A cavity that cannot be filled or extracted is usually amenable to root canal treatment to preserve the tooth. When a tooth is infected with decayed bacteria and the nerve cannot be filled at once, the tooth can be preserved by root canal treatment. Root canal treatment is a routine treatment for endodontics and periapical diseases, removing the infected nerve from the root of the tooth, sealing the root canal with medication to completely remove the infected material from the root canal, and finally filling the root canal tightly. After treatment, the tooth can be preserved without extraction. After root canal treatment the tooth loses the nutrient supply from the nerve and becomes weaker, it is easy to splinter when you eat hard things and crown restoration is recommended. Therefore, the cavity can not be filled and can not be extracted can be root canal treatment, after treatment to maximize the preservation of the function of the tooth, the specific can go to the dentist to check.