Developing Rat Molars Research Articles

In-vitro study of calcium-45 and phosphorus-32 uptake in developing rat molar enamel using quantitative methods

In-vitro quantitative studies were conducted on rat molar tooth expiants to determine the effect of the enamel organ on enamel mineralization during the secretory phase of formation. Control explants were compared to contralateral pairs which had (1) the enamel organ removed, (2) heat-treatment, or (3) treatment with the metabolic inhibitor dinitrophenol (DNP). Removal of the enamel organ enhanced enamel mineralization and 45Ca exchange with the enamel. Heat-treatment altered the enamel matrix to increase Ca uptake. DNP inhibited mineralization but increased 45Ca exchange through the enamel organ. The findings suggest that the enamel organ controls Ca flux into the forming enamel during the secretory phase and slows the rate of mineralization.

In-vitro study of the cellular control of 18F uptake in the enamel of developing rat molar teeth

Molar expiants from 6-day-old rats were cultured for 4 h in medium containing approx. 2μCi/ml 18F. Control-cultured expiants were compared to their contralateral pairs which had been subjected to: (1) the enamel organ removed prior to incubation; (2) the expiants heat-treated (65 °C for 10 min); or (3) a metabolic inhibitor, 5mM dinitrophenol (DNP), added to the medium. The Ca concentration of the medium indicated that the expiants became mineralized during incubation. Both removal of enamel organ and heat-treatment enhanced uptake of 18F from the medium. DNP had no consistent effect. As the pattern of 18F uptake was similar to that for net Ca uptake by mineralizing enamel, the findings suggest that there is no direct cellular control of F − flux through the enamel organ during the secretory phase of enamel formation.

In vivo and in vitro Study of 90Sr in Developing Rat Molar Enamel

The uptake patterns of 90Sr in developing rat molar enamel were studied in vivo and in vitro. Autoradiographic methods were used that preclude loss or translocation of tracers associated with water-soluble compounds in the sections. In eight-day-old rats injected with the tracer, 90Sr uptake in the enamel was significantly less than for dentin and bone, particularly at early sacrifice times. The uptake pattern of 90Sr was somewhat different from that previously observed for 45Ca. The in vitro experiments indicated that the viable intact enamel organ limits uptake of 90Sr by enamel in both the secretory and maturation phases of enamel formation.

In vivo and in vitro study of 48V uptake in developing rat molar enamel.

The uptake of 48V in developing rat molar enamel was studied in vivo and in vitro using autoradiographic and quantitative methods. It was shown that the uptake of 48V in enamel is less than in bone and dentin, and that plasma protein binding of 48V is primarily responsible for the limited uptake in enamel.

The penetration of intravascularly perfused lanthanum into the ameloblast layer of developing rat molar teeth

Eight-day-old rats were intravascularly perfused with an isotonic saline solution containing lanthanum to determine the permeabilities of the junctional complexes in the ameloblast layer of developing molar teeth to this tracer. At no stage in tooth enamel development did lanthanum penetrate through the extracellular space into enamel, suggesting that, to enter enamel, calcium must pass through a portion of the ameloblast.

The origin and localization of dentinal fluid in developing rat molar teeth studied with lanthanum as a tracer

Dentinal fluid was investigated in the developing upper molar teeth of 15-day old rats. Intravascularly administered lanthanum was deposited in the lumen and the pericapillary space of subodontoblastic capillaries, the inter-odontoblast spaces, the predentine and the peri-odontoblast spaces in the dentinal tubules. The terminal capillaries were fenestrated with endothelial cell junctions easily penetrated by lanthanum. Micropinocytotic vesicles and fenestrae may participate in the trans-endothelial transport. Once lanthanum was in the pericapillary space, the tracer appeared also in the predentine via the inter-odontoblast spaces. There appeared to be no true tight junctions between the odontoblasts. Lanthanum permeated freely in the predentine and accumulated at the predentine-dentine junction but did not penetrate into the intertubular dentine. Much lanthanum was deposited in the peri-odontoblast spaces of dentinal tubules. A little penetrated the peritubular dentine near the predentine-dentine junction. It is concluded that the dentinal fluid is a transudate from the terminal capillaries and circulates mainly within the dentinal tubules.

Influence of the Pulpal Route on Uptake of 45Ca in Enamel and Dentin of Developing Rat Molars

45Ca uptake in developing enamel and dentin was studied by autoradiography. The findings indicate that the pulpal route does not supply significant amounts of calcium to the rapidly mineralizing enamel. Disruption of the odontoblastic layer did not seem to result in altered penetration of calcium into the dentin in a manner similar to that described for disruption of the matrix secreting cell layer of enamel and of bone.

In vivo and in vitro study of59Fe uptake in developing rat molars

Autoradiographic methods were used to study 59Fe uptake in vivo in mineralizing tissues of young rats. Localization of 59Fe was observed in the ameloblastic layers of molars. In vitro studies were performed which demonstrated that 59Fe uptake in developing rat molar enamel was limited by the metabolic activity of the cells of the enamel organ.

