The developing enamel of rat incisors was dissected into a series of samples extending from the newly-formed partially-mineralised matrix to the mature.enamel. Chemical analysis showed that, on a dry weight basis, the tissue achieved the composition of mature enamel well before the completion of mineral uptake. The enamel at this stage was porous and relatively soft. As more mineral was acquired, its hardness increased. Throughout the developing region, the Ca:P ratio remained fairly constant, but the CO2:P and Mg:P ratios both decreased due, apparently, to dilution by an influx of relatively C02- and Mg-free mineral.

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Recently developed micro-sampling and micro-analytical techniques have been used to determine the distribution of calcium, phosphorus and protein in individual enamel sections. Absolute values for calcium, phosphorus and protein were variable (30–40% calcium, 13–23% phosphorus and 0.002–0.015 mol amino acids/100 µg enamel), but consistent patterns of distribution were revealed in the tissue. The average values for calcium (37.5%), phosphorus (17.5%) and Ca:P ratio (2.1) agreed with those quoted in the literature. The volume of tissue occupied by the mineral and the significance of the composition patterns with respect to enamel formation and caries are discussed.

An experimental investigation has been made into the possibilities of retarding the progress of carious attack by infiltrating cariostatic material into enamel lesions. The problems associated with this kind of procedure are discussed against the background of experimental observations made using a formulation based on a resorcinol-formaldehyde resin.

An investigation of the changes taking place in the enamel and the enamel organ during enamel development has been carried out by analyzing small samples of tissue dissected from developing incisors of rat and bovine incisors. Observations showed that the synthesis of the enamel matrix and its subsequent loss were associated chiefly with a change in the major matrix components. This consisted of a selective loss of amelogenin components prior to secondary mineralization. Before this loss, some increase in the proportion of smaller molecular weight components suggested the possibility of limited breakdown. Even at the earliest stages examined, significant concentration of mineral ions was present. This increased steeply after most of the organic matrix had been removed. The Ca/P ratio of this mineral was constant throughout development. The concentration of minor inorganic ions (F, Mg and CO3) decreased as the tissue developed and a tendency was observed for certain ions (F, 32PO4) to penetrate and concentrate in the enamel, apparently as a consequence of the lost matrix being replaced by water, just prior to the steep increase in mineral content of the tissue.

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