KCLE OF CHELATION IN DECALCIFICATION SYSTEMS 655 



ments were inadequately controlled, and, since the media were not 

 saturated with calcium phosphate, some solution of tooth substance 

 would be expected in these mixtures bv ordinary ionic equilibria 

 witliout in\'olving complex formation. Sucrose, ATP and other or- 

 ganic phosphates, and sialic acid were also suggested by Eggers Lura 

 as possible chelating agents. Chelation by sucrose is of particular 

 interest because it provides a possible explanation, on the chelation 

 theory, of the undoubted fact that the ingestion of much sucrose 

 increases caries. Blackwell et al. (1961) have shown, however, that 

 high unphysiological pH values are necessary for sucrose to attack 

 the enamel surface. ATP and most other organic phosphates of 

 plaque are present inside the bacterial cells and out of contact with 

 the enamel surface. If these substances were released from auto- 

 lyzing dead cells, much of the organic phosphate would be broken 

 down by the enzymes of the plaque. These substances, although 

 powerful chelators, would not therefore seem to be present under 

 conditions in which they could have much eflFect on the enamel. The 

 position of sialic acid will be discussed below. 



Tests on the Chelating Towers of Tlaqtie Extracts 



In an attempt to test the effecti\'eness of the chelators in plaque, 

 we have made salivarv extracts of plaque pooled from over a dozen 

 subjects and shaken them with a piece of bone containing Ca^'^ 

 (Jenkins and Dawes, 1963). Control media contained a similar piece 

 of bone shaken with saliva supernatant only. The radioactivity en- 

 tering the two media — salixarv supernatant alone and saliva super- 

 natant containing any soluble chelating agents of plaque— was 

 identical and could be accounted for by ionic exchange, due allow- 

 ance being made for variations in surface area of the bone samples 

 bv prior incubation of both bone samples with salivary supernatant 

 alone. These experiments were carried out four times in all, and 

 lent no support to the suggestion that alkaline plaque contained 

 effective concentrations of chelating agents. Admittedly, the plaque 

 constituents were diluted sixfold in making the extracts, but this is 

 probably compensated for by the great sensitivity of the radio- 

 active method of detecting whether the bone dissolved. We should 

 like to emphasize the importance of studying salivary extracts of 



