cytotoxicity of chlorhexidine-hydrogen peroxide combination in different concentrations on cultured human periodontal ligament fibroblasts

background: a strong antimicrobial synergism between chlorhexidine (chx) and hydrogen peroxide (h2o2) has been reported, but there is not enough data on the cytotoxicity of this combination. the primary aim of this study was to evaluate the cytotoxicity of chx-h2o2 combination in different concentrations and secondary aim is to assess the infl uence of h2o2 on cytotoxicity of chx on cultured human periodontal ligament (pdl) fi broblasts. materials and methods: the pdl cells were cultured from healthy human third molar teeth and were exposed to six prepared solutions (0.2% and 2% chx separately and in combination with 1% and 3% h2o2). the mtt assay was applied to assess their effects on the viability of the pdl cells. two-way analysis of variance approach and subgroup analysis was performed to evaluate the differences in mean cell viability values. a level of p < 0.05 was considered as statistically signifi cant. results: all tested solutions were toxic to pdl cells. there was a signifi cant interaction effect between chx and h2o2. the 2% chx combined with 3% h2o2 was the most and 0.2% chx was the least cytotoxic solutions. the 2% chx was signifi cantly more toxic than 0.2% chx and h2o2 combinations. the cytotoxicity of 0.2% chx and h2o2 combinations did not signifi cantly rise by increasing the concentration of h2o2 from 1% to 3%. conclusion: h2o2 affected the cytotoxicity of chx in a variable concentration-dependent manner. based on the results of this study, it can be concluded that 2% chx alone and in combination with either 1 or 3% h2o2 are signifi cantly more toxic than 0.2% chx alone and in combination with 1 and 3% h2o2. therefore, to benefi t from the synergistic antimicrobial effect between chx and h2o2, with a minimal cytotoxicity, it is recommended to use 0.2% concentration of chx combined with 3% h2o2. key words: chlorhexidine, cytotoxicity, hydrogen peroxide, root canal irrigation solution