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PubMed1999

Blood circulation as source for osteopontin in acellular extrinsic fiber cementum and other mineralizing tissues.

Osteopontin (OPN) is one of the major non-collagenous proteins in root cementum and other mineralized tissues. Although most of this mineral-seeking protein is thought to be produced by local tissue cells, some of it might enter the mineralizing matrix from the blood. To test this hypothesis, we followed the distribution of a single dose of purified porcine or rat 125I-labeled OPN injected i.v. in rats, in mineralizing and non-mineralizing tissues and in subcutaneously implanted collagenous implants. The animals were killed 30 or 48 hrs after injection. Tissues (calvaria, tibia, lower and upper jaws) were harvested and processed for radioautography and biochemical analysis. Tissues as well as calcifying collagenous implants proved to have taken up radiolabel. In EDTA extracts of long bones, the majority of the radiolabel was demonstrated to be associated with intact OPN. The iodinated protein was also found in the acellular extrinsic fiber cementum (acellular cementum) layer investing the continuously growing incisors, in laminae limitantes, cement lines, and in forming bone near the mineralization front. Further, the label was present in the circumpulpal dentin of the incisors, and some of it appeared to have been incorporated into developing enamel. It is concluded that OPN in acellular cementum and other mineralizing tissues may-at least partially-originate from sources outside the direct environment following its transportation via serum.

Animals↗
PubMed2002

Noggin blocks osteoinductive activity of porcine enamel extracts.

Enamel extracts induce biomineralization such as osteogenesis and cementogenesis, but the molecular component responsible for this activity remains uncertain. We fractionated enamel extracts from developing pig teeth and isolated the osteoinductive fraction. Proteins from pig enamel scrapings were extracted under alkaline conditions (pH 10.8) and fractionated with the use of a Sephadex G-100 (size exclusion) column. The ability of each fraction to enhance alkaline phosphatase (ALP) activity was assayed in ST2 cells, a mouse bone marrow stromal cell line. The osteoinductive fraction of enamel extracts (OFE) was found in fractions 44 and 45, which induced ST2 cells to express the phenotype of bone-forming osteoblasts, and to form mineralized nodules. Furthermore, the ALP activity of ST2 cells exposed to OFE was reduced by noggin, an antagonist of BMPs, and OFE reacted with BMP-2/4 antibody in dot-blot analysis. These results indicate that OFE contains BMPs that contribute to the induction of biomineralization.

Alkaline Phosphatase↗
PubMed2001

New genes involved in odontoblast differentiation.

The odontoblast phenotype has been mainly approached by the biochemical characterization of dentin matrix proteins and by extrapolation of the knowledge of bone cell biology, since dentin and bone share many similarities. In fact, direct investigations of the odontoblast phenotype have been hindered by the limited number of cells within the dental pulp and the difficulty in microdissection and isolation of a pure population of these cells. To overcome these obstacles, we previously developed a cell-culture system that promotes differentiation of human dental pulp cells into odontoblasts. This material now permits the study of odontoblasts through molecular biology techniques. Therefore, we constructed a cDNA library enriched for odontoblast-specific genes using the suppression subtractive hybridization technique (SSH). This library led us to identify new genes expressed by odontoblasts. In this paper, we will focus on some genes implied in various functions associated with odontoblast differentiation, such as cell polarization (MAP1B), dentin mineralization (PHEX, osteoadherin), and relationships between odontoblasts and nerve cells (reelin). Another important fact is that about 40% of the cDNA were unknown genes. Therefore, one can speculate that some of them will be odontoblast-specific, since, until now, only one gene (DSPP) presents this characteristic.

Cell Adhesion Molecules, Neuronal↗
PubMed1989

Hypocalcification and hypoplasia in permanent teeth of children from different ethnic groups in South Africa assessed with a new index.

