In vivo uptake of fluoride by surface enamel of cleaned and plaque-covered teeth.

Utilizing a newly developed biopsy method, the F uptake in the outer 3 mum of enamel from a single topical application of neutral NaF or amine F solution was tested on cleaned and plaque-covered premolars in 12- to 14-year-old children. Cleaned teeth treated with neutral NaF acquired only insignificant amounts of F. The presence of plaque seemed to enhance the deposition of F in surface enamel. The findings were discussed in relation to the possible mechanisms of action of topically applied fluorides. Topical treatments with amine F increased surface enamel F considerably more than the NaF. The F uptake was similar in cleaned and plaque-covered teeth. It was suggested that the usually performed plaque-removing procedures prior to topical F applications are superfluous and may even be disadvantageous.     

In vitro studies of fluoride uptake in human enamel

abstract — In a closed agitated system, which included an enamel surface and a continuously magnetically stirred buffer at pH 4.0, 5.0, 6.0 and 7.0, the reaction (Ca₅(PO₄)₃OH)_S+F−→(Ca₅(PC₄)₃F)_S+OH− was investigated kinetically by measuring the fluoride ion activity. The buffers initially contained 1 part/10⁶ fluoride. Six experiments were carried out at each pH. It was found that the reaction followed first order kinetics. The rate of the reaction was very slow at pH 7.0, but increased considerably when pH was lowered, and at pH 4.0 it was 100 times that at pH 7.0. In supplemental experiments it was found that reducing the area of the enamel surface reduced the rate of the reaction. The results are discussed with reference to equilibrium conditions in water-apatite systems, assuming that equilibrium cannot be attained when hydroxyapatite is dissolving and fluorapatite is being formed. The findings are considered to explain the increased amount of fluoride present in the residual apatite in developing carious lesions, and may initiate new principles in the local treatment of teeth with fluorides.     

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     

A field biopsy method for fluoride determinations in human surface enamel

ABSTRACT An enamel biopsy method was developed that is especially intended for use under primitive clinical conditions in field studies. Three successive enamel layers, each of 1 μm or less, were etched off the same delimited area of 3 mm² by means of perchloric acid, using a microsampler with disposable tips. The biopsy technique was applicable to the vestibular surface of almost all teeth, causing no perceptible damage to the enamel surface. Based on cumulated data from the successive enamel layers, curves were drawn from which F levels at various depths in the outer 3 μn of the enamel could be interpolated. F levels in surface enamel of maxillary first premolars in 40 12–13-year-old children in a locale with 0.5 mg F/l in the drinking water were found to be 3,800, 2,400 and 2,000 parts/10⁶ in three successive enamel layers of 0.6, 1.0 and 1.1 μm, respectively, demonstrating a decrease in F concentration of about 1,800 parts/10⁶ within this depth interval. Identical F concentrations were found in bilateral premolars.     

Calcium fluoride formation on enamel and its influence on uptake of fluoride in the apatitic lattice

abstract – Human dental enamel was exposed to a pH 4 buffer containing 150 parts /10⁶ fluoride. It was found that due to the arising degrees of saturation with respect to calcium fluoride and appetites, surface enamel dissolved coincident with a formation of calcium fluoride. The calcium fluoride redissolved while it kept the liquid saturated with respect to tiiis salt. During this second period, fluorapatite was formed while hydroxyapatite dissolved. Finally, all calcium Ouoride was dissolved and the unreacted fluoride was taken up in the apatidc lattice. The results are discussed with reference to the conditions of the oral cavity and enamel solubility experiments.     

Stability of fluoride levels in surface layer of normal enamel during a 21-month fluoride mouthrinsing program

A 21-month trial of the caries-preventive effect of a 0.2% NaF mouthrinse included monitoring changes in the concentration of F in normal enamel. Subsamples of 25 children were randomly selected from groups receiving either normal dental treatment (Control group); additional fortnightly professional prophylaxes (Test group); or prophylaxes plus fortnightly 2-min fluoride rinses (Test + F group). At the start of the trial the sound labial surface of tooth 24 (occasionally 23 or 22) was etched with 2 N HCL and the etchant analysed for F, Ca and phosphate. The contralateral tooth was sampled at the end of the trial. The caries increments (DFS) for the three groups over 21 months were Control, 2.88; Test, 2.51 and Test + F, 1.77, the last being significantly less than the others (P<0.05). The average sound enamel surface F concentrations were similar for the three groups at the start and the end of the trial. F parameter calculations showed that all differences were non-significant. Thus this factor could not explain the reduced caries increment due to F mouthrinsing. F biopsies for the purpose of predicting likely-clinical effectiveness of neutral 0.2% NaF mouthrinsing will find little application in public health dentistry.     

