Q 



PHYSICAL CHEMISTRY OF ENAMEL DISSOLUTION ''^OD 



librium with a phase different from hydroxyapatite, which must, 

 therefore, be covered l)y this other phase. 



Previous work ( Gray et aJ., 1962 ) has shown that the initial sohi- 

 bihty rates of normal enamel and fluoridated enamel were the same. 



TABLE III. Equilibrium Solubility Constants Determined from 

 Synthetic and Natural Phosphates in Acid Buffer Solutions 



Hvunan enamel 



Synthetic apatite 

 Synthetic apatite 



Saliva + lactic acid 



(Fosdick and Starke, 1939) 4.4 X 10' 



HCl + NaCl (Ericsson, 1949) 2.8 X 10"' 



Saliva + lactic acid (Ericsson, 1949) 4.5 X 10-' 



4.1 X 10- 



" The value of the Ksp determiiu'd in the present work across all systems (85) was 

 5.4 (± 2.7) X lO"''. An average value of 4.1 (± 2.0) X 10"' was ol)taine(l from data 

 which included 61 systems from the literature. 



Fluoridated enamel became less soluble only after fluoride accumu- 

 lated in the acid solution, suggesting that inhibition resulted from 

 the deposition of calcium fluoride from the reaction products onto 

 the enamel surface. Furthermore, there is no fundamental reason 



