A separate study out of India, which was published this year in the Annals of the Rheumatic Diseases, found twice as many cases of periodontal disease in 91 patients with RA compared to 93 patients without RA. Because none of the people with arthritis had taken disease-modifying antirheumatic drugs (DMARDs), the drugs’ suppression of the immune system could not be blamed for the disparity.

While research hasn’t proven a cause and effect, increasingly it is showing that periodontal disease in people with RA doesn’t always come after RA – in some cases it precedes it, says Dr. Molitor.

A Common Pathway

Researchers studying the RA-periodontal disease connection have found likenesses in the joint and oral tissues, as well as in the inflammatory processes that affect them.

“If you look at the tissues of the mouth in periodontitis and the tissues of the joint in RA, there are a number of similarities – including the types of cells that are infiltrating tissues of the mouth in periodontitis and the tissue of the joint,” says Clifton O. Bingham III, MD, associate professor of medicine and director of the Johns Hopkins Arthritis Center at Johns Hopkins University in Baltimore. He also notes that the levels of proinflammatory proteins like tumor necrosis factor, interleukin-1 and interleukin-6 are also similar in RA and periodontitis. 

Research has also shown a genetic link between the two. In a study published in  Journal of Periodontology, scientists in Israel found HLA-DR4 – a genetic type that occurs with high frequency in people with rheumatoid arthritis – in 8 out of 10 patients with rapidly progressive periodontitis, compared to just a little over a third of a healthy control group.       

Such findings led doctors to believe that there may in fact be a relationship between the two driven by an underlying disease process, says Dr. Bingham.

A potential advance in the understanding of that disease process came around a decade ago when scientists began to understand that one of the early markers of RA is the development of antibodies to citrullinated peptides.