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At least 19 recordsLinked to original sources
PubMed1977

Quantitative analysis of cell turnover in the enamel organ of the rat incisor. Evidence for ameloblast death immediately after enamel matrix secretion.

During renewal of the enamel organ in the rat incisor cohorts of epithelial cells are transported sequentially through presecretory, secretory and maturation zones to the gingival margin where the life cycles of these cells terminate. This process was examined kinetically by determining the absolute flux of cells within each of these zones of amelogenesis. It was found that the efflux of ameloblasts, stratum intermedium and papillary layer cells from the presecretory zone was about equal to the efflux plus expected growth within the secretory zone. However, between the secretory and maturation zones about 50% more ameloblasts entered the maturation zone than were required to account for the egress at the gingival margin and the expected growth. Since there was no similar imbalance between these zones for papillary layer cells, it was concluded that this discrepancy must represent a 50% reduction in the size of the ameloblast population during the maturation stage of amelogenesis. It was calculated that a little over 25% of the loss occurred immediately at the start of maturation within the region of postsecretory transition and the remaining 25% of the loss occurred throughout the subsequent regions of the maturation zone. In addition to the kinetic analysis graphic reconstructions, or surface maps, of ameloblast nuclei were prepared. These maps illustrated the characteristics of ameloblast nuclear packing within the three zones of amelogenesis and they provided quantitative confirmation that as ameloblasts progress through the maturation zone, there is a loss of cells in an amount predicted by the kinetic analysis.

Ameloblasts↗
PubMed1979

3H-glucosamine electron microscope autoradiography after isolated labeling of the enamel organ or the dental papilla followed by reassociated toothgerm culture.

Electron microscope autoradiography was performed after isolated labeling with 3H-glucosamine of the enamel organ or the dental papilla of Swiss mice followed by reassociated toothgerm culture for 9.30 h and 19 h. After these two time intervals in case of an enamel organ labeling, numerous silver grains were observed in the intercellular spaces of the stellate reticulum indicating a concentrating and storing role of the latter. After dental papilla labeling, an almost complete absence of radioactivity was noted at 19 h. suggesting that 3H-glucosamine is not stored by the dental papilla. A clear labeling of the basement membrane area and of the adjacent aperiodic filamentous material found on the pulpal side was only observed after enamel organ labeling with 3H-glucosamine, suggesting an epithelial origin of the glycosaminoglycans found in these structures.

Animals↗
PubMed1977

A comparative study of alkaline phosphatase in calcifying cartilage, odontoblasts and the enamel organ.

The enzyme alkaline phosphatase (AP) (EC 3.1.3.1) in three different calcification areas was studied by means of a spectrophotometric micro method using p-nitrophenylphosphate as a substrate. Rat maxillary incisor odontoblasts and enamel organ from the zones of matrix formation and maturation and tissue from rabbit metatarsal cartilage were allowed to react with the substrate in glycine-NaOH buffer at room temperature. The reaction was found to be linear for a minimum of 20 min. The pH optima for AP from these tissues were in the pH range of 10.0-10.3. In order to compare AP from the four calcification areas different parameters were studied. Heating at 56 degrees C or 60 degrees C for varying times revealed that the enzymes were almost completely inactivated after 10 min. Mg2+ ions activated the enzymes by about 25% at concentrations of 2.5 mM (enamel organ 1.25 mM); while only higher concentrations of Mg2+ had an inactivating effect, Ca2+ and PO3-4 ions were inactivating at varying concentrations. F- ions showed no effect on AP activity at concentrations below 250 mM (enamel organ 125 mM) but caused inactivation of the enzymes at about 50% at 1 M. EDTA was found to be a very effective AP inactivator at concentrations above 0.06 mM, whereas urea did not noticeably affect the enzyme reactions at concentrations below 1 M. At higher concentrations, inactivation was observed. In order to determine AP localization in the epiphyseal plate successive 40-mum-thick, freeze-sectioned slices were analyzed. The activity was highest nearest the zone of cartilage calcification and decreased towards the reserve cell zone. It was concluded that the same AP isoenzyme is present in these quite different calcification loci.

Alkaline Phosphatase↗
PubMed1978

Morphologic changes in the rat enamel organ following a single intraperitoneal injection of sodium fluoride.

Enamel organs in developing teeth of young rats were studied after single intraperitoneal injections of a high dose of sodium fluoride (60 mg NaF/kg body wt.). The study employed primarily light microscopy, but electron microscopy was used to clarify some of the light microscopic findings. The pathogenesis of the fluoride-induced changes was followed during 72 h. Cellular changes were consistently found in the molars, but were never seen in the incisors. In the maxillary molars, ameloblastic injury was most commonly seen on the mesial surfaces of the cusps. One hour after injection, the most prominent findings were swollen mitochondria in the secretory ameloblasts and cleft formations between the ameloblasts and the enamel matrix. The clefts were filled with a stippled material. Some of the clefts gradually expanded to cystic cavities. The stippled material began to calcify after 24 h and formed small, darkly stained globules. After 72 h dearranged ameloblasts were found as islands intermingled with calcified rounded structures in the stellate reticulum. In stratum intermedium numerous atypic autophagic vacuoles appeared 2 h after injection. No light microscopic changes were observed in the postsecretory ameloblasts.

