[Approximal caries in children]

A longitudinal radiological study in children (N = 549) who participated in a comprehensive maintenance program (they were treated in the clinic of the Department of Pedodontics of the Academic Centre for Dentistry Amsterdam) suggests that changes in the approximal surfaces of deciduous molars may differ from the changes in the approximal surfaces of permanent (pre)molars. Regression and initiation possibly occur more frequently in the deciduous teeth than in permanent teeth.

Electron probe X-ray microanalysis of calcium and phosphorus distribution in developing hamster tooth germs in vitro and in vivo

The aim of the present study was to investigate the spatial distribution of Ca and P in dentin and enamel of developing first (M1) and second (M2) maxillary hamster molars (age: 3-5 days) in comparison with cultured molars. For culturing the germs were dissected from 3-day-old hamsters and incubated for 1 and 2 days, respectively, in a modified BGJb medium. Electron probe X-ray measurements were carried out on 3 regions extending in a vertical axis from cusp tip over cusp middle to cusp base next to the cervical loop region. Neither the in vivo nor the in vitro group was statistically different in the Ca and P concentration in the regions of dentin. In both groups the measurements in enamel showed a gradient with an increase in Ca and P from enamel surface towards dentin-enamel junction and a gradient with an increase from cusp base towards cusp tip. Direct comparison of the in vivo group with the in vitro group did not demonstrate a statistical difference between the mineral content of the 4-day-old germs and the 1-day culture germs, respectively the 5-day-old germs and the 2-day culture germs. The results indicate a high correspondence between the mineralization process of in vitro and in vivo tooth germ development.

Micro-PIXE (proton-induced X-ray emission) study of the effects of fluoride on mineral distribution patterns in enamel and dentin in the developing hamster tooth germ

Micro-PIXE (proton-induced X-ray emission) analysis was performed on unfixed and anhydrously prepared sections from developing enamel and dentin from hamsters injected with a single dose of 20 mg NaF/kg body weight. Fluoride, apart from inducing the formation of the characteristic paired response in the enamel (i.e., a hyper- followed by a hypomineralized band in the secretory enamel), also induces the formation of sub-ameloblastic cystic lesions under the transitional and early secretory enamel accompanied by relatively intense hypermineralization of the underlying cystic enamel surface. These cystic lesions, however, were only found to be associated with certain isolated populations of these cells. In addition, these lesions were restricted to the smooth surfaces of the tooth germ only. Cystic lesions such as those seen under the transitional and early secretory ameloblasts were not observed under the fully secretory or maturation stage ameloblasts. Why fluoride induces the formation of cystic lesions in some ameloblast populations while other cells in the same stage of development apparently remain unaffected, is a matter which needs further investigation.

Posteruptive age dependency of cariogenic changes in enamel of permanent teeth of children

During a cariogenic attack at the enamel surface a white spot can be formed (initiation) or disappear (regression) or remain the same (stabilisation). In the present clinical study it was shown that at least regression and stabilisation depend significantly on the posteruptive age and may be associated therefore with changes in porosity or mineral composition in the young enamel surface after eruption. In contrast, the progression of a white spot towards a cavity, which took place in this study almost exclusively in the fissures, does not change with posteruptive age. An explanation for this may be that in such white spots remineralization is less effective due to retention of acids in the fissures. On the other hand, rapid development of a cavity from sound enamel within half a year decreased with posteruptive age.

X-ray micro-analysis of the mineralization patterns in developing enamel in hamster tooth germs exposed to fluoride in vitro during the secretory phase of amelogenesis

The developing enamel from three-day-old hamster first maxillary (M1) molar tooth germs exposed to fluoride (F-) in vitro was analyzed for its mineral content by means of the energy-dispersive x-ray microanalysis technique. The aim of this study was to obtain semi-quantitative data on the F(-)-induced hypermineralization patterns in the enamel and to confirm that the increase in electron density observed in micrographs of F(-)-treated enamel (Lyaruu et. al., 1986, 1987b) is indeed due to an increase in mineral content in the fluorotic enamel. The tooth germs were explanted during the early stages of secretory amelogenesis and initially cultured for 24 hr in the presence of 10 ppm F- in the culture medium. The germs were then cultured for another 24 hr without F-. In order to compare the ultrastructural results directly with the microprobe data, we used the same specimens for both investigations. The net calcium counts (measurement minus background counts) in the analyses were used as a measure of the mineral content in the enamel. The aprismatic pre-exposure enamel, deposited in vivo before the onset of culture, was the most hypermineralized region in the fluorotic enamel, i.e., it contained the highest amount of calcium measured. The degree of the F(-)-induced hypermineralization gradually decreased (but was not abolished) in the more mature regions of the enamel. The unmineralized enamel matrix secreted during the initial F- treatment in vitro mineralized during the subsequent culture without F-. The calcium content in this enamel layer was in the same order of magnitude as that recorded for the newly deposited enamel in control tooth germs cultured without F-.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of fluoride by young children and prevalence of mottled enamel

