This study demonstrated that the rate of ECC in children from Qingdao was 59.4%, which shows that the caries prevalence among the children is still quite high. Thus, the families and government should pay attention to the effects of ECC on children, and initiate early interventions on factors fueling ECC.
The prevalence and severity of ECC was higher in children with IDA compared to those without the disease. This phenomenon was associated with the functions of salivary glands which is impaired IDA, leading to reduced salivary secretion and low buffering capacity. Consequently, there is ineffective washing of dental plaque and food residues, which easily leads to dental caries [15]. In addition, the interplay between ECC and IDA was due to decreased iron ions in saliva, which inhibit the activity of S. mutans and promote the formation of cariogenic biofilms when the body is in an iron deficient state [13, 16].
In sync with previous studies, our data showed that lower family annual income was associated with IDA [26, 27]. This could be because families with low income might not live a healthy life which include intake of iron-rich foods or lack immunity to combat infections, which increases the probability of having IDA [26]. However, the data showed that lower household income was not significantly associated with rate of ECC but was a risk factor for the co-occurrence of IDA and ECC. This might be due to suppressed systemic immune functions when the body is in an iron-deficient state, thus a higher susceptibility to cariogenic bacterial infection [28].
About half of the childbearing age women suffer from IDA [2], and the occurrence of IDA during pregnancy as well as pregnant women who do not have a scientific and reasonable diet plan have a higher risk for IDA. If a mother does not have IDA during pregnancy, her iron can meet the needs of a 4 or 5 months baby [29]. Otherwise, reduced maternal iron reserves and insufficient iron transmission from the placenta to the fetus increase children’s IDA risk. However, our study demonstrated that there is no correlation between maternal anemia during pregnancy and IDA occurrence in children aged 4 to 6 years old. This may be related to acquisition of iron from food. The development of children's primary teeth starts from the sixth week of an embryo to the completion of development at about 3 years. Thus, there is an assumption that insufficient intake of iron ions in the early development of primary teeth would lead to a higher rate of caries in primary teeth. Besides, inflammatory response that accompany ECC produce uncertain cell factors, which restrain the production of hemoglobin and further reduce the iron level [30].
In addition, a longer duration of breastfeeding was significantly associated with IDA and ECC. The content of iron in breast milk is insufficient for the infants’ growth and development [29]. Moreover, prolonged breastfeeding may interfere with saliva flow in the children and hinder their self-cleaning function, increasing the risk for IDA and ECC. The American Academy of Pediatrics suggests that exclusively breastfed infants should be supplemented with 1 mg/kg of iron daily from the fourth month until the time when the infant can consume sufficient iron-containing foods to reduce nutritional deficiencies [31]. However, most parents usually do not provide iron supplements, which might be related to the increased risk of cognitive development impairment [32].
There was wide public awareness of IDA, the most important type of anemia in children aged 2 years or under [33]. The age between 6–23 months is critical for children's growth and development. This is the period where iron reserves from a mother's pregnancy are completely consumed and the body's demand for iron is very high. Insufficient supply of nutrients in the body at this period leads to increased risk of IDA [34, 35]. Besides, unhealthy eating habits such as food avoidance and partial eating during this period would likely lead to future IDA, consistent with the findings in our questionnaire survey. Children aged 2 years or less with an IDA history were shown to be more likely to develop IDA at 4–6 years old, and the body is more prone to ECC in a state of nutritional deficiency.
Our study also showed that children’s intake of iron supplements reduces ECC and IDA, but it is not clear whether intake of iron supplements improves the nutritional status or increases the resistance to cariogenic bacteria [36, 37]. Besides, whether iron supplements can directly supplement iron and thus inhibit enamel demineralization is yet to be determined [28]. Excessive use of iron preparations in children increases the risk of development of tooth black stains and affects the appearance of teeth [38]. Therefore, children should take iron preparations in an appropriate amount.
On the other hand, data has shown that meat contains a large amount of heme iron and other forms of iron ions that can be well absorbed. Limited or lack of consumption of meat food increases the probability of IDA [39]. In contrast, our study showed that there was no significant association between the frequency of meat intake and IDA. Seafood in Qingdao is rich in iron, and the consumption of seafood can supplement iron in children [40].
IDA was shown to fuel ECC in severe cases of primary teeth caries in preschooler's in Qingdao. Factors that influence IDA, such as IDA history at 2 years old or less, mother's history of IDA during pregnancy, breastfeeding until 2 years old, and lower family income were shown to also cause ECC. Similarly, intake of iron preparations can inhibit the occurrence of ECC and IDA. Our study showed that the factors that influence IDA can lead to caries. However, there is need for in vivo and in vitro experiments to verify whether IDA has a significant effect on the development of children's primary teeth.
Our study was limited by use of limited items that were involved in the questionnaire to perform a comprehensive analysis between IDA-associated factors and ECC. The reliability of the questionnaire survey depended on the parent's memory and could trigger a recall or reaction bias. Although the sample size was sufficient for the survey, there are 10 districts and counties in Qingdao, thus the two districts that were randomly selected with the PPS method may not completely represent the whole city. Moreover, those children who did not cooperate with the doctors were excluded and could have influenced the outcome of this study. Finally, development of ECC or IDA takes a long time, which is influenced by many factors. Therefore, a longitudinal study will better illustrate the factors that mediate ECC and IDA.
