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

本研究的目的是探讨在体外继发龋的发展过程中，邻近釉质表面的变化。应用原子力显微镜（AFM）观察银汞合金（AM）、复合树脂（CR）和玻璃离子水门汀（GI）对脱矿牙釉质表面（0.6mm × 3.6mm）的影响。脱矿釉质表面通过浸入0.2M乙酸缓冲液（pH4.0）中产生。测量釉质表面的钙含量和化学成分。此外，我们还检测了变形链球菌MT3940在牙釉质表面的粘附情况。AFM显示脱矿2分钟后，CR修复的样品中边缘釉质表面出现凹陷，在两个样本中，釉质表面在5 min时发生形态学变化，而在GI附近的釉质表面即使在20 min后也没有发现变化. AM或CR附近釉质表面脱钙量高于GI。脱矿牙釉质表面的P205含量在AM和CR试件边缘区较中心区显著降低。虽然样品AM和样品CR的边缘区域的Ca/P原子比增加，但样品GI的任何分析区域的Ca/P比均未发生变化。结果表明，GI抑制了釉质表面的初始脱矿和细菌粘附，而AM和CR则抑制了釉质表面的初始脱矿和细菌粘附。

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.