Does a biological link exist between periodontitis and rheumatoid arthritis?

Table 1 Similarities between periodontal structures and articular joint

Supporting periodontal structures	Articular joint
Periodontal structures comprise of cementum, alveolar bone, periodontal ligament, gingival crevicular fluid and gingiva	Articular joints comprise of articular cartilage, bone, ligaments, synovial cavity, synovial fluid, and synovial capsule
Cementum is an avascular tissue	Articular cartilage is an avascular tissue
Periodontal ligament is a thin connective tissue that surrounds the root connecting it to the alveolar bone	Synovial tissue is a thin layer of connective tissue. It consists primarily of two cell types- type A synoviocytes (macrophage derived) and type B synoviocyte (fibroblast derived)
Periodontal ligament is collagenous and consists of epithelial rests of malassez, fibroblasts, osteoblasts and ground substances (hyaluronic acid and proteoglycans-fibronectin and laminin)	Synovial fibroblasts are the most abundant and produce the structural components of the joints including collagen, fibronectin and laminin
Gingival crevicular fluid is an infiltrate of blood	Synovial fluid is an infiltrate of blood

Table 2 Similarities in pathogenesis periodontal disease and rheumatoid arthritis

PD	RA
Chronic immunoinflammatory disease	Chronic immunoinflammatory disease
Periodontal pathogen is the main etiological agent with some element of autoimmunity	Bacteria/peptide as an adjunct antigen in autoantibody production
HLA-DR antigen association	HLA-DR antigen association
Inflammatory infiltrate mainly consists of B cells, plasma cells, PMN, T cell, dendritic cell, and macrophages	Inflammatory infiltrate consists of T cell, B cell, plasma cell, dendritic cell, mast cell, macrophages, and few granulocytes
Increases level of IL-1, TNF-α, PGE2, MMPs, NF-κB, RANK/RANKL/OPG, osteoclast activation	Increases level of IL-1, TNF-α, PGE2, MMPs NF-ĸβ, RANK/RANKL/OPG, osteoclast activation
Th1, ↑ ed Th2 and Th 17	Th1 = Th2 and Th 17
Role of nitric oxide	Role of nitric oxide
Genetic and environmental influences	Genetic and environmental influences
Bacterial DNA of anaerobes and high antibody titres against heat shock protein of P.gingivalis, P. Melanogenicus and P. Intermedia[95]	Bacterial DNA of anaerobes and high antibody titres against heat shock protein of P. gingivalis, P. Melanogenicus and P. Intermedia[95]

PD: Periodontal disease; RA: Rheumatoid arthritis; IL: Inflammatory mediator; MMPs: Matrix metalloproteinases; HLA: Human leukocytic antigen; HLA-DR: Human leucocyte antigen- D related; RANK: Receptor activator of nuclear factor kappa-β; RANKL: Receptor activator of nuclear factor kappa-β ligand; OPG: Osteoprotegerin; P. gingivalis: Porphyromonas Gingivalis; P. intermedia: Prevotella intermedia; P. melaninogenicus: Prevotella melaninogenicus; TNF: Tumor necrosis factor; NF-κB: Nuclear factor - kappa β; IL: Interleukin; PGE2: Prostaglandin E2.