BACKGROUND
Sodium hypochlorite (NaOCl) is the most commonly used irrigant in root canal treatment because of its antimicrobial activity and tissue-dissolving capacity. Since these properties are related to its physicochemical characteristics, changes during chairside handling may be clinically relevant. This study aimed to evaluate time-dependent changes in pH, active chlorine content, and surface tension of NaOCl kept in transparent, open-lid containers during a typical chairside root canal treatment period.
MATERIAL AND METHODS
A commercially available 5% NaOCl solution was tested under 3 conditions: fresh (T₀), after 1 hour (T₁), and after 2 hours (T₂) of exposure in standardized transparent, open-lid containers under ambient clinic conditions (≈22°C). For each outcome (pH, active chlorine content, and surface tension), 3 groups were evaluated (n=10 per group), yielding 90 measurements in total (3 outcomes×3 groups×n=10). Data were analyzed using one-way analysis of variance followed by Duncan’s multiple-comparison test (P<0.05).
RESULTS
pH decreased significantly after 1 hour and further decreased after 2 hours, compared with fresh NaOCl (P<0.05). Surface tension did not differ significantly among groups (P>0.05). Active chlorine values did not differ between T₀ and T₁ (P>0.05), whereas T₂ showed significantly higher measured active chlorine than both T0 and T1 (P<0.05).
CONCLUSIONS
In this in vitro study, leaving NaOCl in transparent, open-lid containers for up to 2 hours was associated with decreased pH and increased measured active chlorine values, while surface tension remained unchanged. Further studies are needed to determine the clinical relevance of these physicochemical changes.

Keywords: Chlorine; pH; Sodium Hypochlorite; Surface Tension