From 1977 to 1989, the American Academy of Periodontology (AAP) went from 2 main periodontal disease categories
to 5 (Table 1).1 The 1989 periodontal disease classification was a significant improvement over previous classifications. In particular, the effect of systemic disease on periodontal health was recognized and added as a category. Also, more criteria for earlyonset diseases were added. However, the 1989 classification had its shortcomings including: lack of a
category for strictly gingival diseases; overlap between disease categories; difficulty in fitting
certain patients into any of the existing categories; similarity of microbiological and host response features in
purportedly different disorders; an emphasis on age of onset that became a problem as patients aged into a new
category; and some unclear classification criteria.