Green Synthesis of Silver Nanoparticles Using Ocimum tenuiflorum and Ocimum gratissimum: Development of a Dental Varnish with Enhanced Antibacterial Properties

Background: The growing resistance of oral pathogens to conventional antimicrobial agents has created a demand for innovative, natural alternatives in dental care. Ocimum tenuiflorum and Ocimum gratissimum are widely recognized for their medicinal properties, particularly their antimicrobial potential. This study investigates the green synthesis of silver nanoparticles (AgNPs) using these herbal extracts and their incorporation into a dental varnish. The varnish underwent comprehensive characterization using Fluorescent analysis, NMR analysis, Zeta potential studies and UV-Vis spectroscopy to evaluate its structural and physicochemical properties. Methods: Silver nanoparticles were synthesized using Ocimum tenuiflorum and Ocimum gratissimum herbal extracts via a green synthesis approach. The synthesized AgNPs were incorporated into a dental varnish and their antibacterial efficacy was tested against Staphylococcus aureus, Streptococcus mutans, Lactobacillus sp., Enterococcus faecalis and Escherichia coli. The antibacterial activity was evaluated using the agar well diffusion method and time-kill curve assay. Inhibition zones were measured at concentrations of 25 µg/mL, 50 µg/mL and 100 µg/mL and results were compared with a commercially available dental varnish. Results: The AgNP-based dental varnish demonstrated superior antibacterial activity across all tested concentrations. The inhibition zones for S. aureus were 10 mm, 14 mm and 26 mm at 25 µg/mL, 50 µg/mL and 100 µg/mL, respectively, outperforming the commercial varnish's 9 mm inhibition zone. For S. mutans, the Ocimum-based varnish showed inhibition zones of 24 mm, 27 mm and 34 mm, which significantly exceeded the standard varnish's 9 mm. Lactobacillus sp. exhibited inhibition zones of 20 mm, 22 mm and 31 mm, while E. faecalis showed 9 mm, 11 mm and 14 mm. E. coli displayed the highest inhibition zones of 27 mm, 30 mm and 35 mm, compared to the 9 mm zone produced by the commercial varnish. The time-kill curve assay demonstrated that the Ocimum-based varnish at 100 µg/mL effectively reduced bacterial counts of E. coli and S. mutans to 10 CFU/mL within 5 hours. Similar reductions were observed for S. aureus, Lactobacillus sp. and E. faecalis, indicating potent bactericidal activity with increasing concentrations. Conclusion: The Ocimum-mediated AgNP dental varnish exhibited superior antibacterial efficacy compared to the commercial dental varnish, particularly at 100 µg/mL. The enhanced antibacterial activity, combined with the eco-friendly green synthesis process, suggests that Ocimum tenuiflorum and Ocimum gratissimum-based AgNPs hold promising potential as effective and safe alternatives in dental care for combating oral pathogens. Further in vivo studies are recommended to evaluate the varnish’s clinical performance and long-term safety.