Comparative Dissolution Rates of Enamel, Dentin, and Bone

I. Effect of the Organic Matter

¹ Eastman Dental Center, Rochester, New York

The dissolution rates of powdered enamel, dentin, and bone have been compared in 0.1 M acetate buffers over the pH range of 3.5-5.5.

It has been found that the relative order in which these substances dissolve (for the particular mesh sizes employed) varies with the pH of the decalcifying medium. At pH 5.0, bone dissolved fastest, followed by dentin and enamel in that order. At pH 3.5, however, the order is completely reversed, with enamel showing the fastest dissolution rate and bone, the slowest. This contrasts with the dissolution patterns obtained with these tissues from which the organic matter was removed, where over the pH range tested bone always dissolved faster than dentin and dentin faster than enamel.

It appears that the organic matter of bone, and to a lesser extent that of dentin, retards the dissolution rate of these tissues. This retarding effect, moreover, appears to increase with decreasing pH. The organic matter of enamel seems to have little effect on its dissolution rate.

It is suggested that the increasing interference of the organic matter of dentin and bone as pH decreases is the result of a progressive increase in its degree of swelling and/or positive charge, which act to retard the diffusion processes involved in dissolution. The swelling of the organic matter may in effect be considered as an increase in the thickness of the stationary layer about each particle, which in accord with Fick's Law, as applied to dissolution phenomena, should retard dissolution.