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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.

By calculation, apatite is more soluble than brushite at low pH and less soluble at high pH. Apatite, therefore should be able to transform spontaneously to brushite at low pH and brushite to apatite at high pH. The aim was to describe this mutual conversion as related to the aqueous phase composition. Powdered enamel, brushite or 1:1 mixtures of the two salts were suspended in distilled water for up to 12 weeks at 20 degrees C, pH was adjusted to 4, 5, 6, 7, 8, 9 or 10 by drops of perchloric acid or potassium hydroxide. The calcium and the phosphate concentrations and pH were determined, and the nature of the calcium phosphate powder was examined by X-ray diffraction. At pH 8 and above, brushite was invariably converted to apatite, whilst it was transformed to octacalcium phosphate at pH 7. In the pH range 6-4 brushite was not converted to apatite and enamel apatite was not transformed to brushite spontaneously within 2 months. In the enamel apatite suspensions, the apatite ion product altered with pH, which explained why apatite did not transform to brushite at pH 5-4. At pH 3.7, however, the enamel apatite was converted to brushite. No transformation of apatite to brushite was identified in apatite-brushite mixtures at pH 6-4. Supplementary experiments showed that ethanol, used as an agent for removal of water, salted out the water-free dicalcium phosphate, monetite.

A computer program for calculation of ion-activity products, in aqueous calcium-phosphate solutions and suspensions, was used to construct solubility diagrams which demonstrate the stability and instability fields of the calcium phosphates relative to various parameters. With increasing pH, the solubility of all calcium-phosphate salts decreased (with a solubility increase above pH 12); the most important factors in apatite solubility were pH, the fluoride concentration and the ion strength. It was inferred that apatite owes its instability below pH 5 to its increasing solubility relative to that of brushite. Calculation on amorphous tricalcium phosphate showed that this salt in the pH range above 5 was so soluble that the concurrent supersaturation with respect to either brushite or apatite would induce their formation causing the instability of the amorphous salt.

Various amounts of enamel-apatite powder were suspended in an acetate buffer (pH 4.5) containing sufficient fluoride to give molar ratios of fluoride/apatite from zero to unity. The suspensions were equilibrated at 20 degrees C for periods between 4h and 1 year, with continuous gentle stirring. Solubility studies showed dissolution of hydroxyapatite, formation and re-dissolution of calcium fluoride and formation of fluorapatite. The amount of mineral dissolved was low during the fluorapatite formation and increased by a factor of approx. 10 as equilibrium was approached. The fluoride content of the solid apatite, which ranged from 0.1 to 70 mol% fluorapatite, only influenced the solubility slightly, whereas the fluoride content of the bathing solution had a large effect. X-ray diffraction showed a linear correlation between the fluoride content and the a-axis of the apatite.

Deep buccal cavities in 99 teeth in eight young monkeys were filled with the following combination of materials: a light-cured microfilled composite with or without a base, a chemically cured composite with a base, a silicate cement, and a zinc oxide-eugenol cement. The acid etch technique and intermediate layer of resin was used in the composite group. Pulp reactions and presence and location of bacteria were studied after 8 days and after 90 days. In the short observation period the inflammatory reactions were more pronounced when unlined composite fillings were evaluated compared with silicate cement fillings and with lined fillings. Bacteria were seen in all unlined cavities and a significant association between presence of bacteria and moderate to severe inflammatory responses was found. The most severe inflammatory reactions were seen when bacteria were found in the dentinal tubules. After 90 days slight inflammatory changes prevailed in all groups. A significant correlation between bacteria and inflammatory reactions could still be observed.

The aim of the present study was to describe the intraoral pattern of dental fluorosis among fluoride tablet consumers. One hundred and forty-two children, of whom 56 had participated in a fluoride tablet program of 0.5/1.0 mg NaF per day were examined blindly for possible fluoride-induced enamel changes. A low prevalence of dental fluorosis was found among non-participants. The later in life the tooth was formed, the higher was the prevalence. The subjects who had participated in the fluoride tablet program showed a significantly higher prevalence of fluorosis. They could be divided into three groups: Group 1 exhibited a tooth prevalence pattern not statistically different from that of the non-participants, group 2 showed dental fluorosis in almost all teeth except in those formed before the start of the tablet program. In group 3 the early and the late formed teeth showed very little fluorosis while those formed in the few years just after the initiation of the fluoride tablet intake were affected by fluorosis.

