This study was undertaken to determine the changes in the dissolution rate of enamel in acid at different developmental stages of rat incisor enamel. Four groups of Wistar rats received water with 0, 25, 50, and 100ppm fluoride, respectively, for 10 weeks. Six windows were prepared on the enamel surface of the maxillary incisors, corresponding to the developmental stages of (A) matrix formation, (B) early maturation, (C) late maturation, (D) pigmented enamel against alveolar bone, (E) enamel attached to gingivae, and (F) erupted enamel. The acid dissolution rates were determined at each site using a slightly modified version of the procedure described by Nakagaki (J. Dent. Hlth 28; 498-518, 1979).
The results are summarized as follows.
1) The rate of enamel dissolution in every group was the highest in the matrix formation stage and decreased as the enamel developed.
2) The acid dissolution rate of enamel dropped sharply in a stepwise fashion between sites A and B and then again between sites C and D.
3) The dissolution rate at sites B and C in the maturation stage decreased significantly with increasing intake of fluoride.
4) The dissolution rate at sites D and E, where enamel was pigmented, increased significantly with fluoride intake. The iron pigmentation and porosity in this region of fluorosed enamel might be responsible for the change in the dissolution rate of the pigmented enamel.
