Some of the teeth after root canal treatment have serious caries and a lot of dentin loss, or the root canal treatment has to open the pulp cavity in order to remove the pulp cavity, so that the dentin loses some dentin. After root canal treatment, the tooth is deprived of the nerve, blood vessel and lymphatic supply in the pulp chamber, which makes the tooth brittle and prone to fracture. The teeth are subjected to a force of ten to thirty kilograms in the front teeth and fifty to seventy kilograms in the back teeth when eating, drinking and biting. If the tooth is not protected by braces, it may cause the tooth to split, and once the tooth splits, it can only be extracted, so the tooth is usually protected by braces after root canal treatment.