PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION 223 



TABLE I. Effectiveness of Water-Soluble Polymers INIixed with 



Acidic Buffer for the Formation of Incipient Caries-like Lesions 



AND Inhibition of Dissolution of Enamel Surface 



with several materials are listed in Table I. Synthetic polymers of 

 simple structure, such as ethylene oxide condensates or polyvinyl 

 alcohol, as well as an inorganic thickening agent, finely divided 

 silica, were completely ineffective. The solutions dissolved the 

 enamel surface just as would have occurred if the polymer had 

 been absent. The most effective compounds were polysaccharides, 

 such as derivatives of cellulose. The testing of eligible materials was 

 by no means exhaustive, but complexity, lack of purity, and unde- 

 sirable ionic properties precluded interest in many undoubtedly ef- 

 fective compounds. Hydroxyethyl cellulose, a nonionic synthetic 

 derivative of cellulose, was unusually effective and was selected as 

 the polymeric ingredient of the decalcification medium. The choice 

 of hydroxyethyl cellulose was based on (1) effectiveness, (2) non- 

 ionic character, (3) inertness to salt effects, (4) the fact that hy- 

 droxyethyl cellulose thickened rather than solidified the solutions 

 and permitted a good contact ]:)etween enamel and the decalcifica- 

 tion medium, and (5) minimal changes in viscosity over the tem- 

 perature range of interest. The particular samples used were found 

 to contain an acidic buffer salt, sodium acetate, which had to be 

 taken into account when total undissociated acid was calculated. 

 The amount of this buffer capacity was determined from pH titra- 

 tion curves using both acid and base titrants. 



