Temporomandibular disorder (TMD) is a general term utilized to describe musculoskeletal and neuromuscular diseases of the temporomandibular joint (TMJ), masticatory muscles, and associated structures [1]. The prevalence of TMD ranges from 5% to 31% depending on the studies [2,3]. TMD encompasses a wide range of risk factors, including physical, psychosocial, and psychological aspects. As a result, a comprehensive biopsychosocial model is frequently utilized to explain TMD [4]. Within this model, parafunctional oral habits are recognized as a factor spanning all domains—biological, psychological, and social [5]. It is widely acknowledged that parafunctional oral habits can increase the risk of TMD-related symptoms [6,7]. However, some studies have indicated that the influence of parafunctional oral habits on TMD remains controversial [5,8], and their impact on adolescent TMD patients has not been sufficiently explored.

For the effective diagnosis of TMD, Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) was developed, where TMD was evaluated by Axis I and Axis II components [3]. Especially, psychosocial factors are precisely dealt in Axis II of TMD. Patients who experience long-lasting TMD become psychologically intimidated, and psychological distress can directly result in somatic pain, which aggravates symptoms of TMD [9]. Additionally, psychological distress can directly contribute to the incidence of first-onset TMD [7]. Prolonged TMD, pain, and psychological distress correlate to create a vicious circle of amplified suffering in patients.

Meanwhile, prevalence of TMD in adolescents varies widely in the studies from 7% to 68% [10,11]. In adolescent patients, the psychological effects of TMD and chronic pain are similar to those in the adult patients, which include somatization or aggressive behavior [12]. Especially in children and adolescents who are in the developmental stage, TMD and chronic pain in children and adolescents can cause developmental impairment. And consequences of TMD on psychosocial status can persist into adulthood, including growth disturbance, appearance defects, social withdrawal, or even cognitive impairment [13]. Also, psychosocial impairment during the developmental stages of children and adolescents is much more likely to result in psychological disorders [12].

Among psychological disorders, depression is one of the most prevalent conditions among adolescents [14]. Depression is defined by serial experience of sad or irritable mood, worthlessness, and accompanied cognitive changes including difficulty in concentrating, memory alteration, and sleep disturbance [15]. Prevalence of depression in adolescents is steadily increasing: prevalence of major depressive disorder increased from about 1.3% in 2015 to 8.0% in 2020, and global prevalence of depressive symptoms increased from 24% in 2011 to 37% in 2020 [14]. Depression in adolescents was investigated as the leading causes of illness and disability by world health organization in 2021, which include suicide, academic difficulties, social maladaptation, and incidence of other mental disorders [14]. Importance of early intervention to adolescent depression has been emphasized in numerous previous studies in order to prevent more severe depression in adulthood.

However, interaction between TMD and psychology in adolescents has not been studied well despite to its immense influence to the developmental period of adolescents. This study aims to investigate the relationship between depression that have been surveyed utilizing the Symptom Checklist-90-Revised (SCL-90-R) and pain-related factors in adolescents with TMD. The main hypotheses were as follows: 1. Given the higher prevalence of psychological disorders in older adolescents, older adolescent TMD patients will exhibit higher depression score compared to younger adolescent TMD patients; 2. Depression score will be correlated with various clinical factors of TMD, including the visual analog scale (VAS) score, onset duration, diagnostic type, TMD index, and parafunctional oral habits. With this study, we will be able to confirm whether the depression of adolescent TMD patients can be predicted utilizing the pain-related factors.

1. Study Population and Groups

This study utilized retrospectively collected data from patients aged between 10 to 18 years who visited the Department of Orofacial Pain and Oral Medicine at Kyung Hee University Dental Hospital between November 2020 and May 2023 due to the TMD-related symptoms. Among the patients, those who completed the psychological examination with the SCL-90-R were included in this analysis. While patients with a history of fracture injury, orofacial surgery, severe degenerative disease that could cause drastic deformity of the orofacial bony structures, severe cognitive disorder that could make patients impossible to answer the questionnaire, and incomplete clinical or psychological data were excluded.

A total 185 patients (116 female and 69 male patients; mean age 15.15±2.17 years) were enrolled to the study after the screening procedure. The patients were then divided into three age groups: group 1, young adolescents aged 10-13 years; group 2, middle-aged adolescents aged 14-16 years; and group 3, and older adolescents aged 17-18 years. Age group distribution followed the school age of South Korea, which had been utilized in previous studies [16,17].

