Photodynamic killing of Enterococcus faecalis in dentinal tubules using mTHPC incorporated in liposomes and invasomes

The present in vitro study investigates the antimicrobial photodynamic efficiency of the photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC) incorporated in liposomes (LIP) and highly flexible invasomes (INV) on the endodontopathogenic species Enterococcus faecalis in infected dental root canals. A total of 48 root canals were prepared mechanically to file size ISO 50 and inoculated with E. faecalis for 48 h. In the test groups, the infected root canals were subjected to aPDT with either mTHPC linked to LIP or INV. The controls were either incubated with 1 % chlorohexidine gel (CHX, positive control) or root canals were irrigated with normal saline (NaCl, negative control). After treatment all canals were mechanically enlarged (ISO 50-110), and the debris of each filing process was subjected to bacterial culture analysis. Both mTHPC formulations showed a significant antimicrobial effect. A bacterial reduction by up to 3.6 log-steps was ascertained for INV directly at the root canal wall. aPDT using INV (ISO 60) was more effective than CHX, which caused a decrease in only 1.2 log-steps. It was found that both liposomal mTHPC formulations were capable to suppress E. faecalis inside the dentinal tubules up to 300 mu m. The results show that mTHPC linked to LIP and INV is capable of efficiently reducing E. faecalis in dental root canals. As evidenced, E. faecalis is resistant to several conventional antibacterial treatment measures. In this context, photodynamic treatment with mTHPC delivered by INV is superior to temporary dressing with 1 % CHX gel applied for 24 h.