Periodontitis and Rheumatoid Arthritis: Shared Pathophysiology, Bidirectional Association, and Therapeutic Implications—A Narrative Review

Periodontitis (PD) and rheumatoid arthritis (RA) are chronic inflammatory disorders that impose substantial individual and societal burdens worldwide. PD is characterized by progressive destruction of the periodontal ligament and alveolar bone, leading to tooth loss, impaired oral function, and sustained systemic inflammatory burden. RA, affecting approximately 0.5–1% of the population, is a chronic autoimmune disease marked by persistent synovial inflammation, progressive joint destruction, disability, and reduced quality of life. Increasing evidence indicates that these conditions are biologically and clinically interconnected. Both diseases share key pathogenic pathways, including microbial dysbiosis, immune dysregulation, chronic inflammation, genetic susceptibility, and aberrant autoantibody responses. Particular attention has focused on keystone periodontal pathogens such as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, which may promote protein citrullination and the formation of anti-citrullinated protein antibodies (ACPA), thereby providing a plausible mechanistic bridge between periodontal infection and systemic autoimmunity. Shared genetic risk factors, including HLA-DRB1 susceptibility alleles, further support a common host predisposition. Clinical, epidemiological, and translational studies increasingly support a bidirectional association. Individuals with PD appear to have a higher risk of RA development, whereas patients with RA demonstrate greater prevalence, severity, and progression of periodontal disease. Interventional studies suggest that nonsurgical periodontal therapy may reduce local periodontal inflammation, circulating inflammatory biomarkers, and RA disease activity indices, while effective pharmacological control of RA may also improve periodontal outcomes. This narrative review critically evaluates the PD–RA relationship across four interconnected domains: (i) epidemiological and clinical associations between PD and RA, (ii) key mechanisms underlying RA pathogenesis, (iii) shared biological pathways linking both diseases, and (iv) the extent to which treatment of one condition influences the other. Particular emphasis is placed on major sources of heterogeneity and confounding—including smoking, metabolic comorbidities, disease stage, therapeutic exposure, and variable diagnostic definitions—that may explain inconsistencies across the literature. By integrating current mechanistic and clinical evidence, this review provides a structured synthesis that extends beyond a descriptive overview of association studies. A clearer understanding of the periodontal–rheumatologic axis may facilitate risk stratification, identify novel therapeutic targets, and support integrated multidisciplinary care. Targeting both oral and systemic inflammation may improve outcomes in patients with coexisting PD and RA and may potentially reduce the risk or severity of one condition in individuals already affected by the other.