## 4 Discussion
### Discussion of the Results  
The wear values investigated on the basis of intraoral scanners showed higher values than those obtained from the optical profilometry (Tables 1-3). 23 out of 30 measurements, based on the IOS, exhibited wear deviations of less than 10% compared to WLP. In order to decide from which values IOS are suitable for wear measurement, it was necessary to define a threshold value. [PERSON] et al. measured a maximum difference of 12.6% between the applied IOS and the optical profilometry [7]. Based on these findings, a threshold of 10% was established. The maximum deviation was 19% (+45 \(\upmu\)m). One potential explanation for the outlier values (>10% from WLP) is that for the manual wear simulation a diamond bur was used. The cross-sections visualize that WLP detected the traces caused by the diamond bur when simulating the wear facets (Figure 4) by grinding. The cross-sections of the surfaces delivered by TD (Figure 5), Tr3 (Figure 6), and OC (Figure 7), show a smoother texture of the wear areas. The IOS were not able to detect the peaks in detail resulting from the grinding procedure. In particular, the pronounced peaks at t2 compared to tI and t3 provide a rationale for explaining the increased deviations at the wear level t2 (tooth 27). With respect to the present study, wear measurements based on the IOS led to higher wear results than those evaluated with the WLP data at the same stage because pronounced surface structures were captured less detailed by the IOS. Conventional wear measurement requires several working steps, such as impression taking and cast production. The digital workflow of the wear measurement is decisively determined by the data acquisition and the analysis strategies. Key aspects are the characteristic of the triangle meshes and the alignment and measuring strategies. Figure 9 shows the variety of triangular structures. Poor mesh quality is characterized by triangles with a low edge ratio or tiny interior angles and non-equilateral triangles. Extremely tilted triangles may be the cause of misleading wear measurements. High-quality meshes are defined by homogenous triangles, comprising the same homogenous, equilateral triangles in their neighborhood while keeping the detail and edge sharpness of the geometry [34; 35]. In future investigations, it has to be elaborated to what extent the mesh quality and a kind of re-meshing is necessary for the context of wear measurement. The three most common strategies for superimposing datasets are an exclusively landmark-based approach, a standard best fit alignment, and a reference best fit [12; 36; 37]. In terms of wear measurement, the exclusively landmark-based alignment is inaccurate, especially due to the difficulty of positioning landmarks with micrometer accuracy. In contrast, the standard best-fit alignment, including the whole surface of the datasets, is based on an iterative closest point (ICP) algorithm. The absolute distance between two datasets is minimized as far as possible. Another modification of the standard best fit alignment is the reference best fit. If it is possible to determine which areas of the scanned tooth surface have been worn, these changes can be excluded. The operator manually determines the areas to be included in the alignment. Although the reference best fit is user-dependent and therefore more error-prone, [PERSON] et al. were able to achieve the most accurate results in their investigation. Applying the exclusive landmark-based alignment or the standard best fit alignment, wear has been underestimated [12]. Therefore, the reference best-fit alignment is the preferred alignment strategy. Due to the manual wear simulation, the worn areas were known and excluded to achieve the best possible alignment. In clinical situations, this is only possible to a limited extent by identifying grinding and clenching facets.