A study suggested oral bacteria may contribute to some cases of knee osteoarthritis and rheumatoid arthritis. The researchers tested the synovial fluid, which is found in the joints, of 36 people with knee arthritis. Five of the patients had gum bacteria in their fluid. For two of the patients, the bacteria found in the joint fluid was a genetic match to bacteria found in the mouth.
Bacteria in the joints could exacerbate arthritis, the researchers said. However, because the study was small, more research is needed to prove that mouth bacteria can cause or worsen arthritis.