Purpose: The purpose of this study was to evaluate the antimicrobial effects of photothermal therapy using indocyanine green (ICG) and an 810-nm infrared diode laser on Streptococcus gordonii biofilm attached to zirconia surfaces in vitro.
Methods: A biofilm was formed using the static method on zirconia disks placed in a 24-well plate. The biofilms were subdivided into the following six treatment groups: control, commercial photodynamic therapy (PDT), chlorhexidine gluconate (CHX), laser only (L, 810-nm infrared diode), ICG, and laser with ICG (PTT). After treatment, each disk was agitated and the solution with detached bacteria was spread directly on a blood agar plate. Cells were cultured under anaerobic conditions and colony-forming units were counted. Confocal laser-scanning microscopy was used to assess the survival according to the height of the biofilm.
Results: The PTT, PDT, and CHX groups showed a significant reduction in S. gordonii viability (p<0.05), while the L and ICG groups showed no significant difference compared to the control group (p = 0.32, p = 0.97; respectively). In confocal laser-scanning microscopy images, the PTT, PDT, and CHX groups presented most of the dead bacteria in both the upper and lower levels of biofilm.
Conclusion: Within the limitations of this in vitro study, PTT with ICG was effective in significantly reducing the viability of S. gordonii bacteria on zirconia. Further studies are needed to establish a standardized PTT protocol to treat peri‑implant diseases.
Keywords: Indocyanine green; Microbial viability; Peri-implant disease; Photodynamic Therapy; Photothermal therapy; Zirconia.
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