Light Energy Dose and Photosensitizer Concentration Are Determinants of Effective Photo-Killing against Caries-Related Biofilms

Abstract

Caries-related biofilms and associated complications are significant threats in dentistry, especially when biofilms grow over dental restorations. The inhibition of cariogenic biofilm associated with the onset of carious lesions is crucial for preventing disease recurrence after treatment. This in vitro study defined optimized parameters for using a photosensitizer, toluidine blue O (TBO), activated via a red light-emitting diode (LED)-based wireless device to control the growth of cariogenic biofilms. The effect of TBO concentrations (50, 100, 150, and 200 μg/mL) exposed to light or incubated in the dark was investigated in successive cytotoxicity assays. Then, a mature Streptococcus mutans biofilm model under sucrose challenge was treated with different TBO concentrations (50, 100, and 150 μg/mL), different light energy doses (36, 108, and 180 J/cm2), and different incubation times before irradiation (1, 3, and 5 min). The untreated biofilm, irradiation with no TBO, and TBO incubation with no activation represented the controls. After treatments, biofilms were analyzed via S. mutans colony-forming units (CFUs) and live/dead assay. The percentage of cell viability was within the normal range compared to the control when 50 and 100 μg/mL of TBO were used. Increasing the TBO concentration and energy dose was associated with biofilm inhibition (p < 0.001), while increasing incubation time did not contribute to bacterial elimination (p > 0.05). Irradiating the S. mutans biofilm via 100 μg/mL of TBO and ≈180 J/cm2 energy dose resulted in ≈3-log reduction and a higher amount of dead/compromised S. mutans colonies in live/dead assay compared to the control (p < 0.001). The light energy dose and TBO concentration optimized the bacterial elimination of S. mutans biofilms. These results provide a perspective on the determining parameters for highly effective photo-killing of caries-related biofilms and display the limitations imposed by the toxicity of the antibacterial photodynamic therapy’s chemical components. Future studies should support investigations on new approaches to improve or overcome the constraints of opportunities offered by photodynamic inactivation of caries-related biofilms.

Magnetic-Responsive Photosensitizer Nanoplatform for Optimized Inactivation of Dental Caries-Related Biofilms: Technology Development and Proof of Principle

“…Encapsulating the TBO inside the microemulsion was also associated with improved TBO’s biocompatibility. Our previous report showed that 100 μg/mL TBO did not induce significant toxicity against mouse monocyte-macrophage cells . However, the results of this study illustrated that TBO alone was very toxic against the human gingival fibroblasts, as the percentage of fibroblast viability was 33.4%.…”

“…When the TBO was incorporated inside the microemulsion, the viability increased by 1-fold, resulting in more enhanced viability. Such results may encourage higher concentrations of TBO within the microemulsions to maximize the antibacterial reduction, as increasing the concentration of TBO is associated with an enhanced antibiofilm effect . Unlike most of the nanoparticles, increasing the SPIONs concentration was associated with improved biocompatibility.…”

“…In dentistry, aPDT has been extensively investigated to control several oral diseases, including caries, periodontitis, peri-implantitis, and endodontic infections . As a photosensitizer, TBO is a member of the nonporphyrin phenothiazinium family capable of targeting the bacterial membrane and accumulating inside the mitochondria to attack the targeted cells . TBO has shown a great antibacterial effect against oral pathogens such as S.…”

“…For oral biofilm-associated diseases, especially dental caries, the antimicrobial P.S. based on cationic phenothiazine dye, toluidine blue O (TBO), has been well-studied and mediated expressive photodynamic results. , However, some difficulties still need to be improved in aPDT, such as specific targeting and biological compatibility.…”

Application of Nanoparticles in Endodontics

“…This process causes environmental changes that result in hydroxyl radicals, which are one of ROS's reactive forms [35]. Following the activation of the device by light,PS, the targeted cells are killed by a succession of released oxygen ions and free radicals [36,37]. One of the significant benefits of aPDT is its reliance on enhanced penetration and accessibility of oxygen species [38,39] Type II: Light activates the PS, which then reacts on molecular oxygen with in ground state so create excited state oxygen.…”