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.     

Fluoride uptake from a composite restorative by enamel

The purpose of the study was to determine the in vitro uptake of fluoride by enamel adjacent to a fluoride-releasing composite restorative material containing 11.2 mg/g of fluoride. Blocks of human enamel were placed close to cured discs of the composite in synthetic saliva for periods of up to 24 hours. The fluoride content of successive acid-etch biopsy layers of the enamel blocks was determined by specific ion-electrode analysis, and atomic absorption analysis for calcium was used to determine the layer thickness. After 24 hours, a fluoride content of 5400 ppm was found for the outermost 10-micron layer of enamel. Based on the in vitro demonstration of appreciable fluoride uptake by adjacent enamel, the fluoride-releasing composite gives promise of having anticariogenic properties in vivo.     

不同钙摄入量对大鼠氟牙症发生的影响

目的 观察不同钙摄入量对大鼠氟牙症发生的影响。方法 分别用含低钙、中低（即标准钙）、高钙量的饲料喂养大鼠并使其摄取０．１ｍｏｌ／ＬＮａＦ水，同时设对照组。２个月后处死动物，分别用氟离子电极、显微放射照相、扫描电子显微镜检测各组动物上中切牙釉质平均氟含量及矿化程度和结构。结果 随摄入钙量的增加，大鼠上中切牙釉质中的氟含量减少，釉质平均吸光度值减低，釉质矿化程度增加结论牙齿发育期摄钙量越多，牙齿氟中毒     

In vitro fluoride uptake by bovine enamel from aesthetic restorative materials

Objectives.  The purposes of this in vitro study were to determine whether different types of fluoride-containing restoratives produce differing levels of fluoride uptake by bovine enamel, and to determine the effect of time on this uptake.
Methods.  Seven aesthetic restorative materials were evaluated. Forty bovine enamel slabs were prepared for each tested material, five of which were used to determine baseline fluoride concentrations. Each slab was attached to a disc of the tested material and suspended in synthetic saliva for up to 64 days. After removal, the specimens were acid etched with perchloric acid, and the dissolved enamel was analysed for fluoride and calcium. Fluoride was determined by direct potensiometric analysis, whereas the amount of calcium was evaluated by means of atomic absorption spectrophotometry.
Results.  Higher values of fluoride uptake, not significantly different, were recorded in the first two groups. A statistically significant difference was found in fluoride uptake between Fuji II LC and the three compomers in all test intervals. No significant differences were found in the amounts of fluoride uptake between the three compomers. The highest fluoride uptake from all compomers was recorded by F2000.
Conclusion.  Enamel acquired significant amounts of fluoride from all materials with variations during the test intervals.     

In vitro fluoride uptake by enamel and dentin. A comparative study of two varnishes

The uptake of fluoride in enamel and dentin after application of an experimental fluoride varnish has been studied and compared with the uptake from a commercially available varnish (Duraphat). Each varnish was applied to 10 extracted human cuspid teeth. Successive etchings with perchloric acid were carried out separately in enamel and root dentin to obtain samples at three different depths. The concentrations of fluoride and calcium in the samples were determined, and the fluoride uptake was calculated. The experimental varnish gave a significantly greater fluoride uptake at all three sample depths in both enamel and dentin.     

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.     

Effects of CO2 laser on fluoride uptake in enamel

OBJECTIVES: The objective of this study was to investigate the effects of CO(2) laser on fluoride uptake in the loosely- and firmly-bound forms in enamel. METHODS: Five human molars were cut into halves before being treated with 2.0% NaF topical gel. Each half had three windows on the enamel surface, including one control and two experimental windows irradiated by two laser therapies. One half of each tooth was treated with 1 M KOH solution to remove the loosely-bound fluoride (calcium fluoride). A tooth section was obtained from each window and the relative fluorine concentration was analyzed with Secondary Ion Mass Spectrometry (SIMS). The morphology of the enamel surfaces in the windows was examined using an Environmental Scanning Electron Microscope (ESEM). RESULTS: Significant laser-induced increases in the uptake of fluoride were revealed in both loosely-bound and firmly-bound apatitic fluoride, with both laser treatments (all p<0.001). Calcium fluoride-like deposits on the enamel surfaces receiving the combined laser-fluoride treatment were revealed by ESEM. CONCLUSIONS: The finding of this study substantiated the laser effect in increasing the fluoride uptake into enamel.     

