In situ detection of apoptosis in dental and periodontal tissues of the adult mouse using annexin-V-biotin

An early event in apoptosis is exposure of phosphatidylserine, an aminophospholipid normally present in the inner leaflet of the plasma membranes, at the outer leaflet of the plasma membrane facing the extracellular space. Annexin V (Anx-V) is a 35-kDa protein with high affinity for phosphatidylserine, which can be applied to detect apoptosis. We injected biotin-labelled Anx-V intravenously in adult mice and examined the tissue distribution of Anx-V-labelled cells in dental and periodontal tissues using ABC-peroxidase histochemistry. In the continuously erupting incisors, strong and frequent immunostaining was observed in transitional stage and late maturation stage ameloblasts with less frequent staining in preameloblasts. Frequency of staining in odontoblasts and pulp cells was low but increased slightly at older stages of dentinogenesis. Labelling was also seen in phagocytic or phagocytic-like cells in the enamel organ and pulp. A positive staining was furthermore found in fibroblasts of the periodontal ligament in continuously erupting incisors and in fully erupted molar teeth. Staining intensity and the number of positive cells were enhanced by antigen retrieval using high-pressure cooking. We conclude that Anx-V-biotin labels dental cells in early stages of cell death and indirectly cells that have ingested labelled apoptotic cells during the course of the experiment. The data confirm that during amelogenesis most cell death occurs in transitional stage and late maturation stage ameloblasts. Thus, labelling with Anx-V is a useful marker for studying cell death and the dynamics of clearance of apoptotic cells during tooth development.

Development of transplanted pulp tissue containing epithelial sheath into a tooth-like structure

The aim of these studies was to find out whether intact neonatal pulp tissue containing residual epithelial cells can induce the development of a tooth-like structure in situ. First maxillary neonatal hamster molar pulps containing adhering undifferentiated epithelial cells were transplanted submucosally in the oral cavity of recipient mothers for periods ranging from 2-8 weeks and the tissues were then processed for light microscopy. Developing tooth-like structures containing mineralised tubular dentine, predentine and a vascularised pulp-like chamber lined with functional odontoblast-like cells were observed in the specimens within 2 weeks of transplantation. Enamel and root formation were not observed. These data indicate that neonatal dental pulp tissues containing epithelial cell remnants have the capacity to develop into tooth-like structures and that this could be the explanation for the development of tooth-like structures sometimes observed in infants after extraction of a natal tooth.

Daunorubicin-induced pathology in the developing hamster molar tooth germ in vitro

The aim of this study was to evaluate, under organ culture conditions, the cytotoxic effects of daunorubicin on tooth development. Three-day-old maxillary hamster second molars were exposed for 24 h in vitro to 108-10-4 M daunorubicin and then evaluated biochemically and histologically. At 10-6 M daunorubicin dose-dependently decreased tooth germ dry weight, cell proliferation ([3H]thymidine uptake), and insoluble [32P] phosphate uptake (phosphorylation of macromolecules). [45Ca]calcium uptake, a marker for mineralization, was significantly affected only at the highest concentration (10-4 M) tested. Histologically, 10-6 M daunorubicin induced necrosis of the proliferating but not the differentiated protein-secreting cells. At 10-4 M, however, all cells were dead. These results indicate that daunorubicin is particularly toxic to the proliferating cells of the tooth germ. Thus, it can be postulated that children treated with daunorubicin may develop defects in the erupted teeth mainly associated with those regions that were in the proliferating stage at the onset of anticancer chemotherapy.

