Protaper nickel-titanium root canal files are a modern endodontic technique in which the use of nickel-titanium instruments and crown-down technique for root canal preparation has become a widely recognized technique in endodontics. I. Protaper nickel-titanium root canal files 1. Machine instruments (1) There are six files, 21m and 25m: SX, S1, S2, F1, F2, F3Sx, similar to the G-drill, are used for the formation of the root canal opening; S1 prepares the middle 1/3 of the root canal; S2 prepares the middle and lower 1/3 of the root canal; S1 and S2 are also useful for the preparation of the apical area. F1, F2, F3 are used for the preparation and completion of the apical area. preparation and completion. Sub-coronal hair is also used. (2) Specialized micro drive system X-SMART II. Basic sequence of clinical use of Protaper instruments (for machine use) 1. Take standard radiographs of the teeth to be treated (in case of a large number of teeth, a whole row of surface tomograms can be taken). 2. Establish a straight entrance to the root canal in order to obtain access to the apical foramen (not the opening at the canal mouth) and to completely remove the contents of the pulp chamber (including the pulp angle). 3. Rinse with 1-2％ sodium hypochlorite and EDTA (or 3％ hydrogen peroxide) alternately. 4.Roughly estimate the working length according to the X-ray film, and use 10# and 15# K files to unblock the root canal. 5.SX or GG drill 2#, 3# open the root canal mouth and the upper 1/3-2/3 of the root canal (straight part of the root canal) 6.Measure the working length 7.S1, S2 reach the working degree in turn, and carry out the preparation of the middle of the root canal. 8.Complete the apical preparation with F1-F3. 9.Measure the accurate root canal length again 10.Ultrasonic root canal cleaning 3.Nickel titanium instruments for machine use precautions 1.Do not push hard during operation. 2.When you encounter resistance, withdraw and continue to the next step. 3, each pumping an instrument, before a check whether the file needle has cracks, deformation may. Should make the rinsing solution to flush the root canal and maintain the root canal in a wet state during the preparation. 4.The speed of instrumentation is 150-350rpm. 5.Each instrumentation should only stay in the root canal for 4-6 seconds. 6.In case of heavy curvature of the root tip, combined application of surgical instrument preparation is recommended.