Periodontitis refers to the inflammation of the supporting structures of the tooth (bone, gums and periodontal ligament). "perio"- surrounding and "-itis" - inflammation. There are several types of bacteria involved in the development of this disease. It is a destructive disease caused by an increase in a number of certain enzymes with 'destructive' properties.There have been studies that support the idea that Vitamin D could reduce the risk and severity of periodontitis. One mechanism would be production of "cathelicidin"and "defensins" which have antimicrobial properties. Another mechanism would be reduction of MMPs or what they refer to as Matrix metalloproteinases, an enzyme that promotes destruction through digesting collagen. Collagen comprises majority of the framework of the bone, gum and periodontal ligament.
Still, the best way to prevent peiodontitis is to reduce plaque through practicing good oral hygiene (brush, floss and rinse) and of course visiting your dentist every 6 months. :)