Soft teeth are caused by the following reasons: first, dentin allergy, dentin allergy because the enamel on the surface of the teeth is worn away, revealing the dentin tubules inside, after eating cold, hot, sour or sweet food, patients will feel the discomfort of sour and soft teeth, and need timely desensitization treatment. Secondly, the teeth are soft because the patient likes to drink carbonated drinks, because carbonated drinks are high in sugar and acidic, it is easy to corrode the enamel on the surface of the teeth, which will make the patient feel the teeth are soft when biting. If plaque is not cleaned for a long time, it will lead to the defect of the tooth body, and the tooth body will disintegrate and collapse because of the attack of bacteria, thus the tooth will be soft and need to be filled in time.