ROLE OF CHELATION IN DECALCIFICATION SYSTEMS 657 



The sialic acid concentration of plaque was also found to be very 

 low (averaging 3.7 /xg/lOO mg wet plaque), and, as with citrate, 

 plaque rapidly metabolized added sialate. 



None of this evidence from the experiments on plaque extracts 

 and from the concentration of individual substances reported to 

 have chelating properties supports the hypothesis that chelation is 

 important in caries. 



Conclusion 



The position may be summarized as follows: There is no evidence 

 which clearly supports the hypothesis that decalcification in caries 

 results from chelators in the plaque. The evidence for acids is very 

 considerable, in spite of uncertainties about the pH on the inner side 

 of the plaque or about the critical pH necessary for decalcification 

 in that area. On the other hand, very few experiments have been 

 carried out on the action of plaque chelators. 



Since it cannot be denied that some chelating agents are present 

 in the plaque, it is possible that they may be active during the in- 

 tervals between meals and during sleep, when the plaque is in the 

 neutral or alkaline conditions which favor chelation. The experi- 

 meiits reported here suggest that such activity must be weak and 

 probably unimportant as compared with the action of acid. More 

 experiments are needed on the quantitative effects and distribution 

 within the plaque both of chelators and of acids before a final de- 

 cision can be reached. 



There are no grounds for believing that chelators are alone re- 

 sponsible for caries. There is no experimental evidence for the view 

 that enamel protein is a source of chelators in caries. The low con- 

 centration of organic matter in enamel is a weighty objection to the 

 theory, and the answers given to this objection are purely specula- 

 tive. 



Summary 



1. The nature of chelation and its possible biological importance 

 are described. 



2. The unique solubilizing powers of citrate are pointed out, al- 



