ABSTRACT
In order to obtain more knowledge about the causation of periodontal diseases the various forms of the disease have to be classified. In the past 130 years, various classification systems for periodontal diseases based on the understanding of the nature of these diseases at the time the classifications were proposed. Revisions to existing systems have been largely influenced by three dominant paradigms that reflect thinking at the time the classifications were proposed: the clinical characteristics paradigm (1870-1920), the classical pathology paradigm (1920-1970), and the infection/host response paradigm (1970-present). The changes in the paradigm have always been followed by the conceptual changes in the classification of periodontal disease. Although classification systems for periodontal diseases currently in use are firmly based on, and dominated by, the infection/host response paradigm, some features of the older paradigms are still valid and have been retained.