## 2 Materials and Methods  
A randomized, cross-sectional, in vitro study was carried out on resin blocks (Endo-Training-Bloc, Dentsply Maillefer, Ballaigues, Switzerland) with a degree of curvature of 40\({}^{\circ}\), which were worked on by fourth-year dental students at the Universidad Europea de Madrid (UEM) in 2022. This study was approved by the UEM research ethics committee (CIPI/213006103). Informed consent was required to be signed by all participants, indicating that the outcome of the practice would not affect their final grades. The eligibility criteria included students who had never performed endodontics with rotary files and who agreed to take part in the study. A total of 84 resin blocks were used and marked on their undersides with a handpiece and a milling cutter. The blocks for the PTG system were marked with the letter \"P\", followed by the corresponding numbering (1-42). Those for the BS system were marked with a \"B\", followed by the corresponding number (1-42). Subsequently, preoperative photographic records of each of the blocks were taken with a camera (Canon MKII, Ota, Tokyo, Japan) and a 60 mm macro lens (Canon, Ota, Tokyo, Japan). To ensure that the photographs were taken at the same distance and positioned in the same place without the possibility of moving the camera or specimens, a stable, wooden platform was fabricated. Once these preoperative recordings were made, the blocks were placed in individual blank, opaque envelopes, along with a fresh set of files, and distributed by an independent investigator to ensure randomization. Once the students opened their envelopes and checked which group they were in, they were distributed and received a specific, 45-min training on the objective of the study and the characteristics of the system they had to work with: the alloy, design, and work sequence, according to the manufacturer's instructions. In addition, they were given a step-by-step sheet detailing the procedure, indicating that they had no time limits in which to perform the artificial canal instrumentation. The 42 students in the PTG group started working by preflaring the coronal third using K-file #10 and K-Flexofile #15-25 hand files. They proceeded to determine the working length with a K-file #10 hand file. They then performed the glidepath with the K-Flexofile #15 hand file. They went on to use rotary instrumentation, for which they used a 16:1 reduction handpiece with an X-Smart electric motor (Dentsply Sirona, Ballaigues, Switzerland), adjusting the speed to 350 rpm. They used shaping files (S1 and S2) with a planing action during the withdrawal movement. The torque for the S1 was 4 N/cm and 1.5 N/cm for the S2. Subsequently, the finishing files (F1 and F2) were used. The latter files were used with a pecking motion, passively up to the working length. All files were removed immediately after reaching the working length (without remaining more than 1 s). The torque for the F1 was 1.5 N/cm and 3 N/cm for the F2. The 42 students in the BlueShaper group started working by performing a coronal manual preflaring of the canal using a K-file #10, and then performing a rotary preflaring with the Z1 file (500 rpm, torque 4 N/cm) mounted on an X-Smart motor, up to the place reached by the K #10 file or until a slight resistance was felt. After determining the working length with the K #10 file, a manual glide path was performed with the K-Flexofile #15. Then, a Z1 file (500 rpm) was passed to the working length with a planing action. The instrumentation was finished with Z2 (500 rpm, torque 4 N/cm), Z3 (500 rpm, torque 4 N/cm), and Z4 (350 rpm, torque 4 N/cm) files in a pecking motion, passively up to the working length, removing the file immediately (without remaining more than 1 s). Both groups had to clean the file coils frequently with gauze during instrumentation, checking for signs of distortion or wear, irrigate after using each file (2 mL distilled water), and perform patency with a K #10 file. After instrumentation, a final wash was performed with distilled water for 1 min.