Root canal treatment for a tooth that has lost a piece requires treatment depending on the condition of the missing tooth. You can choose observation, filling treatment, restorative treatment and so on. 1. Observation: If a piece of a baby tooth is lost during root canal treatment and the permanent tooth is about to erupt, it is recommended to observe the tooth first and adjust and grind the tip of the tooth, so as to avoid damaging the mucous membrane and the lingual body. 2. Filling treatment: When a tooth is lost, if the defect is not big and does not affect the neighboring surfaces of the tooth and the buccal-lingual surfaces, it can be filled directly, i.e., it can be repaired by using the method of dental defect bonding. 3. Restorative treatment: when a piece of the root canal treated tooth is lost, due to the large dentin defect, the adjacent surface of the tooth and the buccal-lingual surface is harmed, then the remaining dentin tissue does not have enough resistance. At this time, filling treatment is not recommended, and you can choose to have a high inlay restoration or full crown restoration. Root canal treatment of the tooth lost a piece, it is recommended that the patient is admitted to the hospital in time to visit the stomatology department for treatment, to avoid further aggravation of the condition.