176 



A. I. DARLING 



Fic. 1. MicroradiuL^iapli ul a .;;uuiid section of early caries of human dental 

 enamel cut transverse to the prisms. (X 350.) (Reproduced bv kind permission 

 of the editor of the British Dental Journal.) 



stration by Gustafson ( 1961 ) of increased radiopacity in the trans- 

 lucent zone. From his evidence it appears that this can occur, though 

 probably only in a relatively small proportion of lesions. He and 

 Kostlan ( 1962 ) have also shown zones of highly mineralized enamel 

 occurring occasionally within the demineralized area of the body of 

 the lesion. The author has also observed these areas, Gustafson 

 ( 1961 ) believes that there is reprecipitation of minerals in the trans- 

 lucent zone, and Kostlan ( 1962 ) has suggested that both these un- 

 usual features may arise from remineralization of the translucent 

 zone during a resting period of caries, with by-passing of this zone 

 when a new attack occurs. The explanation is attractive, but like so 

 much in caries is difficult to prove. 



For many years polarized light has been used for the examination 

 of enamel and the carious lesion. It would be impossible to review 

 all the literature on this subject in this paper, but the earlier work 

 has been excellently reviewed by Gustafson (1945, 1957) and by 



