Effect of high fluoride concentration on bovine dentin demineralization in narrow grooves in vitro

Previously, a dentin groove model was developed to investigate caries at plaque retention sites, such as marginal gaps, and pits and fissures. The aim of the present study was to investigate the in vitro effect of fluoride on the demineralization of dentin in the depth of the grooves at various distances from a freshly prepared resin-modified glass ionomer cement (RMGIC), which was used as the source of high fluoride release. Three parallel grooves (280 microm wide x 500 microm deep) were cut in the labial surface of 20 bovine coronal dentin discs. In 10 discs, the surface area (approximately 6 mm2) between the first groove and the edge of the disc was covered with RMGIC. The discs were exposed to an acidified methylcellulose gel system for 1 or 2 wk. Changes in mineral content were obtained by transverse microradiographic analysis. The results showed that integrated mineral loss (IML) was reduced up to 60% in the RMGIC groups, although the lesion depth was not significantly influenced by RMGIC. The pattern of demineralization differed between groups: the subsurface lesions in RMGIC groups did not decrease in IML towards the base of the groove to the same degree as in the control groups. It is concluded that high amount of fluoride inhibits loss of mineral, while not affecting the lesion depth. The homogeneity of the lesions with depth in the RMGIC group may be explained by a fluoride-induced inhibition of demineralization at the entrance of the grooves.