Structural studies on calcium fluoride formation and uptake of fluoride in surface enamel in vitro.

The structural changes in human enamel during exposure to an acetate buffer, pH 4, containing 150 parts/10(6) fluoride have been studied using scanning electron microscopy and polarized light microscopy. After exposure for 2 h the enamel surface was covered by a fine-granular layer of calcium fluoride. The underlying enamel was highly eroded with an increased pore volume in the outer layer. Following an equilibration period of 3 months the uptake of fluoride in the apatite lattice had resulted in a highly mineralized, 100-micrometer-thick surface layer rich in fluoride covering a subsurface porous zone with an unchanged fluoride content. The deeply located, caries-like porous zone may have provided calcium and phosphate for saturation of the liquid.     

Structural studies on calcium fluoride formation and uptake of fluoride in surface enamel in vitro

abstract — The structural changes in human enamel during exposure to an acetate buffer, pH 4, containing 150 parts/10⁶ fluoride have been studied using scanning electron microscopy and polarized light microscopy. After exposure for 2 h the enamel surface was covered by a fine-granular layer of calcium fluoride. The underlying enamel was highly eroded with an increased pore volume in the outer layer. Following an equilibration period of 3 months the uptake of fluoride in the apatite lattice had resulted in a highly mineralized, 100-μm-thick surface layer rich in fluoride covering a subsurface porous zone with an unchanged fluoride content. The deeply located, caries-like porous zone may have provided calcium and phosphate for saturation of the liquid     

Effect of soluble calcium on fluoride uptake by enamel from sodium monofluorophosphate

The fluoride uptake by sound, acid-etched and artificial white spot lesions treated with sodium monofluorophosphate in dentifrice slurries, abrasive slurries, or calcium chloride solutions was determined. Fluoride uptake by sound enamel decreased in the presence of soluble calcium; however, uptake by etched and white spot enamel was greatly enhanced. The optimum Ca:MFP molar ratio was 0.5. Because fluorine-containing dentifrices probably inhibit dental caries by interaction with white spots or at the initial stage of acid-attack, the soluble calcium contained in saliva or a dentifrice might enhance the anti-caries effect of monofluorophosphate.     

Study of the fluoridated adhesive resin cement--fluoride release, fluoride uptake and acid resistance of tooth structures.

The objectives of this study, were to evaluate the fluoride release from fluoridate adhesive resin cement, fluoride uptake into surrounding tooth structures and the effect of their acid resistance. Several specimens were prepared using a plastic ring mould, from extracted human premolars, and prepared from enamel and dentin of the central area of the buccal surface of bovine teeth. The fluoride release rate of fluoridate adhesive resin cement (PN 200) per day was higher than other materials during the 7-day study period. Fluoride released and fluoride uptake by tooth structures was higher in the fluoridate adhesive resin cement. WDX analysis showed the fluoride concentration on dentin contact area was higher than that of enamel after 60 days of immersion in deionized water. The calcium release values were similar for enamel and dentin plates in the various test materials. The present findings indicated the important enhancement of tooth structure acid resistance by fluoridate material.     

The effect of time of exposure on fluoride uptake by human enamel from acidulated fluoride solutions in vitro.

Fluoride uptake on and in enamel during topical application of acidulated solutions was studied. The variables were different time intervals and different pH levels of the treatment solutions. The experiment was carried out with human enamel exposed to 2% NaF solutions, pH 3.5 and 5.5, for 30 sec, 60 sec, 5 min, and 60 min. The amounts of fluoride formed on (as calcium fluoride) and in (as fluorapatite) enamel were determined by chemical assessments, and scanning electron microscopy provided the visualization of the deposits on the surface. It could be demonstrated that the two pH levels caused deposition of large amounts of calcium fluoride and that almost twice as much was deposited at pH 3.5 as at 5.5. The amount of deposit increased rapidly with time of exposure in both situations compared with similar experiments with neutral fluoride solutions. Firmly bound fluoride was incorporated in the enamel only during the 60-min incubation.     