Fluoride uptake from restorative dental materials by human enamel

abstract – The purpose of the study was to determine the uptake in vitro of fluoride from restorative materials by tooth ename1 and whether prior etching of the ename1 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, αy) ¹⁶O 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 ename1 was 226 parts/10⁶. All materials, except the composite, increased clearly the fluoride content of the underlying enamel. 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 contents of surface enamel in high- and low-fluoride areas studied with a sensitive physical method

abstract — Fluoride content was measured with a sensitive physical method in the enamel of the four smooth surfaces of 12 primary and 12 permanent teeth from areas with drinking water of high- and low-fluoride content. In the high-fluoride area (1.9 parts/10⁶ in drinking water) the average fluoride content of the surface enamel was 1,826 parts/10⁶ and in the low-fluoride area (0.05 parts/10⁶. Permanent teeth contained about 20% more fluoride than primary teeth. In two children in the low-fluoride area the fluoride content of the enamel was exceptionally high in the vestibular surface, presumably owing to local application of fluorides.     

Fluoride concentrations of the surface enamel of children living in an optimally fluoridated community

Abstract – The present study was undertaken in a community, where the tap water has been optimally fluoridated since 1959 (1.0–1.2 ppm). The material consisted of 92 children and adolescents including 30 sibling-couples. The mean age of the participants was 11.8 ± 2.45 (SD) yr. 56 children had consumed fluoridated water all their life, the others only a part of the developmental period of their permanent dentition. Enamel biopsies were taken from 212 permanent teeth and 33 primary teeth by etching the tooth surface for 6 or 30 s. The etch depth was calculated from the mean of dissolved enamel calcium and phosporus. The fluoride concentration in the outermost enamel was almost similar in the teeth of the lifelong residents and the rest of the children. Towards the deeper layers the amount of fluoride decreases depending on its availablity during the development of the enamel. There was no striking similarity neither in the fluoride concentration nor in the amount of dissolved enamel between the siblings when compared with the other children. The posteruptive incorporation of fluoride takes place only on the outermost surface of the enamel. The results suggest that in subsurface layers the fluoride exposure during tooth formation is the dominating determinant of enamel fluoride concentration.     

Morphologic changes in the rat enamel organ following a single intraperitoneal injection of sodium fluoride

abstract — Enamel organs in developing teeth of young rats were studied after single intra peritoneal injections of a high dose of sodium fluoride (60 mg NaF/kg body wt.). The study employed primarily light microscopy, but electron microscopy was used to clarify some of the light microscopic findings. The pathogenesis of the fluoride-induced changes was followed during 72 h. Cellular changes were consistently found in the molars, but were never seen in the incisors. In the maxillary molars, ameloblastic injury was most commonly seen on the mesial surfaces of the cusps. One hour after injection, the most prominent findings were swollen mitochondria in the secretory ameloblasts and cleft formations between the ameloblasts and the enamel matrix. The clefts were filled with a stippled material. Some of the clefts gradually expanded to cystic cavities. The stippled material began to calcify after 24 h and formed small, darkly stained globules. After 72 h dearranged ameloblasts were found as islands intermingled with calcified rounded structures in the stellate reticulum. In stratum intermedium numerous atypic autophagic vacuoles appeared 2 h after injection. No light microscopic changes were observed in the postsecretory ameloblasts.     

Fluoride reactions with dental enamel following different forms of fluoride supply

abstract – The reactions with dental enamel of NaF as tablets dissolved in different beverages or supplied with NaCl, simulating domestic salt fluoridation, were studied in tests with enamel surfaces and enamel powder. It was confirmed that powdered enamel can react quite differently from enamel surfaces under certain conditions. Enamel surfaces took up much more fluoride (F) from orange juice than from water or milk, and neither the low pH nor the citrate content of the juice increased the formation of unstable CaF₂ in the enamel, as judged from a KOH leaching test. The F uptake by enamel surfaces from 0.25 mM NaF in 175 mM NaCl, corresponding to a dish prepared with salt containing 500 parts/10⁶ F, was about 80% greater than from the same NaF concentration in water. This NaCl concentration did not increase the formation of CaF₂ in the enamel, as judged from the KOH test, while 350 mM NaCl caused a moderate increase. The investigations support the administration of NaF tablets with orange juice and the plans for domestic salt fluoridation.     