Histochemical and electron probe analysis of secretory ameloblasts of developing rat molar teeth.

Calcium was not found in secretory ameloblasts and stratum intermedium cells when treated with OsO4-pyroantimonate or when surfaces prepared by fracturing fresh, rapidly frozen, developing molar tooth germs were subject to electron probe X-ray analysis. Pyroantimonate reaction product, considered to be calcium, was found in mitochondria of enamel organ cells which were first placed in a bath containing calcium and potassium. The plasma membrane was disrupted in cells ehich showed mitochondrial localization of reaction product. The results provide no data which indicates that enamel organ cells have a direct, active role in the movement of calcium into the enamel. Rather, it is suggested that the secretory enamel organ might serve as a selective barrier in regulating the initial mineralization of enamel.

Comparison of P with Ca Distribution in Developing Rat Molar Enamel In Vivo and In Vitro

The distribution of 45Ca and 33P in developing rat molar enamel has been studied using freeze sectioning and autoradiographic methods. The distribution patterns of the two tracers in vivo were dissimilar. The use of in vitro methods showed that flux of 33P into enamel is not influenced by the cells of the enamel organ. It is suggested that the factors controlling movement of calcium and phosphorus into mineralizing enamel may be similar to those proposed for bone.

The binding of calcium within the Golgi saccules of the rat odontoblast.

Odontoblasts of developing rat molar teeth were treated with OsO4-pyroantimonate to ascertain the localization of calcium. In addition, some tooth germs were incubated in solutions which were intended to allow for the escape of diffusible ions prior to fixation in OsO4-pyroantimonate. In tissues treated directly with OsO4-pyroantimonate, antimonate reaction product was found chiefly in abacus bodies and secretory granules of the Golgi region and in secretory granules in the distal pole of the cell. Lesser amounts of reaction product were found in the extracellular space, mitochondria, nucleus and generally throughout the cell. Tissues pre treated to allow for the escape of diffusible ions showed reaction product, identified as containing calcium, only in the abacus bodies and secretory granules. These results are considered to reflect the binding of calcium within the Golgi apparatus of the odontoblast. Moreover, since it has been shown by others that the abacus bodies and secretory granules contain collagen precursor, it is suggested that the collagen precursor is being seeded with calcium within the Golgi apparatus and that this intracellular calcium binding will play a role in facilitating the major wave of extracellular mineralization of the dentin which is to follow.

The pattern of sudanophilia in developing rat molar enamel

The pattern of sudanophilia in developing rat molar enamel follows closely that of calcification as described by other authors, starting at the dentine-enamel junction and spreading across the enamel towards the ameloblasts. It is possible that, as with other tissues, lipids take part in this calcification process. Since not all the sudanophilic material is removed by lipid solvents, some other non-lipid constituent of the matrix which stains with Sudan black may be also involved.

Cementogenesis in developing rat molars.

Cementogenesis in developing rat molars.

Dynamics of dental epithelium during tooth eruption.

The dental epithelium of developing rat molars was labeled with tritiated thymidine administered by gastric intubation. Labeled ameloblasts were lost from all enamel surfaces at approximately the same time by desquamation into the gingival sulcus. The other cells of the dental epithelium proliferated to form the renewing epithelial cuff.

Carbon 14 Tryptophan Metabolism in Developing Rat Molars

The unique absence of tryptophan in dentin collagen and its presence in enamel protein(s) provide a specific biological marker for the study of amelogenesis. Isotopic tryptophan was administered to young rats. The incorporation, distribution, and turnover of the labeled precursor was expressed in auto-radiographs and radiochemically determined specific activitv.

An autoradiographic study of tryptophane-H 3 incorporation into rat enamel and dentine matrices

l-tryptophane-H 3 was administered intraperitoneally, 1 μc/g of body weight, to 9-day-old NMRI-D rats. The rats were killed, 1, 4, 8 and 24 hr and 7 days post-injection. The incorporation and distribution of tryptophane-H 3 were evaluated in autoradiographs of the developing mandibular first molars. At 1 hr the cytoplasm labelling of the ameloblasts was considerably greater than the odontoblast labelling. The cytoplasm grain density over the ameloblasts gradually decreased as the labelling of the enamel matrix increased. At 4 and 8 hr the labelling was primarily concentrated over the predentine and the first 4 layers (layer = 9·3 μ × 130.2 μ) of enamel matrix. At 7 days the dense labelling of the enamel matrix was diffusely spread throughout; whereas, the dentine remained sparsely labelled. The observation that tryptophane is a component of the organic matrices of enamel in developing rat molars is confirmed by autoradiography.

Effect of Diet Fed During the Postnatal Period on Developing Rat Molars

Effect of Diet Fed During the Postnatal Period on Developing Rat Molars