142 



R. F. SOGXNAES 



Fig. 29. Quantitatively determined radioisotope gradients within the outer 

 layers of enamel of unerupted (upper arrows) and erupted (lower arrows) 

 rhesus monkey teeth 8 days after intravenous injection of 5 millicuries P"^-. 

 Corner figures, reading from top to bottom, give values for surface, subsurface, 

 and interior enamel in percentages of dose X 10' mg of enamel. In each group 

 of teeth, whether erupted or not, one notes that there is at least a twofold 

 elevation of radioisotope uptake in the relatively younger anterior teeth 

 (left arrows), indicating a prolonged mineralization period of the outer 

 enamel, even after crowns are completed as far as can be judged bv clinical 

 x-ray diagnosis. (From Sognnaes, 1957fl.) 



By the same token, the two erupted teeth (lower arrows) were 

 both surrounded bv the biologically radioactivated saliva. Thus — 

 and for the same reason as above — their different response must be 

 due to differences not in the environmental reagents but in the sub- 

 microscopic structure of the enamel itself. It must be assumed that 

 the most recently erupted incisor ( which shows twice as high a radio- 

 active phosphorus uptake as the first permanent molar) must still 

 be in the stage of submicroscopic mineralization. In other words, 

 some of the inorganic enamel cr\'stals have \'et to reach their full 