Ameloblasts↗
PubMed1978

Basement membrane reconstitution and cytodifferentiation of odontoblasts in isochronal and heterochronal reassociations of enamel organs and pulps.

The restoration of the basement membrane and the terminal differentiation of odontoblasts were studied in iso- and heterochronal reassociations between dental mesenchyme and enamel organs. It was suggested that the cytodifferentiation of odontoblasts was triggered by the basement membrane secreted by the enamel organ of a specific stage.

Animals↗
PubMed1978

Fine structure of the stratum intermedium, stellate reticulum, and outer enamel epithelium in the enamel organ of the kitten.

Stratum intermedium, stellate reticulum and outer enamel epithelium at the secretion stage in lower second molars of 1 week old kittens were studied with the electron microscope after perfusion fixation. All cell types had a well-developed Golgi apparatus, free ribosomes and little RER. In the stratum intermedium, cytoplasmic processes occasionally contained many vesicles of different types and were connected to neighbouring cells by gap junctions. The number of gap junctions in the stratum intermedium increased greatly with advanced secretion. The cells of the stellate reticulum had large sheet-like cell extensions and surrounded large extracellular spaces. Often, two cell extensions ran parallel to each other, with a narrow extracellular space between them. The narrow spaces were filled with a fluffy material. The outer enamel epithelium showed a smooth basal surface when close to a blood vessel. Facing a larger expanse of connective tissue, the basal surface became folded, the basal lamina formed extended loops into the connective tissue and showed areas of increased density, and cell processes extended through the lamina into the connective tissue. The blood vessels associated with the outer enamel epithelium had many pericytes and resembled post-capillary venules. Macrophages showing vacuoles, aggregations of small vesicles, and peripheral flaps of cytoplasm were present, mainly in the stellate reticulum. These observations are compared with the structure of the human enamel organ, as reported in the literature, and their possible functional significance is briefly discussed.

Ameloblasts↗
PubMed1975

Inorganic pyrophosphatase in isolated enamel organ and odontoblasts from the rat incisor.

The inorganic pyrophosphatase (PPiase) activity was determined by a colorimetric method in the odontoblasts and the parts of the enamel organ related to enamel matrix formation and enamel maturation. The effects on PPi hydrolysis by EDTA, R 8231, urea and heat treatment were found to be almost identical to those reported for nonspecific alkaline phosphatase (APase) in the same tissues. The Mg2+ activation curve for PPiase was also similar. Like those of APase, these characteristics of PPiase activity were identical in the three locations studied. It is suggested that the close similarity in the properties of PPiase and APase is due to activity of the same enzyme, a concept which is in agreement with recent biochemical and histochemical studies of calcification.

Animals↗
PubMed1975

Demonstration of adenosine triphosphate hydrolysis in the enamel organ of the mouse incisor.

The hydrolysis of adenosine triphosphate in the mandibular enamel organ demonstrated that the Mg++-activated ATPase was destroyed by pre-treatment with either heat or alcohol, substrate specific for ATP, stimulated by the addition of glutathione or dinitrophenol, and inhibited by oligomycin. The distribution of reaction product was the same with Mg++, Mn++ or Zn++ as the activating cation. Omission of Mg++ from the incubation medium, or replacement with Ca++ or Sr++ resulted in marked hydrolysis of ATP in the cells associated with enamel matrix formation, with loss of enzyme activity in the cells of the zone of enamel matrix maturation. Hydrolysis of ATP by the cells of the stratum intermedium, stellate reticulum and papillary layer was dependent upon Mg++, Mn++, or Zn++.

Adenosine Triphosphatases↗
PubMed1978

Calcium-stimulated ATPase activity in homogenates of the secretory enamel organ in the rat.

The activity of calcium-stimulated ATPase (E.C. 3.6.1.3) in homogenates of the secretory enamel organ of rat incisors was studied biochemically. ATP hydrolysis was estimated from the amount of inorganic phosphate liberated. An analysis of the total degradation of ATP was initially performed to ensure that the enzyme assays pertained to the original substrate, ATP, and were not influenced by reaction products formed. Standard incubations were run in tris-maleate buffer, pH 8.2, with 3 mM ATP, 3 mM Ca2+ and 0.5 mM R 8231 at 37 degrees C. The presence of R 8231 was necessary to inhibit nonspecific alkaline phosphatase. The calcium-stimulated ATPase was completely inhibited when heated at 55-60 degrees C for 5 min. The pH optimum was found to be 8.2. The hydrolysis was substantially dependent on Ca2+ and was fastest when the ATP:Ca2+ ratio was 1:1. High substrate concentrations inhibited the hydrolysis. The addition of 1 mM Zn2+ and Ni2+ to the incubation medium markedly inhibited the hydrolysis as did, though less strongly, p-hydroxymercuribenzoate, oligomycin, EDTA and ruthenium red. l-Cysteine, mercaptoethanol, iodoacetic acid and sodium azide were without effect. F- was without effect unless added to a final concentration above 15 mM to media where Ca2+ had first been allowed to react with ATP.

