ULTRASTRUCTURAL AND CHEMICAL STUDIES ON CARIES 191 



in spaces of enamel rods ( Fig. 3 ) . The sound tissue showed no evi- 

 dence of penetration of silver in the same period of time. 



Observations on the morphology, size, and electron density of 

 crystallites within individual enamel rods at times suggested re- 

 gional differences in these characteristics. The crystallites located 

 at the periphery of rods appeared larger, more electron dense, and 

 generally better preserved than those within rods (Fig. 2). It may 

 be speculated that such crystallites have been selectively spared 

 from dissolution or selectively recrystallized in the carious process. 



Individual crystallites studied in sections and in triturated samples 

 of carious enamel showed evidence of morphological changes (Figs. 

 5 and 6) referable to the carious process. The changes included 

 localized and generalized surface erosion with establishment of 

 spaces between adjoining crystallites (Figs. 6a and 6b). Also, per- 

 forations in transverse direction (Fig. 6c) were common findings. 

 Occasionally, crystallites appeared to present perforations in longi- 

 tudinal directions (Fig. 5). The most severely affected crystallites 

 were seen as mere vestiges with little resemblance to the crystallites 

 of sound enamel. Others (Fig. 6d) appeared remarkably similar to 

 segments of crystallites observed in sound enamel (Figs. 7 and 8). 

 The many apparent spaces seen in carious tissues suggested that 

 many crystallites had been entirely dissolved. 



Organic material was found in all samples of carious enamel stud- 

 ied after artificial demineralization, embedding, sectioning, and stain- 

 ing. Frequently, rod sheaths appeared distinctly outlined (Fig. 9), 

 displaying a fine fibrillar component. In some preparations similar 

 fibrils were also seen within rods and in interrod areas, while in 

 other preparations these areas were devoid of matrix. (Inteipreta- 

 tion of these findings in relation to the process of dental caries must, 

 however, await further clarification of the modifying influence of 

 certain technical procedures.) In other sections there appeared to 

 be more organic material in the carious (Fig. 10) than in the sound 

 tissue (Figs. 11 and 12). This finding may represent the presence of 

 extraneous organic material derived from oral fluids. With the stain- 

 ing procedures available at present, however, it was not possible to 

 distinguish between extraneous and intrinsic organic material. 



Carious dentin studied in sections displayed a most interesting 



