208 E. JOHANSEN 



vealed an interesting pattern of distril)otion of mineral. The highest 

 concentration of crystalHtes was usually found adjacent to dentinal 

 canals, whereas intercanalicular areas were extensively demineral- 

 ized. Individual crystallites from both regions often appeared con- 

 spicuously large, indicating resistance to dissolution, possibly due 

 to a change in their composition. Studies of the organic phase 

 showed a remarkably intact collagenous matrix with individual 

 fibrils displaying banding and cross striations. It was concluded 

 that proteolysis follows demineralization in dentinal caries. 



In the chemical studies of carious enamel and dentin it was found 

 that the two tissues were in several respects similarly affected by 

 the carious process. Both tissues showed an increase in water (and 

 organic material) but a decrease in ash. Analyses of the ash fraction 

 revealed relatively minor changes in calcium and phosphorus con- 

 tent, but a marked decrease in magnesium and carbonate. The 

 fluoride content of carious enamel and dentin was much higlier than 

 that of the sound tissue. It was theorized that these chemical changes 

 were, in part, brought about by a recrystallization process which re- 

 sulted in the formation of crystallites of reduced solubility. 



Acknowledgments. Financial support for the original studies dis- 

 cussed in this report was obtained from the following sources: the 

 National Institute of Dental Research, United States Public Health Serv- 

 ice, Research Grant D-689; the American Chicle Company; the Colgate- 

 Palmolive Company; and the University of Rochester. 



The technical assistance of Diane Anderson in the preparation of the 

 illustrative material is gratefully acknowledged. 



References 



Armstrong, W. G. 1961rt. A quantitative comparison of the amino acid 

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Armstrong, W. G. 1961/j. Reaction //} vitro of sound dentin with glucose, 

 glucosamine and carbohydrate fermentation and degradation prod- 

 ucts. Arch. Oral Biol, 5, 179-189. 



Bernick, S., Warren, O., and Baker, R. F. 1954. Electron microscopy of 

 carious dentin. /. Dental Research, 33, 20-26. 



Bhussry, B. R. 1958. Chemical and physical studies of enamel from human 



