Effect of Bioactive Composites on Microhardness of Enamel Exposed to Carious Challenge

This study verified if experimental composites containing calcium phosphate nanoparticles exert a protective effect against enamel demineralization. Three experimental resin-based composites containing 60 vol% of fillers were manipulated. Filler phase was constituted by silanized barium glass and 0%, 10% or 20% (by volume) of dicalcium phosphate dihydrate (DPCD) nanoparticles functionalized with the monomer triethylene glycol dimethacrylate (TEGDMA). Cavities (10 x 2 x 2 mm) were prepared in bovine enamel and restored using one of the experimental materials (n=10). Specimens were exposed to pH cycling (demineralizing solution: pH 5.0/4h, remineralizing solution: pH 7.0/20h, 14 days). Enamel Knoop microhardness (100g/10s) was measured on the surface (SH) and after transversal sectioning up to 90 μm depth (cross-sectional microhardness, CSH). Microhardness values and the percent of microhardness loss were analyzed ANOVA/Tukey test and Student's paired t-test (alpha: 5%). The materials did not differ in respect to SH. Enamel adjacent to DCPD-containing composite restorations showed smaller reductions in CSH (-1.2% to -3.5%) than the enamel from control group (-12.5%), while CSH of enamel restored with resin-modified glass ionomer was similar to the other groups (-4.5%). DCPD-containing composites reduced enamel demineralization in comparison to a conventional composite.