A new descriptive index, the HHI (hypocalcification-hypoplasia index), is described for comparing enamel defects in groups of people. The index was used in a study completed in 1986, in which 1251 11-year-old children from different ethnic groups resident in South Africa were examined: 210 rural black, 203 urban black, 206 urban colored, 426 urban Indian, and 206 urban white. The index can be used as a screening examination, and the results from these different ethnic groups are presented.

Child↗
PubMed1989

Scanning electron microscopy of trypsin-treated enamel from fluorosed rat molars.

Fluoride-induced pitting and porosity of teeth have long been observed, but little progress has been made in determining their origin. We have observed, in the trypsin-treated surfaces of enamel, pits that disappear on completion of maturation, following the removal of the protein matrix and full mineralization. Since these pits were considered to be similar to those seen in fluorotic teeth, this scanning electron microscope (SEM) study was undertaken to determine the effect of fluoride on these transient developmental pits during enamel matrix maturation. A group of 20 eight-day-old rats was given daily intraperitoneal injections of NaF (20 mg/kg [9 mg F-/kg] body weight) for five days. Twenty control animals received intraperitoneal injections of isotonic saline. Maxillary and mandibular molars were dissected from the 13-day-old animals, washed in HEPES buffered (Ca2+/Mg2+) free basal medium, Eagle's (BME), incubated in 3% trypsin/BME for 5-10 min at room temperature, then indirectly sonicated in BME for 2-4 min. Clean crowns were fixed in 2.5% glutaraldehyde for three hr, dehydrated, critical-point-dried, and sputter-coated for SEM. Pits in the surfaces of developing enamel were observed in all groups. In control teeth, the pitting was restricted to the cervical margin, whereas in teeth from the fluoride-treated animals, pits were observed on some cuspal surfaces in addition to the cervical margin. These results confirmed that pits in trypsin-treated surfaces of developing enamel are a transient developmental event and showed that, in the presence of a high dose of fluoride, the maturation of enamel is modified with retention of the pits.

Animals↗
PubMed1989

Enamel hypomineralization viewed from the pattern of progressive mineralization of human and monkey developing enamel.

Microradiograms and their computer-aided image analysis of ground sections of the developing enamel of human permanent third molars and monkey permanent teeth (Macaca fuscata) indicate that the mode of progressive mineralization of enamel is completely different between the matrix formation and maturation stages. During the former stage, the enamel matrix is slightly mineralized. During the latter stage, which takes a much longer period than the previous stage, the increase in the secondary mineralization takes place first slightly, from the surface toward the inner layer, and then heavily, from the inner layer toward the surface. The narrow outer layer mineralizes very slowly during the middle and late stages of maturation, but finally achieves the highest mineralization of the entire enamel layer. The very narrow innermost layer mineralizes slowly without expanding its width. The former three processes seem to be under the direct control of the ameloblasts. Hypoplastic areas which appear during the matrix formation stages are not necessarily accompanied by hypomineralization. Dysfunction of the cells immediately after the completion of matrix formation appears to cause hypomineralization throughout the entire width of matrix except for the innermost layer. Disorders of the cells occurring during the middle and/or the late stage of maturation--due to chronic metabolic disturbances, such as fluorosis--induced hypomineralization localized mainly at the outer layer. The hypomineralized enamel is not necessarily accompanied by hypoplasia. The process of enamel mineralization is not necessarily fully synchronized with that of tooth eruption. Therefore, the narrow outer layer, especially in the fissure and cervical regions, is sometimes hypomineralized even after the teeth have erupted normally.

Animals↗
PubMed1989

Crystal morphology and decalcification patterns compared in rat and human enamel and synthetic hydroxyapatite.

