140 R. F. SOGNNAES 



visible despite the fact that the radiodensity appeared normal. Even 

 several weeks after the etching we could detect dye penetration in 

 depth along the Retzius lines when sections were stained with 

 toliiidine blue. In this respect, the rehardened enamel (notwith- 

 standing its high x-ray density) behaved differently from intact 

 enamel of mature teeth. Possibly the affinity for toluidine blue sug- 

 gests the presence of an amorphous mucous substance which could 

 be contributed by saliva. The dye-binding capacity of the organic 

 matter present in the rehardened enamel remained greater than in 

 intact enamel, suggesting that we are not dealing with a true recon- 

 stitution to the original status of normal mature enamel, despite the 

 seemingly dense deposition of inorganic matter. In other words, the 

 normal organic-inorganic linkage of enamel (which has few if any 

 free organic radicals) does not appear to become reconstituted. It 

 would seem very inappropriate, therefore, to refer to enamel remin- 

 eralization as a genuine healing process ("echte Heilungsvorgang," 

 Rheinwald and Staehle, 1949), least of all a process attributable to 

 a biological capacity inherent within the enamel itself as apparently 

 implied in some earlier writings. 



Theoretical Basis for Retnineralization 



On the strength of these experimental observations it would ap- 

 pear that the hard tissue destructions that affect the teeth are not 

 entirely one-way processes, even within the seemingly inert biolog- 

 ical makeup of the dental enamel, which is both acellular and avas- 

 cular and in fact the densest of all biological tissues. 



It is now more than three decades since Andresen ( 1926 ) pre- 

 sented the first comprehensive discussion of the potentialities for 

 remineralization of enamel. In retrospect, it is noteworthy that his 

 clinical interest in this subject preceded by ten years the theoretical 

 concept of an ionic exchange mechanism in the seemingly stable 

 dental hard tissues (this new biological principle did not come to 

 light until Chievitz and Hevesy in 1936 for the first time traced the 

 pathway of intravenously injected man-made radioactive phosphorus 

 into the calcified substance of bones and teeth). Only recently has 

 this concept been extended to definitive zones of enamel of adult 



