Evaluation of Hardness Development of Bulk Fill Composites at Two Time Intervals

Objectives: The aim of the study was to examine hardness changes and bottom/top hardness ratio of high-viscosity bulk fill composites prepared in specific increments and to compare with a conventional composite at two time intervals.
Methods: Two high-viscosity bulk fill composites [Sonic Fill (Kerr)(SF), Xtra Fil (Voco)(XF)] and one conventional composite [Grandio (Voco)(GD)] were used in the study. The conventional composite was chosen because it is considered as a reference for the physico-mechanical properties. The test specimens were made using a 6mm diameter x 2mm height teflon mold for GD, 4mm height mould for XF and 5mm height mould for SF. The mould height complies with the maximum increment thickness specified by the manufacturer. Each sample was supported on a glass slide to obtain a smooth surface on the composites. Twenty samples were prepared from each composite and divided into two groups (n=10). The samples were cured using Demi Plus LED (Kerr Corp.,USA) from the top for 20s and 40s according to the groups. Microhardness properties of the samples were measured using Highwood HWDM-3 (TTS Unlimited Inc., Japan) at the top and bottom immediately post cure and after 24 h of storage in distilled water at 37^οC. The results were analyzed by one-way ANOVA, Tukey HSD and Paired Samples T Test (p<0,05).
Results: The microhardness values ​​of SF and XT groups were found similar to each other and significantly lower than GD group. All samples showed significant increase of microhardness after 24h of storage in distilled water compared to initial values. Bottom/top microhardness ratio found higher than %80 for all groups.
Conclusions: Although the tested high-viscosity bulk fill composites hardness values were lower than conventional composites, the similarities in hardness developments and bottom/top hardness ratio of their specific increments at two time intervals seems to beneficial for the clinical use of these composites.