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Action of urea solutions on human enamel surfaces.

In this study, the influence of urea solutions on both young and mature enamel was investigated. The urea concentrations were 5 and 0.1 M; the interaction period varied between 3 h and 3 months. The hydrogen (H)-bond destruction due to urea produces tiny micro-channels. The scanning electron microscope (SEM) investigations on replicas and by direct observations indicated that: (i) urea solutions destroy H-bonds in specific areas; (ii) these areas are most likely isolated prisms in the perikymata; (iii) interprismatic regions are, in contrast to these prisms, hardly influenced by the urea solutions. It is suggested that the special areas with relatively weak H-bonding are similar to the area attacked initially in artificial caries-like enamel lesions.