This starts with the dangers of periodontitis and the causes of periodontitis. Periodontitis is the first cause of tooth loss in adults, and is an oral disease that affects the life of the teeth and is closely related to diseases of various systems of the body, with a prevalence rate of more than 90% among adults in China. The cause of periodontitis is the accumulation of a large number of bacteria in the mouth, especially plaque that adheres to the root surface of the teeth, near the gums, and calculus that provides a place for the accumulation of plaque. In order to control periodontitis, the removal of plaque becomes the first task, and the control of plaque is also the most important means of preventing dental hard tissue diseases such as dental caries. In addition to good oral hygiene, plaque removal requires regular visits to dental clinics to remove the calculus and plaque that accumulate on the surface of the teeth using ultrasonic methods, so oral hygiene is the most important and most routine.