Effect of Beam Profiles From Different Light Emission Tip Types of Multiwave Light-emitting Diodes on the Curing Profile of Resin-based Composites.

Light activation is an important clinical step for achieving success in restorative procedures. This study evaluated the influence of beam profile from different light emission tip types of multiwave light-emitting diodes (LEDs) on the curing profile of resin-based composites. Experimental composites were produced containing either camphorquinone (CQ) or diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) as a photoinitiator. Multiwave LEDs with either a bundle light guide tip (Bluephase G2, Ivoclar Vivadent) or a microlens tip (VALO Cordless, Ultradent) were characterized using a beam profiler. Block-shaped samples (5×5×3 mm depth) of the two composites were cured in a custom-designed mold with the multiwave LEDs positioned to compare the regions exposed to the 420-495 nm (blue) and 380-420 nm (violet) emittances. To map the curing profile, the degree of conversion (DC) of longitudinal thin cross sections from each block was evaluated using transmission FT-NIR. Radiant exposure transmitted through the composites during curing was evaluated at different thicknesses. Data were analyzed using analysis of variance and Tukey test (α=0.05; ß=0.2). The results indicated that there were differences in the beam profile and the overall radiant exposures transmitted through the composites using each multiwave LED (p<0.01, df=1 F=73.18). However, there were no differences in the curing profiles provided by the two multiwave LEDs (p=0.89, df=12 F=0.52), and similar effects were found according to the different LED emittance regions (p=0.09, df=5, F=2.11). When considering up to 1 mm in depth, no differences in the DC were found between the composites containing either photoinitiators. Starting at 2 mm in depth, the composite containing TPO showed a decrease in DC in the 420-495 nm emittance region, while the composite containing CQ showed a similar decrease in cure efficiency only at 3-mm depth under both 380-420 nm and 420-495 nm emittance regions. Thus, despite the fact that the nonuniform light beam emitted from the two multiwave LEDs was visually distinctly different when delivering 24 J/cm2, this difference did not seem to affect the curing profile of the composites. However, light transmission within 380-420 nm seems to be reduced with depth, directly affecting the curing profile of composites containing a photoinitiator with absorbance falling within this emission range.

The Combination of CQ-amine and TPO Increases the Polymerization Shrinkage Stress and Does Not Improve the Depth of Cure of Bulk-fill Composites.

OBJECTIVES: To evaluate the effect of combining camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the depth of cure and polymerization shrinkage stress of bulk-fill composites. METHODS AND MATERIALS: Experimental bulk-fill composites were produced containing equal molar concentrations of either CQ-amine or CQ-amine/TPO. The degree of in-depth conversion through each millimeter of a 4-mm-thick bulk-fill increment was evaluated by Fourier transform near-infrared microspectroscopy using a central longitudinal cross section of the increment of each bulk-fill composite (n=3). Light-transmittance of the multi-wave light-emitting diode (LED) emittance used for photoactivation (Bluephase G2, Ivoclar Vivadent) was recorded through every millimeter of each bulk-fill composite using spectrophotometry. The volumetric shrinkage and polymerization shrinkage stress were assessed using a mercury dilatometer and the Bioman, respectively. The flexural modulus was also assessed by a three-point bend test as a complementary test. Data were analyzed according to the different experimental designs (α=0.05 and ß=0.2). RESULTS: Up to 1 mm in depth, adding TPO to CQ-based bulk-fill composites increased the degree of conversion, but beyond 1 mm no differences were found. The light-transmittance of either wavelengths emitted from the multi-wave LED (blue or violet) through the bulk-fill composites were only different up to 1 mm in depth, regardless of the photoinitiator system. Adding TPO to CQ-based bulk-fill composites did not affect volumetric shrinkage but did increase the flexural modulus and polymerization shrinkage stress. CONCLUSION: Adding TPO to CQ-based bulk-fill composites did not increase the depth of cure. However, it did increase the degree of conversion on the top of the restoration, increasing the polymerization shrinkage stress.

Light-emitting Diode Beam Profile and Spectral Output Influence on the Degree of Conversion of Bulk Fill Composites.

OBJECTIVES: To evaluate the beam profile and the spectral output of monowave and polywave light-emitting diodes (LEDs) and their influence on the degree of conversion (DC) of bulk fill composites. METHODS: A monowave LED (Smartlite Focus, Dentsply) and a polywave LED (Valo Cordless, Ultradent) were characterized using a resin calibrator and a laser beam profile analyzer. Two bulk fill composites, Sonic Fill 2 (SF) containing camphorquinone (CQ) and Tetric EvoCeram Bulk Fill (TEB) containing CQ associated with alternative photoinitiators, were placed in custom-designed molds (n=3) and photoactivated by the monowave or polywave LED with 20 J/cm2. To map the DC, longitudinal cross sections (0.5 mm thick) from the center of the restoration were evaluated using FT-NIR microscopy. SF and TEB light transmittances (n=3) through 4-mm-thick specimens were evaluated during curing. Data were analyzed using a split-plot analysis of variance and Tukey test (α=0.05; ß=0.2). RESULTS: The monowave LED had a radiant emittance of 20 ± 0.5 J/cm2 over 420-495 nm, and the polywave LED had an emittance of 15.5 ± 0.4 J/cm2 over 420-495 nm and of 4.5 ± 0.2 J/cm2 over 380-420 nm. The total radiant exposure at the bottom of TEB was 2.2 ± 0.2 J/cm2 with the monowave LED and 1.6 ± 0.3 J/cm2 with the polywave LED, and for SF it was 0.4 ± 0.1 J/cm2 for both LEDs. There were no differences in the curing profiles produced either by the monowave or the polywave LED (p=0.9), according to the regions under influence of blue and/or violet emission at the same depth. There was no statistical difference in the DC for SF using the monowave or polywave LED at any depth (p=0.29). TEB had a higher DC at up to 2 mm in depth when the polywave LED was used (p<0.004), but no differences were found when starting at 2.5 mm. CONCLUSIONS: Monowave and polywave LEDs emitted nonhomogeneous light beams, but this did not affect the DC homogeneity of bulk fill composites. For composites containing CQ associated with alternative photoinitiators, polywave LEDs had a higher DC, but only at the top part of the restoration; lower wavelength absorption photoinitiators were ineffective in deeper areas.