Combined and independent cytotoxicity of sodium hypochlorite, ethylenediaminetetraacetic acid and chlorhexidine

AimTo evaluate the capacity of commonly used root canal irrigants to induce cytotoxic effects, when applied singly or in combination. The hypothesis tested was that the irrigants were less cytotoxic when applied in combination than independently. MethodologyMRC5 cells were grown as monolayer cultures at 37 degrees C in an atmosphere containing 5% CO2 in air and 100% relative humidity. Cells were exposed to sodium hypochlorite (NaOCl), ethylenediaminetetraacetic acid (EDTA), chlorhexidine (CHX) and their combinations (NaOCl/EDTA, NaOCl/CHX, EDTA/CHX) in serial dilutions. Growth medium was Dulbecco's modified Eagle's medium supplemented with 10% foetal bovine serum and antibiotics and was used as control. The effect on cell survival was estimated after 6 and 24h of exposure by means of the sulforhodamine B assay, in reference to controls. Dose-response curves were plotted, and 50% inhibitory doses (IC50) were subjected to statistical analysis (anova and post hoc comparison test; P<0.05). Analysis of cell survival and interaction of the irrigants was performed using CalcuSyn dose effect analyzer software to calculate a combination index (CI). ResultsThe tested irrigants were cytotoxic in dose- and time-dependent manner. CHX was the most cytotoxic irrigant tested, followed by NaOCl, whilst EDTA was the least cytotoxic irrigant tested. The difference between CHX and NaOCl was significant (P<0.05) as well as between NaOCl and EDTA (P<0.05). Based on CalcuSyn modelling, a mainly antagonistic effect was recorded with NaOCl/CHX and NaOCl/EDTA combinations. The combination EDTA/CHX had an additive to antagonistic effect. ConclusionsCHX was significantly more cytotoxic than NaOCl and EDTA. NaOCl was significantly more cytotoxic than EDTA. The combined action of irrigants did not produce a significant increase in their cytotoxicity.