Determination of microhardness of bulk-fill resins at different depths.

The aim of this study was to determine Vickers microhardness (HV) in bulk fill resins at different depths. Test specimens were prepared with different bulk fill resins: Filtek Bulk-Fill (3M ESPE) [FBF], Surefill SDR flow (Dentsply) [SDR], Fill-UP (COLTENE) [FU] and Surefill (Dentsply) [SF]. Semi-cylindrical test specimens were prepared in a mold 6 mm in diameter and 4 mm thick (n=5). A 1000 mW/cm2 light curing unit was applied (Coltolux LED - Coltene) for 20 seconds. HV was determined with three indentations (Vickers Future Tech FM300, 300 g, 8 s) at four depths: 1, 2, 3 and 4 mm from the top surface to the interior. Data were recorded immediately (t0) and 24 hours later (t24). Results were analyzed with two-way ANOVA (p<0.05), and multiple comparisons were performed using Tukey's test. Mean and SD of HV at t0 for each mm were: [FBF] t0: 49.23(4.65) / 48.32(3.36) / 44.38(2.06) / 40.59(2.58); [FBF] t24: 61.37(3.47) / 62.63(3.03) / 57.27(5.22) / 56.37(5.88);[SDR]t0:27.81(3.13) / 28.07(2.4) / 27.24(2.94) / 25.71(3.0); [SDR] t24: 35.11(2.16) / 35.17(1.96) / 35.53(1.81) / 33.18(2.08); [FU] t0: 41.43(1.41) / 39.87(0.88) / 38.11(1.81) / 39.09(1.92); [FU] t24: 49.27(1.54) / 48.77(1.77) / 48.65(1.88) / 46.76(4.93); [SF] t0: 71.35(7.09) / 67.39(9.76) / 68.95(6.21) / 64.1(8.35); [SF] t24: 76.06(6.61) / 75.31(9.37) / 75.2(11.57) / 69.81(12.14). ANOVA showed significant effect of material, depth and recording time (p<0.05), and Tukey's test showed that recording sites (depths) differed significantly, giving four homogeneous groups. Under the conditions of this study, it can be concluded that microhardness of bulk-fill resins can be affected by depth and post-curing time.