## 1 Introduction  
Occlusal devices are an important evidence-based therapy option in patients diagnosed with temporomandibular dysfunction [1]. Arthralgia of the temporomandibular joints, myalgia of the temporomandibular muscles or bruxism with parafunctional tooth grinding, gnashing, or clenching are common indications [2, 3, 4, 5]. Occlusal devices aim to protect the teeth and restorations from excessive occlusal forces and trauma including the possible reduction of tooth wear [5, 6, 7, 8]. Another indication is testing a new vertical occlusal dimension prior to extensive prosthetic rehabilitation [9]. To fabricate conventional occlusal devices, a physical cast is essential. Depending on the type of occlusal device, vacuum thermoforming, sprinkling, or injection molding are commonly used methods to produce occlusal devices from auto-, heat-, or light-polymerized acrylic materials [10, 11, 12, 13, 14, 15]. To produce conventional therapeutic devices a technician needs to be involved and many time-consuming working steps are necessary. As an alternative, computer-aided design/computer-aided manufacturing (CAD/CAM) can be approached [15]. Within the digital workflow, data acquisition is the first step [10, 16, 17]. For that purpose, intraoral scans or extraoral scans of conventional gypsum casts are necessary [10, 16, 18]. Based on the obtained virtual casts an occlusal device is designed using a computer aided design software (CAD) [16, 17]. Then, this virtual plan is translated into reality by computer aided manufacturing (CAM) [16,17]. CAM can be distinguished into subtractive and additive manufacturing techniques [16, 17, 18]. Both technologies allow unlimited reproduction of the occlusal device based on the existing data in case of damage, fracture, loss or if therapeutic needs require an adjustment of the design [16, 19]. In subtractive processes, objects are milled out from prefabricated acrylic resin blocks resulting in high material waste and wear of the milling burs [16]. Additionally, from one blank only a very limited number of pieces can be milled. This results in high time-consumption for manufacturing [17]. On the other hand, volume changes such as shrinkage can be prevented due to the prefabrication of the used materials [20]. In contrast, 3D-printing shows less material waste, a greater degree of freedom due to additive fabrication layer-by-layer from a sliced STL file, and the possibility to print multiple objects simultaneously [21, 22, 23]. Additive manufacturing comes with a variety of technologies to process materials in order to build 3D parts. Producing occlusal devices, stereolithography (SLA) and digital light processing (DLP) are mainly used [17, 18, 19]. SLA and DLP polymerize photosensitive resins with light. DLP cures one layer of resin at a time using a light source, as for example light-emitting diodes, with wavelength ranges from deep ultraviolet to visible [24, 25]. SLA polymerizes one layer point by point with UV light or laser [24, 25, 26, 27]. Next to SLA and DLP, continuous liquid interface production (CLIP) is categorized as vat polymerization technology. CLIP is characterized by an oxygen-permeable membrane to inhibit radical polymerization at the surface close to the UV source [24, 28]. Hence, it prevents the attachment of a 3D printed object to the oxygen-permeable curing window [29]. Other technologies used in dentistry are fused filament fabrication (FFF) as a material extrusion method, material jetting (MJ), and binder jetting (BJ) technologies as well as powder bed fusion technologies such as selective laser sintering or melting (SLS/M) [28, 30]. Fused filament fabrication (FFF) is based on the melting of thermoplastic materials which can then be extruded through a print head or nozzle to form objects by filament layering [31]. For material jetting (MJ) a liquid photosensitive resin is selectively extruded by a print head with hundreds of nozzles and polymerized with UV light [26, 32].