Periodontitis is an inflammation of the periodontium. The periodontium consists of the supporting tissues of the dental organ: the gum, the cementum, the alveolar-dental ligament and the alveolar bone. It is the evolution of gingivitis (inflammation and swelling of the gum visible on the left of this drawing) which has spread to the underlying tissues. Periodontitis is formed by a periodontal pocket associated with a loss of attachment of the tooth with the support tissues that can be seen particularly in this drawing with damage to the alveolar bone.