Search

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-. From these results, and in combination with the ultrastructural data obtained in previous studies, it is concluded that in vitro: (1) F- treatment during the secretory phase of amelogenesis induces hypermineralization of the preexposure enamel; (2) F- decontrols or abolishes enamel crystal growth in length and promotes crystal growth in thickness, thus producing enamel hypermineralization; and (3) enamel matrix secreted during F- exposure retains its capacity to support crystal growth when F- is removed from the culture environment. [ABSTRACT FROM AUTHOR]

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, pyroantimonate (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 deceased 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 viva. [ABSTRACT FROM AUTHOR]

A single systemic dose of cyclophosphamide (CY) has been shown to enhance cellular immunity in a variety of antigen models. The immunoenhancing effects of CY have been attributed to its ability to selectively abrogate suppressor cell function. Previous studies from our group have demonstrated that local administration of distinct cytostatic drugs at the sensitization site can induce a similar enhancement of delayed-type hypersensitivity as systemic CY, with the obvious advantage of avoiding systemic side-effects. In the present study we investigated the effects of local administration of an optimally immunopotentiating dose of the active CY-derivative Z 7557 and, in selected experiments, of etoposide (VP-16) and systemic CY on mononuclear cells in draining lymph nodes. Whereas CY caused a long-lasting and marked depletion of B-cell areas, locally administered Z 7557 and VP-16 relatively spared B cells and even induced an increase in B- and T-cell numbers in (keyhole limpet haemocyanin-) sensitized mice. At Day 4 the CD4/CD8 ratio was slightly reduced in drug-treated mice. Interestingly, drug treatment reduced the proportion of interdigitating cells staining with the monoclonal antibodies NLDC-145 and MIDC-8. Upon isolation, dendritic cells (DC) from sensitized, Z 7557-treated mice showed longer dendritic protrusions and an enhanced accessory cell function compared to DC from saline-treated controls. These findings suggest that immunoenhancing effects of cytostatic drugs may occur via an effect on DC.