Three-Dimensional Modeling and 3D Printing of Biocompatible Orthodontic Power-Arm Design with Clinical Application  
[PERSON]  
1 Department of Stomatology and Maxillofacial Surgery, Faculty of Medicine, Comenius University in Bratislava, 812 50 Bratislava, Slovakia; [EMAIL_ADDRESS] Department of Stomatology and Maxillofacial Surgery, Faculty of Medicine, Comenius University in Bratislava, 812 50 Bratislava, Slovakia; [EMAIL_ADDRESS] Department of Stomatology and Maxillofacial Surgery, Faculty of Medicine, Comenius University in Bratislava, 813 72 Bratislava, Slovakia; [EMAIL_ADDRESS] Department of Stomatology and Maxillofacial Surgery, Faculty of Medicine, Comenius University in Bratislava, 813 72 Bratislava, Slovakia; zrako@dime. intraoral scanning. It must be understood that dental treatments were necessarily highly individualized already, even in the analog era. Therefore, incoming novel technologies, such as AM, during their beginnings, were facing the strong competition of existing and well-established workflows, such as dental impressions techniques or CAD/CAM systems based on subtractive manufacturing, which is the opposite of AM [3]. It took some time for these technologies, such as 3D face-scanning, 3D printing, cone-beam computer tomography (CBCT), and others, to become more efficient than some analog processes. Having a 3D model of an exact digital reproduction of the patient anatomy is only the first step. To be able to implement the AM process into the clinical field, and to have it in direct, long-term contact with the patient's body, the biocompatible materials must be well developed and certified. Only in recent years have wider numbers of class IIa biocompatible dental resins, suitable for long-term dental applications, been approved and EU-certified [4; 5; 6]. Our early experiences with fused deposition modeling (FDM), digital light processing (DLP), stereolithography laser resin printing (SLA) and laser sintering processes taught us possible clinical applications, which had both the merit of economical affordability, and the sustainability of such processes. Most of our clinical applications currently take advantage of DLP and SLA biocompatible resin printing [1]. The clinical implementation of AM processes in the orthodontic field today is technologically superior to most of the older existing processes, however, it does require the knowledge and skillsets not regularly taught in medical faculties [7; 8]. The economical affordability aspect shall not by diminished. In dentistry, the resin 3D printing is used for the manufacturing of surgical guides, splints, long-term provisional crowns and bridges and many other applications. In orthodontics, 3D biocompatible printing is used for individualized retainers, dental splints, biomechanical power-arms (PA) and power-caps (PC), and Carriere Distalizers or surgical dental splints for orthognathic surgeries [9]. Our experience in 3D printing models for operative planning in situations of complex congenital heart defects [10] or in ophthalmology for stereotactic radiosurgery planning [11] taught us about the limits of low-cost FDM printing. For example, our experimental FDM 3D printing of scaffolds for mesenchymal stem cells (MSCs) colonization was not successful due to accuracy issues with PLA 3D printing in 2011. Since then, however significant technological progress has been made, and we are captivated by 3D printing with materials with dynamic properties. As the material properties and shape of 3D printing is changing, it will in time be called 4D printing. For example, shape-memory polymers (SMPs) have the ability to change from an initial shape into a stress-free, temporary shape. For our applications, the current ideal form of AM is DLP (or SLA) in combination with biocompatible resins. In the future, the shape would change, which might be a breakthrough in orthodontics, where clear aligners are used to apply light, continuous forces on the teeth.