1. Study population
We conducted a cross-sectional survey with 112 patients (74 females [66.1%]; mean age, 35.90±17.60 years) with painful TMD who visited the Department of Orofacial Pain and Oral Medicine of Kyung Hee University Dental Hospital (Seoul, South Korea). They voluntarily participated for management of painful TMD over a 7-month period from March 2021 to October 2021 and included those who were not infected with or had never been infected with COVID-19. All patients were examined by two experts who specialized in orofacial pain and TMD diagnosis based on the DC/TMD Axis I criteria 9.
The exclusion criteria comprised: (1) patients aged <18 years, (2) patients with other systemic muscular disorders (e.g., fibromyalgia, rheumatoid arthritis, inflammatory joint disease), (3) patients with neurologic impairment or diseases (e.g., stroke, tumor, epilepsy), (4) pregnancy, (5) patients with a history of psychiatric disorders, and (6) inability to provide informed consent.
The inclusion criteria were diagnosis of painful TMD according to the DC/TMD Axis I classification, report of pain at the TMJ and/or masticatory muscles for >3 months, and experienced the first TMD signs and symptoms after COVID-19. Patients completed a comprehensive questionnaire that included the DC/TMD and the Oral Behavior Checklist. Patients with painful TMD were divided into three groups as follows: pain of muscle origin (myalgia, n=38), pain of joint origin (arthralgia, n=43), and muscle–joint mixed TMD pain (mixed TMD pain, n=31).
All participants provided written consent for the study, which was approved by the Ethical Committee of Kyung Hee University Dental Hospital (KHD IRB no. KH-DT21023). This study was conducted in accordance with the principles of the Declaration of Helsinki.
2. Clinical data collection
Experienced orofacial pain specialists conducted the comprehensive clinical and radiographic examinations. TMD pain and clinical disease characteristics were assessed using standard, validated, and reliable self-reported questionnaires.
2-1. Characteristics of TMD Pain
The duration of pain derived from the TMJ and/or masticatory muscles was reported in days. TMD pain was scored subjectively by the patients, ranging from 0 (no pain at all) to 10 (worst pain imaginable) using a visual analog scale (VAS).
2-2. Clinical factors
TMJ sounds were recorded as present when a clicking, popping, or crepitus sound was audible in the TMJ on either side. Mouth opening limitation (MOL) was defined as <30 mm gap between the maxillary and mandibular incisal tips, and a complaint of muscle stiffness that can be confirmed clinically. TMJ locking involves locking during mouth opening or closing, and is recorded as present when one cannot open or close their mouth, respectively, at will.
2-3. Contributing factors and comorbidities
We investigated self-reported parafunctional activities using the Oral Behavior Checklist, which includes jaw-related behaviors such as teeth clenching and bruxism 19. Headache was evaluated using the dichotomous question, “Do you have any headaches associated with TMD?” The presence of self-assessed tinnitus, sleep problems, psychological distress, family history, and microtrauma history were also reported with a binary answer. Each variable was recorded as a binary answer (yes/no) for all patients, as described in our previous study 20.
3. Psychological distress
The World Health Organization (WHO) declared the COVID-19 outbreak as a global pandemic on March 11, 2020 21. In this study, three questionnaires were used to examine the psychological aspects of patients with TMD, and they completed the questionnaires at two time points: before the declaration of the COVID-19 pandemic (BC), and the present time after the WHO declaration (AC). At BC, the patient filled out the questionnaire considering their situation at that time.
3-1. Beck Depression Inventory-II (BDI-II)
The 2nd edition of the Beck Depression Inventory-II (BDI-II) consists of 21 items evaluated on a 4-point Likert scale (0-3) to measure the severity of depressive symptoms. The total BDI score is considered key in determining depression severity. Higher total BDI scores and levels indicate more severe depressive symptoms. The standard cut-off scores for each level were: 0–9, minimal depression; 10–18, mild depression; 19–29, moderate depression; 30–63, severe depression 22. Total BDI scores (BDI-BC, BDI-AC) and levels (BDI level-BC, BDI level-AC) were recorded before and after the COVID-19 declaration.
3-2. Beck Anxiety Inventory (BAI)
The Beck Anxiety Inventory (BAI) consists of 21 self-reported items (4-point scale) and is used to assess the intensity of physical and cognitive anxiety symptoms during the past week (score range, 0-63). The standard cut-off scores for each level were: normal, 0–7; mild, 8–15; moderate, 16–25; and severe, 26–63. Among the most widely used anxiety measures, the validity and reliability of the BAI have been verified 23. Higher total BAI scores and levels indicate more severe anxiety symptoms. The BAI total scores (BAI-BC, BAI-AC) and levels (BAI level-BC, BAI level-AC) were recorded.
3-3. The Global Assessment of Recent Stress (GARS) scale
The Global Assessment of Recent Stress (GARS) scale evaluates the stress perception over the past 6-24 months based on recent life changes 24. It is based on eight sub-items on work/school-life, interpersonal relationships, relationship changes, illness and injury, economic problems, non-routine events, changes in daily life, and overall stress level. Stress was evaluated on a scale of 0-9 for each of the eight sub-items (0-72), with higher scores indicating higher stress 25. The GARS total scores (GARS-BC, GARS-AC) were recorded and analyzed.
4. Statistical Analysis
The data were analyzed using SPSS Statistics for Windows, Version 26.0, (IBM Corp., Armonk, NY, USA). Continuous variables are presented as means and standard deviations (SD), and categorical variables are presented as frequencies and percentages. The inter-rater reliability between the two experts in the diagnosis of painful TMD was assessed using Cohen’s kappa coefficient and was 0.92 for myalgia, 0.95 for arthralgia, and 0.92 for mixed TMD pain groups. In case of a discrepancy in the diagnosis between the two experts, the patient was assigned to a TMD group following an in-depth discussion.
A paired t-test was performed to compare the scores for depression (BDI), anxiety (BAI), and generalized stress (GARS), and VAS scores at BC and AC. The mean difference between the TMD groups and comparison of the mean values of the continuous variables in the three TMD groups separated by TMD pain source was analyzed using analysis of variance (ANOVA) with Tukey’s post hoc test. For categorical variables, the chi-square test and Fisher’s exact test with Bonferroni adjusted post hoc analysis were used to determine the equality of proportions. Spearman’s correlation analysis was used to determine the correlations between BDI-AC, total scores of the psychological questionnaire, and TMD pain severity. Spearman’s correlation coefficients (r) ranged from −1 to +1, with −1 indicating a perfectly linear negative correlation and +1 indicating a perfectly linear positive correlation. Generalized linear models were used to identify factors significantly correlated with the BDI-AC total score. The estimated β for BDI-AC was calculated using multiple linear regression analyses after adjusting for BDI-BC. Subsequently, logistic regression analyses were performed to identify significant predictors that increased BDI level-AC in patients with painful TMD. The odds ratio for BDI level-AC was calculated using multiple logistic regression analysis after adjusting for BDI-BC. For all analyses, a two-tailed p-value <0.05 was considered statistically significant.