ELECTRON l\IICH()SCOPY 



lightly etched with acid the Stack's protein 

 dissolves, so that the prismatic structure is 

 enhanced. 



The chalky enamel of enamel caries (which 

 is known to be the first stage of all carious 

 lesions) can he sectioned more easily, and 

 it is seen that at this stage Stack's protein 

 has gone, and the crystallites in it are being 

 washed away, while Pincus' protein and the 

 crystallites embedded in it remain (K. Little, 

 J. Roy. Micr. Soc, 78, Dec, 1958). Bacteria 

 are not seen in this earliest stage of caries 

 (Fig. 21). This problem of enamel caries pro- 



FiG. 20. Section of developing human dental 

 enamel, before calcification. Stack's protein, liable 

 to be degraded in dental caries, is the less dense of 

 the two organic components of the matrix. Forma- 

 lin fixation. Embedding medium removed. Ura- 

 nium shadowed. X5000. 



vides a good example of how, while the ini- 

 tial obsen'ations must be made using elec- 

 tron microscopy, since the important details 

 are too small to resolve with the light mi- 

 croscope, work with the light microscope 

 can then be interpreted by making use of 

 this information, as has been done by A. I. 

 Darling {Brit. Dent. J., 105, 119, 1958). 

 Once it was shown that the initial stage of 

 caries was almost certainly the loss of Stack's 

 protein; further advances are possible using 

 histological methods. For example, if teeth 

 are treated with ethylene diamine, a protein 

 solvent in which apatite is completely in- 

 soluble, sections viewed under polarized light 

 show the translucent appearance typical of 

 the earliest zone of enamel caries. (A. I. 

 Darling and K. V. Mortimer, lADR British 

 Section, 1959). Again, by normal histological 

 methods it can be demonstrated that an im- 

 portant action of fluorine is to modify the 

 formation of enamel matrix (A. I. Darling 

 and A. W. Brooks, lADR British Section, 

 1959). In normal enamel treated with a for- 

 mic acid solution, sections viewed in the 

 electron microscope show chalky enamel ap- 

 parently identical wdth that formed in 

 natural caries. When fluorized teeth are 

 similarly treated, electron microscope exam- 



FiG. 21. Section of chalky enamel. Stack's protein has mostly gone, leaving the crystallites which 

 had been embedded in it free to be washed out during processing. The prism walls are intact, with the 

 crystallites still held in place by the organic matrix. Embedding medium removed. Stereoscopic photo- 

 graph. X3000. 



290 