2. Clinical Data Collection

Clinical data were collected from the medical records at the patients’ initial visit, where history taking and clinical examinations were conducted by skilled dentists with training in standardized examination protocols. The patient interview was conducted during the first hospital visit, during which all patients were asked about their subjective pain intensity using the VAS, the duration of pain (defined as the time from the initial recognition of symptoms to the hospital visit), patient history, and parafunctional oral habits related to TMD. Patient history and parafunctional oral habits were recorded according to the self-report questionnaire of patients. Regarding the patient history, parafunctional oral habits and attributing factors, patients were asked whether they think they have certain history, habitual behaviors and symptoms or not. All of the patient history, parafunctional oral habits, and attributing factors were recorded dichotomously as yes or no. Additionally, insomnia was defined to be hard to fall asleep or stay asleep, and sleep problem was defined to have any kind of sleep disturbance including insomnia. After the patient interview, palpation and mouth opening examination were conducted according to the guidelines of DC/TMD.

TMD indices were calculated based on the results of the clinical examination, including the palpation index (PI), dysfunction index (DI), and craniomandibular index (CMI). The PI was calculated by adding the number of pain-provoked muscle palpation sites and dividing them by the total number of palpation sites. The DI was calculated by adding the number of positive events related to TMD, including TMJ pain during jaw movement, joint noise, and pain on TMJ palpation, and dividing it by the number of all events. The CMI was the average of the PI and DI [18].

In addition, panoramic image taking was performed at the first visit of patients. All of the radiographic images were taken by following the imaging criteria of the Department of Oral and Maxillofacial Radiology in Kyung Hee University Dental Hospital, with 70kVp and 12mA of exposure. Two skilled dentists (YHL and TSK) diagnosed the TMJ osteoarthritis (OA) based on panoramic image. OA in panoramic radiography was diagnosed when the indistinct cortical bone outline of TMJ exists, which is described in Fig. 1.

3. Psychological Data Collection

Depression status of the patients was collected and analyzed utilizing the SCL-90-R checklist. All patients answered 90 questions on the SCL-90 R at the first visit. Patients scored each question from 1 to 5, ranging from not absolutely to extremely. T-scores of the nine psychological subscales and three indices were calculated with results of the questionnaire. The final psychological data of the patients were statistically analyzed with other variables in two ways: by the T-score itself, and by the psychological groups according to the score. The psychological groups were divided into three groups: those with a score under 59 that are normal state, those with a score between 60 and 69 with a tendency for psychological distress, and patients with scores over 70 who certainly have psychological distress [19].

4. Statistical Analysis

Statistical analysis of all data was performed utilizing IBM SPSS Statistics for Windows (version 25.0, IBM Corp.). Descriptive statistics were utilized to calculate percentages, means, and standard deviations (SDs). One-way analysis of variance test with post hoc analysis for continuous variables and the chi-square test for distributed variables were conducted to compare disparities in variables between age groups. Spearman’s correlation analysis was utilized to calculate the Spearman’s correlation coefficient (rho) and evaluate the monotonic relationship between variables. Linear regression analysis and a generalized linear model were utilized to investigate the correlation between psychological status and clinical factors, with each psychological state as the dependent variable and the clinical factors as independent variables. The correlation coefficient (B), standard error, p-values, and 95% confidence intervals (95% CIs) were investigated. In all statistical analyses, a p-value<0.05 was considered statistically significant.

5. Ethics Approval and Consent to Participate

The procedures for human subjects in this study were conducted according to the ethical standards of the Committee on Human Experimentation of our institution and the 1975 Declaration of Helsinki. This study was approved by the appropriate ethics review board of the Kyung Hee University Dental Hospital (IRB number: KH-DT23016). Informed consent was obtained from all participants in the study.

1. Characteristics of Patients and Diagnosis of Temporomandibular Disorder

Demographic and clinical characteristics of the patient are presented in Table 1. Mean age and SDs of each age groups are 12.22±0.87 in group 1, 14.99±0.88 in group 2, and 17.57±0.50 in group 3. In all age groups, female accounted for a greater proportion. Patients in age group 2 and 3 were more likely to experience some clinical symptoms than patients in age group 1, including TMJ pain (83.3% and 78.7% vs. 60.9%, respectively, p=0.015) and jaw stiffness (51.3% and 54.1% vs. 30.4%, respectively, p=0.032).

