When it is mild, the tooth tissue is defective and there will be discomfort when encountering acid and sweetness; when it is serious, the infection penetrates deep into the tooth pulp and causes pulpitis, there will be pain when encountering heat and cold, spontaneous and severe pain, waking up with pain at night, and even the affected side of the head and face will be involved in pain; the infection penetrates further into the tissues around the tooth root and becomes apical inflammation, there will be symptoms such as swollen pockets in the tooth bed, pus flowing, and not daring to bite the tooth. Tooth decay is treatable, but the procedure and difficulty of treatment vary with the severity of the disease. The main treatment is to control the infection and prevent reinfection. The conventional method is root canal treatment, which needs to be carried out in the dental department of the dental specialist hospital. If your tooth is severely damaged, but the root can still be retained, then after root canal treatment, you need to go to the restoration department to do full crown or pile crown to restore the shape and chewing function of the tooth; if the root is also destroyed, then you can only extract the affected tooth and do dentures. Tooth decay can be completely prevented, and killing tooth decay in the cradle can save a lot of unnecessary pain, time, energy and financial resources needed for medical treatment, and good oral hygiene habits are the key.