Atomic force microscopic study of enamel surface changes during development of secondary caries

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The purpose of this study is to investigate enamel surface changes adjacent to restorations during development of secondary caries in vitro. We observed demineralized enamel surface (0.6mmX3.6mm) changes adjacent to amalgam (AM), composite resin (CR) and glass ionomer cement (GI) by atomic force microscopy (AFM). The demineralized enamel surfaces were produced by immersing in 0.2M acetic buffer (pH4.0). The amounts of calcium and chemical contents on the enamel surfaces were measured. Moreover, the adherence of Streptococcus mutans MT3940 to the polished or demineralized enamel surfaces adjacent to restorations were detected.The findings were as follows :1. AFM showed depressions at the marginal enamel surface in the specimen restored with CR after demineralization for 2 min., while no change was observed on the enamel adjacent to AM.In both specimens, enamel surfaces were changed morphologically at 5 min. However, no change was detected on the enamel surface adjacent to GI even after 20 min.2. The amounts of calcium demineralized from enamel surfaces adjacent to AM or CR were higher than that of GI.3. The P_20_5 contents on demineralized enamel surfaces at the marginal area of specimen AM and specimen CR were remarkable decrease as compared with the center area on enamel surfaces. While the Ca/P atomic ratio were increased at the marginal area of specimen AM and specimen CR, the Ca/P ratio did not change at any analyzed area of the specimen GI.4. The number of adherence on the enamel surfaces next to GI was less than that of AM and CR.There were no difference of the number of adherence between polished enamel and demineralized enamel.These results indicated that GI inhibited initial demineralization and bacterial adherence on the enamel surface, as compared with AM and CR.AFM was beneficial to these analysis.