Bone morphogenetic protein-7 (osteogenic protein-1, OP-1) and tooth development

Bone morphogenetic proteins (BMPs) form a family of growth factors originally isolated from extracellular bone matrix that are capable of inducing bone formation ectopically. We studied the expression, tissue localization, and function of BMP-7 (OP-1) during tooth development in rodents. Patterns of BMP-7 gene expression and peptide distribution indicated that BMP-7 was present in dental epithelium during the dental lamina, bud, and cap stages. During the bell stage, BMP-7 mRNA expression and protein distribution shifted from dental epithelium toward the dental mesenchyme. With advancing differentiation of odontoblasts, BMP-7 protein staining in the dental papilla became restricted to the layer of fully functional odontoblasts in the process of depositing (pre)dentin. Secretory-stage ameloblasts exhibited weak immunostaining for BMP-7. A restricted pattern of staining in ameloblasts became apparent in post-secretory stages of amelogenesis. Also, cells of the forming periodontal ligament were immunopositive. Histological analysis of tooth development in neonatal BMP-7-deficient mice did not reveal obvious changes compared with wild-type mice. We conclude that, in developing dental tissues, BMP-7 has distribution and expression patterns similar to those of other BMP members but is not an essential growth factor for tooth development, possibly because of functional redundancy with other BMP members or related growth factors.

Derived protein and cDNA sequences of hamster amelogenin

Hamster enamel protein extracts were analyzed by RP-HPLC and the isolated fractions by SDS-and Western blotting using polyclonal antibodies against recombinant mouse amelogenin and anti-peptide antibodies against the mouse exon 4-encoded sequence. Total RNA was extracted from enamel organ epithelia and, using a 3' rapid amplification of cDNA ends (3' RACE) technique, the coding regions for three different amelogenin isoforms were cloned along with the 3' non-coding region. DNA sequencing revealed that the hamster amelogenin isoforms are 180, 73 and 59 amino acids in length, respectively. The 59-residue amelogenin corresponds to the leucine-rich amelogenin protein (LRAP), the 73-residue amelogenin corresponds to LRAP with the inclusion of the exon 4-encoded sequence, while the 180-residue amelogenin is the most abundant amelogenin isoform. Edman degradation was performed on purified hamster amelogenin, which provided the amino acid sequence in the region encoded by the 5' PCR amplification primer used in cloning. Therefore, the entire derived amino acid sequence of hamster amelogenin was revealed. The hamster amelogenin amino acid sequence was aligned with all its known homologues. Hamster differs from rat and mouse amelogenin at only three amino acid positions. Southern blot analysis using a panel of restriction enzymes gave the same pattern for hamster DNA obtained from males and females, suggesting that in hamster, as in mouse, amelogenin is expressed from a single gene located on the X chromosome.

Effect of methotrexate on cell proliferation in developing hamster molar tooth germs in vitro

Amongst the most frequently used drugs for the treatment of acute lymphoblastic leukaemia (ALL) belongs methotrexate (MTX), an inhibitor of pyrimidine (thymidine) synthesis. We examined effects of MTX on cell proliferation during tooth morphogenesis in organ culture by exposing hamster molar tooth germs to 10(-7) to 10(-3) M MTX for 24 h. In the presence of serum, only the highest concentration of MTX (10(-3) M) induced a small, nonsignificant decrease in cell mass without histological changes but, unexpectedly, increased uptake of [3H]thymidine. In serumless conditions increase in cell mass (dry weight) and incorporation of [3H]thymidine was lower than in serum-supplemented conditions. Exposure to MTX in serumless conditions reduced the increase in cell mass even further without histological changes and, again, strongly enhanced incorporation of [3H]thymidine to the same proportion as measured in the serum-supplemented cultures exposed to MTX. The data suggest that only exposure to high levels of MTX reduces proliferation activity, shown by reduction in cell mass. The enhanced [3H]thymidine uptake under MTX exposure was explained by blockage of the internal biosynthesis of thymidine, by which action more radiolabel was taken up from the medium. The data also suggest that serum contains (growth) factors that stimulate cell proliferation, thereby increasing cell mass and [3H]thymidine incorporation.

