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.
Highlights
Carious lesions on restored teeth recur at alarming rates
The mechanism behind Antimicrobial photodynamic therapy (aPDT) is based on prompting oxidative photo-damage of the targeted bacteria
The emission spectrum peak of the light-emitting diode (LED) source was 667 ± 3 nm, which was overlapped with the peak absorbance of toluidine blue O (TBO)
Summary
Carious lesions on restored teeth recur at alarming rates. The onset of primary or recurrent carious lesions is triggered by the biofilm growth over the tooth surface or tooth–material interface [2,3]. Caries-related biofilms are composed of a densely filled community of microbial cells. These bacterial cells can produce and survive in acidic environments and surround themselves with an exopolysaccharide (EPS)-rich matrix [4,5]. This biofilm is composed of many different microbial species, the leading role in its formation and pathogenicity is attributed to Streptococcus mutans [6,7]
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