Additionally, frequent parafunctional oral habits and attributing factors for each age group are illustrated in Fig. 2. Patients in age group 3 were more likely to have clenching habits than those in age group 1 (57.4% vs. 21.7%, p=0.001). In the panoramic image, OA was observed in 48 patients (25.9%).

2. Depression of Patients and Correlation with Age

Table 2 displays the psychological states of patients as observed in SCL-90-R results. The average depression score in the SCL-90-R was 40.95±8.38 among all patients. Furthermore, the average depression scores for each age group were 37.54±8.38 in age group 1, 40.71±7.61 in age group 2, and 43.25±9.90 in age group 3 (p=0.004). Fig. 3 illustrates the depression scores across continuous age and age groups. Statistical analysis revealed significant differences in mean depression scores between age group 2 and 1 (40.71 vs. 37.54, p=0.004) and between age group 3 and 1 (43.25 vs. 37.54, p=0.004). Additionally, totally 10 patients (5.4%) scored above 60 for depression, marking the second-highest rate in the study. The prevalence rates of depression in age group 1, 2, and 3 were 2.2%, 6.4%, and 6.6%, respectively. However, the prevalence of depression did not exhibit a significant correlation with age (p>0.05).

3. Correlation between Depression and Clinical Factors

Spearman’s correlation analysis was conducted to prove the correlation between depression and clinical factors (Supplementary Table 1), and Fig. 4 illustrates the factors that had statistically significant correlation with depression. In adolescent TMD patients, sex was closely related to the depression (rho=0.173, p=0.019). In addition to age group, continuous age was correlated with depression (rho=0.193, p=0.008). Pain intensity and pain duration had no significant relationship with depression (p>0.05). In the TMD index, depression was found to be associated with DI (rho=0.243, p=0.001) and CMI (rho=0.218, p=0.003).

In terms of patient history, depression had statistically significant relationship with history of jaw locking (rho=0.149, p=0.043), tinnitus (rho=0.225, p=0.002), self-reported stress (rho=0.441, p<0.0001), and trauma history (rho=0.207, p=0.005). Regarding the attributing factors, sleep problems had the most significant relation with depression (rho=0.249, p=0.001), followed by chin buttressing (rho=0.216, p=0.003), irregular diet (rho=0.189, p=0.010), insomnia (rho=0.183, p=0.012), and much talking tendency (rho=0.181, p=0.014). Radiological interpretation of OA showed no statistically significant correlation with depression (p>0.05).

4. Generalized Linear Model of Depression

The regression analysis was utilized, particularly with generalized linear models, to predict depression with the investigated factors. Depression was selected as an independent variable, and clinical factors were set as dependent variables. The results of generalized linear model of depression are displayed at Fig. 5.

In adolescent TMD patients, age group was the factor most closely related to depression, and age group 3 (17-18 years) was significantly related to depression (B=2.651, 95% CI: 0.363-4.940). This was the largest coefficient value in the statistically significant results. Clenching habit also had significant relationship with depression (B=1.433, 95% CI: 0.170-2.696). Other factors that had statistically significant relationship with depression were score of obsessive-compulsive (B=0.581, 95% CI: 0.427-0.735), and score of somatization (B=0.246, 95% CI: 0.047-0.445). Radiological interpretation of OA showed no statistically significant correlation with depression (B=3.170, 95% CI: –9.159-16.578).

In this study, we aimed to investigate the relationship between depression and age, clinical TMD symptoms, attributing factors, and parafunctional oral habits in adolescent TMD patients. Total 5.5% of adolescents exhibited abnormal depression scores in this study. In adolescent TMD patients, older adolescents and female patients were more likely to have depressive symptoms than young adolescents or males, respectively. Intensity and duration of pain had limited relationship with depression. Regarding patient history, tinnitus, self-reported stress, history of limited mouth opening, and presence trauma history had significant relationship with depression. Among the attributing factors, sleep problems showed the strongest association with depression, followed by irregular diet, chin buttressing, and a tendency for excessive talking.

