Methylene Blue and Hydrogen Peroxide for Photodynamic Inactivation in Root Canal - A New Protocol for Use in Endodontics

Antimicrobial photodynamic inactivation of Pseudomonas aeruginosa persister cells and biofilms

Pseudomonas aeruginosa is a hard-to-treat human pathogen for which new antimicrobial agents are urgently needed. P. aeruginosa is known for forming biofilms, a complex aggregate of bacteria embedded in a self-generated protective matrix that enhance its resistance to antibiotics and the immune system. Within the biofilm, persister cells, sub-populations of slow-growing or growth-arrested cells, are associated with recalcitrance of infections and antibiotic treatment failure. Here, we investigate the influence of the anionic photosensitiser chlorophyllin (CHL)1 exposed to red light alone and in combination with an activator of the mechanosensitive channels butylparaben (BP) on P. aeruginosa growing cells, persister cells, and biofilms. Antimicrobial susceptibility tests were performed using the broth microdilution checkerboard method. Serine hydroxamate (SHX) was used for the induction of persister cells. Under illumination, a combination of CHL (250 µg/ml) and BP (97.12 µg/ml) reduced the number of growing cells and persister cells by 2.2±0.46 log10 and 1.7±0.15 log10, respectively after 30 min of exposure at 79 J/cm2. A higher concentration of BP (194.23 µg/ml) or longer exposure time (60 min at 158 J/cm2) effectively eliminated approximately ≥99.99 % of growing and persister cells. Visual evidence from confocal and TEM images illustrates the influence of CHL and red light, which intensifies when combined with BP. Nevertheless, the addition of BP did not enhance the efficacy of CHL against biofilms; CHL (500 µg/ml) reduced biofilm viability by 2.6 log10 at 791 J/cm2. No toxicity has been observed in darkness. This study highlights the potential antimicrobial effect of CHL against P. aeruginosa.

Regenerative endodontic therapy in immature teeth using photobiomodulation and photodynamic therapy; a histomorphological study in canine model

BACKGROUND

Regenerative endodontic therapy (RET) is still coming up short to demonstrate histological evidence for true regeneration with clinically feasible protocol of cell homing in single visit approach.

AIM

The aim of the present study is to evaluate the regenerative potential of photobiomodulation (PBM) on RET in immature roots when photodynamic therapy (PDT) protocol is implemented for root canal disinfection in canine model.

MATERIALS AND METHODS

Seventy-two root canals were recruited, with sixty assigned to experimental groups and twelve to positive and negative controls. Following the induction of pulp necrosis and apical periodontitis, the roots were divided into two experimental groups: Group I received RET followed by PBM (seven sessions with an 808 nm diode laser at 300 mW for 90 s), and Group II received RET without PBM. Follow-ups were conducted at 1, 2, and 3 months (subgroups A, B, and C respectively). Qualitative and quantitative assessment was carried out histologically. All data were statistically analyzed with the Mann-Whitney U test and Bonferroni's adjustment, as well as Chi square test.

RESULTS

The newly formed hard tissue highly resembled true dentine where the dentinal tubules looked well organized lined by poly layers palisading pattern of rounded odontoblast-like cells with cytoplasmic processes extending through the predentine layer. GI exhibited statistically significantly higher scores of vital tissue infiltration and hard tissue deposition in subgroups A and B (P ≤ 0.05). The inflammatory cells scores were significantly lower in GI than in GII at all time intervals. However, no significance could be detected regarding apical closure.

CONCLUSION

The disinfection protocol of PDT and subsequent irradiation with low power laser in PBM protocol pose a promising potential for regenerative endodontics in immature teeth.

Photodynamic therapy: An emerging therapeutic modality in dentistry

Photodynamic Therapy (PDT) is a rapidly evolving, non-invasive treatment modality with considerable promise in dental pharmacotherapeutics. This review article comprehensively examines PDT, beginning with its principles and then delving into its diverse applications in dentistry, including periodontal disease, endodontics, oral cancer, dental implants, and dental caries. Each area presents the latest research and discusses the potential benefits and challenges. The unique advantages of PDT are highlighted, such as selective targeting, broad-spectrum antimicrobial effect, lack of resistance development, and its synergistic effect with other treatments. However, challenges such as photosensitizer delivery, light penetration, oxygen availability, and the need to standardize protocols are also acknowledged. The review further explores future perspectives of PDT in dentistry, including advancements in photosensitizer design, overcoming hypoxic limitations, personalized protocols, integration with other therapies, and standardization and regulation. The potential of advanced technologies, such as nanotechnology and synthetic biology, to improve PDT outcomes is also discussed. The review concludes that while PDT has shown immense potential to revolutionize dental pharmacotherapeutics, further high-quality research is needed to translate this potential into everyday dental practice. The promising future of PDT in dentistry suggests a more effective and less invasive treatment option for a range of dental conditions.

