A quantitative microradiographic study on the organic matrix of developing human enamel in relation to the mineral content

Abstract

Ground sections from enamel of developing deciduous incisors from stillborn infants were examined by quantitative microradiography. The amounts of mineral salts were calculated from measurements in small areas along tracks across the enamel. After demineralization and freeze-drying of the sections, the organic matter was determined at the same measuring points. When the amount of mineral and organic matter was plotted as a function of distance from the enamel surface, the percentage of total volume occupied by mineral salts increased smoothly from the surface towards the enamel-dentine junction, with higher amounts in the incisal parts compared to the cervical regions. The distribution pattern of the organic material was completely the reverse. The highest amounts of organic matter (30–35 per cent by volume) were accordingly in the peripheral cervical parts, whereas the lowest organic content (2–5 per cent by volume) was at the enamel-dentine junction in the incisal region. Contrary to the generally held opinion that the bulk of organic matter is lost during the earliest stage of mineralization, this investigation suggests that the withdrawal of organic matter is a continuous process with a linear decrease of organic matter during an equally gradual deposition of mineral salts.