## 4 Discussion
The use of the DIC technique in this study provides a solid framework for analyzing the deformation behavior of aligner systems [17; 25]. The ability of the technique to capture highly detailed strain and displacement fields provides significant insight into the mechanical properties of the alignment materials. However, it is essential to consider that different investigations may use different methodologies which may influence the results [14]. In our study, the highest values of rigid displacement in both the maxillary and mandibular arches for each of the three axes was recorded by the SP group, in which the specimens were fabricated using the Spark Trugen system. Within each studied axis, the Spark Trugen system showed significantly higher values compared to the other two tested aligner systems. Within axis Z, both maxillary and mandibular, the Taglus Premium system showed significantly higher values compared to the Scheu CA\({}^{\text{\text{\textregistered}}}\) Pro+ Clear Aligner system. In terms of elastic deformation, in the maxillary arch, the Scheu system showed lower values in the X-coordinate compared to the other two systems tested. In the mandibular arch, both the Taglus and Spark systems showed higher values at the Z-coordinate compared to the Scheu system. The results of these experiments reproduce the actual operating conditions of the aligners that have a direct clinical significance in the biomedical field. The current study found that the Spark system exhibited the most considerable rigid displacement. This observation is consistent with previous findings that reported significant deformation of PET-G-based aligners under mechanical stress. For instance, a study performed by [PERSON] revealed a full-field mechanical deformation behavior of PET-G-based aligners including the Spark system [17]. The study demonstrated that PET-G aligners undergo significant deformation when subjected to mechanical loads, which supports our findings. The CA Pro+ Clear Aligner system demonstrated lower values of elastic deformation compared to the Spark and Taglus systems. This finding is supported by studies that have shown that certain alignment materials are designed to provide more stability and less deformation under stress [26; 27]. A study that highlighted the image correlation to measure shape and deformation emphasized that different materials used in the composition of aligners react different to mechanical loads, which is consistent with our findings for the CA Pro+ system [26]. According to the literature, the polymer composition and the manufacturing process are responsible for the deformation and relaxation behavior of materials used for aligners [18; 22]. For example, a previous study showed that polymers with a higher modulus of elasticity exhibit a lower elastic deformation, which confirms the findings of this study in which the aligner system made of copolyester and thermoplastic elastomer showed the lowest elastic deformation values [9; 24]. In addition, the increased deformation resistance in the mandibular area of all the three systems is consistent with previous research highlighting the variability of deformation behavior depending on the dental arch thus suggesting the need for customized approaches in orthodontic treatments [27]. Based on the study findings, the clear aligner system based on copolyester and thermoplastic elastomer emerged as the most suitable and user-friendly option, particularly due to its superior resistance to elastic deformation and rigid displacement in compression tests. This is in line with other consistent findings in the literature, in which aligners with higher stability and lower deformation are often preferred for consistent orthodontic results [24; 28]. Given its demonstrated stability, the clear aligner system based on copolyester and thermoplastic elastomer should be further recommended to patients seeking reliable and durable aligner solutions that guarantee effective and predictable treatment outcomes.