The prevalence and severity of periodontitis increases with age, with a significant increase in prevalence after the age of 35 years, peaking at the age of 50-60 years, and decreasing thereafter, probably due to the fact that some of the periodontally destroyed teeth have been extracted. Tooth loss is the end result of untreated periodontitis. It is now generally accepted that periodontitis accounts for 30-44% of the causes of tooth extraction and is the leading cause of tooth loss in our adults. However, most adults suffer from mild to moderate periodontitis. Severe cases account for only 5-20% of the population. Only a small number of people show phased active destruction in a few tooth sites, with very few sites experiencing rapid progression. The most susceptible tooth sites are the mandibular incisors and maxillary molars. Local pathological factors: 1. Plaque is a group of microorganisms that adheres to the surface of the teeth and cannot be removed by mouth rinsing or water rinsing. It is now recognized that plaque is the initiating factor of periodontal disease and is the main pathogenic factor causing periodontal disease. 2.Tartar is mineralized plaque deposited on the tooth surface. Tartar is also divided into supragingival tartar and subgingival tartar according to its deposition site and nature. Supragingival tartar is located on the tooth surface above the gingival margin and can be seen directly by the naked eye. It is deposited more frequently in the cervical region of the teeth, especially in the areas opposite the openings of the large salivary ducts, such as the buccal side of the maxillary molars and the lingual side of the mandibular anterior teeth. Subgingival tartar is located on the root surface below the gingival margin, in the gingival pocket or in the periodontal pocket, and cannot be seen directly by the naked eye; it must be probed with a probe to know the deposition site and the amount of deposition. Subgingival tartar can be formed on any tooth, but it is more frequent on the adjacent and lingual surfaces. 3, traumatic occlusion in the bite, if the bite force is too large or abnormal direction, beyond the periodontal tissue can withstand the force, resulting in periodontal tissue damage occlusion, known as traumatic occlusion. Traumatic occlusion includes early contact during occlusion, dental interference, night grinding, etc. 4, other factors including food embedding, bad restorations, mouth breathing, etc. also contribute to the inflammatory process of periodontal tissues. Systemic pathological factors: Local factors are the main ones for the occurrence of periodontal disease. Systemic factors are facilitators in the development of periodontal disease. Systemic factors can reduce or alter the resistance of periodontal tissues to external stimuli, making them susceptible to disease, and can promote the development of gingivitis and periodontitis. Systemic factors include endocrine disorders, such as abnormal secretion of sex hormones, adrenocorticotropic hormones, thyroxine, etc. Dietary and nutritional aspects can include vitamin C deficiency, vitamin D and calcium and phosphorus deficiency or imbalance, malnutrition, etc. Hemophilia is extremely closely related to periodontal tissue. Patients with leukemia often have swollen gums, ulcers, and bleeding. Spontaneous bleeding of gums can occur in hemophilia, etc. Long-term use of certain drugs such as phenytoin sodium can cause fibrous hyperplasia of the gums; patients with certain types of periodontal disease such as juvenile periodontitis often have a family history and are thus considered to have a genetic component. In short, the etiology of periodontal disease is complex, and in the treatment not only should we pay attention to the elimination of local factors, but also take into account the state of the whole body in order to obtain a better treatment effect. Symptoms of periodontitis: 1. Early self-conscious symptoms are not obvious: patients often only have excitation of raw gingival bleeding or bad breath, similar to the symptoms of gingivitis. The gingival margin, gingival papillae and attached gingival swelling, soft texture, crimson or dark red, easy to bleed on probing, can be seen during examination. 2, with the further spread of inflammation, the following symptoms: (1) periodontal pocket formation: due to the expansion of inflammation, periodontal membrane is destroyed, alveolar bone gradually resorption, gingival and root separation, so that the gingival sulcus deepened and the formation of periodontal pockets. The depth of periodontal pockets can be measured with a probe, and different degrees of resorption of alveolar bone can be found during X-ray examination. (2) periodontal pus overflow: periodontal pocket wall ulcers and inflammatory granulation tissue formation, pus secretions remain in the pocket, so lightly press the gums, visible pus overflow. And often have bad breath. (3) Loose teeth: Due to the destruction of periodontal tissues, especially when the alveolar bone resorption is aggravated, the power to support the teeth is insufficient, and the teeth become loose and displaced. At this time, patients often feel weakness and dull pain in biting, and bleeding gums and bad breath are aggravated. When the body’s resistance decreases and the drainage of fluid from periodontal pockets is poor, periodontal swelling and swelling can form. In this case, the gums are oval in shape, red and swollen, with increased tooth looseness and percussion pain. Patients feel localized severe throbbing pain, and sometimes there are multiple abscesses at the same time, which is called multiple periodontal abscesses. At this time, the patient may have symptoms such as increased body temperature, general discomfort, enlarged submandibular lymph nodes, and pressure pain.