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PubMed1995

Enamel mineralization and the role of ameloblasts in calcium transport.

Amelogenesis is a dynamic and unique process of cell-matrix interactions in that matrix synthesis, degradation and resorption all proceed simultaneously, coupled with mineral depositions in a compartment between ameloblasts and dentin or dental papilla. Accumulation of data suggest the role of ameloblasts in tooth morphogenesis and matrix formation, but no fully acceptable explanation has been given concerning the role of ameloblasts in calcium transport. In this article, old and new points of issue raised regarding the role of ameloblasts in calcium acquisition are reviewed and possible mechanisms whereby the ameloblasts prevent the rise of cytosolic calcium while actively or less actively transporting calcium are elaborated upon based on recent findings.

Ameloblasts↗
PubMed1995

Localization of plasma membrane Ca2+ pump mRNA and protein in human ameloblasts by in situ hybridization and immunohistochemistry.

The distribution of the plasma membrane Ca(2+)-pump (PMCA) proteins in human ameloblasts was examined immunohistochemically using monoclonal antibodies JA8 and 5F10. Further, the distribution of mRNA transcripts derived from two PMCA genes, PMCA-1 and PMCA-4 was examined using in situ hybridization. In rats, the PMCA-1 gene is purported to code for PMCA proteins with a role in maintaining the intracellular Ca2+ levels in nonepithelial cells. Other genes including the PMCA-4 gene may code for PMCA proteins characteristic of Ca2+ transporting epithelia. The present results show immunohistochemical staining in the Tomes processes and plasma membranes of human ameloblasts. Our studies also demonstrate a gradation of expression of the PMCA-1 and PMCA-4 mRNA transcripts which parallels the onset and progression of enamel mineralization. These studies suggest that PMCA proteins in human ameloblasts may function both in intracellular Ca2+ homeostasis and in regulating the vectorial Ca2+ influx into mineralizing enamel.

Ameloblasts↗
PubMed1995

Mechanistic understanding of enamel mineralization under fluoride regime.

In order to learn more about how the microenvironment for enamel mineralization is modified by fluoride at low concentrations (0 through 1 ppm) and how excess fluoride retards the degradation and removal of amelogenins, we studied precipitation reactions in an in vitro model utilizing a dialysis chamber. The results showed that, with the limited supply of Ca ions through the ultrafiltration membrane, the solution composition surrounding the seed crystals showed a proximity to the steady-state condition after 12-24 h equilibration. Major findings were that (a) fluoride overcame partially the inhibition of precipitation and growth reactions by enamel proteins and (b), with this accelerating effect of fluoride, the steady-state Ca concentrations in the media surrounding the seed crystals decreased substantially as a function of fluoride concentration. The overall results support the concept that the presence of fluoride in the mineralizing milieu can modify markedly the steady-state concentrations of mineral lattice ions, particularly decreasing free Ca2+ concentrations, which in turn may modulate protease activities in situ.

Amelogenin↗
PubMed1995

Dentin mineralization and the role of odontoblasts in calcium transport.

Dentin is formed by two simultaneous processes, in which the odontoblasts are instrumental--the formation of the collagenous matrix, and mineral crystal formation in this matrix. This pattern of formation is similar to that of bone, another mineralized connective tissue. Dentin and bone also have chemical compositions which are similar but with distinct differences. It is of fundamental importance to understand how the ions constituting the inorganic phase are transported from the circulation to the site of mineral formation and how this transport is regulated. For dentinogenesis, calcium is essentially the only ion for which data are available. Recent evidence suggests that a major portion of the Ca2+ ions are transported by a transcellular route, thus being under cellular control. The cells maintain a delicate Ca2+ ion balance by the concerted action of transmembraneous transport mechanisms, including Ca-ATPase, Na+/Ca2+ exchangers and calcium channels, and of intracellular Ca(2+)-binding proteins. The net effect of this is a maintenance of a submicromolar intracellular Ca2+ activity, and an extracellular accumulation of Ca2+ ions in predentin, at the mineralization front. Predentin can be regarded as a zone of formation and maturation of the scaffolding collagen web of the dentin organic matrix. In addition to collagen, it contains little but proteoglycan. Simultaneous with mineral formation, additional non-collagenous macromolecules are added to the extracellular matrix of dentin, these presumably being transported within the odontoblast process. Among these are highly phosphorylated dentin phosphoprotein (phosphophoryn) and another pool of proteoglycan.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1995

Evidence of two types of odontoblasts during dentinogenesis in elasmobranchs.

