The method of duplicating food samples (double plate approach) for determination of daily fluoride intake has the advantage of greater accuracy than indirect calculations of intake using diets and table values of the fluoride content in the most frequent components of food and beverages in a child's diet. When tracing fluoride sources in a child's diet, assuming that up to 80% of fluoride in the diet of preschool children comes from drinks [7, 14], the authors focused their attention on the fluoride content of bottled water as public water supplies in the centres concerned, where the samples of child's diet were collected, contained 0.08-0.15 ppm fluoride and the provision of bottled water for children is very popular. The bottled table mineral water available locally was richer in fluoride (> 0.7 ppm) and is obligatorily labelled as "not suitable for children up to 7 years". Bottled mineral water is given to children irregularly and rarely [14, 15]. In an attempt to collect data on the preference for individual brands of bottled water and other beverages provided by families to preschool children, the authors failed to obtain any generalizable results due to both the broad range and the frequent changes of the brands of bottled water that the children consumed and individual and changing habits among families.
The double plate approach therefore provides better evidence for alimentary fluoride intake than the "basket" approach. Even so, the results of this study should be interpreted with caution as they depended on how thoroughly and accurately the parents duplicated the food and drinks that their child actually received. Another limitation of this study is that the duplicate plate method was conducted for only 24 hours, both at baseline and after six months. Recent studies have suggested that it should be done at least for two consecutive days [24–26] in order to provide more accurate estimates. An attempt was made to reduce that limitation of the daily fluoride intake estimates by collecting food samples on days when their parents were off work and at home.
In the results, the values of daily fluoride intake, in proportion to the child's weight were below the previously recognized "optimal" intake of 0.05 to 0.07 [3, 7, 9], and reached the lower limit of this range only in their maximum values. It should also be taken into account that the measurements and calculations, did not allow for the alimentary intake of fluoride from swallowed fluoridated toothpaste. In few published studies, this part of the daily fluoride intake was measured and added to fluoride intake from food sources [3, 21–23].
The changes in measured values of fluoride intake and other calculations that were found, when comparing the two measurements with a 6-month interval, were not significant (p < 0.190). The average proportion of fluoride intake from liquid food components was 92.2% (at baseline 95.8% and six months later 86.6%). This result is consistent with results of other studies [20, 22].
Children aged 4 to 5 years accidentally swallow 30 to 40% of the tooth paste when cleaning teeth [22, 27]. However the estimate of alimentary fluoride intake from toothpaste in preschool children must be treated with caution as it is highly variable among children [19, 28] due to the amount of toothpaste used, its flavour [29] and other factors.
In this study, parents were instructed that the amount of toothpaste, the children were to use for brushing teeth should be the size of a small pea.
When adding the values of unwanted fluoride intake from the toothpaste shown in the age-matched children in the literature [3, 20–23] (0.17-1.21 mg per day) it is possible to estimate that fluoride intake on average would reach the lower limit of the safe range (0.05 to 0.07 mg/kg bw/day). This range is supported by previous studies [3–5]. However, for some children this range could be exceeded.
Given that at present, the topical effect of fluoride in the mouth, whether from toothpaste, rinses or other application forms is considered more effective than fluoride intake through the alimentary route and it is moreover associated with the removal of plaque as cariogenic agent, it is useful to maintain alimentary fluoride intake in preschool children below the safe range of daily intake. Furthermore, it should be strictly individualized. If fluoride supplements (tablets) are considered their doses should take the other intakes of fluoride into consideration [30, 31]. In addition, child's food and beverages always contain a certain amount of fluoride, therefore it is necessary to monitor daily intake regularly.
Thus the issue of the alimentary intake of fluoride has two facets relating to its possible contribution to the caries preventive effect of topically applied fluorides and the risk, to enamel maturation. During the period when the enamel of permanent teeth is maturing it is vulnerable even to small over-doses of fluoride. Assuming that alimentary fluoride comes mainly from water or drinks and that part of the absorbed fluoride enters the oral environment via saliva, the intake of drinks occurs several times a day and thus the absorbed fluoride can exert some adjunct effect to topically applied fluorides. On the other hand it has to be born in mind that the apparent advantage of the frequent intake of drinks can contribute to the harmful effect of fluoride over-doses on maturing enamel.
The dynamics of fluoride absorption, whether coming from food or swallowed toothpaste depends on the stomach contents, pH and some ions such as calcium and can have a major impact upon the relative risk of developing fluorosis. The enamel maturation can be endangered both by the long-lasting over-intake of fluoride or, to some extent, by the steep peaks of plasma fluoride due to its quick absorption from empty stomach [1, 30].
In summary, this study has demonstrated that alimentary fluoride intake in older preschool children cannot compromise the enamel development of anterior permanent teeth. Even though the drinking pattern of children can differ among families this pattern can be stable within families. Thus it is important to consider the whole dentition when assessing risk benefit and any relative changes to fluoride dose over the whole period of tooth development.
Irrespective of the generally accepted major impact of topical fluoride in caries prevention its systemic intake in preschool children can contribute both to its benefit and to the risk of developing fluorosis. One of the main issues of dental public health is to minimize the risk of fluoride overdose by the fluoride and diet counselling both in individual and community levels.