This is the first study comparing the differential associations between a comprehensive set of factors at multiple levels and toothbrushing behavior after lunch versus after dinner. We found a distinct pattern of association between the two. Several points that deserve discussion.
First, individual-level factors that were strongly associated with toothbrushing after lunch included younger age, higher education level, and occupation of white-collar job whereas the same variables were less strongly or not at all associated with brushing after dinner. Those in the 50–59,60–69, and 70–79 age brackets were 0.73, 0.65, and 0.68 times less likely to brush their teeth after lunch but were more likely to brush their teeth after dinner compared to the age bracket younger than 30. Similarly, those who work in service/sales or agriculture/fishery/labor/mechanical work, or were students/housewives/unemployed were 0.60, 0.41, and 0.69 times less likely to brush their teeth after lunch compared to office workers, respectively, while they did not differ with respect to the likelihood of brushing teeth after dinner compared to office workers.
The bottom four Si/Dos in toothbrushing rate after lunch both for men and women (Jeju. Gyeoungsangbuk-do, Jeollanam-do, and Jeollabuk-do in Figure S1) were also in the top four with respect to the proportion of the population engaged in agriculture/fishing/labor/mechanical work (Table S4). The same four Si/Dos also had the highest proportion of the population aged 50 or older, an age group that showed much lower odds of toothbrushing after lunch. These factors are assumed to make a substantial contribution to between Si/Dos variation in brushing after lunch (Table S4).
It is striking that groups who were least likely to brush their teeth after lunch reported a similar (or even higher likelihood) of brushing after dinner compared to reference groups. It is possible that people compensate for their inability to brush after lunch by making up for their behavioral deficit after dinner. That is, people may still have a predisposing motivation for toothbrushing (i.e., a desire to maintain good oral hygiene), yet they are blocked by environmental circumstances, e.g., construction workers having no place to rinse on a worksite. People generally use public restrooms, however, they may not be considered sufficiently hygienic. Furthermore, since they do not have their own space (as office workers do), they cannot carry personal belongings conveniently.
It is also worth noting that there was a stronger association between education level and toothbrushing after lunch compared to toothbrushing after dinner. The effects of brushing after lunch (fresh breath, clean teeth) are observable by colleagues at work, whereas brushing after dinner is only noticed by intimate family members. It is possible that more educated individuals perform behaviors to seek approval from others compared to those with lower educational attainment.
Regarding Si/Gun/Gu characteristics, high oral health inequality within Si/Gun/Gu was strongly associated with reduced likelihood of toothbrushing after dinner. Higher health inequality implies many conditions that lead to health disparities in society and those conditions are detrimental to all members of society. Furthermore, some types of health inequalities have spillover effects on the rest of society.[24] For example, infectious disease, or alcohol or drug abuse that affect a small fraction of the population, yet harm the rest of society. However, this theory linking the inequality in health to individual health does not easily apply to oral health inequality. It is necessary to investigate the mechanism linking higher oral health inequality at Si/Gun/Gu-level and a lower likelihood of individual’s toothbrushing behavior.
Finally, the factors we considered in our analyses explained 67.4% of between-Si/Do variation and 57.1% of between-Si/Gun/Gu variation in toothbrushing after lunch whereas, in toothbrushing after dinner, they rather increased the variation, which suggests that the factors generating variation at Si/Do- and Si/Gun/Gu-level are not the same between toothbrushing after lunch and after dinner. There are other factors affecting variation in toothbrushing after dinner at those contextual levels that we could not include in our analyses.
This study has some limitations. First, the cross-sectional design of the study restricts causal interpretation. However, reverse causation is not theoretically plausible in most of the variables. Second, we attempted to include variables as comprehensively as the data allowed. However, there are factors that affect toothbrushing behavior but have not been surveyed in CHS. Despite limitations, our study provides useful insights into how factors at different levels differentially predict toothbrushing behaviors depending on the time of day and thus how we can tailor interventions to address them. Despite these limitations, our study can provide important policy implication that interventions to improve toothbrushing behavior need to be tailored depending on the time of day.