Inside each tooth that looks hard on the surface, there is actually a hollow structure called “root canal”, which is a channel for the nerve and blood vessels (i.e. pulp tissue) to maintain the nutrition and sensory function of the tooth. Factors such as tooth decay, tooth trauma, and hidden fracture can easily lead to infection of the pulp tissue and even deep bone tissue, causing pain that cannot be solved by injections or medication. Root canal treatment is the best treatment method to get the exact long-term effect and long-term preservation of the affected tooth by thoroughly cleaning the infected tissues in the root canal with professional instruments, enlarging and shaping the root canal, rinsing and disinfecting, and tightly filling with special materials. With root canal treatment, toothache is no longer a fear; many teeth with large defects or teeth that would otherwise be extracted can be preserved and function well as chewers. In addition to the fact that patients need many visits (3-5 visits, once a week) and the cost is relatively high, it also requires a high level of skill from the doctor and the hospital hardware facilities. The doctor must not only know the complex root canal system inside the tooth like the roots of a tree, be patient and persistent when treating it (sometimes it takes an hour just to find the hidden root canal opening), but must also have good medical ethics and responsibility. In addition, the hospital must be equipped with strong hardware support, such as strict sterilization procedures, clear filming equipment, advanced treatment instruments, etc. If the first root canal treatment is unsuccessful, it will not only be less successful, but also more difficult and expensive to treat again. After the root canal treatment, it is better to put a “brace” to prevent the tooth from being bitten and cracked.