## 4 Discussion  
### Material and Method  
Due to its thermal and optical properties, zirconia is a suitable material for in-vitro accuracy measurements. Therefore, the zirconia was the material of choice in the present study [17; 18; 19]. In terms of the concept of the ground truth, a reference model is established that can be used to collect datasets that serve as a reference (gold standard) to study the performance of the acquisition systems under investigation like it is described by [PERSON] et al. [20]. Furthermore, various research groups investigating the accuracy of optical impression systems follow this workflow: one master model was digitized with both a high-accuracy optical impression system to establish a reference dataset and the optical impression system under investigation [7; 8; 21; 22; 23]. Commercially available intraoral optical impression systems have the potential to simplify clinical wear measurement. However, there is a need to investigate their suitability compared to conventional methods [13].  
According to the consensus paper \"Severe Tooth Wear: European Consensus Statement on Management Guidelines\" [24], it is of major interest whether tooth wear shows physiological or pathological patterns. Based on this decision, the management of tooth wear is characterized by multi-layered aspects of diagnosis, patient enlightenment, and monitoring to clarify the severity of wear, wear progress, and its probably multifactorial origin. Especially TWES [25] is a well-established and further developed (TWES 2.0) tool in the context of the multifaceted complex of tooth wear diagnosis and management. Nevertheless, [PERSON] et al. define the use of intraoral scanning systems as a prospective standard in the dentist's daily routine and as a supporting tool alongside taxonomies like TWES. Additionally, it appears advantageous to explore different approaches and combine multiple benefits of different systems to provide the best possible treatment for patients.  
Figure 8: The distribution of the accuracy values (Trueness (**A**)and Precision (**B**)) based on the Kruskal-Wallis-test is shown by the boxplot diagrams. The box shows the range of the calculated values and the median value.  
Advantages of intraoral scans are their ease of production, the storage of the 3D data for permanent documentation and availability, and the possibility of quick analysis of the entire arch by superimposing different scans. By true color display, the character of the wear facets is also visible. Consequently, the detection, analysis, treatment, and monitoring of tooth wear require various features to arrive at therapeutic decisions [26].  
The key prerequisite for the introduction of digital wear measurement on the basis of digital intraoral impressions as a standard method is the sufficient accuracy of the digital workflow. Therefore, the optical impression systems were compared with the optical profilometry, which is the gold standard and shows the highest accuracy in wear measurement with a resolution of 0.2 \(\upmu\)m in vertical direction [2, 27, 28]. The test was performed as a direct, pure comparison of the acquisition systems because the IOS data were compared with the data from WLP, obtained by direct profilometry of the samples. In clinical reality, using WLP as a measurement tool, several additional steps are necessary, like impression taking and cast production. These steps were avoided intentionally in order to obtain the pure profilometry data without any bias. In contrast, to the investigation of [PERSON] et al., the novelty of the present study is that the study model is made out of zirconia, due to the fact that metallic surfaces lead to higher accuracy values [29]. Lava C.O.S. was very accurate but a mandatory powder system. Therefore, this investigation considered powder-free scanning systems to check if they can provide similar results.