Diabetes causes blood vessel changes. The thickened blood vessels can impair the flow of nutrients and removal of wastes from body tissues. This impaired blood flow can weaken the gums and bone, putting them at greater risk for infection.
In addition, if diabetes is poorly controlled, higher glucose levels in the mouth fluids will promote the growth of bacteria that can cause gum disease. On the other hand, uncontrolled periodontal disease may make it harder to control the diabetes.
A third factor, smoking, is harmful to oral health even for people without diabetes. However, a person with diabetes who smokes is at a much greater risk for gum disease than a person who does not have diabetes.
Paired with poor oral hygiene, diabetes can lead to gingivitis, the first stage of periodontal disease, or to periodontitis, which is severe gum disease.