Effect of polymerisation protocols on water sorption, solubility and hygroscopic expansion of fast-cure bulk-fill composite.

OBJECTIVE: This study examines the effect of two light-curing protocols from a LED polywave light curing unit (LCU) on water sorption, solubility, and hygroscopic expansion of fast and conventional bulk-fill resin-based composites (RBCs) aged in distilled water for 120 d. METHODS: Three bulk-fill RBCs materials were studied: Tetric PowerFill® (fast photo-polymerised composite) (TPF), Tetric EvoCeram bulk-fill (EVO), and GrandioSo x-tra bulk-fill (GSO) (conventional photo-polymerised composites). Specimens were prepared within a 3D-printed resin mold (8-mm diameter x 4-mm height) and light-cured from one side only with 2 modes of polywave LCU (Bluephase® PowerCure): 3 s mode and for 20 s in "Standard" mode. Water sorption and solubility were measured at fixed time intervals for 120 d of distilled water storage, then reconditioned to dry to measure desorption for 75 d, all at 37 ± 1 °C. Hygroscopic (volumetric) expansion was recorded at the same time intervals up to 120 d. Data were analysed through SPSS using Two-way ANOVA, One-way ANOVA, independent t-tests, and Tukey's post-hoc correction tests (p < 0.05). RESULTS: TPF, when irradiated for 3 s demonstrated minimal water sorption (0.83%), solubility (1.01 µg/mm3), and least volumetric expansion (1.64%) compared to EVO and GSO. While EVO showed the highest water sorption (1.03%) and solubility (1.95 µg/mm3) at 3 s. GSO had the lowest sorption (0.67%) and (0.56%) in 3 s and 20 s protocols, respectively. Nevertheless, all the sorption and solubility data were within the ISO 4049 limits. SIGNIFICANCE: For TPF, fast (3 s) polymerisation did not increase either water sorption or solubility, compared with 20 s irradiation. However, with the two comparative bulk-fill composites, fast cure increased water sorption by 15-25% and more than doubled solubility. These findings were consistent with the lesser volumetric expansions observed for Tetric PowerFill at both the fast and standard protocols, indicating its relative stability across polymerisation protocols.

Thermography and conversion of fast-cure composite photocured with quad-wave and laser curing lights compared to a conventional curing light.

OBJECTIVES: This study investigated effects of the different emittance-mode protocols from three light curing units (LCUs): (i) a Laser (Monet); (ii) a quad-wave (PinkWave); (iii) a conventional LED (Elipar S10) on the temperature rise (ΔT) and degree of conversion (DC) when photo-curing fast or conventional bulk-fill resin-based composites (RBC). The aim was to correlate ΔT and DC, and the radiant exposure delivered to RBC specimens. METHODS: A 3D-printed resin mold of 4 mm depth was filled with two bulk-fill RBCs: Tetric PowerFill® (fast photo-polymerised composite) (TPF) or Tetric EvoCeram® Bulk-Fill (EVO). Three LCUs were used: (i) Monet laser for 1 s and 3 s (MONET-1 s, MONET-3 s); (ii) PinkWave quad-wave used for 3 s in Boost mode (PW-3 s) and for 20 s in standard mode (PW-20 s); (iii) Elipar S10 for 5 s (S10-5 s) and for 20 s in standard mode (S10-20 s). 2-dimensional temperature maps were obtained before, during and for 60 s after the LCU had turned off using a thermal imaging camera. Thermal changes were analysed at five depths: (0, 1, 2, 3, and 4 mm from the top surface of the RBC). The maximum temperature rise (Tmax) and the mean temperature rise (ΔT) were determined. Cylindrical-shaped specimens were prepared from each material using a stainless-steel split mold (4 × 4 mm) and light-cured with the same protocols. The DC was measured for 120 s and at 1 h after LCU had turned off using Fourier Transform Infrared Spectroscopy (FTIR). Data were analysed using Three-way ANOVA, One-way ANOVA, independent t-tests, and Tukey post-hoc tests (p < 0.05). RESULTS: Radiant exposures delivered by the various irradiation protocols were between 4.5-30.3 J/cm2. Short exposure times from MONET-1 s and PW-3 s delivered the lowest radiant exposures (4.5 and 5.2 J/cm2, respectively) and produced the lowest ΔT and DC. The longer exposure times in the standard modes of PW-20 s, S10-20 s, and MONET-3 s produced the highest Tmax, ΔT, and DC for both composites. The ΔT range among composites at different depths varied significantly (31.7-49.9 °C). DC of TPF ranged between 30-65% and in EVO between 15.3-56%. TPF had higher Tmax, ΔT for all depths and DC compared to EVO, across the LCU protocols (p < 0.05), except for PW-20 s and MONET-3 s. The coronal part of the restorations (1-2 mm) had the highest ΔT. There was a positive correlation between ΔT and DC at 4-mm depth after 120 s SIGNIFICANCE: Longer, or standard, exposure times of the LCUs delivered greater radiant exposures and had higher DC and ΔT compared to shorter or high-irradiance protocols. The fast photo-polymerised RBC had comparatively superior thermal and conversion outcomes when it received a high irradiance for a short time (1-5 s) compared to the conventional Bulk-Fill RBC.