Spatiotemporal expression of the homeobox gene S8 during mouse tooth development

The murine S8 gene encodes a nuclear homeodomain containing transcription factor that is expressed at sites of epithelial-mesenchymal interactions, including those in cranofacial tissues. The spatiotemporal expression of S8 mRNA was examined in tooth primordia by in situ hybridization. S8 transcripts were found in all stages of tooth development in 13- to 16.5-day-old mouse embryos (E13-E16.5), covering the early bud stage up to the late bell stage. S8 mRNA was found exclusively in the ectomesenchyme and its derivatives that originate from the neural crest: future pulp cells, odontoblast precursors and dental follicle cells. Expression was highest at the late cap and early bud stages and declined at the mid-bell stage, in both first molar and incisor primordia. In E13 jaw explants grown in organ culture for 48 h, S8 mRNA was still present in first and second molar primordia after culture. At E15.5, S8 mRNA was also transiently present in the surrounding osteogenic tissue. It is concluded that the distribution pattern of S8 mRNA during tooth development indicates a role for the gene in defining the identity of dental papilla and follicle cells. It is speculated that the time-restricted expression of S8 in tooth primordia involves establishing the definitive form of the tooth organ.

Gene expression and immunolocalisation of amelogenins in developing embryonic and neonatal hamster teeth

Amelogenins are a group of related matrix proteins, synthesised and secreted by ameloblasts during the formation of dental enamel. We have examined expression patterns and the tissue distribution of amelogenins by in situ hybridisation and by immunohistochemistry of developing teeth of embryonic (E12-E15) and neonatal (1- to 4-day-old) golden hamsters. Amelogenin expression and (intracellular) immunostaining for amelogenins were first observed in late embryonic stages in E14 incisors and E15 first molars in partially polarised pre-ameloblasts located along a thin layer of predentine before any overt deposition of enamel. Expression of mRNA and protein staining for amelogenins increased with age and early pre-dentine became immunopositive. The highest mRNA levels and substantial immunostaining for amelogenins were noted in neonatal-stage secretory ameloblasts fully engaged in enamel matrix deposition. After completion of the secretory phase, amelogenin gene expression continued at a lower level in post-secretory stages and was seen in transition-phase and maturation-phase ameloblasts. No amelogenin transcripts were observed in odontoblasts at any stage of their development. However, young odontoblasts stained weakly with anti-amelogenin antibodies before they formed the first layer of dentine, although this staining disappeared in odontoblasts at later stages of development. We conclude that amelogenin gene transcription occurs as early as the polarisation stage of pre-ameloblasts and is closely followed by translation of mRNA into amelogenin proteins. Odontoblasts do not transcribe the amelogenin gene and probably endocytose and digest amelogenins from the pre-dentine. Amelogenins are also transcribed but at a low level in post-secretory stages of amelogenesis.

Effects of actinomycin D on developing hamster molar tooth germs in vitro

The aim of this study was to evaluate the toxic effects of actinomycin D on the developing hamster tooth germ in organ culture. Hamster tooth germs during early secretory amelogenesis were exposed in vitro for 24 h to 10(-9) M-5 x 10(-5) M actinomycin D. Actinomycin D dose-dependently (> or = 10(-7) M) decreased the tooth germ dry weight but mineralization was affected only by doses > or = 10(-5) M. However, the uptakes of TCA-insoluble 32P and [3H]thymidine were significantly reduced dose-dependently from > or = 10(-8) M actinomycin D, indicating that the drug inhibits the synthesis of phosphate-containing macromolecules as well as DNA synthesis. Histologically, 10(-8) M actinomycin D was the lowest dose which was not toxic to any cell type in the developing tooth germ. At 10(-7) M actinomycin D, the most sensitive cells were the proliferating pre-odontoblasts followed by pre-ameloblasts; the mature secretory ameloblasts and odontoblasts appeared unaffected. Higher doses resulted in increased cytotoxicity to the secretory cells and, eventually, total degeneration of most cells. The data suggest that children treated for cancer during tooth development using anti-chemotherapy cocktails containing actinomycin D (serum levels > 10(-7) M) may develop defects later on in the mature dentition as a direct consequence of the toxicity of the drug to the tooth organ.

