A tooth that has had its nerve extracted is clinically known as a dead pulp tooth, i.e. a tooth that has undergone root canal treatment. The retention time of the tooth root cannot be generalized and usually varies from person to person. Most of them can be preserved for 5-10 years or even longer if the patient is active in filling and full crown restoration, and has good dietary habits, maintains good oral hygiene and is able to clean the oral cavity properly. Nerve extraction and nerve killing is commonly referred to as removing necrotic pulp. This operation can make the tooth lose nutrition supply, self-repair and metabolism ability disappear, the tooth itself hardness decreases, and it is easy to break. If the patient has a large cavity and a lot of filling, and the full crown is not restored, the crown may split after a certain bite, and in some cases, it even splits to the root of the tooth, and then it needs to be extracted and the root cannot be preserved. Therefore, patients are usually advised to have a full crown restoration to prolong the life of the tooth, and some patients also choose to wear braces to protect the tooth after root canal treatment. However, as long as the tooth is properly treated and protected, the tooth can be used for a long time after root canal treatment and the roots can be preserved, and some patients have the same life expectancy as normal teeth after full crown restoration. Take care not to eat foods that are too hard.