Effect of Radiant Exposure on the Physical and Mechanical Properties of 10 Flowable and High-viscosity Bulk-fill Resin Composites

Physicomechanical properties of resin-based composites photo-polymerized using laser, polywave and quadwave curing lights

OBJECTIVES

This study evaluated the fracture toughness (KIC), energy absorption E and Vickers hardness (VH) of resin-based composites (RBC) photo-polymerized with new light curing unit (LCU) technologies: one laser diode (Monet Laser - AMD Lasers), one polywave™ LED (PowerCure - Ivoclar) and one quadwave LED (PinkWave - Apex).

METHODS

Two conventional: Evo, Tetric EvoCeram (Ivoclar) and FS, Filtek Supreme (Solventum); and two bulk-fill: PF, PowerFill (Ivoclar) and AF, Admira Fusion x-tra (VOCO) were tested. The RBC specimens were photo-polymerized for 1 second with the Monet, 3 seconds with the PinkWave in the 3-second-high output mode, and the 10-second standard mode using the PowerCure light. The power (mW), irradiance (mW/cm2), radiant exposure (J/cm2), and emission spectrum (mW/cm2/nm) were measured using a fiberoptic spectrometer attached to an integrating sphere. KIC (KIC, MPa·m1/2) was obtained using an 8.2 mm diameter and 2.0 mm thick metal mold. After 24-hour storage at 37 °C, the KIC was measured in a universal testing machine at a rate of 0.5 mm/min. The energy absorption (E, N/mm) up to failure was calculated. The Vickers hardness (VH, Kg/mm2) was measured at the bottom of the KIC specimen. Data were analyzed using a two-way analysis of variance followed by the Tukey multiple comparison test (α = 0.05).

RESULTS

Both the KIC and VH were significantly influenced by the light-curing unit/exposure time and by the RBC used (p < .001). The Monet emitted the highest power (1501.4 mW) but delivered the lowest radiant exposure (3.0 J/cm2). In general, the KIC values did not differ when RBCs were photo-polymerized with PowerCure in the standard 10 s or 3 s modes, except for the Admira Fusion x-tra. The KIC, VH and energy absorption to failure values were higher for all RBCs when photo-polymerized with PowerCure in the Standard mode for 10 s and lowest with the Monet used for 1 s. Filtek Supreme had the highest VH values regardless of the curing light unit/exposure time. The VH was better at detecting differences between the LCUs/exposure time and the RBC.

SIGNIFICANCE

Short 1-3 s exposure times produce inferior physicomechanical properties in some RBCs compared to a 10 s exposure at a lower irradiance. Clinicians should understand how much energy the manufacturers of the RBCs are recommending should be delivered to their RBC.

Comparative study of the shrinkage behavior of three bulk-fill resin-based composites using the aluminium tooth model with a MOD cavity

This study evaluated the cusp tip deflection of aluminium tooth models with a mesial-occlusal-distal (MOD) cavity filled with three bulk-fill resin-based composites (RBCs), Aura Ultra Universal (Aura), Admira Fusion x-tra Universal (Admira), and Filtek One shade A2 (Filtek One), to assess the level of shrinkage stress they could produce. The models were prepared using a primer, adhesive and a single RBC increment photo-cured for 20 s at a radiance exitance 1.25 W/cm2. The RBC axial shrinkage strain (ε) and stress (S) were also measured. Micro-computed tomography in combination with silver nitrate infiltration showed no interfacial debonding. The mean cusp tip deflection for Admira was found to be smaller than those for the other two RBCs. Although ε and S for Aura were higher than those for Filtek One, their mean cusp tip deflections were not significantly different. These results could be explained by the temporal behavior of their elastic modulus.

Effect of Three Heating Guns on the Temperature of Two Bulk-Fill Resin-Based Composites

OBJECTIVE

To evaluate the effect of three heating guns-Phasor (Vista Apex, Racine, USA), VisCalor (VOCO, Cuxhaven, Germany), and Compex HD (AdDent Inc. Danbury, USA)-on the temperature changes of two bulk-fill resin-based composites (RBCs): VisCalor Bulk (VBF, VOCO) and Filtek One Bulk Fill Restorative (OBF, Solventum, St. Paul, USA).

MATERIALS AND METHODS

Temperature changes were measured using a thermal camera (PI 640i, Optris Infrared Measurements, Berlin, Germany) during insertion and photocuring in a simulated proximal box of a Class II cavity and within the RBC capsules during heating. The RBCs were photocured using the Bluephase PowerCure (Ivoclar, Schaan, Liechtenstein) for 20s. Data were analyzed using repeated measures ANOVA and Tukey's test for each RBC (α = 0.05). The temperature of the RBCs at the same depth were analyzed by t-test (α = 0.05).

RESULTS

OBF heated with Compex produced the lowest temperature rise at the pulpal floor (2.7°C ± 0.4°C), while VBF heated with Phasor produced the highest (8.8°C ± 2.4°C). The greatest temperature increases were at the top of the restoration. OBF heated with Phasor reached 48.6°C ± 4.7°C. The Phasor and VisCalor produced two temperature peaks in the RBC inside the capsule, while the Compex maintained a steady peak temperature.

CONCLUSION

The heating gun and RBC produced different temperatures when heating, inserting, and light-activation of the RBCs.

CLINICAL SIGNIFICANCE

The choice of RBC and heating gun can substantially affect the temperature of the RBC and influence its handling properties.

Radiopacity and Filler Content of Dual-Cure Resin Core Material, Dual-Cure Resin Cement, and Bulk-Fill Resin Composites Used for Restoring Endodontically Treated Teeth

OBJECTIVE.