Effect of Laser Irradiation Modes and Photosensitizer Types on Antimicrobial Photodynamic Therapy (aPDT) for Streptococcus sobrinus in the Crown Dentin of Bovine Teeth: An Experimental In Vitro Study

This study aimed to assess the impact of different laser irradiation modes and photosensitizer types on the bactericidal efficacy of antimicrobial photodynamic therapy (aPDT). Dentin plates were prepared by sectioning the crown dentin of bovine teeth infected with Streptococcus sobrinus (n = 11). Nine aPDTs involving the combination of three 1% solutions of photosensitizers (brilliant blue, BB; acid red, AR; and methylene blue, MB) and three irradiation modes of semiconductor lasers (50 mW for 120 s, 100 mW for 60 s, and 200 mW for 30 s) were performed for each infected dentin plate, and the control consisted of the specimens not applied with aPDT. The bactericidal effects in 10 groups were evaluated using both assays of the colony count (colony-forming-unit: CFU) and adenosine triphosphate (ATP) (relative-light-unit: RLU). The data obtained were analyzed using the Kruskal-Wallis test (α = 0.05). The most aPDT groups exhibited significantly lower RLU and CFU values compared with the control (p < 0.05). The effect of irradiation modes on RLU and CFU values was significant in the aPDT group using BB (p < 0.05) but not in the aPDT group using AR or MB. The aPDT performed with AR or MB exerted a remarkable bactericidal effect.

Hydrogen peroxide preoxidation as a strategy for enhanced antimicrobial photodynamic action against methicillin-resistant Staphylococcus aureus

Antimicrobial photodynamic treatment (aPDT) is a photooxidative process based on the excitation of a photosensitizer (PS) in the presence of molecular oxygen, under specific wavelengths of light. It is a promising method for advanced treatment of water and wastewater, particularly targeting disinfection challenges, such as antibiotic-resistant bacteria (ARB). Research in improved aPDT has been exploring new PS materials, and additives in general. Hydrogen peroxide (H2O2) a widely applied disinfectant, mostly in the food industry and clinical settings, present environmentally negligible residuals at the usually applied concentrations, making it friendly for the water and wastewater sectors. Here, we explored the effects of preoxidation with H2O2 followed by blue light-mediated (450 nm) aPDT using curcumin (a natural-based PS) against methicillin-resistant Staphylococcus aureus (MRSA). Results of the sequential treatment pointed to a slight hampering in aPDT efficiency at very low H2O2 concentrations, followed by an increasing cooperative effect up to a deleterious point (≥7 log10 inactivation in CFU mL-1), suggesting a synergistic interaction of preoxidation and aPDT. The increased performance in H2O2-pretreated aPDT encourages studies of optimal operational conditions for the assisted technology and describes potentials for using the described strategy to tackle the issue of ARB spread.

Oxygen Availability on the Application of Antimicrobial Photodynamic Therapy against Multi-Species Biofilms

Methylene blue (MB)- or Curcumin (Cur)-based photodynamic therapy (PDT) has been used as an adjunctive treatment for periodontitis. Its actual clinical efficacy is still in question because the lack of oxygen in a deep periodontal pocket might reduce the PDT efficacy. We aim to investigate the effect of oxygen on PDT efficacy and to examine if the addition of hydrogen peroxide (HP) could improve PDT performance anaerobically. To this end, we cultured 48 h saliva-derived multi-species biofilms and treated the biofilms with 25 µM MB or 40 µM Cur, HP (0.001%, 0.01% and 0.1%), light (L-450 nm or L-660 nm), or combinations thereof under ambient air or strictly anaerobic conditions. MB- and Cur-PDTs significantly reduced biofilm viability in air but not under anaerobic conditions. HP at 0.1% significantly enhanced the killing efficacies of both MB- and Cur-PDTs anaerobically. The killing efficacy of Cur-PDT combined with 0.1% HP was higher anaerobically than in air. However, this was not the case for MB-PDT combined with 0.1% HP. In conclusion, this study demonstrated that the biofilm killing efficacies of MB- and Cur-PDTs diminished when there was no oxygen. HP at 0.1% can enhance the efficacy of PDT performed anaerobically, but the level of enhancement is photosensitizer-dependent.

