Cross-sectional associations between effort-reward imbalance at work and oral diseases in Japan

Introduction

Oral diseases are one of the global public health problems (Watt et al., 2019). The risk of developing oral diseases, such as dental caries and periodontal diseases, remains high throughout life, with no decrease observed in the incidence of dental caries at any age (Whelton, 2004; Hall-Scullin et al., 2017). The incidence of periodontal diseases rapidly increases in the mid-to-late 30s, after which it decreases due to tooth loss, but the prevalence remains high (Kassebaum et al., 2014). Dental caries frequently causes severe pain which can negatively affect work performance (Sheiham & Croog, 1981; Reisine, 1988). Periodontal diseases and dental caries can cause tooth loss (Pitts et al., 2017; Kinane, Stathopoulou & Papapanou, 2017), in turn, affecting eating, sleeping, and communication (Sheiham & Croog, 1981; Reisine, 1988). Oral diseases potentially produced a $187.61 billion productivity loss in 2015 (Righolt et al., 2018). The economic burden of oral diseases seems to worsen (Kassebaum et al., 2017). Preventing oral diseases is essential.

Psychological stress is a potential risk factor for oral diseases. It can result in immune system dysfunction, increased stress hormones, cariogenic bacterial counts, and poor oral health behaviours, which exacerbate oral conditions (Gomaa et al., 2016; Sabbah, Gomaa & Gireesh, 2018). Work stress, which is common in industrialised countries such as Japan, has become more prevalent in the workplace and can negatively impact workers’ health (Siegrist, 2016). The effort-reward imbalance model is a widely accepted model for the assessment of work stress (Siegrist, 1996; Montano, Li & Siegrist, 2016). It focuses on the failure in reciprocity in terms of high efforts spent and low rewards received. The model predicts increased risks for depression (Rugulies, Aust & Madsen, 2017), hypertension (Gilbert-Ouimet et al., 2014), coronary heart disease (Li et al., 2015), and type 2 diabetes (Kumari, Head & Marmot, 2004) when effort-reward imbalance is high. Thus, psychological stress at work might also deteriorate oral health.

Our previous systematic review revealed a lack of evidence on the association of work stress with oral diseases (Sato, Saijo & Yoshioka, 2021). Notably, most previous studies did not use the widely accepted measures for work stress assessment and did not include potential confounders, such as socioeconomic status and work-related variables (Freeman & Goss, 1993; Linden, Mullally & Freeman, 1996; Genco et al., 1999; Hayashi et al., 2001; Akhter et al., 2005; Bandar, 2009; Ramji, 2011; Mahendra et al., 2011; Islam et al., 2019). In this cross-sectional study, we aimed to examine the associations of work stress, according to the effort-reward imbalance model, with dental caries, periodontal status, and tooth loss, taking potential confounders into consideration.

Methods

Results

The first source population included 184 regular employees of a medical university and the second source population included 435 regular employees enrolled from among the registrants of an online research company. Table 1 shows the characteristics, including the effort-reward imbalance ratio and dental status of the participants. The mean ERI ratios (with standard deviations) of the first source population and the second source population were 1.08 (0.34) and 1.14 (0.52), respectively. The median number of DMFT (with 1st and 3rd quantiles) of the first and second source populations were 6 (3, 11) and 8 (4, 12), respectively. The median numbers of DT, FT, and MT (with 1st and 3rd quantiles) of the first and second source populations were 0 (0, 0) and 0 (0, 0), 3 (0.75, 7) and 7 (3, 11), and 7 (3, 11) and 0 (0, 0), respectively. The percentages of patients with poor periodontal status among the first and the second source populations were 0.5% and 6.7%, respectively. In both source populations, more than 70% of the participants had university degrees or higher. In the first source population, over 70% were professional or engineering workers. The second source population mainly included administrative and managerial, professional and engineering, and clerical workers.

Table 2 shows the association of the effort-reward imbalance ratio with the DMFT. In the first and second source population, a one-unit increase in the ERI ratio was associated with −2.81 (95% CI [−4.70 to −0.92]; p-value = 0.004) and −0.84 (95% CI [−1.80 to 0.12]; p-value = 0.085) changes in the DMFT from a fully adjusted linear regression model, respectively. Table 3 shows that a one-unit increase in the ERI ratio was associated with a 1.55 (95% CI [1.04–2.32]; p-value = 0.032) risk of poor periodontal status in the second source population.

Discussion

This study reports the cross-sectional associations of work stress, according to the ERI, with dental caries, poor periodontal status, and tooth loss. ERI was associated with a low number of dental caries and tooth loss, and an increased prevalence of poor periodontal status.

The current results show a negative association between work stress and the number of decayed and filled teeth (caries experienced teeth). There is only one previous study on work stress and the number of teeth with caries (Segura Marcenes & Sheiham, 1992; Sato, Saijo & Yoshioka, 2021). In a previous study, work stress was assessed using the demand-control model, and the dependent variable was DMF tooth surfaces. One unit increases in work mental demand and work control score were associated with 0.19 (95% CI [−0.91 to 1.29]) and 0.87 (95% CI [0.18–1.91]) increases in DMF teeth surfaces. This inconsistency might be due to the DMFT and DMF teeth surfaces which included caries experiences that occurred before exposure to work stress. For a more accurate understanding of the association between work stress and dental caries, the incidence of dental caries should be measured.