The goal of the present investigation was to study whether periodic use of fluoride-gel treatments resulted in an increased prevalence of dental fluorosis. 269 children, from 14 to 16 years of age, who had received semi-annual or quarterly fluoride-gel treatments were examined for possible fluoride-induced enamel changes. Further, in order to determine the amount of fluoride retained during the gel treatment, the expectorate was analyzed in 18 younger children presently participating in the prophylaxis program. It was found that the retention of fluoride averaged 7.3 mg per treatment (up to 0.5 mg fluoride per kg body weight). An increased prevalence of dental fluorosis was not observed, even after up to five yearly treatments were given during tooth formation periods. The background prevalence of dental fluorosis in a low-fluoride area in Denmark is described.

Three groups of 1-month-old rats were kept on water containing 0.2, 56.5 and 113 parts/10(6) F-, respectively, for a period of 2 months. These groups were set up in order to study the relationship between long-term administration of high doses of waterborne fluoride, plasma values of fluoride and calcium and changes in forming dentin and enamel of the rat incisor. The microradiographic study revealed that increased levels of fluoride caused a delay in mineralization of the enamel. In the 113 parts/10(6) group the radiolucent areas in the enamel exhibited a distinct periodicity along the tooth, a phenomenon which cannot at present be explained. In the dentin the fluoride interfered with the process of mineralization giving rise to radiolucent and radiopaque banding in the experimental groups. With increasing levels of fluoride in the water supply a significant increase of plasma fluoride was recorded. In contrast the serum calcium values in both experimental groups were reduced to the same extent, which differed significantly from that of the control group. It is concluded that the fluoride doses which are needed to create fluorotic changes in rats may interfere with calcium metabolism and basic mineralization processes.

The aim of this study was to describe the variations with time in the concentrations of fluoride in drinking water sources in Greenland, Kenya, Greece, Denmark and Ireland. Water samples were collected monthly and shipped to laboratories in Aarhus for electrometric analyses. In Narssaq, Greenland the fluoride concentration of a single piped water supply ranged from 0.3 to 2.8 ppm, the variations being related to climate, precipitation and temperature over the year. Water from the Athi River, Kenya had a fluoride content ranging from 0.3 to 1.2 ppm, the higher concentrations being associated with the dry seasons. The fluoride concentration in piped water from mountain rivers in Mourjes, Greece, ranged over the year between 1.3 to 2.0 ppm, the changes being apparently unrelated to rainfall. Marked variations in fluoride concentrations from 0.5 to over 3.5 ppm were observed in water from artesian wells in Assiros, Greece. In drinking waters from boreholes in Boennerup Strand, Denmark, fluoride concentrations ranged with time from 1.4 to 2.4 ppm, the variations being unrelated to climate or precipitation, while little variation in fluoride concentrations was found in water from boreholes in either Roedvig or Egens, Denmark. Water obtained from two sources of artificially fluoridated water supplies from Ireland showed considerable variations with time, although pooled samples indicated relatively constant levels over the year. The study indicates that the results of single fluoride ion measurement from any given source should not be taken as being a reliable indicator of fluoride exposure from drinking water.(ABSTRACT TRUNCATED AT 250 WORDS)

Samples of 200 mg powdered enamel apatite were suspended in 10 ml of aqueous solutions made from phosphoric acid and calcium hydroxide for 60 days at 20 degrees C. Calcium and phosphate concentrations were determined by spectroscopy; pH and the concentrations of fluoride and carbonate by electrometry. The solubility product of hydroxyapatite varied linearly from 10-56.9 at pH 4.6 to 10-52.8 at pH 7.6. The carbonate concentration in the aqueous phase was too low to account for calcium carbonate complex formation of significance to the solubility product. After the equilibration, X-ray diffraction analysis of the powder showed that the salt was unchanged pure apatite with no trace of a transformation to brushite or any other calcium phosphate. A re-equilibration of some of the powder samples for another 60 days produced similar solubility products. Thus the change of the solubility product was most likely attributable to a pH-induced change of the ionic composition of the enamel crystal surface.

