The purpose of this study is to observe and compare the dynamic change of artificially demineralized enamel by remineralization solutions of different degrees of saturation at pH 4.3.

In this study, 30 enamel specimens were demineralized artificially by lactic acid buffered solution. Each of 10 specimens was immersed in pH 4.3 remineralization solution of three different degrees of saturation (0.22, 0.30, 0.35) for 10 days. After demineralization and remineralization, images were taken by a polarizing microscope (× 100). The density of lesion were determined from images taken after demineralization and remineralization.

During remineralization process, mineral deposition and mineral loss occurred at the same time. After remineralization, total mineral amount and width of surface lesion increased in all groups. The higher degree of saturation was, the more mineral deposition occurred in surface lesion and the amount of mineral deposition was not much in subsurface lesion. Total demineralized depth increased in all groups.

Since it was reported that incipient enamel caries can be recovered, previous studies have quantitatively evaluated that enamel artificial caries have been remineralized with fluoride, showing simultaneously the increase of width of surface layer and the decrease of width of the body of legion. There is, however, little report which showed that remineralization could occur without fluoride. In addition, the observations on the change of hydroxyapatite crystals also have been scarcely seen.

In this study, enamel caries in intact premolars or molars was induced by using lactic acidulated buffering solutions over 2 days. Then decalcified specimens were remineralized by seven groups of solutions using different degree of saturation (0.212, 0.239, 0.301, 0.355) and different pH (5.0, 5.5, 6.0) over 10 days. A qualitative comparison to changes of hydroxyapatite crystals after fracturing teeth was made under SEM (scanning electron microscopy) and AFM (atomic force microscopy).

The results were as follows:

1. The size of hydroxyapatite crystals in demineralized area was smaller than the normal ones. While the space among crystals was expanded, it was observed that crystals are arranged irregularly.

2. In remineralized enamel area, the enlarged crystals with various shape were observed when the crystals were fused and new small crystals in intercrystalline spaces were deposited.

3. Group 3 and 4 with higher degree of saturation at same pH showed the formation of large clusters by aggregation of small crystals from the surface layer to the lesion body than group 1 and 2 with relatively low degree of saturation at same pH did. Especially group 4 showed complete remineralization to the body of lesions. Group 5 and 6 with lower pH at similar degree of saturation showed remineralization to the body of lesions while group 7 didn't show it. Unlike in Group 3 and 4, Group 5 and 6 showed that each particle was densely distributed with clear appearance rather than crystals form clusters together.

Dental caries is the most common disease in the oral cavity. However, the mechanism and treatment of dental caries is not completely understood since many complex factors are involved. Especially the effect of pH on remineralization of early stage of dental caries is still controversial.

In this study, dental caries in dentin was induced by using lactic acidulated buffering solutions and the loss of inorganic substance was measured. Also decalcified specimens were remineralized by three groups of solution with different pH (group of pH 4.3, 5.0, and 5.5). Then, the amount and the area of inorganic substance precipitation was quantitatively analyzed with microradiograph. Also a qualitative comparison of the normal phase, the demineralized phase, and the remineralized phase of hydroxyapatite crystal was made under SEM.

The results were as follows;

In microradiograghic analysis, as the pH increased, the amount of remineralization in decalcified dentin tended to increase significantly. As the pH decreaced, deeper decalcification, however, occurred along with remineralization. The group of pH 5.5 had a tendency to be remineralized without demineralization (p < 0.05).

In according to the results of this experiment, the decalcifying and remineralizing process of dentine is neither simple nor independent, but a dynamic process in which decalcification and remineralization occur simultaneously. The remineralization process occurred from the hydroxyapatite crystal surface.