238 MICROSCOPIC ANATOMY OF THE TEETH 



would therefore consider the following to be a much nearer 

 approach to the actual proportions in dentine. 



Fresh human dentine : 



Free water (which can be dried out at 212 F.) . 10 

 Dry dentine ....... 90 



100 

 Dried human dentine : 



Organic matter . . . . . .19-6 



Combined water . . . . 8-4 



Salts 72 



100 

 Von Bibra in one analysis gives : 



Organic matter (tooth cartilage) . . . 27-61 



Fat . . 0-40 



Calcium phosphate and fluoride . . . 66-72 



Calcium carbonate ...... 3-36 



Magnesium phosphate ..... 1-08 



Other salts 0-83 



100 



In these analyses the large amount of organic matter 

 present in dentine compared with that in enamel is especially 

 to be noticed, and the great preponderance of phosphate 

 over carbonate of calcium in both dentine and enamel. 



Black (3) undertook a careful investigation to determine 

 the percentage of lime salts in the dentine of teeth of 

 apparently different density, and came to the conclusion 

 that there is a scarcely appreciable difference between the 

 percentages of lime salts in all the teeth examined. 



He stated ' that neither the density, nor the percentage 

 of lime salts, nor the strength, is in any degree a factor in 

 predisposing the teeth to caries or hindering its inception 

 or progress '. It was pointed out, however, by Professor 

 W. D. Miller that the resisting power might not depend so 

 much on the percentage of lime salts in the teeth as upon the 

 molecular conditions present ; the degree of stability of 

 the compounds formed with the organic material of the 

 tooth. Although the amount of the salts in the tissues may 



