Rheumatoid arthritis (RA) is an autoimmune disease marked by inflammation and painful joints. People with RA are more likely to have periodontal disease, and one study found that they had more missing teeth than people who don’t have RA.
Chronic inflammation is common to both conditions. Although scientists haven’t found evidence that one condition causes the other, a 2009 study found that people with a severe form of RA had less pain, swelling, and morning stiffness after their periodontal disease was treated.
Source: http://www.webmd.com/