The fine structure of the odontoblasts in the sting rays, Dasyatis akajei, Dasyatidae, and Urolophus aurantiacus, Urolophidae, was examined using light and transmission electron microscopy. In the dentinogenesis stage, the odontoblasts have been classified into two types, that is, dark cells and light cells, based on differences in their fine structure. Many dark odontoblasts found along the predentine displayed well-developed organelles with secretory activity around the nuclei. They contained large amounts of expanded rER, widely distributed Golgi apparatus and secretory granules. In contrast, light odontoblasts showed a relatively clear cytoplasm and extended long processes which passed through the predentine and penetrated into the dentine. They contained large numbers of microtubules in the processes and many mitochondria around the nuclei. It is suggested that the light odontoblasts play an important part in material transport to the dentine and/or act as a sensory organ of the tooth. The dark odontoblasts seem to produce the organic matrix of the dentine and to prepare for mineralization in the dentine.

Animals↗
PubMed1998

Enamel mineralization and an initial crystalline phase.

In this communication, we summarized our recent experimental approaches to an unsettled issue, i.e., the nature and role of an acidic precursor in enamel mineralization. The objectives we specially focused our attention on are: the composition, structure and high resolution images of enamel crystals at various developmental stages, thermodynamic and kinetic consideration of octacalcium phosphate (OCP) vs hydroxyapatite (HA) precipitation in physiological media simulating the enamel fluid, reversible changes in the composition and structure of OCP, effects of fluoride at low concentrations and enamel proteins on OCP hydrolysis, and adsorption of enamel proteins onto OCP and fluoridated hydrolysates at neutral pH and room temperature. On the basis of all experimental evidence, we propose that enamel crystal growth comprises two events: the two-dimensional growth of an OCP-like precursor in a narrow outermost zone adjacent to the ameloblasts and the subsequent overgrowth of apatite units on the template under discrete fluid environment in the underlying region distant from the cell layer. The experimental data also support the concept that the whole process of enamel mineralization is modulated substantially through interaction between enamel proteins and crystals including the acidic precursor.

Adsorption↗
PubMed1976

Reprecipitation phenomena arising during the preparation of demineralised sections. III Scanning electron microscopic examinations of secondary calcium phosphate deposits.

Sections of teeth partly demineralized in 10% formic acid were examined by X-ray diffraction, microradiography and scanning electron microscopy. In the undemineralized circumpulpal dentin, the tubules were empty, lying in a matrix containing hydroxyapatite. In the "plume" areas of remineralisation, the tubules were filled with mineral deposits. X-ray diffraction revealed the presence of brushite and monetite in these areas. In the outer layers of dentin the tubules were empty, lying in a matrix containing some residual hydroxyapatite. These findings confirmed that the remineralisation process occurred within the dentinal tubules.

Calcium Phosphates↗
PubMed1992

Macroscopic sectioning of undecalcified tissues.

An inexpensive laboratory apparatus designed to section undecalcified teeth and bone has been constructed. It consists of an electric motor with a mandrel bearing a carborundum sectioning disk centered within a Plexiglas enclosure. A coolant flows from a reservoir positioned in the upper portion of the Plexiglas enclosure to prevent desiccation or burning of the tissues. Undecalcified tissue can be cut into a series of thin, 0.5-1 mm slices to facilitate studies of pulpal enzymes, tooth morphology and design of dental cavity preparations.

Humans↗
PubMed1975

Effect of oxytetracycline and purified calcein (DCAF) on the apposition and mineralization of rat incisor dentin.

Thirty male rats in groups of ten were given intraperitoneal injections of oxytetracycline and purified calcein (DCAF) every day for 10 d in order to determine whether these fluorescent hard tissue markers per se had any adverse effects on weight development and dentin apposition and mineralization. It was found that oxytetracycline and DCAF in doses of 15 mg/kg, which are the routine doses used by the author in hard tissue studies, do not seem to have any measurable influence on these parameters, while their ability to cause fluorescence is fully satisfying in dentin as well as in bone.

Animals↗
PubMed1975

[The effect of tetracycline antibiotics on the calcium and magnesium content of rat incisors].

Using electron probe microanalysis, the authors determined the calcium and magnesium contents in the incisors of rats treated with different doses of tetracycline and oxytetracycline, and in those of untreated rats. The contents of these elements were significantly lower in the dentine of the treated animals than in that of the control animals, whereas the enamel samples showed no statistically significant differences. The concentration tendency in different tooth sections, from the periphery to the pulp canal, i.e., decrease in calcium and increase in magnesium, was not influenced.

Animals↗
PubMed1976

Autoradiography of 99Mo in developing rat teeth and bone.

Four littermate, 8-day-old rats were given intraperitoneal injections of 99Mo and sacrificed at 1, 4, 24, and 96 h. Autoradiography of whole-body freeze-dried sections was carried out to study distribution of the tracer, particularly in bones and teeth. The tracer was rapidly cleared from the soft tissues except for the kidney and urinary bladder. Uptake in growing bone was moderate and relatively transient. The dentin showed moderate uptake, but enamel in the final mineralization phase showed the most intense concentrations of 99Mo of all mineralized tissue. The tracer did not appear in the pulp, enamel organ, or early enamel matrix.

Animals↗