Amani M. Harrandah
The oral cavity harbors one of the most diverse microbial ecosystems in the human body, second only to the gut. Periodontitis, a chronic inflammatory disease arising from oral microbiota dysbiosis, has been increasingly associated with systemic disorders such as diabetes mellitus, atherosclerosis, rheumatoid arthritis, inflammatory bowel disease, and neurodegenerative conditions. Although hematogenous dissemination of oral pathogens and inflammatory mediators has long been proposed as a mechanistic link, emerging evidence identifies the oral–gut axis as a novel bidirectional pathway. Swallowed oral pathobionts, such as Porphyromonas gingivalis and Fusobacterium nucleatum, can colonize the gut, disrupt the intestinal barrier, and induce dysbiosis, immune imbalance, and metabolic alterations that aggravate systemic inflammation and disease progression. In contrast, gut dysbiosis, especially in obesity or high-fat-diet models, can exacerbate periodontal tissue destruction through hyperuricemia, altered bone metabolism, and Th17/Treg immune imbalance. Experimental and clinical studies further support this reciprocal relationship, implicating microbial, metabolic, and immune crosstalk in both oral and systemic pathology. Understanding this oral–gut–systemic axis offers a paradigm shift in diagnostics and therapeutics, focusing on precision interventions such as microbiome modulation, probiotics, and integrated oral care to mitigate systemic inflammatory burden and improve overall health outcomes.