There are three causes of toothache as follows: 1. It is relatively mild, called dentin allergy. 2. It may be due to decay, forming a deeper cavity, then there may be hot and cold irritation pain when eating hot and cold food. 3. There is another cause that is more serious, which is pulpitis. When pulpitis occurs, the tooth will have irritation pain when encountering hot and cold, and it is also likely to have spontaneous pain. If it is dentin allergy, you can apply some anti-allergy medicine locally or use anti-allergy toothpaste, and brush more teeth will be effective. If it is a deep cavity, you must go to the hospital for treatment in time to remove the decayed material and fill it with resin or other filling materials, and it can be filled in one time. In the case of pulpitis, root canal treatment is necessary, and the above are most of the causes of tooth pain.