ATTRITION OF THE HYPSODONT TOOTH 



TABLE IV. Effect of Acids Occurring in Plants on the 



Hardness of Sheep's Teeth 



(Initial average Knoop Hardness Number: dentine, 47; enamel, 203) 



167 



" Too soft to measure. 



** That is, a slight increase. 



most of these experiments. The presence of a hydroxy group did 

 not consistently influence chelating activity of the acids, whereas the 

 amino group (in aspartic) practically eliminated it. 



Solutions of citrate equivalent in concentration to the organic 

 acids in grass (chiefly malate and citrate), at pH's from 5.5 to 6.5, 

 dissolve finely ground sheep's teeth, apatite, and tricalcium phos- 

 phate, especially at the lower pH values. Even acetate under similar 

 conditions has an appreciable action, about one-fourth that of the 

 citrate. 



Grass and clover press juices, however, have little solvent action 

 on these phosphatic substances. When the phosphatic substances, 

 after treatment with grass press juice followed by washing, are 

 further extracted with 50 per cent w/v ammonium sulfate, small 

 amounts of calcium and phosphate, in excess of the controls, are 

 dissolved. This indicates that the action of constituents of the grass 

 juice has produced a weakening in the apatite lattice, thereby in- 

 creasing the solubility of its constituent atoms. 



Barnicoat and Hall (1960) pursued this investigation with the 

 electron microscope, using a technique which in addition to facilitat- 

 ing the study of the microstructure of enamel and dentine enables 



