## 4 Discussion  
The measurement method outlined in this paper uses a vision system to record the movements of two markers fixed on a patient's face. The movement quality during jaw opening was assessed by registering deviations from the standard curve in the frontal plane in individuals with mild TMD compared to healthy individuals. In the study, two parameters were assessed--the maximum deviation occurring during the entire opening and closing cycle and the normative deviation. The results indicated that the maximum deviation from the curve was not significantly greater than in the control group. Significant deviations in jaw movements may be caused by a displaced articular disc, which, if repositioned, will cause the jaw to return to its proper path, but if not, it may be the cause of a constant displacement of the jaw during movement towards the joint with a locked disc [23; 24; 25; 26; 27]. The subjects in the study exhibited significantly more clicking in the right and left joints than the control group. However, since our study did not register significant differences in maximum deviation, this may be due to a lack of advanced changes in the temporomandibular joint disc, which quickly reduces despite hypermobility or slipping from the head of the jaw and does not result in large lateral deviations. In the study, we observed that the mean deviation was significantly different in individuals with mild TMD compared to healthy individuals. The mean deviation is a parameter that, unlike the maximum deviation, does not indicate the maximum lateral deviation of the jaw during opening, but it qualitatively evaluates the movement of abduction and adduction. The results of this parameter show us how much the jaw does not maintain its correct path but deviates laterally to one side or the other. Therefore, since there were no differences in the maximum range of deviation, but there was a significant difference in mean deviation between the study and control groups, there were more than one deviation from the standard curve, but each one was quite small. It seems that the cause of differences in mean deflections was not likely due to problems with the disc, which, although it was in dislocation in 60% of patients, quickly reduced. Differences in normative deflections could also be suspected in people who have bilateral disc problems, but among the examined patients, there were only two such cases. [PERSON] and [PERSON] suggest that this may be due to a lack of muscular coordination between the right and left sides [28]. We suspect that this may be related to the occurrence of parafunctional activities of the masticatory system. Parafunctions, as non-physiological activities habitually performed within the masticatory system, usually occur against the background of stress [29] and can be asymmetric [30; 31]. Examples of parafunctional activities that can be included here are: sucking or biting the lip or cheek on one side, biting objects, or playing with the tongue [30; 32]. It would seem, therefore, that habitually repeated asymmetric activities could affect deviations in jaw movement. In our study, all individuals in the study group had at least one asymmetric parafunctional activity of the masticatory system. Nevertheless, we did not observe a correlation between the number of asymmetric parafunctions and normative deviation. Interestingly, [PERSON] et al. [33] suggest that one-sided clenching caused by uneven contacts on the right and left sides causes greater tension in the temporal muscle on that side and changes in jaw movement. We did not find studies by other authors that indicate a relationship between lateral deviations of the jaw and the occurrence of parafunctions.