The purpose of this investigation was to compare morphology and dissolution patterns by ultrastructural examination of rat and human enamel crystals as well as synthetic apatite crystals. Mature enamel crystals were of particular interest, since crystal maturation appears to be inhibited in amelogenesis imperfecta. Specimens were isolated from developing and mature rat incisor enamel. Rat enamel, mature human enamel, and synthetic apatite were thin-sectioned without decalcification and examined by transmission electron microscopy. Some sections were exposed to acid, and selected synthetic apatite sections were further treated for removal of embedding plastic, followed by vacuum-shadow-coating with carbon. Results showed that cross-sections of rat, human, and synthetic crystals had a distortion in the flattened hexagonal outline in regions where the growth of one crystal impinged on another. Crystal dissolution occurred preferentially along the c-axis, producing a central defect or hole in the crystals. Preliminary studies with weak acid on mature human enamel indicate that the relatively soluble crystal core is quickly dissolved, while the outer shell remains intact over a much longer period of time. In the mature rat and human enamel, this crystal hole formation had a consistent dimension of approximately 10-nm thickness. The crystal hole dimension was the same size as crystals that are formed during the early secretory phase in rat amelogenesis. Acid-treated synthetic apatite also showed dissolution of the crystal core along the c-axis, but dimensions of the hole were not consistent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Strategies for improving the assessment of dental fluorosis: focus on chemical and biochemical aspects.

In order to assess fluoride accumulation and effects in developing dental tissues, one must determine the concentration profile of fluoride in the tissue and to assess separately the labile (i.e., free ions in fluid and ions associated with organic matter) and stable (i.e., incorporated into apatite lattice) pools of fluoride. Free fluoride ions in the mineralizing milieu markedly affect the driving force for precipitation and, as a result, the nature of precipitating crystals. The fluoride incorporated into the crystalline lattice increases the stability of the formed mineral. Improvement in the understanding of the mechanism of dental fluorosis requires more comprehensive information about the effects of fluoride on the ionic composition of the fluid phase, the nature of the initially precipitating mineral(s), the interactions between crystals and matrix proteins, and the enzymatic degradation of the proteins. Recent observations relevant to the role of fluoride in enamel formation include: (1) that there are threshold concentrations of fluoride below which the precipitation and hydrolysis of thin-platy octacalcium phosphate is facilitated but beyond which de novo apatite precipitation prevails; (2) that the presence of fluoride in the mineralizing milieu most likely affects the steady-state concentrations of mineral lattice ions; (3) that incorporation of fluoride into the stable pool is retarded by the presence of matrix proteins, particularly amelogenins, which inhibit the growth of apatite crystals; (4) that increasing the degree of fluoridation of apatite crystals enhances the adsorption of amelogenins onto the crystal surface, and (5) that amelogenins pre-adsorbed onto apatite crystals are more resistant to enzymatic cleavages by trypsin (used as a prototype of amelogeninases).

Ameloblasts↗
PubMed1996

Toward understanding the function of amelogenin using transgenic mice.

The purpose of this study was to establish transgenic mouse lines as a tool to investigate the function of amelogenin during mineralization by causing ectopic production of amelogenin and studying its effect. The mouse amelogenin (mAme) was cloned from a 16-day-old whole mouse embryo cDNA library and was determined to be "full-length" mouse amelogenin (with a complete coding region) by comparison with the mouse amelogenin reported previously by Snead et al. (1985) and Lau et al. (1992). The overexpression construct contained: (1) the rat osteocalcin (OC) promoter (1.8 kb); (2) the adenovirus splicing casettes, including introgenic (Int) sequence (0.3 kb); (3) the full-length mAme cDNA (0.8 kb); and (4) the polyadenylation signal sequence from the pSG5 mammalian expression vector. Both Southern blotting and polymerase chain-reaction (PCR) analyses were performed, by means of a specific probe and a pair of oligodeoxynucleotides to OcIntmAme(A)+, respectively. The animals which showed transgene-positive in both analyses were further used to establish F1 animals. Heterozygocity was confirmed with F1 animals by PCR analysis of DNA from the F0 x FVB/N pups. Three independent transgenic F1 heterozygous lines (640t, 706t, and 708t) have now been established. The generation of F2 homozygous lines is under way. The heterozygous transgenic animals are currently being analyzed for alterations in the morphology and structure of various bone tissues.

