Association of siblings’ presence and oral health-related quality of life among children: a cross-sectional study

The Global Burden of Disease Study 2017 estimated that oral diseases affect nearly 3.5 billion people worldwide [1]. It is estimated that 60–90% of school‐aged children globally are affected by oral health problems [2], and these problems negatively affect child overall health [3]. According to the World Dental Federation, oral health is multi-faceted and includes the ability to speak, smile, smell, taste, touch, chew, swallow, and convey a range of emotions through facial expressions with confidence and without pain, discomfort, and disease of the craniofacial complex [4]. In this broader concept of oral health, assessment of oral health is not only focused on the biological level, but also on emotional and social functional level.

Oral health-related quality of life (OHRQoL) is a self-report measurement of oral health status, which captures functional, social, and psychological impacts of oral disease [5]. Unlike traditional measurements focusing on clinical indices, OHRQoL is more concerned about impact of oral health problems on quality of life [6]. As a generic instrument, OHRQoL can investigate the impact of oral health conditions in relation to general health perceptions, allowing for comparisons between different diseases [7]. More importantly, OHRQoL can simplify understanding of health burdens of oral disease for health policy makers [8]. As oral health is crucial for general health, OHRQoL is recognized by World Health Organization (WHO) and serves as a segment of the Global Oral Health Program [9].

OHRQoL is not only affected by oral health conditions, but also related to socio-demographic and contextual factors [10]. Previous studies showed that children with different demographical backgrounds [11] (e.g., gender, ethnic background) and family socioeconomical status [12] had different OHRQoL. The siblings’ number is also a key family characteristic. Previous studies found siblings’ number was negatively associated with child health [13, 14] and health expenditure [15]. This negative association is consistent with quantity–quality trade-off perspective. According to quantity-quality trade-off theory, an increase in the quantity of children tends to decrease available resources for investing in the human capital per child, which consequently leads to a trade-off between quantity and quality of children [27]. However, little is known about the relationship between number of sibling and children’s OHRQoL.

Although evidence of association between sibling’s number and OHRQoL is lacking, there are some evidences linking sibling’s number with other oral health outcomes. Having two or more siblings is associated with lower odds of regular brushing and annual dental visits [16], and having siblings is more likely to increase the incidence of caries [17]. In particular, caries are more common in the second born child than the first child [18], further supporting this negative relationship. These existing evidences show that the sibling number is negatively associated with dental visits as well as oral health condition. Moreover, dental caries was a common oral condition affecting children’s OHRQoL [19], and dental visit was also associated with OHRQoL [20]. Current evidences suggest a negative association between sibling’s number and children’s OHRQoL.

Thus, the aim of the current study is to examine the association between presence of siblings and children’s OHRQoL by using 12-year-old children oral health survey data in Beijing, China. Considering the significant urban–rural disparities in socioeconomic situations and healthcare accessibility in China [21], and both socioeconomic status and dental-care attendance are positively associated with OHRQoL [22], there is a need to further access the possible interaction effect between siblings’ presence and locations on children’s OHRQoL. There is also a need to see whether the combined demographical characteristics will result in a greater effect on children’s OHRQoL.

This is the one of few studies assessing the OHRQoL of Chinese schoolchildren. The first contribution of this study is assessing the effect of siblings’ presence on children’s OHRQoL. Results show that non-single children were more likely to report OIDP and have lower OHRQoL. The second contribution is testing the interaction effect between siblings’ presence and locations on children’s OHRQoL. An excessive risk for OIDP was observed among non-single and rural children.

The prevalence of OIDP in Chinese schoolchildren was 60.0%, which was similar to children of the same age group in Sudan (52%) [27] and Uganda (62%) [34], but lower than those in Thailand (85.2%) [35]. The highest impact reported in the current sample was on eating (41.8%), which is consistent with previous studies [27, 35, 36].

Only active caries was negatively associated with children’s OHRQoL in this study, which were consistent with previous studies [27, 37]. Active caries cause pain, discomfort, and functional illimitation, which explains the association of active caries and OHRQoL. Previous studies showed that gingival bleeding was not associated with children’s OHRQoL [27, 37, 38], similar result was found in this study. However, a negative relationship between extensive calculus and/or gingivitis and children’s OHRQoL was found in some literatures [39]. The inconsistent results might partial due to the measurements, since many studies with non-significant results only report presence or absence of gingival bleeding (gingivitis) and lack assessment of the severity and extent of gingivitis. Thus, future studies are encouraged to apply more precise method in measuring severity [27] and extent of gingivitis [39], which helps to find a more solid evidence in association between periodontal health status and children’s OHRQoL.