Uptake and retention of fluoride by intact enamel in vivo after application of neutral sodium fluoride

abstract – The uptake and retention of fluoride in surface enamel in vivo after a single topical application of a neutral 2 % NaF solution was studied on the basis of 2–3 μm thick enamel biopsies from maxillary central incisors in adults and children. The biopsy technique included delimiting of the sampling area by means of abrasive-resistant, adhesive tape, punched with perforations of known sizes admitting of two biopsies on different places on the same tooth surface. This method made it possible to calculate the depth of each biopsy and to perform the comparative studies with intradental control. The F uptake was estimated by comparing F concentrations in biopsies taken before and 1 week after topical treatment. In teeth of 10- to 11-year-old children the F concentration increased 259 ± 393 parts/10⁶, which is statistically significant ( P < 0.002). The mean uptake in teeth of adults, 22–27 years of age, was 179 ± 401 parts/10⁶ which did not exhibit statistical significance ( P > 0.10). The F concentrations in biopsies taken 1 week and 8 weeks after treatment from teeth in children were almost identical, indicating that the acquired F is firmly fixed in the enamel for 2 months or longer.     

Fluoride and enamel solubility

abstract — The present paper deals with the solubility of enamel and the influence of fluoride on the degree of saturation with respect to hydroxyapatite. Enamel surfaces were exposed to 8 ml buffer at various pH values. The buffers were analyzed at suitable intervals for calcium, phosphate, fluoride and pH and the ionic activity products for fluorapatite, hydroxyapatite, calcium fluoride, brushite and octacalcium phosphate were calculated. It was found that the buffers were supersaturated with respect to fluorapatite and remained unsaturated with respect to the other salts investigated. Under these conditions fluorapatite was formed while hydroxyapatite dissolved, the system thus tending toward equilibrium at which the liquid phase is saturated concurrently with respect to both apatites. It is suggested that at least a part of the solubility reducing effect of fluoride is due to fluoride rendering the liquid phase supersaturated with respect to fluorapatite. This results in formation of fluorapatite, rendering the liquid phase unsaturated with respect to hydroxyapatite.     

Enamel microhardness and fluoride uptake underneath fermenting and non-fermenting artificial plaque

abstract – Washed cells of Streptococcus sanguis were used to form artificial plaque on the surface of bovine enamel and incubated underneath buffer solutions, initial pH 6, for 36 h at 37°C. The decrease in the microhardness of the enamel surface under fermenting "plaque" could be prevented with fluoride. Enamel under a fermenting "plaque" took up significantly more (P < 0.01) fluoride than enamel under a non-fermenting "plaque" (initial F⁻ in buffer: 10 parts/10⁶). The) artificial plaque did not accumulate fluoride. Within fermenting "plaques", the pH decreased significantly more without fluoride ( P <0.01) than with fluoride. Fluoride combined with sucrose more than negated the softening of the enamel caused by sucrose fermentation, i.e. it increased the hardness above the original values. The diffusion of fluoride through the fermenting artificial plaque was more rapid than through a non-fermenting plaque. These findings suggest that caries-conducive circumstances may promote fluoride uptake by enamel compared with non-caries-conducive circumstances.     

Relationships between fluoride in enamel, DMFT Index and fluorosis in high- and low-fluoride areas in South Africa

The DMFT Index, degree of fluorosis (DEGF), and enamel fluoride concentration (F) were determined in 88 children living in a high- and 79 children living in a low-fluoride area in South Africa. The following interrelationships between these parameters were found: in both areas there was a significant negative correlation between log F and age; in the high-fluoride area there was a significant positive correlation between log F and DEGF; and in the combined data from the two areas there were significant correlations between log F and area, log F and age, and log F and DEGF, and a significant association between DEGF and area. There were no significant correlations between DMFT and log F and between DMFT and DEGF.     

In vitro enamel fluoride uptake from topical fluoride agents

The F acquired by enamel from APF, Duraphat and Fluor Protector was evaluated in this in vitro study. The topical F agents were applied to the tooth surfaces for 4 min, the teeth were suspended in synthetic saliva and the topical F agents removed after 2 h or 4 h. The teeth were resuspended in synthetic saliva for 1, 3 and 6 months, respectively. Three successive enamel biopsies were done on the control and experimental tooth halves and the F and P content of the etching solutions determined. The fluoride concentrations were adjusted to standardized depths of 3.0, 6.0 and 9.0 μm, respectively. Enamel acquired significantly more F from Fluor Protector and Duraphat than from APF. The fluoride acquired by enamel from the topical F agents was inversely related to the enamel F concentration prior to topical F application.     

