Influence of Type of Acid, pH, Molarity, and Saturation on Rate of Enamel Penetration

¹ Department of Dental Science, Tufts University School of Dental Medicine, Boston, Massachusetts

Four characteristics of acidic buffers—kind of acid, pH, molarity, and degree of saturation—were studied for their influence on penetration and cavitation of enamel sections. Penetration was proportional to time of etch, with the relative penetration rate given by the order of citrate, lactate, and acetate. Cavitation occurred most frequently with citrate, less often with lactate at low pH's, and seldom with acetate. The penetration was greater with low pH and high molarity, except for anomalous behavior with citrate in the pH range of 4.0-4.4. Saturation seemed to be unimportant at the molarities studied. The rate of penetration was dependent on the quantity of un-ionized acid in the buffer, as expressed by the formula

Penetration rate = (9.69 x HAC)^0.754.

When in vivo data of other investigators were used to calculate penetration rates of caries-susceptible plaques, there was some degree of correspondence between the predicted and observed results.