Nuclear DNA fragmentation during postnatal tooth development of mouse and hamster and during dentin repair in the rat

The TUNEL (transferase-mediated, dUTP-biotin nick end labeling) method for in situ labeling of DNA strands was utilized to localize DNA fragmentation in cells involved in tooth formation in the neonatal mouse and hamster. Positive reactions for the presence of DNA fragments were obtained in some epithelial cells of the cervical loop region of incisors, late secretory, transitional and early maturation stage ameloblasts, stratum intermedium cells and in shortened ameloblasts just before eruption. Also, cells of the periodontal ligament of the continuously erupting incisors stained positive shortly before eruption. Odontoblasts were negative but became strongly positive during the formation of physiological osteodentin at the tip of developing incisors. Osteodentin matrix and the surfaces of unerupted enamel and cementum just prior to eruption stained for DNA fragments as well. DNA fragmentation could be elicited in odontoblasts and underlying pulpal tissues of mature erupted molars after mechanical injury to the odontoblast processes during cavity preparation. We conclude that, in rodents, DNA fragmentation and cell death are biological processes which take place in a variety of cells involved in formation of teeth. The TUNEL staining technique is a simple but powerful tool to examine the fate of cells and tissues undergoing either programmed cell death (apoptosis) or fragmentation of nuclear DNA induced by external factors leading to pathological changes.

Degradation of hamster amelogenins during secretory stage enamel formation in organ culture

Increasing amelogenin heterogeneity during pre-eruptive enamel formation has been explained by proteolytic cleavage of a parent amelogenin, differences in posttranslational modifications, translation of multiple alternative spliced mRNA transcripts or combinations of these possibilities. We investigated the possibility of proteolytic degradation of amelogenins during secretory amelogenesis by pulse-labelling amelogenins with [3H]proline followed by a pulse chase, all under organ culture conditions. The results indicate that during pulse chase, hamster molar tooth explants rapidly released substantial amounts of the radioactivity into the culture medium, as non-trichloroacetic-acid precipitable, noncollagenous 3H-activity at the expense of radioactivity associated with the proteins in the enamel space. Simultaneously, there was a continuous mineralization of the forming enamel in vitro as shown by an increase in total calcium content of the explants. Western blotting, microdissection studies and fluorography of radiolabelled matrix proteins after SDS-PAGE indicated that after an 8-h labelling, three radioactive amelogenin species could be extracted from forming enamel, one prominent species of molecular mass 26 kDa and two less prominent ones of 28 and 22 kDa. During pulse chase more amelogenin bands with lower molecular mass became apparent, a pattern similar to that observed in vivo. Examination of amelogenin blots with the glycan assay showed that none of the hamster amelogenins stained for carbohydrate. We conclude that changes in the amelogenin profiles during enamel development of cultured hamster explants are similar to those observed in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of fluoride in saliva during the early cariogenic changes in the enamel of boys and girls

In boys and girls cariogenic changes in the dental enamel in relation to fluoride (F-) concentrations in stimulated and unstimulated saliva were studied in a six-month period. Also the use of various types of applications of F- was assessed. No difference in the use of F- between boys and girls before and after the interval was observed. Also no clear differences were found between boys and girls in the levels of F- in both types of saliva, determined at the end of the six-month period. The most important finding was that for all children, a significantly positive relationship was found between the disappearance of white spots turning into sound enamel (regression) and the F-concentration in unstimulated saliva. In addition, girls who developed new white spots had higher levels of F-, but those who developed new cavities had lower F- levels in both types of saliva. Apparently F- can prevent dental caries by acting very early on remineralization and demineralization processes in enamel surfaces.

