Determination of physicochemical, cytotoxic, and whitening properties of plasma-activated liquids for their potential use as mouthwashes.

Multiple drug resistance (MDR) among antibiotic-resistant bacteria poses a major challenge in modern medicine, prompting interest in alternative antimicrobials like mouthwashes and toothpastes. Plasma-activated liquids (PALs), produced by exposing liquids to cold atmospheric plasma (CAP), are enriched with reactive oxygen and nitrogen species (RONS) that may have antimicrobial properties. However, their biocompatibility with mammalian cells remains underexplored. In this study, three formulations were subjected to CAP: (L1) zinc sulfate and calcium chloride, (L2) xylitol and sodium fluoride, and (L3) deionized water. Using a dielectric barrier discharge (DBD) system, we assessed the physicochemical, cytotoxic, and whitening effects of the resulting PALs. In vitro assays showed that PALs were non-cytotoxic to L929 fibroblast cells at concentrations up to 1.5% for PAL1, 10% for PAL2, and 15% for PAL3. PAL2 and PAL3 preserved over 90% cell viability. Scratch assays indicated that while nontreated (NT) NT1 and NT3 reduced fibroblast migration, CAP treatment enhanced cell movement over time. PAL1 did not significantly affect proliferation but increased metabolic activity by 25%, suggesting a selective pro-survival effect. Hydrogen peroxide was the predominant RONS: 6.9 mg·L-1 in PAL3, 5.8 mg·L-1 in PAL1, and 2.7 mg·L-1 in PAL2. All PALs demonstrated measurable whitening of human enamel, with PAL3 showing the most significant colour change (ΔE). These results support the potential of PALs as safe, multifunctional agents for use as modern mouthwashes.