Comparison of photodynamic therapy protocols on in vitro peri-implantitis models

Peri-implantitis is a periodontal disease characterized by soft tissue inflamma- tion and bone tissue resorption. Increasing antibiotic resistance hinders the cure of peri- implantitis with antibiotics. In addition, mechanical and chemical interventions may disrupt the osseointegration of the implant because they can cause alterations in the surface roughness. Antibacterial photodynamic therapy is a non-invasive light-based treatment that utilizes photosensitive molecules and it is considered to be a strong alternative to cure bacterial infections. Chlorin e6 is an anionic second-generation photosensitizer. It has low cytotoxicity and high photodynamic properties however there is no study showing the antibacterial efficacy of chlorin e6 for peri-implantitis, to the author's knowledge. In this thesis, we aimed to demonstrate the antibacterial effect of chlorin e6 on both planktonic bacteria and a realistic in vitro peri-implantitis model. We compared the results with methylene blue as it is widely studied for peri- implantitis. Further, we utilized potassium chloride, an inorganic salt, to enhance the effect of photodynamic therapy. The results showed that methylene blue-mediated pho- todynamic therapy outperformed chlorin e6 on planktonic bacteria and caused almost a 6-log reduction in bacterial load. However, in the in vitro PI model there were no statistically significant differences between chlorin e6 and methylene blue. The highest antibacterial effect was achieved with the chlorin e6-mediated photodynamic therapy with the addition of potassium chloride. This thesis showed that chlorin e6-mediated photodynamic therapy potentiated with potassium chloride can be an alternative to methylene blue to cure peri-implantitis.