Amelogenin↗
PubMed1996

Quantitative immunocytochemistry of Ca(2+)-Mg2+ ATPase in ameloblasts associated with enamel secretion and maturation in the rat incisor.

Our previous studies revealed intense membrane-associated labeling for Ca(2+)-Mg2+ ATPase (Ca(2+)-pump) in secretory and maturation ameloblasts in the rat incisor, both by enzyme cytochemistry and by immunohistochemical techniques. The purpose of the present study was to map the distribution of Ca(2+)-pump protein at the cellular and subcellular levels by means of a Ca(2+)-pump-specific monoclonal antibody and electron microscopic immunogold cytochemistry. Tissue specimens were dissected from secretory, early, and late enamel maturation zones. We quantified results by comparing gold particle densities over ameloblast lateral and distal plasma membrane regions, supranuclear cytoplasm, regions of the ruffled borders, and nuclei. The highest concentration of gold particles was seen over the distal membranes of early-maturation ameloblasts relative to those in late-maturation and secretory stages. Cytoplasmic labeling was less than that of the distal and lateral membranes, and gold particles located over nuclei were considered to be due to non-specific binding. These results are consistent with our earlier findings and suggest a role for the plasma membrane Ca(2+)-pump in the regulation of calcium availability to mineralizing enamel.

Ameloblasts↗
PubMed2001

Proteoglycans in dentinogenesis.

The predominant proteoglycans present in predentin and dentin are the chondroitin-sulphate-rich decorin and biglycan and the keratan-sulphate-rich lumican and fibromodulin. These are small, interstitial, leucine-rich proteoglycans which have recently been shown to exist in gradients across the predentin. Antibodies recognizing chondroitin sulphate show a decreasing gradient from the pulpal aspect toward the mineralizing front, the converse being true for keratan sulphate. Antidecorin shows an increase toward the mineralization front. Evidence from biochemical, autoradiographic, and immunohistochemical studies implies that such changes may be brought about by gradients of metalloproteinases. This offers the possibility that the proteoglycans organize the collagen network for receipt of phosphoproteins and phospholipids, the former being evident only at the onset of dentin formation. The suggestion is raised that glycosaminoglycan-depleted leucine-rich protein cores act as sequester points for receipt of phosphoproteins in particular. The rigid, spatially oriented glycosaminoglycan chains on decorin and biglycan are known to bind calcium and may feature directly in mineral initiation.

Animals↗
PubMed1993

Dentinogenesis.

The formation of dentin, dentinogenesis, comprises a sophisticated interplay between several factors in the tissue, cellular as well as extracellular. Dentin may be regarded as a calcified connective tissue. In this respect, as well as in its mode of formation, it is closely related to bone. Using dentinogenesis as an experimental model to study biomineralization provides several practical advantages, and the results may be extrapolated to understand similar processes in other tissues, primarily bone. After describing dentin structure and composition, this review discusses items such as the morphology of dentinogenesis; the dentinogenically active odontoblast, transport, and concentrations of mineral ions; the constituents of the dentin organic matrix; and the presumed mechanisms involved in mineral formation.

Animals↗
PubMed1995

Molecular mechanisms of dental enamel formation.

