Periodontitis is a chronic inflammation disease that, apart from caries, remains the main cause of tooth loss, that lead to a deterioration of the quality of life. Non-surgical treatment is the basic form of periodontal therapy, regardless of the stage of the disease. Novel supportive treatment methods are constantly implemented to improve the effects of non-surgical treatment, including photodynamic therapy that leads to a selective photosensitization of bacteria with the simultaneous participation of a photosensitizer applied into the periodontal pocket. The aim of the study is to evaluate the use of adjunctive photodynamic therapy on clinical and microbiological parameters in the non-surgical treatment of periodontitis. The clinical study involved 30 generally healthy, non-smoking patients. After a periodontal examination standard non-surgical treatment was applied. 6 weeks later a control periodontal clinical examination was performed and then periodontal pockets were subjected to a photodynamic therapy (PDT) using the FotoSan 630 cm Dental lamp with a perio tip and the FotoSan agent CMS Dental medium density photosensitizer. A significant improvement in clinical parameters including BoP (reduction 73,3%, p <
0,05), PD (reduction 1,9 mm, p <
0,05) and CAL (gain 0,6 mm, p <
0,05) and a significant reduction of red complex bacteria after application of PDT compared to SRP alone was observed. The application of supportive photodynamic therapy improve the effectiveness of periodontal non-surgical treatment including clinical parameters and reduction in subgingival bacteria biofilm.