Antimicrobial photodynamic therapy against oral biofilm: influencing factors, mechanisms, and combined actions with other strategies

Oral biofilms are a prominent cause of a wide variety of oral infectious diseases which are still considered as growing public health problems worldwide. Oral biofilms harbor specific virulence factors that would aggravate the infectious process and present resistance to some traditional therapies. Antimicrobial photodynamic therapy (aPDT) has been proposed as a potential approach to eliminate oral biofilms via in situ-generated reactive oxygen species. Although numerous types of research have investigated the effectiveness of aPDT, few review articles have listed the antimicrobial mechanisms of aPDT on oral biofilms and new methods to improve the efficiency of aPDT. The review aims to summarize the virulence factors of oral biofilms, the progress of aPDT in various oral biofilm elimination, the mechanism mediated by aPDT, and combinatorial approaches of aPDT with other traditional agents.

Galleria mellonella-A Model for the Study of aPDT-Prospects and Drawbacks

Galleria mellonella is a promising in vivo model insect used for microbiological, medical, and pharmacological research. It provides a platform for testing the biocompatibility of various compounds and the kinetics of survival after an infection followed by subsequent treatment, and for the evaluation of various parameters during treatment, including the host-pathogen interaction. There are some similarities in the development of pathologies with mammals. However, a limitation is the lack of adaptive immune response. Antimicrobial photodynamic therapy (aPDT) is an alternative approach for combating microbial infections, including biofilm-associated ones. aPDT is effective against Gram-positive and Gram-negative bacteria, viruses, fungi, and parasites, regardless of whether they are resistant to conventional treatment. The main idea of this comprehensive review was to collect information on the use of G. mellonella in aPDT. It provides a collection of references published in the last 10 years from this area of research, complemented by some practical experiences of the authors of this review. Additionally, the review summarizes in brief information on the G. mellonella model, its advantages and methods used in the processing of material from these larvae, as well as basic knowledge of the principles of aPDT.

The role of the light source in antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (APDT) is a promising approach to fight the growing problem of antimicrobial resistance that threatens health care, food security and agriculture. APDT uses light to excite a light-activated chemical (photosensitiser), leading to the generation of reactive oxygen species (ROS). Many APDT studies confirm its efficacy in vitro and in vivo against bacteria, fungi, viruses and parasites. However, the development of the field is focused on exploring potential targets and developing new photosensitisers. The role of light, a crucial element for ROS production, has been neglected. What are the main parameters essential for effective photosensitiser activation? Does an optimal light radiant exposure exist? And finally, which light source is best? Many reports have described the promising antibacterial effects of APDT in vitro, however, its application in vivo, especially in clinical settings remains very limited. The restricted availability may partially be due to a lack of standard conditions or protocols, arising from the diversity of selected photosensitising agents (PS), variable testing conditions including light sources used for PS activation and methods of measuring anti-bacterial activity and their effectiveness in treating bacterial infections. We thus sought to systematically review and examine the evidence from existing studies on APDT associated with the light source used. We show how the reduction of pathogens depends on the light source applied, radiant exposure and irradiance of light used, and type of pathogen, and so critically appraise the current state of development of APDT and areas to be addressed in future studies. We anticipate that further standardisation of the experimental conditions will help the field advance, and suggest key optical and biological parameters that should be reported in all APDT studies. More in vivo and clinical studies are needed and are expected to be facilitated by advances in light sources, leading to APDT becoming a sustainable, alternative therapeutic option for bacterial and other microbial infections in the future.

Improving antimicrobial activity against endodontic biofilm after exposure to blue light-activated novel curcumin nanoparticle

New therapies involving natural products and nanobiotechnology open additional perspectives to reduce endodontic infections. Curcumin is a natural polyphenol extracted from the dry rhizome of curcuma long Linn with therapeutic properties for application in nanobiotechnology and as a photosensitizer for photodynamic therapy. This study aimed to synthesize a novel polymeric nanoparticle of poly (lactic-co-glycolic acid) (PLGA) loaded with curcumin (NP+Cur), and evaluate its antimicrobial activity against endodontic biofilms. Additionally, its biocompatibility using oral keratinocytes was assessed. The polymeric NP+Cur was prepared by the nanoprecipitation method. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were calculated for the three endodontic bacteria (Enterococcus faecalis, Streptococcus oralis and Actinomyces viscosus). Antibacterial activity of NP+Cur against single- and multispecies biofilm pre-formed on the botton 24-well plate and into dentin tubules of bovine teeth were evaluated by colony forming units and confocal laser scanning microscopy. The pre-irradiation time was 5 min followed by exposure to blue light-emitting diode at 450 nm for the photodynamic treatment. Cell viability using oral keratinocytes was assessed by Alamar Blue assay. MIC and MBC showed antibacterial activity of NP+Cur against endodontic bacteria. A treatment of pre-formed biofilms of endodontic bacteria with NP+Cur also significantly decreased bacterial viability. The concentration of 325 μg/mL of photoactivated NP+Cur was the one that most reduced the viability of the endodontic bacteria evaluated. Regarding biocompatibility, NP+Cur 325 μg/mL and pure nanoparticles showed a cell viability greater than 80%. The novel polymeric nanoparticles loaded with curcumin may be a promising adjunct use to treatment of endodontic infections.

