On-demand caries prevention: on-site generated slightly acidic electrolyzed water as a potent and biocompatible anti- Streptococcus mutans agent

Abstract

Dental caries remains a prevalent public health disorder dominated by Streptococcus mutans . Novel biocompatible antibacterial agents are urgently required for caries control. Slightly acidic electrolyzed water (SAEW), rich in endogenous hypochlorous acid, boasts broad bactericidal effects and minimal cellular toxicity, yet rapid degradation during storage limits its reproducibility. Thus, this study adopted freshly prepared SAEW to systematically assess its anti-cariogenic performance for translational reference. In vitro, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of SAEW against planktonic S. mutans were determined, and bacterial growth was monitored. Morphology was examined by scanning electron microscopy (SEM). Biofilm structure, viability, and membrane integrity were assessed by confocal laser scanning microscopy (CLSM) with live/dead staining. The cytotoxic effects of SAEW on human gingival fibroblasts (HGFs) were evaluated using the CCK-8 assay. 25 Sprague-Dawley rats were randomized into five groups: blank control, caries model, 0.12% chlorhexidine, high-concentration SAEW, and low-concentration SAEW groups. All non-blank rats received cariogenic induction and daily topical intervention. Salivary streptococcal loads were quantified, and mandibular caries severity was graded via Keyes scoring combined with radiography. Freshly prepared SAEW exhibited definitive antibacterial activity against S. mutans Its MIC and MBC against planktonic bacteria were 6.25 ppm and 12.5 ppm, respectively. SAEW compromised bacterial cell membrane integrity (activity reduced to 94.5 ± 0.8% in the high-concentration group). At its effective antibacterial concentrations, SAEW showed no significant cytotoxicity to human oral cells (Cell viability exceeded 80%). In a rat caries model, SAEW significantly reduced oral streptococcal levels and mitigated the severity of carious lesions (caries scores at superficial, moderate, and deep dentinal levels were (10.2 ± 1.30), (6.60 ± 0.89, and (1.00 ± 0.71) in the high-concentration group, all P < 0.05). No obvious histopathological alterations or systemic toxicity were induced by SAEW. Freshly prepared SAEW eliminates planktonic S. mutans primarily by disrupting cell membranes, with favorable cytocompatibility at working concentrations. It restrains cariogenic colonization and relieves caries progression in rodent models, marking a promising eco-friendly candidate for clinical caries prevention.