PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION '^Sl 



the outside of the rods and slowly permeating to the center of the 

 rod. 



Diamond knife sections of these samples with the embedding ma- 

 terial ( methyl methacrylate ) remo\ ed were then demineralized with 

 hydrochloric acid (0.005 n) to remove the inorganic substance and 

 expose the organic content (Figs. 23 and 24). Normal mature enamel 

 (Fig. 23) had a sparse organic residue which generally collapsed 

 during the demineralizing procedure, so that little or no correlation 

 with the original enamel structure was possible. In the incipient 

 carious lesion region, produced either naturally or in vitro ( in vitro, 

 Fig. 24), the content of organic residue appeared to be much more 

 appreciable and was easily correlated with the enamel rod structure, 

 similar to enamel matrix of unerupted teeth, as well as the original 

 undemineralized specimen (Fig. 21). The higher than normal or- 

 ganic content of natural lesions has been demonstrated by other 

 investigators using chemical analyses and light microscopy ( Bhussry, 

 1958; Johansen, 1962). The organic residue found in the present 

 study seems to be concentrated in the enamel rod proper, where the 

 greatest mineral content was observed. Furthermore, the highest 

 organic content was always found in the relatively sound outer laver 

 of the lesion at the surface and appeared to be located in the same 

 vicinity as the mineral. Additional studies are in progress to identify 

 the source of these residues and their relationship to the organic 

 moietv of normal enamel. 



The reality of the spaces observed in the incipient carious lesion 

 by electron microscopy (Figs. 20, 21, and 22) can be demonstrated 

 bv infiltrating the enamel with a material which is visible in electron 



Fig. 20. An electron micrograpli of a section through a natural incipient 

 carious lesion cut from an undemineralized sample of adult human enamel us- 

 ing a diamond knife. The interrod spaces have been enlarged by the decay 

 process and material has been leached out of the rod proper. (X 5000.) The 

 appearance of normal enamel can be seen in parts of Fig. 22 or 36. 



Fig. 21. An electron micrograph of a section through an incipient cariovis 

 lesion produced by a 72-hour exposure at 37°C to a medium consisting of 0.05 

 M lactic acid and 0.03 m CaCb plus 6 per cent hydroxyethyl cellulose at pH 

 3.5. The appearance is the same as that found in the natural lesion of Fig. 20, 

 with loss of mineral from the interrod region and some leaching out of the rod 

 interior. Undemineralized. ( X 5000. ) 



