The hollow structure inside the tooth is called "root canal". It contains dental nerves and blood vessels to maintain the nutrition and sensory function of teeth. Root canals of incisors and premolars are generally 1, maxillary first premolars are generally 2, and molars are generally 3-4. Different teeth and different people are different, but they are all similar. Tooth decay, tooth trauma, tooth crack and other factors. , are easy to cause root canal infection. When the inflammatory secretion in the root canal compresses the tooth nerve, it will cause pain. Because teeth are hard tissues and the root canal is too narrow to expand, the toothache is so severe that injections and medicine can't solve the problem. According to the causes of toothache, root canal therapy is the best way to treat toothache and preserve teeth for a long time. During the treatment, the doctor first drilled a hole in the tooth (under anesthesia) to relieve the pressure in the root canal and release inflammatory secretions. The effect was immediate, and the patient immediately felt that his teeth did not hurt. Then, the doctor will use professional instruments to clean the infected and necrotic nerve and vascular tissue in the root canal, and then use special tools to expand, shape and disinfect the root canal. Finally, when the affected tooth has no discomfort symptoms at all, the root canal is densely filled with special materials, so that the shape of the tooth can be completely restored.