Temporal changes and gender differences related to orofacial symptoms in two cohorts of 75‐year‐old Swedish subjects examined in 2007 and 2017: A repeated cross‐sectional study

Abstract Objectives To compare two cohorts of 75‐year‐old persons, born 10 years apart, in regard to reported symptoms related to temporomandibular disorders (TMD) and orofacial complaints with special reference to gender differences. Material and Methods In 2007, a questionnaire comprising questions on social factors, general and oral health, and a series of attitude‐related questions was mailed to all individuals born in 1932 living in two Swedish counties (N = 5195), and in 2017 to all born in 1942 (N = 7204). The response rate for the cohort examined in 2007 was 71.9% (n = 3735) and 70.7% (n = 5091) for the cohort examined in 2017. Bivariate statistical analyses were applied. Results Reported bruxism and pain from the temporomandibular joint were significantly higher in the 1942 cohort compared to the 1932 cohort, while reports of oral lesions and daytime dry mouth were lower. Women reported problems significantly more frequently in most of the domains investigated in both 2007 and 2017, that is, TMD, burning mouth, sensitive teeth, oral lesions, taste changes, daytime/night‐time dry mouth, except bad breath. Conclusions TMD‐related symptoms increased while complaints from oral lesions and daytime mouth dryness decreased between 2007 and 2017. Temporal changes were otherwise few, but the findings underline the gender inequalities that exist, to the disadvantage of women. This must be considered when planning for clinical care/dental education to appropriately address the needs of older people.

gradually decreases with age but it is unclear how TMD affects older adults (Yadav et al., 2018). This notwithstanding, the question of how TMD prevalence is related to aging is not so clear and the oftenstated view that it decreases with age has been questioned (Carlsson et al., 2014).
Frequencies of orofacial symptoms in the elderly, and differences between genders, show few definitive conclusions. As regards the prevalence of burning mouth, a wide range from about 1% to~20% (using varied diagnostic criteria) has been reported (Kohorst et al., 2015). In another study comparing middle-aged and older patients with TMD and burning mouth, reported pain intensities were significantly higher in the older burning mouth group (65−84 years) while higher somatization and depression scores were found in the younger group (45−64 years). No such differences between the old and young groups were found among TMD patients but there was a significantly higher ratio of women in both the TMD and burning mouth patients (Honda et al., 2015). Overall, these findings confirm that burning mouth may constitute a significant problem among older patients and especially in women.
Life expectancy is increasing rapidly, while in parallel, the older population is generally healthier and they also increasingly retain their natural teeth into old age compared to their predecessor cohorts (A. K. Johansson, Omar et al., 2020). These developments are changing the nature of the demand for and utilization of dental services worldwide. Given these dynamics, it is important to document the contemporary oral health status among the elderly in order to obtain knowledge of possible trends for the benefit of both patients and dental professionals.
The objective of this study was to compare two cohorts of 75-year-olds examined in 2007 and 2017 with respect to reported TMD and orofacial symptoms, and with special reference to temporal changes and gender differences. The first hypothesis was that there are no differences between the two 75-year-old cohorts born 10 years apart and the second hypothesis was that women are generally more affected by oral health-related problems than men.

| MATERIALS AND METHODS
In 2007 and 2017, a questionnaire was sent to all 75-year-olds (born 1932 and 1942, respectively) residing in Örebro and Östergötland counties in Sweden. The response rates in 2007 and in 2017 were 71.9% (n = 3735; N total = 5195) and 70.7% (n = 5091; N total = 7204), respectively.

| Questionnaire
The questionnaire comprised 56 questions in 2007 and 55 questions in 2017. Three questions about occupation that were included in 2007 were removed in the 2017 survey and substituted with two questions, one on type of residency and one on the ability to take themselves to the dentist. The questionnaire has been previously described and its methodological aspects discussed (Unell, 1999;Unell et al., 1997). In an early study in this series of investigations using the same methods and questionnaire, clinical examination was performed in 941 randomly selected subjects of the total sample in order to validate and quantify the responses regarding the reported number of remaining teeth and jaw opening capacity (Unell et al., 1997). There was good congruence between self-reports and clinical registrations. Other oral conditions have not been validated. The questionnaire was split into six different categories which were related to: (i) social (viz. place of birth, marital status, education, residency), (ii) general health (e.g., physician visits, tobacco habits, medications), (iii) oral status (e.g., satisfaction with teeth, oral problems, oral hygiene habits, number of teeth), (iv) a series of attitude-related questions (viz. oral function and appearance of teeth), and (v) experience and use of dental care services. A total of three mailing rounds of the questionnaire were performed. The first comprised information about the study, the questionnaire, and a prepaid reply envelope. The second was a reminder letter only and the third contained again a reminder, the questionnaire, and a prepaid reply envelope. In this paper, we focus on reported TMD and orofacial symptoms while other domains from the questionnaire have previously been reported (A. K. Johansson, Omar et al., 2020. Computer. χ 2 tests were used to analyze differences between the 2007 and 2017 cohorts as well as between men and women. The significance level was set at p < .05.

| Ethical considerations
The Ethics Committee in Uppsala, Sweden, approved the study (Dnr 2016/424). Informed consent was obtained from all the participants.
There were no significant differences between 2007 and 2017 as regards reported TMJ sounds and mouth opening difficulties in the total samples. There were, however, gender differences regarding TMJ sounds in the 2017 cohort, and in both cohorts regarding opening difficulties with women reporting significantly more problems (Table 1). It should be noted that "a fair amount" or "excessive problems" constituted only a few percent in all four domains related to TMD.

