Chemical and physical properties of altered and sound enamel—I: ASH, Ca, P, CO 2, N, water, microradiolucency and density

Abstract

Diffusely stained, otherwise normal enamel, when examined by soft X-ray showed shallow areas of low mineralization, similar in degree of radiolucency, but not penetration, to white and brown spot enamel. For every reduction in mineral volume, an equal and opposite increment of loosely bound water was found. In both normal and altered enamel, the weight loss on ashing at 900 °C, not attributable to CO 2, appeared to be independent of mineral content as indicated by density and X-ray. However, the nitrogen portion was inversely proportional to density while the non-nitrogen portion was reciprocally related to the Ca:P ratio. It is suggested that the loss on ashing (other than CO 2 or protein) is “bound” water acting as a bridge between the protein and mineral phase. It is further postulated that the lowered CO 2 content of altered enamel reflects preferential loss of CO 2 from the surfaces of crystallites reduced in size.