This is the first study examining the oral health of five-year-old children registered in the CAUNICO. We found that 41% of participants with a per capita income greater than R$ 170, reported receiving BF. Based on the program guidelines, this circumstance should not occur. We speculate that many poor families may have income that is not officially declared (e.g. temporary work) and because of that, they are kept in the program. These inconsistencies were also found in previous studies examining coverage and focus of BFP [37, 38].
Our analysis suggests that children whose families were early recipients of BF, receiving benefits for up to 2 years, had 78% lower odds of developing dental caries than non-recipients. This result indicates that BF, in its initial years, acted to prevent dental caries among five-year-old children. Several studies have indicated that CCTs positively impact children’s health, including birth weight, illness, and morbidity [11, 16,17,18,19,20,21] . Yet, the mechanisms by which CCT programs benefit the health of the population remain unclear. Some authors have argued that the benefit only occurs when CCT programs are combined with a coordinated primary health care system [12, 17]. Our results contribute to the current debate on this issue.
Although free-of-charge dental care is available in the Brazilian primary health care system, through the country’s FHP [13, 14], regular oral health check-ups are not part of the BF health conditionality. Thus, there are no incentives for children registered in the BF to visit a dentist. In fact, our results showed that more than 63% (n = 146) of our sample had never visited a dentist, even though the majority of participants reported regularly visiting the health unit (due to BF health conditionalities). Further, a recent study conducted with the primary health care teams in Fortaleza demonstrated that most dentists performed no systematic effort to promote oral health or dental care to children and their caregivers covered by the BFP because they felt that it was beyond their responsibilities  . Two possible explanations may help interpret our findings. Firstly, it can be postulated that by having access to health care services, including regular clinical appointments with nurses , as part of the BF health conditionality, caregivers may be better informed and feel more motivated to take care of their children’s oral health. Secondly, BFP is likely to improve children’s oral health by enhancing the quality of daily food intake. These explanations are supported by the most recent systematic review examining the effect of the BFP on nutritional outcomes , in which a positive association between this program and increased consumption of different food groups and food and nutritional security was found.
Another possible explanation for low caries among children registered in the BFP is that a small increase of income may reduce the impact of stress-related factors on children’s oral health. Living in poverty is associated with a high degree of stress. Studies showed that children in poverty are more likely to experience an unsafe and unhealthy home and to reside in families characterized by psychosocial risk factors such as high levels of conflict, violence, and family turmoil, and low levels of cohesiveness and warmth, [39, 40]. As a result, children growing up in low-income homes are understood to experience higher levels of stress than their counterparts [39, 40]. The pathways explaining these relationships are not completely understood. Nevertheless, one of the possibilities recently contemplated in the literature is related to hormone secretion [41, 42]. Children growing up in poverty may show early signs of allostatic load, including elevated secretion of cortisol and epinephrine, and higher blood pressure .
With regards to oral health, Boyce et al. (2006)  examining stress-related psychobiological processes that might account for disproportionate rates of dental caries among kindergarten children (five to six years old) in the US identified that a low family social position was associated with financial stress, basal activation of the child’s hypothalamic-pituitary-adrenocortical axis, and higher counts of oral cariogenic bacteria . These authors also showed that: 1) cariogenic bacteria and salivary cortisol secretion were both independently associated with the presence of caries; 2) the highest risk of dental caries was among children with high levels of both salivary cortisol and cariogenic bacteria; and 3) cortisol reactivity to stress was associated with thinner, softer, and thus more vulnerable enamel surfaces. Additionally, maternal allostatic load as a measure of exposure to chronic stress—has been linked to adverse caretaking behaviours, such as taking a child to the dentist, and correlated with presence of caries in children . Thus, the convergence of psychosocial, infectious, and stress-related biological processes appears to be implicated in the production of greater cariogenic bacterial growth, increased physical vulnerability of the developing dentition, and poor oral health care behaviours, and hence dental caries.
