## 4 Discussion
To evaluate whether the left and right chewing tests were conducted with symmetrical muscular patterns, the symmetrical mastication index (SMI, %) was assessed. The Symmetrical Masticatory index is computed using the center of the two confidence ellipses to assess whether the left and right masticatory trials were performed with symmetrical muscular patterns. The SMI, according to [PERSON] et al., ranges from 0% (asymmetric muscular pattern) to 100% (symmetric muscular pattern). Several studies confirm the data introduced by [PERSON] et al. in 2000 [24; 25]. Additionally, [PERSON] et al. noticed that TMD patientsshowed significantly greater difficulty in chewing, reduced symmetrical mastication index (SMI), and increased standardized activity during EMG tests than healthy subjects. In the study by [PERSON], the mean SMI% value was evaluated during unilateral gum chewing: 30 healthy subjects measured 66.50 \(\pm\) 18.33 and 46 subjects suffering from TMD scored 44.76 \(\pm\) 29.20 [24]. The SMI mean value measured in this study was significantly lower than expected (24.59 \(\pm\) 24.19) and was calculated as follows by the BTS Dental Contact Analyzer software version 4.0.43.2:  
\[\text{SMI}=100.0\ -\ \left((\text{DistDxSx}/(2\ \times\text{Math.Max}(\text{ModMedDx}, \text{ModMedSx})))\ \times\ 100.0\right)\]  
DistDxSx = distance from the centroid of the left side flipped with respect to the centroid of the right side  
Math.Max(ModMedDx, ModMedSx) = Maximum distance between the two centroids  
The SMI values calculated in this study appear to fall below the TMD cut-off values described by [PERSON] et al. and [PERSON] et al., but this study's subjects did not exhibit any signs or symptoms of TMD or chewing impairments. This value seems to be less accurate of the actual health condition of the subjects belonging to the study, as it is worth noting that [PERSON] et al. also observed that 56% of the control subjects scored an SMI lower than 55% [24]. The frequency of the unilateral chewing cycle, intended as masticatory rhythm (bps), is not a common value found in dentistry literature. To convert \"bps\" (bites per second) to \"Hz\" (Hertz), we assumed the average duration of a single bite or chewing cycle was 1 s 1 Hz = 1 bps/average duration of a bite. The measurements of this work converted parameters in Hz showed a slight increase compared to the values reported by [PERSON] in elderly subjects, with 1.77 \(\pm\) 0.3 Hz on the right and 1.71 \(\pm\) 0.25 Hz on the left [26]. Healthy individuals typically exhibit a notable level of masticatory frequency stability, whereas those wearing complete dentures or diagnosed with temporomandibular disorders (TMD) often demonstrate decreased mastication frequency compared to their healthy counterparts. Furthermore, chewing frequency has been reported to range from 1.00-1.6 Hz [24]. The distance from the center of the graph and the center of the ellipse, also called ModMed, was evaluated and was similar among healthy subjects [24]. In 2021, researchers conducted an analysis of new functional measures for evaluating the activity of masticatory muscles. They compared these measures to the existing and widely used indices in both healthy and individuals suffering from TMDs [27]. However, consensus on the appropriate indices for assessing masticatory muscle activity using surface electromyography (sEMG) during chewing has not been reached yet. Regarding the kinematics of movements, a variable representing the degree of symmetry between chewing on the right side and chewing on the left side was introduced. This was done by considering the angle between the true vertical and a line passing through the highest point of the opening path and the point farthest from the vertical line. The symmetry (ratio) between the right angle (MAR) and the left angle (MAL) was then expressed as a percentage \(\frac{MAR}{MAL}\times 100\).