In adolescent TMD patients, depression had significant relationship with age. In general, both TMD and depression are age-independent when comprehensively considered across all ages. Although degenerative changes of TMJ was frequent in elderly, prevalence of comprehensive TMD was highest in 20s and 30s and tended to decrease in elderly, and the association between age increase and prevalence of TMD was not significant in patients over 40 years old [20,21]. Additionally, the prevalence of depressive symptoms was highest in individuals in their 20s and did not increase with age [22]. The tendency for depression in adolescents to increase in proportion to age is a unique feature of psychological disorders in children and adolescents [23]. In South Korea, the prevalence rate of psychological disorders was reported to often differ between middle school and high school students, which were age groups 2 and 3 in this study [24]. This might be as a result of the change in the proportions of externalizing and internalizing problem behaviors, which is significantly different between middle and high school students in South Korea [24]. Externalizing problem behaviors include aggressive behavior, juvenile delinquency, and violence, whereas internalizing problem behaviors include anxiety, depressive mood, and suicidal ideation. Externalizing problem behaviors exhibited a gradual increase until the third grade of middle school, followed by a gradual decrease during the high school period. In contrast, internalizing problem behaviors showed no significant difference between the middle school and high school periods. The internalization of psychological distress in high school students elucidates the correlation observed between age group 3 and depression in this study, all of which are classified as internalizing problem behaviors. However, studies about correlation between age and depression in adolescent are still lacking, and further studies would be needed to confirm this correlation globally.

Regarding the clinical factors, CMI had a statistically significant correlation with depression in adolescent TMD patients. CMI was developed for standardized evaluation of TMD symptoms, and can effectively reflect the severity of symptoms, and thus, CMI also shows correlations with several factors related to TMD [18]. For example, Kim et al. [25] reported that CMI had significant correlations with the psychological state observed at SCL-90-R and Minnesota Multiphasic Personality Inventory in adult TMD patients. As an extension of the previous study, this study successfully proved that the association between psychological state and CMI can also be applied to adolescent TMD patients.

In this study, depression in adolescent TMD patients had large number of history and oral habits of patients. Among the oral habits, clenching habit were significantly associated with depression in generalized linear model, whereas bruxism was not significantly related. One of the possible causes of daytime clenching in adolescents is neurodevelopmental disorders, which is closely related to psychological state of adolescents [26,27]. Neurodevelopmental disorders can cause impairments in social and executive functioning, and can act as stressors for adolescents [28]. And regardless of the cause, patients with clenching habit was reported to have more psychological distress than those without clenching [29]. Bruxism is widely recognized in the literature as being closely associated with TMD, anxiety, and depression [30,31]. The controversial results of this study may be attributed to the lack of accurate diagnostic methods for bruxism, such as polysomnography [32]. Further studies are needed to evaluate the impact of bruxism and clenching on depression in adolescent TMD patients, utilizing precise diagnostic and classification methods.

Irregular diet and sleep problem were closely related to depression in adolescent TMD patients in this study. Prior studies have reported that dietary habits are a behavioral risk factor for mental health disorders in adolescents [33,34]. An inappropriate diet can cause a deficiency of certain nutrients implicated in brain function, which can affect depression risk through impaired neurological pathways, pain control, or emotional regulation [35]. Among the inappropriate diet, habitual irregular diet can result in several comorbidities that are closely related to the development of psychological disorders [35]. Additionally, maintaining a regular diet is a type of social rhythm, which is a series of habitual daily behaviors that can modulate the biological clock [36]. Collapsed social rhythms can result in social withdrawal and depressive mood, and patients with depression often have insufficient ability to recover and perform daily functions, leading to serial collapse of other daily functions [37]. And one of the results of disrupted daily functions in adolescents is sleep problems [38]. In adolescents, sleep conditions are directly related to brain development, and shifts in sleep behavior can change the developmental pattern of brain matter, leading to impaired functional outcomes in several domains including learning ability, memory, social adaptation, emotional regulation and motivation [39]. Thus, sleep and diet are sharing a similar role in depression of adolescents, in maintaining daily social rhythms, encouraging brain development, and regulating emotions. Although prior studies posit that the association between depression, diet, and sleep is not universal [40,41], the influence of inappropriate diet and sleep disturbance on depression seems to exist in adolescent patients with TMD, at least in this study.

Tinnitus was highly associated with depression in adolescent TMD patients. The global prevalence of tinnitus is approximately 14%, with a higher incidence observed in older adults compared to younger adults [42]. Especially, prevalence of tinnitus in TMD patients was approximately 30%, which is approximately eight times higher than that in patients without TMD [43]. Continuous somatosensory information of tinnitus in cervical and temporomandibular area is transferred to the brain through the dorsal root ganglion or trigeminal ganglion, which can have the same role as chronic pain of orofacial area and therefore directly result in psychological distress [44]. However, despite the close relationship between tinnitus and psychological disorders, tinnitus and depression in adolescent patients has not been well studied. Since tinnitus in adolescent patients with TMD was related to depression in this study, further studies are needed to investigate the detailed mechanism of the interaction between tinnitus, psychological distress, and TMD in adolescents.

