Development of Carious-Like Lesions in Partially Saturated Lactate Buffers

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Abstract
Marked differences were observed when human enamel surfaces were exposed to partially saturated lactate buffers containing varying amounts of calcium and phosphorus at different pH values and at a constant pH 4.3. The degree of saturation of these buffers was defined as the ratio of the activity product for hydroxyapatite in solution to a working estimate of the solubility product constant for enamel (KE= 5.5 × 10––55). It was observed that when using buffers in a well-defined saturation range (2–7 × 10––8), subsurface lesions were produced within a 72-hour time period. Within the same time frame, however, cavitations were produced using buffers of a relatively low degree of saturation (10––9–10––13) and essentially no mineral loss could be detected by microradiography or polarized light microscopy using relatively highly saturated buffers (3.5 × 10––7 –– 4 × 10––6). The results obtained are shown to be consistent with a proposed caries model which explains the observed histological features of the incipient lesion. Based on these findings it was concluded that the driving force for enamel demineralization is best described by the degree of saturation of the demineralization medium with respect to enamel and not by simpler parameters such as pH. It is noted, therefore, that extreme caution must be taken when interpreting observed changes in pH in both in vivo and in vitro experimental caries systems.