Root canal filling (1) Review the purpose and timing of root canal filling (2) Steps of root canal filling (1) Remove the temporary seal, remove the sterilized cotton twist or cotton ball to check if there is any oozing or odor, and insulate and dry the root canal. (2) Verify the working length: Use a root canal file (master file type) with a marked working length to probe the root canal to determine if the working length can be reached smoothly. (3) Try the main adhesive tip: select the same type of adhesive tip as the main file, mark the working length with forceps and place it into the root canal to check whether it can reach the root tip smoothly. If the master tip is shorter than the working length, it means that the selected master tip is too large, change to a smaller one and try again until it is suitable (see the picture on the right). (4) Modulation of root canal filling paste: take appropriate amount of root canal paste powder and liquid on the sterilized glass plate, use the sterilized mixing knife to mix it into paste, the mixing knife needs to use certain pressure to make a uniform and fine paste. (5) Root canal filling: Take the combined paste and solid filling lateral pressure method as an example. A, first fill the paste: use the root canal side pressure or expand the needle dipped in the root canal paste into the root canal, stick to the root canal wall in a straight line to pull out the needle, bring out the air bubbles and facilitate the filling of the paste. Repeat this step until the paste is filled. B. Filling the adhesive tip: After the paste filling is completed, the disinfected and marked primary adhesive tip is dipped in a little paste and inserted into the root canal up to the crown reference point mark. Before filling the secondary adhesive tip, push out the gap by inserting the side pressure into the root canal and insert the corresponding type of adhesive tip until it is filled. C. Cut off the adhesive tip: cut off the adhesive tip at the flush root canal opening with a hot digger, then press and squeeze the root canal opening with a dry cotton ball in the direction of the root tip, wipe off the excess paste, and cushion the bottom with zinc phosphate cement. (6) Post-operative radiographs were taken to check and judge the root canal filling situation: Proper filling: the filling in the root canal was tight, and the filling was 0.5-1.0 mm from the root tip. Underfilling: the filling in the root canal was more than 1 mm from the root tip, and/or there was an incompatible transillumination image in the root canal at the root tip. Overfilled: The root canal is filled with the filling material and beyond the apical foramen. (2) Check for fractures or loosening of threads before using the instrument. (3) Use the instrument in accordance with the number, do not skip the number, otherwise it will be difficult to reach the working length and easy to form a step.