The in vitro uptake of fluoride by secretory and maturation stage bovine enamel

The objectives of this study were to determine the specific surface area of secretory-stage and of maturation-stage enamel, to compare the fluoride uptake by isolated enamel at these two stages on a surface-area basis, and to examine the effect of the organic matrix on the fluoride uptake by whole enamel. Fetal bovine secretory and maturation stage enamel samples were collected, and a portion of the enamel at each developmental stage was treated with hydrazine for removal of the organic matrix. The specific surface areas of the enamel mineral, as determined by the multi-point BET method, were 59.3 m2/g in the secretory stage and 37.9 m2/g in the maturation stage. Whole and deproteinated enamel samples were equilibrated in buffered solutions containing 10(-5) to 10(-3) mol/L fluoride, and the uptake was measured with a fluoride specific electrode. The results indicate that the in vitro fluoride uptake was controlled solely by the surface area of the apatitic mineral and that the organic matrix did not contribute to the fluoride uptake.     

In vitro study of cellular influence on 45Ca uptake in developing rat enamel.

The in vitro method for culture of molar teeth from eight-day-old rats, as reported in this study, appeared to sustain reasonably normal activity in the cells of the enamel organ and pulp through culture periods of four to eight hours. Inhibition of metabolic activity in the explants by addition of 5 mM iodoacetate or 2,4-dinitrophenol to the culture medium, or by heating at 70 C for 10 minutes, did not appear to affect the intensity or pattern of 45Ca uptake in the more advanced, rapidly mineralizing areas of the enamel. Neither did stripping of the enamel organ from the surface of the enamel have a demonstrable effect in those areas. However, metabolic inhibition with 2,4-dinitrophenol, heat killing or stripping of the enamel organ resulted in increased 45Ca uptake in newly formed enamel adjacent to the secreting ameloblasts. It is hypothesized that calcium flux into newly formed enamel matrix is controlled, in part, by movement of the calcium, which diffuses between the ameloblasts toward the enamel surface, away from the enamel through the ameloblasts.     

Enhanced fluoride uptake from mouthrinses

It has been shown in laboratory and animal studies that tooth enamel becomes considerably more reactive toward low levels of fluoride after receiving pre-treatment which forms dicalcium phosphate dihydrate (DCPD) in the enamel as an intermediate. This in vitro study was undertaken to determine the effect on human enamel fluoride uptake of incorporating DCPD-forming rinses into a conventional fluoride rinsing program. In one group, enamel samples received a one-minute rinse with 0.2% NaF each day for 20 days. Samples in the second group were treated identically, except that they were also given a one-minute DCPD-forming rinse prior to the first, sixth, eleventh, and sixteenth fluoride rinses. At the end of the rinsing program, all samples were washed in 1 M KOH to remove labile fluorides. The enamel biopsy data showed that the fluoride uptake resulting from 0.2% NaF alone was not statistically significant, whereas uptake produced by the DCPD-forming plus NaF rinses was significant. The results suggest that the DCPD-forming rinse may improve the efficacy of fluoride rinse programs.     

Increased fluoride uptake and acid resistance by CO2 laser-irradiation through topically applied fluoride on human enamel in vitro

OBJECTIVES: The aim of the current in vitro study was to evaluate the effect of CO(2)-laser treatment immediately after applying amine fluoride solution on enamel. It was hypothesized that such a treatment would increase enamel fluoride uptake, and reduce dissolution rate and thermal surface alterations. METHODS: Fluoride uptake was determined in 40 human enamel sections randomly assigned to four groups (n=10), which were either left untreated (1), exposed to a 1% amine fluoride solution for 15s without irradiation (2), irradiated for 15s with a continuous-wave carbon dioxide laser (3), or laser-treated for 15s through the amine fluoride solution applied immediately beforehand (4). Fluoride uptake was determined with an ion selective electrode after acid dissolution of the specimens (surface and subsurface layers). For the determination of acid resistance, another 40 enamel sections were treated according to the above protocol. Acid resistance was determined in surface and subsurface layers by measuring eluted calcium upon 3% lactic acid exposure with atomic absorption spectrometry. Enamel surface alterations after laser irradiation were monitored using scanning electron microscopy. RESULTS: Laser irradiation through the fluoride solution led to significantly higher fluoride contents in the surface enamel layer compared to fluoride treatment alone or laser treatment alone (p=0.002). Laser treatment with or without fluoride resulted in an increased acid resistance of enamel specimens. Fewer surface alterations were observed upon SEM examination of specimens irradiated through the amine fluoride solution compared to counterparts treated with laser only. CONCLUSIONS: CO(2) laser light application through an amine fluoride solution may be useful and effective in the prevention of caries.     

