Root canal treatment, commonly known as nerve extraction, involves the dentist opening the diseased pulp cavity, removing the inflamed and necrotic pulp tissue with various instruments, disinfecting and cleaning the pulp cavity (including the pulp cavity walls), and finally sealing the pulp cavity tightly with dental cement pins and other materials. After root canal treatment, the tooth must be observed for a period of time to make sure that it is symptom-free before proceeding to the restorative treatment. There are two ways to repair the defective tooth: one is to fill the cavity directly with a filling material; the other is to make a crown to cover the tooth. Root canal treatment is only meaningful if the tooth can be retained after root canal treatment. The direct filling method using filling material is easy and convenient but not durable. Therefore, most dentists generally recommend braces for teeth after root canal treatment. After root canal treatment, the tooth is usually left with a hollow shell around it, and the tooth itself becomes brittle and easy to break due to the loss of nutrient supply from the pulp, and the back tooth may bear up to 50 to 70 kg of force when chewing. Do I need to put a nail in it? When a tooth’s has undergone root canal treatment, the center of the crown is usually empty due to the tooth’s own structure and the need for treatment. At this time, if a brace is made directly, its resistance to fracture is very poor, and it is usually necessary to put a pile nail in the root to make a strong nucleus to counteract the fracture force in the use of the tooth. For posterior teeth, a crown must be made on the posterior tooth after root canal treatment, otherwise there is a high chance of tooth fracture when it is subjected to biting force in the future. If a few of the posterior teeth after root canal treatment are to have a single crown, it may not be necessary to have a pile as long as there is enough tooth mass left, but if the posterior tooth after root canal treatment is to be used as a pillar tooth for a denture, it is best to have a pile regardless of the amount of tooth mass. In the past, if a tooth decayed into the pulp chamber, the tooth was almost inevitably extracted because the root canal treatment technology was not advanced at that time. Nowadays, the technology of root canal treatment is changing rapidly, which also greatly improves the chance of tooth preservation. It is better to do braces on the teeth after root canal treatment to protect the teeth from chewing force and reduce the chance of fracture, so as to finally achieve the purpose of preserving their own teeth. Many patients think that if they don’t eat hard things, they won’t split, but clinically we see many cases of splitting because they didn’t do braces and finally had to pull them out, which is regrettable, so we suggest that it is better to do crown protection thoroughly.