## 4 Discussion
This variable was created to facilitate the comparison of kinematic data with electromyographic data, which are expressed in the literature using the SMI index (%), describing the symmetry through the overlap of the electromyographic trace on the right side with that on the left side [28,29]. In general, this study found only weak correlations between variables related to mandibular kinematics and variables related to electromyographic activity of the masseter and anterior temporal muscles. This may be attributed to the fact that the process of mastication involves multiple intra-oral structures, such as the lips, tongue, and hard and soft palates, which play a role in food intake and size reduction. However, these structures were not assessed in this research protocol as human studies typically focus on surface masseter and anterior temporalis EMG activity due to their non-invasive nature and ease of measurement. Based on the negative correlation (\(-0.42\)) obtained between the SMI (%) muscular symmetry index and the symmetry variable between the masticatory angles \(\frac{MAR}{MAT}\times 100\), it can be deduced that as the complexity of the masticatory path increases, functional symmetry between the right and left sides tends to decrease (Figure 10). However, it's important to note that the magnitude of the correlation indicates a moderate strength, which means that while there is an association between the variables, it is not particularly strong. Based on the literature review, the SMI % parameter for healthy participants in the study was found to significantly deviate from the indicated values. Thus, we conclude that this parameter is not reliable or reproducible in this analysis. Furthermore, a positive weak correlation has been noted between the masticatory height MHR and the work produced by the masseter muscle MMIR on the right side. A corresponding positive weak correlation has been observed between the masticatory height MHL and the work produced by the masseter muscle MMIL on the left side (Figures 11 and 12). The jaw-closer muscles, especially the masseter, perform most of the mastication work during the jaw-closing power stroke. Therefore, the observed results suggest that greater work is produced by the masseter muscles when the amplitude of mouth opening during the chewing cycle is larger. In people with particularly large movements, the increased work of the masseter muscles may cause overexertion and noticeable movements during chewing. Moreover, a weak positive association was noted between the right condylar slope (CSR) and the activity of the right anterior temporal muscle (TAIR). Also, a weak positive correlation was detected between the left condylar slope (CSL) and the activity of the right anterior temporal muscle (TAIL). It follows from this positive correlation that as the work produced by the temporalis muscle increases, so does the CS. In other words, as the temporalis is a postural muscle that also comes into action in retrusive movements, the greater the CS, the greater the activation and work expressed by the temporalis muscle (Figures 13 and 14). In a study published in 2022, the possible correlations between mandibular kinematics and electromyography during the chewing cycle were evaluated using a Motion Capture System and landmarks on the two mandibular angles, specifically at the Nasion and Frankfurt planes. The study found a correlation between the vertical amplitude of the opening path and the electromyographic activity of the suprahyoid muscles [30]. Several limitations of this study should be considered when interpreting the findings. First, we recruited only healthy young male and female participants, so these findings could not be generalized to other/older populations. Considering the effects of age, particularly regarding the effects of dental status or oral dryness, recruiting other populations would help clarify how these conditions affect masticatory behaviors. Moreover, volunteer subjects were not asked which was their preferred or habitual chewing side.