Micro-CT analysis of fluoride releasing restorative materials on affected dentin and evaluation of remineralizing effects of these materials on adjacent tooth tissues

The purpose of this study was to evaluate fluoride release, micro hardness change of adjacent enamel to restoratives and mineral density change of dentin restored with strengthened restorative glass ionomer cement (Fuji BULK), glass hybrid restorative system (EQUIA Forte Fil) and giomer (Beautifil Bulk Restorative) after pH cycle. For the analysis of fluoride release and adjacent enamel microhardness change, cavities with a size of 3 × 1.5 × 1.5 mm were prepared in the middle of the crown of sound human molar teeth (n = 8), to obtain negative control group half of these preparations were filled with dental wax and the other half with tested material, then samples kept in distilled water for 24 hours at 37 ° C. The samples were then subjected to a pH cycle for 5 days. For the analysis of restored dentin mineral density change using micro-CT, 6 human posterior teeth with proximal caries advanced to half of dentin were used. Caries depth of these teeth were examined by radiographs. After excavation procedures which were standardized with DIAGNOdent pen, teeth were restored with tested materials. For mineral density analysis, samples were exposed to same pH cycle protocol. To examine the change in mineral density, micro-CT scans were performed before and after the cycle. The data obtained were analyzed by repeated measurements ANOVA, generalized estimation equations (GEE) and Wald chi-square tests (α = 0.05). The maximum cumulative fluoride release was related to EQUIA Forte Fil, followed by Fuji BULK and Beautifil Bulk Restorative in descending order (p=0.000). All tested restorative materials were found to cause less decrease in enamel microhardness after the cycle compared to the control group (p = 0.041). It was observed that restorative material significantly affected (p = 0.035) enamel micro hardness after the pH cycle. The pH challenge promoted a higher microhardness loss for Beautifil Bulk Restorative, specimens restored with Fuji BULK presented the lowest values for microhardness loss. As a result of micro-CT analysis, all of the materials presented potential to cause significant increase (p = 0.000) in mineral density after the pH cycle. Fuji BULK enhanced remineralization more than both EQUIA Forte Fil and Beautifil Bulk Restorative (p= 0.000). All tested fluoride releasing restorative materials, although their effects differ, inhibited demineralization of enamel adjacent to the restoration and increased remineralization of remaining dentin. Keywords: bioactive restorative material, fluoride, pH cycle, microhardness, micro-CT