Hydrogen peroxide enhances the efficacy of photodynamic therapy against Candida albicans biofilms

The present study aimed to evaluate the effectiveness of hydrogen peroxide (H₂O₂) combined with antimicrobial photodynamic therapy (aPDT) on biofilms formed by Candida albicans strains which are either susceptible to or resistant to fluconazole. Biofilms were grown and treated with H₂O₂, followed by the application of Photodithazine® (P) and red light-emitting diode (LED) (L) either separately or combined (n = 12). After the treatment, biofilms were evaluated by estimating colony-forming unit ml^-1, extracellular matrix components [water -soluble and -insoluble polysaccharides, proteins, extracellular DNA (eDNA)], biomass (total and insoluble dry-weight), and protein concentration. Biofilms formed by both strains presented a significant reduction in cell viability, biomass, extracellular matrix components (both types of polysaccharides, eDNA), and proteins (in the soluble and insoluble portion of biofilms) compared to the control. Microscopy images of the biofilms after treatments showed disarticulation of the matrix and scattered fungal cells. The application of H₂O₂ can disturb the organization of the extracellular matrix, and its association with aPDT potentiated the effect of the treatment.

Membrane damage as mechanism of photodynamic inactivation using Methylene blue and TMPyP in Escherichia coli and Staphylococcus aureus

The worldwide threat of antibiotic resistance requires alternative strategies to fight bacterial infections. A promising approach to support conventional antibiotic therapy is the antimicrobial photodynamic inactivation (aPDI). The aim of this work was to show further insights into the antimicrobial photodynamic principle using two photosensitizers (PS) of different chemical classes, Methylene Blue (MB) and TMPyP, and the organisms Escherichia coli and Staphylococcus aureus as Gram-negative and Gram-positive representatives. Planktonic cultures of both species were cultured under aerobic conditions for 24 h followed by treatment with MB or TMPyP at various concentrations for an incubation period of 10 min and subsequent irradiation for 10 min. Ability to replicate was evaluated by CFU assay. Accumulation of PS was measured using a spectrophotometer. The cytoplasmic membrane integrity was investigated by flow cytometry using SYBR Green and propidium iodide. In experiments on the replication ability of bacteria after photodynamic treatment with TMPyP or MB, a killing rate of 5 log₁₀ steps of the bacteria was achieved. Concentration-dependent accumulation of both PS was shown by spectrophotometric measurements whereby a higher accumulation of TMPyP and less accumulation of MB was found for S. aureus as compared to E. coli. For the first time, a membrane-damaging effect of TMPyP and MB in both bacterial strains could be shown using flow cytometry analyses. Furthermore, we found that reduction of the replication ability occurs with lower concentrations than needed for membrane damage upon MB suggesting that membrane damage is not the only mechanism of aPDI using MB.

Bioluminescent Models to Evaluate the Efficiency of Light-Based Antibacterial Approaches

The emergence of microbial resistance to antimicrobials among several common pathogenic microbial strains is an increasing problem worldwide. Thus, it is urgent to develop not only new antimicrobial therapeutics to fight microbial infections, but also new effective, rapid, and inexpensive methods to monitor the efficacy of these new therapeutics. Antimicrobial photodynamic therapy (aPDT) and antimicrobial blue light (aBL) therapy are receiving considerable attention for their antimicrobial potential and represent realistic alternatives to antibiotics. To monitor the photoinactivation process provided by aPDT and aBL, faster and more effective methods are required instead of laborious conventional plating and overnight incubation procedures. Bioluminescent microbial models are very interesting in this context. Light emission from bioluminescent microorganisms is a highly sensitive indication of their metabolic activity and can be used to monitor, in real time, the effects of antimicrobial agents and therapeutics. This chapter reviews the efforts of the scientific community concerning the development of in vitro, ex vivo, and in vivo bioluminescent bacterial models and their potential to evaluate the efficiency of aPDT and aBL in the inactivation of bacteria.