The prevalence of mottled enamel in the permanent dentition of children participating in a fluoride (F-) program at the dental school of the Vrije Universiteit (Amsterdam) was investigated in a study utilizing the Thylstrup-Fejerskov (TF) index. The randomly chosen children received a F- regime considered optimal by the Dutch Advisory Committee for Prevention of Oral and Dental Diseases. From the children examined (n = 83; 49 boys and 34 girls; mean age, 13 years and 5 months), 74% exhibited mottled enamel in a slight to moderate degree. More teeth were affected and the degree of mottling was higher when children started to use F- at an earlier age. Unintentional ingestion of toothpaste containing 0.15% F- during frequent toothbrushing in combination with the daily intake of F- tablets before the age of four may explain the high prevalence of mottled enamel. After these treatments, F- concentrations in plasma of young children can reach values which can directly affect the developing tooth germ.

Micro-PIGE determination of fluorine distribution in developing hamster tooth germs

A micro-PIGE (Proton-Induced gamma-ray Emission) technique based on the delayed 5/2+----1/2+ nuclear transition of fluorine (E gamma = 197 keV, t1/2 = 87 ns) emitted after 19F(p,p', gamma)19F reaction was used to detect and study the distribution of fluorine in the developing enamel organ during pre-eruptive stages, i.e., the transitional to early maturation stages of enamel formation in neonatal hamsters administered a single IP dose of sodium fluoride (20 mg NaF/kg body weight). The aforementioned nuclear reaction is unique for fluorine, and therefore detection of gamma-rays emanating from this reaction in a biological specimen implies a positive identification of fluorine at that particular site. Calcium and phosphorus X-rays were also recorded and used as parameters for assessment of the relationship between the degree of mineralization and fluoride incorporation into the enamel organ. The highest fluorine concentration in the enamel organ was recorded in the dentin near the dentin-enamel junction (DEJ). In the enamel, the highest concentration of fluorine was found to be associated with the more mature areas of the enamel near the DEJ, but gradually decreased in the direction of the enamel surface. Fluorine was not detected in the control germs. These results suggest that administration of fluoride in high doses during the pre-eruptive stages of enamel formation leads to incorporation of the ion into the forming dentin and enamel mineral, and that the enamel matrix does not seem to bind fluoride avidly.

Prevalence of mottled enamel in permanent dentition of children participating in a fluoride programme at the Amsterdam dental school

The prevalence of mottled enamel in the permanent dentition of children participating a fluoride (F-) programme at the Amsterdam Dental School has been investigated in a pilot study, utilizing the Thylstrup-Fejerskov (TF) index. From all children examined (n = 83) 74% exhibited mottled enamel, in a slight to moderate degree. More teeth were affected and the degree of mottling was higher when children started to use F- at an earlier age. Unintentional ingestion of toothpaste containing 0.15% F- during frequent tooth brushing in combination with the daily intake of F- tablets before the age of four may explain the high prevalence of mottled enamel.

The effects of cadmium on the p-nitrophenyl phosphatase and inorganic pyrophosphatase activities of alkaline phosphatase in developing hamster tooth germs

p-Nitrophenyl phosphatase (p-NPP-ase) and inorganic pyrophosphatase (PPi-ase) activities originate from the same alkaline phosphatase enzyme. Only the PPi-ase site has zinc (Zn2+) as a cofactor. Cadmium (Cd2+) in concentrations from 10(-5) mol/l upwards inhibited the PPi-ase activity, but did not inhibit the p-NPP-ase activity at all. In mineralizing tooth germs Cd2+ may replace Zn2+, thereby changing the specific stereoconfiguration in the active centre needed for PPi-ase activity, but not that for p-NPP-ase activity.

