Disparities in the experience and treatment of dental caries among children aged 9–18 years: the cross-sectional study of Korean National Health and Nutrition Examination Survey (2012–2013)

Table 1 summarizes the general characteristics of the children included in this study. A total of 1,253 participants were included in the initial dataset. Of these participants (n = 1,253), 808 (64.5 %) had experienced dental caries, and 445 (35.5 %) had not experienced dental caries. Among those who experienced caries (n = 808), 582 (72.0 %) did not receive treatment for their dental caries, and 226 (28.0 %) received treatment for their dental caries. The 1253 participants were divided into low (34.4 %), middle (31.8 %), and high (33.8 %) income households, respectively. Those who having experience of caries (P = 0.976) was shown to be 64.7 %, 64.7 %, and 64.1 % in low-, middle-, and high-income households, respectively. The non-treatment of caries among children having experienced caries (P = 0.005) was shown to be 77.8 %, 72.9 %, and 65.3 % in low-, middle-, and high-income households, respectively. Both experience and non-treatment of caries among children who experienced caries were most frequent in low- and middle-income households and least frequent in high-income households. Most children in this population had mothers with a middle- and high-school graduate education level (61.1 %).

Table 2 presents the results from the logistic regression analysis. Several other factors were associated with the experience of caries: female sex (OR 1.91 [95 % CI 1.41–2.59]) and low self-rated dental health status (OR 2.95 [95 % CI 1.77–4.92]). Low and middle-income household was strongly associated with the non-treatment of caries among children experiencing caries (low, OR 2.11 [95 % CI 1.16–3.86]; middle OR 2.14 [95 % CI 1.27–3.62]). In addition, the non-treatment of caries was associated with female sex (OR 0.65 [95 % CI 0.45–0.95]); brushing teeth less than once per day (OR 2.76 [95 % CI 1.13–6.71]); and irregular dental checkups (OR 3.76 [95 % CI 2.58–5.49]).

Table 3 shows a subgroup analysis of gender and regular dental checkups with respect to the household income level. A stepwise trend by income level was found for each variable, but it was only statistically significant with respect to regular dental checkups. A negative association was found between the household income level and non-treatment of caries among children experiencing caries (OR 3.58 [95 % CI 1.25–10.24]) irrespective of regular dental checkups.

This study examined two associations: (i) between parental SES and the experience of dental caries and (ii) between parental SES and non-treatment of dental caries in those children having experienced dental caries. Parental factors were assumed to be associated with the experience and treatment of caries during childhood [27].

The findings from this study, however, found only partial associations between parental SES factors and dental health inequalities. In particular, parental SES factors appeared to influence the non-treatment but not the experience of dental caries. The household income level was the sole factor in this association. Although previous studies have linked children’s dental health status and maternal education level, no statistically significant association was observed in this study [15, 20]. The findings of this study therefore suggest that children who have experienced dental caries in low- and middle-income households are more likely to be associated with non-treatment than those from high-income households. In particular, those from low- and middle-income households who had regular dental checkups were more likely to have untreated caries than those from high-income households.

The results of our study did not indicate any significant associations between parental SES, particularly lower household income and lower parental education level, and children’s experience of caries. However, several previous studies did find associations between parental SES and experience of dental caries [5, 10, 19, 28, 29]. In studies in the United states and Brazil, both lower household income and lower education level of the caregiver are likely associated with experience of dental caries among children [5, 28]. Moreover, lower household income was associated with experience of dental caries among children in another study in the US as well as a domestic study [10, 19]. In a study in Japan, a longer maternal education period was related to a decreased risk of dental caries among children, although there was no association with household income [29]. There are some differences between our study and these previous studies that may explain this discrepancy. First, as the two different dependent variables cover different lengths of time period, this may have led to unalike results. One previous study based on the same KNHANES data reported lower household income was related to experience of dental caries among children. In the study, the number of caries at the moment of the survey were used as the dependent variable rather than including previous occurrences [19], which may explain the discrepancy in findings between these two studies. The DMFT score in the current study covered a longer time period due to the inclusion of past and present caries and included the current treatment and disease status, the dependent variable in our study may have been affected by other factors. Parental SES which has changed during the period of growth could affected as well. In addition, there has been Korean government-funded efforts to reduce the incidents of caries among children via the promotion of preventive dental health such as community water fluoridation and dental health education by community health centers [19, 30], which may reduce the impact of parental SES on the incidence of dental caries. Fortunately, there has been a global movement to improve children’s dental health [9].

