In vitro investigation of nanohardness values of dual cure bulk-fill composite resins at different time intervals

Introduction and Aim: In this study, it is aimed to investigate the nanohardness values of dual cure bulk-fill composite resins at different time intervals in vitro. Material and Method: In the study, nanohardness values of Fill-Up, HyperFIL, Cention N dual cure bulk fill composite resins in the experimental group and Reveal HD, a light-cured bulk-fill composite in the control group, were compared comparatively. The universal color of Fill-Up, Cention N and HyperFil composites was used, and the A2 color of Reveal HD was used. The dual cure bulk-fill composites used in the experimental group are divided into 2 subgroups. The first group was polymerized with a LED light source and the second group was chemically polymerized in line with the manufacturer's instructions. The composite resins in the experimental group were placed in cylindrical plexiglass molds at two different depths, 5 and 10 mm. In the control group, molds with a depth of 5mm were used and their polymerization was provided by a LED light source. The nanohardness values of the lower and upper surfaces of the samples were measured by using the Hysitron TI 950 TriboIndenter device located at the Technology and Research Center of Mustafa Kemal University 24 hours and 7 days after polymerization. Degree of conversion of the samples were calculated by dividing the lower surface hardness value of each sample by the upper surface hardness value. Results: In our study, the data was analyzed by using the SPSS 21 program with 95% confidence. As a result of the statistical evaluations, according to the hardness measurement and polymerization degree findings, there was no statistically significant difference between the nanoshardness values and polymerization degrees measured 24 hours after the light or chemical polymerization of dual cured bulk-fill composite resins and the values measured on the 7th day. It has been observed that light polymerization of HyperFIL and Fill-Up dual cure bulk-fill composite resins has no effect on nanoshardness and polymerization degree values. When Cention N dual cure bulk-fill composite resin was polymerized with a light source, higher values of nanohardness and polymerization degree were obtained. When the groups were compared according to the brands, it was seen that the highest nanohardness and elastic modulus values belong to Cention N in both polymerizations. While Cention N showed the highest degree of polymerization in the light polymerized group, it was found as HyperFIL in the chemically polymerized group. Conclusion: As a result, it was determined that the tested dual cure bulk-fill composites reached their final hardness and polymerization degree 24 hours later. Cention N showed the highest surface hardness values and degree of polymerization.