24'2 



.1. A. CRAY AND M. D. FRAXriS 



I0.0-- 



< 



— (D 



CD \ 



3 CM 



^ i 



en \ 



rl E 



1.0- 

 0.001 



1 1 \ — I — I — I I I I 



1 1 i 1 — I — TTT 



SLOPE = 



I I I I I I I 



J I I I I I I I 



0.01 



0.1 



ADDED CaClg CONCENTRATION (moles / li ter ) 



Fig. 31. A logarithmic plot of the data from Fig. 30 for the enamel dis- 

 solution rate during incipient carious lesion formation as a function of CaCL 

 concentration was a straight line. The rate was, therefore, proportional to the 

 CaCL) concentration taken to a power equal to the slope of this plot. 



1962) and the known lactate concentration vvhicli had been added. 

 The undissociated acid content arising from hydroxyethyl celkdose 

 was determined from pH titration curves. The hydrogen ion con- 

 centration was calculated from the pH measurement. The contribu- 

 tion of the various acid sources is given in Table II. It is immediately 

 apparent that the rate of enamel dissolution over all pH values and 

 lactate concentrations can be summarized by a single straight-line 

 function of total available acid concentration for a given calcium 

 chloride concentration. A separate linear function with a different 

 slope is required for each calcium level. 



In the absence of organic material, lactate buffer of any apprecia- 

 ble concentration destroyed the surface and only a slight advancing 

 front of decalcification occurred (extending only 5 to 10 microns 

 into the enamel for 0.05 m lactic acid at its "as is" pH of 2.6 ) . The 

 loss of enamel and, to some extent, the advancing decalcification 

 front are apparent in a photomicrograph (Fig. 34) or in a micro- 



