Abstract: BACKGROUND: The preparation of curved root canals is a difficult point in root canal treatment, and the main way used in clinical preparation for curved root canals is to gradually deepen the technique, but this technique is prone to lateral penetration when preparing curved root canals, resulting in treatment failure. In view of this situation, some scholars have proposed the use of touch activation technology to prepare, but there are few studies on the influence of this technology combined with different mechanical nickel-titanium instruments on the forming effect of curved root canals at home and abroad.
OBJECTIVE: To observe the shaping effect of WaveOneGold, Trunatomy and M3-Pro mechanized nitinol device preparation root canal by using resin simulated root canal step-down technology and tactile controlled activation. 
METHODS: 60 single-bending resin simulated root canals were divided into 6 groups (n=10) according to the random number table method according to the nitinol instrument used. The A1 group was prepared with step-down + WaveOneGold; the A2 group was prepared with step-down + Trunatomy, and the A3 group was prepared with step-down + M3-Pro. Tactile controlled activation + WaveOneGold was used for preparation in group B1; tactile controlled activation + Trunatomy was used for group B2, and tactile controlled activation + M3-Pro was used for preparation in group B3. After the preparation was completed, the pre-preparation and posterior root canal images are obtained using a dental surgical microscope. The root canal offset was analyzed before and after preparation. 
RESULTS AND CONCLUSION: (1) When WaveOneGold was used, the root canal deviation at 1, 4, and 7 mm from the apex was smaller with the tactile controlled activation technique than with the step-down technique (P < 0.05); when Trunatomy was used, the root canal deviation at 6, 8, and 10 mm from the apex was smaller with the tactile controlled activation technique than with the step-down technique (P < 0.05); when M3-Pro was used, the root canal deviation at 1, 2, and 3 mm from the apex was smaller with the tactile controlled activation technique than with the step-down technique (P < 0.05). (2) When the step-down technique was used, the root canal deviation at 1, 4, 5, and 7 mm from the apex was smaller with the Trunatomy than with the other two files (P < 0.05), and the root canal deviation at 1, 2, 3, and 6 mm from the apex was larger with the M3-Pro machine-made nickel-titanium instrument than with the other two files (P < 0.05); when the tactile controlled activation technique was used, the root canal deviation at 2, 5, 6, 8, and 9 mm from the apex after preparation with the Trunatomy file was smaller than that of the other two groups (P < 0.05), and the root canal deviation at 1, 4, 5, 6, and 7 mm from the apex after preparation with the M3-Pro file was larger than that of the other two groups (P < 0.05). (3) The results showed that the three files could cause root canal deviation when preparing root canals. The three files combined with the tactile controlled activation technique could reduce the root canal deviation at some sites of the root canal. The root canal deviation at some sites of the Trunatomy file was less than that of the other two files.

Key words: root canal preparation, tactile controlled activation, step-down, curved root canal, root canal , deviation, WaveOneGold, Trunatomy, M3-Pro, engineered dental material