PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION 



237 



CALCULATED FROM PO4 ANALYSES 

 • 4 "C 

 ^ 37 "C 



80 120 160 



EXPOSURE TIME (HOURS) 



Fig. 26. Enamel dissolution as a function of time during exposure at 4°C 

 and 37°C to a medium consisting of 0.05 m lactic acid and 0.03 m CaCl2 plus 

 6 p6r cent hydroxyethjl cellulose (with low buffer content) adjusted to pH 

 3.5. Temperature had little effect on the enamel dissolution rate. The rate was 

 decreased by addition of CaClo (compare with Fig. 25). 



The next series of observations deal with enamel dissolution rate 

 (expressed as mg of enamel dissolved per cm- of enamel surface 

 exposed per 96 hours exposure) as a function of hydrogen ion con- 

 centration (i.e., pH), lactate concentration, and calcium concentra- 

 tion (Figs. 28 to 33). These quantitative results are higher than the 

 preceding measurements because a different sample of hydroxyethyl 

 cellulose was used that contained a greater quantity of the buffer 

 salt impurity. The results become comparable when the decalcifica- 

 tion rate is plotted as a function of total acid. 



The rate of enamel dissolution during incipient carious lesion 

 formation increased with increasing hydrogen ion concentration. 

 The rate is a nonlinear function of the hydrogen ion concentration, 

 and the slope of the function decreases as the hydrogen ion concen- 



