Association between overtime work hours and preventive dental visits among Japanese workers

Periodontitis and caries are the most common causes of permanent tooth loss [1‐4]. Permanent tooth loss is associated with a reduction in intraoral function, and an increased risk for depression and cognitive decline [5, 6]. In addition, periodontitis has been identified as a risk factor for systemic diseases such as diabetes and coronary heart disease [7‐9].

Previous studies reported that overtime work increased the risk for developing diseases such as coronary heart disease, stroke, diabetes, and mental health disorders [9‐13]. Recently, overtime work has been identified as a risk factor for increased morbidity of dental diseases, such as caries and periodontitis [4, 9]. A survey of medical doctor trainees showed 71.4% had delayed or missed preventive dental examinations, with the main reason being lack of time because of work commitments [14].

Preventive dental visits to maintain good oral condition (e.g., check-ups, professional teeth cleaning, and oral hygiene advice) has beneficial effects for oral health, and poor oral hygiene is a major risk factor for periodontitis and caries. Professional teeth cleaning combined with oral hygiene advice results in a reduction in plaque and gingival bleeding [15]. In addition, dental visits reduce the incidence of periodontitis [16]. Women and older individuals are more likely to attend preventive dental visits [17]. Highly educated people also have more frequent dental visits for check-ups than poorly educated people [18]. Research suggests that overtime workers have fewer opportunities to visit hospital for general medical treatment than those that do not work overtime [19]. However, if opportunities for preventive dental visits decrease, the morbidity associated with these diseases may increase. In addition, an increase in periodontitis may influence the increase of other diseases such as coronary heart disease.

A previous cross-sectional study examined the association between working hours and use of preventive health services [20]. Individuals working long hours (> 60 per week) were significantly less likely to attend dental check-ups and cancer screening (e.g., mammograms) than those working shorter hours. Factors contributing to these results were time barriers to making appointments for screening visits and time barriers to keeping any appointments made. Another study revealed that 71% of participants reported delaying or skipping preventive dental examinations because of lack of time to schedule and attend appointments [14]. However, it is difficult to apply those results more generally because the sample size in that study was small and all participants were medical doctors.

The impact of visits to a dental clinic for preventive purposes (rather than for dental examinations) has not been examined. Therefore, we conducted the present study to examine the association between overtime work and preventive dental visits among men and women in different age groups. Preventive dental visits refer to visits to a dental clinic for preventive purposes, rather than for a set dental check-up.

This cross-sectional study included participants from six companies in Japan (five manufacturing companies and one information and communications company). Participating companies did not conduct dental examinations. A self-administered questionnaire was disseminated to 32,026 workers across the six companies between July and October 2017. Participants received an explanation about the study and were informed that completion of the self-administered questionnaire was voluntary. The number of participants (response rate) from each of the six companies was 5728 (81.4%), 4083 (71.0%), 3943 (43.3%), 2302 (72.7%), 709 (11.7%), and 418 (46.5%). This gave a total of 17,183 participants (overall response rate: 53.7%).

The questionnaire collected information on personal characteristics, such as educational background, working conditions (working pattern [daytime, shift work, night shift and semi-night shift], mean overtime hours per month), preventive dental visits, and oral status (see Additional file 1). For the purpose of this study, 1674 shift workers (1580 shift work, 33 night shift, 28 semi-night shift, and 33 with missing data) were excluded to eliminate the effect of shift work on the frequency of preventive dental visits. Workers aged 60 years and over (n=662) were also excluded from the study population because working conditions in Japan change significantly for those over age 60 years. Therefore, 14,847 workers who provided valid responses were included in the present analysis.

This study used a web-based survey. The study design was explained to all employees and employers via email, the company’s intranet homepage, or the company’s occupational health and safety committee. Employees could freely choose whether to participate in this study. Employees’ responses to the questionnaire were not disclosed to their employers. The research protocol was approved by the Ethics Committee of Medical Research, University of Occupational and Environmental Health, Japan (H26–026).

Overall, 11,179 men (75.3%) and 3668 women (24.7%) responded to the questionnaire (Table 1). The age distribution (≤29, 30–39, 40–49, and 50–59 years) was 8, 21, 37, and 34% in men and 20, 25, 35, and 20% in women, respectively. The majority of men were married (79%), whereas the number of single and married respondents was almost the same for women. Overall 6% of respondents (both men and women) had dental problems.

Table 2 shows the association between preventive dental visits and demographic characteristics excluding those with missing data (n=2) for outcomes. In total, 1037 men (9.3%) and 511 women (13.9%) attended quarterly preventive dental visits, and 2672 men (23.9%) and 1165 women (31.8%) attended annual preventive dental visits. In any analysis of annual and quarterly preventive dental visits, the proportion of respondents attending preventive dental visits tended to increase as age increased for both men and women. In addition, the proportion of respondents attending preventive dental visits decreased as working hours increased. Men and women with dental problems tended to proactively visit a dental clinic more often.