The aim was to describe the dimensions of the fluorhydroxyapatite unit cell and the solubility of fluorhydroxyapatite as a function of the fluoride concentration in the apatitic lattice. Various amounts of powdered human dental enamel were suspended in a pH 4.5 acetate buffer containing fluoride. The suspensions were equilibrated for 365 days at 20 degrees C. After equilibration the fluoride concentration in the apatite varied from 0.003 to 0.89 (mole fraction). X-ray diffraction showed that the length of the alpha-axis decreased with increasing fluoride concentration, whilst a broadening of the (300) reflection indicated the presence of mixtures of various fluorhydroxyapatites. The solubility of the apatite after the long equilibration decreased slightly with increasing fluoride concentration in the solid. In a few samples the fluoride concentration in the aqueous phase was still discernible, indicating that even after 365 days, equilibrium had not been attained. In these samples the amount of dissolved apatite was extraordinarily low.

Human dental enamel was exposed to a pH 4 buffer containing 150 parts/10(6) fluoride. It was found that due to the arising degrees of saturation with respect to calcium fluoride and apatites, surface enamel dissolved coincident with a formation of calcium fluoride. The calcium fluoride redissolved while it kept the liquid saturated with respect to this salt. During this second period, fluorapatite was formed while hydroxyapatite dissolved. Finally, all calcium fluoride was dissolved and the unreacted fluoride was taken up in the apatitic lattice. The results are discussed with reference to the conditions of the oral cavity and enamel solubility experiments.

A 3-year experimental toothbrushing study was conducted in a natural fluoride area in Denmark to evaluate the anti-caries effect of a 2% sodium monofluorophosphate dentifrice. In a previous report the results for the total population of 1,407 schoolchildren, representing a broad age-span (7-12 years), at the commencement of the study in 1970 were given. In the present report results are presented for two subpopulations of "8-year-olds" and "11-year-olds" at the commencement of the study. Differential analysis of the effect of the test dentifrice on defined types of surfaces for the two subpopulations is given. The evaluation was performed using both the conventional DMF-indices and the recently published ECSI-Index6. The evaluation showed that the test dentifrice had a valuable anti-caries effect in both age groups, above and beyond the effect of the waterborne fluoride. Proximal surfaces were affected most baneficially by the active agent both in relative and absolute terms. However, an appreciable caries-preventive effect was also found on the "pit and fissure" surfaces.

The aim of this review has been to suggest that future fluoride preventive programs should be based on what is at present known about the possible cariostatic mechanisms of fluoride. The relative role of enamel fluoride in caries prevention has become increasingly questioned during the last two decades. No significant relationship has been demonstrated between caries experience of the individual and fluoride content of the enamel. Furthermore, the fluoride content in surface enamel between teeth developed in low and "optimal" fluoride areas is too small to explain any significant effect on dissolution rate of the enamel. As the major explanation for the cariostatic effect of fluoride must therefore be sought in its local effect on the oral environment, the possible effects on plaque colonization, composition and metabolic activities are discussed. The effect of even low concentrations of fluoride in the liquid phase on enamel dissolution is described, and it is concluded that the major cariostatic effect of water fluoridation, fluoride tooth paste and mouth rinses can probably be ascribed to regular increases in fluoride ion activity in the oral fluids. The effect of high concentrations of topical fluoride solutions is thought to be a result of a slow dissolution of calcium fluoride deposited in initial caries lesions, whereby an increased fluoride ion concentration is maintained locally for longer periods of time. Finally, the clinical consequences of these considerations are described.

Dental fluorosis among 456 14-16-year-old schoolchildren who had resided continuously since birth in their respective study areas was recorded using the Thylstrup and Fejerskov classification system. The children fell into four groups according to fluoride concentration of their drinking water: (1) less than or equal to 0.1 ppm; (2) 0.3-0.5 ppm; (3) 0.5-1.25 ppm; and (4) 1.26-2.0 ppm. It was found that the later in childhood the tooth was formed, the higher was the prevalence of dental fluorosis. The fluoride concentration in the drinking water affected the prevalence of dental fluorosis in all teeth except the lower incisors, which are formed very early in life. Apart from these teeth, the proportionate increase of dental fluorosis with increasing water fluoride concentration was almost the same for all tooth types. However, the actual amount of increase in the prevalence and degree of fluorosis was greatest among those teeth that formed later during childhood. The observed fluorosis is presumed to result from and reflect the drinking water habits in the population as well as the patterns of use of fluoride prophylactics.

