## 5 Clinical Application  
### Temporary Anchorage Device-Borne Appliances  
When skeletal anchorage is employed, the non-digital workflow consists of unguided implant insertion, followed by a conventional silicone molding with impression caps. Then, the appliance is manufactured based on a plastered model with laboratory analogs, mainly consisting of preformed components. Once finished, the appliance can be installed unless it does not fit properly.  
In contrast, for skeletally anchored appliances manufactured using a digital workflow, the clinician can choose and alter the mode of installation. The appliance can be designed to be fastened onto formerly placed implants, or it can be installed simultaneously with the implants using an insertion guide for the implantation, or it can be attached to the teeth prior to the implantation (_Direct Screws_). In the latter case, the appliance itself serves as an insertion template [33].  
Taking a closer look into the various options of implant installation helps with outlining the respective advantages and disadvantages.  
A common way to place an implant-supported appliance into the oral cavity is to set the implants at their determined position using an insertion guide (Figure 7A,B). This ensures a perfect match with the printed appliance (Figure 7C). Fixing the appliance to its skeletal anchor requires a mechanism that locks the appliance on top of the implants and prevents rotations. If a fixation screw is used, adapting the appliance, or changing to a completely different device, is possible [33] (Figure 7D). The adhesive bond between the appliance and teeth occurs before the insertion of the fastening screws.  
In case of _Direct Screws_, the appliance itself serves as the guide [33] (Figure 8). In this case, the practitioner adhesively attaches the appliance to the teeth and then uses the hole of the appliance's connectors as an insertion aid. This installation method can be advantageous because it eradicates a possible mismatch between implants and the appliance, and eliminates the need for an additional 3D-printed insertion guide.  
When implant placement is performed prior to intraoral scanning, appliance installation is performed similar to conventional approaches. In case of immediate loading, one must consider that primary stability of the implants reduces within the first 4-6 weeks after insertion due to a loss of primary stability. Nonetheless, immediate loading of the implants has been reported to be not detrimental or even beneficial in terms of implant stability [62; 63].  
The molar coupling of digitally printed appliances can be achieved by means of printed shells or palatally attached tubes. These couplings do not penetrate the attached soft tissue and usually remain coronally to the interproximal contacts [64]. It may be speculated that this can lead to higher failure rates, which, however, can be reduced by etching the surface of the teeth and using an adhesive system instead of temporary cement. Additionally, no rubber-based separation of teeth is required prior to appliance insertion [7; 65]. The preformed shape of customized, 3D-printed molar shells thus obviates the need to adapt bands, which may increase comfort for both the patient and practitioner [7; 40]. Even  
Figure 8: Direct screw insertion: (**A**) Implant placement with appliance itself serving as a guide. (**B**) Completed installation of the appliance from Figure 7 on two mini-implants (with fixation screws) and a posterior direct mini-implant inserted through the appliance itself.  
Figure 7: Appliance installation with guide: (**A**) Guided implantation. (**B**) Vertical control is achieved through a stop between the guide and the insertion tool. (**C**) Try-in on implants. (**D**) Appliance fastened on two implants by fixation screws.  
though limited evidence is available, the digitally printed shells seem to provide clinically acceptable survival rates [7].