This study aimed to evaluate trends in the prevalence of dental caries in preschool children and associated factors considering the age-period-cohort effects. Our findings showed a significant change in the prevalence of dental caries according to different time variation of age, period, and cohort. Although previous studies have evaluated the prevalence of dental caries considering APC effects [12-14], the assessment of these factors in pre-schoolers in the last two decades had not been explored yet. Moreover, household income, use of dental services, and parents’ perception of child oral health were also associated with dental caries experience, even in the presence of these time variations effects. That highlight the influence of socioeconomic and behavioural factors in caries occurrence.
Age impacted the occurrence of caries, indicating that older children have a greater experience of dental caries. It is well stablished in the literature, with a notable gradient in its occurrence according to the increases of age [9]. Our study brought similar results, indicating that 5-year-olds are about six times more likely to have caries when compared to 1-year-olds. A possible explanation for this finding is due to the increase in the number of teeth exposed to risk factors according to eruption chronology and age of such exposition. Further, dental caries is a cumulative disease and the dmft index measures past and present caries experience [12]. Thus, the longer exposure of teeth to risk factors over the years and the cumulative effect of oral problems, as well as harmful eating habits, such as a greater intake of cariogenic foods [19,20] may impact higher levels of dental caries according to age.
Over the years analysed, the general prevalence of caries decreased between 2008 and 2013 and had a slight increase in the last period (2019) but not statistically significant. A recent systematic review has shown that in the last two decades there have been no significant improvements in the prevalence of untreated dental caries in the primary dentition, maintaining some stability [1]. In addition, in Latin American and Caribbean countries, although the prevalence of caries has been reduced, it is still considered high, being around 55% for the primary dentition [21]. Another possible explanation for the increase in caries prevalence is the worsening of economic indices that occurred before the last period. Between the years 2015 and 2016, Brazil faced one of the five biggest economic crises in its history [22]. Since the occurrence of dental caries in pre-schoolers in 2019 is the result of worse conditions in the first years of life, lower income, worse housing conditions, and parental unemployment may result in higher levels of disease over time [6,23].
Our findings also demonstrated the cohort effects, which refer to variation among groups born in different years. We showed that there is a significant difference between the cohorts, but without a clear and linear progression or regression. Based on the entire distribution of the prevalence we could suggest that younger cohorts presented lower levels of dental caries. This result is in agreement with the most recent evidence, showing that, globally, dental caries rates in this age groups have declined over the last few decades [1,21]. This decline over the years may be due to the use of preventive methods, such as the widespread use of fluorides in water supplies and toothpastes, as well as changes in the social and economic characteristics of the population [21]. Despite that, dental caries reduction has not occurred equally in the population, and non-white individuals, whose mothers present less education and income, remain with a higher burden of the disease, which reflects a global polarization of dental caries, especially in middle- and low-income countries [4,24].
Our findings also displayed that the pre-schoolers from families with lower income were more likely to present dental caries than their counterparts even when considering time variations. In the present study we considered household income as a proxy to individual socioeconomic status [27] and family income has been associated with several oral health outcomes and also with dental caries in the primary dentition in previous studies25,26. Individuals from poorer socioeconomic backgrounds are more exposed to several risk factors that can affect oral health [27], they usually live in worse housing conditions and present poorer health behaviours, such as less access to dental services and poor oral hygiene habits [17,28]. Thus, our study corroborates to the knowledge that socioeconomic conditions leads to worse oral health conditions, such as a higher prevalence of dental caries.
Individuals who did not use dental services in the last year before the data collection period were protected from experiencing dental caries. A previous study showed that children who higher levels of dental caries visited the dentist more frequently than counterparts [29]. Thus, it is hypothesized that individuals who presented more dental caries may experience more pain episodes and difficulties in daily life [2,30], leading to a greater search for dental services. This result highlights that the use of dental services behaviour remains for curative treatment and approaches focused in changing it for a preventive dental care routine are extremally important. Furthermore, our findings displayed that the parent’s perception of their child’s oral health as fair or poor was related to a higher prevalence of dental caries, in agreement with previous studies [6,31]. It has been shown that parents who negatively perceive their child’s oral health status may be less likely to care with children’s oral health hygiene, which may be related to a higher experience of dental caries [31].
This study has some limitations that need to be considered. First, the data analysis includes only three points in time, what could not allow to trace all time effect, especially for period-effect. However, our trend study evaluated deciduous teeth and considered a temporal period of 10-years, which permits tracing a well stablished pattern in the occurrence of the disease in this population. Furthermore, this is a time-series study and such design does not allow us to trace cause-effect relationships and, for that, longitudinal studies are encouraged. However, the same strategy has been used in other studies and provide us substantial information about the populational behaviour facing a specific disease [12,32].
Some strengths of the study also need to be highlighted. First, our data are from a representative sample of pre-schoolers in the city, considering neighbourhoods from different socioeconomic backgrounds, reinforcing the external validity of our findings. In addition, the sample points used for data collection covered about 90% of the children vaccinated municipally in each survey period. Finally, it should be noted that our study considered the APC effects during early childhood. Understanding the pattern of dental caries occurrence and the predisposing factors in this period is essential to prevent poor oral conditions throughout the life course.