Enamel structure in human primary incisors was histologically examined in order to compare the observations with those from recent studies on incipient carious and fluorosed enamel. Ground sections from mandibular incisors of five full-term human infants were examined in polarized light using aqueous media (water, Thoulet's media), alcohols with different refractive indices, and quinoline. Imbibition graphs were made along traverses from the amelodentinal junction (ADJ) to the enamel surface. Quantitative assessments of the birefringence in different media along the traverses indicated a change in the relative volumes of crystallites and surrounding medium with a continuous growth of crystallites toward the ADJ. The influence of organic material is discussed in relation to the differences in calculated form birefringence observed within the specimens. When examined in quinoline, a 30-40-mum-thick surface zone appeared distinct positively birefringent, indicating that the outermost enamel reacted as a molecular sieve. Because of the lower content of minerals the interpretation of this zone differed from that of similar "dark zones" observed in carious and fluorosed enamel.

Fluoride concentrations in mixed saliva were measured at different intervals following topical treatments with various fluoride preparations and procedures such as dentifrice, tablets, mouthrinse and topical solution. The results were related to available caries reduction data from corresponding clinical trials previously published. Salivary fluoride levels varied widely reflecting the different dosages applied, whereas the caries reduction data irrespective of type of treatment appear very similar, with a magnitude of about 30%. When combining salivary fluoride data with recent understanding of enamel-fluoride kinetics it was possible to explain the clinical caries reductions.

A rare case of extensive dermal uptake of Tc-99m MDP associated with renal failure is reported. The mechanism of Tc-99m MDP uptake in such examples of metastatic calcification is not proved, but may relate to adsorption onto hydroxyapatite crystals. This phenomenon is useful in demonstrating distribution of nonvisceral metastatic calcification.

Some fruit juices and carbonated acidic drinks, recognized as agents causing dental erosions, were analyzed for calcium, phosphate, fluoride and pH. Ionic activity/concentration products for hydroxyapatite and fluorapatite were calculated. It was found that all liquids analyzed were unsaturated with respect to both apatites, which explains their erosive effect.

The aim of the present study was to describe the patterns of dental fluorosis in the primary and the permanent dentition of children born and reared in two different fluoridated areas, one in which powdered milk suspended in tap water was commonly used (Narssaq, Greenland: 1.1 ppm fluoride in the water) and one in which cow's milk was provided (Vordingborg, Denmark: 1.4-1.6 ppm fluoride in the water). Dental fluorosis was recorded by Thylstrup and Fejerskov's classification. In both locations, the prevalence of dental fluorosis increased the later in life the tooth type was formed. The prevalence of dental fluorosis in the earliest formed teeth was higher in the area where powdered milk was suspended in fluoride-containing tap water than where pasteurized cow's milk was used. In the first permanent molars, the maxillary incisors, and the canines, the prevalence was rather similar in the two areas. In the latest formed teeth, the premolars, the level of fluorosis was higher in Vordingborg. The pattern of dental fluorosis suggests that when powdered milk was used frequently, the children were exposed to a higher fluoride intake earlier in life than were those consuming cow's milk during infancy and childhood.

