The aim of this study was to evaluate the antibacterial activity and cytotoxic effect of the compound SIAB-GV3, a new formulation presenting as an aqueous suspension of silicon dioxide (SiO2) functionalized with silver (Ag+) nanoparticles and benzalkonium. The product is formulated as an adjuvant for the treatment of inflammatory diseases of the oral cavity. This study demonstrates that SIAB-GV3 possesses strong antimicrobial activity against most of the common oral pathogens, in particular against Streptococcus pyogenes, Porphyromonas gingivalis and Aggregatibacter actinimycetemcomitans. The cytotoxic effect against human embryo lung fibroblasts (HELF cells) was evaluated at different times, from 1 h to 168 h, using concentrations of SIAB-GV3 ranging from 50 mg/ml to 0.0008 mg/ml. At the concentration of 10 mg/ml, commonly used in clinical practice, the compound results cyto- toxic after about 2 hours, this time being much longer than the typical time of local application, which is no more than 10 minutes. In conclusion, our findings suggest that SIAB-GV3 has a good antibacterial activity against the most common oral pathogens even at very low concentrations and a low cytotoxic activity, thanks to the synergistic effects of Ag nanoparticles, silicon dioxide and benzalkonium.