## 4 Discussion
This likely induces deterioration of the microparticles and microlayers present in the slot base produced by the 3D-printing production processes. This phenomenon could make the slot surface smoother and more uniform, facilitating sliding mechanics. Nevertheless, further electron microscopic studies are needed to confirm this hypothesis. As previously mentioned, in addition to the bracket material, the archive type and its size play a significant role in the friction generated in the system. For the purposes of this study, two of the most commonly used types of archive, nickel-titanium and stainless steel, of two different cross-sections, 0.016-inch and 0.019 \(\times\) 0.025-inch, were tested in combination with the three types of bracket investigated. The results show that stainless-steel archives seem to generate less frictional resistance than nickel-titanium archives with the same cross-section (Table 1). Previous studies comparing the frictional resistance of these two alloys have shown conflicting results [39; 40]; as demonstrated by [PERSON] et al. [9], the wire will deflect more as the stiffness of the wire decreases, forming a greater angle of engagement with the base of the slot, thereby possibly leading to greater friction. However, [PERSON] et al. [18] found no differences in their study comparing nickel-titanium and stainless-steel archives. This variability in results is probably due to the different measurement methods adopted. Indeed, the authors compared the different alloys with a passive configuration between the brackets, a situation rarely found in clinical reality [18]. Moreover, the literature demonstrates that elastomeric ligatures increase friction with the archives [31]. Several studies in the literature have investigated frictional resistance during labial orthodontic treatment [9; 10; 11; 12; 13; 15; 17; 18; 19; 20; 30; 36; 40], but only one previous study has compared frictional resistance between metallic, aesthetic and 3D-printed brackets. Specifically, [PERSON] et al. [28] conducted an analysis of the frictional resistance associated with 3D-printed brackets, but they performed their tests by exchanging only one bracket on the model with the investigated ones; the other metal brackets were kept in place during each test, and this could have altered the friction results. Moreover, in [PERSON] et al. 's study [28], the tip and translation variations were not analysed. This study too has limitations. In particular, the biological intraoral context was simulated by irrigating the wire with water using a pipette before beginning traction and not a combination throughout the testing. Moreover, just one type on elastic ligatures has been tested. Hence, further studies on in-house 3D-printed resin brackets are needed in order expand on our findings. Mechanical in vivo studies are needed to evaluate IH3 DBs' frictional resistance intraorally in order to provide orthodontists with more comprehensive knowledge of the biomechanical properties of this promising aesthetic device. Furthermore, although the resin used has IIa certification, it should be considered that further in vivo studies should analyse the possibility of the dispersion of resin particles within the oral cavity and its possible toxicity. Finally, further in vivo studies are needed to evaluate the effects of biological factors on friction [18; 19; 20]. Among the biological factors influencing friction resistance, plaque certainly plays a key role. Which form of brackets causes more plaque accumulation is a debated topic in the scientific literature, which has not yet found a common consensus. However, given the design of the IH3 DBs, which feature a single fin that allows for better brushing, plaque accumulation is assumed to be lower, thus decreasing the friction resistance.