Moderate and severe periodontitis basically requires subgingival scaling. Gingivitis and periodontitis are caused by the accumulation of tartar, soft tartar and plaque on the surface of the gums and roots, and are treated by three main methods: ultrasonic scaling, also known as scaling, subgingival scaling and periodontal flap surgery. In common gingivitis and mild periodontitis, where the roots are not obviously exposed, ultrasonic scaling can remove all the plaque and tartar from the tooth surface, and subgingival scaling is not necessary in this case. When the periodontal destruction is serious, the root exposure is obvious, especially the lesion at the root bifurcation of the posterior teeth, the ordinary ultrasonic scaling cannot completely remove the tartar and plaque on the root surface, and manual subgingival scraping is needed to remove the infected material, only then can the periodontal inflammation be completely treated.