Abstract
The present study was to determine the surface of enamel subsurface lesions ultrastructurally, chemically and thermodynamically by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (ESCA), and the contact angle method. Enamel specimens (3 mm in diameter) were prepared from extracted, caries-free human incisors using a diamond core drill. The surface of enamel specimens was polished with the standard methods. The subsurface lesions were produced by immersing in demineralizing solution for O, 2, 4, 8 and 24 hours at 37℃. The demineralizing solution (pH5.0) was prepared from 0.1M lactic acid, 0.2% calbopol, and 50% saturated hydroxyapatite. The AFM images showed that crystal interspaces were the pathways of acid attack at the surface of subsurface lesions. The AFM crystal images detected remineralized crystals at the parts of the surface of subsurface lesions after demineralization for 4 hours. The remineralized crystals were square and significantly different from the enamel crystals of the controls. These remineralized crystals and crystal interspaces increased at the surface of subsurface lesion with increasing demineralizing periods. Judging from the crystal structure, the remineralized crystals could be brushite. The results of ESCA analysis indicated that Ca/P atomic ratio increased at the surface of subsurface lesions as compared with the controls. The increase of Ca/P atomic ratio depended on the decrease of the P contents at the surface of subsurface lesion. The contact angles of the surface of subsurface lesions were lower than those of the controls. These results indicated that the remineralized crystals were produced on the surface of subsurface lesions. The presence of the remineralized crystals on the surface of subsurface enamel lesion could alter the characterizations of the enamel surface.
