc diffusion, minimum inhibitory concentration (MIC) and minimal lethal concentration (MLC) methods, with the following microorganism strains: Staphylococcus aureus (gram +), Escherichia coli (gram −) and Aspergillus niger (fungus). The MIC concentration for the three strains was found to range from 1.25 to 2.45 μg and the MLC allowance ranges from 2.45 to 9.81 μg.