## 5 SEM Microscopic Analyses
### Fracture Surface Studies  
Below, in Figure 24, a general view of the exemplary fracture surfaces is presented, along with the surfaces coated with graphite prepared for the SEM analysis. The samples of the NextDent Denture 3D and NextDent C&B MFH Bleach materials were obtained by mechanical tearing along the delaminations formed in the samples (Figure 22a), which followed the direction of the applied loads. The Graphy TC-80 DP material samples fractured and fragmented during testing--views of the sample fragments after testing are shown in Figure 24c. The analyses were primarily focused on the areas where the highest number of defects were observed during surface grinding studies. This area is marked with the letter A in the figure.  
The results of the SEM observations in the form of topography and microstructure images of the fractures are presented in Figures 25-27. The analysis revealed that both on the surfaces of the NextDent Denture 3D and NextDent MFH Bleach samples (Figures 25a,b and 26a,b), arrangements of high faults are visible in the surface topography, located in the area marked with the letter A. In the remaining part of the fractures (central area), low faults are visible on the flat fracture surface. Beneath the high faults, numerous tears and delaminations of the materials are observed, running along the fatigue bands formed in this area (Figures 25c and 26c), accompanied by microcracks causing delamination.  
Figure 23: Scrap view of the Graphy TC-80 DP sample: (**a**) general view of delamination and crack propagation at 60\(\times\) magnification, (**b**) general view of delamination and crack propagation at 150\(\times\) magnification, (**c**) crack path, and (**d**) crack face.  
Figure 24: General view of sample breakthroughs of specimens subjected to fatigue testing: (**a**) NextDent Denture 3D, (**b**) NextDent C&B MFM Bleach, and (**c**) Graphy TC-80 DP. Samples after surface preparation with carbon are marked in boxes.  
Figure 25: View of the NextDent Denture 3D plastic breakthrough surface: (**a**) low fault system visible in the surface topography in area A, (**b**) visible delamination and fragmentation, (**c**) banded structure in the fatigue zone, and (**d**) view of the microstructure with revealed filler particles on the breakthrough surface in the fatigue zone of the plastic.  
Figure 27: Fracture surface view of the Graphy TC-80 DP material: (**a**) the arrangement of high faults visible in the surface topography in area A, (**b**) detachment of the material layer, (**c**) visible delaminations and sharp-edged material bands, and (**d**) view of the plane with a pattern of band-arranged faults.  
Figure 26: Microstructure view with revealed delaminations on the ground surface of the NextDent C&B MFH Bleach material: (**a**) low fault system visible in the surface topography in area A, (**b**) visible delamination and fragmentation, (**c**) banded structure in the fatigue zone, and (**d**) microstructure view with revealed filler particles on the surface of the breakthrough in the fatigue zone.  
On the fracture surfaces, the observations confirm the presence of filler particles typically associated with the matrix material, but a few particles are also visible resting freely on the surface (Figures 25d and 26d). Observations revealed that in the NextDent Denture 3D material, additional transverse microcracks formed perpendicular to the direction of the fatigue bands (Figure 25d), a phenomenon not observed in the NextDent MFH Bleach material.  
In turn, the fracture surfaces of the Graphy TC-80 DP material exhibited the most complex surface topography in terms of the presence of high faults.  
The formed faults created a network of elevations and depressions with varying orientations and angles of inclination of their walls. In such a surface topography arrangement, it was challenging to identify the fracture origin or determine fatigue bands. The fault pattern in the area marked as Area A in Figure 24 is illustrated at different magnifications in Figure 27.