Orthodontic treatment is considered to be an important measure in the multidisciplinary combination of treatment of severe periodontal disease. However, when orthodontic treatment can be started and how to assess the periodontal status during treatment still rely on the clinical experience of the doctor’s judgment. Today, we read a clinical case report published in AJODO by Japanese scholars, in which the authors applied a new method to assess the etiology and status of aggressive periodontitis, which can more accurately guide clinical treatment, and is worth learning from. In general, our clinical method of evaluating the etiology and status of aggressive periodontitis is clinical and radiological examination, which is more subjective. The new method is this: in addition to the conventional clinical examination, the authors also did ELISA to check the antibody titer of serum pathogenic microorganisms and PCR to check the pathogenic microorganisms. The authors concluded that this method is not only suitable for aggressive periodontitis but also for patients with severe chronic periodontitis. The benefit of microbial antibody titers and PCR examination is not only to identify the main pathogenic changes in periodontitis, but also to quantify the severity of periodontal disease and the efficacy of conventional periodontal treatment (high antibody titers indicate severe disease). In a word, quantitative examination of pathogenic microbial changes before, during and after the start of orthodontics is an effective tool to guide whether orthodontics can be started and carried out smoothly. Let’s take a closer look at the initial data of this case: It can be seen that 12, 21, 22, 24, 33, 34, 35, 36, 42, 46 have severe bone loss. A: Standard dental radiographs show 12, 21, 22, 24, 33, 34, 35, 36, 42, 46 with severe bone loss; B: Clinical periodontal pocket and probing bleeding examination, 21 with a pocket depth of 12 mm; C shows the patient’s antibody titers against different pathogenic microbial antigens, suggesting that the main pathogenic microorganism of periodontitis in this patient is an associated Actinomyces Aactinomycetemcomitans, which is a common causative agent of aggressive periodontitis. The periodontist extracted his left incisor with severe periodontal disease (21) and treated him with periodontal basic therapy and anti-infective treatment. One year later the patient was advised to visit the authors to explore the possibility of orthodontic treatment. The situation at that time was as follows: (Note that the left incisor 21 in the above picture is a temporary tooth, presumably cemented to the adjacent teeth) Based on the patient’s oral condition, the authors developed an orthodontic treatment plan with the proposed extraction of 12, 34 and 46 distal mesial roots and regular periodontal maintenance and antibody titer and PCR monitoring during the orthodontic treatment. Antibody titers and PCR monitoring during the whole treatment: Note: Graph A shows the amount of actinomycete antibodies during each orthodontic procedure, and graph B shows PCR monitoring of 3 bacteria (including pathogenic actinomycetes). The antibody titer decreased after basic periodontal treatment, and after the periodontal flap procedure, the antibody titer decreased to the minimum and the periodontal status was optimal! Although the periodontal status improved after the initial periodontal treatment, the antibody titers remained high and instead of starting orthodontic treatment immediately, the authors recommended that the patient undergo periodontal flap surgery. Take a look at the periodontal flap surgery and the postoperative periodontium: The periodontal situation has improved considerably. The lower left 6(36) was obvious. The authors then started orthodontic treatment. At the end of the treatment: The treatment was not bad. Only because some of the upper anterior teeth had really little periodontal attachment and loosened significantly, the authors gave her fixed porcelain teeth to keep them.