## 2 Materials and Methods
The other shoulder represents the miniscrew head (Figure 4A,C). The virtual model of the bushing and miniscrew was then imported into Real Guide software. Three miniscrews with the relative bushings were virtually positioned in the integrated model of the patient maxilla and dental arch. The miniscrew insertion sites were meticulously selected to avoid important anatomical structures like nerves or artery bundles and to maximize the bone thickness at the level of temporary anchorage devices (TADs). Furthermore, the miniscrew bicortical engagement was secured by penetrating the cortical bone layer of the oral cavity vault and nasal floor, to further enforce the TADs primary stability [11], as shown in Figures 5 and 6. Bone thickness at the level of miniscrew insertion sites was measured with the software ruler (Figure 6). These measurements allowed to select the proper length for the miniscrews, that was 13 mm for the anterior right and left ones, and 11 mm for the posterior one. Lastly, the three miniscrews were positioned in a non-parallel way, preferably with divergent apical ends, in order to enhance the vertical stability of the appliance during the clinical use (Figures 1 and 5). Figure 4: Bushing and miniscrew utilized in the DIVA appliance. (**A**) Virtual model of the bushing (a) and miniscrew (b). The head of miniscrew is represented by (c). (**B**) Physical bushing produced with additive manufacturing (d) and conventional prefabricated miniscrew (e). (**C**) Drawing with dimensions expressed in mm. Figure 5: Bushings and miniscrews positioned in the patient CBCT. (**A**) Posterior view (**B**) Lateral view. Bushings and miniscrews are positioned in such a way to achieve miniscrew bicortical anchorage (engagement of cortical bone of oral cavity vault and nasal floor). Also, they are not parallel and preferably diverge apically. After the placement of the three virtual miniscrews and bushings relative to the patient maxilla CBCT, the Dental Wings software (Dental Wings, Montreal, QC, Canada) was used to design the other parts of the appliance, consisting of: the connecting bars that join the three miniscrew bushings, the T-shaped rest on the lingual surface of the incisors, the rests on the occlusal surface of the premolars, the two longitudinal rods, the molar tubes that are connected to the bands of the maxillary first molars and the hooks (Figure 1). The orientation of the two rods along which the molar tubes slide is designed to guide the sagittal movement of molars, as reported in previous publications [12,13]. The rods have a diameter of 1.1 mm, while the molar tubes an inner diameter of 1.2 mm. Once the virtual design of the appliance was concluded, the fabrication was performed with selective laser melting technology by the Mysint 100 machine (Sisma, Piovene Rocchette, Italy) using the Mediloy S-Co Cobalt-Chromium alloy (Bego, Bremen, Germany). The main processing parameters are summarized in Table 1, while the chemical composition of the Cobalt-Chromium alloy is indicated in Table 2. After AM, heat treatment was performed at 800 \({}^{\circ}\)C for 15 min. The appliance was manually polished with tungsten burrs and polishing tips with decreasing size of abrasive particles. The molar tubes of the appliance were then laser-welded to conventional prefabricated molar bands. The completed appliance was disinfected with an ethanol and propanol solution (Zeta 7, [PERSON], Badia Polesine, Italy). The appliance was then cemented in the oral cavity (Figure 7A) and finally the miniscrews were inserted through the appliance bushings into the maxillary bone using the appliance itself as a surgical guide. The premolar occlusal rests are cut immediately after miniscrew insertion, since their only purpose is to help in a precise appliance and miniscrews positioning. An elastic chain was then attached from the hook on molar tubes to the hook on the anterior portion of rods to generate the force for mesial movement of the maxillary molars (Figure 7B).