## 4 Discussion
Marginal fit and internal fit depends on both clinical, and laboratory procedures and numerous parameters, but this in vitro study investigated only the laboratory procedures, represented by additive manufacturing (AM) technologies, lately entered in the dental field, compared to traditional casting and CAD/CAM milling [16,31]. The 3D printed medical models represent a very controversial factor because several authors considered that errors might occur in the creation process, segmentation, processing, and also during the printing process [32]. Although it is a thorough process, and it needs a lot of attention for every step, including the used software, which may have some inaccuracies, the 3D process is one of the most widespread techniques. The results allowed us to obtain precise patterns for traditional casting [33,34,35,36]. The prepared teeth may have complex shapes with grooves, boxes, and sharp edges, which are difficult to mill. On top of that, the milling process is relatively complicated, costly, and time-consuming. Additionally, grinding a small structure from a large block of material creates a substantial amount of waste material [37]. The smaller diameter milling tool is the one that dictates the accuracy of the final product, so a larger burr than the details that must be reproduced can lead to a loose restoration [38]. The discrepancy between bur and details is the reason why the AM technologies are gaining popularity among practitioners, being able to produce complex structures with internal morphology, and allowing unused material to be processed again. Complex 3-dimensional [3D] shapes can be formed quickly and precisely by the additive process, without unnecessary waste. Sometimes standard technologies cannot solve the patient problem, and digital workflow is the only suitable for the clinical case [39]. CAD/CAM technologies can be considered a good alternative for the conventional wax-up technique to produce patterns for traditional alloys casting and pressing of ceramic ingots. The previous study assessed traditional casting technology, and measurements were made for internal and marginal fit using silicon replica for patterns obtained by 3D printing, cast frameworks, and final ceramic fused to metal crowns. The best adaptation was found in the resin-pattern group, with small increases of gap after casting and after ceramic pressing [34]. This suggests that further studies are necessary to develop a better workflow to increase the accuracy after investing and casting the resin patterns. The problems that can occur during AM fabrication consist of shrinkage that occurs during the manufacturing or in post-processing stages. This is why the specimens fabricated for this study had so many support structures spread across all occlusal surfaces [38]. Frameworks fabricated with CAD/CAM systems demonstrate better fit and passivity than those made by conventional castings. Laboratory variables involved in traditional casting generated by the inconsistency of volumetric and linear expansion of the materials used, including impression material, gypsum products, waxes, investments, and metal casting, are eliminated with CAD/CAM technologies [40; 41]. The present study used a 50 \(\upmu\)m space for cement in the preparation process of all structures. CAD/CAM systems offer the possibility to use a constant, established in advance, die spacer [42]. Differences in the accuracy of fit between CAD/CAM and cast frameworks have been observed in studies with implant-supported prostheses [43], showing the superiority of CAD/CAM results. However, these studies compared different types of restorations obtained by CAD/CAM, over-casting, traditional casting without a consistency regarding the fabrication process, or research methodology [44; 45; 46]. Furthermore, although some scientific evidence has shown that layering procedures can distort frameworks [36; 47; 48], in this study, the same veneering material was applied to all structures.