Objectives: The polymerization shrinkage of methacrylate-based composites is among the most important causes of failure of composite restorations. The manufacturers claim that Bulk-fill composites have a lower polymerization shrinkage than conventional composites. This study aimed to assess the polymerization shrinkage of five Bulk-fill composites in comparison with a conventional composite. Materials and Methods: In this in-vitro experimental study, composite discs (n=30) were fabricated using everX Posterior (EXP), Filtek Bulk-fill Posterior (FBP), Sonicfill 2 (SF2), Tetric N-Ceram Bulk-fill (TNB), X-tra fil (XF), and Filtek Z250 conventional composite at the center of a metal ring bonded to a microscope slide and were covered with a coverslip. This assembly was transferred to a linear variable differential transformer (LVDT). Light-curing (1200 mW/cm2) was performed from underneath the slide for 30 seconds. The deflecting disc method and LVDT were used to assess the dimensional changes of the samples (indicative of polymerization shrinkage) at 1, 30, 60, and 1800 seconds following the onset of light irradiation. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’ s test. Results: The groups were significantly different regarding polymerization shrinkage (P<0. 002). The polymerization shrinkage of the tested composites following the onset of light irradiation ranged from 0. 19 to 3. 03. EXP showed a significantly higher polymerization shrinkage than other composites at 30, 60, and 1800 seconds after light irradiation, while XF showed the lowest polymerization shrinkage at the aforementioned time points. Conclusions: The tested Bulk-fill composites had a polymerization shrinkage similar to that of the conventional composite.

Background. Due to incomplete polymerization of composite resin restorations, residual monomers adversely affect their mechanical properties and biocompatibility. Preheating of composite resins is advised to increase the degree of conversion and reduce monomer elution. This study aimed to analyze the effect of preheating and repeated preheating on the amount of monomer released from a Bulk-fill composite resin. Methods. Forty samples were prepared using Filtek One Bulk fill Restorative composite resin. Samples in one group were fabricated at room temperature, whereas the composite resins in the other groups were cured after 1, 10, or 20 repeated preheating cycles (55 °C), 10 in each group. Eluted urethane dimethacrylate (UDMA) and bisphenol-A-glycidylmethacrylate (BisGMA) monomers were measured with high-performance liquid chromatography (HPLC) 24 hours and 30 days after immersion. The data were evaluated using one-way ANOVA and post hoc Tukey tests. Paired-sample t tests were used to test the differences between time intervals. Results. At both time intervals, the greatest amounts of released BisGMA, UDMA, and total monomers were obtained from the control group, whereas 10 preheating cycles resulted in the least monomer elution. The decrease in monomer elution was not statistically significant after 10 preheating cycles compared with that after one preheating cycle (P>0. 05). The group with 20 preheating cycles showed a greater amount of monomer elution compared to that with 1 and 10 cycles, which was statistically significant (P < 0. 05). The amount of released monomers on day 30 was significantly higher than on day 1 (P<0. 01). Conclusion. Preheating of the Bulk-fill composite resin was shown to be effective in reducing monomer elution. However, monomer elution was adversely affected after repeated preheating cycles of 20.

Objective: Bulk-fill composites are a group of composite resins designed for easy and fast filling of large cavities. This study aimed to assess the color stability of Bulk-fill composites subjected to xenon radiation and evaluate their color change (DE) following polymerization.Methods: In this in vitro experimental study, 30 specimens (4mm in height and 8mm in diameter) were fabricated of x-traFil and Tetric N-Ceram universal color Bulk-fill composites and A2 shade of Grandio composite (as control). Bulk-fill composites were placed in the mold in 4mm thickness according to the manufacturers’ instructions. In the control group, composite was applied to the mold in two layers each with 2mm thickness. Tetric and Grandio composites were cured for 20 seconds and x-traFil was cured for 10 seconds with a LED light-curing unit. A total of 15 specimens (five of each composite) were used for each test. For assessment of color change due to polymerization, L*, a* and b* color parameters were measured before and immediately after polymerization and also 30 days after immersion in distilled water in an incubator at 37oC and 70% humidity using a spectroradiometer. For xenon test, the specimens were subjected to color analysis after 48 hours of storage in distilled water. Next, they were subjected to xenon lamp radiation in xenon environment chamber for 122 hours at 22oC and 25% humidity and then the color parameters were measured again. The mean and standard deviation (SD) of all values were calculated. One-way and repeated measures ANOVA were used to compare DE and DL among the groups. Tukey’s HSD test was used for pairwise comparisons.Results: The value of DE immediately after polymerization was the lowest for Grandio (4.91) and the highest for Tetric (9.44). Thirty days after the polymerization, DE was the lowest in Grandio (3.07) and the highest in Tetric (9.27); DE showed a decreasing trend over time in all specimens. Under xenon light radiation, Grandio showed the lowest (1.50) and Tetric showed the highest DE (11.15).Conclusion: Following polymerization and under xenon lamp radiation, DE of conventional composite was less than that of Bulk-fill composites.