Hydrogen peroxide potentiates antimicrobial photodynamic therapy in eliminating Candida albicans and Streptococcus mutans dual-species biofilm from denture base

BACKGROUND

Candida albicans (C.albicans) is the primary pathogen of denture biofilm. Moreover, it could establish a cross-kingdom relationship with bacteria to enhance its virulence and resistance to antifungal drugs. This study aimed to investigate the efficacy of antimicrobial photodynamic therapy (aPDT) in combination with hydrogen peroxide (H₂O₂) against C.albicans and Streptococcus mutans (S.mutans) dual-species biofilm formed on polymethyl methacrylate (PMMA) disk, and explore its involved mechanisms.

METHODS

C.albicans and S.mutans were grown on PMMA disk for 48 h to form biofilm and received different treatments. The treatments included:1) phosphate-buffered saline (PBS) group,2) 100 mM H₂O₂ group,3) aPDT group,4) aPDT+ H₂O₂ and 5) H₂O₂+aPDT group. Colony forming units (CFU), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and scanning electron microscope (SEM) were used to evaluate the antimicrobial effects. Extracellular polysaccharide substance (EPS) production and observation, cell permeability of biofilm, and uptake of toluidine blue O (TBO) by biofilm were assessed to investigate the involved mechanism.

RESULTS

There was no significant difference between PBS group and H₂O₂ group in viable microorganisms and metabolic activity of biofilm. The treatment protocols containing aPDT group reduced microorganism numbers and metabolic activity when compared to PBS group or H₂O₂ group (P<0.05). H₂O₂+aPDT treatment showed the highest antimicrobial efficacy in comparison with other treatments (P<0.05). Pretreatment with H₂O₂ could decrease EPS production and enhance cell permeability, leading to increased TBO uptake in biofilm.

CONCLUSION

Pretreatment with H₂O₂ improved aPDT efficiency in eliminating dual-species biofilm from PMMA disk by reducing EPS amount, enhancing cell permeability, and increasing TBO uptake.

Oral bacterial decontamination using an innovative prototype for photocatalytic disinfection

OBJECTIVES

The aim of this study was to evaluate the effectiveness of a prototype photocatalytic device for bacterial decontaminations of the oral cavity.

METHODS

Sixty-four subjects (18-65) were selected and randomly assigned to eight groups (n = 8), according to oral disinfection protocol: (G1): distilled water (control); (G2): 1.5% hydrogen peroxide (HP); (G3): 3.0% HP; (G4): 0.12% chlorhexidine (CHX); (G5): Germinator; (G6): 1.5% HP + Germinator; (G7): 3.0%HP + Germinator; (G8): 0.12% CHX + Germinator. Stimulated saliva was collected before and after a 3-min mouthwash and/or Germinator application. The patients were kept relaxed and retained saliva 5-10 min, spitting out into the tube for 3 min. The percentage bacterial reduction was checked by counting the colony-forming units (CFUs) after culturing on blood agar plates. Data were subjected to one-way ANOVA followed by Tukey's post hoc test (α = 5%) for statistical significance.

RESULTS

The highest bacterial reduction was observed in groups 3 (3.0% HP), 6 (1.5% HP + Germinator), and 7 (3.0% + Germinator), with no statistically significant difference between them (p > 0.05). Groups 6 (1.5% HP + Germinator) and 8 (0.12% CHX + Germinator) showed higher bacterial reduction than groups 2 (1.5% HP) and 4 (0.12% CHX) (p < 0.05). Finally, group 5 (Germinator) showed higher bacterial reduction than control group (DW) and group 4 (0.12% CHX) (p < 0.05).

CONCLUSIONS

The photocatalytic disinfection was effective against oral bacteria and improved the antimicrobial action of 1.5% HP and 0.12%.

CLINICAL SIGNIFICANCE

The photocatalytic disinfection can be an alternative protocol to provide the oral decontamination.

Photodynamic Therapy in Endodontics: A Helpful Tool to Combat Antibiotic Resistance? A Literature Review

BACKGROUND

Antibiotic resistance has become a growing global problem where overprescription is a contributing factor for its development. In the endodontics field, complementary treatments, such as antimicrobial photodynamic therapy (aPDT), have been described to eliminate residual bacteria from the root canal space and reduce complications. The aim of this review is to describe the literature evidence up to now regarding the advantages, efficiency, and clinical outcomes of this therapy in endodontics as a possible tool to combat antibiotic resistance.

