The number of root canals is related to the infection status of the pulp and the periapical area, as follows: 1. One-time root canal treatment is not significantly different from the conventional two root canals in terms of indications. This includes living pulp teeth, such as teeth in abnormal positions, where the patient does not want to change the position of the tooth through orthodontic means, which can be restored aesthetically and functionally through crown restoration after root canal treatment; all types of pulpitis and chronic periapical inflammation with sinus tract formation at the root tip, where the existence of the sinus tract can enable the apical inflammation to gain access to drainage, and after one-time root canal treatment can eliminate the infection from communicating with the pulp cavity, which can speed up the apical In addition to the above indications, two root canals are also suitable for chronic periapical inflammation without sinus tract formation. The first of the two root canal treatments is mainly for root canal cleaning and rinsing and sealing; the second is mainly for filling the root canal; 3. The three root canal treatments are mainly for acute periapical inflammation. The first time the pulp is opened and drained to allow the symptoms to be relieved, and then the second time the canal is cleaned, flushed and sealed, and the third time the canal is filled.