If a 7 year old child has a big tooth inside that is rotten and only the root and crown are left, then the tooth needs to be extracted, but if there is no pain and the nerve is not injured, then the tooth does not need to be extracted. The first molar of a 7-year-old child has already erupted, and this tooth is a permanent tooth. If it is rotten, different treatments should be chosen according to the degree of destruction of the tooth. 1. If the tooth is rotten and only the root or crown is left, this case can be treated with root extraction in a hospital, which is suitable for patients who have deep decay and cannot keep the root. 2. If the tooth is not painful and the nerve is not injured, you can choose to remove the decayed tissue and use appropriate filling materials to repair the tissue defect, which is suitable for patients who have not injured the nerve and have the value of preservation. Patients are advised to go to the hospital for timely examination and choose the correct treatment plan at the same time.