The success rate of a perfect root canal for a tooth that has been treated for the first time is about 90%. A tooth that has been treated before but failed is treated as a secondary root canal, and the success rate of treatment is reduced. The degree of reduction is inversely proportional to the difficulty of the root canal treatment, generally the more difficult the root canal treatment, the lower the success rate. However, the success rate derived from a group survey is not really meaningful for individual patients, but for individual patients it depends on the specific situation of the affected tooth, and the possibility of failure of any treatment is often determined by the limitations of medical science in understanding the disease.