After root canal treatment, the tooth is usually left with an empty shell around the tooth, and due to the loss of nutrient supply from the pulp, the tooth itself becomes more brittle and easy to fracture, and the back tooth may bear up to 50 to 70 kg of force when chewing, and the tooth is in danger of splitting at any time in use, so the doctor usually recommends that the tooth after root canal treatment be protected by braces. When the tooth 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 the 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 after root canal treatment, otherwise there will be a high chance of tooth fracture when bearing the biting force in the future. If a few posterior teeth after root canal treatment are to have a single crown, as long as the remaining tooth mass is repaired sufficiently, it is not necessary to make a pile, but if a posterior tooth after root canal treatment is to be used as a pillar tooth for dentures, it is better to make a pile regardless of the remaining 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, and the chance of tooth preservation has been greatly improved. Therefore, it is better to have braces on the teeth after root canal treatment to reduce the chance of fracture and finally achieve the purpose of preserving one’s own teeth.