## 3 Results and Discussion  
The research presented in this paper was based on a dental model of the upper part of the human jaw (Figure 3). Prior to use, the model was measured using an GOM ATOS Core 185 (GOM GmbH, Braunschweig, Germany) photogrammetric measurement system, which was adopted as the base model in the further comparative analyses \"Model 0\". Additionally, the base model was digitized using a GE Phoenix v | tome l x s240 (Waygate Technologies, Wunstorf, German) micro-CT device to complete the measurement information with surfaces inaccessible to scanning with structured light. The next step was to prepare impressions on the human jaw model. The following impression compounds were used in the study: silicone--Express XT Penta Putty (3M Oral Care, St. Paul, MN, USA) and Polyether Impregum Penta (3M Oral Care, St. Paul, MN, USA) (Figure 4). A geometric evaluation of the models obtained using different dental materials was presented by the authors in [31; 32; 33; 34; 35]. The present study focuses on a multiscale analysis of the objects considered. The finished impressions were measured using a photogrammetric measuring system and micro-CT. Plaster models were then cast using Student Class II dental plaster (Zhermack S.p.A., Badia Polesine, Italy) (Figure 5). Once the plaster had set, the models were measured using micro-CT before being removed from the impression to identify defects resulting from the separation of the impression compound and the plaster model. The plaster models, after removal from the impressions, were finally measured using an optical scanner and micro-CT.  
Figure 3: Dental model of the lower part of human jaw: (**a**) Actual view; (**b**) Digital “model 0”. As part of the research carried out, we attempted to replace plaster materials with models produced using 3D printing (Figure 6) [40]. The use of rapid prototyping technology allows models to be made based on a jaw's digitized model, which avoids defects associated with the drying process of a model made from dental plaster and from damage caused in the process of separating the plaster model from the impression. The models created during the 3D printing process were made using a ZORTRAX M200 Plus (Zortrax S.A. Olsztyn, Poland) printer. As already mentioned, the scanning on the 3D optical scanner resulted in raw data in the form of a point cloud. This model was transformed into a triangular network after  
Figure 4: Dental impressions from silicone material (**a**) and polyether material (**b**). Figure 5: Example of a plaster model of a jaw: (**a**) Front view; (**b**) Top view. Figure 6: Example of a jaw model made using a 3D printer: (**a**) Side view; (**b**) Top view. polygonization. Some areas of the model were difficult to digitize, such as the interdental spaces and the border between the teeth and the gum. The source of these difficulties lies in the complex geometry of elements, which consists of freeform surfaces arranged in such a way that they become an obstacle for measurements using the optical method. The inability to measure these zones resulted in some gaps in the model. Some of these gaps were closed with special algorithms to estimate the area based on the neighboring rows of triangles around the gap. In other words, in areas where it was not possible to record measured points, the area was calculated mathematically. Not all gaps could be closed, as further modifications to the model would lead to a loss of accuracy. In the case of the model obtained using the CT scanner, a full representation of the jaw model was achieved. Nevertheless, the model from the 3D scanner was adopted as a reference due to its overall higher accuracy. Figure 7 shows a comparison of the two models, with one obtained from the 3D scanner and the other from the micro-CT. Figure 7 shows that the deviations between the 3D scanner and micro-CT ranged from \(-0.12\) mm to \(0.26\) mm.