Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2025 Feb 22;25(1):287.
doi: 10.1186/s12903-025-05657-4.

Killing effect of antibacterial photodynamic therapy with long-term exposure against young and mature Enterococcus faecalis biofilms in dentin

Tianfeng Du  1 , Yiting Wang  2 , Xiaoke Liu  3 , Weifang Zhao  1 , Bowen Yang  1 , Kang Gan  1 , Juanfang Zhu  4
Affiliations

Killing effect of antibacterial photodynamic therapy with long-term exposure against young and mature Enterococcus faecalis biofilms in dentin

Tianfeng Du et al. BMC Oral Health. .

Abstract

Background: The main cause of pulpal and periapical diseases is bacterial infection, but mechanical and chemical preparation in root canal therapy is difficult to completely remove the bacterial microorganism. Antibacterial photodynamic therapy (aPDT) is a medical method that kills microorganisms by activating a photoactive agent or photosensitizer by exposure to visible light of a specific wave-length in the presence of oxygen. The present study aimed to evaluate the killing in vitro effect of aPDT with 0.01% methylene blue (MB) against young and mature Enterococcus faecalis (E. faecalis) biofilms in bovine and human dentin with the long-term exposure using confocal laser scanning microscopy (CLSM).

Methods: Prepared bovine and human dentin blocks and their structure were observed by scanning electron microscopy (SEM). Semicylindrical bovine dentin blocks and human root canal dentin blocks were inoculated with E. faecalis and incubated in air to form 1- and 3-week-old biofilms. The biofilms in dentin were subjected to aPDT with 0.01% MB, 5% NaOCl and saline with the exposure of 3, 12 and 30 min. The dead portions of bacterial cells in E. faecalis biofilms were analyzed with using LIVE/DEAD bacteria viability staining and CLSM.

Results: A clean dentin surface in bovine dentin blocks were verified with SEM. In bovine and human dentin blocks, significantly more bacteria were dead when aPDT with MB and 5% NaOCl were used with the long exposure time (12 and 30 min) than with 3 min (P < 0.05). The speed of killing was fastest during the first 3 min, and few more bacterial cells were killed after 12 min in the disinfection groups. 5% NaOCl exhibited the highest effectiveness of bacterial killing in dentin at each time point than aPDT with MB groups (P < 0.05). The proportion of killed bacteria was higher in young biofilms than in mature biofilms in aPDT with MB and NaOCl groups (P < 0.05). Moreover, there were no clearly visible changes in structure of bovine dentin surfaces subjected to aPDT with MB for 30 min.

Conclusion: aPDT with 0.01% MB has the capability to kill bacterial cells in E. faecalis biofilms on bovine and human dentin blocks. Young E. faecalis biofilms in dentin canals were more susceptible to disinfection approaches than mature biofilms.

Keywords: Enterococcus faecalis; Bacterial biofilms; Confocal laser scanning microscopy; Photodynamic therapy; Root canal disinfection.

PubMed Disclaimer

Conflict of interest statement

Declarations. Ethics approval and consent to participate: Ethical approval The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Science and Ethics Commission of the First Affiliated Hospital of Zhengzhou University. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests. Informed consent: Not applicable.

Figures

Fig. 1
Fig. 1
Experimental procedure diagram for the aPDT
Fig. 2
Fig. 2
SEM images of sterile bovine dentin blocks (A) Clean bovine dentin blocks; (B) 1-week-old E. faecalis biofilms on bovine dentin blocks; (C) 3-week-old E. faecalis biofilms on bovine dentin blocks
Fig. 3
Fig. 3
CLSM images of 1-week-old and 3-week-old E. faecalis biofilms in infected bovine dentin blocks after being subjected to: (A1) 3-minute PDT with 0.01% MB; (A2) 12-minute PDT with 0.01% MB; (A3) 30-minute PDT with 0.01% MB; (B1) 3-minute 5% NaOCl; (B2) 12-minute 5% NaOCl; (B3) 30-minute 5% NaOCl; (C1) 3-minute sterile saline; (C2) 12-minute sterile saline; (C3) 30-minute sterile saline. (A) 1-week-old E. faecalis biofilms on bovine dentin blocks; (B) 3-week-old E. faecalis biofilms on bovine dentin blocks; (A) 1-week-old E. faecalis biofilms on bovine dentin blocks; (B) 3-week-old E. faecalis biofilms on bovine dentin blocks; (C) Proportion of dead E. faecalis cell volume in 1-week-old biofilms; (D) Proportion of dead E. faecalis cell volume in 3-week-old biofilms
Fig. 4
Fig. 4
CLSM images of 1-week-old and 3-week-old E. faecalis biofilms in infected human dentin blocks after being subjected to: (A1) 3-minute PDT with 0.01% MB; (A2) 12-minute PDT with 0.01% MB; (A3) 30-minute PDT with 0.01% MB; (B1) 3-minute 5% NaOCl; (B2) 12-minute 5% NaOCl; (B3) 30-minute 5% NaOCl; (C1) 3-minute sterile saline; (C2) 12-minute sterile saline; (C3) 30-minute sterile saline. (A) 1-week-old E. faecalis biofilms on human dentin blocks; (B) 3-week-old E. faecalis biofilms on human dentin blocks; (C) Proportion of dead E. faecalis cell volume in 1-week-old biofilms; (D) Proportion of dead E. faecalis cell volume in 3-week-old biofilms
Fig. 5
Fig. 5
SEM images of bovine dentinal tubules subjected to: (A) 12-minute PDT with 0.01% MB; (B) 30-minute PDT with 0.01% MB; (C) no treatment (control)
See this image and copyright information in PMC

References

    1. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Pathol. 1965;20:340–9. - PubMed
    1. Fulghum RS, Wiggins CB, Mullaney TP. Pilot study for detecting obligate anaerobic bacteria in necrotic dental pulps. J Dent Res. 1973;52:637.
    1. Keudell K, Conte M, Fujimoto L, Ernest M, Berry HG. Microorganisms isolated from pulp chambers. J Endod. 1976;2(5):146–8. - PubMed
    1. Peters OA, Schönenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. J Endod. 2001;34(3):221–30. - PubMed
    1. Paqué F, Balmer M, Attin T, Peters OA. Preparation of oval-shaped root canals in mandibular molars using nickel-titanium rotary instruments: a micro-computed tomography study. J Endod. 2010;36:703–7. - PubMed

LinkOut - more resources