Histology of enamel organ and chemical composition of adjacent enamel in rat incisors

Abstract

By avoiding chemical fixation and using a freeze-drying technique, it proved possible to examine the enamel organ of rat mandibular incisors histologically while retaining the adjacent enamel of the same tooth for chemical analysis. The dramatic alterations which occur in enamel organ histology, such as ameloblast shortening and the development of hte papillary layer, could then be compared directly with mineral uptake and mineral content of the adjacent enamel. Both enamel and adjacent enamel organ were sampled as a continuous series of pieces, 0.5 mm in width, from youngest (apical) to oldest (incisal) tissue. Short ameloblasts were associated directly with the beginning of a rapid uptake of phosphate ions during the maturation phase and also coincided with the beginning of a steep rise in mineral content. By implication, some loss of matrix may also occur at this point. Development of the highly vascular papillary layer preceded ameloblast shortening and may be associated with changes in the organic matrix prior to its disappearance from the tissue. Further development of this layer was associated with ameloblast shortening. This may also therefore be associated with mineral uptake during maturation.

X‐ray microtomographic study of mineral distribution in enamel of mandibular rat incisors

“…However, from the naked-eye appearance of partially dried enamel of the rat incisor, Robinson & Kirkham (1984) identified 5 stages of enamel development : (1) soft translucent, (2) soft cracked, (3) white opaque, (4) hard translucent and (5) brown pigmented enamel. These stages were shown to be related to changes in the chemistry and histology of the enamel organ (Robinson et al 1981). Analyses of dissected enamel particles along rat incisors (Hiller et al 1975) showed that both the Ca and P concentrations increase from the growing root apex towards the more mature incisal end.…”

“…These minima are artifacts that seem to correspond to the beginning of the maturation phase. This correspondence is based on the fact that a similar artifact at the apical end, this time a raised phosphorus level (closely related to the mineral concentration), can be seen in Figure 6 of Robinson et al (1981) ; this turning point corresponds to a position at which ameloblast height is reduced by 50 %, an indication of the beginning of the maturation phase. After transformation of the data (Fig.…”

Ultrastructural and Cytochemical Studies of Resorptive and Digestive Functions of Secretory Ameloblasts in Kitten Tooth Germs

“…Biochemical studies have shown the beginning of a decrease of protein and a change of the amino acid composition of the enamel matrix during the formative stage of amelogenesis in human and rat teeth [Fukae and Shimizu, 1974;Robinson et al, 1977Robinson et al, , 1981, A close relation with ameloblast cell morphology, however, remains uncertain. Secretory ameloblasts may, therefore, func tion in the resorption of the enamel matrix as well as in matrix formation.…”

Tracer, Cytochemical, and Freeze-fracture Study on the Mechanisms whereby Secretory Ameloblasts Absorb Exogeneous Proteins

“…The enamel protein that occupies about 20%, by weight, of the developing immature enamel accounts for only 0.1-0.4% after mat uration [Deakins, 1942;Eastoe, 1960;Weidmann and Eyre, 1971;Glick, 1979]. The progressive changes of the enamel matrix have been thought to associate closely with the modulation of ameloblasts through their life cycle [Smith, 1979;Robinson et al, 1979Robinson et al, , 1981. Secretory ameloblasts, the cells in the secretory zone of the ameloblast layer [Warshawsky and Smith, 1974], synthesize and release enamel-matrix precursor in addi tion to transferring calcium ions into the enamel matrix.…”