METHODS

A review of the literature from 2010 to 2021 was carried out using the PubMed and Web of Science databases. Two steps were taken: First, articles were compiled through the terms and MeSH terms "Photochesdmotherapy" and "endodontics." Then, a second search was conducted using "photodynamic therapy" and "antibiotic resistance" or "drug resistance, microbial."

RESULTS

A total of 51 articles were included for evaluation: 27 laboratory studies, 14 reviews, and 10 clinical studies. Laboratory studies show that aPDT achieves significant bacterial elimination, even against antibiotic-resistant species, and is also effective in biofilm disruption. Clinical studies suggest that aPDT can be considered a promising technique to reduce bacterial complications, and reviews about the issue confirm its advantages.

CONCLUSION

The benefits of aPDT in reducing complications due to its antibacterial effects means a possible decrease in systemic antibiotic prescription in endodontics. In addition, it could be an alternative to local intracanal antibiotic therapy, avoiding the appearance of possible antibiotic resistance, as no bacterial resistance with aPDT has been described to date.

Synergetic antimicrobial effect of chlorin e6 and hydrogen peroxide on multi-species biofilms

Antimicrobial photodynamic therapy (aPDT) has been considered as a potential alternative to antibiotics for the treatment of biofilm infections. There is evidence that an additional H₂O₂ enhances the antimicrobial efficacy of aPDT. However, the minimum H₂O₂ concentration to achieve this synergistic effect is unclear. A saliva-derived multi-species biofilm was treated with the photosensitizer chlorin e6 (Ce6, 50 µM), H₂O₂ (0.3, 3.3, 33.3 mM), or their combination for 5 min, followed by no irradiation or irradiation at 15 J (cm²)^-1 (λ = 450 nm or 660 nm), with or without oxygen. Biofilm viability and metabolic activity were evaluated. The combination of 33.3 mM H₂O₂ and Ce6-aPDT strongly enhanced antimicrobial efficacy compared with either component alone, irrespective of oxygen availability and irradiation wavelength. In particular, the combination resulted in a 6.6-log colony forming unit (CFU) reduction anaerobically under blue irradiation. This combination is a promising treatment for biofilm infections, especially those thriving in an anaerobic microenvironment.

Retrospective clinical evaluation of root canal treatment with or without photodynamic therapy for necrotic teeth and teeth subjected to retreatment

PURPOSE

To compare the effect of photodynamic therapy (PDT) as a procedure to complement root canal treatment (RCT), for both primary treatment and retreatment.

METHODS

This was a retrospective study based on analysis of clinical records. A total of 214 teeth that had undergone RCT on either a primary or retreatment basis, with or without complementary PDT, were evaluated. For 118 teeth that met the previously established inclusion criteria, the time until healing was evaluated. Complementarily, the need for application of calcium hydroxide (CaHy) between visits and the number of visits necessary for completing the treatment were assessed. Data were analyzed using the Mann-Whitney and χ² tests with a significance level of P < 0.05.

RESULTS

Periapical radiolucency resolution was achieved at 15 ± 9.33 months in the RCT + PDT group and 20.35 ± 22.1 months in the RCT group (P = 0.07). For primary treatment, CaHy was necessary in 72.4% of the RCT cases and 16.4% of the RCT + PDT cases (P < 0.01). For retreatment cases, CaHy was used in 82.7% of the RCT cases and 17% of the RCT + PDT cases (P < 0.01). In the RCT group, more than two visits were necessary for primary treatment in 18.6% of the cases, compared with 13.10% in the RCT + PDT group (P = 0.31), whereas for retreatment, more than two visits were necessary for 64.9% and 49.1% of cases, respectively (P = 0.05).

CONCLUSION

In comparison with RCT alone, teeth receiving RCT + PDT showed less variation in the time needed for periapical lesion healing, fewer cases required CaHy, and fewer cases required more than two visits to complete the treatment.

Effects of antimicrobial photodynamic therapy on antibiotic-resistant Escherichia coli

