ULTRASTRXJCTURAL AND CHEMICAL STUDIES ON CARIES 195 



Artificial demineralization of soft carious dentin and staining with 

 phosphotungstic acid or lead preparations revealed an abundant 

 matrix of collagenous fibrils (Fig. 22). The presence of typical 

 cross-banding in longitudinal sections (Fig. 23) suggested that 

 most fibrils were intact, resembling those of sound dentin (Fig. 26). 

 However, areas with marked reduction in numbers of fibrils were 

 seen, both in close proximity to bacteria (Fig. 24) and, in some 

 regions, at a distance from bacteria. Observations on homogenate 

 preparations of carious dentin also revealed collagenous fibrils with 

 typical banding but devoid of crystallites ( Fig. 25 ) . The persistence 

 of these fibrils in the carious tissue strongly supports the point of 

 view that demineralization precedes proteolysis in dentinal caries. 

 (For comparison with bone resorption see Hancox and Boothroyd, 

 chapter 18 in this volume.) 



Composition 



Interpretation of the electron microscopic observations presented 

 above raised a number of questions pertaining to the chemical com- 

 position of the carious tissues. In an attempt to clarify some of these 

 points, a number of analyses were carried out. Several pertinent find- 

 ings will be summarized by representative data. 



Determination of major elements and carbonate of carious enamel 

 revealed a reduction of calcium, phosphorus, magnesium, and car- 



FiG. 5. Section of carious enamel showing crystallites of varying size and 

 shape. (X approx. 40,500.) 



Fig. 6. Crystallites from carious enamel. 



6a. Surface erosion with resulting space (S) between adjacent crystallites. 

 Triturated preparation. (X approx. 77,000.) 



6b. Apparent localized erosion of adjacent crystallites with estabhshment of 

 channel-like space (S). (X approx. 124,750.) 



6c. Transverse perforation in crystallite (S). (X approx. 124,750.) 



6d. Segments of well preserved crvstallites within the lesion. ( X approx. 

 124,750.) 



Fig. 7. Section of sound permanent enamel showing distinct outlines of in- 

 dividual crystallites. Several apparent junctions (/) between ends of crystallites 

 have been marked. ( X approx. 103,700.) 



Fig. 8. Section of sound permanent enamel illustrating obliquely cut crys- 

 tallites. (X approx. 124,750.) 



