DENTAL HARD TISSUE DESTRUCTION 



137 



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Fig. 27. A, B, C. Microradiographs of monkey incisors: A, immediately 

 after etching with 5 per cent nitric acid for 5 minutes; B, C, comparable teeth 

 examined 7h months later. Note the apparent hypercalcification in the periph- 

 erallayer after "remineralization." (X 90.) 



D, E, F. D, E, ground sections of enamel seen in transmitted light (D) 

 and in microradiograph (E) 2 days after in vivo etching. F, microradiograph 

 of comparable tooth 1 week after etching. Note dense surface. ( X 90. ) 



G, H, I. G, etching with orthophosphoric acid (as used in dental cements) 

 is seen to penetrate along the Retzius lines in the ground section shown in 

 transmitted light. H, I, micrographs of comparable teeth, extracted 1 and 2 

 weeks later, show a resumption of microdensity in the peripheral enamel 

 layer. (X 90.) 



