# Different Techniques of Creating Bone Digital 3D Models from Natural Specimens
## 4 Discussion
Several studies show that models can serve not only as an addition to cadaver dissection but also can serve as a valuable alternative to natural specimens when access to the cadaveric material is limited [47,48]. Some authors reported that different medical specialists have focused on 3D scanning and printing technologies to enrich the medical education process with modern technologies [49,50]. All 3D technologies complement each other, and their integration can open new possibilities for the creation of new, valuable, and revolutionizing products [51; 52]. The implementation and application of 3D models can be divided into three main categories: visualization, simulation, and physical replication to obtain a functioning model (implant or prosthesis). The visualization aspect prioritizes the overall appearance over the topological accuracy of the model. There are different areas, such as education, where the original look of a scanned bone is significant for the education process. Such an application requires a 3D model creation technique to capture not only the topological data, but also the visual ones. As can be seen in Figure 3, no texture is captured during microcomputed tomography scanning, and the final result consists only of topological data. Two other techniques, photogrammetry, and 3D scanning can capture visual data; however, their capabilities differ. As the camera image sensor is important for the photogrammetry process, it is for 3D scanning. In this study, a mid-level 3D scanner was used, which negatively impacted the resolution of the obtained texture map; it cannot compete with the texture map obtained with the help of the photogrammetry technique (Table 4). More advanced, industrial-grade 3D scanners capable of competing with photogrammetry in terms of the resolution of 3D model texture maps, are far more expensive and can cost up to 30,000 euros. In its turn, the equipment for photogrammetry can be obtained for less than 3000 euros. Photogrammetry is a relatively simple and inexpensive method of creating realistic 3D digital models that can be used in almost any setting to produce digital models [53]. Following special guidelines, these models can be metrically accurate, promoting self-directed learning and a greater understanding of complex anatomical structures [54]. However, creating a series of models through photogrammetry can be time-consuming [55; 56]. In relation to the simulation and physical replication aspects, the density and accuracy of the polygonal mesh are more important factors than the resolution, or presence of the texture map. The data from Table 3 demonstrate that the microcomputed tomography technique is the most preferable way to obtain high density polygonal mesh, as well as this technique produces the most accurate results in terms of topology. Another crucial aspect is the presence of inner structures that are impossible to capture using any other technique (Figure 2). These data are necessary for implant production, or correct computer biomechanical simulation. It is important to note that the first requirement for the creation of an anatomically accurate 3D printed model is a high-resolution volumetric dataset. Most models are created from computed tomography (CT) data, but it is possible to create models from datasets with modalities such as magnetic resonance imaging (MRI) and ultrasound [57]. Today, digital platforms and data storage include many massive medical image datasets [58]. Access to high-quality virtual images can offer a unique possibility for acquiring information about normal anatomy and/or anatomical variations. Differentiation of tissue density (from low to high) allows the segmentation technique to be used for different anatomical structures [59]. Depending on the imaging modality, different features can be observed, and different image segmentation algorithms can be applied.