Abstract
Remineralization phenomena have been investigated by studying the recrystal growth process of partially dissolved hydroxyapatite crystals. When apatite crystals were dissolved in organic acid, an initial acid attack site was found both on the basal and prism planes of the apatite crystal. The purpose of the present study was to investigate how these attacked sites recover, when introduced in a remineralizing solution. From the thermodynamic analysis based on the concentration of the calcium and phosphate dissolved, it was suggested that lactic acid is more effective indissolving apatite than acetic acid at the initial pH between 3.0 and 4.0. This difference could be well accounted for based on the difference in dissociation constants and the affinity of the acids used to free calcium ions.
In view of fact that the degree of solution supersaturation in saliva with respect to biologically interested calcium phosphates is varied in stimulated and unstimulated saliva, two types of remineralizing solutions were prepared; one supersaturated (e. g. stimulated saliva) and the other undersaturated (e. g. unstimulated saliva) with respect to octacalcium phosphate (OCP). The initial remineralization was observed predominantly as re-crystal growth on the basal plane, while the subsequent remineralization pattern varied with the degree of supersaturation. With the higher supersaturation, in which OCP was possibly formed transiently, remineralization was initially inhibited in the presence of 10μM of F-, presumably due to suppression of OCP nucleation. With the lower supersaturation, the acid-attacked sites were the sites for remineralization. Once the HAp crystals were nucleated, they grew along the c-axis, resulting in restoring the demineralized region. Presence of F- in this case simply accelerated the remineralization. These findings may be of interest in considering the orientation of newly formed microcrystals in the remineralized layer.
