It is a common bacterial infection disease, which can lead to periapical inflammation and pulpitis and inflammation of alveolar bone and jaw bone, and if the treatment is not timely, the crown will be completely destroyed and the tooth will be lost. To judge the severity of dental caries, mainly through the clinician’s examination. During the examination, the patient lies on the treatment chair, and the tooth condition is examined by dental forceps, double curved probe, plane mouth mirror and other tools, according to the clinical manifestation, the caries is divided into seven grades from 0 to 6, and the condition is gradually serious as the grade increases: Grade 0: completely healthy tooth surface; Grade 1: early enamel visual change; Grade 2: obvious color or transparency change of enamel; Grade 3: limited enamel destruction, but no Grade 4: deep dentin black shadow is visible; Grade 5: obvious cavity with exposed dentin; Grade 6: obvious large cavity with exposed dentin. If the caries is superficial, the surface of the affected tooth is pigmented and the sulcus is dark gray; if the caries is deeper, the cavity is grayish white, yellowish brown or blackish brown, and the affected tooth has soreness when touching with the probe; if the caries is deep, the cavity is bigger and the pain is obvious when probing with the probe; if the caries is serious, only the residual crown or the residual root is left in the tooth and the chewing function is lost.