The aim of the present paper was to identify some chemical and structural factors which may prevent a full remineralization of caries lesions and to study whether it is possible to overcome such obstacles. Samples of powdered enamel apatite were equilibrated with solutions metastably supersaturated with respect to enamel hydroxyapatite and fluorapatite. After 10 min and 60 min of equilibration at 20 degrees C the suspensions were centrifuged and the calcium and phosphate concentrations and the pH were determined in the supernatant. In parallel studies, 50 75-microns-thick sections of 27 fluorotic teeth of a severity of 5-7 according to Thylstrup and Fejerskov's classification were examined by microradiography and in polarized light using distilled water, and Thoulett's media or seen dry in air. Five obstacles inhibiting remineralization were identified: 1) Although remineralizing solutions or saliva are supersaturated with respect to enamel apatite the total amount of calcium and phosphate dissolved in it is small, so that after precipitation of the dissolved mineral only 1/20,000-1/30,000 of the volume of the mineralizing solution is occupied by mineral. 2) The concentration gradients from the mineralizing solution into the enamel is small, which indicates a slow diffusion into and out of the lesion. 3) The uptake of calcium and phosphate by the enamel apatite crystals is so rapid that the aqueous phase within the pores can be presumed to be only marginally supersaturated in the deeper parts of the lesion. 4) The surface layer of the enamel lesions was found to be a serious obstacle to remineralization so that a subsurface area remains hypomineralized after exposure to salivary remineralization even for a lifetime. 5) Nucleation of new apatite crystals to substitute lost crystals is an unsolved problem.

Sodium fluoride 10, 20 or 40 mg/kg body weight was given intraperitoneally to rats (6-11 days old and 90-95 days old). Blood analyses showed an initial increase in plasma fluoride concentration. The subsequent decrease in fluoride was paralleled by a decrease in total plasma calcium. These plasma concentrations were normal at blood collection 4 days after fluoride injection. The baby rats differed from the older rats in that their initial plasma calcium was higher and that the drop in plasma calcium concentration was less pronounced than in the old rats. A diet low in calcium and phosphate enhanced the effects of fluoride on total plasma calcium. The data indicate that the effect of large doses of fluoride on lowering the plasma calcium level is modified by the calcium intake.

Fluoride 27 mg was given perorally to 14 subjects. It was found that the serum fluoride concentration increased followed by a decrease to normal levels during 24 h. Serum concentrations of calcium and phosphate decreased initially whereas those of serum immunoreactive parathyroid hormone increased. After 24 h the measured quantities were within normal limits. The results are discussed with reference to mineralization of hard tissues and to fluoride treatment of osteoporotic patients.

Intact enamel surfaces were exposed to 20 ml of 0.1% HCl for various periods. When the acid was unsaturated with respect to both hydroxyapatite and fluorapatite the surface enamel was etched away. With time the liquid close to the enamel became supersaturated with respect to fluorapatite but remained unsaturated with respect to hydroxyapatite. Under this condition subsurface lesions developed. These observations are discussed with reference to the use of diffusion-restricting agents in laboratory caries experiments.

In a liquid (22 degrees C) saturated with and in contact with powdered bone apatite, the fluoride ion activity was adjusted to 1-10 parts/10(6). Due to the fluorapatite (FAP) supersaturation produced hereby, a rapid formation of this salt occurred leading to a decrease of the concentration of the ions involved. When no more fluoride was available in the liquid, the concentrations of calcium and phosphate increased again, due to dissolution of presumably hydroxyapatite (HAP). Fifty four rats were given either 10, 20, or 40 mg NaF per kg body weight intraperitoneally. The animals were sacrificed from 5 min to 96 h after the injection. The fluoride concentration in plasma increased to a peak, after which it decreased. Plasma calcium decreased and remained low until the fluoride had attained normal levels. The intensity of mineralization of the growing dental hard tissue was monitored on microradiographs. Corresponding to the plasma fluoride peak and the decrease of plasma calcium, a hypermineralized layer was formed while a hypomineralized zone was formed during plasma calcium increase after disappearance of fluoride. Similarities and dissimilarities between the in vitro and the in vivo experiments are discussed.

Seven days before a fluoride injection of 20 mg sodium fluoride per kg body weight, 3-month-old rats grown on a standard pellet diet containing 0.8% calcium and 1.4% phosphate were given a diet of rice with only 0.025% calcium and 0.1% phosphate. Microradiographs of the continuously growing incisors showed a hypermineralized and subsequent hypomineralized zone. Blood analysis demonstrated a decrease and a subsequent reestablishment of plasma calcium concentration. In some experiments calcium and phosphate were administered to compensate the hypocalcemia which prevented the hypomineralized zone from arising. A delay of calcium and phosphate administration led to formation of a mineralized band within the hypomineralized zone. The results are discussed with reference to calcium homeostasis.