## 2 Digital Workflow: From Intraoral Scan to the Printable Data
### Digital Appliance Design  
In order to design and manufacture an appliance, the intraoral scan generally requires further processing, including mesh repair, hole filling, and removal of invalid data. Usually, a base is added to the dental arch to form a model (Figure 1). Software tools that enable digital planning range from open-source over freeware to proprietary solutions. Currently, there is great variability in software complexity, sometimes necessitating a steep learning curve. The computer-aided design of the orthodontic appliances enables the planning of all steps, including the positioning of orthodontic mini-implants (Figure 2) or osteosynthesis screws and the position of shells or attachments. Moreover, functional elements can be adapted, for example, by modifying their shape, adjusting the inclination and tilt of gliding mechanisms, or manipulating the expansion of orthodontic screws. Simulation of planned tooth movements is also possible, enabling clinicians to oversee and predict treatment outcomes. Additionally, communication with technicians is simplified. Groups of teeth required to move in a specific direction can be connected to active elements of the appliance, and comparison of actual with predicted tooth movements enables validation (Figure 3). Figure 1: Processing of an intraoral scan to a digital model: (**A**) Removal of noise at the edges, and virtual placement within a digital socket. (**B**) Completed digital model (software: Appliance Designer, 3 Shape). Figure 2: (**A**) Virtual implant planning on a digital model. (**B**) Virtual design of an insertion guide, that can be 3D-printed (software: Blender, Blender Foundation). When skeletal anchorage is employed, an accurate fit of the digitally planned appliance is fundamental to avoid overloading of the orthodontic implants. One option is to perform data acquisition after implant insertion. Sometimes, scanners show problems recognizing the metallic implants, which can be improved using scanning spray or scan bodies [40]. The other option is to insert the mini-implants upon digital planning through guides and utilize the planned position for the appliance design. Digitally planned insertion guides allow implant and appliance insertion within the same visit [40; 41; 42; 43] (Figure 2). This can also be achieved by using so-called _Direct Screws_, which are inserted after the adhesive bond of the appliance onto the teeth [33]. As the appliances themselves serve as an insertion aid, no additional guide is needed. When installing a printed _Mentoplate_ with supra-constructions for orthodontic tooth movement, a guided insertion is mandatory to precisely achieve the planned position and ensure the fit of supra-construction and teeth. Digital positioning of (mini-)implants is an already established process in prosthodonic and orthodontic treatments. For insertion of orthodontic screws in the anterior palate, 3D radiographic images are oftentimes not needed. Nonetheless, radiographs can help to estimate the available bone supply [40; 44], and they are indicated in case of palatially displaced teeth, limited bone supply, or pathologies, including clefts (Figure 4). Lateral cephalograms provided a sufficient approximation when compared to cone-beam computed tomography (CBCT) for most of the patients [41; 45; 46]. In case of displaced teeth, patients with craniofacial anomalies, or in case of insufficient bone height visible on a cephalogram, optimal insertion sites and angles can be identified with the help of 3D radiographs [46]. In case of impacted teeth, the optimal vector for force application may also be incorporated in the digital design based on the information from CBCT [12] (Figure 4B). The digital design of mini-plates for the chin bone requires a CBCT to enable an accurate fit. The segmented chin may be matched with an intraoral scan to create an appliance with transmucosal extensions. As root localization is clearly visible in the CBCT, damage of (unerupted) teeth or roots during screw insertion can be avoided.