[Fluoride and mottled enamel]

The prevalence of mottled enamel in permanent teeth of children, visiting the pediatric clinic of the Dental School ACTA in Amsterdam and using fluoride, has been examined utilizing the Thylstrup-Fejerskov index for enamel fluorosis. Of all children examined (n = 83) 74% exhibited mottled enamel, varying from a very mild to a moderate degree. The amount and degree of mottling increased when children started using fluoride at an earlier age. A high frequency of toothbrushing along with a high concentration of 0.15% fluoride in toothpaste, in combination with ingesting fluoride tablets, may be responsible for the high prevalence of enamel fluorosis.

Antagonism of fluoride toxicity by high levels of calcium but not of inorganic phosphate during secretory amelogenesis in the hamster tooth germ in vitro

Whether the interference by fluoride (F-) with secretory amelogenesis in vitro could be modulated by altering the levels of calcium (Ca) and inorganic phosphate (P) in the medium was investigated. Hamster first upper molar tooth germs in the secretory phase of amelogenesis were exposed to 10 microM-1.31 mM (0.2-25 parts/10(6)) of F- in vitro for 2 days in the presence of either low (1.2 mM), moderate (2.1 mM) or high (4.1 mM) levels of Ca, or moderate (1.6 mM) and high (3.6 mM) levels of P. The biosynthesis and secretion of enamel matrix proteins under each of the experimental conditions were examined by labelling with [3H]-proline during the last 24 h of culture, and mineralization by labelling with 45Ca and [32P]-orthophosphate. With moderate levels of Ca and P (control medium), F- increased the uptake of 45Ca and 32P in a dose-dependent manner; F- did not inhibit the synthesis of matrix proteins but to a moderate extent impaired their secretion. In explants grown in the presence of 52 microM of F- the superficial layers of enamel matrix deposited in vitro (fluorotic matrix) failed to mineralize. Increasing P levels in the medium had no clear histological effect, whereas lowering Ca levels sometimes seemed to aggravate the F- effect. Raising Ca levels improved the histological pattern: in spite of the presence of F-, high Ca levels allowed a limited mineralization of the superficial layer of fluorotic matrix along with a strong rise in mineralization of the deeper layers of pre-exposure enamel. High Ca levels also considerably reduced the cellular changes in secretory ameloblasts induced by 52 microM of F- and slightly counteracted the inhibition of matrix secretion, as measured biochemically. Some of the effects of F- on secretory amelogenesis in vitro can thus be reversed by raising Ca levels in the medium. Therefore, the effect of F- on secretory amelogenesis in vitro seems to be primarily interference with the enamel mineralization process per se and, secondarily, an impairment of matrix secretion.

The effect of colchicine on protein secretion by differentiating odontoblasts and ameloblasts in the hamster tooth in vitro as shown by radioautography with 3H-proline

We have examined radioautographically the protein synthetic and secretory activity of differentiating odontoblasts and ameloblasts, exposed for 9 h in vitro to various concentrations of colchicine in the presence of 3H-proline. Colchicine impairs the cytodifferentiation of the dental epithelium into ameloblasts and of the dental mesenchyme into odontoblasts; the effects depend on the dose. However, dental epithelial cells are more sensitive to the drug than dental mesenchymal cells. In stages prior to odontoblast differentiation, colchicine enhances the number of radioautographic grains over the dental epithelium without changing the grain counts over the dental basement membrane area. This suggests that in vitro the dental epithelium synthesizes and secretes proline-containing components that are not constituents of the dental basement membrane. Also, during the subsequent stages of ameloblast differentiation colchicine increases the number of radioautographic grains over the preameloblasts. The present data suggest that the primary in vitro target of colchicine is not the dental mesenchyme, but the dental epithelium. The data also indicate that differentiating ameloblasts synthesize and secrete significant amounts of proteins in vitro prior to the first deposition of enamel.

The effects of quaternary ammonium chloride (alpha C12 DME AHCl) on enamel hardness and mineral loss under intra oral cariogenicity test conditions

The effects of a quaternary ammonium compound; 2-hydroxy-ethyl-2-hydroxydodecyl-dimethyl-ammonium chloride (alpha C12 DMEAHCl) on enamel hardness and mineral loss in enamel slabs were studied under intra-oral cariogenicity test conditions. The quaternary ammonium compound without fluoride reduced enamel softening as well as the mineral loss from enamel significantly up to a depth of 100 microns from the surface. Moreover the Ca/P molar ratio of the treated enamel was comparable to untreated enamel controls. These findings suggest that the quaternary ammonium compound itself inhibits mainly demineralisation rather than remineralization under intra-oral cariogenicity test conditions.

