Scientific Papers

DC/TMD axis I subtyping: generational and gender variations among East Asian TMD patients | BMC Oral Health

This study is the first to explore the generational and gender differences in DC/TMD axis I subtypes and serves as a resource for similar work in other cultures. As the prevalence of TMD subtypes differed between the three generations and gender variances in the number/frequency of TMD conditions/categories were generation-dependent, the first and third hypotheses were endorsed. The second hypothesis was only partly supported as women had more TMD conditions but were similarly susceptible to painful TMDs when compared to men. The global adoption and systematic translation of the DC/TMD and its antecedent, the Research Diagnostic Criteria for TMDs (RDC/TMD), have facilitated data coalition and comparison across countries. Manfredini et al., in their meta-analysis of 3,463 TMD patients, specified a female-to-male (F:M) ratio of 3.3 and overall prevalences of 45.3% for myalgia, 41.1% for disc displacements, and 30.1% for TMJ arthralgia/degenerative joint disease based on the RDC/TMD [8]. Though the F:M ratio of East Asian TMD patients (3.1) was comparable, dissimilarities in the frequencies of myalgia (31.2%), disc displacements (76.8%), and TMJ arthralgia/degenerative joint disease (45.7%/37.5%) were discerned. Apart from racial differences, the inconsistencies could also reflect variations in eligibility criteria, TMD definitions/groupings, and methodology employed. Gen X, Y, and Z formed 85.5% of all “first-visit” TMD patients with the “millennials” comprising the majority of eligible patients. The latter was not surprising as Gen Y constituted the largest proportion of the workforce and were found to have poorer health, more chronic conditions, and moderate-to-severe psychological distress (which are associated with TMDs) than their preceding generation [5,6,7, 24, 40]. Furthermore, “millennials” also experience higher levels of negative emotions, worry, and rumination than older generations when exposed to significant “life events” such as the Covid-19 pandemic [41]. The three most common TMD subtypes encountered in Gen Y were all joint-related (TMJ disorders), namely disc displacements (76.0%), arthralgia (45.4%), and degenerative joint disease (36.9%).

Generational difference in TMD subtypes/categories

The “birth cohort” comparison approach employed offered a unique framework for examining generational differences in illness expression, health beliefs, help-seeking behaviors, and treatment decision-making as individuals from each cohort were reckoned to have similar characteristics [42]. Generational variations in the type, number, and duration of TMD conditions were detected. Gen X and Y reported substantially longer durations of TMD illness (mean of 26.0 to 32.9 months) at their initial visit when contrasted to Gen Z (mean of 12.9 months), suggesting delayed or deferred help-seeking behaviors. This might be attributed to the self-reliant/cynical nature of Gen X and the optimistic/tolerant disposition of Gen Y [22, 23]. While Gen X and Y presented substantially higher prevalence and number of pain-related conditions than Gen Z (Gen X ≥ Y > Z), the converse was true of disc displacements and the number of intra-articular conditions (Gen Z > Y ≥ X). Although findings can be explained by purported age-related experiential changes such as workplace stressors, generational differences in general/mental health, emotional responses, pain beliefs, and attitudes may also play a part [14, 40, 41, 43, 44]. Younger generations were found to agree more with current pain neuroscience and accepted pain as “normal and part of the survival mechanism” and that its presence does not indicate “something wrong with one’s tissues” [44]. Gen Z, being digital natives, are known to process the latest information faster than any other generations. While TMD pain is the usual reason for TMD treatment-seeking, Gen Z patients sought help mostly for TMD dysfunction (mainly disc displacements) and had lower occurrences of arthralgia, myalgia, and headache than Gen Y and X [1]. Considerable differences in the number of pain-related conditions and frequency of painful TMDs were also observed (Gen X > Y > Z). Findings corroborated those of other clinical investigations alluding to an increase in pain prevalence with advancing age. However, the results of experimental investigations were ambivalent with studies indicating both increased and decreased pain thresholds with age [45].