Tooth enamel is a unique mineralized tissue in that it is acellular, is more highly mineralized, and is comprised of individual crystallites that are larger and more oriented than other mineralized tissues. Dental enamel forms by matrix-mediated biomineralization. Enamel crystallites precipitate from a supersaturated solution within a well-delineated biological compartment. Mature enamel crystallites are comprised of non-stoichiometric carbonated calcium hydroxyapatite. The earliest crystallites appear suddenly at the dentino-enamel junction (DEJ) as rapidly growing thin ribbons. The shape and growth patterns of these crystallites can be interpreted as evidence for a precursor phase of octacalcium phosphate (OCP). An OCP crystal displays on its (100) face a surface that may act as a template for hydroxyapatite (OHAp) precipitation. Octacalcium phosphate is less stable than hydroxyapatite and can hydrolyze to OHAp. During this process, one unit cell of octacalcium phosphate is converted into two unit cells of hydroxyapatite. During the precipitation of the mineral phase, the degree of saturation of the enamel fluid is regulated. Proteins in the enamel matrix may buffer calcium and hydrogen ion concentrations as a strategy to preclude the precipitation of competing calcium phosphate solid phases. Tuftelin is an acidic enamel protein that concentrates at the DEJ and may participate in the nucleation of enamel crystals. Other enamel proteins may regulate crystal habit by binding to specific faces of the mineral and inhibiting growth. Structural analyses of recombinant amelogenin are consistent with a functional role in establishing and maintaining the spacing between enamel crystallites.

Amelogenesis↗
PubMed2002

Cystic fibrosis transmembrane regulator gene (CFTR) is associated with abnormal enamel formation.

Cystic fibrosis (CF), a chloride ion transport disorder, is caused by mutations of the cftr gene and is the most common autosomal-recessive heritable disease in Caucasians. CFTR knockout mice have enamel with crystallite defects, retained protein, and hypomineralization, suggesting a role for CFTR in enamel formation and mineralization. This investigation examined CFTR expression and elemental composition in developing murine incisor teeth. RT-PCR showed cftr mRNA expression in the normal mouse apical incisor tissue but not in the CFTR knockout tissue. Elemental analysis by energy-dispersive x-ray spectroscopy showed relatively decreased chloride in secretory-stage CF enamel. Iron and potassium were significantly increased, and calcium was significantly decreased (p value = 0.05) in the CF mature enamel. Abnormal enamel mineralization, ion concentrations, and molecular evidence of cftr mRNA expression by odontogenic cells strongly suggest that CFTR plays an important role in enamel formation.

Amelogenesis↗
PubMed2002

Assessment of enamelysin (MMP-20) selectivity to three peptide bonds on amelogenin sequence.

Recent studies have highlighted the potential role of the metalloproteinase enamelysin (MMP-20) in controlling some of the most critical stages during enamel development. This study was aimed to assess the selectivity of enamelysin to the three most abundant cleavage sites on the amelogenin sequence, and to gain insight into the factors that control the pattern of amelogenin processing during enamel mineralization. Three deca-peptides with sequences based on pig amelogenin and including the proteolytic cleavage sites W/L, S/M, and P/A were synthesized as substrates. Statistical analysis revealed no significant differences in the rates of cleavage among the three peptides, indicating comparable selectivity of enamelysin for these peptide bonds. Considering the selective appearance of amelogenin proteolytic products, we suggest that amelogenin folding and assembly are the primary factors in controlling the pattern of its proteolysis during the secretory stage of enamel development.

Alanine↗
PubMed2002

Odontoblasts enhance the maturation of enamel crystals by secreting EMSP1 at the enamel-dentin junction.

The temporal expression patterns and activity distributions of enamelysin and EMSP1, which are the major proteinases in immature enamel, were characterized. Extracellular matrix fractions from developing porcine incisors, individually comprised of predentin, dentin, and four secretory-stage enamel samples, including the highly mineralized enamel (HME) at the enamel-dentin junction (EDJ), were isolated, and their resident proteinases were identified by zymography. Soft-tissue fractions, which included cells from the extension site of enamel formation (ESEF), secretory- and maturation-stage ameloblasts, and odontoblasts, were characterized histologically and by RT-PCR for their expression of enamelysin and EMSP1. A significant finding was that EMSP1, expressed by odontoblasts, concentrates in the HME, but is not detected in predentin or dentin. We conclude that odontoblasts deposit EMSP1 via their cell processes into the deepest enamel layer, which facilitates the hardening of this layer and contributes significantly to the functional properties of the EDJ.

Ameloblasts↗