## 2 Materials and Methods
### Canal Instrumentation and Force and Torque Measurement  
Simulated J-shaped resin canal blocks (Endo Training Bloc, length of 17 mm, taper of 0.02; Dentsply Maillefer, Ballagues, Switzerland) were instrumented with the Reciproc Blue R25 instrument (#25/0.08 taper at tip), using a previously reported automated instrumentation and torque/force sensing device [32]. The instrumentation setup included a motor-driven test stand (MX2-500N; Imada, Aichi, Japan) paired with a torque/force sensing unit. The test stand featured a vertically movable stage and a platform designed to secure the canal block. The movable stage was equipped with a holder to secure the handpiece of the X-Smart Plus endodontic motor (Dentsply Sirona, Ballagues, Switzerland). The system was programed to perform up-and-down movement at a speed of 50 mm/min regardless of the load. A sensing unit was designed to monitor the vertical force and torque generated on the block in real time. It comprised a load cell (LUX-B-ID, Kyowa, Tokyo, Japan) to measure vertical force, and strain gauges (KFG-2-120-D31-11, Kyowa) for detecting torque. The platform holding the root canal block was attached to the torque sensor through a round metal rod with a flat central section, where the strain gauge was mounted. The force directed toward the coronal side of the root canal model was defined as the upward force, while the force directed toward the apical side was defined as the downward force. For torque, based on the design of the Reciproc Blue instrument, a clockwise rotation was defined as non-cutting torque, while a counterclockwise rotation was designated as cutting torque. The Reciproc Blue instrument was operated in Reciproc  
Figure 1: Flowchart showing the experimental design of this study. SEM: scanning electron microscopy.  
All mode, which executed a time-dependent reciprocal motion with a predetermined clockwise-and-counterclockwise rotation, independent of the torque value.  
Thirty resin canal blocks were subjected to manual glide path creation with a working length of 16 mm using #10 and #15 stainless steel K-files ([PERSON], Munich, Germany) by one operator (KH). Then, the blocks were randomly assigned to three groups based on the pecking amplitude (\(n=10\) each): (1) small-amplitude group (Group S; 1 s apically and 0.5 s coronally); (2) medium-amplitude group (Group M; 2 s apically and 1 s coronally); and (3) large-amplitude group (Group L; 4 s apically and 2 s coronally).  
The automated instrumentation using the Reciproc Blue consisted of two steps: an initial step to 13 mm and a second step to 16 mm (full working length). Throughout the instrumentation process, an intracanal lubricant (RC-Prep; Premier, Plymouth Meeting, PA, USA) was applied. After the first instrumentation step, the canal was irrigated with 1 mL of distilled water, and patency was confirmed using a manual #10 K-file. The Reciproc Blue instrument was employed in a single canal. Blocks in which instrument separation or ledging occurred were excluded from further analysis.  
The upward and downward force and counterclockwise torque produced during the automated instrumentation were measured simultaneously every 0.02 s. The output signals were amplified with an amplifier (PCD-400A, Kyowa) and sent to a computer equipped with data recording software (DCS-100A, Kyowa), which was used to determine the maximum and cumulative values.