This study used Electron Cryo-tomography (ECT) and fluorescent images to evaluate antimicrobial photodynamic therapy (aPDT) on the envelope architecture of a Gram-negative bacteria and the effects of combined therapy of aPDT and antibiotics. Standard and clinical suspension of Escherichia coli were submitted to photodynamic treatment with methylene blue solution (100μM) and a 100 mW LED emitting at 660 nm with 3 and 18 J of energy. As a control group, a suspension of E. coli was submitted to penicillin V for 60 min at 30 °C, to compare the damage in cell wall structure. After treatment, ECT images were collected and E. coli biofilms were grown in glass-cover slides and stained with live/dead staining for fluorescence analysis before and after treatments. Bacteria were also submitted to disc diffusion and MIC₅₀ tests with Ampicillin, Amoxicillin + Clavulanic acid, Clindamycin and Erythromycin. For in vivo experiment Galleria mellonella larvae were infected with E. coli and treated with antibiotics, aPDT or combined therapy. ECT images presented damage to cell walls and vesicles structures inside and outside the bacteria and fluorescent images showed dose dependent effect of aPDT. Antibiotic or aPDT alone did not improve the survival of caterpillars, but the combined therapy significantly increased survival curve. ECT and fluorescent images shows that aPDT seems to promote micro-damages to cell envelope and causes the production of membrane vesicles permeabilizing cell membranes. The results showed that pre-treating bacterial cells with a photosensitizer and light make them more susceptible to antibiotics and could be an alternative to local infection treatment by resistant bacteria.

Laser-Assisted aPDT Protocols in Randomized Controlled Clinical Trials in Dentistry: A Systematic Review

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) has been proposed as an effective alternative method for the adjunctive treatment of all classes of oral infections. The multifactorial nature of its mechanism of action correlates with various influencing factors, involving parameters concerning both the photosensitizer and the light delivery system. This study aims to critically evaluate the recorded parameters of aPDT applications that use lasers as the light source in randomized clinical trials in dentistry.

METHODS

PubMed and Cochrane search engines were used to identify human clinical trials of aPDT therapy in dentistry. After applying specific keywords, additional filters, inclusion and exclusion criteria, the initial number of 7744 articles was reduced to 38.

RESULTS

Almost one-half of the articles presented incomplete parameters, whilst the others had different protocols, even with the same photosensitizer and for the same field of application.

CONCLUSIONS

No safe recommendation for aPDT protocols can be extrapolated for clinical use. Further research investigations should be performed with clear protocols, so that standardization for their potential dental applications can be achieved.

Microbial Composition of Oral Biofilms after Visible Light and Water-Filtered Infrared a Radiation (VIS+wIRA) in Combination with Indocyanine Green (ICG) as Photosensitizer

In view of increasing antibiotic resistance, antimicrobial photodynamic therapy (aPDT) is an alternative treatment method used to eradicate the microbial community of oral biofilms that can be responsible for different oral infections. In order to investigate changes in the microbial composition after application of aPDT with visible light and water-filtered infrared A (VIS+wIRA) in combination with indocyanine green (ICG), oral microorganisms of the initial and mature biofilm were evaluated by mass spectrometry (MALDI-TOF-MS). To determine surviving microorganisms using MALDI-TOF-MS, an in situ biofilm was irradiated with VIS+wIRA for five minutes in the presence of ICG (300 and 450 µg/mL, respectively). Treatment with chlorhexidine (0.2%) served as positive control. Identified microorganisms of the initial biofilm treated with ICG showed a clear reduction in diversity. The microbial composition of the mature oral biofilm also showed changes after the implementation of aPDT, which mainly resulted in a shift in the percentage of bacterial species. The resulting destruction of the microbial balance within the oral biofilm by aPDT using VIS+wIRA and ICG can be seen as an advantageous supplementary approach in the adjunctive treatment of periodontitis and peri-implantitis.

Antimicrobial photodynamic therapy fighting polymicrobial infections – a journey from in vitro to in vivo

The batericidal effects of antimicrobial photodynamic therapy (aPDT), using methylene blue as a photosensitizer and pulsed red LED light for activation, were tested in various environments in vitro and in a wound model in mice infected with a fecal bacterial suspension.

Potassium iodide enhances the photobactericidal effect of methylene blue on Enterococcus faecalis as planktonic cells and as biofilm infection in teeth

OBJECTIVE

To explore the effectiveness, biosafety, photobleaching and mechanism of antimicrobial photodynamic therapy (aPDT) using methylene blue (MB) plus potassium iodide (KI), for root canal infections.

METHODS

Different combinations and concentrations of MB, KI and 660 nm LED light were used against E. faecalis in planktonic and in biofilm states by colony-forming unit (CFU), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM). Human gingival fibroblasts (HGF) were used for safety testing by Cell Counting Kit-8 (CCK8) and fluorescence microscopy (FLM). The photobleaching effect and mechanisms were analyzed.

RESULTS

KI could not only enhance MB aPDT on E. faecalis in both planktonic and biofilm states even in a hypoxic environment, but also produced a long-lasting bactericidal effect after end of the illumination. KI could accelerate photobleaching to reduce tooth staining by MB, and the mixture was harmless for HGFs. Mechanistic studies showed the generation of hydrogen peroxide and free iodine, and iodine radicals may be formed in hypoxia.

