**4. Discussion**

The outbreak of the COVID-19 pandemic generated a global public health emergency [55–58]. Taylor et al. reported that psychological responses to previous epidemics and pandemics depended on individual vulnerabilities such as intolerance, insecurity, disease susceptibility, and anxiety [59]. Therefore, the authors of the present study conducted research on the assessment of the level of stress, the method of coping with stress, and the occurrence of symptoms of SS disorders in students of physiotherapy during the COVID-19 pandemic.

Multiple researchers emphasized the importance of mental stress in shaping the pathology of the SS [17–20]. Stressors with somatic consequences are largely dependent on the patient's personality type and the ability to cope with stress. The long-term effects of stressors breaks the body's adaptive mechanisms and lead to the accumulation of various disorders, including SS disorders [60]. According to the authors' research on a group of 188 physiotherapy students, the symptoms of SS disorders were found in 150 participants (80%). Research conducted by Emodi-Perlaman et al. showed that the COVID-19 pandemic had a significant adverse effect on the psychoemotional state of Israeli and Polish populations, leading to an increase in bruxism and TMD symptoms [61]. In the author's own research, symptoms of bruxism, i.e., tooth clenching, were found in 75 participants and teeth grinding in 34 (50% and 22.7%, respectively). In studies by Przyta ´nska et al., patients with high levels of stress reported parafunctional functions, i.e., awake bruxism, almost six times more often [62].

As it results from the conducted research, in the group of students with symptoms of SS disorders, higher scores were observed in the stress severity rating scale compared to the group without SS symptoms. The difference between the groups was statistically significant, which may indicate a significant role of stress in the development of SS disorders. De Medeiros et al. conducted research among Brazilian medical students and indicated that social isolation and stressful situations caused by the pandemic may increase the number of people with TMD symptoms [63].

It is generally accepted that mental stress causes increase in the muscular tension in different parts of the body [64,65]. The body posture adopted in stressful situations related to the so-called "fight or flight" reaction affects muscle contractions within the SS, leading to pain in the head and neck area. Therefore, muscle contractions in the body's upper quadrant may be a part of a stress-related defensive behavior [14–17]. In our study, the majority of physiotherapy students reported at least one symptom of SS and pain. The most common symptoms were headache (68%), neck and shoulder pain (58%), and teeth clenching (50%). Many clinical studies seem to confirm the relationship between the occurrence of SS disorders and severe stress, mostly in young people entering adulthood [66–69]. According to Quintiliani et al., as many as 89.4% of the respondents experienced an increase in perceived stress during the pandemic (66% reported moderate stress and 23.4% high stress) [70].

The authors of the study, by using the PSS 10 scale, found that the average stress intensity among physiotherapy students was in the range of six sten (19 raw points), indicating the average intensity of stress. Similar conclusions were drawn by other authors assessing the intensity of stress in emergency medical students, who also obtained an average value of six [70]. Importantly, in the present study, as many as 46.3% of the respondents obtained results in the range of 7–10 sten, which, according to the current interpretation of the research tool (PSS 10), qualifies them as high stress subjects. It is also worth noting that the maximum score on the PSS 10 scale in the group with symptoms of SSD was higher than in the control group.

The relationship between stress and neurological disorders, and tension headaches and migraines has been expensively described [71–74]. The results of our own research confirmed the existence of positive correlations between the intensity of stress and the symptoms of SS disorders, because with the increase in the intensity of the sense of stress, the intensity of headache and pain in the neck and shoulder girdle also increased. The

above fact should prompt clinicians to evaluate the structures of SS in patients who report the above-mentioned pain symptoms in their history.

According to the literature, SS disorders and higher levels of stress are more common in women than in men [75–78]. Wang et al. found three times higher levels of depression and health anxiety in women than in men during the COVID-19 pandemic [79]. Moreover, in the research by Liu et al., women were stronger predictors of PTSS symptoms after the pandemic [80]. Our results are in accordance with the abovementioned findings, as we discovered that women with a symptom of SS disorders were characterized by a significantly higher level of stress and a type D personality (*p* < 0.005) compared to men (*p* > 0.05).

The analyses carried out by the authors of the publication with the use of the Mini-COPE test were aimed at examining the activity that students undertake in a stressful situation. These actions are known as "coping methods". Research conducted by Babicka-Wirkus et al. on a group of 577 students from 17 Polish universities showed that, during the COVID-19 pandemic, students most often used coping strategies such as acceptance, planning, and seeking emotional support [81]. The analysis of the authors' results did not bring similar conclusions, because out of 14 strategies, four were significant predictors, i.e., positive thinking strategies, discharge, taking psychoactive substances, and blaming oneself. The results also showed that the higher the level of perceived stress, the more frequently the remaining three strategies were used. The level of perceived stress most strongly influenced the frequency of using the discharge strategy, which is a strategy focusing on revealing negative emotions and is associated with a feeling of mental discomfort. The results obtained by the authors allow for the conclusion that maladaptive stress coping strategies in students, especially during the pandemic, may have long-term consequences for their psychophysiological health and academic achievement. According to the research, the presence of SS symptoms did not contribute to changes in the way of coping as all coping strategies retained their statistical significance (*p* < 0.05).

As it was shown in the study, the intensity of type D personality manifestations was positively and moderately strongly associated with the general intensity of stress (rho = 0.690; *p* < 0.001). Students experiencing higher levels of stress exhibited more symptoms of type D personality, and those with more severe symptoms showed higher levels of stress. In a study by Cho et al. conducted among Korean students, it was observed that type D personality is related to the level of perceived stress. Additionally, it has been concluded that there are gender differences in type D personality, stress, and coping strategies [82].

By analyzing the available scientific literature and the results of our own research, it can be determined with high probability that the COVID-19 pandemic increases the intensity of stress and may influence the development of SS disorders.

More research is required to better understand the impact of COVID-19 stressors on stomatognathic disorders.

The major limitation of the present study is the fact that it was carried out in a very specific population. Therefore, the results cannot be extrapolated convincingly to the general population.
