Diabetes mellitus is a significant health problem, since the number of diabetic patients is continually increasing. In Greece, 7.7-19.5% of the population aged >50 years suffers from diabetes mellitus, and the proportion of undiagnosed cases is also high. It is in fact estimated that in 30% of patients the diagnosis is made incidentally in the course of some other examination  or because of the appearance of a complication.

The relationship between periodontitis and diabetes mellitus has been studied extensively, as far back as the 1960s, and today we can speak of a two-way relationship. Periodontitis is classified as the 6^th complication of diabetes mellitus, and indeed its incidence, severity and rate of progression are greater in diabetics. More specifically, the risk of developing periodontitis is approximately 3 times higher in diabetics, while the destruction of the periodontal tissues begins much earlier. The patient's glycaemic control is also important, because the level of control of diabetes mellitus affects the development, progression and treatment of periodontitis, in the sense that the poorer the glycaemic control, the greater the periodontal destruction, while there are indications that well-controlled diabetics respond to periodontal treatment in the same way as non-diabetics.

Conversely, periodontal disease also affects the severity of diabetes mellitus and makes glycaemic control more difficult. Diabetic patients with generalised advanced periodontitis show poorer glycaemic control and a greater risk of serious complications. A small improvement in glycaemic control levels has also been observed after non-surgical periodontal treatment.