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Acta Odontol Scand. 2015 Aug;73(6):474-80. doi: 10.3109/00016357.2014.992810. Epub 2014 Dec 29.

Monomer conversion and shrinkage force kinetics of low-viscosity bulk-fill resin composites.

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Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb , Zagreb , Croatia.



To investigate the subsurface degree of conversion (DC) and shrinkage force formation of low-viscosity (flowable) bulk-fill composite materials.


Three flowable bulk-fill resin composites [SureFil SDR flow (SDR; Dentsply DeTrey), Venus Bulk Fill (VB; Heraeus Kulzer) and x-tra base (XB; VOCO)] and one conventional flowable control composite material [EsthetX flow (EX; Dentsply DeTrey)] were tested. The materials were photoactivated for 20 s at an irradiance of 1170 mW/cm2 and the DC (n=5) was recorded at 0.1-, 1.5- and 4-mm depth using Fourier transform infrared spectroscopy. Shrinkage forces (n=5) of 1.5-mm-thick specimens were continuously recorded for 15 min using a custom-made stress analyzer. Data were statistically analyzed by ANOVA, Tukey's HSD and Bonferroni's post-hoc tests (α=0.05).


SDR generated the significantly lowest shrinkage forces (22.9±1.4 N), but also attained the significantly lowest DC at 1.5-mm depth (67.5±0.8%). The conventional flowable composite EX generated the significantly highest shrinkage forces (40.7±0.7 N) and reached a significantly higher DC (74.4±1.3%) compared to SDR and XB at 1.5-mm depth. The shrinkage force values of VB (29.4±1.1 N) and XB (28.3±0.6 N) were similar (p>0.05). All materials attained significantly higher DC at 4-mm depth than at the near-surface.


The tested low-viscosity bulk-fill materials show lower shrinkage force formation than a conventional flowable resin composite at high levels of degree of conversion up to 4-mm incremental thickness.


Bulk-fill materials; flowable resin composites; polymerization; shrinkage stress

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