Biomineralization during early stages of the developing tooth in vitro with special reference to secretory stage of amelogenesis

In this survey we summarize data on mineralization of enamel mostly obtained in organ culture experiments in our laboratory. Historically, the enzyme alkaline phosphatase has been proposed to stimulate mineralization by supplying phosphate or by splitting away inorganic pyrophosphate PPi, a potent inhibitor of mineralization. Localization of alkaline phosphatase in developing teeth by enzyme histochemistry shows that cells of the stratum intermedium contain extremely high levels of alkaline phosphatase but secretory ameloblasts that are engaged in deposition of the matrix and in transport of mineral ions lack alkaline phosphatase. The function therefore must be an indirect one, since no activity was seen at the site of enamel mineralization. We propose that the main function of alkaline phosphatase in the stratum intermedium is to transport phosphate or nutrients from blood vessels near the stratum intermedium into the enamel organ. Another function of the enzyme in stages of cell differentiation was deduced from inhibition experiments with the specific alkaline phosphatase inhibitor I- pBTM, showing that in tooth organ culture the enzyme may be involved in the generation of phosphorylated macromolecules from P ions originating from pyrophosphate. Calcium plays an indispensable role in enamel mineralization in vitro. Low calcium concentration in the culture medium prevented initial dentin mineralization and enamel formation. Moreover, differentiating ameloblasts did not become secretory, in contrast to odontoblasts that secreted a layer of predentin matrix. Variations in phosphate concentration in the culture medium do not seem to affect tooth organ cultures adversely during mineralization in vitro. Exposure to F-, however, has adverse effects on enamel mineralization depending on concentration and exposure time and produces a variety of disturbances. Many of the fluoride-induced changes in the enamel organ are reversible: young ameloblasts recover and resume secretion and mineralization of the fluorotic matrix when fluoride is removed from the medium. This recovery is enhanced when medium calcium levels are increased. Only the changes in the hypermineralized enamel remain irreversible. Thus, we hypothesize that fluoride induces a local hypocalcemia in the enamel fluid surrounding the enamel crystals by stimulating a hypermineralization of the pre-existing enamel crystals.

Effects of vincristine on the developing hamster tooth germ in vitro

Vincristine is one of the cytostatic drugs present in cocktails commonly used for the treatment of cancer in children. The aim of this study was to evaluate biochemically and histologically the toxic effects of this drug on the developing tooth in vitro using the organ culture model in order to be able to predict what damage the drug can induce in the developing teeth from children undergoing anti-neoplastic chemotherapy. The most profound effect of the drug (10(-8)M-10(-4)M vincristine) on the developing tooth germ was the induction of mitotic arrests at the cervical loop and in the inter-cuspal regions. The 10(-4)M-10(-6)M vincristine doses were cytotoxic to most cells in the developing tooth germ. The 10(-7)M vincristine dose apart from induction of mitotic arrests, did not appear to be cytotoxic to the mature differentiated secretory cells. However, this dose induced incomplete nuclear polarization of the differentiating ameloblasts and odontoblasts. At 10(-8)M vincristine, the only effect observed were mitotic arrests; the secretory cells did not appear to have been affected at all. On the other hand, mineralization (TCA-soluble 45Ca and 32P uptake) was dose-dependently decreased from 10(-7)M vincristine upwards. 10(-9)M vincristine, the lowest dose tested, did not induce any changes in the developing tooth germ. The organ culture data indicate that 10(-9)M vincristine is the highest (safe) dose which does not induce any toxic effects in the developing hamster tooth germ.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of oral hygiene on early enamel caries

For 548 children aged 4-16 years, mean (+/- SD) age 10.3 +/- 2.7 at visit 1, the dental status was recorded at four consecutive 6-monthly visits. Simultaneously oral hygiene was scored according to a modified patient hygiene performance (PHP) index after application of disclosing solution and before the dental examination. The following cariogenic changes could be observed: initiation (white spot formation), progression (cavitation), stabilisation and regression (disappearance of a white spot). The PHP score was examined in relation to these changes in smooth surfaces, as well as in fissures. For fissures when oral hygiene worsened, stabilisation of a white spot increased significantly. Also, regression of a white spot into sound enamel increased with poor oral hygiene, but the significance was only marginal. White spots turning into cavities, however, did not change with poor oral hygiene. It was speculated that under low oral hygiene conditions the remaining plaque of children receiving intensive fluoride treatment can bind fluoride to the fissure surfaces, thereby promoting enamel maturation concomitant with stabilisation and regression of white spots, which in an earlier study were also found to be dependent on posteruptive age.

