048 G. N. JENKINS AND C. DAWES 



proteolytic bacteria might attack the proteins of enamel, releasing 

 from them various breakdown products which would then form 

 chelation compounds with the mineral matter of the enamel (the 

 proteolysis-chelation theory). Then the organic and mineral phases 

 of enamel would be destroyed more or less simultaneously. This 

 approach is a direct challenge to the acid theory, which in its modern 

 form is based on results which are interpreted as showing that tooth 

 substance does not dissolve in saliva or plaque until acids have 

 lowered the pH of the environment to a critical value, usuallv be- 

 tween 5 and 6. 



As long ago as 1949, Eggers Lura suggested a nonacid decalcifica- 

 tion theory of caries, and although he has modified his views he still 

 believes that chelators arising in the plaque are more important than 

 acids (Eggers Lura, 1949, 1957, 1961). 



Detailed critiques of these theories have recently been published 

 (Bibby et al., 1958; Jenkins, 1961), and only the main points will be 

 discussed here. 



Evidence Needed to Prove the Proteolysis-Chelation Theorij 



Before the proteolysis-chelation theory is accepted, experimental 

 evidence must provide positive answers to the following questions: 

 Do bacteria exist in the mouth which can attack the organic matter 

 of enamel without previous decalcification? Are the products of this 

 breakdown chelating agents? If so, are the amounts of chelators 

 formed adequate to dissolve the inorganic matter to form a carious 

 cavity? 



The existence of bacteria which can attack undecalcified 

 ENAMEL. No study appears to have been made of the effect of 

 bacteria on isolated enamel protein, presumably owing to the dif- 

 ficulty of obtaining this material. On the assumption ( not supported 

 by the analyses of Stack, 1955) that enamel protein is a keratin, 

 Schatz et al. ( 1957, 1958 ) cultured oral bacteria in media containing 

 keratin from carefullv washed hair, wool, and feathers as the only 

 source of nitrogen. They reported that both human and animal saliva 

 contained bacteria which grew on these media, and considered that 

 the existence of oral keratinolvtic bacteria was thereby proved. This 



