Now doctors have found another link and a way to help alleviate joint pain for some people.
Jan Sidley sees a gum specialist regularly, to keep her gum disease under control.
"He has literally saved my teeth," she said.
In the process, he may have eased her arthritis symptoms.
It's possible, according to researchers at Case Western University. They recruited patients with both gum disease and arthritis.
They found, as they cleared the gum infections, the patients' arthritis joint pain and swelling decreased.
Past research has already linked gum disease to serious ailments, such as heart disease, stroke, and diabetes.
"The common dominating factor in all of them is what we call systemic inflammation," said Dr. Nabil Bissada of Case Western.
Dr. Bissada says toxins from a gum infection can travel through the blood and make an inflammatory disease like arthritis worse.
It's one more reason to take care of your mouth and regularly see your dentist.