Enamel demineralization under driving forces found in dental plaque fluid

The present study was carried out to examine the kinetics of enamel demineralization in vitro under driving forces for demineralization (i.e., the degree of saturation with respect to enamel, DS(En)) similar to those found in dental plaque fluid. Thin sections of human enamel were exposed at 25 degrees C to lactic acid solutions with DS(En) values (DS(En) = [(Ca2+)5(OH-)(PO4(3-))3/K(En)]1/9; K(En) = 5.5 x 10(-55)) ranging from 0.28 to 0.79. Lesion development was monitored by quantitative microradiography. Enamel mineral loss in solutions with DS(En) values of 0.28, 0.32 and 0.36 was first detected after 3, 3, and 7 wk of continuous exposure, respectively. Consistent with previous findings, subsurface demineralization was observed and rates of mineral loss increased significantly with decreasing DS(En) values. However, no mineral loss was observed in sections of enamel exposed to solutions with DS(En) values of 0.41 and 0.79, even after 11 months. These results suggest that (outer) enamel mineral behaves as a mineral phase that is less soluble than that dictated by the solubility product constant (K(En)) used in this study. Furthermore, these results indicate that the kinetics and general features of the demineralization process are maintained over a wide range of DS(En) values, including conditions that better reflect those found in the oral cavity. These findings are particularly relevant to the assessment of the cariogenic potential of dental plaque fluids.