Enterococcus faecalis Endodontic Biofilms Inactivation by Photodynamic Therapy In Vitro

F. FOSCHI1, J.T. MORRIS2, K. RUGGIERO1, A. ABERNETHY1, P. STASHENKO1, and N.S. SOUKOS1, 1 The Forsyth Institute, Boston, MA, USA, 2 Harvard School of Dental Medicine, Boston, MA, USA Objectives: To investigate the efficacy of photodynamic therapy on Enterococcus faecalis root canal biofilms. Methods: In a model of dentinal tubule infection, 48 extracted, human, single-rooted teeth were selected, and the root canals were widened to apical size of 0.465 mm with crown down instrumentation. The smear layer was removed with 17% EDTA and 6% NaOCl. After sterilization by autoclaving, the specimens were infected with E. faecalis (ATCC 29212) in brain heart infusion broth (109 cells/ml) and were incubated for 3 days to allow a biofilm to form. The presence of E. faecalis biofilms was demonstrated by scanning electron microscopy. The specimens were then subjected to photodynamic therapy (PDT). Following treatment with methylene blue (MB) (25 or 50 µg/ml) for 5 min, the specimens were exposed to light at 662 nm with a power density of 150 mW/cm2 and energy fluence of 45 J/cm2. Light was delivered from a diode laser via a flexible fiber optic with multiple cylindrical diffusers that uniformly distributed light at 360o. Controls consisted of MB only, light only and no treatment (positive control). Following PDT, the canal contents were sampled by flushing with 1 ml of BHI broth, serially diluted and cultured on blood agar to determine the colony forming units (CFU). Results: PDT achieved a 95.5-98.2% reduction of CFU. MB alone reduced CFU by 87.5-92.6%. Surprisingly, light alone also showed a bactericidal effect, ranging between 59% and 69%. Conclusions: The results show that PDT may be developed as an adjunctive technique to kill residual bacteria in the root canal system after standard endodontic treatment. Supported by NIDCR grant RO1-DE-14360.