The association between receiving BF and oral health was even more prominent among extremely poor families. The ORs from children of families with a per capita income lower than R$170 were 95% lower than those not receiving BF with a per capita income greater than R$170. This finding suggests that BF is more effective in the poorer strata of the population. Similarly, Amudahan et al. (2013)  found that the India CCT (Janani Suraksha Yojana) had a higher impact on institutional birth deliveries among a poorer section of intended CCT beneficiaries. Thus, CCT programs appear to mitigate the impact of inequalities on children’s well-being.
In the present study, a large proportion of five-year-old children registered in the BFP had never visited a dentist (63.48%), yet 44.11% of the sampled children had untreated dental caries. Children who reported visiting a dentist had higher odds of having dental caries than their counterparts, an aspect that was explained by analysis showing that our sampled children would mainly visit the dentist when in pain. This suggests that these children are also not receiving proper preventive nor restorative dental care, as the proportion of dental caries is still high among the sampled children. These results are similar to Petrola et al.’s (2016)  research conducted with a similar sample of participants in the city of Fortaleza, in which it was shown that more than 60% of children 7 years old or less, enrolled in the BFP, had never received fluoride therapy or participated in oral health education activities and almost 78% had never visited a primary health care dentist. Petrola et al. (2016)  also found that one third of the family health dentists interviewed did not provide dental care to children covered by the BFP, as they reported that this care was beyond their responsibilities. Our findings are somewhat worrisome. Childhood caries affects a child’s general health, learning ability, quality of life, and can have a life-long impact on oral health [45, 46] . Children who experience caries as infants or toddlers are at greater odds of developing further caries in their primary and secondary dentitions  .
Comprehensive public policy programs can help prevent children’s dental caries among low-income families. For instance, the Early Head Start program in the US, which targeted low-income families and has an oral health component, including daily teeth brushing activities and dental check-ups, has improved teeth brushing among enrolled children , improved access to dental care , and increased preventive/diagnostic/restorative dental care utilization  . Therefore, we speculate that the inclusion of oral health in the BF health conditionality will likely improve children’s oral health outcomes. The oral health teams, which are integrated in the ESF, are one of the largest primary dental care models across the globe. They operate in 4937 of the 5570 Brazilian municipalities, caring for approximately 72 million individuals (roughly 35% of the population) in 2017 . Such extensive dental care network could provide systematic comprehensive dental care for children enrolled in the BFP, especially if oral health were included in the BF health conditionality.
While some authors have argued against the BFP (because the mandatory conditionalities could potentially breach unconditional rights to citizenship), thus supporting Unconditional Cash Transfer (UCT) programs , several studies have shown important effects of the BFP on the health outcomes of Brazilian children [11, 12, 17,18,19,20,21]. Alves and Escorel (2013)  examined the social impact of BFP among low-income families and identified that the program contributed to families' social inclusion, especially in the economic and social dimensions. Nevertheless, it is known that BFP has limitations regarding work or political civil engagement of participants . Both programs (UCT and CCT) have advantages and limitations. Yet, it is unclear which one would be the best option for the Brazilian context. Thus, further research is needed to compare social, economic, and health outcomes of UCT and CCT programs in Brazilian context.
This study is not without limitations. First, our findings are based on a cross-sectional analysis, which prevented us to establish a causal pathway. However, our analysis provides a first insight into the association of BFP on five-year-old children’s oral health. This analysis is part of a larger research aiming to analyse this relationship longitudinally. Second, our analysis grouped individual recipients and non-recipients of BF. This grouping may underestimate the heterogeneity within each group. However, we were able to classify, in our final analysis, participants by length of enrolment in the BFP, a strategy that may remedy this limitation. Third, participants were included based on their self-reported enrolment in the BFP. However, it is known that 73% of residents in the northeastern region of Brazil with a monthly household income of less than 1 MW (R$788.00) are assisted by FHT in public primary health care units in the region . Thus, it was likely that we would have found our target population among patients assisted by FHT.