Impact of the COVID-19 pandemic on clinical and psychological aspects of temporomandibular disorders

Temporomandibular disorders (TMD) is characterized by dysfunction and pain of the temporomandibular joints (TMJ), masticatory muscles, and surrounding structures. The prevalence of TMD in the general population has been reported as approximately 5–12% with women showing twice the risk compared to men [1, 2]. Although the etiology of TMD has not been clearly identified, previous research has shown that psychological factors such as anxiety and depression play a major role in its occurrence and prognosis [3]. Painful TMD showed increased associations with bronchitis and asthma as with widespread pain in adolescents. Also, those with painful TMD reported a higher number of systemic conditions compared to those free of TMD [4].

In November 2019, Coronavirus 2019 disease (COVID-19) broke out in Wuhan, China, rapidly spreading worldwide. The main symptoms of infected patients ranged from mild headaches to severe respiratory problems which led to death [5]. The World Health Organization (WHO) declared COVID-19 a pandemic in March, 2020 after which most governments implemented social distancing and partial to overall lockdown to prevent further spread of the virus. Decrease in social interactions with the rise of health threats, difficulty in accessing medical facilities, and income declines due to economic instability were among the many changes that affected people both physically and mentally. Not only did the majority of people fail to meet others and fulfill their social responsibilities, but also the fear of death and illness was prevalent [6, 7].

Studies reported that the incidence of musculoskeletal dysfunction and pain increased with COVID-19 infection [8] and 45.1% of patients still showed symptoms of musculoskeletal pain post-COVID recovery with de novo pain presenting in many [9]. Furthermore, research on orofacial pain conditions showed a high prevalence of TMD symptoms [10] and also twice the risk of TMD events in COVID-19 patients [11]. Recent research showed that chronic TMD patients with were more sensitive to distress caused by the pandemic and their psychological alterations resulted in increased orofacial pain levels [12]. As literature suggests, TMD is a complex disorder that is influenced by various biological, psychological, and social factors, all which were impacted by the pandemic condition and could have acted as health risks. Unfortunately, most related studies consisted of relatively small sample sizes and were based on results from online surveys and questionnaires.

Therefore, the aim of this study was to define the clinical and psychological characteristics of two large independent groups of well-defined TMD patients and seek their differences according to COVID-19 pandemic period to assess its influence on disease characteristics. Also, further analysis was done to investigate clinical indices that were closely related to TMD of higher pain levels in each pandemic period to define points of care to be emphasized in the post-pandemic era and their role in the biopsychosocial model of TMD.

The main goal of this retrospective study was to compare clinical characteristics of TMD patients before and during the pandemic and to investigate risk factors associated with higher pain intensity according to COVID-19 period. The results of this study showed that there were changes in clinical characteristics of TMD during the COVID-19 pandemic. More patients reported pain on palpation of the masticatory muscles while fewer patients reported pain on TMJ area palpation during the pandemic. At the same time, more patients reported the presence of nocturnal bruxism and tooth clenching. Those experiencing pain regardless of intensity increased during the pandemic while those reporting disability due to TMD decreased. Different psychological conditions were associated with moderate to severe TMD pain during the pandemic indicating a change in the influence of psychological factors on TMD pain characteristics.

The patients who sought care during the lockdown presented more masticatory muscle pain, TMJ sounds, and self-reported parafunctional habits than those who attended before the pandemic. These findings were corroborated by aggravation of TMD symptoms and oral parafunction reported during the COVID-19 pandemic in previous literature [21]. Patients showed greater rates of myalgia, headache, and degenerative joint disease during the pandemic than those who visited before. They also had significantly more pain-related and intra-articular TMD conditions [22]. A study on rheumatoid arthritis patients also reported a significant increase in the prevalence of fibromyalgia and disease activity during the pandemic compared to pre-COVID-19 periods [23]. However, the results of our analysis showed that fewer patients reported pain on TMJ and cervical muscle palpation during the pandemic. The consequences of COVID-19-related musculoskeletal pain symptoms are not yet fully understood and diverse physiological processes have been proposed to be associated with a wide range of clinical symptoms [24]. Our result is congruous to an Italian study showing that the prevalence of TMD pain and joint sounds incremented in correlation with gender, age, and stress level during the pandemic [25]. TMJ noise is the most common symptom in TMD patients. However, its intensity does not show a direct positive association with pain nor functional limitation levels of TMD. TMJ noises may be identified as an early sign of TMD and as the disease progresses into degenerative joint disease [26]. Previous studies have shown that patients with oral parafunctions had a higher prevalence of TMJ noise compared to those without [27]. Studies have also presented a correlation between nocturnal bruxism and the diagnosis of TMD [28]. Parafunctional habits are considered to be involved in peripheral mechanisms which are likely to play a part in TMD onset while the chronification of TMD symptoms is more likely to depend on central components including sensitization and genetic factors. Bruxism is generally considered as innocuous unless the forces exerted in addition to other aggravating factors outpace physiological resilience and result in elevated risk of structural change and deep pain input [29]. As the global health emergency had been ongoing for three years, people’s mental stress has increased due to concerns about infection and social distancing. Since mental stress is known to have a negative effect on oral parafunctions the significant increase of bruxism observed in our TMD patients during the COVID-19 outbreak could be a direct result of deteriorating mental health. Accumulated psychological distress can induce sympathetic activity which leads to the release of endogenous steroids, promoting vasoconstriction of muscles and increase in peripheral vascular resistance [30]. Increased sympathetic signals and hyperarousal can account for sleep deprivation as well, which may heighten mental stress levels to create a vicious cycle [31]. Since oral parafunction was not investigated objectively the increased level of parafunctional habits observed in this study may be interpreted as a result of an increase in patient awareness during the daytime. Psychosocial factors including perceived stress, depression, and anxiety have been proposed to generate awake bruxism [32, 33].

