The Oral-Brain Axis: Mechanistic Insights Linking Periodontitis With Alzheimer's and Parkinson's Diseases

Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are major causes of disability and mortality worldwide. Emerging evidence suggests that chronic peripheral inflammation and microbial dysbiosis may contribute to neurodegenerative processes. The oral-brain axis has recently gained attention as a biological framework linking oral microbial communities, systemic inflammatory responses, immune regulation, and central nervous system function. Within this context, periodontitis, a prevalent chronic inflammatory disease driven by oral dysbiosis, has been proposed as a potential modifiable risk factor for neurodegeneration. This narrative review examines current evidence supporting the oral-brain axis and its role in the relationship between periodontitis and neurodegenerative disorders. Key mechanisms include systemic dissemination of periodontal pathogens and their virulence factors, persistent inflammatory signaling, blood-brain barrier dysfunction, neuroimmune activation, oxidative stress, and protein aggregation. Particular attention is given to the contribution of Porphyromonas gingivalis and associated virulence factors to neuroinflammation, amyloidogenesis, and neuronal injury. Epidemiological, clinical, and experimental studies linking periodontal disease with cognitive decline, Alzheimer's disease, and Parkinson's disease are also discussed. Current evidence supports a biologically plausible association between periodontal disease and neurodegeneration through interconnected microbial, inflammatory, and vascular pathways. Although causality remains to be established, the oral-brain axis provides valuable insight into potential mechanisms underlying this relationship. Improved understanding of these interactions may facilitate the development of preventive and therapeutic strategies that integrate oral healthcare with approaches aimed at preserving neurological health and reducing the burden of neurodegenerative diseases.