Effect of fluoride-releasing filling materials on underlying dentinal lesions in vitro

Fluoride-releasing materials placed over carious tissue are assumed to enhance remineralisation of the underlying lesion. This remineralisation, however, also depends on the availability of calcium and phosphate, which may be supplied by the pulpal fluid. The aim of this study was to measure the fluoride release of glass ionomer cements (GICs) into underlying dentin and to measure the effect of the released fluoride on the remineralisation of the underlying dentinal lesions using transversal microradiography. Discs of fluoride-releasing GIC were placed on top of dentinal lesions in an in vitro model. The discs and the dentin slabs were covered completely by a protective layer of nail varnish, leaving only the pulpal side of the dentin slab open, and hence the dentinal tubules as the pathway for the incubation fluid to the GIC disc. Specimens were incubated in a remineralisation buffer. The materials tested were a conventional GIC, an experimental GIC that was designed to have a high fluoride release, and an inert material. Fluoride was found to penetrate through the dentin slab into the surrounding fluid. Fluoride uptake from the experimental GIC was higher than from the conventional GIC. Mineral content-depth profiles after 10 weeks' remineralisation revealed that in the outer 30 microm of the lesion a higher mineral deposition occurred for the experimental GIC than in both other groups. No differences in the overall change of integrated mineral loss were found for the tested materials. We conclude that high fluoride release from filling materials only results in superficially increased remineralisation of underlying demineralised dentin.