Correlated physiochemical and age changes in embryonic bovine enamel.

Whole enamel scrapings from unerupted teeth of embryonic calves have been separated into fractions of varying density by stepwise centrifugation in bromoform-toluene mixtures of increasing specific gravity. Partition of enamel in this manner yields individual fractions of increasing mineral phase age and maturation. Whole scrapings and isolated fractions of the fetal bovine enamel were examined by X-ray powder diffraction, scanning electron microscopy, and atomic absorption and infrared spectroscopy to determine time-related changes in the physiochemical nature of the constituent mineral phase particles. These analyses showed poorly crystalline hydroxyapatite (HA) as the only detectable solid phase of calcium phosphate present in all fractions, its degree of crystallinity increasing with increasing density. Molar Ca/P ratios and magnesium content were highest in lowest density fractions. Carbonate vibration bands at 875 and 1420-1450 cm-1, common to mineralized tissue, were observed in intermediate and higher density fractions and in whole unfractionated enamel. Another carbonate band at approximately 705 cm-1, unusual to vertebrate calcified tissue, was detected in low density fractions and disappeared rapidly with increasing enamel maturation. Its precise relation with the enamel mineral phase has not been determined.