Cytotoxicity Analysis of Mixed Chlorhexidine and Sodium Hypochlorite Solutions

New antimicrobial therapies have been introduced in Endodontics for periapical lesions and treatment-resistant infections. Association of irrigating solutions and intracanal medications, such as 1% sodium hypochlorite (NaOCl) solution and 2% chlorhexidine (CHX) solution has shown promising results. However, inside the root canal system the NaOCl and CHX interact producing byproducts (Bps) represented by a liquid (Lq) and a solid precipitated (Sd) that will remain on the canal walls. Objectives: To study the cytotoxicity of such Bps and CHX using cultured fibroblasts. Methods: Equal parts of 1% NaOCL and 2% CHX solutions were mixed and the Bps were obtained. Three drug solutions were tested: cell culture medium conditioned by the Sd byproduct (SdM), Lq and CHX. They were diluted in fresh medium in 4 different concentrations (100%, 1%, 0,5%, 0,1%) and applied to the cultured fibroblasts (FMM1 cell lineage). In the control wells the cells grew on fresh medium. Cytotoxicity was measured by using the MTT reduction assay in 36 replicates per concentration per solution. Oral fibroblasts were seeded (103 cells/well) into 96 well plates. Twenty-four hours later, the cultures were exposed to the tested drugs during 15min. The cell viability was analyzed 24h later. Results: At 100% concentration all tested drugs are highly cytotoxic; however, the diluted drugs presented IC50 of 0.5% for CHX, 0.75% for Lq and 0.80% for Sd. Conclusion: The solution of 1% NaOCl is able to reduce the cytotoxicity of the 2% CHX solution; thus the presence of Bps inside the root canal system would be less prejudicial to the periodontal tissue than the CHX alone.