^238 



J. A. CxRAY AND M. D. FRANCIS 



16 



lI2 



E 

 o 



^' 



E 



Q 

 CO 



LlI 



<4 

 ijj 



40 80 '20 160 



EXPOSURE TIME (HOURS) 



200 



240 



Fig. 27. Comparison of enamel dissolution rate as a function of time during 

 exposure to mediums containing 0.05 m lactic acid plus 6 per cent hvdroxvethvl 

 cellulose (with low buffer content) at different CaCl. concentrations and pH 

 values. Increasing the CaCL concentration or the pH value decreased the rate 

 of enamel dissolution during incipient carious lesion formation. The line of 

 short dashes is from Fig. 25 and the line of long dashes is from Fig. 26. 



tiat!on is increased. The enamel dissolution rate was measured as a 

 function of pH for a medium at 0.05 m lactate concentration and 

 two different calcium chloride concentrations. The data are plotted 

 as a function of hydrogen ion concentration (Fig. 28). Increasing 

 calcium chloride concentration caused a decrease in the rate and 

 hence in the slope of the rate curve. 



The rate of enamel dissolution increased linearly with increasing 

 lactate concentration at an\ pH level or calcium chloride concentra- 

 tion. The effect of lactate concentration on rate was determined for 

 two different pH values and three different calcium chloride con- 

 centrations (Fig. 29). The slope of these linear plots varied with 

 the different hydrogen ion and calcium chloride concentrations. 



