A method of assessing the periodontal status, first defined by Ramfjord in 1967, and used to establish the need for treatment and to evaluate the results following treatment. It is a modification of the periodontal disease index of Russell. Six teeth are examined and scored for gingivitis, calculus and plaque deposits, mobility, lack of tooth contact, and depth of gingival crevice (mobility and lack of tooth contact may be omitted). The PDI is the total of the scores for each tooth divided by the number of teeth examined: the higher the score, the more severe the periodontal disease.
Ramfjord S. P. The Periodontal Disease Index (PDI). J Periodontol 1967;38(6):Suppl:602–10.
http://www.medal.org/visitor/www%5CActive%5Cch9%5Cch9.01%5Cch9.01.15.aspx An overview of the periodontal disease index on the Medical Algorithms website.