## 2 Materials and Methods  
In this study, we compared the load-deflection of a commercial aligner resin (Graphy Resin TC-85 DAC) with a resin created by blending two different (Ortho Flex, New York, NY, USA and NextDent Ortho Rigid, Soesterberg, The Netherlands) resins and classic nickel-titanium wires (0.016'' \(\times\) 0.016'' and 0.016'' \(\times\) 0.022'' Forestatent). For the 3D-printed resin samples, a 25 \(\times\) 5 \(\times\) 0.6 mm parallelepiped was designed using Rhinoceros Software (v7.13 Robert McNeel & Associates, Seattle, WA, USA) and exported as an STL binary file and generated machine code with 3D Sprint (NextDent). In addition to nickel-titanium wires, Graphy samples, and OrthoFlex specimens (sample 1), we decided to test six new blended resins (samples 2-7), obtained by adding different percentages of NextDent Ortho Rigid to NextDent Ortho Flex resin (increments of 10%, 19%, 27%, 42%, 54%, and 65%, respectively). Five samples were produced for each material type. As regards Graphy Clear Aligners, they were printed, according to the company guideline, by an AccuFab-L4D printer (Shinging 3D Tech. Co., Ltd., Hangzhou, China) using Tera Harz TC-85 DAC resin. Printing was performed under 45 deg alignment to the building platform with a standard of 100 um layers. After printing, the specimens were removed from the printer's platform and put in a spinner machine for 6 min. The specimens were then dried using compressed air to avoid an excess of resin during the post-curing of aligners. The printing supports were removed from specimens, cured in the Tera Harz Cure with nitrogen generator (THC2) curing machine (Graphy, Seoul, Republic of Korea), and post-polymerized for 14 min. Then, the specimens were washed in an ultrasonic cleaning machine at 80 deg for 2 min and then in water for 1 min. After the washing procedures, samples were dried for 5 min in a dryer machine. Finally, samples 1-7 (OrthoFlex specimens and the six blended resins) were printed using a NextDent 5100 3D Printer and cured with the recommended settings for the NextDent Ortho Flex resin (Figure 1). The cleaning process was divided into two steps: First, the printed parts were cleaned in ethanol for three minutes to remove any excess resin. For this purpose, an ultrasonic bath was used (Elma EP20H Easy, Elma Schmidbauer GMBH, Singen, Germany). Later, the printed parts were subjected to another bath in ethanol for two minutes. After a rest of at least 10 min, as indicated in the official instructions for the use of the resin, the printed samples were placed in a UV-light-curing box to complete polymerization (LC-3 DPrint Box, NextDent, Soesterberg, The Netherlands). After curing, the specimens were subjected to mechanical testing using a three-point bending test. The specimen was securely clamped into the testing machine, ensuring the test region was free from obstructions or constraints. The device applied a controlled bending force at specific points along the sample while measuring the applied load and the resulting deflection [18; 19]. More specifically, we used a three-point bending test instrument owned by the University of Insubria (Buster model 8526) (Figure 2). The setup of the test consisted of a three-point bending test with 5 mm between the center and the ends. Each sample was evaluated with bending of 1 mm, the instrument was calibrated to perform 20 steps, and each step was 50 microns. The descent speed was set at 500 microns/minute. Then, 20 steps in one direction, and when the maximum deflection point was reached, 20 steps in the opposite direction, were taken to assess the deflection, and a total of 40 steps were sampled. The chamber in which the tests were carried out was a controlled atmosphere, with a temperature of 28 \({}^{\circ}\)C and 80% humidity, the maximum operating temperature at which the testing instrument maintains its accuracy and reliability. Each test was repeated 5 times for each sample.