654 G. N. JENKINS AND C. DAWES 



could be dissolved by chelation in a year. They assumed that the 

 rate of decalcification in a cavity in vivo was the same as in their 

 experiments in vitro, allowing for the much lower protein content 

 of enamel as compared with bone. Though fullv realizing the limi- 

 tations of this calculation, Schatz et al. at least think that it shows 

 that chelation could have effects of the right order of magnitude. 

 However, the rate in vivo is verv unlikelv to be as rapid or as con- 

 stant as that in vitro, and the whole basis of the calculation is there- 

 fore unsound. 



In conclusion, the proteolvsis-chelation theor\' is original and stim- 

 ulating, but most of the experiments so far carried out to answer 

 the questions raised above are either negative or susceptible to 

 alternative explanations, or do not resemble sufficientlv the condi- 

 tions in carious cavities to be relevant. When this evidence is con- 

 trasted with the mass of evidence on the acid theor\', which — though 

 mcsth circumstantial and inconclusixe — so largeh' faxors the theor\', 

 the probabilities seem against proteolvsis-chelation in the form so 

 far discussed. 



Possible Chelators in Placjue 



The original chelation theorv of Schatz et al. ( 1955 ) , which did 

 not confine the source of chelators to the organic matter of enamel, 

 is more plausible than the later proteolvsis-chelation theorv. It can- 

 not be denied that man\' substances in foods, saliva, and plaque 

 possess chelating powers. The question that arises is whether the 

 concentrations are sufficientlv high to decalcifv enamel, and in par- 

 ticular whether their action is quantitativelv comparable with that 

 of acids. Plaque is known to have a high calcium concentration 

 (Allen and Moore, 1957; Dawes and Jenkins, 1962), and it is possi- 

 ble that much of it is present in a chelate or complexed form. If so, 

 the chelators mav be alreadv bound to so much calcium that they 

 are unlikelv to combine with the much less soluble surface of the 

 enamel. 



Eggers Lura (1960) has tested the efl^ects of certain chelating 

 agents dissolved in ammonia buffer at pH 7.8 on the enamel surface. 

 He stated that alkaline solutions of nucleic acid, PTE, salivary mucin, 

 and amino acids produced signs of decalcification, but the experi- 



