()56 G. N. JENKINS AND C. DAWES 



plaque. A very difFerent, and we l^elieve a misleading, result might 

 have been obtained if aqueous extracts of plaque had been used. 

 The crucial issue which we believe needs testing is whether chela- 

 tors are active in a salivary medium saturated with calcium phos- 

 phate. 



The Concentration of Certain Chelating Agents in Phique 



The concentrations in plaque of several substances which have 

 been suggested as chelating agents have also been investigated. 

 Citrate concentrations were estimated in plaque collected before 

 and after a glucose rinse, and the rate of breakdown of citrate 

 added to plaque was determined. The results (Table III) show 



TABLE III. Citrate and Lactate Concentrations in Dental Plaque 



that the concentrations were extremely low; they are, in fact, near 

 the limit of detection by the method. The concentration after the 

 glucose rinse was significantly ( p < 0.05 ) lower than before, which 

 is surprising, as it was expected that carbohydrate metabolism 

 would have increased the citrate concentration. The rapid rate of 

 breakdown of added citrate presumably explains why plaque citrate 

 is at too low a concentration to act as a chelator. 



Lactate concentrations in over 60 plaques whose pH exceeded 

 7.0 ranged from 0.06 to 0.27 mg/100 mg wet plaque. These figures 

 are in fair agreement with those of Moore et al. (1956). Leach and 

 Dodge (1961) found that as high a concentration as 0.9 per cent 

 lactate exerted no detectable chelating action, from which it may 

 be concluded that the much lower concentration of lactate in neu- 

 tral plaque is of no importance as a chelating agent. 