Table 3 shows the results of the association between preventive dental visits and overtime work hours, stratified by sex and age. Overtime work had a statistically significant association with quarterly preventive dental visits among men aged 50–59 years, with aORs (95%CI) of 0.73 (0.56–0.95, p=0.019), 0.75 (0.54–1.04, p=0.085), and 0.55 (0.34–0.90, p=0.017) for < 20, 20–40, and ≥40 h overtime/month, respectively (reference: men of the same age with no overtime). No such trends were observed in men aged < 50 years and women of all ages. Overtime work had a statistically significant association with annual preventive dental visits among men aged 40–49 years, with aORs (95%CI) of 0.76 (0.61–0.95, p=0.017), 0.84 (0.65–1.09, p=0.194), and 0.72 (0.51–1.00, p< 0.05) for < 20, 20–40, and ≥40 h overtime/month, respectively (reference: men of the same age with no overtime). Similar results were observed for men aged 50–59 years, with aORs (95%CI) of 0.75 (0.61–0.91, p=0.004), 0.76 (0.59–0.97, p=0.028), and 0.63 (0.45–0.88, p=0.007) for < 20, 20–40, and ≥40 h overtime/month, respectively (reference: men of the same age with no overtime). No such trends were observed in men aged < 40 years and women of all ages.

Table 4 shows the results of the sensitivity analysis among workers without dental problems. The results were the same in both the sex and age categories.

Our study revealed associations between overtime and preventive dental visits among male workers aged in their 40s and 50s. This association was more pronounced in people working longer hours; however, even a small amount of overtime work (< 20 h a month) statistically significantly reduced preventive dental visits.

Some occupational factors, such as overtime work [9] and shift work [22], have been reported to increase the morbidity of dental diseases (e.g., periodontal disease); however, the direct cause has not yet been established. Preventive dental visits reduce the risk for caries and periodontal disease and have an important role in oral hygiene. The results of this study suggested that overtime work may increase dental disease morbidity in workers because of a decrease in preventive dental visits.

Overtime work had significant associations with non-attendance of preventive dental visits among male workers aged in their 40s and 50s. However, men in their 20s and 30s did not show any statistically significant association between long working hours and preventive dental visits. As men get older, they may assume more managerial roles and think more about their responsibilities at work, which may result in putting off preventive dental visits. Among the respondents in this study, the proportion of male managers was 0.1% for those aged ≤29 years and 3.3% for those in their 30s, compared with 32.3% for those in their 40s and 43.9% for those in their 50s. Previous research has shown that workers delay or skip preventive dental examinations because of lack of time or not wanting to burden their co-workers by delegating additional work [14]. Previous studies have also shown that workers who have more frequent dental visits are more likely to be absent from work [23]. In addition, many workers do not want to take time away from their jobs, and may therefore stop making preventive dental visits to avoid delaying or not completing work. However, few studies have investigated the reasons for failure to attend preventive dental visits, and more research is needed on this topic. This study also showed that there was no statistically significant association between long working hours and preventive dental visits among women of all ages. The proportion of female workers in managerial positions in this study was considerably lower than that of males (0% for those ≤29 years, 2.3% for those in their 30s, 11.6% for those in their 40s, and 10.4% for those in their 50s). However, the sample size of women in this study might not have been sufficient, and further studies with more women are needed.

The younger generation had a lower percentage of people who received preventive dental visits, although the proportion increased with age (Table 2). We also observed that women attended preventive dental visits more regularly than men. This was consistent with a previous study in the Japanese population, which reported that 6.5% of men and 9.0% of women attended 3-monthly preventive dental visits, and 31.4% of men and 39.9% of women attended annual preventive dental visits [17]. Similar sex differences were observed in the present study (quarterly preventive dental visits: men 9.6%, women 14%; annual preventive dental visits: men 37.8%, women 47.8%).

The influence of overtime work hours on preventive dental visits in men was greater for annual visits, compared with quarterly visits. A previous study found oral health literacy was associated with the frequency of using regular dental care [24]. For workers attending quarterly dental visits, longer working hours did not appear to affect their dental clinic visits.

The results of this study suggested that even a relatively small amount of overtime work is likely to increase the risk for dental disease because it reduces the frequency of preventive dental visits. We believe that improving management of working hours and reducing the amount of overtime work are important factors for promoting preventive dental visits, which play a vital role in oral health. In addition to reducing overtime hours, it is important to consider other options, such as conducting dental examinations in workplace settings [25] or allowing workers to visit dental clinics during working hours, particularly younger workers and male workers aged over 40 years.

The main strengths of this study were the large sample size and the detailed analysis of Japanese people belonging to large companies. Our analyses were classified by the frequency of preventive dental visits and stratified by sex and age and adjusted for many covariates. This study also had some limitations. First, we were unable to examine causal relationships because this was a cross-sectional study. It is difficult to assume a relationship whereby preventive dental visits affect overtime. Future longitudinal analyses using prospective cohort designs should be conducted. Second, our study used a self-administered questionnaire to collect data on overtime and frequency of preventive dental visits, and recall bias might be present. Consideration should be given to obtaining objective data on overtime in further studies, such as obtaining company personnel data. Regarding preventive dental visits, it is difficult to distinguish between dental visits for treatment and preventive dental visits in objective data for receipts in Japan. Therefore, it is necessary to verify the validity of preventive dental visits by interviewing some respondents and asking them about their specific behavior and the purpose of their dental visits. The third limitation is the possibility of selection bias because the data were from employees of six large companies. The effects of overtime work may differ in our study population from those in the general population because background factors were evened out.

Our study revealed an association between overtime and preventive dental visits among male workers aged in their 40s and 50s. In addition to reduction of overtime work, access to oral health measures in the workplace will help improve oral health in for people who work full-time.