ULTRASTRUCTURAL AND CHEMICAL STUDIES ON CARIES 207 



down by collagenase appear different from that of the sound tissue 

 ( Armstrong, 196 !« ) . 



In conchision, it might be stated that the findings lend support to 

 the general idea that demineralization precedes proteolysis in the 

 development of carious lesions. It is evident, however, that the 

 carious process in all its phases is a most complex phenomenon, at 

 present not readily characterized in a single concept. 



Summary 



A series of electron microscopic and chemical studies were carried 

 out to characterize carious lesions in enamel and dentin. The ultra- 

 structural observations on the inorganic phase of the tissues were 

 carried out on ultrathin sections, homogenate preparations, and 

 triturated samples. After demineralization, the organic phase was 

 studied in ultrathin sections stained with lead preparations and 

 phosphotungstic acid, in unstained sections, and in homogenate 

 preparations. The chemical composition was studied in samples that 

 had been dried to constant weight or ashed. 



In carious enamel, ultrastructural observations on the inorganic 

 phase often revealed structureless areas of varying width delimiting 

 enamel rods. Crystallites were found to be sparsely distributed, with 

 some evidence for the existence of microchannels between them. 

 Those at the periphery of enamel rods occasionally appeared to be 

 in a better state of preservation. Individual crystallites were found 

 to vary considerably in morphology; some showed generalized and 

 localized surface erosion, some displayed perforations, and others 

 appeared as mere vestiges with little resemblance to crystallites 

 found in the sound tissue. Segments of seemingly unaltered crystal- 

 lites were also encountered. Demineralized carious enamel studied in 

 stained sections showed evidence of organic material. Persistence of 

 the organic matrix was indicated by the occurrence of rod sheaths, 

 even though rods and interred areas frequently lacked the fine fibrils 

 observed in the sound tissue. Sometimes an apparent increase in 

 organic material was encountered. This finding was thought to be 

 related to an influx of organic material from oral fluids. 



The electron microscopic observations on soft carious dentin re- 



