Acid Dissolution Rate of Sound and White-Spot Enamel Treated with Tin(II) and Fluoride Compounds

Abstract

The dissolution rate in acid was measured for enamel treated with SnF2, SnCl2 and NaF using a differential and an integral method. The influence of enamel condition was examined by using both normal sound enamel and enamel with a white spot surface produced in-vitro by exposure to an agar-lactic acid medium to simulate an incipient carious lesion. All enamel was polished before use to remove the organic coatings and the more acid resistant surface layers. The enamel samples were treated 5 min. with 3030 ppm Sn(II) and/or 970 ppm F-. The samples were then exposed to 0.1 M, pH 4.5 lactate buffer at 37[degree]C for 2 min. intervals in the differential method and for up to 4 hrs., in the integral method, and the solutions were analyzed chemically for dissolved Ca and phosphate. Using the differential method, treatment with all the compounds reduced the rate of sound enamel dissolution to the same extent, but SnF2 had a greater effect than SnCl2 or NaF on white spot enamel. By the integral method, NaF treatment reduced the enamel dissolution rate at all time intervals, with equivalent results on normal or white spot enamel. The SnCl2 treatment greatly reduced the dissolution rate for short intervals, more so than NaF; but this inhibition was lost completely with longer acid exposures using either type of enamel. The SnF2 treatment nearly arrested the enamel dissolution rate during the initial acid exposures; but SnF2 became equivalent to NaF with longer exposures on sound enamel. The SnF2 always had a greater effect than NaF on white spot enamel. The experimental conditions which give results correlating best with known clinical studies are longer exposure periods using white spot enamel.