Abstract:
Nowadays fluoride releasing restorative materials are widely used in an attempt to prevent secondary caries. The purpose of this study was to investigate the effect of fluoride released from different materials on the hardness of human enamel and dentin as a function of distance. The 116 enamel and 108 dentin specimens prepared from freshly-extracted non-carious permanent premolars were divided into 4 groups. Cavities (3x3x1 mm) were prepared on the surface of each specimen. In groups I and II, the prepared cavities were filled with resin composite (Clearfil APX, Kuraray, Osaka, Japan) using dentin adhesive (Clearfil Liner Bond II, Kuraray, Osaka, Japan) to use as negative and positive controls, In groups III and IV, the prepared cavities were filled with resin modified glass ionomer cement (Fuji LC, GC, Tokyo, Japan) and polyacid modified resin composite (F2000, 3M, Minnesota, USA). Surface microhardness of all specimens were measured prior to the forming of artificial caries lesion using microhardness tester. Then all the specimens were immersed in demineralization solution at pH 5.0 for 24 and 72 hours to from artificial caries lesion. The specimens in group II were immersed in demineralization solution with fluoride 10 ppm. After caries-induced procedure, surface microhardness of all the specimens were measured. Then the specimens were cross-sectionally cut to measure the subsurface hardness with nanohardness tester using Berkovich indenter. The investigated areas were the areas adjacent to the restored material by running a mapping of a nanoindentation hardness test, 4 rows of 6 indentation with a separating space of 50 microns. Finally the experimented specimens were analyzed with scanning electron microscope using EDS (Energy Dispersive Spectrometer) technique to quantify fluoride content both on the surface and subsurface of the experimented specimens. The results showed that there were statistical differences (P<0.05) between the series of 100 and 300 microns of groups III and IV which the cavities were filled with resin modified glass ionomer and polyacid modified composite. Nanohardness test exhiblited the statistically difference in the subsurface of enamel and dentin within 50 up to 100 microns compared to 300 microns in the same group. The EDS found that fluoride quantity was higher in the area adjacent to the restoration and related to the high hardness area. The conclusion was fluoride releasing materials had effected on preventing artificial in the area within 100 microns and also depend on the type of materials.
