This classification system of periodontal disease was developed during the International Workshop for a Classification of Periodontal Diseases and Conditions (IWCP) October 30th – November 2nd 1999. It is normally referred to as IWCP 1999 classification but also as the AAP 1999 classification. This system is based on loss of attachment. The severity of the disease is categorized as Slight (1-2mm of loss of attachment), Moderate (3-4mm of loss of attachment), or Severe (≥5mm of loss of attachment).
The classification of periodontal disease includes 8 main categories with several subdivisions.