## 4 Discussion  
In orthodontics, friction is a clinical challenge, especially when relying on sliding mechanics. Physical/mechanical factors that influence sliding resistance include the arch-wire properties (material, cross-sectional section, shape/size, surface texture, and stiffness), ligature type and method, and bracket material and design. There are also biological factors to consider, such as saliva, plaque and biofilms [18; 19; 20]. The biomechanics required for orthodontic tooth movement cause friction at the slot-archwire interface, and this can reduce the applied forces by as much as 12-60% [25; 26; 27; 28]. Hence, frictional resistance must be carefully examined in order to achieve an optimal orthodontic treatment outcome. With this in mind, the aim of this research was to evaluate the differences in the friction properties between a new, modern, in-house 3D-printed resin bracket (IH3 DB) and commonly used metallic and aesthetic brackets, all in combination with three different archives types. Among the three types of buccal brackets investigated (composite, IH3 DB and metallic bracket), the greatest frictional resistance test values were recorded for the composite brackets in all the planned tip and translation configurations (described in Table 1). This is in accordance with the literature, in which various authors [9; 10; 11; 12; 13] report having found higher frictional resistance values for aesthetic brackets than metal ones. In fact, their poor biomechanical frictional proprieties prevent many orthodontists from using them [21]; indeed, high frictional resistance can force the orthodontist to use heavy forces during labial orthodontic treatment. This can induce anchorage loss, patient discomfort and irreversible damage to the tooth-supporting tissues [16]. The higher resistance value of such brackets can be attributed to the intrinsic characteristics of the bracket material, including their surface hardness, roughness and stiffness [20]. In comparison, the present study shows that IH3 DBs express friction values that may be slightly higher than metal ones but are significantly lower than the aesthetic brackets analysed. Specifically, significant pairwise differences were found between IH3 DBs and composite brackets, and metallic and composite brackets, in combination with the 0.019 \(\times\) 0.025-inch SS archive (\(p=0.007\) and \(p=0.028\), respectively), while no significant differences in performance were found between IH3 DBs and metallic brackets with the same type of archive (Table 4). It is possible to conclude that, during sliding mechanics, IH3 DBs and metal brackets offer comparably lower frictional resistance, while aesthetic brackets produce greater resistance to sliding. [PERSON] and co-workers reported in their study on the fracture resistance of temporary crowns using the BEGO Verseosmile Temp material and a digital light-processing (DLP) printer, concluding that provisional crowns moulded with this material can be considered a viable alternative for long-term provisional restorations [29]. These results are confirmed by the literature findings that the smooth slot surfaces of metallic brackets cause less frictional resistance than those of aesthetic ones. Indeed, the latter have greater surface roughness and friction, which can increase the force expressed to range from 200 g to 500 g, more than conventional metallic brackets. This is due to both the topographical surface of the ceramic and the wire detritus that settles in the slot, especially on its base and in its edges [30; 31; 32; 33; 34; 35; 36; 37]. Indeed, conventional metallic brackets also display increased surface roughness after clinical use [38]. It is likely that the slot surface also plays a role in the lower frictional resistance results associated with IH3 DBs. In particular, it could be hypothesized that the 3D-printing resin has a lower deterioration resistance than nickel-titanium and stainless-steel archives.