The dissolution curves of human acid-treated enamel powder are characterized by a rapid initial step followed, after 10 or 15 minutes, by a second stage, with release of very small amounts of calcium. Increase in pH and addition of fluoride ions tend to diminish, for short intervals, the amount of dissolved apatites. For higher pH values the decrease is noted over a longer time. Study of the relative ionic variation of human enamel powder from young and adult patients subjected to acid requires infra-red vibration band analyses. Special attention was given to the absorptions at 610 cm-1 (phosphate groups), 880 cm -1 (C032- in OH- sites and HPO42-), 1410 cm -1 (C032- in phosphate sites) and 1550 cm-1 (CO3 2- in OH- position). All results were related to vibration band at 610 cm-1. A preferential loss of carbonates in the two possible sites was always observed for 10 or 15 minutes, followed by a high release of phosphate. The increase of pH or small amounts of fluoride displaced the preferential carbonate loss to longer times. In the presence o.f higher fluoride levels a disappearance of the preferential loss of carbonates was noted. A continuous increase of HP042- in the absence of fluoride occurred; however a straight line with a smaller shape was present, with fluoride addition.
