**4. Discussion**

According to the present research carried out on a group of 150 physiotherapy students, the most common symptoms of SS disorders were headaches (51.3%), neck and shoulder girdle pain (43.1%), and teeth clenching (35.6%). The studies carried out by Glaros et al. show that involuntary tooth contact is one of the most typical parafunctions observed more frequently in TMD (temporomandibular joint dysfunction) patients than in healthy people [27]. Similar conclusions were also drawn by Moreno et al., who found a correlation

between TMJ disorders and head and neck pain [28]. According to Emodi-Perlman et al., the COVID-19 pandemic had a significant negative influence on the psycho-emotional state of the Israeli and Polish populations, leading to the worsening of bruxism and TMD symptoms [29]. De Medeiros R.A. et al. drew similar conclusions by conducting research on Brazilian medicine students. According to their study, social isolation and stressful situations caused by the pandemic may increase the number of people with TMD symptoms [30]. For several years, great interest of researchers and practitioners has been aroused by the so-called 'distressed personality'—type D. It is considered a risk factor for somatic diseases and is of high importance as far as the perception of the environmental stress is concerned [31].

In the author's own research on a group of 300 physiotherapy students, the presence of type D personality was found in 160 participants (53.3%). In accordance with O'Riordan et al., type D people perceive their life events as significantly more stressful than people with a different personality type. Type D personality people also report increased perceptions of negative social relationships and less social support [20]. What is more, people with type D personality are characterized by a worse quality of life and they assess their own health condition as worse [32]. In the context of the studied groupfuture physiotherapists- numerous studies should also be cited, in which it was shown that employees characterized by type D personality perceive their work environment as more stressful with more frequent occurrence of occupational burnout syndrome [33–36]. According to the authors, the above-mentioned considerations indicate that the high prevalence of type D personality among physiotherapy students may become an obstacle in providing effective rehabilitation services to patients.

The results of many studies have shown that the type D personality is a significant predictor of cardiovascular diseases (ischemic heart disease, hypertension), as well as somatic diseases, such as cancer, peptic ulcer disease, and skin diseases [37–41].

In a study by Condén et al., a strong relationship was found between the type D personality with psychosomatic symptoms and musculoskeletal pain [42].

However, there are no scientific studies on the evaluation of the relationship between the type D personality and the occurrence of symptoms of stomatognathic system disorders. The studies presented in the literature, taking into consideration related constructs, especially neuroticism, confirm the role of the experience of negative emotions and reserves in relations with other people as those elements of personality that favor the assessment of stress and intensify its the negative effects. According to Moayedi et al., neuroticism may contribute to the pathophysiology of muscular TMD because there is a correlation between chronic pain in TMD and the patient's neurotic personality [43].

On the other hand, according to the research of Southwell et al., TMJ dysfunctional individuals obtain higher results regarding neurotic and introversion scales [44]. Serra-Negra et al. have shown that children with a high level of neuroticism in their personality domain are more prone to sleep bruxism [45].

Research over the past twenty years has indicated a connection between several psychological variables and TMD [46–48]. Indeed, it is easy to observe differences in the severity of personality traits, experienced levels of stress, depression, and catastrophic situations between TMD patients and those without the disorder. A well-known example of the association of psychosocial risk factors in chronic TMD is the insecurity that accompanies long-term suffering [48]. What is more, it should also be noticed that there are psychological factors associated with the initial pain symptoms in TMD, as well as socio-demographic variables that contribute to the perception of craniofacial pain [48]. One of the most important determinants influencing the behavior and functioning of an individual is their personality.

The authors of the present study, by utilizing the DS-14 questionnaire, which is used to evaluate the occurrence of type D personality, have observed that it is significantly more common in people reporting symptoms of SS disorders than in asymptomatic people. (*p* = 0.00000). These results suggest that people with symptoms of SS disorders have

personality traits that make them prone to perceived life stress. It is also worth mentioning that significantly higher values of both type D personality components (NA and SI) were observed in women than in men with symptoms of SS disorders. The above-mentioned data may prove that not only type D personality may predispose to SS disorders, but also gender may be an additional factor influencing the frequency of SS dysfunctions. Yeow's research on a group of 157 psychology students has shown that 50% of men and 46.4% of women had a type D personality. Moreover, women had higher HS when compared to men [49]. Cho S. et al. have observed that type D personality is related to the level of perceived stress. Additionally, it was concluded that there are gender differences in type D personality, stress, and stress coping strategies [50].

The authors of the present article, by comparing both dimensions of the type D personality (NA and SI), noted statistically significant differences between the groups in terms of symptoms, i.e., headache, face pain, TMJ and shoulder girdle, acoustic symptoms and TMJ blocking, teeth clenching and grinding as well as increased masticatory muscles tension. In the symptomatic group, the NA dimension showed higher average values than SI, that is related to the individual's tendency to experience strong negative emotions such as anxiety, anger, irritation, and hostility. After analyzing the obtained data, it can be claimed that the type D personality, and above all the dimension of negative affectivity, is one of the predictors of symptoms of SS disorders. The research results presented in the literature indicate a relation between the NA dimension and unfavorable eating and shopping habits, symptoms of depression, anxiety, insomnia, alcohol abuse and a low level of life satisfaction.

There are many strategies and methods in the field of psychotherapeutic treatment applied to individuals with a disturbed personality. Currently, the main method is a long-term psychodynamic psychotherapy. The literature offers numerous reliable studies confirming the effectiveness and usefulness of this treatment procedure if conducted by a psychologist [51–53]. If the disorder is correctly qualified and the therapy is durable (long-term in nature), it is possible to obtain real changes in the patient's functioning, which are conducive to better functioning in many aspects of their life. One can also find a growing number of reports confirming the effectiveness of other methods of psychotherapy (e.g., modifications of cognitive-behavioral therapy) [54]. It cannot be forgotten that the basic therapeutic factor, independent of the applied psychotherapeutic approach, is establishing a therapeutic relationship between the therapist and the patient, based on mutual trust, safety, and commitment. The progress in the field of psychotherapy of personality disorders observed in recent years is a hope for many patients, who can thus avoid gradual degradation of their lives and have a chance to function better on daily basis. Pharmacotherapy as a method of treating personality disorders is of complementary importance and psychotropic drugs are recommended mainly for symptomatic indications, e.g., to control severe depression, anxiety, or short-term psychotic symptoms [55].

By analyzing the available scientific literature and the results of our own research, it is possible to determine with high probability that the distressed personality may have a great influence on the functioning of the stomatognathic system, in particular on the development of the masticatory organ parafunctions and head and neck pain.

Further research is necessary to better understand the impact of the type D personality on the occurrence of stomatognathic system disorders.

#### **5. Limitations**

The presented results, indicating the predictive role of the type D personality in the development of symptoms of SS disorders, should be treated with great caution. First of all, due to the cross-sectional nature of the research and also due to the small group of respondents. One should also remember about the multifactorial determinant of SS disorders, which means that personality is only one of the numerous factors determining the occurrence of SSDs. A particularly important limitation of the presented studies is the lack of assessment of occlusal conditions, including the occurrence of malocclusion in the study group, which constitutes an important etiological factor of the stomatognathic system disorders. In addition, possible missing teeth and traumatic nodes within the masticatory apparatus may be the cause of the appearance of micro and macro injuries in the examined system. Therefore, the authors see the need to continue the research carried out, taking into account the role of occlusion in the formation of SSD.
