## 3 Discussion  
Digital orthodontics is gaining more and more acceptance among clinicians in their everyday practice. It started with the intraoral scanning process for the development of virtual models instead of cast ones [14], and is nowadays extending to other processes such as the virtual design of the orthodontic appliances followed by the 3D printing technology [15]. At first the digital workflow was used for simple orthodontic appliances such as trans-palatal arch, lingual arch or Hyrax expander [16]. In the recent years it is being adopted for more complex appliances such as the miniscrew retained ones, which has opened a new and promising perspective in modern orthodontics. Palatal miniscrew assisted appliances can be divided into two main groups based on their target movement: appliances for the transverse expansion of the maxilla [17; 18] and appliances for sagittal and vertical dental movements (mesialization, distalization, intrusion, extrusion). For the latter group, a variety of appliances have been proposed [19; 20; 21] but only recently a digital workflow has been incorporated [3; 4; 5; 22; 23; 24]. In all digital workflows currently in use, the miniscrews are inserted first, often with the help of a surgical guide, and the appliance is secured afterwards with a fixation mechanism [3; 4; 5]. The methodology for the DIVA appliance of the present study differs from the common workflow, in that the appliance is the first component to be cemented intraorally, and the miniscrews are inserted subsequently with the appliance serving as a surgical guide for their insertion. This workflow avoids the need for a surgical guide for the miniscrews insertion and reduces the chair-time in office by simplifying the clinical procedure. [PERSON] and colleagues previously reported a similar protocol for Maximillary Skeletal Expander (MSE), a particular type of miniscrew assisted rapid palatal expander [25]. Instead, the purpose of the DIVA appliance presented in this study is to generate the sagittal or vertical movement of teeth. In addition, the appliance is fully customized and entirely produced with additive manufacturing (AM) technology, with the exception of molar bands. Although the production of molar bands with AM technology could have further simplified the workflow, conventional prefabricated bands are still very common in the orthodontic clinical practice, because they are made with a more ductile material, that offers a better retention and less accidental debonding. Adhesion of bands produced with AM technology is object of future studies. Given that the appliance is serving as a surgical guide, its precise positioning in the oral cavity is of crucial importance. For this reason, the occlusal rests on the premolars are included in the initial design of the appliance and serve as a guide for the positioning of the DIVA appliance in the oral cavity. They are immediately cut after the insertion of the miniscrews. Another important aspect of the DIVA appliance is its vertical stability. In fact, during tooth movement, the appliance could accidentally move apically towards the palatal  
Figure 7: DIVA appliance positioned in the oral cavity. (**A**) After cementation of the appliance at the level of molar bands, incisal and premolar rests. (**B**) After insertion of miniscrews through the bushings and placement of elastic chains between the hooks. Occlusal rests on premolars are cut and removed. mucosa and create tissue impingement. To avoid such an occurrence, in the phase of design of the appliance, the virtual bushings are not placed parallel, but preferably with a slight apical divergence. Since the bushings are the guide for the miniscrew insertion, miniscrews are also going to be not parallel after their insertion in the maxillary bone. This lack of parallelism will create undercuts between the miniscrews and the main structure of the appliance, which avoids any vertical movement during the orthodontic treatment. [PERSON] et al.