Periodontitis is a condition that is treated with a second scaling, and it is very common in clinical practice because periodontitis itself is a chronic and progressive disease. After the first scaling, many patients do not maintain good periodontal hygiene during the maintenance period, and at the second visit, it is found that there are still deep periodontal pockets and more subgingival tartar, so it is necessary to perform two scaling sessions to clean the newly formed subgingival tartar, especially for some patients who smoke for a long time and have poor oral hygiene. for patients with poor oral hygiene. However, it should also be noted that for periodontitis, if the maintenance is good and the patient is able to maintain good oral hygiene after one thorough cleaning and scaling, then in most cases, during subsequent follow-up visits, supragingival scaling alone can achieve better maintenance of periodontal hygiene and there is no need to perform subgingival scaling every time.