[Microradiographic investigations of carious changes in the enamel in the ground sections made perpendicularly to...

Carious changes in the enamel in the undermineralized ground sections made perpendicularly to tooth axis were investigated using microradiography. By this way, relationship between carious invasion and the enamel lamellae and tuft, which has been not able to be examined in the longitudinal ground sections, could be clarified. 1) Direction of progress of demineralization and contour of demineralization front in the enamel are closely related to arrangement of enamel prisms. This findings strongly suggest that carious demineralization progresses along the enamel prisms. 2) Mode of carious demineralization in the enamel lamellae can be divided into two types; in the first type, demineralization progresses through the enamel lamellae more quickly than in the surrounding enamel and, in the second type, the enamel lamellae and its surrounding enamel show higher mineralization degree than the demineralized part in the rest of enamel, probably due to remineralization. The second type is observed more frequently than the first. 3) Mode of carious demineralization in the enamel tuft are also divided into two types; the first type which shows that demineralization progresses more quickly through the enamel tuft than the surrounding enamel and the second type that the enamel tuft and its surrounding narrow enamel are highly mineralized probably due to remineralization, whereas the rest of enamel is prominently demineralized. The second type is more frequently observed than the first. 4) In the ground sections made perpendicularly to tooth axis, it is more clearly observed that the interprismatic area is very highly remineralized whereas the main body of prism is easily demineralized, than in the longitudinal ground sections. 5) Striae of Retzius is composed of the band which appear to resist to demineralization and that which is easily demineralized. However, in the later case, demineralization which progresses laterally along the band can not be observed. 6) The degree and width of hypermineralized layer appeared in sound enamel along the demineralization front seem to be related to the rate of demineralization and arrangement of enamel prisms.