Diabetes mellitus and periodontitis are both chronic inflammatory diseases, which contribute significantly to morbidity and are a major health care burden. The interrelationship between diabetes mellitus and periodontitis has been studied for many years. It has been accepted that the supposed interrelationship between diabetes mellitus and periodontitis is a two-way relationship. In this sense, the presence of one condition tends to increases the risk and severity of the other, and vice versa. However, the mechanisms for this two-way relationship still remain unknown.