Relevance. Recent data from the World Health Organization highlight the high global prevalence of periodontal diseases. Among middle-aged adults in European countries, the prevalence ranges from 50% to 76%, while in Russia it reaches 86.2% in this group and approaches 100% by the age of 60–65. The diagnosis and prognosis of chronic periodontitis remain pressing challenges in clinical periodontology. While periodontal diseases have multifactorial etiology, microbial factors are primary. In particular, bacteria of the red complex – Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola – are considered key contributors to the progression of inflammation and tissue destruction in the periodontium. Objective. To detect and quantify red complex bacteria in patients with varying severity of chronic periodontitis.

Materials and methods. The study included 126 patients diagnosed with chronic periodontitis, categorized as mild (n = 39), moderate (n = 42), and severe (n = 45). A control group consisted of 39 periodontally healthy individuals. Subgingival plaque samples (from periodontal pockets in patients and from gingival sulci in controls) were analyzed using real-time polymerase chain reaction (PCR) on a DT-96 thermal cycler (DNA-Technology, Russia) with the ParodontoScreen diagnostic kit.

Results. The severity of periodontitis strongly correlated with the presence of P. gingivalis, T. forsythia and T. denticola, with correlation coefficients of 0.997, 0.929, and 0.888, respectively (p < 0.05). The number of genomic equivalents of these microorganisms also correlated with disease severity, with coefficients of 0.948, 0.984, and 0.889, respectively (p < 0.05).

Conclusion. The study confirms the significant role of red complex bacteria in the pathogenesis and progression of chronic periodontitis, supporting their relevance for diagnostic and prognostic applications in periodontal care.