Abstract
The rate of enamel rehardening was studied in mineralizing solutions adjusted to various conditions of pH and two levels of ionic strength. With solutions containing the equivalent of 3 and 6 mM calcium ( Ca P 1.67), rehardening of buffer-softened enamel was observed from pH 5.0 to 7.4. Higher pH levels gave higher rates of rehardening, but the absolute hardness recovery was greater with solutions adjusted to intermediate pH levels applied over longer periods of time. Addition of 0.15 M NaCl prevented the spontaneous precipitation of the mineralizing solutions except at high pH range, but it did not affect the rehardening rate. Treatments of softened enamel with cupric chloride solutions inhibited subsequent rehardening. This inhibition was reversed by treatment with calcium chloride solutions. Apparently enamel rehardening involves mineral deposition on an active surface of microspaces which develop inside the enamel structure during the softening procedure.
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