Rural children or non-single children were more likely to report the lower OHRQoL in this study. Based on the social determinants of oral health, demographical factors might have indirect effects on OHRQoL via oral health status or dental care utilization [40], which could explain the association between demographical factors and OHRQoL. Previous studies show that the sibling number decreased the chance of annual dental visit and increased the chances of having caries [16, 17]. Dental visit and caries were positively and negatively associated with OHRQoL, respectively [20, 41, 42]. These series of evidences indicate that single children tend to have better oral health status as well as OHRQoL. One-child policy effectively encourage parents to have only one child leading to positive consequences for child’s physical health status [43]. Our findings support the policy-related determinants of child oral health. First, one-child policy led to greater involvement by parents in child’s care [44]. It is important for parents to participate in and supervise children’s tooth brushing in early childhood, which is highly related to oral hygiene tooth-brushing habits in later childhood. Second, one-child policy limits siblings’ presence, which can decrease parental dental neglect and increase the possibility of children’s dental care utilization [16, 45].

However, association of demographical variables and OHRQoL is relatively low. The following reasons might explain the low ORs: first, Beijing government has been conducting an oral health program for schoolchildren since 2005, including offering oral health education, oral health examinations, and pit and fissure sealing [46]. This oral public health care might narrow oral health gap among different groups since the disadvantage groups enjoy more benefits from free public health service [47]. Second, since demographical factors might have indirect effects on OHRQoL via oral health status, inclusion of the dental variables weakens the ORs on demographical factors.

In this study, the synergistic interaction results showed that the excessive risk increase for OIDP among non-single and rural children, but the effects were non-significant for non-single and urban children or for single and rural children. First, for non-single and urban children, the oral healthcare resources are more accessible and parental oral health awareness are higher in urban area, which might alleviate the negative impact of sibling’s number [48]. Second, for the single-rural children, although they were inaccessible to community’s oral healthcare, their parents were more likely to participate or invest in children’s oral health as being the only-child in the family [45]. Enjoying sufficient oral healthcare resources in family environment might reduce the negative impact of living in rural area. However, a synergistic interaction effect was found among non-single and rural children was found at the 85% confidence intervals. As the application of the confidence level (95% CI) to the interaction significance test could obscure a possible synergism, an 80% CI was applied in the previous interaction study [31]. In the current study, an 85% CI was applied. In this study, the excessive risk increase for OIDP was observed among those who were non-single and rural children. The maldistribution of oral healthcare resources between rural and urban areas might contribute to the additional risk. Oral healthcare resources were unequally distributed in urban and rural areas in China [49, 50], and one third of rural residents failed to use the oral health services because of the long distance to dental clinics [51]. Non-single and rural children are exposed to insufficient oral healthcare resources per capita in a family and have poor accessibility of oral healthcare services in the community, and these two factors combined may lead to the interaction effect. Moreover, one child policy was more strictly enforced in urban areas [52]. Overlapping of location and sibling factor might contribute to the interaction effect.

The findings of current study support the one-policy might have positive effects in children’s OHRQoL. China unveiled the universal two‐child policy since 2016, and family size will be larger in the future [53]. To improve children's oral health and oral health equity, oral health policy makers should pay attention to the impact of family planning policy on children's oral health and the corresponding policy should be developed when necessary.

Several limitations of the current study should be mentioned. Due to the one child policy implemented in China, we only collected data on single or non-single children and failed to investigate the impacts of the number of siblings on children’s OHRQoL. It is well known that one-child policy affected the sex ratio in China [54], and sex ratio is not likely to change current result. According to statistical data of Beijing in 2015, male to female ratio among Beijing children aged 10–14 years is 107:100, which is close to 1:1. Results from the gender-weighted data were consistent with current results, which further suggests that the sex ratio is not likely to change current result. However, the national sex ratio was more imbalanced than that in Beijing. When the evidence is applied to other children, the possible impact of gender should be considered. Due to sample size limitation, we did not conduct gender-stratified analysis, but we included gender as a controlled variable in this study and tried to control its effect. Future research can further test the multiple interaction among gender, single children, and location. Besides, only the severity of oral health daily impacts was assessed, and the OIDP score and prevalence were calculated in this study. Future studies could apply the original version assessing the frequency and severity of both impacts and conduct a more detailed analysis.

Children with siblings are more likely to report a lower OHRQoL, which indicates that the quantity-quality trade-off might exist in children’s OHRQoL. The synergistic interaction effect between presence of sibling and place of residence on children’s OHRQoL was found, suggesting that non-single and rural children are vulnerable population in oral health. These finding suggests that oral health intervention programs should give priority to non-single and rural children.