Sodium Thiosulfate as a Neutralizing Agent: Implications for Dental Pulp Stem Cell Survival after Sodium Hypochlorite Irrigation

Introduction/Background High concentrations of 5% sodium hypochlorite (NaOCl) reduce Human Dental Pulp Stem Cell (hDPSC) viability, despite its widespread use in endodontics. Sodium Thiosulfate (STS), an antioxidant with antimicrobial properties, may help reduce NaOCl-associated cytotoxicity. This study evaluated the effect of 5% STS following exposure to 1.5% and 5% NaOCl for different durations on hDPSC viability. Materials and Methods This in-vitro study was conducted at ProSTEM Laboratory (Prodia Stem Cell Indonesia), Jakarta, using primary hDPSCs from extracted human teeth. Groups were tested in triplicate and repeated twice by two operators. Cells (P3-P4,80% confluence) were starved for 24 hours and exposed to 1.5% and 5% NaOCl, followed by 5% STS for 30- and 60-second exposures. DMEM served as the control group, while the NaOCl and NaOCl-STS groups served as experimental groups. Cell viability was assessed using the MTT assay. Data were analyzed using one-way ANOVA ( p < 0.05) with post hoc LSD test. Results The comparison between the 5% NaOCl group and the 5% NaOCl + 5% STS (60-second) group was not significantly different ( p > 0.5). Descriptively, mean cell viability remained above 70% in all experimental groups. Discussion Within the limitations of this in vitro study, STS showed a possible trend toward higher hDPSC viability following 5% NaOCl exposure. All STS-treated groups maintained viability above the cytotoxicity threshold. Conclusion Although 5% STS demonstrated a slight numerical change in hDPSC viability, the difference was not statistically significant. These findings are a preliminary observation and require further study using optimized STS-to-NaOCl ratios.