## 1 Introduction  
Digital technologies, such as 3D scanning and printing, have expanded the range of treatment options in various medical disciplines in recent years [1, 2, 3, 4, 5]. In dentistry, a wide range of possible implementations have been reported across specialties, including the fields of orofacial orthopedics and orthodontics [6]. In contemporary orthodontics, scanning dental arches for metric analyses or the creation of digital set-ups are routinely performed. A relatively new application is the design and clinical application of individual metal-printed orthodontic appliances [7]. Especially in complex cases, where conventional techniques and preformed devices do not fulfill all requirements, individualized 3D-designed and printed appliances may be advantageous [7, 8]. In addition, appliances created using a digital workflow are reported to offer many advantages in terms of patient comfort, treatment efficacy, and predictability [7, 8]. As every orthodontic (and orthopedic) force is associated with a reactive force of equal magnitude, orthodontic treatment success necessitates sufficient anchorage to avoid side effects, including undesired tooth movement of dental anchorage units [9, 10]. Therefore, orthodontic anchorage is a term for all measures preventing those reactive forces and moments [11]. Typically, either teeth (dental units) or extraoral attachments are used. Extra-ancharge can be achieved by integrating the bone into the resistance unit by means of so-called temporary anchorage devices (TADs). This concept is called skeletal anchorage, and it gained popularity in recent years owing to a reduction in side effects and increased treatment efficacy [8, 9, 10, 12, 13, 14, 15, 16, 17]. Among the TADs, orthodontic mini-implants are frequently employed due to their ease of application and the favorable cost-benefit ratio [18, 19]. In the upper jaw, the anterior palate proved to be the most favorable insertion site with the highest survival rates [15, 20, 21]. In the mandible, however, mini-implants usually have to be inserted into the alveolar ridge [22, 23, 24], where failure rates range from 14% to 16% [25, 26, 27]. The lower success rates were mainly attributed to the reduced bone quality and the proximity to the dental roots. In addition, a risk of root contact or even penetration exists [25; 26]. Since mini-implants are inserted between the roots, the extent of possible orthodontic tooth movement is implicitly limited. Mini-implants inserted into the mandibular buccal shelf did not gain much acceptance in most of the countries because of their very low survival rates [27], despite their advantage not to limit tooth movements. Alternatively, the chin below the dental roots was identified as a possible insertion site due to its high bone quantity and quality. Nonetheless, mini-implants are not well-suited for the area, and thus special mini-plates, such as the Mentoplate, were developed [28; 29]. These plates can be fixed to the bone using regular osteosynthesis screws, but require a slightly more invasive surgical procedure for insertion and removal, when compared with mini-implants. TAD-borne appliances are regarded as \"non-compliance\" devices as patients only need to keep them clean, but are not requested to wear them for a certain amount of hours (they have to wear them 24 h/day) [30]. These appliances also permit longer time intervals between appointments and hence a reduction of the overall chair-time [10; 12; 31]. The application of digital workflows to design and manufacture TAD-borne appliances appears to be particularly promising. The placement of the mini-implants can be planned, which allows the identification of the optimal insertion position based on digital models and, optionally, using radiographs. Utilizing printed insertion guides [32] or the appliance itself [33] allows for implant insertion and appliance installation in one appointment. Owing to the precise fitting, the risk of screw overloading, and therefore the risk of implant failure, can be reduced [34; 35].