In the present study, work stress was negatively associated with tooth loss. There were two previous cross-sectional studies in which the dependent variables were self-reported tooth loss and having four or more lost teeth (Hayashi et al., 2001; Sato et al., 2020; Sato, Saijo & Yoshioka, 2021). Two studies have reported an increased risk of tooth loss due to work stress. Our results are inconsistent with those of the two previous studies. In this study, the number of tooth losses were few. Furthermore, as with dental caries, this inconsistency might be due to the characteristic of the dependent variable, missing teeth, which included tooth loss that occurred before exposure to work stress. Owing to these limitations, it is difficult to derive conclusions from the current results. The incidence of tooth loss should be used as an outcome in future research.

Work stress was associated with an increased risk of poor periodontal status, which is consistent with previous studies (Sato, Saijo & Yoshioka, 2021). Eight of nine previous studies reported a significant association between work stress and periodontal status, but only one study used the accepted measure for work stress and adjusted for potential confounders (Segura Marcenes & Sheiham, 1992; Sato, Saijo & Yoshioka, 2021). Our results support the previous study results.

Work stress was associated with a risk of poor periodontal status and not with dental caries and tooth loss. According to previous reviews (Tikhonova et al., 2018; Castro et al., 2020), periodontal diseases seem to be more sensitive to psychological stress than dental caries. Work stress brings about uncontrolled metabolism and impaired immune system, which can exacerbate periodontal diseases (Kinane, Stathopoulou & Papapanou, 2017). Besides, the definition of periodontal diseases is based on current inflammation activities in the supporting structures of the teeth (Chapple et al., 2018). The above features might facilitate the observation of the cross-sectional association between work stress and poor periodontal status than dental caries and tooth loss.

This study has two strengths. First, work stress was assessed using a widely accepted measure. Previous studies on work stress and oral diseases have often used nonspecific questionnaires (Sato, Saijo & Yoshioka, 2021). This study captured work stress more accurately than previous studies. Second, this study included potential confounders, such as socioeconomic status and work-related variables. Our review revealed only two studies among the 11 studies included in the systematic review considered the potential confounders sufficiently (Sato, Saijo & Yoshioka, 2021). Our study is superior to previous studies in terms of these two points. However, our study had three limitations. First, periodontal status was assessed using a self-reported questionnaire which potentially has a self-reported bias (Yamamoto et al., 2009; Beltrán-Aguilar et al., 2012). This questionnaire was not validated among young or female workers (Yamamoto et al., 2009). Furthermore, the cut-off point of this questionnaire was defined based on 7 mm or more of the clinical attachment loss, which differs from the 2018 periodontitis case definition by the European Federation of Periodontology and American Association of Periodontology with Centers for Disease Control (Botelho et al., 2020). This limitation can produce a bias. In addition, the participants with work stress may have had exaggerated responses to questions on periodontitis screening. When interpreting the periodontal status results, these limitations should be considered. In the second source population survey, DMFT was estimated using intraoral photographs with mobile phones. Molars had a relatively higher percentage of undiagnosable status than incisors and premolars, and some DT and FT were missed. Therefore, DMFT could have been underestimated in the second source population. This unvalidated method can bring about a bias. However, the results in the second source population were consistent with those in the first source population, for which DMFT was assessed on the clinical examination. Second, in the two-source population, many participants had a high socioeconomic status. More than 70% of participants had university degrees or higher. The social gradients of oral diseases have been reported (Borrell & Crawford, 2012; Schwendicke et al., 2015). Additionally, blue-collar workers were also small in number. Participants in the two-source population had better oral conditions than those in the national survey (Ministry of Health, Labour & Welfare, 2016). The results of people with low socioeconomic status and blue-collar workers might have been underestimated in this study. In addition, in the first source population, 358 participants were dropped out because they did not attend the dental examination. This loss of participants can produce a bias; however, the basic characteristics of included participants were almost similar to those of dropped out participants (Table S2). Finally, this study was cross-sectional; therefore, a temporal association was not established. Further cohort studies are required.

Conclusions

Effort-reward imbalance at work was associated with a low number of dental caries and tooth loss, and an increased prevalence of poor periodontal status. One feature of oral diseases is causing mostly irreversible destruction of teeth and periodontal tissue. Therefore, previous studies highlight the importance of preventive care for oral diseases (Watt et al., 2019). To prevent oral diseases, occupational specialists should recognise that work stress is associated not only with mental health, cardiovascular disease, and metabolic disease, but also with periodontal status. Furthermore, support from supervisors might attenuate the negative impact of ERI on tooth loss (Sato et al., 2020). Building a supportive work environment might be also a preventive factor for oral diseases in workplaces. Moreover, periodontal diseases potentially bring about presenteeism among workers (Yoshiono et al., 2017; Zaitsu et al., 2020; Sato et al., 2022). The importance of periodontal health in the workplace should be noted. For dental caries and tooth loss, a future cohort study including the incidence of oral diseases is needed to describe the association of work stress more accurately.

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