Autoradiographic, ultrastructural and biosynthetic study of the effect of colchicine on enamel matrix secretion and enamel mineralization in hamster tooth germs in vitro

First upper molar tooth germs of two to three days old hamsters were exposed in vitro to colchicine in concentrations ranging between 10(-7) and 10(-4) M in the presence of 45Ca and/or [3H]-proline for various times up to 18 h. Enamel mineralization was determined by chemical extraction of in vitro incorporated 45Ca and verified ultrastructurally. Quantitative autoradiography compared with water extracts from total explants radiolabelled with [3H]-proline showed a dose-dependent decrease of grain counts over the extracellular enamel to the similar extent as the decrease in radiolabelled amelogenins in water-extracts. It was concluded that water-extracts from total explants represent amelogenins from the extracellular compartment. Enamel matrix secreted in vitro during exposure to high doses of colchicine failed to mineralize and the complete loss was provoked of the distal parts of the secretory ameloblasts including the distal junctional complexes. Nevertheless, the mineralizing pre-exposure enamel neither hypermineralized nor increased uptake of 45Ca. These data do not support the hypothesis that secretory ameloblasts restrict transepithelial calcium transport by directing most of the calcium ions away from the mineralization front. The biosynthetic data furthermore suggest that enamel matrix proteins, only extractable with guanidine-HCl-EDTA, change their physico-chemical nature during secretory amelogenesis in vitro either during secretion or upon their extracellular mineralization.

Localization of cellular calcium in differentiating ameloblasts and its relationship to the early mineralization process in mantle dentin and enamel in hamster tooth germs in vitro

The relationship between the distribution of calcium in the cells of the enamel organ and the mineralization process in mantle dentin and enamel was investigated at the ultrastructural level in cultured hamster second maxillary molar tooth germs explanted before the onset of mineralization (bell stage). During the early stages of pre-odontoblast and pre-ameloblast differentiation, pyroantimcnate (PA) reaction product for calcium was observed only in the nuclei. However, an abrupt increase in PA reaction product appeared in the apical cytoplasm of both the pre-odontoblasts and pre-ameloblasts prior to the onset of mantle dentin mineralization. In the pre-dentin, the PA reaction product was localized mainly on the striated collagen fibers. The PA reaction product in the apical poles of these cells increased concomitantly with increasing mantle dentin mineralization. The amounts of PA reaction product along the plasma membranes and in the cytoplasm decreased in the direction of the basal (stratum intermedium) pole. The highest PA activity in the cytoplasmic side of the plasma membranes of the ameloblasts was found during the secretory phase of amelogenesis. However, in the area around the tips of the Tomes' processes, membrane-associated and cytoplasmic PA activity was low or absent but gradually increased toward the ameloblast cell body, an indication of the presence of a calcium gradient in the processes.

These results indicate that in vitro: (1) both odontoblasts and (pre)-ameloblasts are involved in the calcium acquisition necessary for the initial stages of mantle dentin mineralization; (2) in ameloblasts, there is a calcium gradient in the direction of the mineralization front from the earliest stages of mantle dentin mineralization onward; (3) enamel matrix does not seem to be involved in calcium translocation to the enamel mineralization front; (4) the Tomes' processes seem to regulate transmembrane calcium transport to the mineralization front; and (5) the distribution of calcium in the enamel organ is comparable with that found in vivo.

Effect of alkaline-phosphatase inhibition by 1-p-bromotetramisole on the formation of trichloroacetic acid-[32P]-insoluble phosphate from inorganic [32P]-phosphate and [32P]-pyrophosphate in non-mineralizing and mineralizing hamster molar tooth-germs in vitro

In culture, 1-p-bromotetramisole (pBTM), a specific inhibitor of alkaline phosphatase, significantly inhibited the formation of trichloroacetic acid (TCA)-insoluble [32P]-phosphate from inorganic [32P]-phosphate in the proliferating non-mineralizing second (M2) maxillary molar germs but had no effect in the actively mineralizing first (M1) germs. Addition of 10(-5) M inorganic pyrophosphate in the culture medium with a [32P]-phosphate label increased the inhibition of the formation of TCA-insoluble [32P]-phosphate in the M2. pBTM almost completely inhibited the formation of TCA-insoluble [32P]-phosphate from inorganic [32P]-pyrophosphate in the non-mineralizing M2. In the actively mineralizing M1, the compound significantly inhibited but did not abolish the formation of TCA-insoluble phosphate. These results confirm earlier biochemical findings that alkaline phosphatase possesses a pyrophosphatase activity probably related to the turnover of phosphorylated macromolecules necessary for cell differentiation and proliferation.

