On a percentage basis the number of aerobic bacteria decrease and anaerobic bacteria increase as the disease progresses. When evaluating the microbiology in a diseased mouth anaerobic cultures are indicated since aerobic cultures tend to be nonproductive. Periodontitis can be characterized by the cardinal sign of destruction of the alveolar bone. The features include conversion of junctional epithelium to pocket epithelium, and destruction of the connective tissue matrix of gingiva and periodontal ligament. Histologically periodontitis is characterized by several stages and closely resembles a typical humoral immune response.
Most veterinary dentists refer to a staging system when characterizing an animal's mouth.
Because periodontitis is usually progressive, staging allows for improved record keeping and treatment planning. None of the stages is totally unique and therefore a great deal of variation can occur in an animal's mouth. The author uses a six stage system for adult periodontitis. Stage 1 is gingivitis. Stage 2 is chronic gingivitis that does not progress to periodontitis.