LAUSR

Introduction The literature reveals controversies regarding the formation of para‐chloroaniline (PCA) when chlorhexidine (CHX) is mixed with sodium hypochlorite (NaOCl). This study aimed to investigate the stability of PCA in the presence of NaOCl and to examine the in vitro cytotoxic effects of CHX/NaOCl reaction mixtures. Methods Different volumes of NaOCl were added to CHX (mix 1) or PCA (mix 2). Upon centrifugation, the supernatant and precipitate fractions collected from samples were analyzed using high‐performance liquid chromatography. The cytotoxic effects of both fractions were examined on human periodontal ligament and 3T3 fibroblast cell lines. Results High‐performance liquid chromatographic analysis showed no PCA signal when NaOCl was mixed with CHX (mix 1). In mix 2, the intensity of PCA was decreased when NaOCl was added to PCA, and chromatographic signals, similar to that of CHX/NaOCl, were also observed. The mortality of precipitates exerted on both cell lines was lower compared with that of supernatants. Conclusions The discrepancy in the data from the literature could be caused by the instability of the PCA in the presence of NaOCl. The CHX/NaOCl reaction mixture exhibits a wide range of cytotoxic effects. HighlightsNo para‐chloroaniline (PCA) signal was detected when sodium hypochlorite (NaOCl) was mixed with chlorhexidine (CHX).The intensity of PCA was decreased when NaOCl was added to PCA.Discrepancy in the literature could be caused by the instability of PCA in the presence of NaOCl.The mortality of precipitates exerted on the cell lines was lower compared with supernatants.