Household income level likely contributed partially to the relationship between parental SES and non-treatment among children experiencing dental caries. This study found that children in low- and middle-income level households were more likely to not have received treatment of dental caries than those with high-household incomes. This finding was consistent with previous studies in the US and Korea [5, 10, 31] and can be explained by the healthcare policy in Korea. Although universal health coverage through the Korean National Health Insurance (KNHI) was designed to reduce the gap between socioeconomic classes in terms of accessibility and availability to healthcare services, the limited benefit coverage of the KNHI is known to be a problem, causing high economic burden to low-income patients [32, 33]. The limited benefit coverage is mainly due to the high percentage of out-of-pocket payment and uncovered medical services [33]. The high costs of out-of-pocket spending for medical services are a relatively greater burden to low-income households in terms of affordability. According to a previous study, economic burden due to spending costs for dental care was the most common concern among low-income groups who paid out-of-pocket [34]. In addition, the proportion of uncovered medical services is particularly large for Korean dental care services, resulting in severe economic disparities in the use of dental services [35]. Due to these factors, children from low- and middle-income households were associated with non-treatment of dental caries due to the economic burden from the use of medical services. This important finding highlights household income–related disparities in access to dental care services among children and also indicates the existence of a financial barrier to dental care services.

This study also assessed the impact of other factors, such as demographic characteristics and dental health behaviors, on the experience and non-treatment of dental caries. This study found that female children were more likely than male children to have dental caries; however, male children were more likely to experience non-treatment of dental caries than female children. This result suggests that females care more about their dental health than males despite the higher incidence of dental caries among females. No characteristics of dental health behavior were significantly associated with the incidents of dental caries except self-rated dental health status, which was negatively correlated with the incidents of dental caries in agreement with a previous study showing the association between low self-rated dental health status and more experience of caries [6, 36]. This result suggests that more experience of caries can be associated with low self-rated dental health due to the tooth pain from current or previous caries. Although self-rated dental health status was not associated with the non-treatment of caries [37], several factors were significantly negatively associated with the non-treatment of dental caries including the frequency of tooth brushing and regular dental checkups. Our study found that infrequent brushing were more likely to be associated with non-treatment of caries, which is consistent with the finding of the previous study in Mexico [38]. This finding suggests that unhealthy dental care behaviors including infrequent tooth brushing among those having experience of caries can more easily lead to non-treatment of caries. In particular, our study found that children who did not have regular dental checkups were more likely to be related with non-treatment of dental caries, which is consistent with the findings of previous studies [11, 36].

In addition, our study found that children in low- and middle-income households who had regular dental checkups were more likely to not receive treatment than those in high-income households. In previous study, regular dental checkups were found to be a beneficial factor for professional diagnostic and prophylactic services, which are important for dental health [14, 39]. Therefore, children who had regular dental checkups also had information about their dental status based on diagnostic results, and they were able to make a clear decision regarding treatment before the disease deteriorated [14, 40]. On the other hand, those who did not have regular dental checkups may not have been able to acknowledge whether they had any caries or not. However, our findings showed that although children who had regular dental checkups were more clearly aware of their medical needs, there was nevertheless a household income–related disparity in the treatment of caries. Our findings show that low-income children are more likely to not receive treatment of caries due to financial barriers even when children have already recognized that they need to receive treatment. Similarly, the lack of association between regular dental checkups and treatment of caries suggests that the current dental care services are not effective enough to lessen the financial barriers even for those with clear medical needs.

There are several limitations to this study. First, this study is based on cross-sectional data, which reduces the ability to determine an association between the factors and the experience and non-treatment of dental caries. Second, this study did not address the impact of paternal factors. Although the original study intended to use information from both parents, a significant amount of paternal information was missing from the data. Third, there was an association found between the self-rated perception of dental health status and untreated caries. A further study should be conducted to investigate the association between low self-rated health and untreated caries. Finally, this study did not analyze certain characteristic variables that are observed only in students, such as variables that address the length of time staying at school and the significant pressure to study faced by Korean students. A future study should consider such confounding variables to determine the influence on dental health, such as the stress associated with studying and the number of hours during which students are engaged in school activities.

This study reveals several important policy implications. First, the financial barriers to obtain restorative dental health services need to be eliminated. There exists an invisible barrier that prevents children from low-income households from receiving treatment. It may be more difficult for low-income households to afford the financial burden of children’s dental treatment, which may represent a significant proportion of the medical expenditure from their limited household income. The most effective policy would be a coverage increase in dental services. According to a previous study in Korea, the lack of coverage has resulted in access barriers and dental health disparities, and the wealthy receive the most advantage from the dental health gradient [41]. Second, the distribution of resources for dental services should focus more on the low-income households. Third, the lack of association between regular dental checkups and treatment of caries highlights the need for effective dental care, particularly for low-income household children. The need for dental health services increases as the level of household income decreases. Therefore, supportive policies with proper intervention can reduce the gap in dental care access between the high- and low-income households [1, 5, 10, 25].

This study revealed that parental SES-related inequalities were associated with the treatment of dental caries. In particular, those from low- and middle-income households who had regular dental checkups were more likely to have untreated caries than those from high-income households. There is a need to reduce household income-related disparities in children’s dental health treatment. Through the findings presented here, we hope to contribute to the establishment of a dental health policy that reduces household income-related inequalities in dental care.