Third degree caries generally refers to deep dentin caries, aseptic inflammation of pulp, periapical lesion, cold water stimulation can cause pain. The main symptom is soreness to temperature stimulation and chemical stimulation, especially to temperature stimulation, and the pain disappears immediately after the stimulation is removed. The main sites of third degree caries are: occlusal surface, adjacent surface of teeth, lip surface and buccal surface of teeth, and the main causes are bacteria and plaque, food and the oral environment where the teeth are located. Standardized brushing is an important measure to prevent the occurrence of dental caries, especially for children, it is especially important to develop good oral hygiene habits.