| Orofacial symptoms
For the total samples in both cohorts only "oral lesions" and "do you have dry mouth during the daytime?" showed significant changes over the examination time points, the former showing a decrease from 2007 (15.4%) to 2017 (12.2%) (p < .001) and similarly so for the latter (37.5% vs. 34.8%) (p < .05). Also, women reported problems significantly more frequently in both 2007 and 2017 for "burning mouth," "oral lesions," "sensitive teeth," and dry mouth during daytime and nighttime (Table 2). Regarding "Change of taste," women had significantly more difficulties than men in 2017 but not in 2007, and "bad breath" was significantly more common among men in both 2007 and 2017.
"A fair amount" or "excessive problems" were relatively infrequently reported in most of the domains related to orofacial symptoms, except

| DISCUSSION
In general terms, there have been declines in survey response rates over the past decades (Czajka & Beyler, 2016  Temporal changes between 2007 and 2017 in TMD and orofacial symptoms were relatively uncommon in the two cohorts. In another study, two cohorts of 70-year-old subjects were examined 8 years apart, and no significant difference between the two cohorts for prevalence of TMD symptoms was found (Österberg & Carlsson, 2007).
In a previous report on the present samples, the 2017 cohorts reported much better general and oral health, the latter parameter is expressed as a significant improvement in chewing function, a stronger belief that they could keep their teeth throughout the whole of their lives, a substantially higher frequency of a full or almost full dentition, and a marked reduction in edentulousness and denture wearing (A. K. Johansson, Omar et al., 2020). In line with this, it might be expected that the same trend would be seen in relation to TMD. This was however not the case, with TMD-related problems in fact increasing.
This can be seen as support for the recent trend to emphasize psychological and behavioral factors as being more important than occlusal disturbances in the etiology of TMD.
Reported oral lesions and daytime dry mouth decreased, while the other examined symptoms showed no significant differences. The conclusion may thus be drawn that despite the global improvement in oral health among the elderly, there will still be a number of oral problems that need to be taken care of by the dental profession in the future aging population.
Not unexpectedly, women reported a significantly more frequent occurrence of TMD-related problems than men in both 2007 and 2017 (except for TMJ sounds in 2007), which is in line with a systematic report on gender differences for TMD-related problems (Bueno et al., 2018). On the other hand, and not so expectedly, approximately one-third more (36%) of the women reported TMJ pain in 2017 compared to 2007 (representing an increase from 10.0% to 13.6%) whereas for men it remained at about the same level (7.0% vs. 7.2%). As regards self-reported bruxism, both women and men showed substantial increases between the two same-aged cohorts, with bruxism increasing in women from 14.5% to 18.1% and in men from 11.0% to 15.1%. This corresponds to a 25% for women and a 37% increase for men of self-reported bruxism in 2017 compared to 2007. An increase in the prevalence of bruxism over time has also been shown in another study, (Egermark et al., 2001) and it has been suggested that this is related to the increased chronic stress in modern society (Wieckiewicz et al., 2014). It has however to be noted that self-reported bruxism maybe is connected to bias and a definite diagnosis should also incorporate a clinical inspection in addition to polysomnography for sleep bruxism and electromyography for awake bruxism (Lobbezoo et al., 2018).
In a similarly-designed study to the present one, of two cohorts of 50-year-olds examined 10 years apart in 1992 and 2002, there was a significantly higher prevalence of TMD-related symptoms as well as impairments of other self-reported health parameters in those born 10 years later (Unell et al., 2006). A recent systematic review had similar findings, with the authors referring to a changing epidemiology of TMD and the inference drawn that TMD prevalence was on the rise (Ryan et al., 2019). Our findings would suggest that this seems also to be the case for elderly Swedish women, but not for men.
Symptoms of burning mouth were reported almost twice as common in women compared to men in both 2007 and 2017 (~10% vs.~5%). In another study and with stricter criteria applied, 0.17% of women were affected compared to only 0.04% of men among all age groups, although the highest prevalence was found in women aged 70−79 years, and to a lesser extent also in men of the same age group (Kohorst et al., 2015). In line with these results, the present findings confirm that burning mouth may constitute a significant problem among older patients and especially in women.
Reported oral lesions showed a decrease from 2007 (15.4%) to 2017 (12.2%). Taste changes were reported to be just under 10% in both cohorts, with women having significantly more of this condition in 2017. These findings show that these conditions are common in the elderly and, again, that women are more affected.
Bad breath was a commonly reported finding in both 2007 (19.3%) and 2017 (17.8%). A gender difference was also reported in the present study where men reported significantly more problems with bad breath than women, although to a lesser degree than in a Brazilian report (Nadanovsky et al., 2007). Nevertheless, bad breath is a significant problem in all age groups and continues to be so even among the elderly.  (Blaizot et al., 2020). Thus, there was a wide range of tooth sensitivity prevalence which may have depended on diagnostic criteria applied, although there was a significant association between tooth sensitivity and female gender.
The prevalence of dry mouth was high both in the daytime (>30%) and night-time (>50%), and with a striking gender difference. Mouth dryness was about 10% more common in women than in men both at night-time and daytime and in both the 2007 and 2017 cohorts. The prevalence of reported dry mouth steadily increases from age 50 years (A. K. . Although report of dry mouth is not necessarily a symptom of hyposalivation, a recent systematic review and meta-analysis found a prevalence of over 30% in people aged over 60 years (Pina et al., 2020). A previous study emphasized the difference in the prevalence of daytime and night-time dry mouth and suggested that "that day and night-time xerostomia may be different conditions or at any rate have a somewhat different background" (A. K. Johansson et al., 2012). In this regard, salivary flow is lower at night which could be a part of the explanation for this finding (Dawes, 1972).
The commonness of dry mouth and its overrepresentation in women further underlines the role that gender might play when assessing oral health in elderly people.
Two limitations with regard to the self-administered question-