T.G. Deaton

Effect of an Acute Maternal Fluoride Dose on Fetal Plasma Fluoride Levels and Enamel Fluoride Uptake in Guinea Pigs

We conducted this study to measure maternal plasma, fetal plasma, and fetal enamel fluoride concentrations for four hours following an oral F dose to near-term pregnant guinea pigs. We placed female guinea pigs on de-ionized (Group I) or 3-ppm-F (Group II) drinking water prior to breeding and during gestation. On the 57th day of gestation, we administered a maternal dose of NaF solution (0.6 mg Flkg) by stomach tube. We collected samples of maternal plasma, fetal plasma, and fetal enamel at baseline, at 15 and 30 min, and at one, two, and four h after administration of the dose. We assayed samples for F using a modification of the micro-diffusion and ion-specific electrode method. Group I mean baseline F values were: maternal plasma, 0.016; fetal plasma, 0.002 ; and fetal enamel, 7. 0 ppm. Group II mean values were: 0.055, 0.004, and 19.0 ppm. After the maternal fluoride dose, the mean maternal plasma [F] rose sharply for 30 to 60 min and declined to about 50% of peak values by four h. Fetal plasma [F] changed less in absolute values, but similarly to maternal changes relative to baseline. Fetal enamel mean [F] rose more in Group II than in Group I. Baseline F status had an important effect on F uptake in fetal enamel following an actue maternal fluoride dose.

Role of the Enamel Organ in Limiting Fluoride Uptake During the Maturation Phase of Enamel Development

Autoradiographs of molar teeth from 15-day-old rats that had been injected with 18F showed no tracer uptake in the late-mineralizing enamel. Autoradiographic and quantitative in vitro experiments indicated that the enamel organ limited fluoride uptake during the maturation phase of enamel formation.

Diffusion of Fluoride Through the Rat Enamel Organ in vitro

This study investigated the diffusion of fluoride through the enamel organ in vitro. The rat molar explants used were entirely in the secretory stage or predominantly in the maturation stage of enamel formation. The removal of the enamel organ or metabolic inhibition with iodoacetate caused significant increases in enamel fluoride uptake at both stages of enamel formation. Inhibition with dinitrophenol caused a significant increase only in the maturation phase. Uptake of fluoride in enamel was related to the fluoride concentration in the medium, except in the maturation stage explants, where increasing the medium fluoride concentration from 0.05 ppm to 0.08 ppm did not significantly increase fluoride uptake at any of the three observation times. The findings indicate that the enamel organ exists as a diffusion-limiting membrane to the movement of fluoride from the extracellular fluid compartment to the developing enamel.

The Short-term Uptake and Retention of Fluoride in Developing Enamel and Bone

Eight- and 12-day-old rat pups were injected intraperitoneally with fluoride. Plasma, molar enamel, and bone samples were collected at observation times up to six hr after injection. In a second series, adult rats maintained for six weeks on water containing 5 ppm F were injected with fluoride. Plasma, incisor enamel, and bone samples were collected at the same observation times as those used in the first series. Fluoride assays were conducted by means of the microdiffusion, ion-selective-electrode method. In the suckling rats, plasma [F] levels peaked at 15 min and returned nearly to baseline in one hr. Significant increases in the [F] of developing enamel and bone were observed. No significant decline from the peak [F] seen in the hard tissues was observed over the six-hour period. Similar results were seen in the developing enamel of the adult rats. The data gave no evidence of a short-term reversible component of fluoride uptake in developing enamel. Apparent increases in F uptake in enamel and bone beyond peak plasma values suggest the presence of a diffusion-limiting membrane for fluoride from the extracellular fluids into the mineralizing matrix.

Enamel Fluoride in Nursing Rats with Mothers Drinking Water with High Fluoride Concentrations

The purpose of this study was to determine the F levels in plasma and molar enamel from rat pups whose mothers had received various levels of F during pregnancy and/or lactation. Rats were started on water containing 0 (Group I), 50 (Group II), or 100 (Group III) ppm F at the beginning of pregnancy or on the day of delivery. The mothers and pups were killed 13 days after delivery, and plasma F levels, milk Flevels, and pup molar enamel F levels were determined. The mean maternal plasma F concentrations were 0.02 ± 0.005 ppm in Group I, 0.10 ± 0.031 ppm in Group II, and 0.21 ± 0.057 ppm in Group III. The milk F values were about twice as high as the respective plasma concentrations. The plasma F concentration in control pups was 0.003 ± 0.0002 ppm, and there was a rise to 0.006 ± 0.0002 ppm in Group III. Enamel F concentrations were 0.62 ± 0.13 ppm, 4.72 ± 0.79 ppm, and 8.80 ± 1.74 ppm, respectively. The plasma and enamel F values obtained from pups were not significantly different between the pre-natal/post-natal, and the post-natal-only groups. It was concluded that: (1) fluoride levels in the plasma and enamel of control rat pups were much lower than those found in adult rats, (2) such values could be increased only slightly when high doses of F were given to the mother, and (3) unlike values reported for other species, rat milk fluoride concentrations were higher than the respective plasma values.

