The root of the tooth is sore and soft as soon as you bite something after 20 days of filling, which is considered to be caused by pulpitis, apical periodontitis, dentin allergy, etc. It can be treated by re-filling, using medication or improving dietary habits. 1. Pulpitis: If the degree of tooth decay is more serious, the filling material will be closer to the pulp tissue, which may cause irritation to the pulp tissue causing pulpitis, due to the inflammation stimulation will lead to the root of the tooth is sore and soft when you bite something. Root canal treatment is needed. 2. Periapical inflammation: If the pulpitis further develops to form periapical inflammation, the root of the tooth will be sore and soft when eating, and there is a sense of floating. You can go to the hospital for root canal treatment in time, and you can follow the doctor’s instructions to use artificial oxalic metronidazole capsules, metronidazole tablets and other drugs for anti-inflammatory treatment. 3. Dentin hypersensitivity: usually due to the filling before the tooth surface of the enamel protective layer has been destroyed, which leads to bite things stimulate the pulp nerve, thus appearing the root of the tooth sore and soft situation. Normally, you should avoid eating too much cold and spicy food to avoid stimulating the teeth to cause discomfort, and also need to carry out desensitization treatment. After 20 days after the filling of the teeth, a bite of the tooth root soreness, should be timely medical diagnosis, so as to avoid aggravation of the condition, the use of drugs need to follow the doctor’s instructions.