**1. Introduction**

The SARS-CoV-2 pandemic has significantly impacted the mental health of populations around the world [1]. As the pandemic-related threat developed, people were forced to change their lifestyle [1]. The economy and its mechanisms, tourism industry, the functioning of culture, and teaching methods at all levels of education have been transformed [1,2]. At medical universities in Poland, necessary recommendations were introduced, i.e., hybrid teaching, limited social and professional contacts, as well as restricted access to university hospitals. As medical college education is largely based on practical skills, students became concerned about their development. Moreover, the uncertainty accompanying senior-year students as to how to fill in the gaps in education could have influenced the level of stress they felt. The pandemic also had a negative impact on attention span and enhanced learning difficulties, which resulted in increased concerns about final exam results.

Dalewski, B.; Pałka, Ł.; Sobolewska, E. The Influence of the COVID-19 Pandemic on the Stress Levels and Occurrence of Stomatoghnatic System Disorders (SSDs) among Physiotherapy Students in Poland. *J. Clin. Med.* **2021**, *10*, 3872. https:// doi.org/10.3390/jcm10173872

**Citation:** G ˛ebska, M.; Kołodziej, Ł.;

Academic Editor: Michele Roccella

Received: 2 July 2021 Accepted: 27 August 2021 Published: 28 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Social isolation resulting from the pandemic, fear for oneself and loved ones, and financial instability also had a negative impact on the psychophysical health of students. The everyday uncertainty created an environment of anxiety and depression, and the quarantines contributed to a loss of social ties, deepening the feeling of loneliness or anger [3]. These stress factors could lead to the development of health problems associated with the whole body. Psychological factors, especially stress and the ability to deal with it, play a significant role in the etiology of stomatognathic system disorders (SSDs). Coping with lockdown measures was also associated with increased alcohol intake in men [4,5].

Stress that accompanies our daily lives contributes not only to cardiovascular, digestive, and respiratory diseases, but also increases muscle tone of the SS. As a consequence, symptoms such as: bruxism, pain in the temporomandibular joints (TMJs), and headaches may appear. Long-term symptoms of SSDs may contribute to irreversible changes in this system, resulting in impaired chewing, swallowing, speech, and breathing functions [6–20]. Additionally, long-term reports about TMJ internal derangements were released [21–25]. Hypothalamus, limbic system and reticular formation are responsible for psychological processes in humans [26]. These centers, through gamma-efferent fibers, which supply the muscle spindles, influence the myogenic activity of the body. In long-term stressful situations, they cause an increase in muscle tonus, also in the facial part of the skull, contributing to the formation of myogenic dysfunctions of the SS [5].

In 1926, Hans Hugon Selye introduced the concept of stress to health sciences. In medical terms, it is defined as a disorder of the body's homeostasis caused by physical or psychological elements [6–8]. It can be caused by mental, physiological, anatomical [7,8], or physical factors [9–11,14]. Stressful situations lead to increased muscle tension, which is the body's natural response to threat. SS muscles, like other skeletal muscles in the human body, can react with increased tension, pain, and/or hypertrophy when strained [7].

People react differently to stressors, which may depend on the personality type of the individual [27]. At the end of the 1990s, the concept of distressed personality (type D) was introduced into the literature, which resulted in an increased interest in the problem of the relationship between personality and somatic diseases [28]. Type D consists of two main dimensions—negative affectivity and social inhibition. Negative emotionality is expressed as a tendency to experience strong negative emotions such as fear, anger, irritation, and hostility. On the other hand, social inhibition is associated with the tendency to refrain from expressing negative emotions and behavior consistent with these emotions. People with type D personalities tend to be worried, tense, and blamed [29]. They are characterized by a pessimistic way of looking at the world, low self-esteem, and low level of satisfaction with life [30]. Type D personality has been found to be a significant predictor of cardiovascular disease, gastric and duodenal ulcer, and skin diseases [31–34].

Medical college students may be particularly prone to the negative effects of the pandemic. This study is a quantitative analysis examining the impact of the psychological effects of the pandemic on the occurrence of stress and stomatognathic system disorders among students of physiotherapy. The results of this research may help in preparing appropriate future intervention programs and effective prevention strategies in crisis situations at universities [32,35–38].

The aim of this study was to assess stress severity, coping with stress strategies, and the presence of type D personality in students with symptomatic stomatognathic system disorders. We hypothesized that stress, the ability to cope with it, and the type D personality may influence the development of SS disorders.

#### **2. Materials and Methods**

The research was conducted from October to December 2020 among randomly selected students of physiotherapy at the Pomeranian Medical University in Szczecin. The sample consisted of 188 participants (125 female and 63 male) aged 20 to 35 years (mean =22.72). All participants agreed to voluntarily participate in the study by signing an informed consent. They were asked to fill in the survey consisting of two parts: the first part

included a respondent's particulars (age, sex, year of study) and ten close-ended questions concerning the symptoms of SSDs and pain (Likert scale) [39–45]. The second part consisted of standardized psychological questionnaires, PSS10 (perceived stress scale), Mini-Cope (Inventory for measuring coping with stress), DS14 (Type-D scale) [46–54]. As a result of the activities performed, 150 participants (study group-P1) with SSD symptoms and pain were selected from the group. The remaining 38 participants who did not report any symptoms from SSD were enrolled into the control group P2.

The sample size was calculated based on the data on a specific population (finite population) and the formula for the minimum sample size was as follows:

$$N\_{\min} = \frac{P(\mathbf{1} - P)}{\frac{\epsilon^2}{Z^2} + \frac{P(\mathbf{1} - P)'}{N}}$$

where:

*P*—estimated fraction size,

*Z*—value resulting from the adopted significance level (α), calculated using the cumulative distribution function of the normal distribution,

*N*—size of the general population (in the case of a finite population),

*e*—maximum estimation error.

After entering the data, namely:

*P*—50%

*Z*—1% (0.01)

*N*—8017

*e*—10%

The finite population sample size equaled: 163

The inclusion and exclusion criteria were as follows: Inclusion criteria:


Exclusion criteria:


The differentiating factor between the study group (P1) and the control group (P2) was the lack of symptoms of SS disorders in the control group.

Among 1st and 2nd year students of physiotherapy who met the inclusion and exclusion criteria, the study group (P1) and participants without symptoms of SSD (P2) were selected on the basis of the SSD symptom questionnaire.

The main goal of the present study was to compare the groups that are as homogeneous as possible in terms of everyday functioning and exposure to stressful situations while studying during the pandemic. Therefore, a small sample size resulted from the limited number of physiotherapy students.
