## 4 CAD-CAM Devices Production
### Clear Aligners  
The digital workflow for producing clear aligners is based on the orthodontic setup followed by 3D printing sequential digital models, each representing a single step of the programmed orthodontic movements. Afterward, clear aligners are produced by thermoforming a biocompatible transparent thermoplastic sheet using a vacuum thermorformer. Figures 18-20 show, respectively, the digital setup and manufacturing process of clear aligners. There are two clinical and managerial scenarios for dentists and orthodontists in the decision-making process for using clear aligners. The first option is to refer to third-party companies that make a digital platform available for the orthodontic setup and industrial equipment for clear aligner production. The second option is to establish an in-office CAD-CAM workflow with dedicated equipment. In this case, clinicians should be aware of all the variables that could occur throughout the productive process and could influence the accuracy of the clear aligners, which, in turn, reflect their capability to generate the planned tooth movement. For this reason, the knowledge of the characteristics and performances of different 3D printing systems and the materials used for clear aligner production is fundamental considering that the market offers a wide range of products for this purpose. Concerning 3D printing systems, previous studies suggest that most of the available technologies could be appropriate for producing clear aligners, including SLA, DLP, and LCD technologies [47; 48] even though anatomical characteristics of the printed objects could introduce some bias in the prototyping process. For example, a recent study suggests there are differences in the accuracy error of prototyping models with aligned or crowded dentition and criticizes that studies on this topic are generally performed on aligned dentition, which does not reflect the clinical pre-treatment scenario of orthodontic patients [49]. Other well-documented factors potentially affecting the accuracy error of printed objects are model orientation [50], layer thickness [51], and post-curing methods [52]. Figure 17: Example of digital workflow for the production of surgical splint (3 Shape, Copenhagen, Denmark) and clinical application. Figure 19: Post-printing process. (**A**), Model removal from printer platform; (**B**) support removal; (**C**), 2-propanol bath; (**D**,**E**), air drying at room temperature; (**E**,**F**), thermoforming procedure. Figure 18: Example of digital workflow for the production of occlusal splint. (**A**–**C**), Digital setup using Ortho Analyzer software (3 Shape, Copenhagen, Denmark); (**D**), models sequence ready for 3D printing using low-budget 3D printer (Photon S—Anycubic Technology Co., Shenzhen, China). Clear aligners are made from a variety of thermoplastic materials. The most common materials are polyvinyl chloride, polyurethane, polyethylene terephthalate, and polyethylene terephthalate glycol [53]. Thermoplastic polyurethane (TPU) has recently demonstrated favorable properties for clear aligner production, including good mechanical and elastomeric characteristics, chemical and abrasion resistance, adhesive properties, and ease of machining; however, the characteristics of the material used are also influenced by the heat generated during the thermoforming process. A recent study by [PERSON] et al. [54] demonstrated that thermoforming process can change the surface hardness of various polymers; additionally, it can reduce the transparency and thickness of material and increases solubility. Furthermore, depending on the type of thermoplastic material used and the specific thermoforming procedure employed, the thermoforming process might decrease the thickness of the material and, consequently, the stiffness and the flexural modulus [53]. The next step in this process will be to directly 3D print clear aligners, which increases the efficiency and reliability of their production by eliminating all variables influenced by a thermoforming process.