Scanning micrographs of the ameloblasts and enamel rods of rat incisors

Correlation of apical and lateral membrane modulations of maturation ameloblasts

Maturation ameloblasts of rat incisor teeth have smooth-ended and ruffle-ended apical membrane configurations. It has also been reported that maturation ameloblasts have several lateral membrane configurations. The purpose of this study was to determine the correlation between the modulations of lateral and apical cell membranes of murine incisor ameloblasts in the maturation stage of amelogenesis. Maxillary and mandibular incisors were dissected, demineralized, embedded in paraffin, sectioned and then de-paraffinized, and the enamel organs were prepared for scanning electron microscopy. Additional mouse and rat incisor enamel organs were fixed and teased apart during dehydration, then observed in the SEM. The lengths of smooth- and ruffle-ended ameloblast segments were measured, and the site, length, and frequency of each lateral membrane configuration were determined within each segment. The lateral membrane configuration with folds forming from 12 to 14 channels around the periphery of the cells was most predominant in both smooth- and ruffle-ended cells. Cells surrounded by from six to eight channels were the only other lateral membrane configuration observed in ruffle-ended ameloblasts. Smooth-ended ameloblasts had lateral membrane configurations with either dense or sparse microvillous projections in addition to both types of channel cells. The observation that channelled extracellular spaces are always associated with ruffle-ended cells suggests that channels somehow function in conjunction with the ruffled apical membrane in resorption and removal of enamel matrix proteins. The smooth-ended ameloblasts lack tight apical junctions, and their microvillous lateral membranes permit the passage of plasma fluids around cells to the maturing enamel surface.(ABSTRACT TRUNCATED AT 250 WORDS)

The secretory stage of amelogenesis in rat mandibular incisor teeth observed by scanning electron microscopy

In the scanning electron microscope (SEM), the structural organization of rat incisor enamel was divided into five regions: the initial prismless layer at the dentin-enamel junction; the decussating rods of inner enamel; intermediate enamel, where the structure changes from inner to outer enamel; outer enamel with parallel rods; and the surface prismless layer. There were alterations in the orientation of the ameloblasts and characteristic changes in the morphology of the Tomes' processes during the secretion of each of these regions. Initially, the developing Tomes' processes were seen within shallow pits which also contained fibrous material from dentin matrix. During the deposition of inner enamel, alternate rows of Tomes' processes were held at right angles to each other by cytoplasmic projections which originated from the proximal regions of the Tomes' processes. The cytoplasmic projections reorganized to perpendicular orientation relative to the enamel surface during the synthesis of outer enamel. Tomes' processes of outer enamel appeared as elongated flaps extending parallel to the long axis of the tooth. In the late secretory stage, the microvillous projections disappeared and the Tomes' processes were withdrawn into button-shaped structures which coalesced to form a smooth surface that rested on the enamel.