CONCLUSION

aPDT with MB plus KI could be used for root canal disinfection and clinical studies are worth pursuing.

Inactivation of oral biofilms using visible light and water-filtered infrared A radiation and indocyanine green

Aim: To investigate the antimicrobial photodynamic therapy (aPDT) of visible light and water-filtered infrared A radiation in combination with indocyanine green (ICG) on planktonic oral microorganisms as well as on oral biofilm. Methods: The irradiation was conducted for 5 min in combination with ICG. Treatment with chlorhexidine served as a positive control. The number of colony forming units and bacterial vitality were quantified. Results: All tested bacterial strains and salivary bacteria were killed at a level of 3log_10. The colony forming units of the initial mature oral biofilms were strongly reduced. The high bactericidal effect of aPDT was confirmed by live/dead staining. Conclusion: The aPDT using visible light and water-filtered infrared A radiation and ICG has the potential to treat periodontitis and peri-implantitis.

The potential of commercially available phytotherapeutic compounds as new photosensitizers for dental antimicrobial PDT: A photochemical and photobiological in vitro study

The present study evaluated the effectiveness of extracts of commercially available Curcuma longa, Citrus lemon, Hamamelis virginiana and Hypericum perforatum as photosensitizers in Antimicrobial Photodynamic Therapy (aPDT). Each photosensitizer (PS) was analyzed in a spectrophotometer between 350 and 750 nm to determine the ideal light source. Once the absorption bands were determined, three light sources were selected. To determine the concentration of use, the compounds were tested at different concentrations on bovine dentin samples to evaluate the risk of staining. Once the concentration was determined, the PSs were evaluated for dark toxicity and phototoxicity on fibroblast and bacteria culture. Each compound was then irradiated with each light source and evaluated for the production of reactive oxygen species (ROS). The bacterial reduction was tested on E. faecalis culture in planktonic form and on biofilm using an energy of 10 J and an Energy Density of 26 J/cm². The tested compounds exhibited light absorption in three bands of the visible spectrum: violet (405 nm), blue (460 nm) and red (660 nm). At a 1:6 concentration, none of the compounds caused tooth staining as they did not exhibit significant toxicity in the cells or bacterial suspension. Additionally, significant ROS production was observed when the compounds were irradiated at each wavelength. When aPDT was performed on the plactonic and biofilm bacteria, significant microbial reduction was observed in both cases, reaching a reduction of up to 5Logs. In conclusion, extracts of Curcuma longa, Citrus lemon, Hamamelis virginiana and Hypericum perforatum exhibited potential for use as photosensitizing agents in aPDT.

Exploring the Galleria mellonella model to study antifungal photodynamic therapy

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) shows antimicrobial activity on yeast of the genus Candida. In aPDT, the depth at which the light penetrates the tissue is extremely important for the elaboration of the treatment. The aim of this study was to evaluate the action of aPDT on experimental candidiasis and the laser impact in the tissue using Galleria mellonella as the infection model.

METHODS

G. mellonella larvae were infected with different Candida albicans strains. After 30 min, they were treated with methylene blue-mediated aPDT and a low intensity laser (660 nm). The larvae were incubated at 37 °C for seven days and monitored daily to determine the survival curve, using the Log-rank test (Mantel Cox). To evaluate the distribution of the laser as well as its depth of action in the larva body, the Interactive 3D surface PLOT of Image J was used. The effects of aPDT on the immune system were also evaluated by the quantification of hemocytes in the hemolymph of G. mellonella after 6 h of Candida infection (ANOVA and Tukey's test).

RESULTS

In both the ATCC 18,804 strain and the C. albicans clinical strain 17, aPDT prolonged the survival of the infected G. mellonella larvae by a lethal fungal dose. There was a statistically significant difference between the aPDT and the control groups in the ATCC strain (P = 0.0056). The depth of laser action in the insect body without the photosensitizer was 2.5 mm and 2.4 mm from the cuticle of the larva with the photosensitizer. In the larvae, a uniform distribution of light occurred along 32% of the body length for the group without the photosensitizer and in 39.5% for the group with the photosensitizer. In the immunological analysis, the infection by C. albicans ATCC 18,804 in G. mellonella led to a reduction in the number of hemocytes in the hemolymph. The aPDT and laser treatment induced a slight increase in the number of hemocytes.

CONCLUSION

Both aPDT and laser treatment positively influenced the treatment of experimental candidiasis. G. mellonella larvae were a useful model for the study of light tissue penetration in antimicrobial photodynamic therapy.