## 4 Results
### Fatigue Testing  
To complement the thermal expansion analysis, fatigue resistance was assessed through incremental and cyclic loading tests, allowing for the evaluation of mechanical stability under simulated functional conditions. The results of the incremental load test are presented in Figure 14. The graph shows the gradual change in load amplitude (bottom chart) and the corresponding change in sample height (top chart). Significant changes in both signals are visible at the final load level of 40.0 MPa, at which point severe structural failure occurs. Such a high load caused large deformations, leading to the complete destruction of the sample. This suggests that the fatigue limit is below 40.0 MPa, beyond which the material cannot maintain structural integrity. A thorough analysis of the chart (Figure 14) reveals increasing deformation of the tested materials even under small loads. At a load level of 20.0 MPa, the height of the sample consistently decreases. This effect intensifies as the load increases. These findings indicate that prosthetic restorations fabricated from these resins will gradually change their dimensions under functional loads over time. However, the dimensional changes in the sample at this load level do not exceed 0.1 mm over a length of 25.0 mm (0.4%). In the main studies, where the load amplitudes are significantly higher, the deformations are correspondingly greater. It is also worth noting that the considered load of 20.0 MPa falls within the initial elastic region of the static compression curve (Figure 7). The primary fatigue tests involved uniaxial compression of the samples under cyclically varying loads with a fixed load amplitude until failure. The failure criterion was defined as the occurrence of a crack in the sample. The cycle asymmetry coefficient was R = \(-\infty\) (referred to as zero-based compression). The load had a sinusoidal waveform with a frequency of 2 Hz. This frequency was chosen to approximate the loading frequency of an implant during the chewing process. Additionally, such a low frequency prevented the  
Figure 14: Cumulative sample of fatigue test; examples of stresses from cycles for the material NextDent Denture 3D. samples from heating during loading, ensuring that their mechanical properties were not altered due to temperature changes. A total of 54 samples were tested, and the results are presented in Table 4.  
The obtained results are presented graphically in the chart shown in Figure 15. The results are primarily limited to the range of quasi-static fatigue strength (below  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{**No. **} & \multicolumn{3}{c}{**Dimensions**} & \multicolumn{2}{c}{**Force**} & \multicolumn{2}{c}{**Stress**} \\ \cline{3-8}  & & \multicolumn{3}{c}{**[mm]**} & \multicolumn{2}{c}{**[N]**} & \multicolumn{2}{c}{**[MPa]**} & \multirow{2}{*}{**Cycles**} \\ \hline \multirow{9}{*}{**Cyp. **} & 1 & 9.95 & 9.50 & 25 & 3250 & 34 & 85,053 \\  & 2 & 9.95 & 9.50 & 25 & 3850 & 41 & 1491 \\  & 3 & 9.95 & 9.50 & 25 & 3850 & 4  
1000-10,000 cycles). Figure 15 provides a graphical representation of the fatigue strength results, illustrating the relationship between the applied stress and the number of cycles to failure. The analysis of the presented chart (Figure 15) indicates that the Graphy TC-80 DP material exhibits the best fatigue properties among the tested materials. At the same load level, this material endures the highest number of cycles before failure compared to the other materials. Additionally, the slope of the fatigue curve for Graphy TC-80 DP is the lowest among all the tested materials, indicating that variations in load amplitude have a smaller impact on its lifespan compared to the others. The NextDent Denture 3D material (pink line) demonstrates the lowest fatigue resistance, as evidenced by its lower cycle count before failure. This material consistently failed at lower stress levels and exhibited greater dimensional changes under load.