## 4 Discussion
In this study, to simulate oral cavity conditions, the aligners were fully immersed in a humid environment at 37 \({}^{\circ}\)C and subjected to constant loading for 3 h. The stress within thermoplastic materials induced by the initial deformation tends to cause a deterioration of the mechanical properties over time, as these materials are viscoelastic [27]. This phenomenon, known as stress relaxation, leads to a further loss of a thermoplastic's ability to move a tooth over time, making the prediction of orthodontic forces and tooth movement much more challenging [5]. The force analysis on the upper central incisors showed significant differences between the various points analyzed. At the gingival and middle points, NHVH recorded the highest forces, followed by NHH, F22, NHZ, and finally AS, which showed significantly lower values. The design with horizontal and vertical thickness gradients of NHVH proved particularly effective in concentrating the force in the gingival areas, where it tends to dissipate the most. At the incisal point, NHH exerted the highest force (16.3 N), followed by NHVH (14.7 N), a small but statistically significant difference. The NHZ and AS aligners showed lower forces, with AS being significantly less effective. The aligner shear also influences these results: the NHZ aligners exert lower forces than the other NOXI aligners, particularly at the gingival point, probably due to the geometry of the zenithal shear, which, while maintaining a uniform force, does not reach the initial intensity of other models. The cutting difference is also evident when comparing the two thermorformed aligners, as the straight-cut aligner exerts significantly higher forces than the scalloped-cut aligner. To better understand the force dissipation observed in the gingival regions and the differences between aligners, it is important to consider the biomechanical behavior of aligners during thermoforming. As highlighted in the study by [PERSON] et al. [28], aligners typically exhibit a greater gap at gingival areas compared to occlusal or incisal points after thermoforming procedures. This phenomenon can be attributed to the stretching behavior of the plastic material, which is more pronounced in the tapered anterior regions and at the gingival level during manufacturing. Consequently, the force transmission in these areas is less efficient due to greater dissipation across the larger gap. Conversely, at the occlusal and incisal points, where the aligner fits more closely to the tooth surface, forces are more concentrated and thus more effective in inducing tooth movement. These findings align with the results of the present study, which confirmed that the highest average forcesare observed at the incisal/occlusal points, followed by the middle point, and finally the gingival point, further demonstrating the greater dissipation of force in the gingival region. Comparing the results with the study by [PERSON] et al. [29], it appears that 3D-printed aligners made of polyamide (PA) perform very differently from those made of Tera Harz TC-85. [PERSON] found that 3D-printed aligners produce 77% lower forces than thermoformed ones for peak force and almost 90% lower for stabilized force. The superiority of PA over Tera Harz TC-85 in this study suggests that the mechanical properties of the material significantly influence the ability to generate and maintain orthodontic forces. In the present study, at the gingival and middle points of the molar, the NHVH aligner exerts a significantly higher force, followed by NHH, F22, NHZ and finally AS, which shows the lowest force values. Given the similar values, Cohen's D was calculated at the occlusal point between the NHZ aligner and the F22 aligner. The resulting value is relatively low (0.075), indicating that the relationship is statistically significant but negligible. Therefore, it can be concluded that the force exerted by F22 and NHZ is almost equivalent. An important observation concerns the force distribution between the different aligners.