initiative 
So far, most studies linking periodontal disease to systemic diseases have focused on diabetes, cardiovascular disease and adverse pregnancy outcomes. However, there are other systemic diseases and conditions that may be related to periodontal disease, but that still need many more studies to provide real, solid evidence. These diseases are primarily chronic obstructive pulmonary disease (COPD), pneumonia, chronic kidney disease, rheumatoid arthritis, cognitive impairment, obesity, metabolic syndrome and cancer.
The associations found in cross-sectional studies and case-control studies have in no event indicated any causality, and more long-term cohort studies and randomized clinical trials need to be performed. The big problem with the studies conducted up to now is the use of certain markers to define disease occurrence, which in many cases, do not verify true disease existence. In addition, the definition of periodontal disease is not standardized for all studies, making it very difficult to compare the results obtained.
It seems clear that the existence of chronic infection and an elevated pro-inflammatory profile may have systemic implications, as has been shown for cardiovascular disease and diabetes, although higher quality studies are needed in order to inform the general public about the uni- or bi-directional relationships between periodontal disease and the various systemic diseases and conditions.
- Linden GJ, Herzberg MC. Periodontitis and systemic diseases: a record of discussions of working group 4 of the Joint EFP/AAP Workshop on Periodontitis and Systemic Diseases. J Periodontol 2013; 84(4 Suppl.):S20-S23