Scanning Electron Microscopy of Monkey Secretory-and Transitional-stage Enamel Organ Cells

Abstract

This scanning electron microscope (SEM) study of secretory- and transitional-stage enamel organ cells of the permanent dentition of Macaca mulatta and Macaca arctoides was undertaken because the topography of these cells in primates has not been described in the literature. Comparison of our results with murine enamel organ morphology reported previously revealed not only many similarities, but also some significant differences. Tooth buds of the permanent dentition were routinely prepared for SEM. Murine secretory-stage ameloblasts have been described to be 65-70 μm long, with smooth lateral membranes, but those of monkeys were only 30-35 μ m tall, with four different lateral plasma membrane configurations: smooth, filamentous, longitudinally ridged, and transversely ridged. The filamentous form was most common. Cells were seen with either transverse or longitudinal ridges in the basal half, and with filamentous ridges in the apical portion; this indicates modulation between these forms. Because of the extraordinary similarity between these lateral membrane modulations and those of rat incisor maturation ameloblasts, a comparable function is proposed — namely, that monkey secretory ameloblasts function, in part, in the resorption and mineralization of enamel matrix. There were several layers of rounded stratum intermedium cells basal to monkey secretory-stage ameloblasts, but only one layer of cuboidal stratum intermedium in rodents. The stellate rcticulum cells of rats and monkeys appeared attenuated, with large extracellular spaces. There was little or no reduction in cell length of monkey transitional-stage ameloblasls. The position of the nuclear bulge differentiated transitional- from secretory-stage ameloblasts. The lateral surfaces of monkey transitional ameloblasts had interdigitating bulbous extensions of cytoplasm, whereas those of mice were smooth, and became microvillous late in the transition stage. In this stage, monkey and murine stratum intermedium, stellate reticulum, and the outer enamel epithelium cells changed morphology to become papillary cells with microvillous surfaces. Clusters of papillaty cells were separated from each other by anastomosing blood vessels, with diameters ranging from 10 to 12 μ m in monkeys, but from only 5 to 8 μm in murine incisor teeth.