It is often asked that teeth after root canal treatment or “rotten nerve” treatment are especially prone to fracture, what is the reason? If tooth decay is not treated in time, further development will involve the deeper tissues of the tooth and pulp inflammation will occur. Once the pulp inflammation occurs, it is difficult to save the healthy pulp of the tooth. In order to save the affected tooth, in many cases, the only way is to inactivate the pulp tissue, which is what we usually call root canal treatment and “rotten nerve” treatment. The nutrition of the tooth comes from two sources: one is the pulp tissue, which is made up of blood vessels, fibers, and cells inside the tooth, which provides nutrition directly to the tooth. The other way is through the soft tissues surrounding the tooth, whose nutrients can penetrate into the tooth. After deactivated endodontic treatment, the tooth is deprived of the nutrient supply from the pulp and can only rely on the soft tissues around the tooth alone to provide nutrients. Such a tooth is relatively brittle and is prone to fracture when chewing hard objects. On the other hand, the teeth that need to be treated by endodontic therapy, the original tooth defect is larger, when treating, not only the decayed tooth tissue has to be removed, but also part of the normal tooth tissue has to be removed for endodontic therapy, which further reduces the bearing capacity of the teeth. If there is too steep cusp on the affected tooth, the weak tooth tissue with poor resistance is more likely to make the treated tooth fracture. When chewing, care should be taken not to use the tooth to bite on anything too hard to reduce the chance of tooth fracture. To prevent tooth fracture after endodontic treatment, a porcelain crown can be added to protect the tooth!