Fluoride distribution in sound and carious root tissues of human teeth

Proton probe analysis has been used to provide for the first time quantitative F concentration data in carious root tissues from subjects consuming water containing 1 ppm F. In small lesions at the neck of the tooth with minimal tissue loss the F concentration was significantly higher at the outer lesion edge than at the outer edge of adjacent sound root tissue. In one sample with high F values the lesion edge had 19,000 ppm F and the adjacent sound root surface 5,400 ppm F microg F/g apatite). In large lesions with extensive cavitation F was again concentrated in the outer edge of the lesion and was significantly higher (1,800-4,100 ppm) than in adjacent sound inner dentine (190-290 ppm). Fluoride concentrations varied markedly along the outer edge of both normal and carious root tissues. Fluoride increase at the lesion edge is not an effect of tissue shrinkage but probably a result of remineralisation events during caries. This additional F may be expected to increase tissue resistance to further acid attacks.

Fluoride uptake into the developing enamel and dentine of sheep incisors following daily ingestion of fluoridated milk or water

Incomplete availability of fluoride from fluoride compounds when added to milk is claimed to reduce the effectiveness of fluoridated milk in caries prevention in humans. This study attempts to add to the understanding of the systemic bioavailability of fluoride ingested with milk compared with water, by measuring its uptake into developing incisors of sheep. Twenty-five sheep, aged approximately 10 months, were randomised into five groups and farmed under identical conditions. They were dosed orally each day for 22 weeks with fluoride as sodium fluoride in water or bovine milk. The doses of fluoride were 0.5 or 0.2 mg/kg body weight in milk or water; a control group received no additional fluoride. Tooth length was labelled at the start of dosing with intramuscular injection of tetracycline. After sacrificing, incisors were removed, sectioned, and analysed for fluoride and calcium by proton microprobe scans from the enamel surface to the pulp. Concentrations of ionised fluoride in the milk samples were 30 percent and 20 percent respectively for added fluoride at concentrations of 300 and 750 micrograms/ml. The mean fluoride concentrations in surface enamel, deep enamel, and dentine were dependent on the daily fluoride dose and independent of the carrier (milk or water). The teeth of sheep receiving the higher fluoride dose (0.5 mg/kg body weight) had significantly higher fluoride than those receiving the lower fluoride dose (0.2 mg/kg body weight), which were significantly higher than in the teeth of the control sheep. It was concluded that the bioavailability of fluoride from sodium fluoride mixed with milk or water was similar following metabolism, despite 20-30 percent and 100 percent ionisation in milk and water respectively.

Fluoride content of the enamel and dentine of human premolars prior to and following the introduction of fluoridation in New Zealand

The fluoride content of the enamel and dentine of premolars was used as a determinant of the availability of ingested fluoride in New Zealand prior to and following the introduction of water fluoridation 40 years ago. Premolar teeth, which developed during the periods (PRE and POST respectively) under study, were selected from teeth extracted from 12 to 14-year-old children resident in different geographic areas in the country. The fluoride content, determined by multiple proton microprobe analyses, of surface enamel, deep enamel, and dentine, were for PRE teeth 440, 65 and 115, respectively. For POST teeth the mean values were significantly (p<0.001) higher, by 69, 29 and 102% respectively. The relevance of the change in fluoride content was assessed by comparison with published reports on the fluoride content of teeth developed in communities exposed to low (<0.5 ppm), optimal (1-2 ppm) and high (>3 ppm) naturally occurring fluoride levels in drinking water. The PRE teeth had a fluoride content associated with a low fluoride exposure and POST teeth with optimal fluoride exposure during tooth development. It was concluded that fluoride availability in New Zealand teeth had increased over the past 30 years but this increase is compatible with exposure of the community to optimal rather than excessive levels of ingested fluoride.

The distribution of fluoride in carious human enamel

The proton probe has been used to map F concentration changes in the enamel of 15 teeth showing clinical evidence of caries. Thin sections through the lesions were microradiographed and measurements made of the surface zone (radiodense) and body (radiolucent) areas. Each section was then scanned with a focused beam of 2.5 MeV protons, 2000 spot analyses being performed over areas up to 2 x 3 mm. F was determined by detecting gamma rays from a nuclear reaction and the data used to construct 3-D surface plots. The maximum F concentration in the lesion surface zone was extremely variable, ranging from 1750 to 21,700 ppm, and rarely occurred over the deepest part of the lesion. F levels were elevated in the lesion body but usually to a small extent only. A large increase in F throughout the lesion body was found in 3 lesions only, and was associated with a surface zone that was thin or of low x-ray density. Relatively small F increases in the lesion body were associated with either a thick, x-ray dense surface layer having a greatly increased F level (> 10,000 ppm) or, conversely, with a surface layer having a relatively small F increase. Since F uptake can be regarded as a "marker" of past remineralization events, this study shows that remineralization can and does occur in the body of natural enamel caries lesions, especially when the surface layer is thin or lost. Fluoride availability that encourages the formation of an extremely dense surface layer may result in under-achievement of this natural repair process in the lesion body.

