Preliminary observations of the calcium concentration in developing enamel assessed by scanning electron-probe X-ray emission microanalysis

Abstract

A scanning electron-probe X-ray microanalyser was used to measure the Ca Kα emission from polished longitudinal sections of developing tooth crowns (two 8–11-year-old human mandibular third molars and two 2-day-old rat molars) and apatite fragments embedded in methacrylate. The Ca Kα emission was recorded from 20μ wide strips perpendicular to, and crossing, the edge of the developing enamel. The level recorded from the apatite standard under exactly similar conditions was called 100 per cent apatite. The calcium concentration in developing enamel was found to increase linearly with distance from the surface, at an average rate of 2.7%/μ in the human molar cervical enamel and 1.7%/μ in the rat molar occlusal enamel. In the rat, the maximum concentration (at the enamel-dentine junction) was found to be 65 per cent. In the much thicker human enamel, the Ca Kα emission levelled off at approximately 91 per cent apatite. The results do not determine whether the iso-Ca-content contours in mineralising enamel are exactly parallel to the incremental lines, but it is certain that they are not in transverse relation, and that there is no second, sudden increase in mineral content at least during the stages studied here. No evidence was found of a layer of higher mineral content at the surface of the enamel during its deposition.