The influence of the COVID-19 pandemic, sex, and age on temporomandibular disorders subtypes in East Asian patients: a retrospective observational study

The frequencies of arthralgia (range 13.0–58.0%), myalgia (range 1.9–50.6%), disc displacements with (range 20.0-44.2%) and without (range 0-12.8%) reduction, as well as degenerative joint disease (range 0-55.6%) were found to vary considerably among TMD patient populations [5]. Apart from disc displacement without reduction (range 33.6–38.2%), the prevalence of TMD subtypes/discrete conditions in East Asian patients were within the documented ranges, both before and during the pandemic. In addition to racial variations, the higher frequency of disc displacements without reduction in this study could be contributed partly by the use of supplementary MRIs for verifying this diagnosis. When compared to MRI, clinical protocols have poor-to-moderate validity for diagnosing disc displacements with and without reduction [28]. Patients who sought care during the pandemic had significantly more PT and IT conditions with higher prevalences of myalgia, headache, and degenerative joint disease than those who presented before the pandemic. As most patients experienced chronic TMDs, the higher frequencies of the aforementioned conditions might be the consequence of intensified TMD pain and/or dysfunction or heightened concerns over TMD problems during the pandemic. Findings were consistent with the elevated levels of psychological distress, oral parafunction, and TMD symptoms reported during the COVID-19 pandemic [18, 19, 23]. Psychological distress was posited to trigger a cascade of events culminating in increased sympathetic activity and release of adreno-corticoid hormones leading to muscle vasoconstriction and amplified stress responses [15]. This coupled with increased awake and/or sleep bruxism during the pandemic could result in sustained masticatory muscle contractions and exacerbation of TMD-related myalgia and headache [15, 18, 19].

Women constituted about three-quarters of all TMD patients in this study. Findings were congruent with the greater risk of women developing TMDs and female-to-male ratios (3.3) reported for other TMD populations [2, 24]. When patients were pooled, 7.76% (65/838), 32.46% (272/838), and 34.49% (289/838) with PT, IT, and CT were females. In contrast, 5.72% (48/838), 10.86% (91/838), and 8.71% (73/838) of all patients with PT, IT, and CT were males. The female predominance has been explained by gender differences in biology (especially sex hormones), social roles, psychological distress, somatization, pain experience, and treatment-seeking behaviors [24]. Though no significant difference was discerned before the pandemic, female patients had significantly more TMD conditions (particularly IT conditions) than male patients during the pandemic. This can be attributed in part to women being more distressed by the pandemic than men, and the accompanying increase in oral parafunctional activities [23]. The larger number of IT conditions also explains the significantly greater occurrence of IT and CT conditions in women. The proportion of male patients with PT was greater than female patients suggesting that TMD pain was the primary reason for treatment-seeking in East Asian men.

Adolescents/young adults formed the majority of TMD patients that had a mean age of 32.1 years. Findings corroborated the age distribution in other East Asian studies and the mean age range (30.2–39.4 years) of TMD patient populations [5, 26, 29]. Both before and during the pandemic, MO patients had substantially more TMD conditions (particularly PT conditions), which also clarifies their significantly greater prevalence of PT and CT, than AY patients. Contrariwise, AY patients had a significantly greater prevalence of IT during the two attendance periods. Findings specify that older and younger patients may be predisposed to TMD pain and dysfunction correspondingly. The underlying mechanism for this phenomenon is unknown and may be the product of experiences and physical changes related to age, especially in females [30, 31]. Population-based studies have also shown a twofold greater prevalence of pain in older adults when compared to younger ones [32]. Even though sex and age appeared to have independent effects on the number of TMD conditions and frequency of TMD subtypes both before and during the pandemic, the two variables could be interlinked and confounding effects may exist. Multivariate analyses were thus performed to adjust for confounders and to explore possible interaction effects between sex and age.

While PT and CT were found to be related to sex and age, IT was associated with the pandemic and age in the univariate analysis. After controlling for confounding effects in the multivariate modeling, the odds of PT increased 2.5 folds by being female. Being older increased the odds of PT by 4% and CT by 2%, but reduced the odds of IT by 5%. An interaction effect between sex and age was observed, in which being older and female increased the odds of CT by 2%. Collectively, the results showed that the COVID-19 pandemic, as an impact event, did not consistently influence the prospect of TMD pain and/or dysfunction. Instead, sex and age appeared to play more crucial roles in the development of PT and IT/CT respectively.

Women are known to have more numerous, frequent, and intense somatic symptoms including bodily pains than men. The difference is present in both patient and community-based samples, even with the exclusion of gynecologic or medically unexplained symptoms [24, 33]. Furthermore, they have been reported to have lower pain thresholds/tolerance and a greater ability to discriminate pain which explains partly the markedly greater odds of painful TMDs among female patients [34]. Older females also had marginally greater odds of CT and this was compatible with hormonal changes in women during menopause that is associated with TMJ degeneration and osteoarthritis [31]. Adolescents/young adults had slightly greater odds of IT which was constant with the high prevalence of intra-articular disorders among young people [35, 36]. Purported risk factors for this age group included the female gender, increasing age, awake bruxism, and lip/cheek biting [36].

The present observational study had several limitations. First, the research only involved East Asian TMD patients and findings cannot be extrapolated to other racial/ethnic groups. The study needs to be repeated in Western and other TMD patient populations before absolute inferences can be made. Second, TMD patients who sought care before and during the pandemic may not be completely identical, ensuing in possible sampling bias. Although this was mitigated by comparable sex and age distributions of the BC and DC groups, variances in psychological distress and other confounding variables may be present but were not investigated. Lastly, even as sex and age were found to affect the prospect of PT and IT/CT, the ,“biopsychosocial” processes involved remain undetermined and warrant further explorations.