Ultrastructure of in-vitro recovery of mineralization capacity of fluorotic enamel matrix in hamster tooth germs pre-exposed to fluoride in organ culture during the secretory phase of amelogenesis

The recovery of mineralization capacity of fluorotic enamel matrix was investigated in 3-day-old hamster first molar tooth germs already pre-exposed in organ culture to 10 parts/10(6) F- for 24 h during the secretory phase. The germs were then cultured for another 24 h in a fresh medium without F-. The unmineralized fluorotic enamel matrix secreted in vitro eventually mineralized in the absence of F- but the orientation of the crystals compared to those in the fluorotic enamel was disturbed, especially in the younger regions of the enamel nearest cervical-loop in which the underlaying fluorotic enamel was most hypermineralized; but least disturbed in the more mature parts of the enamel organ in which the fluorotic enamel was less hypermineralized. The subsequent culture in F(-)-free medium did not abolish or reduce the degree of hypermineralization induced by F- treatment during the initial 24 h of culture. It seems that in vitro the inhibitory effect of F- on enamel matrix mineralization during the secretory phase is completely reversible when the ion is removed from the matrix environment, i.e. F(-)-induced synthesis and secretion of defective enamel matrix is not the cause of the lack of matrix mineralization. The F(-)-induced hypermineralization seems to be irreversible.

Comparison of the hardness change and mineral loss in enamel by dimethyl ammonium fluoride (alpha C12 DMEAHF) or NaF treatment under intra oral cariogenicity test conditions

Changes in hardness as well as in Ca and P were determined in enamel slabs after treatment with 3% sucrose together with NaF or alpha C12 DMEAHF (both containing 0.006% F-) under Intra Oral Cariogenicity Test conditions. NaF treatment resulted in a hypermineralization of the surface of the enamel lesion suggesting formation of CaF2. Treatment with ammonium fluoride along with the same low F- concentration inhibits the caries process completely and seems to be a very promising anticaries agent.

Comparison of the effects of 0.1% F- and 0.025% F- on mineral loss in enamel under intra oral cariogenicity test conditions

Although the caries reducing effect of fluoride (F-) is very well known, the optimal fluoride concentration is still unknown. Therefore we compared the effects of a high (0.1% F-) with a low (0.025% F-) concentration under Intra Oral Cariogenicity Test (ICT) conditions using microhardness measurement and microdissection techniques with which it is possible to quantify the amount of Ca and P present in consecutive enamel layers. No significant differences could be demonstrated between high and low fluoride concentrations in the mineral loss in the surface layer as well as in penetration depth measured perpendicularly to the surface. The reduction of mineral loss after ICT was more pronounced with high fluoride concentrations especially in layers deeper than 150 microns. Using 0.025% F- this effect was restricted more towards the surface. Concomitantly with both F- concentrations a higher Ca/P ratio was observed compared to the sucrose treated or untreated controls.

Ultrastructural study of fluoride-induced in-vitro hypermineralization of enamel in hamster tooth germs explanted during the secretory phase of amelogenesis

The effects of fluoride (5, 10 and 20 parts/10(6) F-) were studied in vitro with light and electron microscopy in 5-day-old hamster maxillary second molar tooth germs explanted when most of the ameloblasts are in the secretory phase, and cultured for 24 h in the presence of F-. F- at all doses investigated induced hypermineralization of that enamel which had been secreted in vivo just prior to exposure to F-. The most intense hypermineralization was in the aprismatic enamel near the cervical loop region, where the in-vivo enamel layer was thinnest and gradually decreased (but was not abolished) with the increasing thickness of in-vivo formed enamel in the more mature parts of the enamel organ. The fluoride-induced hypermineralization in the aprismatic enamel layer did not stain at all with dilute toluidine blue solution and was therefore indistinguishable from the underlying dentine in light micrographs. The hypermineralization was due to growth in thickness of the enamel crystals, which in the aprismatic enamel layer resulted in a lateral fusion of all the enamel crystals. Thus fluoride administered during the secretory phase of enamel formation decontrols or even abolishes enamel crystal growth in length and promotes crystal growth in thickness so producing the hypermineralization of the pre-fluoride enamel. Enamel matrix secreted in the presence of fluoride did not mineralize.

