MICROSTRUCTUEAL CHANGES IN EARLY CARIES 



Fig. 5. Micioradiograpli of eailv caries of human dental enamel just before 

 surface breakdown, (x 60.) (Reproduced bv kind permission of the editor of 

 the British Dental Journal.) 



Schmidt and Keil ( 1958), who have done much to make this a vakia- 

 ble tool in dental histopathologw 



In this field there now seems to be general agreement that, when 

 examined in quinoline, whereas "normal" enamel is generally nega- 

 tively birefringent with reference to the length of the prisms, the 

 translucent zone is slightly more negative. From this point pro- 

 gressing toward the enamel surface, there is a fairly rapid transition 

 through iictropic enamel to the dark zone, which is intensely posi- 

 tive, followed bv a transition back through isotropy into the negative 

 birefringence of the body of the lesion. The body of the lesion be- 

 comes less negatively birefringent toward the surface until just in- 

 side the surface the negative birefringence increases sharply to the 

 surface (Fig. 6). At times a positive zone may be found just be- 

 neath the surface zone. In the late stages of the lesion the striae of 

 Retzius in the surface zone often show positive birefringence. All 

 these features have been excellently described by Gustaf son ( 1957 ) , 

 Keil (1935, 1936), and others. 



