Background The present study was aimed to evaluate the effect of pre-heating of bulk -fill resin composites on monomer elution from them. Material and Methods Three different types of resin composites were used including Tetric N-Ceram Bulk Fill, X-tra Fill and X-tra Base. 10 cylindrical samples were prepared from each resin composites. Before light curing, 5 samples were pre-heated until reaching 68˚C, then 5 other samples were polymerized at room temperature. After 24 hours, release of UDMA, TEGDMA and BIS-GMA monomers were measured by High-Performance Liquid Chromatography analysis. Data analysis was performed by two-way ANOVA test, Games-Howell and Sidak post hoc tests. Results Pre-heating did not have any statistically significant effect on the mean values of UDMA, TEGDMA and Bis-GMA elution ( p >0.05). The greatest amount of released Bis-GMA and UDMA was obtained from Tetric N-Ceram Bulk-fill composite. The greatest amount of released TEGDMA was obtained from X-tra Fill composite. X-tra Base composite showed the lowest amount of monomer release ( P <0.001). Conclusions Pre-heating did not have any effect on monomer release from bulk-fill resin composites. Moreover, the amount and the type of monomers released from various bulk-fill resin composites were not similar. Key words: Bulk fill composite resin, elution, HPLC, residual monomer, temperature.

Background . Due to the effect of pre-heating on the degree of conversion of composite resins and the possible effect on cytotoxicity, the effect of pre-heating of bulk-fill composite resins was investigated on cytotoxicity in this study. Methods. In this study, three different types of composite resin were used, including Tetric N-Ceram Bulk-Fil, Xtrafil, and Xtrabase. From each composite resin, 10 cylindrical samples (5 mm in diameter and 4 mm in height) were prepared, with five samples preheated to 68°C, and the other five samples polymerized at room temperature (25°C). Twenty-four hours after polymerization, cytotoxicity was assessed by MTT assay on human fibroblasts. Statistical analysis of data was carried out with two-way ANOVA and Sidak Post-Hoc. The significance level of the test was determined at 0.05. Results. There was no statistically significant difference between the mean percentage of cytotoxicity in terms of pre-heating (P>0.05), but the cytotoxicity of the studied composite resins was significantly different (P<0.001). The cytotoxicity of Tetric N-Ceram Bulk-fil composite resin was higher than that of the two other composite resins. Conclusion. Pre-heating of bulk-fill composite resin did not affect their cytotoxicity. In addition, the cytotoxicity of different bulk-fill composite resins was not the same.

Aim: The present study was carried out with the objective of comparing the compressive strength and setting time of four experimental nanohybrid mineral trioxide aggregates (MTAs) and angelus MTA. Materials and methods:In this research, four experimental formulations of nanohybrid MTA (groups are with the base of Portland cement, containing nanoparticles of zirconia, aluminum oxide, titanium, nanosilica, and gypsum and bismuth trioxide) and angelus MTA were compared. Powder and water were mixed with the ratio determined by a factory for angelus MTA and were mixed at a ratio of 3:1 in experimental samples until the consistency of putty was reached. These were then placed in stainless steel cylinder generators, with a diameter of 4 mm and a height of 6 mm, for testing compressive strength, and in generators with a diameter of 10 mm and height of 2 mm to test setting time. The samples prepared were tested after 24 hours and a month using a strength-testing machine. A 135 G needle was used to test the initial setting time in the prepared samples, and a 456.5 G needle was used to test the final setting time. In the end, data were analyzed using Statistical Package for the Social Sciences (SPSS) software.Results: Experimental nanohybrid MTA P significantly showed the minimum setting time and experimental nanohybrid MTA Q showed the maximum setting time in 30 days (p < 0.05). Angelus MTA had greater compressive strength than the experimental materials in 24 hours. Clinical significance: Considering that experimental MTAs showed less setting time compared with the commercial type, experimental MTAs can be deployed in clinical usage. Conclusion