The effect of daily application of a neutral 0.25% F- mouth-rinse on mineral loss in surface layers of enamel under intra oral cariogenicity tests conditions

The effects of daily use of a 0.025% F- mouth-rinse on microhardness and mineral loss in the enamel lesion has been studied under Intra Oral Cariogenicity Test (ICT) conditions. The penetration depth was changed from 16 to 9 microns by F-. Moreover, the inhibition was found fairly constantly distributed over the whole lesion for the Ca and P loss without any CaF2 formation. In this way the effectiveness of the 0.025% F- mouth-rinse program can be explained.

Localization of calcium in differentiating odontoblasts and ameloblasts before and during early dentinogenesis and amelogenesis in hamster tooth germs

Potassium pyroantimonate-osmium tetroxide cytochemistry has been used to study the distribution of ionic calcium in hamster tooth germs during cell differentiation and during early dentinogenesis and amelogenesis. Before the onset of mineralization, pyroantimonate (PA) reaction product was found in the nucleus of differentiating preameloblasts and preodontoblasts. In the predentin, it was preferentially located along striated collagen fibrils, lying perpendicular to the basal lamina. At the onset of mineralization, a pronounced increase of PA reaction product was evident in the predentin and on the plasma membrane and in mitochondria of both preodontoblasts and preameloblasts opposite the mineralizing mantle dentin. During early enamel mineralization, PA reaction product was present in the "growing" crystal ends, while in the secretory ameloblasts, most of the PA reaction product was localized on the cytoplasmic side of the apical plasma membranes and in mitochondria. When Tomes' processes developed, PA reaction product, both cytoplasmic and membrane bound, was low or absent deep in the processes, but gradually increased toward the apical terminal web. A corresponding gradient of PA reaction product was observed on the opposing enamel crystallites. From this study we conclude that both preodontoblasts and preameloblasts seem to be involved in calcium acquisition necessary for the early stages of mantle dentin mineralization. Tomes' processes seem to regulate the entry of calcium into the enamel mineralization front.

Some properties of carbonic anhydrase from mineralizing hamster molars

Carbonic anhydrase (CA) activity in mineralizing hamster molars was determined with a radiochemical assay. Hamster molar CA appeared to be very similar to CA from other sources. No pH optimum could be determined; the KM was 13.6 mM and CA was strongly inhibited by acetazolamide. EDTA and F- had almost no effect on the CA activity. This lack of fluoride effect suggests strongly that the protective effect of fluoride on dental mineral is not mediated by CA.

Short-term effects of fluoride on biosynthesis of enamel-matrix proteins and dentine collagens and on mineralization during hamster tooth-germ development in organ culture

The effect of various concentrations of fluoride (F-) on cell proliferation, matrix formation and mineralization was examined in hamster molar tooth germs in premineralizing and mineralizing stages. The exposure lasted 16 h (mineralizing stages) and 24 h (premineralizing stages) and the F- levels ranged from 2.63 microM to 2.63 mM; [3H]-thymidine, [3H]-proline, 45Ca and 32PO4 were used as markers for cell proliferation, matrix formation and mineralization, respectively. The proline-labelled amelogenins were isolated by sequential extraction with water and formic acid and their nature examined by SDS-urea-polyacrylamide electrophoresis. Digestion by collagenase was used to assess the amount of proline incorporated into collagens. F- in concentrations up to 1.31 mM inhibited neither biosynthesis of DNA and amelogenins, nor synthesis of collagens and their hydroxylation. Amelogenins extracted from F- induced, non-mineralizing enamel matrix had the same electrophoretic mobility and the same degree of phosphorylation as amelogenins from normal, mineralizing enamel. However, F- increased the uptake of 45Ca and TCA-soluble 32P dose-dependently, starting with 52 microM. Thus, interference with secretion of enamel matrix by F- takes place at much lower concentrations than required to inhibit biosynthesis of enamel matrix.