Effects of inactivated Enterococcus faecalis on the proliferation and osteogenic induction of osteoblasts

The present study aimed to evaluate the effects of Enterococcus faecalis, inactivated by the common intracanal irrigants sodium hypochlorite (NaOCl) and chlorhexidine (CHX), on osteoblasts. E. faecalis was inactivated with 2% CHX or 5.25% NaOCl. Subsequently, the Cell Counting kit-8 assay was used to examine the effects of CHX- and NaOCl-inactivated E. faecalis on MC3T3-E1 osteoblast cell proliferation. Alizarin red staining was used to determine osteoblast mineralization, and osteogenic induction was quantified by determining the optical density of the dye solution. The relative expression levels of osteogenic genes were detected after 1, 4, 7 and 14 days of stimulation with CHX- and NaOCl-inactivated E. faecalis by reverse transcription-quantitative polymerase chain reaction. The results indicated that CHX-inactivated E. faecalis inhibited osteoblast proliferation, whereas NaOCl-inactivated E. faecalis did not suppress cell proliferation. Various concentrations of CHX- and NaOCl-inactivated E. faecalis induced different degrees of osteoblast mineralization. The expression levels of osteocalcin, alkaline phosphatase, runt-related transcription factor 2, osteopontin and osterix were upregulated in cells following stimulation with 10(7) and 10(5) colony-forming units/ml E. faecalis inactivated by CHX and NaOCl; the upregulation of these osteogenic genes occurred at various time points. In conclusion, the present study demonstrated that CHX-inactivated E. faecalis exerted more of an effect on osteoblast proliferation compared with NaOCl-inactivated E. faecalis. In addition, CHX- and NaOCl-inactivated E. faecalis was able to induce mineralization and relevant osteogenic gene expression in osteoblast cells.