The reasons for teeth being afraid of cold are periodontal disease, forming deep caries in the crown, brushing teeth with hard bristle toothbrush horizontally, eating hard food and teeth splitting, etc., as follows: a. Periodontal disease: When suffering from periodontal disease, the gum is atrophied by the stimulation of calculus, the alveolar bone is resorbed, and the root surface of the teeth is exposed and cannot tolerate the stimulation of cold water. Second, the crown of the tooth forms deep caries: when the crown of the tooth forms deep caries or hidden fracture, the cold and hot stimulation will be conducted to the pulp along the dentin tubules, producing pain. 3.Brush the teeth horizontally with hard bristle toothbrush: When brushing the teeth horizontally with hard bristle toothbrush for a long time, the wedge-shaped defect will be formed in the neck of the teeth, and the pain will appear in case of hot or cold. Fourth, eat hard food: when you like to eat hard food or have the habit of grinding your teeth at night, the jaw surface of the teeth will be heavily abraded, the enamel will disappear, the dentin will be exposed, and cold stimulation will lead to tooth sensitivity and even pain. Fifth, teeth splitting: teeth splitting, the exposed dentin will be stimulated by cold water, there will be severe pain.