Trauma history had a significant relationship with depression of adolescent TMD patients. A previous study reported that the trauma history of adolescent patients with TMD had a significant relationship with the psychological state of the SCL-90-R, including somatization, obsessive compulsiveness, hostility, phobic anxiety, and psychoticism, regardless of structural disorders [16]. Trauma in adolescents has long been considered crucial because of its influence on long-term quality of life. As in adults, trauma in adolescents can cause both physical and psychological damage; however, the aftereffects of damage tend to last longer in adolescents than in adults and extend to a wider range, including general health, developmental, psychological, and behavioral outcomes [45].

In contrast, pain intensity and pain duration were not significantly related with depression of adolescent TMD patients in this study. It was reported that emotional health of adolescent was highly associated with the total pain area rather than pain intensity [12]. Therefore, it can be inferred that pain duration might affect to depression only when the long-lasted pain caused widespread pain of adolescents. However, the average VAS scores in this study ranged from 2 to 4, which were not significantly high. This could introduce a bias in the patient pool, potentially overlooking correlations that might exist in patients with higher VAS scores. Further studies are needed to explore the correlation between pain duration, total number of pain sites, and depression in adolescent TMD patients across a broader range of pain intensities.

In this study, TMJ OA in panoramic images was not significantly associated with depression of adolescent TMD patients. Generally, depression is common in patient with OA, and patients with TMJ OA are likely to have higher levels of depression than patient with non-painful TMD [46]. The contradictory result of this study might be due to the followings; diagnostic inaccuracy and impacted of details symptoms of OA. This study utilized panoramic radiography to diagnose OA due to its convenience for clinicians, but panoramic radiography was proven to have limited diagnostic accuracy in detecting OA [47]. Also, correlation between OA and depression was due to the accompanying symptoms of OA including pain, functional disability and joint sound [48]. However, asymptomatic OA even with radiological evidence of joint damage is common in adolescents [49]. Since this study didn’t distinguish asymptomatic OA in analysis, its impact on OA, its impact on depression might be less than expected. Thus, evaluating OA and related depression with panoramic images should be open to controversy, and further studies would be needed with improved diagnostic methods and detailed analysis including accompanying symptoms of OA.

Despite the significance of this study, several limitations should be acknowledged. Primarily, it was a retrospective study, and patient data were collected and analyzed only at specific intervals. Consequently, the study design was unable to capture real-time changes in variables or attributing factors of TMD and depression, which may have resulted in fragmented assessments of patient status and correlations. Additionally, some key psychosocial and sociodemographic factors that could influence the observed correlations were not included in the study. Furthermore, the sample was exclusively derived from a single dental clinic, raising concerns about potential biases.

Nevertheless, to our knowledge, no previous studies have comprehensively investigated the correlation between depression and clinical factors in adolescent TMD patients. Further prospective cohort studies with a more diverse sample pool and extended follow-up periods are necessary to validate our findings and delve into the detailed causal relationships.

In conclusion, score of depression was significantly higher in older adolescent TMD patients than younger adolescents in this study. Furthermore, several clinical factors of TMD displayed significant correlations with the depression of adolescent TMD patients. These factors encompassed sex, DI, CMI, tinnitus, self-reported stress, irregular diet, trauma history, clenching habits, and sleep problems. These findings offer valuable insights for clinicians, enabling them to promptly and effectively evaluate depression in adolescents with TMD.

No potential conflict of interest relevant to this article was reported.

The datasets generated and/or analyzed during the current study are available in in the OSF repository (https://osf.io/rxsqz). The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

None.

The authors extend their special thanks to Jung-Pyo Hong of the Department of Orofacial Pain and Oral Medicine at Kyung Hee University Dental Hospital and Sung-Woo Lee of the Department of Oral Medicine and Oral Diagnosis at Seoul National University.

Conceptualization: YHL. Data curation: YHL, TSK. Formal analysis: YHL. Investigation: YHL, TSK. Methodology: YHL, TSK. Project administration: YHL. Resources: YHL, TSK. Software: YHL, TSK. Supervision: YHL. Validation: YHL. Visualization: YHL, TSK. Writing - original draft: YHL, TSK. Writing review & editing: YHL, TSK. All authors contributed to and approved the submitted manuscript.

Supplementary data is available at https://doi.org/10.14476/jomp.2024.49.4.135.