If the periodontitis is not serious and the number of teeth that need to be scraped is not large, the whole mouth can be scraped at once. If the periodontitis is very serious and the whole mouth needs to be scraped, it is generally recommended to carry out the scraping in several times. 1. Periodontal scaling is mainly performed on teeth where the depth of periodontal pockets is still more than 4mm after scaling, so it is not necessarily necessary to scaling on all teeth in the mouth. If the periodontitis is not severe and the number of teeth that need to be scaled is not large, then the whole mouth can be scaled at once. 2. However, if the periodontitis is severe and the number of teeth that need to be scaled is large, usually under local anesthesia, then a one-time full-mouth scaling may result in a long mouth opening time and a large reaction after the treatment. Therefore, it is generally recommended to do it in several sessions. It is recommended to consult your doctor whether periodontal scaling can be performed in a single session.