This survey reported high prevalence and severity of ECC among preschool children in Guangdong, Southern China, similar to the finding for East China  and higher than that for Southwest China , higher than the national average , and higher than that 10 years ago . A multitude of factors are associated with the prevalence and severity. The findings of this survey inform target factors for collective actions to address this critical oral health problem.
The most obvious limitation of this survey is the retrospective rather than prospective design, which might brought potential recall bias. Hence, we can’t confirm the causal relationship between the associated factors and the results. An additional limitation is that the dmft index is less accurate than the dmfs index, as a tooth has multiple tooth surfaces and ECC typically involves multiple tooth surfaces rather than one. Finally, enamel defects, oral bacteria and fluoride concentrations of drinking water that contribute to ECC were not evaluated. A systematic review showed that the presence of enamel defects and high levels of mutans streptococci were the strongest risk factors associated with ECC . Prospective studies and studies including microbiological detection, enamel defect examination, and determination of the fluorine concentration in drinking water are indicated.
A report showed that the oral health status of preschool children has significantly improved over the past 10 years in China . However, compared with the provincial survey of Guangdong in 2005, the current results showed remarkable increases in the prevalence (67.9% to 78.4%) and mean dmft (4.13 to 5.69) of ECC among 5-year-old children in both urban and rural areas, especially in rural areas. This trend actually shows ECC rates becoming further away from the goal of a caries-free rate of 50% among 5-year-old children for the year 2020 by the WHO . Higher sugar intake  but still inadequate oral healthcare , possibly leading to the increasing trend observed . More attention should be given in Guangdong to children’s dental health for deciduous teeth.
The frequency distribution of dmft showed that two teeth with ECC were the most common, and the position distribution showed that the upper central incisors were the prevailing teeth with ECC. The same finding was shown in the national survey . ECC usually affects the smooth surface, followed by the pit and fissure, which is different from the caries of permanent dentition. Therefore, preventive measures against caries with smooth surfaces should be taken. If ECC of the upper central incisors were prevented, the prevalence might be reduced by 10%.
Risk assessment is an important part of patient-centered, evidenced-based decision making in modern medical services . A systematic review showed that ECC is related to demographic factors, oral hygiene behaviors, dietary behaviors, and socioeconomic factors . The results of the multivariable model showed that associated factors for ECC matched the review.
Dental caries is an irreversible process. As deciduous teeth continue to function and be challenged before replacement, the continuous and cumulative effects cause ECC to develop with time. This might explain why increased age was related to a higher risk and severity of ECC. Additionally, children who initiate toothbrushing at an older age have a higher risk of developing ECC. Therefore, ECC prevention should occur from an early age.
No obvious gender differences in the prevalence of ECC were found for. No evidence showed that the composition of the saliva differs between boys and girls or that there are any differences in tooth structure between the genders . However, the mean dmft was higher in female children. Further exploration is indicated.
Generally, caries are recognized as more severe among people with low socioeconomic status [22, 23]. In this study, the prevalence and mean dmft of ECC in urban areas were lower than those in rural areas, while the opposite was true for the filled rate. Children who had a low parental education level and low household income had higher prevalence and severity of ECC. Rural oral medical service is usually characterized as having insufficient infrastructure, socioeconomic difficulties, artificial barriers such as distance and inconvenience of transport, and a high patients to oral health professionals ratio [15, 24]. Parental factors such as education and income are significant risk factors in the developing of ECC . Therefore, children from rural areas should be given more attention in order to reduce ECC.
A systematic review showed that ECC is related to frequent sweets consumption . In particular, numerous studies have proven that sweets play a key role in the occurrence and development of ECC [27-29]. A diet rich in exogenous sugars is believed to be cariogenic to children . In the present survey, the participants who consumed sweets before sleep were 1.35 times more likely to have ECC and had 0.77 higher dmft than those without this habit. Moreover, children who were sometimes/often fed with sweetened milk/powdered milk had higher dmft than those who were never/rarely fed with that kind of milk. This result suggests that both the timing and frequency of the consumption of sweets influenced ECC.
What interested us was that the children who were exclusively/predominantly breastfed during the first half year of life had a higher risk of ECC. This finding agrees with the results of earlier studies reporting a significant relation between the duration of breastfeeding and ECC in young Chinese children [31, 32], similar to its neighboring province of Zhejiang . Part of the reason might be that breast milk is more likely to cause caries than other types of milk . Additionally, extended breastfeeding contributes to the colonization of Streptococcus mutans , which synergistically induces ECC. Breastfeeding is recommended by the WHO ; however, considering the relationship between breastfeeding and ECC, dental experts recommended weaning from the breast shortly after the child’s first birthday .
It is recommended that the first dental visit should be performed by 12 months to assess the risk of ECC and provide early intervention when needed . Dental visit history is usually a protective factor for ECC in developed areas [38, 39]. However, in this survey, children who had dental visit histories had higher prevalence and dmft scores of ECC than those without dental visits. This difference may be due to the different patterns of visiting dentists. Children in developed areas often visit dentists for preventive examinations and take preventive measures. However, in China, dental treatment has been sought since these children had already experienced oral health problems, which is therapeutic rather than preventive. Visiting dentists only when a problem was perceived was a risk factor for ECC . This finding agrees with the results of some other Chinese studies [32, 41, 42].
There were no significant relations between toothbrushing habits and ECC in this study. However, children who start brushing their teeth at an older age are at higher risk of developing ECC. Moreover, lack of toothbrushing was a risk factor for ECC , and irregular brushing at 18 months of age was a highly significant predictor of developing ECC . Brushing less than twice a day or difficulties brushing teeth during the first year of preschool were significant determinants of ECC at the age of 5 years . Therefore, professionals should give parents special attention and assist in improving and optimizing their toothbrushing behavior during children’s preschool years.
The strengths of this survey include a representative sample which was ensured by an equal-sized, stratified, multistage random sampling approach, the use of a reliable index, and a statistical analysis with a weighted process which made the results be close to reality and permit us to generalize the findings to the population.