Reversible and irreversible effects of temperature on amelogenesis of hamster tooth germs in vitro

Hamster first hamster molar tooth germs in early secretory stage of amelogenesis were cultured for one day in vitro at 6 degrees C, 22 degrees C, 37 degrees C or 45 degrees C in the presence of 3H-proline, 45Ca and 32P-orthophosphate. Other explants were cultured without these labels and after culture examined by histology. The highest temperature tested was lethal to the explants, decreased total dry weight and rapidly increased total uptake of the radiolabelled mineral ions, probably merely due to physicochemical modification of the existing preculture minerals. Optimal synthesis and secretion of amelogenins were measured at physiological temperature (37 degrees C). Effects of exposure to both temperatures below the physiological value were virtually reversible when explants were grown at physiological temperature (37 degrees C) for another day. However, amelogenin secretion during this recovery period did not reach values as high as those found for the first day in explants initially grown at physiological temperature during the first day. We concluded from the four temperatures examined that the optimal temperature for enamel matrix deposition in vitro was 37 degrees C. At this temperature enamel biosynthesis and its secretion are high. Lowering the temperature slows down the metabolism without any apparent harmful effect. Normal development of the tooth explants in vitro resumes when the culture temperature is restored to physiological levels (37 degrees C). For temporary storage of tooth germ explants prior to any reimplantation, we therefore recommend a temperature of 6 degrees C.

Dissimilar expression patterns for the extracellular matrix proteins osteopontin (OPN) and collagen type I in dental tissues and alveolar bone of the neonatal rat

Osteopontin (OPN) is a phosphorylated, sialic acid containing glycoprotein that can be extracted from the mineralized extracellular matrix of bone. In the present study we determined the expression patterns of OPN in dental tissues and alveolar bone of 1-3 day old (neonatal) rats by means of 1) immunohistochemistry, 2) Northern blotting and 3) in situ hybridization. We compared these patterns with those of type I collagen. We localized collagen type I expression in osteoblasts adjacent to alveolar bone and in odontoblasts lining predentin/dentin, but not in the epithelial ameloblasts. For OPN, we observed a weak antigenicity in predentin. Although generally no cellular immunostaining was found, very occasionally a minor immunoreactivity was detected in a small number of pre-mineralizing incisor odontoblasts. On the mRNA level, however, no OPN transcripts could be detected in odontoblasts, either by in situ or by Northern hybridization analyses. Also the odontoblasts of the bone-like dentin (osteodentin) region in the tip of incisors were negative for OPN. In contrast, however, osteoblasts of alveolar bone showed strong positive signals with all three techniques, confirming the sensitivity and specificity of the detection methods. From the data obtained in this study, it can be concluded that during early stages of dentinogenesis OPN presumably is not expressed in developing rat tooth germs. The weak immunostaining observed sporadically in some young odontoblasts is probably due to resorption of OPN of non-dental origin entrapped in the predentin.

Dentin sialoprotein: biosynthesis and developmental appearance in rat tooth germs in comparison with amelogenins, osteocalcin and collagen type-I

