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J. A. GRAY AND M. D. FRANCIS 



2 



Figs. 1 and 2. A section through a typical natural incipient carious lesion 

 with the original enamel surface retained, cut transversely from the mesial sur- 

 face of an upper right first molar. 



Fig. 1. Viewed with ordinary transmitted light, the lesion is apparent by 

 the increase in contrast of the structural features as compared with normal 

 enamel. (X 200.) 



Fig. 2. A microradiograph of the lesion demonstrates the loss of material 

 in the lesion that accentuates the interrod spaces. The relatively sound layer 

 near the surface is readily apparent. ( X 200. ) 



Therefore, an incipient carious lesion will be defined as a sub- 

 surface region of decalcification overlain by a relatively sound layer, 

 with the surface completely intact, at least according to visual or 

 light microscopic observations. It thus becomes apparent that the 

 reactant must, for the most part, be by-passing the surface to diffuse 

 into the enamel and react with subsurface enamel components. 



