Inflammation is the most likely link between periodontitis and other systemic diseases. The function of inflammation is to defend the body against microbial infection, and to repair injured tissues. But, inflammation does have the potential to cause harm.
Bacterial plaque around teeth can cause inflammation. Inflammation generally begins with an influx of plasma fluid (swelling) and defense cells (white blood cells). This creates a reddish halo around the gums, called gingivitis. The purpose of this is to eliminate microbes and clean out damaged tissue. If the plaque biofilm persists around teeth, inflammation can change into a chronic state, involving different, more specific defense cells.
Resolution of inflammation requires certain cellular mechanisms that trigger a “clean and repair” response. When those mechanisms are dysfunctional, inflammation can become a self-sustaining chronic condition, like periodontal disease. However, it is well known that not everyone is equally susceptible to developing periodontal disease. More importantly, many of the people that that show this inflammatory dysfunction may be susceptible to other inflammatory diseases.