**1. Introduction**

The COVID-19 pandemic disrupted the education system in Poland and vastly contributed to social isolation, with all due consequences. That, in turn, had a negative impact on the mental and physical health of students and university graduates. The accompanying stressors could have had influenced the development of increased masticatory muscles tension and numerous parafunctions, and thus the formation of stomatognathic system dysfunctions [1–5]. The relationship between increased stress and disorders of the stomatognathic system and quality of life has been widely described in the literature [6–8]. For example, bruxism, the diurnal and/or nocturnal unconscious teeth clenching and grinding, is commonly triggered by environmental stressors and depends on the personality traits that affect the way stress is controlled and relieved [9–11].

Pałka, Ł.; Kołodziej, Ł.; Sobolewska, E. Type D Personality and Stomatognathic System Disorders in Physiotherapy Students during the COVID-19 Pandemic. *J. Clin. Med.* **2021**, *10*, 4892. https://doi.org/ 10.3390/jcm10214892

**Citation:** G˛ebska, M.; Dalewski, B.;

Academic Editor: Michele Roccella

Received: 28 September 2021 Accepted: 19 October 2021 Published: 23 October 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/).

Therefore, the authors of the present study aimed to evaluate the relationship between the occurrence of symptoms of SS disorders and type D personality in physiotherapy students during the COVID-19 pandemic.

Regarding health psychology, there are three personality types that favor the development of somatic diseases: type A ('coronary personality'), type C ('cancer-prone personality'), and type D ('distressed personality') [12]. Two approaches are taken into account regarding the study of the relationship between personality and disease. The first indicates that certain personality traits are associated with morbidity rate of certain severe health issues such as, for example, type A personality promotes ischemic heart disease, or type C, which was previously associated with cancer [12–14]. The second approach assumes the existence of a general susceptibility to disease and indicates that this susceptibility is the result of personality traits that may favor or inhibit the development of the disease [15]. The growing interest in the problem of the relationship between personality and somatic diseases took place at the end of the 1990s, when Johan Denolett introduced the concept of distressed personality into the literature (distressed personality), i.e., type D personality, which he emphasized at the early 2000s [16,17].

Type D consists of two main dimensions, treated as relatively constant personality traits, i.e., negative affectivity (NA) and social inhibition (SI). Negative affectivity is expressed as a tendency to experience strong negative emotions, such as anxiety, 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. Refraining from revealing emotions is conscious and is undertaken mainly in social situations, primarily for fear of disapproval and rejection by other people [18]. People with a type D personality tend to worry, they feel tense and blame themselves which may result in suicidal behavior [19]. They are pessimistic about the world, have low self-esteem and a low level of life satisfaction. Moreover, they show weak bonds with other people, and use sedatives more frequently [20,21].

Type D personality shows some similarities to other personality characteristics that contribute to the development of somatic diseases, such type A or type C, but above all, to the two dimensions of personality that make up the 'Big Five', i.e., neuroticism and introversion. This relationship was confirmed by De Fruyt and Denollet [22].

The theoretical foundations of the type D personality refer to the biological theory of inhibition and activation formulated by Eysenck [23]. According to this theory, people for whom the stimulating potential is created quickly and with great force and the reactive inhibition appears slowly and disappears quickly, show a tendency towards introverted behavior (for extroverts it is the other way around). On the other hand, the theory of activation refers to individual differences in the level of activity of the cortico-reticular loop that determines the level of activation. The activation level of introverts exceeds the level of activity of extroverts [24]. The tendency to experience negative emotions, characteristic for both type D personality and neuroticism, modifies the behavior and level of functioning in situations requiring the activity of the limbic system [25].

Type D personality is linked to neuroticism by a tendency towards a catastrophic perception of reality, a way of evaluating events as highly threatening and harmful and a feeling of strong anxiety and tension [12]. What is characteristic in social situations is confusion, shyness in the presence of others, a tendency to worry, a pessimistic view of the world, high susceptibility to stress, and a tendency to break down in difficult situations. They are differentiated by the fact that in the type D personality, there is an emphasis on refraining from revealing negative emotions. It is also combined with introversion by refraining from keeping social contacts and shyness [14]. Moreover, introversion, similar to type D, is associated with a lower tendency to search for social support, poorer quality of social contacts and low self-esteem [26]. Therefore, it can be assumed that type D personality is the equivalent of neurotic introversion, yet people with type D personality would feel stress more strongly and experience its' consequences that appear to be more robust for physical and mental health.

The aim of this study was to evaluate the presence of type D personality in students with symptoms of stomatognathic system disorders. We hypothesized that type D personality traits may contribute to the development of symptoms of stomatognathic dysfunction during the COVID-19 pandemic.
