Secondary root canal treatment (clinically known as root canal retreatment) usually requires two to three dressing changes. Root canal retreatment is one of the routine treatment programs in the Department of Endodontics, and is mainly used to treat symptoms such as toothache, loose teeth, or swollen gums that occur after root canal treatment. Root canal re-treatment is different from the first root canal treatment, its treatment is relatively more difficult, first of all, you need to thoroughly clean the original root canal filling medication (such as gum tip), and then re-exchange the medication to disinfect and sterilize the tooth periodically, and then re-fill the root canal after the tooth is free of pain and other symptoms. The number of dressing changes generally depends on the degree of tooth inflammation, usually two to three times.