Abstract
Early enamel caries had been electron microscopically examined and the following findings have been brought to light.
1. Abundant streptococci, bacillary, and filamentous bacteria cover the carious enamel surface in a diffuse manner. However, no bacteria at all are found in the interior of the enamel portion under the bacterial layer during the early stage of caries.
2. The earliest structural alterations in caries, as visible in the bacteria-free modified enamel portion, are a result of mineral loss. As a manifestation of the mineral loss, fine defects innumerably distribute in a diffuse manner in the altered enamel. However, the defects often tend to appear as if they abound especially within the rods, while relatively a few of them being detected in interrod areas and rod sheaths. In keeping pace with the advancement of caries, these fine defects gradually increase in number in the bacteria-free altered enamel zone, particularly most remarkably within the limits of the rods. This tendency corresponds to the different quantities of mineral materials in the enamel structures, and indicates that in the progress of caries, carious destruction of the interrod substance and rod sheath take place less heavily than that of the rod due to mineral loss.
3. In accordance with the increase of carious defects the orientation of crystals in enamel gradually becomes unclear, and finally completely obscure in the bacteria-free altered enamel portion.
