Periodontitis, also known as pyorrhea, is a set of inflammatory diseases affecting the periodontium, i.e., the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of teeth. Periodontitis is caused by microorganisms that adhere to and grow on the tooth's surfaces, along with an over-aggressive immune response against these microorganisms. A diagnosis of periodontitis is established by inspecting the soft gum tissues around the teeth with a probe (i.e., a clinical examination) and by evaluating the patient's X-ray films (i.e., a radiographic examination), to determine the amount of bone loss around the teeth. Specialists in the treatment of periodontitis are periodontists; their field is known as "periodontology" or "periodontics".
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https://www.hindawi.com/journals/crim/2012/535321/ t. roshna and k. nandakumar, “generalized aggressive periodontitis and its treatment options: case reports and review of the literature,” case reports in medicine, vol. 2012, article id 535321, 17 pages, 2012. doi:10.1155/2012/535321
grover hs, luthra s. molecular mechanisms involved in the bidirectional relationship between diabetes mellitus and periodontal disease. j indian soc periodontol [serial online] 2013 [cited 2016 oct 11];17:292-301. available from: http://www.jisponline.com/text.asp?2013/17/3/292/115642
https://www.hindawi.com/journals/mi/2015/259074/ vilana maria adriano araújo, iracema matos melo, and vilma lima, “relationship between periodontitis and rheumatoid arthritis: review of the literature,” mediators of inflammation, vol. 2015, article id 259074, 15 pages, 2015. doi:10.1155/2015/259074
http://ajpgi.physiology.org/content/early/2016/03/25/ajpgi.00424.2015 periodontal dysbiosis linked to periodontitis is associated with cardio-metabolic adaptation to high-fat diet in mice by maxime branchereau et al., american journal of physiology - gastrointestinal and liver physiology published 31 march 2016 vol. no. , doi: 10.1152/ajpgi.00424.2015