Proton microprobe assessment of the distribution of fluoride in the enamel and dentine of developing central incisors of sheep and changes induced by daily fluoride supplements

Ten sheep were given 0.5 mg fluoride (F) and 10 sheep 0.2 mg F/kg body wt orally for periods of 1-6 months while 8 sheep received no additional F. One incisor from each sheep was sectioned longitudinally in the midline and, using the proton microprobe, multiple scans for calcium and F were made across the enamel and dentine. F was determined by proton-induced gamma-ray emission and calcium by X-ray emission. Tooth length and hence the stage of ameloblast activity for each of the 28 teeth at the start of the experiment was determined using a tetracycline marker. In addition, the stage of enamel development of the eight control teeth (no dietary F) at the time of their extraction was assessed from their macroscopic appearance. Continuous changes in F levels occurred in both enamel and dentine throughout tooth development and also in the mature enamel and associated dentine after ameloblast regression. All scans for all stages of tooth development and all F treatments showed a high F concentration at the enamel surface. Early in the secretory phase, a wide-based F peak occupied the entire width of the enamel with a similar F peak in the dentine. In the control teeth, no consistent increase in F concentration occurred at the enamel surface during later development. When F supplements were started early in the maturation phase an increase in F concentration only at the enamel surface was recorded. When F supplements were also given during the secretory phase, higher F concentrations were recorded not only at the enamel surface but also for the inner enamel and dentine plateau. These findings, based on a small number of sheep, indicate that further research is needed to clarify the method and control of F uptake and to determine the changes in these processes during the different stages of tooth development.

Proton probe and acid etching for determining fluoride profiles in porous porcine enamel

An acid-etch technique and a proton probe were used to obtain profiles of changes in fluoride concentrations across enamel of 24 normal and 24 fluorotic porcine teeth. Polished and unpolished sections were used for probe measurements, and blocks of enamel cut from tissue adjacent to the sections were used for acid etching. Additional blocks were etched with acid containing dye to study penetration of acid beyond the sampling sites. Probe-derived values were characterized by wide fluctuations. They were also higher than acid-etch values, and this difference was reduced but not eliminated by polishing the sections prior to scanning. Profiles obtained with the two methods followed a parallel course in fluorotic and normal enamel. Thus, errors due to chemical estimations of enamel depth with the etch technique were not demonstrated, although penetration of acid deep to the surface of the porous fluorotic enamel was observed. Further development of the precision of the probe method is required to optimize the unique advantage provided by the potential accuracy, speed of data collection, and spatial resolution of this method.

Supplementation of domestic sugar (sucrose) with fluoride. Effects on experimental dental caries, plaque pH, and fluoride levels in plaque and enamel

The minimum amount of fluoride which, when added to sucrose, will reduce caries in an intra-oral test was determined. Removable lower-arch appliances were worn by three adult subjects for 1 week, during which time plaque-covered enamel on one side was immersed in a 10 percent sucrose solution containing fluoride for 10 minutes four times per day. The effect of sucrose alone (control) was similarly determined on the other side of the appliance. Concentrations of 2 and 5 ppm F in sucrose solutions (20 and 50 ppm F dry weight) produced highly significant reductions in experimental caries of 43 and 44 percent respectively. A reduction in enamel dissolution due to re-precipitation of fluoride-rich apatite is probably largely responsible for the anti-caries effect. However, decreased plaque acid production may also play a role since the addition of 1 ppm F to 5 percent sugar reduced the plaque pH drop in artificial mouth experiments. Our results substantiate previous reports that fluoridation of sucrose to a level of 20 to 50 ppm F dry weight has potential benefits in caries prevention and may be useful when the F intake is otherwise low.

High resolution fluoride profiles of artificial in vitro lesions treated with fluoride dentifrices and mouthrinses during pH cycling conditions

A pH cycling model which incorporated a severe demineralization component was used to evaluate fluoride uptake and lesion progression for each of a NaF-based dentifrice, NaF-based mouthrinse and a monofluorophosphate (MFP)-based dentifrice. Simultaneous transverse fluoride and calcium profiles across the resulting artificial lesions were obtained using a proton microprobe technique with a resolution of approximately 10 microns. Longitudinal microhardness testing and proton microprobe calcium profiles were used to determine the extent of lesion progression (delta Z) with respect to untreated controls. Under the pH cycling conditions of the present study, the NaF dentifrice and mouthwash were observed to have a considerably higher uptake of fluoride in the lesion than the MFP dentifrice. Although the mineral content profiles of the lesions differed for treatments with each of the fluoride products, the differences were not significantly different in this model.

Uptake of fluorine in cortical and trabecular bone

Nuclear magnetic resonance techniques can measure the fluoride levels in bone of the finger after a patient has ingested F in the treatment of osteoporosis, but does uptake in cortical bone reflect uptake in the critical trabecular bone? Investigation has been made of the relative uptake of fluoride from drinking water into trabecular and cortical bone of the rat. For fine detail of the uptake of F into the femur and vertebra, microprobe techniques were used with a spatial resolution of 10 microns; for broader studies, treating the femur as representative of cortical bone and the vertebra as typical of trabecular bone, chemical techniques using spectroscopy and ion-selective electrodes were employed. The conclusion is that in the rat uptake of F by cortical bone is indicative of uptake by trabecular bone, and that therefore as a working hypothesis NMR measurement of F in the finger may be taken as reflecting uptake of F by trabecular bone.

Proton microprobe determination of fluorine profiles in the enamel and dentine of erupting incisors from sheep given low and high daily doses of fluoride

Developmental defects in incisors were induced by daily oral ingestion of sodium fluoride solutions. Teeth extracted at eruption from sheep that had been subjected to four different fluoride regimens--0.2 or 0.5 mg F/kg body weight daily for 6 months, 2 or 6 mg F/kg body weight daily for 21 days--were analysed for fluorine by gamma emission using a proton microprobe. Calcium and zinc profiles were also measured using proton-induced X-ray emission. Diffuse opacities, similar in appearance to mild human fluorosis, were produced by the first two regimens, whereas the last two produced hypoplastic lesions. Different distributions of fluoride were found in the unerupted enamel and dentine, and these patterns reflected variations in both the duration and concentration of the fluoride dose used to induce the fluorotic lesions.