ROLE OF CHELATION IN DECALCIFICATION SYSTEMS 649 



conclusion was criticized by Mandel and Ellison (1957) on the 

 ground that the bacteria may not have been metabolizing the kera- 

 tin, but various nitrogenous contaminants. The thorough washing to 

 which these sources of keratin were subjected makes this unlikely, 

 although Schatz et al. did not prove conclusively that all non-keratin 

 nitrogenous substances had been removed. 



Whether we accept or reject this evidence for the presence of 

 oral keratinolytic bacteria is probably unimportant because the 

 majority of the enamel protein is not keratin, but mucoprotein and 

 polypeptides (Stack, 1955). There is little doubt that some oral 

 bacteria could attack these substances. 



The question whether enamel organic matter can be attacked 

 without previous removal of the calcium salts is more controversial. 

 Most of the evidence suggests that the calcium salts, both in enamel 

 and in dentine, protect the protein from enzvme attack (Miller, 

 1890; Bibby, 1932; Evans and Prophet, 1950; Roth, 1957), but some 

 previous workers have disagreed (Pincus, 1937; Hurst et al., 1953). 

 Schatz et al. ( 1955 ) measured the oxygen uptake by cultures of oral 

 bacteria in the presence of whole teeth, hair, rat and human dentine, 

 and human enamel ( Fig. 2 ) . Respiration increased with every addi- 

 tion, especially with the human teeth and rat dentine. With human 

 enamel, the rise in oxygen uptake was extremely small and of doubt- 

 ful significance, although in later publications larger eflFects from 

 human enamel were reported (Fig. 3). These results were inter- 

 preted as showing that the organic matter in intact enamel could be 

 metabolized by oral bacteria. 



Evidence for the chelating action of the substances released 

 FROM incubated HARD TISSUES. In another series of experiments 

 by Schatz et al. (1955), bone containing Ca'*'^ was incubated with 

 and without oral proteolytic bacteria and the rises in radioactivity 

 of the media were compared. In the presence of the bacteria 77 

 per cent more Ca"*^ entered the medium (pH 8.4) than in the con- 

 trol medium which remained at pH 7.0, from which it was concluded 

 not only that the bacteria could attack the undecalcified bone, but 

 also that the products of proteolysis dissolved the calcium by chela- 

 tion under these alkaline conditions. 