This study evaluated the effect of filler content and composition on the radiopacity of different resin-based materials used to cement fiberglass posts (dual-cure resin cements or dual-cure resin core materials) and build the core (bulk-fill or dual-cure core resin composites) to restore endodontically treated teeth.

METHODS AND MATERIALS.

Nine resin-based materials were tested: Four dual-cure resin core materials: Allcem Core, FGM; LuxaCore Z, DMG; Rebilda DC, VOCO; and Clearfil DC Core Plus, KURARAY; three dual-cure resin cements: RelyX Universal, 3M Oral Care; RelyX U200, 3M Oral Care; and Allcem Dual, FGM; and two bulk-fill resin composites: OPUS Bulk Fill APS, FGM; and Filtek One Bulk Fill, 3M Oral Care. Thermogravimetric analysis (TGA, %) was performed to determine the filler content. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to evaluate the filler morphology and composition. Radiopacity was measured using digital radiographs (n=10) according to ISO 4049 standards. TGA and radiopacity data were subjected to a one-way analysis of variance (ANOVA) followed by a Tukey post hoc test (α=0.05).

RESULTS.

Except for Luxacore Z, the dual-cure resin core materials and bulk-fill resin composites had higher filler contents than the dual-cure resin cements (p<0.001). Allcem Core exhibited more homogeneous fillers without agglomerates, whereas RelyX Universal presented only nanoparticles. OPUS Bulk Fill APS, Allcem Dual, and Allcem Core, made by the same manufacturer, presented similar sizes, shapes, and distributions of filler content. EDS analysis revealed that oxygen O (8), Si (14), C (6), Al (13), and Ba (56) were the most prevalent elements. The radiopacity of the tested materials is related to the presence of high atomic number elements such as Yr (70), La, (57), Ba (56), Zr (40), Sr (38), and Br (35) in their filler composition. All materials satisfied the ISO 4049 radiopacity requirements.

CONCLUSIONS.

Results were product-specific. Except for LuxaCore Z and Allcem Core, dual-cure resin core materials exhibited filler content similar to that of bulk-fill resin composites and higher than that of dual-cure resin cements. All materials exceeded the ISO 4049-2019 standard for radiopacity of restorative materials.

The dark art of light curing in dentistry

OBJECTIVE

This study was designed to show that the commonly reported irradiance values that are quoted in most publications inadequately describe the light output from light curing units (LCUs).

METHODS

The total spectral radiant power (mW) output from 12 contemporary LCUs was measured with a fiberoptic spectroradiometer and a calibrated integrating sphere. Five recordings were taken for each LCU and exposure mode. In addition, the irradiances (mW/cm²) delivered at 0-mm, 5-mm and 10-mm distances were recorded through a 6-mm diameter aperture and the radiant exposures (J/cm²) from the LCUs were calculated. Light beam profiles from the LCUs were recorded using a beam profiler, and the images were overlaid on a molar tooth to simulate a clinical setting. Data were analyzed using ANOVA followed by Tukey post-hoc test (α = 0.05).

RESULTS

The mean power outputs from the LCUs ranged from 380 to 2472 mW (p < 0.0001). The highest irradiance was recorded from the Cicada CV 215-G7 (3091 mW/cm² in its highest mode) and the lowest from the Radii Cal CX (731 mW/cm²). The emission spectra differed, even among the multi-peak and single-peak LCUs. Radiant exposures from the entire light tip ranged from 18.3 J/cm², Radii Cal CX, in its standard 25 s exposure mode to 3.9 J/cm² from the Monet Laser in a 3 s exposure setting. Half (50 %) of the measured irradiance values from the LCUs differed from the manufacturers' value by more than 10 %. There were significant differences in the impact of distance from the tip. The beam profiles visually highlighted the varying effects of distance from the LCU tip among different units.

CONCLUSION

There were significant differences in the emission spectra, power outputs, tip diameters, irradiances, radiant exposures, and the effect distance from the light tips. These differences underline the importance of manufacturers and researchers correctly measuring and reporting the output from the LCU to ensure that research is reproducible and that patients receive acceptable dental restorations.

CLINICAL SIGNIFICANCE

This article alerts clinicians, researchers and journal editors that providing only the tip irradiance (radiant exitance) value from the LCU is no longer sufficient. Manufacturers and researchers should include information on the spectral radiant power, emission spectrum, tip diameters, and also the effect of distance on the irradiance and radiant exposure, beam profiles and tooth access information when describing an LCU.

Influence of Layer Thickness and Shade on the Transmission of Light through Contemporary Resin Composites

BACKGROUND

Material-dependent parameters have an important impact on the efficiency of light polymerization. The present in vitro study aimed to investigate the influence of the increment thickness and shade of nano- and nanohybrid resin composites on the transmission of curing light.

METHODS

Three contemporary resin composites were evaluated: Tetric EvoCeram® (TEC); Venus Diamond® (VD); and Filtek Supreme XTE® (FS XTE). Light transmission (LT) was recorded in accordance with the sample thickness (0.5 to 2.7 mm) and the shade. Polymerized samples were irradiated for 10 s each using the high-power LED curing light Celalux 2 (1900 mW/cm2). LT was simultaneously recorded using the MARC Patient Simulator (MARC-PS).

RESULTS

LT was strongly influenced by the composite layer thickness. For 0.5 mm-thick samples, a mean power density of 735 mW/cm2 was recorded at the bottom side. For the 2.7 mm samples, a mean power density of 107 mW/cm2 was measured. Only LT was markedly reduced in the case of darker shades. From A1 to A4, LT decreased by 39.3% for FS XTE and 50.8% for TEC. Dentin shades of FS XTE and TEC (A2, A4) showed the lowest LT.

CONCLUSIONS

The thickness and shade of resin composite increments strongly influences the transmission of curing light. More precise information about these parameters should be included in the manufacture manual.