Uptake of fluoride by human surface enamel from ammonium bifluoride and consequent reduction in the penetration in vitro by caries-like lesions

Comparative uptake of fluoride ion into enamel from various topical fluorides in vitro

BACKGROUND

There are many forms of topical fluoride available today, making the decision as to which is most effective to manage the immediate caries risk problem at hand, very difficult. The objective of this project was to determine the concentration and pattern of fluoride ion uptake into enamel from a variety of categories of topical fluoride recently available in Australia.

METHODS

Extracted, intact molar teeth were sectioned to provide six plates of smooth surface enamel. Windows of enamel 2 x 6 mm were exposed to a variety of topical fluorides for periods simulating those used in vivo. Following drying, the slates of enamel were exposed to 2 ml of 0.1 M HCl as a chemical biopsy agent for incremental periods of time. The concentrations of fluoride ion in the biopsy solutions for both test and background (control) slates of enamel were determined directly using a fluoride combination selective electrode in conjunction with a high impedance pH meter. Cumulative amounts of fluoride were determined for each topical fluoride agent.

RESULTS

The concentrations of fluoride ion taken up into enamel were generally proportional to those present in each agent. However, those from APF gel greatly exceeded the amounts taken up from NaF gel. Also, the concentrations taken up from some of the highly concentrated metal fluorides were surprisingly low. Prior etching of enamel increased uptake and prolonged application of APF gel provided no extra benefit.

CONCLUSIONS

Some topical fluorides, e.g., APF gel, provided a greatly increased uptake and to a greater depth than other self-application products. However, the frequency of its use should be considered with caution where patients have glass-based restorations.

Superficial fluoride levels and response to in-vitro caries-like lesion induction of enamel from Bristol (U.K.) and Birmingham (U.K.) human deciduous teeth

Surface enamel fluoride levels were measured in deciduous canine teeth from Bristol, with non-fluoridated water supplies, and Birmingham, with fluoridated water supplies. Three populations studied were from Bristol (teeth shed before 1960), Bristol (after 1975) and Birmingham (after 1975). Up to 75 micron from the enamel surface, fluoride concentrations of post-1975 Bristol and Birmingham teeth were, respectively, X 1.3 and 3.4 greater than those of pre-1960 Bristol teeth. The increase in the Bristol teeth is presumably due mainly to the increased use of fluoride-containing toothpastes, that in Birmingham to fluoridated water plus the use of fluoride toothpastes. No difference in the rates of penetration into enamel of acid-gel induced, caries-like lesions were found between the two Bristol populations; Birmingham teeth showed a reduction of 10 per cent in penetration rate. It is suggested that raised fluoride levels in surface enamel do not reduce solubility sufficiently to account, by themselves, for the recent nationwide marked reduction in caries in children. Possibly, the raising of plaque fluoride levels is a more important factor, affecting demineralization, remineralization and bacterial activity.