Root canal treatment has been done before and now the filling has fallen off, it may need to be refilled, redo the treatment, make crown restoration or extract the affected tooth, it is recommended to go to the hospital for specific radiographs and treatment. 1. If the filling has just fallen out and the tooth is small in size, you can first remove the part of the tooth that is secondary to caries, then refill it and make a crown restoration at a later date. 2. If the radiographs show low-density images at the root tip, root canal treatment or apical surgery should be done again. 3. If the defect area is large, it is recommended to make a crown restoration, and if necessary, to make pile core crown restoration. 4. If the tooth filling is lost and secondary caries has led to pulp chamber penetration or the tooth is fractured beyond repair, it is recommended that the tooth be extracted at a later date.