Enamel dissolution and fluoride uptake from sugar solutions

Solubility studies and fluoride uptake by enamel powder in xylitol-buffered solutions versus sucrose- and glucose-buffered solutions were carried out. The studies were done at a pH range of 4-8. The enamel solubility in the xylitol media was similar to the enamel solubility in the other sugar solutions--increasing with a decreasing pH. The solubility of enamel in the buffered sugar solutions was significantly lower as compared to the solubility in the sugar-free buffered solutions--up to the pH of 6. At the pH values of 7 and 8 the amounts of solubility were similar for the experimental and control solutions. No significant differences were found in the fluoride uptake by the enamel powder from the fluoride-containing sugar solutions at the pH values of 6 and 7.5 respectively. The results point to the conclusion that the xylitol does not differ from sucrose and glucose in its effect on enamel powder solubility and the uptake of fluoride ions by enamel.     

Fluoride uptake from restorative dental materials by human enamel.

The purpose of the study was to determine the uptake in vitro of fluoride from restorative materials by tooth enamel and whether prior etching of the enamel causes a change of uptake. The outermost layer of the labial surface of extracted canines was removed by grinding and the enamel was covered with five different fluoride-containing materials; a silicate, a composite resin, an amalgam, a silicophosphate, and a polycarboxylate luting cement. The material was either removed immediately or after storing the tooth in distilled water. The fluoride content was determined using a sensitive physical method based on the 19F (p,alpha gamma) 16 O reaction. In addition, the fluoride content of enamel after etching for different periods of time and of etched enamel which had been in contact with silicate cement was determined. The mean fluoride content of uncovered interior enamel was 226 parts/10(6). All materials, except the composite, increased clearly the fluoride content of the underlyaing enamal. Etching of interior enamel also increased the fluoride values. No difference could be shown in fluoride uptake from silicate and composite resin between etched and unetched enamel.     

Fluoride uptake in bovine enamel and dentin from a fluoride-releasing composite resin

To determine the fluoride uptake in enamel and dentin, a fluoridating composite resin was fixed at a 100-microns distance from bovine enamel and dentin for 2 weeks. The results revealed a substantial increase in the level of fluoride in both enamel and dentin. This model investigation showed that the fluoride released by the composite resin was effectively taken up by the surrounding tissues. The fluoride released from the composite resin and the subsequent uptake by the tissues would be expected to protect against secondary caries.     

Effects of an acidic calcium phosphate solution and the intraoral fluoride-releasing device on dental caries and fluoride uptake in rats

This investigation comprised two studies evaluating the effects of an acidic calcium phosphate solution (CPS) on fluoride uptake in the enamel, glycolysis of dental plaque, the incidence of dental caries and urinary fluoride concentrations of rats wearing an intraoral fluoride-releasing device (IFRD). In the first study, CPS-fluoride treatment preceded the cariogenic challenge. In the second study, the cariogenic challenge preceded the treatments. In the first study, CPS treatments increased the ability of enamel to bind fluoride. However, the enamel-bound fluoride exerted a negligible effect on plaque glycolysis as measured by the pH decrease after sucrose challenge. In the second study CPS augmented the caries inhibition for both the sulcal-morsal and buccal-lingual surfaces. In both studies the IFRD significantly restricted the development of carious enamel on the sulcal-morsal surfaces and caused elevated concentrations of fluoride in the urine independent of CPS treatments.