Gender difference in TMD subtypes/categories

Three-quarters of the eligible TMD patients were women and they had a significantly greater total number of TMD conditions than men. Findings were consistent with the higher risk of TMDs in women which was attributed to gender disparities in biology, psychological distress, social functioning, pain threshold/tolerance, and help-seeking behaviors [12, 13, 46]. Though it has been reported that women have more severe and frequent pain than men, no significant differences in the prevalence and number of pain-related TMD conditions were noted between genders [46]. This phenomenon could be rationalized by the help-seeking behaviors of male East-Asian TMD patients who appear to be pursuing professional treatment largely for painful TMDs [47]. Despite a similar frequency of disc displacements, women had a 1.4 folds greater prevalence of TMJ degenerative joint disease than men. Fluctuating levels of female sex hormones during puberty, pregnancy, and menopause had been implicated in both TMD pain and TMJ degeneration [12, 13]. However, the underlying mechanisms remain unclear with estrogen playing a possible destructive role in the condylar cartilage but a protective one in the subchondral bone [48]. This could also clarify the high frequencies of TMJ disorders among Gen Y patients who are mostly women.

Generation and gender interaction

Gender variations in the number of pain-related and total TMD conditions changed depending on generation. Likewise, generational variations in the number of intra-articular, total TMD conditions, and TMD duration were detected between women and men. Additionally, significant gender variations in the prevalences of painful and non-painful TMDs were only observed for Gen X. Therefore, an interaction effect where gender may have a different consequence on TMD outcomes depending on generation and contrariwise might be present. The joint or synergistic effect could be significantly greater or lesser than generation or gender acting in isolation and necessitates examination in the multivariate regression model. Univariate analysis indicated that painful and non-painful TMDs were related to generation and TMD illness duration but not gender. After controlling for generation-gender interaction effects in the multivariate model, the risk of painful TMDs was doubled whereas that of non-painful TMDs was halved by being Gen X and female. Though illness duration was significantly associated with painful and non-painful TMDs, ORs were equal to 1 indicating weak or no affiliations. This could be qualified by the high precision (narrow 95% CI) and large sample size achieved with this study [49]. With large sample sizes, the distribution function of the OR tends to converge to a normal distribution centered on the estimated effect. Given the preponderance of women among TMD patients, the greater prospect of Gen X experiencing TMD pain, and younger generations having TMD dysfunction, generational-gender diversities must be considered when formulating TMD care and healthcare policies as well as directing future TMD research. The latter could entail generational-gender effects on patient beliefs, treatment-seeking behaviors, expectations, and decision-making concerning TMDs. Public health initiatives focusing on the mind-body wellness of younger generations, particularly the “millennials”, should also be introduced because of the increased psychological distress and somatic symptoms including TMDs encountered [25, 26]. While conservative management of TMDs typically includes a combination of patient education/self-management, psychological, pharmacological, physical, and occlusal appliance therapy, interventions for central sensitization syndromes such as antidepressants, cognitive behavior, and mindfulness therapy, could also be beneficial for TMDs, owing to the mind-body connections [50, 51].

Study limitations

Generational health research is still in its infancy and this study has its limitations.

First, a cross-sectional design instead of a longitudinal one was applied. While this study yielded valuable information, greater generational insights could be attained by the prospective evaluation of the different generations at the same age (for example generation X, Y, and Z at 25 years of age). However, this research would require about 30 to 40 years to be actualized as each generation spans over 12 to 15 years. Second, only East Asian TMD patients were examined. As some racial and cultural distinctions are foreseen, this study must be repeated in Western and other Asian countries to confirm the present findings. The study could also be extended to other birth cohorts such as “generation alpha” and the “baby boomers”, despite their relatively small numbers, with consideration of explicit physical and psychosocial changes in these generations. Third, the stratification of birth cohorts was based on the American standard and may not be completely applicable to East Asian populations due to variances in political, societal, economic, or technological developments. Nevertheless, the findings serve as an initial step in the study of generational diversity in TMDs. Lastly, just generational-gender variances in physical TMD subtypes were delved into. Follow-up work could incorporate psychosocial and behavioral assessments of the different birth cohorts.

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