Influence of chlorhexidine on in vitro uptake of fluoride in dental enamel

ABSTRACT – Chlorhexidine gluconate and sodium fluoride were found to be compatible in the concentration range of interest in clinical use. Admixture of chlorhexidine to sodium fluoride solutions did not interfere with the fluoride uptake in clinically intact premolars in vitro .     

Early supply of fluoride and enamel fluorosis

abstract – A study of enamel fluorosis in 1,094 children was carried out in areas with a water fluoride content of from <0.2 mg/1 with and without supplementary fluoride, to 2.75 mg/l. The fluorosis was correlated with different infant diets and also with the calculated supply per kilo body weight. As in cattle, 0.1 mg F/kg body weight daily appears to cause fluorosis. This dose may for example be reached with water-diluted gruel powder in low-weight infants with high consumption in low F areas, in normal weight infants in 0.8 areas, and also in high-weight infants in 1.2–1.5 areas. The resultant fluorosis is very mild or mild and not disfiguring. Enamel fluorosis can be avoided or minimized in areas with up to at least 1.2 mgF/1 water if F-supply, e.g. water-diluted gruel and/or supplementary fluoride, is not commenced until 6 months of age when body weight is higher. With a water fluoride content of 2.75 mg F/l a very mild fluorosis is difficult to avoid also with normal water consumption during the 1st year of life.     

Comparison of dental fluorosis and caries in primary teeth of preschool-children living in arid high and low fluoride villages

Abstract The aim of this study was to determine the degree of fluorosis in the primary dentition and the accompanying caries patterns in groups of preschool-children in high and low fluoride areas. Among 331 coloured children, aged 1 -5 years, living in an area with water F concentrations ranging from 2.2 to 4.1 parts/10⁶, 82% were caries free and the dmft values ranged from 0 to 15 with a mean dmft of 0.8 ± 2.1. Varying degrees of fluorosis in the primary teeth were present in 50.6% of the children. In 177 coloured children of similar ages from an adjacent area with 0.2 parts/10⁶ F in the drinking water the dmft values ranged from 0 to 20 with a mean dmft of 5.4 ± 5.8. Only 28% of the children were caries free. None of the children in this area had fluorosis. The caries prevalence was significantly higher in the low fluoride area than in the high fluoride area. The degree of fluorosis found in the primary dentition in the children from the high fluoride area was higher than had been anticipated and was accompanied by a very low caries prevalence.     

In vivo enamel fluoride uptake after use of fluoride products

PURPOSE: To evaluate fluoride uptake in enamel after use of products containing different fluoride components of distinct oral hygiene regimen in vivo. METHODS: 84 healthy subjects (24 females and 60 males aged 19-26 years, mean 22.2) recruited from the students attending the courses of the Medical Faculty of the University of Sassari, Italy, were randomly assigned to one of four treatments groups: A: treated with a dentifrice containing sodium monofluorophosphate (1250 ppm F-); B: treated with dentifrice with 1250 ppm F- from AmF; C: treated with an AmF toothpaste (1250 ppm F-) and a mouth rinse with 250 ppm F- from AmF; or D: treated with a NaMFP toothpaste (1250 ppm F-) plus 1250 ppm NaMFP varnish. Acid-etched enamel microbiopsies on the vestibular surface of the first maxillary premolar were collected at baseline (to), after 20 days of test product use (t1) and after 24 hours without treatment (t2). Fluoride concentration was measured using an ion-specific electrode. All measurements were made in triplicate and analyzed statistically using two-way factorial ANOVA for independent samples standard weighted-means analysis. RESULTS: The fluoride uptake in the enamel shows a considerable variation between the groups. Significant differences were found both within all products in terms of fluoride concentration in enamel for (P < 0.0001 for two-way ANOVA, and later Tukey HSD test). After 20 days of treatment, the group using AmF toothpaste plus AmF mouthrinse had a higher fluoride uptake than the groups using either of the other products (P < 0.05). In conclusion, all products lead to an appreciable amount of fluoride uptake in enamel; AmF products led to higher concentrations. The concentration of fluoride accumulated during treatment phase remained high after 24 hours following the cessation of use.