Endodontic antimicrobial photodynamic therapy: Safety assessment in mammalian cell cultures

Abstract Objectives The purpose of this study was to assess the in vitro synergistic effect of methylene blue (MB) and red light on human gingival fibroblasts and osteoblasts with parameters similar to those that may be applied in a clinical setting for endodontic disinfection. Materials and Methods Both cell types were sensitized with 50 μg/mL MB followed by exposure to red light at 665 nm for 5 minutes with an irradiance of 10, 20, and 40 mW/cm 2 . After photodynamic therapy (PDT), cell viability and mitochondrial activity were evaluated by the neutral red and MTT assay, respectively. The assessment of PDT-induced apoptosis was investigated by western blot analysis using cleaved poly(ADP-ribose) polymerase–specific antibodies. Results Light at 20 and 40 mW/cm 2 with MB had modest effects at 24 hours on osteoblasts in both assays, whereas sodium hypochlorite completely eliminated cells. Western blot analysis revealed no signs of apoptosis in either cell type. Conclusion The data suggest that there is a safe therapeutic window whereby PDT can inactivate endodontic pathogens without affecting host cell viability.