Dental caries is a kind of disease that causes the defect of tooth tissue by demineralization of inorganic material and decomposition of organic matter in hard tissue under the influence of many factors. Its characteristic is that the color and hardness of the decayed part of the teeth change at the beginning of caries, and then the cavity is formed by the substantial defect of the tooth tissue, and the lesion continues to develop to the deep, which can cause complications such as pulp disease, periapical disease, inflammation of jaw bone, and even become an oral lesion and affect the whole body health. Clinical manifestation of dental caries Dental caries is most likely to occur in the fossa and cleft groove of biting surface of molar and bicuspid teeth, and the contact surface of adjacent teeth. The former is called sulcus caries and the latter is called adjacent surface caries. The caries of children occurring in the cervical part of teeth is very rare and can only be seen when the body is extremely weak due to severe malnutrition or certain systemic diseases. According to the degree of caries destruction, it can be clinically divided into superficial caries, medium caries and deep caries. 1.Shallow caries The caries destruction is only in the enamel, the initial expression is brown or dark brown spot or plaque in the enamel, the surface is rough. Following to form surface destruction. Adjacent surface caries begins to occur below the contact surface, and sulcus caries begins in the sulcus, which are not easy to see in the early stage. Only when the caries occurs in the sulcus, it can be seen, but there is food pigmentation in the sulcus of children’s teeth, so the doctor may misdiagnose or miss the diagnosis without careful examination. Shallow caries has no conscious symptoms. 2.Middle caries: The caries has reached the dentin and formed a shallow dentin cavity. The patient will feel the tooth soreness to cold water, cold air or sweet and acid food, but the symptom will disappear immediately after the stimulus is removed. This is because the dentin is sensitive to the stimulus. The effect of medium caries is good when it is treated in time. 3.Deep caries The caries has reached the deep layer of dentin, close to the pulp, or has affected the pulp. The child has painful sensation to cold, heat, acid and sweet, especially sensitive to heat, and the pain still lasts for a certain time before gradually disappearing after a defeat is removed. At this time, most of them need to do pulp treatment to save the tooth. If the deep caries is untreated, the pulp will be secondary infected or pulp necrosis. Bacteria can reach outside the apical foramen through the root and cause periapical inflammation. Focal infection may be formed. If the crown of the tooth is largely destroyed or only the residual root remains, it should be extracted.