Abstract
The nature of in vitro enamel lesions was investigated with changing degree of saturation (DS) of demineralizing lactate buffers with respect to enamel. Microradiographs of enamel thin sections before and after demineralization were analyzed with a computer image analyzer. We particularly examined whether the presence of fluoride ion (F-) is indispensable for the development of subsurface lesions with a relatively intact “surface layer”. The trace amount of fluoride in the buffers was purposely removed, so that possibility of the precipitation of fluorapatite would be substantially eliminated. The present study demonstrated that, for a given DS value, the lesions changed from cavitations to subsurface lesions, to no detectable mineral loss with increasing F- concentration. Similarly, for a given F- concentration, the same lesion sequence was obtained with increasing DS value. The “surface layer”obtained in fluoridated buffers with 1 ppm F- had a higher mineral content, due to initial dissolution of enamel and precipitation of fluoridated apatite. On the other hand, even in the F-removed buffers which were estimated to be under-or slightly supersaturated with respect to fluorapatite, subsurface lesions were observed. The finding suggests that the subsurface demineralization could be caused without precipitation of fluorapatite. These results clearly show the dynamic nature of caries-like lesions.
