Antimicrobial efficacy of methylene blue-functionalized graphene oxide-mediated photodynamic therapy against Enterococcus faecalis in root canal disinfection

This study assessed the antimicrobial efficacy of photodynamic therapy (PDT) using functionalized graphene oxide with methylene blue (MB/rGO) to achieve root canal disinfection against Enterococcus faecalis. In this in vitro study, E. faecalis biofilms were developed on 105 single-rooted teeth after decoronation over 21 days. Bacterial viability was assessed with colony forming unit (CFU) analysis. Six experimental groups with equal numbers of samples (n = 15) were treated with 5 % NaOCl (groups 1 and 2), MB-based PDT (groups 3 and 4), or MB/rGO-based PDT (groups 5 and 6). Sonic activation (groups 2, 4, and 6) was performed at 6000 cpm for 2 min, whereas laser activation (groups 3-6) was performed with a 650 nm, 200 mW laser for 2 min. Post-treatment CFU/mL counts and bacterial load decreases were recorded. A substantial decrease in bacterial load (p < 0.001) was observed across all experimental groups. The highest decrease (99.99 %) was observed in group 6 (modified PDT with MB/rGO), which also had the lowest CFU (1.21 × 103/mL) and the highest negative culture rate (40 %). Group 4 (modified PDT with MB) showed similar efficacy (99.99 % decrease, 33.33 % negative cultures), whereas NaOCl irrigation (group 1) showed the smallest decrease (99.83 %) and no negative cultures. Functionalized MB/rGO with sonic and laser activation achieved the highest bacterial load decrease, and was closely followed by modified PDT with MB. NaOCl irrigation was effective but did not yield negative cultures. Our findings highlight the potential of modified PDT for enhanced root canal cleaning.