Those experiencing pain regardless of intensity (GCPS grade 1,2) increased during the pandemic while those who answered that pain hinders their lives decreased significantly. These results are supported by other papers that have explored the impact of pain experiences and mood disasters during COVID-19. Adjusted coping strategies including increased exercise in the lockdown period could lower pain severity and interference level [34]. Another prior study depicted that the social disability domain improved post-pandemic however, the results were limited to female TMD patients [7]. On the other hand, there are studies that report increase in pain interference in the majority of a pain patient group with social distancing [35]. Studies on pain interference during the pandemic based on GCPS are limited, so it is difficult to directly compare our results with those based on different assessment tools. Fewer occupational activities and increased work-from-home status during the pandemic may be related to the improvement in pain interference scores of our study. Another research concluded that the COVID-19 situation did not affect pain intensity or health-related quality of life emphasizing the importance of individual skills in handling chronic pain [36]. In case of certain conditions such as endometriosis, chronic pain symptoms and global physical impairment even improved post lockdown [37].

Contrary to a recent review reporting a high prevalence of negative psychiatric symptoms during the pandemic [38] and several studies showing COVID-19 to have a considerable negative impact on emotional status which prompted an exacerbation of bruxism and TMD symptoms [39] no significant change was found in our TMD patients before and during COVID-19. The current investigation found a difference in psychological characteristics associated with moderate to severe pain before (depression and somatization) and during (paranoid ideation, psychoticism, and somatization) the pandemic. Somatization consistently predicted painful TMD in both periods. Patients with painful TMD often exhibit moderate to high levels of somatization [40, 41]. Somatization is more prevalent in TMD patients compared to the general population [42]. Also, it is known to predict chronic and widespread pain even without organic disease [43]. Somatization was more prevalent among bruxers and was the only variable that demonstrated a significant correlation with the diagnosis of myofascial pain [44]. Another study reported the association between severe somatization and high interference levels [45]. The positive correlation between pain intensity and paranoid ideation post COVID-19 lockdown might imply pain catastrophizing or maladaptive cognitive measures implemented by patients suffering from moderate to severe pain [46]. The overall results of our study showing increase in those reporting masticatory muscle pain and the consistent association of somatization with moderate to severe pain underline the need of both biological and psychosocial methods to be applied in the evaluation and treatment of TMD for best results. And cardinal psychological and social aspects of TMD are prone to change depending on the presence of specific surrounding conditions [47].

There are several limitations to consider when interpreting the results. All patients in this present study consisted of South Koreans and specific ethnic and cultural factors may have influenced the results and limited its generalizability. Further research comparing results from different countries and ethnic backgrounds may provide valuable data on the impact of the COVID-19 pandemic on TMD characteristics. Secondly, due to the retrospective nature of the study, possibilities of sampling bias exist. However, the total sample size is relatively large compared to other studies on TMD and the patient group was defined based on a well-standardized diagnostic process supporting the reliability of the results. Still, the OR for factors associated with higher than moderate intensity pain are relatively small indicating weak association. Also, investigations were conducted only for a limited period of time during the COVID-19 pandemic. Future studies should be designed to include a longer research period which would have allowed better understanding of the longitudinal impact of the ongoing COVID-19 pandemic. Thirdly, some clinical parameters relied on self-report thus, lacking objectivity. Further research including psychological assessment done by trained experts are needed to elucidate the correlation between pain intensity and mental health in TMD under pandemic conditions. Finally, the study consisted of two independent cohorts of patients from before and during the pandemic analyzed each in a cross-sectional manner. The study design does not allow the evaluation of causation but only differences between the cohorts due to COVID-19. To identify causality, future studies should follow the change in disease characteristics of an identical group of patients before and after the pandemic.

TMD symptoms including masticatory muscle pain, TMJ noise, and parafunctional habits increased during the pandemic compared to pre-COVID-19. On the other hand, subjective pain interference decreased, which implies the importance of individual coping strategies. Somatization emerged as the sole predictor of pain intensity both before and during the pandemic while different psychological aspects were associated with moderate to severe TMD pain according to the pandemic period. Mental health affects individual coping and management strategies in adverse times. The results of our study underline the importance of evaluating psychological profiles, especially somatization, paranoid ideation and psychoticism, of TMD patients in exceptional situations that may cause a change in individual mental status. This will lead to a better understanding of the individual TMD patient and help in planning personalized treatment strategies that will assist the patient in adjusting to the changes occurring in special environments such as the COVID-19 pandemic.