SOLUTION RATE OF TOOTH ENAMEL IN AN ACETATE BUFFER

¹ Westwood Research Laboratory, Westwood, Mass.

Rate studies on enamel solubility in pH 4, 0.2 M, acetate buffer have been carried out by a gravimetric method and by colorimetric determination for phosphate and calcium in the solution. There was a gradual loss of weight of powdered enamel in a nonlinear fashion from the first to the thirtieth minute. Solubility reduction by fluoride treatment ranged from 19 per cent during the first minute to 30 per cent for the period from 10 to 30 minutes.

Tests with fresh and partially reacted enamel and buffers indicated that the gradual slowing in solution rate is attributable to a change in solvent action of the buffer with time rather than a change in the acid resistance of the enamel.

Procedures were developed for microdetermination of calcium and phosphate serially on small portions of a buffer solution at eight times ranging from 1 to 30 minutes after a test was started. There was a gradual decrease in the solution rate of calcium and phosphate for untreated enamel. Treated enamel had lower solution rates for phosphate throughout the time period and for calcium from the tenth to the thirtieth minute. Treatment did not appear to affect calcium solution rate during the period from 1 to 5 minutes. Findings indicated that solubility reduction by fluoride depends upon the duration of the experimental period and whether the effect is judged from determination of weight loss, or calcium or phosphate concentration in buffer.

Instantaneous solution rates for calcium and phosphate in buffer were calculated by drawing tangents to the curves for concentration vs. time. Wide variation in solution rates occurred during the period of 1 to 25 minutes. Tests with 0.1, 0.3, and 1.0 parts per million of fluoride in the buffer indicated considerable influence from traces of fluoride and suggested that fluoride reacts preferentially at high dilutions with sites in tooth enamel that are undergoing decalcification.