The Effects of Parathyroid Hormone, Calcitonin, and Vitamin D Metabolites on Calcium Transport in the Secretory Rat Enamel Organ

The effects of parathyroid hormone (PTH), calcitonin (CT), 1,25(OH)2D3, and 24,25(OH) 2D3 on calcium transport through the secretory stage enamel organ were studied on developing rat molars in vitro. 24,25(OH)2D 3 increased 45Ca uptake by the explants. 24,25(OH)2 D3 plus PTH further enhanced 45Ca uptake and resulted in an increase in net calcium uptake by the developing enamel.

Problems Associated with Estimation of Net Calcium Uptake During Enamel Formation Using 45Ca

45Ca uptake in mineralizing tissues may occur by net Ca uptake or by isotopic exchange. It is rarely possible to differentiate between these effects, making interpretation of the findings difficult. Unfortunately, this problem is not often considered, and 45Ca uptake is usually regarded as representative of only net calcium uptake. The study reported here was undertaken to estimate the extent to which 45Ca uptake in mineralizing enamel is due to net Ca deposition or to isotopic exchange, and to consider the implications. The enamel surfaces of the lower incisors of adult rats were notched at the gingival line, and the eruption distance over 16 hours was measured. This distance was used to establish the position of a 0.3-mm-wide increment of enamel at the beginning and end of the 16-hour period, during which it passed through the early-maturation stage of enamel formation. The rate of Ca uptake was determined by chemical assay. Other rats were injected with 45Ca, mean plasma specific activity values for the experimental period determined, and the rate of Ca uptake through the same area of enamel formation was estimated. The estimates were from two- to nearly ten-fold greater than those established by chemical assay, indicating that from 50 to 90% of the 45Ca uptake occurred by isotopic exchange. 45Ca uptake may indicate more about the labile state of Ca in mineralizing enamel than about the rate of mineral deposition.

Immunohistochemical Localization of Signal Transduction Pathways During Amelogenesis: an Initial Exploration

This study was undertaken to map signal transduction pathway (STP) components uniquely associated with the four major receptor groups and their related STPs in association with the events involved in amelogenesis in the rat. Whole-head, freeze-dried sagittal sections were obtained at the level of the maxillary first molars and picked up on transparent adhesive tape. The sections were not decalcified or fixed, providing optimum conditions for immunohistochemical (IHC) localization. Antibodies to pathway components Gsa, Giα, Gqα, Sos-1, Grb-2, p125Fak, Jak2, and Vav were localized. The respective patterns of localization indicate that the G a-linked, the receptor tyrosine kinase-initiated, and the integrin receptor-initiated pathways are involved in the proliferating pre-ameloblast cells. In the differentiating and differentiated ameloblasts, the Gsa-linked cAMP pathway is involved, apparently reading a factor(s) released by the dentin matrix. The G a-linked, the receptor tyrosine kinase-initiated, the integrin receptor-initiated, and the cytokine receptor-initiated pathways are also up-regulated in the proximal ends of the ameloblasts. These observations indicate that all four of the major receptor groups are involved in amelogenesis and that the role of classes of ligands not previously implicated in enamel formation must now be considered. It seems that the cells of the enamel organ respond to the appearance and disappearance of autocrine and paracrine growth factors, but they also up-regulate specific STPs to enable them to respond to circulating hormones and growth factors whose concentrations in the extracellular fluids remain relatively constant.

The Ca, Pi, F, and Proline Content of Developing Bovine Enamel Under GBHA-stained and Unstained Bands

The surface enamel of fetal bovine teeth was stained with GBHA to indicate the position of bands of smooth-ended and ruffle-ended ameloblasts relative to the developing enamel. The boundaries of the bands were scored, under a dissecting microscope, and the bulk enamel under each band was collected. The enamel samples were assayed for Ca, Pi, F, and proline. The amount of Ca and P i in the enamel increased in successive bands and seemed unrelated to the overlying ameloblast cell type. The loss of proline seemed unrelated to cell type. The fluoride content of enamel increased by approximately 50% in the first stained band immediately adjacent to the secretory zone. The F level returned to secretory values in the succeeding unstained band. Thus, only changes in the F level of developing enamel appeared to be related to GBHA staining patterns.

Fluoride Uptake and Retention at Various Stages of Rat Molar Enamel Development

Suckling rat pups were given intraperitoneal fluoride injections at selected ages so that we could study fluoride uptake in the enamel of the maxillary first molar at various stages of enamel development. Plasma fluoride levels in six-day-old and 11-day-old pups were monitored following the intraperitoneal injection of fluoride. The findings indicate that: (1) fluoride was more easily taken up and retained during the early stages of enamel formation, but fluoride uptake can occur during all stages of enamel formation; (2) when injections were started early in enamel formation, more fluoride was contained in the enamel of the maxillary first molar at 13 days of age; and (3) the same dose of fluoride per gram body weight resulted in greater exposure to elevated plasma fluoride levels in six-day-old pups than in 11-day-old pups.