Ultrastructural changes in the translucent and dark zones of early enamel caries.

Selected areas of early enamel caries ('White spot' lesion) in human teeth were argon-ion-beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter-rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter-rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.