Final answer:
Localized aggressive periodontitis (C) has been excluded from the new classification of periodontitis. It was a term to describe a form of periodontitis affecting younger individuals, which is now included under the broader category of periodontitis.
Step-by-step explanation:
The form of periodontitis that has been excluded from the new classification is localized aggressive periodontitis (C). Periodontitis is inflammation of the gums that is more severe than gingivitis and can spread deeper into the tissues. Necrotizing periodontal disease and periodontitis as a manifestation of systemic disease are still recognized in the current classification system. Localized aggressive periodontitis was a term used to describe a form of periodontitis that affected younger individuals and localized areas of the mouth, but with the new classification system, this term has been revised to be included in the broader category of periodontitis.
Gingivitis progresses to periodontitis when the inflammation and bacterial growth in the gingival space become uncontrolled, causing the gums to recede and expose parts of the tooth normally covered, potentially leading to the erosion of supporting bone and tooth loss.