The first time she came to her daughter’s house for New Year’s Eve, she had a toothache on New Year’s Eve. I found that she had a big cavity in one of her big teeth, and the pain was unbearable when she was stimulated by hot or cold water, and she was diagnosed with pulpitis and needed to kill the nerve for root canal treatment. In fact, many patients have the same question as the mother, why do they have to do root canal treatment when they can’t fill their teeth at once? The reason is that most patients find their teeth problems, dental disease is not limited to the surface of the tooth, located in the middle of the tooth pulp also appeared problems, then the tooth does not necessarily hurt, if the surface of the tooth is filled directly, then after a period of time, the inflammation of the pulp also further deterioration will appear pain, swelling and other symptoms, treatment will become more complex, serious or even impossible to treat. Therefore, when inflammation of the tooth pulp occurs, root canal treatment must be done before filling the tooth. Root canal therapy is internationally recognized as the best way to treat pulpal periapical disease and preserve teeth. The perfect root canal treatment is more difficult and more thorough than other endodontic treatments, but it is a waste of time and expensive. With the development of technology, the materials and equipment used for root canal treatment have become more and more advanced, such as root canal length measuring instruments, root canal motors, nickel-titanium files, hot glue filling instruments, dental microscopes, digital dental film machines, etc. have greatly improved the success rate of difficult root canal treatment. The steps of root canal treatment include: 1, root canal preparation: extracting the pulp and reaming the root canal to shape. 2, root canal disinfection. 3.Tightly filling the root canal with non-toxic and harmless material. Note: (1) X-rays should be taken before, during and after the treatment to understand the lesion and treatment to ensure perfect treatment and reduce complications. (2) Several steps of root canal treatment are a continuous process, please follow up on time (to avoid prolonging the treatment time). (3) Before completing the restorative treatment (filling or full crown restoration), please avoid chewing food with the affected side, or eating sticky food to avoid dislodging of the sealed medication or even fracture of the tooth. (4) After each step of treatment, sometimes there will be pain and swelling and other discomfort, taking anti-inflammatory drugs can gradually relieve, if the swelling and pain worsen, please go to the hospital immediately.