A non-collagenous protein, extracted from rat incisor dentin, is a dentin sialoprotein (DSP). We examined immunohistochemically the developmental appearance and tissue distribution of DSP in 1 to 3-day-old rat molar and incisor tooth germs. The earliest staining for DSP was observed in newly differentiated odontoblasts. In more advanced stages, immunostaining for DSP gradually increased in pre-dentin, odontoblasts and dentin, and appeared in many cells of the dental papilla. In early stages of development before the breakdown of the dental basement membrane, pre-ameloblasts were also positive for DSP. This staining disappeared from the ameloblast cell body soon after deposition of the first layer of mineralized dentin. Radiolabelling of tooth matrix proteins with 14C-serine in vitro followed by immunoprecipitation and fluorography confirmed that DSP was synthesized by tooth-forming cells. The immunolocalization for DSP was different from that of either collagen type-I, osteocalcin or the amelogenins. Whereas collagen type-I and osteocalcin were restricted to the mesenchymal dental tissues, the amelogenins were detectable in both epithelial and mesenchymal dental cells and tissues at the epithelio-mesenchymal interface at early stages of development, prior to the onset of dentin mineralization. We conclude that DSP is expressed in and secreted by odontoblasts and some dental papilla cells from early stages of dentinogenesis onwards, i.e. later than type-I collagen, but before deposition of the first layer of mineralized dentin. In pre-mineralizing stages, some of the matrix proteins may be endocytosed from the pre-dentin by both cell types involved in the epithelio-mesenchymal interaction.

Adriamycin alters the alkaline phosphatase activity in hamster molars during development in vitro

The effect of a 2 hour exposure to adriamycin (1 mg/litre) on alkaline phosphatase (ALPase) activity of the golden hamster 4-5 day old second maxillary molars (M2) was investigated in vitro. The molars were grown in BGJb medium containing 15% fetal bovine serum, glutamine (200 micrograms/ml), vitamin C (250 micrograms/ml), penicillin G (50 micrograms/ml), and streptomycin sulphate (30 micrograms/ml). The gas phase contained 50% O2 + 5% CO2 + 45% N2. The molars were supported on cellulosic membrane filters and grown for 3, 5, and 7 days at the medium-gas interface in a closed humidified chamber. Biochemical analysis indicated a steady increase in ALPase activity throughout this study in the control samples. However, after adriamycin treatment no increase in ALPase activity could be observed. The histochemical data showed that the increased activity in the control was confined to the peripheral pulp, sub-odontoblastic layer, stratum intermedium, ameloblasts and odontoblasts. Although these layers showed a decreased activity after adriamycin treatment, the ameloblasts showed an increase in activity over the control. The data has shown that adriamycin caused a reduction in total ALPase activity in developing molars in vitro; osteodentin production by pulp cells; and appeared to produce an acceleration in the differentiation of ameloblasts.

The effects of adriamycin on dental proteins formation and mineralization in vitro

Second maxillary molars of 4-5 days old golden hamsters were exposed for 2 h in vitro to 1 mg/L adriamycin, rinsed and subsequently cultured up to 7 days without the drug. At days 3, 5 or 7 of culture the synthesis of extracellular tooth matrices and their mineralization were examined by measuring the incorporation of 3H-proline and the uptake of 45Ca and 32PO4 by the explants during a 24 h pulse labeling. Compared with unexposed control explants, exposure to adriamycin for the first 2 h of culture had no effect on total biosynthesis of proline-containing matrix proteins. However, at days 3 and 5 of culture it increased the quantity of water-soluble enamel matrix proteins (amelogenins). Adriamycin also strongly reduced the amount of organically-bound 32P-activity in a fraction extractable with guanidine-HC1-EDTA only, allegedly containing a mixture of mineral-associated proteins from both enamel and dentin. Since this decrease of 32P-activity coincided with the formation of osteodentin in the pulp as shown previously in histological and electron microscopical studies, it was speculated that osteodentin matrix may not contain the highly phosphorylated, dentin-specific phosphoproteins (DPP). Adriamycin also affected the uptake of 45Ca and 32PO4. At day 3 these values were slightly higher than control values but lower at days 5 and 7. It therefore appears that a 2 h exposure to adriamycin in concentrations as low as 1 mg/L causes an acceleration of secretory amelogenesis by tooth germs in vitro. It also induces pulp cells to form osteodentin.

