DENTAL HARD TISSUE DESTRUCTION 115 



then dropped back to normal within 20 minutes. He found, however, 

 that there was no excess secretion of citrate through the saHvarv 

 glands when the citrate was given in a capsule swallowed prior 

 to the test. In other words, it would appear that the transitor\' oral 

 citrate increase following normal ingestion was due to retention 

 of the citrate in the oral ca\'ity, rather than to recirculation through 

 saliva. 



In several in vitro tests Ericsson added citrate to saliva and exam- 

 ined the demineralizing effect of this mixture on powdered enamel 

 bv examining the calcium phosphate content of the solution after 

 20 minutes. From these in vitro tests he concluded that the presence 

 or absence of citrate had no significant effect, whereas acidifying the 

 salivarv mixture to pH 5.5 — the presence of acid, in other words — 

 did increase the enamel solubilitv. 



Demineralization obser\'ed in rats following ingestion of solutions 

 containing high amounts of citrate led McClure and Ruzicka ( 1946) 

 to compare the effect of citrate and of lactate added to the drinking 

 water and adjusted to a pH range between 5.5 and 7.2. When the 

 molar teeth of the rats were weighed upon sacrifice after 2 weeks, 

 relative loss of minerals was determined by the ultimate molar 

 weight. These workers concluded that the acidity of the solutions 

 was particularly destructive at the lower pH, as would be expected, 

 but that citrate was significant in the sense that, like other chelating 

 agents, it could be relativelv destructive even at neutral pH and 

 above. 



Recently there has been considerable writing on the possible 

 implication of a chelating mechanism in the production of erosion 

 as well as of caries (Schatz et al., 1957). In these studies, it was 

 shown that oral proteolytic bacteria can dissolve pulverized rat 

 bone and synthetic hvdroxyapatite and that mixtures of salivary 

 flora in various keratinous media have a high catabolic activity on 

 cow and rat bone. The mineral withdrawal was attributed to some 

 chelating effect of keratin or gelatin derivatives or cell metabolites 

 acting as chelators. Unfortunately there is virtually no research on 

 this problem directlv related to dental tissues per se, let alone to 

 caries or erosion. Though it mav seem attractive to consider a 

 chelation mechanism not requiring an acidic pH, it must be recalled 