Adenosine Triphosphatases↗
PubMed1977

Adenosine triphosphate catabolism in homogenates of rat secretory enamel organs incubated in histochemical lead media.

To investigate how lead, when used as trapping agent, influences the ATP hydrolysis and to study how ATP is catalyzed in histochemical systems, homogenized secretory enamel organs were incubated in histochemical [3H]-ATP media. Aliquots from the media were taken after 3, 10, 20 and 30 min, the ATP and formed metabolites were separated by electrophoresis and radiometrically quantitated. In media lacking both lead and homogenate 2% of the ATP was spontaneously hydrolyzed during 30 min incubation at room temperature. The presence of lead caused an additional 8% hydrolysis at pH 7.2 and an additional 20% hydrolysis at pH 9.4. In the presence of homogenate, however, lead caused a net decrease of the hydrolysis of ATP as well as of ADP and AMP. This enzyme inhibition varied from around zero to some 80%, depending on pH and substrated involved. In homogenate-containing lead media, at both pH 7.2 AND 9.4, ATP was rapidly hydrolyzed primarily to ADP and subsequently to AMP and adenosine and/or inosine. After 5--10 min ADP constituted the predominant substrate at both pH:s. At pH 7.2 ADP remained so for the rest of the incubation, whereas at pH 9.4 AMP was predominant substrate at the end of the incubation. AMP was the finan catabolic product in experiments at pH 7.2, and adenosine and/or inosine at pH 9.4. Inorganic phosphate was liberated almost linearly during the whole incubation period. The results indicate that histochemical studies of substrate specific ATP-ases should be performed with short incubation times and, when high specific activities are present, in large quantities of incubation media to reduce interference by ADP and AMP hydrolyzing enzymes.

Adenosine Diphosphate↗
PubMed1975

[Vascularization and connective tissue penetration, factors in the involution of the enamel organ in the rat].

In the albino rat, at the 21th day of gestation, the capillaries entered the stellate reticulum of the molar and came into contact with the stratum intermedium. This vascular penetration was followed on the 10th day of age by a connective penetration. The stellate reticulum was thus disorganized and was built up by small epithelial islands surrounded by collagen and reticulin fibrils. Finally, the reduced enamel epithelium fused with the oral epithelium and formed the epithelial attachment. After a trophic role, the vascularization, with the help of the connective tissue penetration, had a destructive function. Both vascularization and connective tissue invasion contribute to the enamel organ involution.

Ameloblasts↗
PubMed1975

Cellular renewal in the enamel organ and the odontoblast layer of the rat incisor as followed by radioautography using 3H-thymidine.

Renewal of the cell populations of the incisor was studied in 100 gm male rats injected with a single dose of 3H-thymidine and sacrificed at various times from one hour to 32 days after injection. Radioautographs showed that a cohort of labeled cells within the enamel organ, odontoblast layer, and pulp was carried passively with the erupting incisor from the apical end towards the gingival margin where the life cycle of these cells was terminated. Labeled cells in the upper and lower incisor, although traversing different absolute lengths, were found in approximately the same functional stage of their life cycle at similar times after the injection. Thus, by one and on-half days labeled ameloblasts began inner enamel secretion and, by eight days (upper) or nine days (lower), complement outer enamel secretion. By 32 days labeled ameloblasts had traversed the entire enamel maturation zone and were located at the gingival margin. Labeled odontoblasts followed closely the movement of labeled ameloblasts. The mean rate of ameloblast migration was 567 mum/day on the upper incisor and 651 mim/day on the lower. For the odontoblasts this rate was 55 mum/day (upper) and 631 mum/day (lower). Finally, it was found that as the rat age, the duration of the life cycle for epithelial and pulp cell populations of the incisor increased because of growth within the lonitudinal axis of the tooth. It was concluded that the apical end of the incisor literally "grows backward" in the bony socket, and hence, the duration of the life cycle becomes greater simply because it takes cells longer to physically reach the gingival margin.

Ameloblasts↗
PubMed1979

[Role of dental pulp in the histogenesis of the enamel organ].

The histological study of in vitro cultured associations between dental pulps and outer dental epithelium showed that the predontoblasts initiated the histogenesis of the enamel organ and particularly the differentiation of the inner dental epithelium.

Animals↗