Inclusion Criteria:  1. The patients aged between 30 and 40 years old were diagnosed with severe periodontitis and were treated for the first time, while those in the control group were patients with non-severe periodontitis or healthy people. All the subjects had complete basic information, questionnaire data and clinical examination data. 3. The patient's thinking is clear, there is no barrier to communication, and can cooperate to complete the questionnaire. 4.In addition, the genetic polymorphism test required that the three generations were all Han nationality, with no history of orthodontic treatment, no obvious malocclusion and local stimulating factors, and no Systemic disease (including diabetes, cardiovascular disease, hepatitis, HIV infection, etc.), non-smoking or non-smoking for more than 5 years  Exclusion Criteria:  1. Patients suspected to be invasive periodontitis, the plaque level and the degree of periodontal destruction are disproportionate. 2. Systemic diseases (including diabetes, cardiovascular disease, hepatitis, HIV infection, etc.) 3. Pregnant women, women who are pregnant, lactating or mentally ill. 4.Those who are taking known drugs that affect periodontal tissue or have a history of antibacterial treatment within 6 months. 5.Those who have a history of periodontal treatment within 6 months are excluded. 6.In addition, testing for genetic polymorphism required the exclusion of malignancies or those who had undergone radiotherapy or chemotherapy