Changes in calcium and phosphorus content in young human enamel during demineralization in vitro.

Premolars extracted about 6 months after eruption were divided into four parts by sectioning through the mesial- and distal midplanes. The enamel of each part was subjected to demineralization by hydroxy-ethyl-cellulose (H.E.C.) gel at pH 4 for periods varying between 2 and 24 hrs. The Ca and P contents of the gel as well as that of 10 microns slices prepared from the enamel after demineralization were determined. Then the Ca and P content of the HEC gel as well as that of 10 microns slices sequentially sectioned from the surface of the demineralized enamel inwards, were determined. The data indicate that initially, demineralization was predominant in the layers between 20 and 60 microns depth together with a reprecipitation in the surface 20 microns layer. After about 6 h of demineralization more mineral loss was found from layers deeper than 60 microns. Further, it was shown that the molar Ca/P ratio of mineral loss from these young teeth at depths of between 40 and 50 microns was extremely high (about 3) whereas in older teeth it was normal. This might be due either to preferential dissolution of carbonate containing mineral or to preferential precipitation of HPO4(2)--containing mineral or both especially at that depth.