Effect of ultrasonic activation of photosensitizer dye temoporfin (Foscan) on antimicrobial photodynamic therapy: An ex vivo study

In vitro effects of Er: YAG laser-activated photodynamic therapy on Enterococcus faecalis in root canal treatment

OBJECTIVE

Photodynamic therapy (PDT) plays an important role for root canal disinfection. Nevertheless, the effect of photosensitizers penetrating dentin tubules is limited, which ultimately impedes the disinfection effect of PDT. The study implements an Er: YAG laser to activate methylene blue, the photosensitizer, to determine the bactericidal impact of PDT on Enterococcus faecalis in vitro root canals.

METHODS

We obtained 53 single root canal teeth with intact roots, standardized the root to 9 mm. The root canals were prepared using ProTaper rotary files. Subsequently, the teeth were sterilized, and Enterococcus faecalis was cultured for 3 weeks in vitro using brain heart infusion (BHI). The model of Enterococcus faecalis root canal infection of teeth was constructed by observing Enterococcus faecalis through electron microscope scanning. The teeth were randomly allocated to five treatment groups (n = 10): control, NaOCl, NaOCl + Er: YAG, PDT, and PDT + Er: YAG. Following treatment, the number of colony forming units (CFU)/ml was assessed for each group. Statistical analysis was conducted using one-way ANOVA, with post-hoc analysis using Tukey's test for multiple comparisons.

RESULTS

The colony counts in the remaining groups were significantly lower compared to the control group (P<0.001). Using PDT alone had the least impact on reducing colonies, while using PDT and Er: YAG laser together resulted in a significant reduction in colony counts (P<0.001). There was no significant difference in colony counts reduction between the NaOCl + Er: YAG group and the PDT + Er: YAG group (P = 1.000).

CONCLUSIONS

The combination of Er: YAG laser and PDT significantly enhanced the bactericidal efficacy of PDT against Enterococcus faecalis in root canals. It had a similar impact on eliminating Enterococcus faecalis when compared to the effect of using Er: YAG laser and NaOCl.

Photoinactivation and Photoablation of Porphyromonas gingivalis

Several types of phototherapy target human pathogens and Porphyromonas gingivitis (Pg) in particular. The various approaches can be organized into five different treatment modes sorted by different power densities, interaction times, effective wavelengths and mechanisms of action. Mode 1: antimicrobial ultraviolet (aUV); mode 2: antimicrobial blue light (aBL); mode 3: antimicrobial selective photothermolysis (aSP); mode 4: antimicrobial vaporization; mode 5: antimicrobial photodynamic therapy (aPDT). This report reviews the literature to identify for each mode (a) the putative molecular mechanism of action; (b) the effective wavelength range and penetration depth; (c) selectivity; (d) in vitro outcomes; and (e) clinical trial/study outcomes as these elements apply to Porphyromonas gingivalis (Pg). The characteristics of each mode influence how each is translated into the clinic.

An easily achievable strategy to promote the penetration of methylene blue into dentinal tubules

BACKGROUND

One critical issue that impairs the therapeutic effects of antimicrobial photodynamic therapy (aPDT) in root canal disinfection is the insufficient penetration of photosensitizer into dentinal tubules. Therefore, this study aimed to compare the treatments in enhancing photosensitizers' penetrability for aPDT in root canal therapy.

METHODS

Thirty premolars with a single root canal were randomly divided into three groups (n = 10), using Methylene blue (MB) as a photosensitizer and treated with different approaches: sonic-assisted diffusing group, ultrasonic-assisted diffusing group and the control without treatment. All specimens were observed by stereomicroscope to measure the penetration depth of MB into dentinal tubules.

RESULTS

Both sonic and ultrasonic treatments substantially improved the penetrability of MB. The former achieved a deeper penetration depth than the latter did in the same region of root (P<0.05). Regarding the dye penetration depths at different root regions, the control group showed a declining trend from coronal to apical. In contrast, the penetration depths of sonic and ultrasonic-assisted diffusing groups from highest to lowest were middle > coronal > apical (P<0.05).

CONCLUSIONS

This study showed that both sonic and ultrasonic treatments remarkably promoted MB's penetration depth into dentinal tubules. Maximum penetration was achieved when treated with a sonic approach.

Synergistic Effect of Combination of a Temoporfin-Based Photodynamic Therapy with Potassium Iodide or Antibacterial Agents on Oral Disease Pathogens In Vitro

5, 10, 15, 20-Tetrakis(3-hydroxyphenyl)chlorin (temoporfin) is a photosensitizer used in photodynamic therapy for oral cancer and periodontal disease treatment. This study determined the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of temoporfin. Additionally, the combination of potassium iodide (KI) or antimicrobial agents in oral pathogens under hypoxic or normoxic conditions were determined. We also evaluated the biofilm removal effect and detected the expressions of the antibiotic resistance-related genes and biofilm formation-related genes of methicillin-resistant staphylococcus aureus (MRSA). The results provided reveal that the combination of the temoporfin and KI had a synergistic effect of reducing the MICs and MBCs of Lactobacillus acidophilus and Lactobacillus paracasei under normoxic and hypoxic conditions due to increasing H₂O₂ production. Temoporfin increased the biofilm removal of Aggregatibacter actinomycetemcomitans, Enterococcus faecalis, and Staphylococcus aureus under normoxic condition, and it reduced the antibiotic resistance-related genes expression of MRSA. The combination of temoporfin with ampicillin or chlorhexidine significantly enhanced the bactericidal effect on MRSA. This study provides a potential application of temoporfin on the clinical side against oral pathogens and the prevention of oral diseases.

Enhanced antimicrobial activity through the combination of antimicrobial photodynamic therapy and low-frequency ultrasonic irradiation

The rapid increase of antibiotic resistance in pathogenic microorganisms has become one of the most severe threats to human health. Antimicrobial photodynamic therapy (aPDT), a light-based regimen, has offered a compelling nonpharmacological alternative to conventional antibiotics. The activity of aPDT is based on cytotoxic effect of reactive oxygen species (ROS), which are generated through the photosensitized reaction between photon, oxygen and photosensitizer. However, limited by the penetration of light and photosensitizers in human tissues and/or the infiltration of oxygen and photosensitizers in biofilms, the eradication of deeply located or biofilm-associated infections by aPDT remains challenging. Ultrasound irradiation bears a deeper penetration in human tissues than light and, sequentially, can promote drug delivery through cavitation effect. As such, the combination of ultrasound and aPDT represents a potent antimicrobial strategy. In this review, we summarized the recent progresses in the area of the combination therapy using ultrasound and aPDT, and discussed the potential mechanisms underlying enhanced antimicrobial effect by this combination therapy. The future research directions are also highlighted.