Classification systems are necessary in order to provide a framework in which to scientifically study the etiology, pathogenesis, and treatment of diseases in an orderly fashion. In addition, such systems give clinicians a way to organize the health care needs of their patients.Periodontal diseases have been recognized and treated for at least 5000 years. Clinicians have recognized for many years that there are apparent differences in the presentation of periodontal diseases and have attempted to classify these diseases. Systems of classifications of disease have arisen allowing clinicians to...