134 R. F. SOGXNAES 



In Vivo Demineralization 



In our initial experiments it was decided to produce enamel 

 changes sufficiently extreme to be seen with the naked eve and 

 recorded photographically in the living animal. In the rhesus mon- 

 key this was readily accomplished by exposing the enamel surface 

 to a 5 per cent solution of nitric acid for 3 to 5 minutes. When the 

 surface was washed with a stream of water and then dried by com- 

 pressed air, one could readily detect areas of demineralization by 

 the chalky, opaque appearance of the enamel. 



Figure 26A illustrates the upper and lower incisors of a rhesus 

 monkey before application of the acid. Figure 26B shows the ap- 

 pearance of the teeth 5 minutes after application of the acid. In the 

 upper jaw, the central incisors were isolated with a rubber dam and 

 acid was applied over the whole labial surface (Fig. 26B, top). In 

 the lower jaw, a strip of gauze, soaked in the acid, was placed along 

 the lower half of the labial surface (Fig. 26B, bottom). Here the 

 chalky areas were quite clearlv demarcated from the glossy appear- 

 ance of the rest of the enamel surface. In Fis;. 26C the same teeth 

 are photographed 71 months after application of the acid. Even 

 though the teeth were dried thoroughh' there was no appearance 

 of any chalkiness of the enamel surface. 



It next became necessary to find means whereb\' one could de- 

 termine more precisely to what extent the enamel had been altered 

 during various intervals of time following the acid demineralization. 

 Thin ground sections of the teeth were prepared as described else- 

 where (Sognnaes, 1947) and microradiographs were prepared at 

 various intervals of time following experimental demineralization of 

 the enamel surface of the teeth. The microradiographic films in- 

 dicated that this method reveals considerable demineralization in 

 depth. Furthermore, it was noted that the demineralization was not 

 uniform along a broad front, but was permeating particularly along 

 the lines of Retzius. This pattern was marked enough to be seen also 

 in the sections of the same teeth examined in transmitted light. In 

 addition, the demineralized areas took up a greater amount of stain 

 than did normal enamel when immersed in toluidine blue. 



The above tests made it evident that subsurface alterations in the 



