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

• The chemomechanical preparation provided the highest immediate intracanal bacterial reduction.
• PDT with periodic renewal of the photosensitizer provided an immediate and progressive reduction in bacterial load.
• The chemomechanical preparation using a NaOCl/EDTA alternated irrigation regimen combined with PDT cycles can be a viable choice in eliminating intracanal Enterococcus faecalis biofilm.

Background and objectivePhotodynamic 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 methodsRoot 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.ResultsThe highest bacterial load reduction was observed in S2. In regard to S3, Saline/PDT reduced 1.3 log10 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.ConclusionOur findings suggest immediate and delayed antibacterial effects using the PDT protocol tested.