Eubiosis and dysbiosis in periodontitis-related systemic diseases.

BACKGROUND: This narrative review examines the eubiosis-dysbiosis spectrum in periodontitis and its systemic implications. Evidence is drawn from the literature through 2026; as a narrative review, some selection bias cannot be excluded. Periodontitis, affecting 10%-15% of adults globally, drives systemic health disorders through microbial dysbiosis. OBJECTIVES: This narrative review examines microbial ecological shifts in periodontitis and their implications for cardiovascular disease (CVD), diabetes mellitus (T2D), neurodegenerative disorders, rheumatoid arthritis (RA), and other systemic conditions. METHODS: We have synthesized the current evidence on oral microbiome transitions from eubiosis to dysbiosis, focusing on mechanistic pathways linking periodontal disease to systemic health outcomes. RESULTS: Periodontal dysbiosis may influence systemic health through mechanisms including bacteremia, chronic inflammation, molecular mimicry, and microbiome axis interactions. Individuals with periodontitis show 1.5 to 2-fold increased cardiovascular risk, bidirectional relationships with diabetes (HbA1c reductions of 0.3%-0.5% following periodontal treatment), and associations with Alzheimer's disease, rheumatoid arthritis, and inflammatory bowel disease. Key pathogens including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum have been proposed as keystone species capable of remodeling microbial communities and potentially contributing to systemic effects. CONCLUSIONS: Understanding the eubiosis-dysbiosis spectrum provides crucial insights into oral-systemic health connections and offers therapeutic targets for managing both periodontal and systemic diseases. Integrated medical-dental care approaches, precision medicine strategies, and microbiome-based therapeutics represent promising future directions.