Cariogenic changes in dental enamel of boys and girls in relation to salivary properties. II. Radiological examination

In earlier clinical studies of a group of children subjected to an intense fluoride treatment programme several salivary properties were related to cariogenic changes in the enamel surface, as assessed by mirror and probe. In this study the relationship between salivary parameters and cariogenic changes was investigated on bitewings taken from the same teeth. Inverse correlations were found between the acid producing capacity of the micro-organisms in the saliva (as determined in the Snyder test) and most cariogenic changes detected in bitewings particularly in boys. These radiologically detected changes in enamel were the reverse of those obtained clinically. These discrepancies were explained by differences in sensitivity between clinical and radiological techniques used to diagnose cariogenic changes. In contrast it was confirmed radiologically that for girls the P concentration in saliva and for boys the amount of resting saliva are important for preventing extension of caries into deeper layers of enamel.

The effects of NaF, alpha-C12DMEAHF and alpha-C12DMEAHCl on caries development in dentine in situ

Using histological techniques it was possible to demonstrate that during in situ caries development in bovine dentine, the demineralization process preceded the emergence and changes in the organic matrices. In addition, these data demonstrated as that 0.006% F- given either as the quaternary ammonium compound or NaF completely prevented demineralization by acting primarily on the dentine mineral. Inhibition by the quaternary ammonium compound alone was incomplete probably through repression of acid production by micro-organisms normally resident in the saliva.

Relationship between cariogenic events and salivary tests in boys and girls: oral examination

For boys and girls several salivary tests have been correlated with the following early cariogenic processes developing simultaneously in dental enamel: initiation, regression, stabilization and progression. These events were observed clinically during three consecutive intervals. Only correlations, significant during at least two random intervals were discussed. The Snyder test determined at 24 hours was significantly positively correlated with most events confined to the enamel surfaces and only the Snyder test determined at 48 hours in stimulated saliva appeared to be significantly positively related with deeper processes such as progression. In addition, the mineral composition of Ca2+, P and Mg2+ in saliva was significantly related to cariogenic events in the enamel surfaces of girls, and its viscosity for boys. Finally, and most interesting from a clinical point of view, was the fact that caries progression was negatively related with P concentrations in both unstimulated and stimulated saliva for girls. For boys a negative correlation was found between caries progression and flow of stimulated saliva.

Differences between primary and permanent teeth in posteruptive age dependency of radiological changes in enamel during the development of approximal caries

A longitudinal radiological study of children (N = 549) who participated in a comprehensive preventive maintenance program showed that caries related events in the approximal surfaces of permanent teeth differed from those in deciduous teeth. Changes in the approximal surfaces of the younger permanent teeth were more pronounced than of the older primary teeth and differed significantly from 1 year to 2.5 years. These findings can be explained by posteruptive maturation of tooth enamel.

Possible functions of alkaline phosphatase in dental mineralization: cadmium effects

In mineralizing dental tissues the non-specific alkaline phosphatase, using paranitrophenylphosphate (p-NPP) as substrate, is also capable of splitting inorganic pyrophosphate (PPi). In contrast to the p-NPP-ase part of the enzyme, the PPi-ase part requires Zn2+ as a cofactor for its hydrolytic activity. The PPi-ase activity of the enzyme can be inhibited by cadmium ions (Cd2+), perhaps by replacing Zn2+ from the active site of the enzyme molecule. In addition to splitting PPi, the PPi-ase part of the enzyme may also be involved in the phosphorylation process of yet undetermined organic macromolecules. Cd2+ inhibits this phosphorylation process. Inhibition of the PPi-ase activity can also be accomplished by ascorbic acid known for its capacity to complex bivalent cations. Ascorbic acid may accordingly also remove Zn2+ from the active site of the PPi-ase. It is suggested that in developing dental tissues alkaline phosphatase is not only associated with the transport of phosphate ions towards the mineralization front, but is also involved in the phosphorylation of organic macromolecules, a process activated the PPi-ase part of the enzyme.

[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.