Cytotoxic Effects of Activated Bromine on Cultured Human Fetal Osteoblasts

Sodium hypochlorite, a bactericidal irrigant used in endodontics, has several disadvantages, e.g. inability to remove smear layer, inability to penetrate biofilms, increased corrosion of instruments and hypersensitivity reaction in patients. Sodium bromide when combined with sodium hypochlorite forms activated sodium hypobromite, a biocide that penetrates biofilms, is less corrosive and has better antimicrobial property than chlorine alone. The scope and limitation of sodium hypobromite as an irrigant has not been adequately studied. Objective: To compare the cytotoxic effects of sodium hypobromite and sodium hypochlorite on human fetal osteoblasts (hFOB) by evaluating cell proliferation. Methods: Human FOB, cultured in aMEM and FBS at 34 degrees, were plated at 5000 cells/sq cm in 6 well dishes (2 mL/well). One day after plating, the cultures were treated with a combination of sodium hypochlorite and sodium bromide, resulting into three molar ratios of sodium hypobromite, 1:1, 1:4 and 4:1. Positive control cells were not treated with irrigants, while negative controls were separately treated with hypochlorite or bromide alone. Test solutions were used at a concentration of 0.075% or 0.200% in the media, which were replaced every two days. On 2nd and 8th day post-plating, photomicrographs were obtained. On 8th day, trypsinized cells were counted in a Coulter Counter to determine cell proliferation. Results: At 0.075% concentration, compared to untreated control, all treated groups had significantly (p<0.05) lower cell number. In the treated groups, cells treated with hypochlorite alone had significantly higher cell number compared to other groups. Cells treated with bromide alone had significantly lower cell number compared to other groups. At 0.200% concentration, all treatments were highly cytotoxic, except hypochlorite alone which inhibited cell proliferation. Conclusion: Sodium bromide is more cytotoxic to osteoblasts compared to sodium hypochlorite or activated sodium hypobromite. Study funded by 5T32-DE007288.