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Objective.To investigate both genotoxicity and hardening of bulk-fill composite materials applied in 4-mm layer thickness and photo-activated for different exposure times. Methods.Three flowable bulk-fill materials and one conventional flowable composite were filled in molds (height: 4 mm) and irradiated for 20 or 30 s. The top (0 mm) and bottom (4 mm) specimen surface were mechanically scraped, and eluates (0.01 g composite in 1.5 ml RPMI 1640 cell culture media) prepared for each material, surface level and irradiation time. Genotoxicity was assessed in human leukocytes using both the alkaline comet assay and cytokinesis-blocked micronucleus assay, and Knoop hardness (KHN) was measured at the top and bottom specimen surface (n = 8). Results.At both irradiation times, none of the bulk-fill composites significantly affected comet assay parameters used in primary DNA damage assessment or induced significant formation of any of the scored chromatin abnormalities (number of micronuclei, nuclear buds, nucleoplasmic bridges), whether eluates were obtained from the top or bottom surface. Furthermore, no decrease in KHN from the top to the bottom surface of the bulk- fill materials was observed. On the other hand, the conventional composite irradiated for 20 s showed at 4-mm depth a significant increase in the percentage of DNA that migrated in the tail and a significant increase in the number of nuclear buds, as well as a significant decrease in KHN relative to the top surface. Significance. Bulk-fill resin composites, in contrast to conventional composite, applied in 4-mm thickness and photo-activated for at least 20 s do not induce relevant genotoxic effects or mechanical instability. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Objectives: To investigate the influence of pre-heating of high-viscosity bulk-fill composite materials on their degree of conversion and shrinkage force formation. Methods: Four bulk-fill composite materials (Tetric EvoCeram Bulk Fill-TECBF, x-tra fil-XF, QuixFil-QF, SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram- TEC) were used. The test materials were either kept at room temperature or pre-heated to 68 degrees C by means of a commercial heating device, before being photoactivated with a LED curing unit for 20 s at 1170 mW/cm(2). Shrinkage forces (n = 5) of 1.5-mm-thick specimens were recorded in real-time for 15 min inside a temperature-controlled chamber at 25 degrees C (simulating intraoral temperature after rubber dam application) with a custom- made stress analyzer. Degree of conversion (n = 5) was determined at the bottom of equally thick (1.5 mm) specimens using Fourier transform infrared spectroscopy. Data were analyzed with Student's t-test, ANOVA and Tukey's HSD post-hoc test (alpha = 0.05). Results: Composite pre-heating significantly increased the degree of conversion of TECBF, but had no effect on monomer conversion of the other materials investigated. For each of the test materials, pre-heated composite generated significantly lower shrinkage forces than room- temperature composite. At both temperature levels, TECBF created the significantly highest shrinkage forces, and QF caused significantly higher shrinkage forces than both XF and TEC. Conclusions: Both the composite material and the pre-cure temperature affect shrinkage force formation. Pre-heating of bulk-fill and conventional restorative composites prior to photoactivation decreases polymerization- induced shrinkage forces without compromising the degree of conversion. Clinical significance: Composite pre-heating significantly reduces shrinkage force formation of high-viscosity bulk-fill and conventional resin composites, while maintaining or increasing the degree of monomer conversion, dependent upon the specific composite material used. (C) 2015 Published by Elsevier Ltd.

Background The authors conducted an in vitro study to investigate the influence of various curing protocols on subsurface microhardness of dual-cured resin-based composites. Methods The authors filled molds with four dual-cured resin-based composite core buildup materials: Clearfil DC Core Automix (Kuraray, Tokyo), Core•X flow (Dentsply DeTrey, Konstanz, Germany), LuxaCore Z-Dual (DMG, Hamburg, Germany) and MultiCore Flow (Ivoclar Vivadent, Schaan, Liechtenstein). They light cured the specimens for 20 or 60 seconds immediately after the filling procedure (time delay, 0 seconds) or after a 90-or 300-second delay. Self-cured specimens served as controls. The authors tested 15 specimens in each group. They measured the Knoop hardness number (KHN) at depths of 0.25, 2.00 and 5.50 millimeters two weeks after the initiation of polymerization. Results Light curing with Core•X flow, LuxaCore Z-Dual and MultiCore Flow did not result in significantly higher KHNs at any depth compared with those for the self-cured control specimens. For Clearfil DC Core Automix, immediate light curing for 60 seconds resulted in significantly higher KHNs than those for self-cured specimens only at a depth of 5.50 mm ( P = .0171). The study results showed no significant differences in KHN at different depths for Core•X flow specimens, independent of the curing protocol. All other materials exhibited a significant decrease in KHN at increased depths in only one of the six light-cured groups. Conclusion The results of this study show that photoactivation of the tested dual-cured materials provided no clinically relevant benefit compared with self-curing with regard to the degree of microhardness. Clinical Implications The dominant self-curing mode allows placement of the tested buildup materials in areas inaccessible to a curing light.