A concise explanation of the causes, symptoms and prevention of periodontal disease. The U.S. Department of Health and Human Services defines gingivitis and periodontal disease, related risk factors, symptoms and treatments. Publication available by National Institute of Dental and Craniofacial Research National Oral Health Information Clearinghouse. NIH Publication No. 13-1142. 2013 September.
https://www.nidcr.nih.gov/sites/default/files/2017-09/periodontal-disease_0.pdf