Temperature-Related Ultrastructural Changes in Early Stage Amelogenesis in Vascularly Perfused Rat Incisors

Abstract

Vascularly perfused rat incisors were investigated by electron microscopy in order to achieve further definition of the origin and nature of stippled material in developing enamel. A prolonged (20-minute) pre-wash perfusion of the rat with a physiological solution at 37°C prior to perfusion fixation retained good morphology of the secretory ameloblasts and adjacent enamel, showing virtually no extracellular accumulation of granular material. Granular material appeared throughout the developing enamel after pre-wash perfusion at low temperatures (0-2°C), and accumulated in the extensively dilated extracellular spaces between the proximal portions of Tomes' processes, where numerous coated pits and coated vesicles were located. Vascular perfusion at 37°C, preceded by a cold perfusion, abolished the granular material in the developing enamel, whereas the granular material in the extracellular spaces between Tomes' processes remained as huge droplets of dense material.

These results indicate that at least a part of the matrix protein of rat incisor developing enamel has the physico-chemical property to dissociate at low temperature during pre-wash perfusion and move toward the enamel surface. Thus, in perfusion-fixed specimens, an intimate relationship between the artifactual formation of stippled material and the temperature of the pre-wash perfusate is suggested.

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