Electron Probe Studies of Human Enamel

¹ Institut Dentaire, Faculté de Médecine, Strasbourg, and Bureau de Recherches Géologiques et Minières, Paris, France

After ethylenediamine extraction and potassium iodide impregnation, highly polished ground tooth sections were used for qualitative and quantitative electron probe microanalysis. In mature normal and carious human enamel, calcium, phosphorus, and chlorine could be detected on x-ray spectral recordings using the French electron probe. The comparison of caries-resistant and caries-susceptible enamel showed that the superficial enamel layer does not contain more calcium and phosphorus and that there are no significant statistical differences in the distribution of these two elements in the two groups. Chlorine, which is more concentrated in the superficial enamel layer, decreases gradually in concentration toward the dentinoenamel junction and does not show a differential statistical distribution in caries-susceptible and caries-resistant enamel. Similar distribution and levels of Ca, P, and Cl have been observed in enamel of unerupted teeth with completed crowns. The Ca and P levels of unerupted dentin, however, are notably lower than those of erupted teeth, suggesting the existence of an inorganic maturation of this tissue after eruption, which does not occur in enamel. The electron probe studies of enamel caries, before any cavity formation, confirm the loss of Ca and P in the subsurface, principally along the striae of Retzius, whereas the superficial caries layer has a normal Cl, Ca, and P content.