Caries Prevention by Fluoride Supplementation

Early studies of the preeruptive caries-preventive effects of F supplementation in children were often seriously deficient and thus yielded questionable results. Some of the highest caries reductions, around 80% over several years, were reported by American studies in the mid-1970s,^1,105 but flaws in these studies included self-selection into test and control groups or the absence of concurrent controls, high attrition rates, and nonblinded examiners. The association that practitioners have observed between conscientious use of F supplements and freedom from caries also cannot be taken as evidence of efficacy, because compliance with the F supplementation regimen is naturally higher among dentally aware people who also have other good oral health habits.

Evidence to favor a preeruptive benefit from F supplementation remains limited to retrospective analyses. Positive results have been reported retrospectively,^{5,32,40,41,60,108,166,167} but self-selection bias was evident in all of these studies. Other retrospective studies found no difference in caries experience between those children who reported using F supplements and those who did not.^{14,17,64,74,86,155}

Although the evidence for preeruptive benefits from F supplementation is weak, well-conducted randomized clinical trials using placebos and blinded examiners have shown that it can have posteruptive benefits in school-age children. Studies in which the supplements were chewed, swished, and swallowed under supervision have reported caries reductions of 20%-28% over 3-6 years.^43,50 Caries reductions of 81% were reported in a Glasgow study in which children from lower socioeconomic groups who were initially 5.5 years of age sucked a 1-mg F tablet or a placebo under supervision in schools every school day for 3 years.¹⁴⁸

In summary, F supplements have a posteruptive effect because they meet the goal of maintaining ambient F in the oral cavity. However, there is no good evidence to demonstrate a preeruptive benefit.

Dosing Schedules

To obtain F supplements in the United States and Canada, a prescription by a dentist or physician is required; both the American Dental Association (ADA) and the American Academy of Pediatrics (AAP) maintain schedules of recommended doses of F supplements. However, before 1979 the two schedules did not coincide: the AAP first recommended 0.5 mg/day⁶ for children under 2 years of age, whereas the ADA recommended 0.25 mg/day. The AAP altered its earlier recommendations⁷ in 1979 to bring them into line with those of the ADA and reaffirmed these new recommendations in 1986.⁸

As the dosing schedules for F supplements are revised periodically, the trend has been to make them ever more conservative. In response to the growing evidence that use of F supplements is a risk factor for fluorosis, the ADA revised its schedule in 1994 to reduce the amount of F ingested by young children, and the AAP accepted this schedule a year later.⁹ The current ADA-recommended schedule, based on the age of the child and the concentration of F in the water supply, is shown in Table 26-1. The thinking in Europe is similarly conservative: a European Community group recommended that a supplement of 0.5 mg F be used only for “at-risk” individuals from the age of 3 years onward. This group also declared that F supplementation had no place as a public health measure.³⁴

Fluorosis Risk From Fluoride Supplementation

Reduction of the early AAP recommendation of 0.5 mg/day for children under 2 years of age was overdue, for this dosage probably led to a considerable degree of fluorosis. One study in the Boston area that used the old AAP schedule, for example, was successful in terms of caries reduction, but 67% of the children developed very mild or mild fluorosis.² Excess F ingestion in infancy and early childhood through inappropriate prescription of F supplements is unfortunately more common than it should be. A 1980 national survey of pediatricians found that around 20% of them who practiced in fluoridated areas were prescribing F supplements for child patients who lived in the same communities,¹⁰⁴ a clearly inappropriate action that increases the risk of dental fluorosis. Things were no better 15 years later.¹²⁴ These studies have emphasized the need for continuing education of both physicians and dentists. If supplements are to be prescribed at all, they should certainly not be prescribed for patients who consume fluoridated water.

The major concern now associated with supplement use is that of dental fluorosis. Although fluorosis can develop at any preeruptive stage, late secretion and early maturation have been identified as the developmental times when dental enamel is especially sensitive to ingested F.^42,59,95 Although some studies found no association between supplement use and the development of fluorosis,^15,171 considerably more have reported a clear association.²,^39–41, ^{74,86,94,96,133,153,155,169,170} A series of excellent case-control studies has provided strong evidence for a cause-and-effect relation between use of F supplements and dental fluorosis,^121–123 and a comprehensive meta-analysis also concluded that use of F supplements is a risk factor for fluorosis.⁸³

The weight of evidence is that F supplements, when ingested prior to tooth eruption, are a risk factor for dental fluorosis in both fluoridated and nonfluoridated areas.

Appropriate Use of Fluoride Supplements

Although F supplements are reportedly used by some 16% of American children under 2 years of age,¹¹⁷ their continued prescription in North America needs to be thoughtfully reviewed. As often is the case in public health, their use requires trade-off decisions: F supplements have some beneficial impact on oral health, but there is also the hazard of fluorosis when they are used in an era of wide exposure to F. The reasons why prescription of F supplements for infants and young children needs to be considered carefully can be spelled out as follows:

In light of the advantages and disadvantages of F supplements in a time of widespread F exposure, calls have been made for a reevaluation of their use among young children.^14,82,132 They have a place when used to achieve a posteruptive effect in children older than 7 years, and it is likely that they would be useful in the growing population of older dentate people who are at risk of both coronal and root caries, although this issue has not yet been studied. At the very least, when F supplements are prescribed for infants and young children, parents or guardians should be informed of the fluorosis risk that accompanies the limited cariostatic benefits.

Prenatal Fluoride Supplementation

The question of whether to prescribe F supplements for an expectant woman to increase caries resistance in the offspring has been debated for years. In light of the discussion on dietary F supplements in general, it is not surprising that current views are that any enhanced resistance to caries will be only minor at best. The only prospective randomized trial of prenatal F supplementation found no significant difference in the caries experience of the offspring.¹⁰⁰ Therefore use of prenatal supplements is not recommended.

F can cross the placental barrier and enter the fetal circulation.^31,120 Fetal plasma F levels are correlated with maternal levels, although generally they are lower. F is taken up in the mineralizing tissues of the fetus; fetal enamel levels go up with an increase in maternal plasma F levels.¹²⁰ The most critical time for F uptake in enamel, as noted earlier, is the late secretion and early maturation phase. As a result, prenatal F exposure will have little effect, especially since mineralization of even primary teeth is not far advanced at birth.

Collectively the research evidence suggests that prenatal F administration cannot be supported. As long ago as 1966, the U.S. Food and Drug Administration banned advertisements which claimed that prenatal F administration would increase the caries resistance of offspring.¹⁶¹ No convincing research has emerged since then to change that picture, and hence the ban still pertains. Although there is nothing to suggest that prenatal F supplementation will harm either fetus or mother, no evidence exists to support claims of prenatal benefit.