Monitoring the effectiveness of photodynamic therapy with periodic renewal of the photosensitizer on intracanal Enterococcus faecalis biofilms

Abstract Background and objective Photodynamic therapy (PDT) can eliminate microorganisms in a root canal. However, the parameters for disinfection remain undefined. This study assessed the effectiveness of a PDT protocol against intracanal Enterococcus faecalis biofilms. Materials and methods Root canals were contaminated with E. faecalis for 21 days. The instrumentation was associated to irrigation with 0.85% saline or an alternate irrigation (AI) with 5.25% NaOCl and 17% EDTA. Complementary treatments included saline/PDT and AI/PDT. Four PDT cycles were performed using a diode laser (660 nm, 40 mW) delivered through a tapered optical fiber. In each cycle, the root canal was filled with 1.56 μM/mL methylene blue and irradiated for 150 s. Microbiological samples were collected before (S1) and after (S2) instrumentation; after PDT (S3); and daily over the course of 14 days (S4–S17). Colony-forming units (CFUs) were counted, positive cultures verified, and data subjected to parametric and proportion's tests. Results The highest bacterial load reduction was observed in S2. In regard to S3, Saline/PDT reduced 1.3 log 10 CFU counts ( p  = 0.000 for S2) and no CFUs were recovered after AI/PDT treatment. All canals were CFU-free on the 14th day for saline/PDT, AI and AI/PDT. Positive cultures were observed in 60% of saline-irrigated canals on the 14th day, whereas the saline/PDT, AI and AI/PDT treatments resulted in germ-free canals after 10, 5 and 2 days, respectively. Conclusion Our findings suggest immediate and delayed antibacterial effects using the PDT protocol tested.