Correlation between physical changes in tooth enamel and changes in iodide penetrability following in vitro or intraoral demineralization.

Demineralization of bovine tooth enamel was assessed by various physical means, and results were compared to measured changes in penetrability to iodide ions (delta Ip). Blocks of bovine enamel were exposed in vitro to lactate buffer (pH 4.3) containing 25 mM CaCl2 and 10 mM KH2PO4 for up to 4 days. Delta Ip increased over a wide range with time. A plot with respect to microhardness exhibited a pronounced inflection, with delta Ip rising rapidly at indentation depths greater than 2.5 microns. Microradiography and polarized light microscopy demonstrated subsurface lesions coincident only with the higher delta Ip values. The limited demineralization during the early time periods, therefore, was associated with only minimal changes at or near the enamel surface, yet could be detected readily with the delta Ip system. Demineralization produced intraorally in subjects rinsing with 5% sucrose was accompanied by increases in delta Ip, but no changes in surface microhardness or microscopic appearance of the enamel. It appeared that, under these conditions, demineralization was limited to the surface and corresponded to the very early phases of lesion formation.