# The Link between Periodontal Disease and Oral Cancer--A Certainty or a Never-Ending Dilemma?
## 3 Periodontal Disease and Systemic Disorders  
Although periodontal disease has a local area of manifestation, multiple interferences are known with the general condition for an organism. From this perspective, it must be viewed as a complex pathological process that can only be treated with a combination of medical, surgical, local, and general therapeutic methods. For these reasons, [PERSON] et al. proposed a new concept in periodontal therapy that must be considered a combination of antibacterial treatment of the periodontal disease and therapeutic methods to modulate the body's response [49; 50]. The link between oral disease and general health is not a novel concept. The function of oral infection and inflammation in contributing to disorders in other parts of the body has been investigated and reported for ages. [PERSON], in ancient Greece, healed two patients suffering from discomfort from TMJ disorders by teeth extractions. From 1912 to roughly 1950, we lived in the era of \"focal infection,\" which dominated our thoughts. The \"focal infection theory\" is a historical concept based on the assumption that some infections may cause chronic and acute diseases in different areas of the body. It was extremely popular from 1930 to 1950 when extensive surgical procedures were carried out with the intention of eliminating all infection sources. The pathogens involved in periodontal disease can migrate, develop, and cause various systemic illnesses, including cardiovascular, respiratory, and metabolic (i.e., diabetes and osteoporosis) diseases [51]. Individuals coming to the emergency room with a myocardial infarction were overwhelmingly likely to have periodontal disease, according to [PERSON] and his colleagues [52]. Around 400 to 700 species have been found, and certain commensal bacteria may evolve, into \"opportunistic\" species, with some of them being strictly considered as pathogens. It is feasible to speculate that they may play a role in local or systemic illnesses [53]. Even while it is common to perceive periodontitis as having potentially detrimental effects on the body, the exact contribution of periodontitis to the etiology and progression of systemic disorders is not well understood today, but scientists supposed that periodontitis and systemic disorders have a close link, which leads to an intensification of the inflammatory response and an altered immunological response [54]. Advanced periodontal disease can have a substantial systemic influence on the body, extending beyond the oral cavity due to local inflammation, bone degradation, and tooth loss [55]. Recent advancements in detecting and measuring bacteria using new sequencing methodologies (e.g., metagenomics) have opened up new possibilities for research into the function of the microbiota in cancer formation [56; 57; 58]. There are over 57 systemic disorders that are thought to be linked to periodontal diseases, indicating that the links are established through a shared pathogenic process [59]. Figure 1 shows an association between oral cavity pathogens and general diseases [60]. Despite the fact that diabetes mellitus increases the risk of periodontal disease, epidemiological studies demonstrate that people with well-controlled diabetes have periodontal problems similar to those reported in the healthy population [61]. Periodontal disease and diabetes mellitus were described as a two-way interaction in a work by [PERSON] and [PERSON] [62]. Several randomized control trials, as well as a number of longitudinal and observational investigations, have offered data to back up the idea that periodontitis can have a negative impact on glycemic control [63]. Following the same path, periodontal disease was also associated with respiratory infections. In 2006, [PERSON] and [PERSON] presented a review paper about the etiological relationship between oral health and pneumonia or other respiratory disorders [64]. The authors came to the conclusion that there is reasonable evidence of a link between them.