An in vitro study on the clearance effect of oxygen-releasing photodynamic therapy on Enterococcus faecalis in the root canal

To investigate the clearance effect of photodynamic therapy (PDT) with an oxygen-releasing photosensitizer methylene blue (MB) formula on Enterococcus faecalis in the root canal.

Groups were divided into the MB group and oxygen release MB group. Samples in the MB group were mixed with 50 μmol/L MB solution, and samples in the oxygen release MB group were mixed with 50 μmol/L MB in oxygen release emulsion. N-acetyl-L-tryptophan amide (NATA) and 1,3-diphenylisobenzofuran (DPBF) were used to detect the oxidative activity and singlet oxygen generation of different formulas of MB (MB group, oxygen-releasing MB group), and the oxygen-releasing capacity of the oxygen-releasing photosensitizer formula was analyzed. The single root canal anterior teeth were collected, and the Enterococcus faecalis root canal infection model of isolated teeth was constructed. The distribution of Enterococcus faecalis in the root canal was observed by scanning electron microscopy. The isolated teeth with Enterococcus faecalis root canal infection were divided into three groups: the conventional root canal therapy group, MB-PDT therapy group, and oxygen-releasing MB-PDT therapy group, with 10 teeth in each group. Bacterial samples in the root canals of each group were obtained, the number of colonies was analyzed(CFU/mL) after 24 h of in vitro culture, and the clearance rate of Enterococcus faecalis in the root canal by photodynamic therapy was evaluated. The remaining isolated teeth with Enterococcus faecalis root canal infection were divided into 3 groups, with 5 samples in each group. Bacterial samples at a depth of 1000 μm in the dentin tubules of the upper root, middle root and lower root segment were obtained and cultured in vitro for 24 h for calculations. The number of colonies (CFU/mL) was analyzed, and the clearance rate of Enterococcus faecalis in the dentin tubules of different segments of the root canals in each group was analyzed.

The oxidation activity and singlet oxygen generation capacity in the oxygen-releasing MB group were stronger than those in the MB group. Scanning electron microscope detection showed that Enterococcus faecalis was distributed in dentinal tubules, indicating that the model of root canal infection in vitro was successfully constructed. The clearance rate of Enterococcus faecalis in the oxygen-releasing MB-PDT therapy group was higher than that in the conventional therapy group and the MB-PDT therapy group (P<0.05). Oxygen-releasing PDT significantly improved the bactericidal effect in the lower dentinal tubules, and the clearance rate of Enterococcus faecalis was better than in the other two groups (P<0.05).

Photodynamic therapy with the oxygen-releasing photosensitizer MB can achieve a better root canal bactericidal effect and can significantly improve the clearance effect of Enterococcus faecalis in the deep dentin of the lower root segment.