Curing Depth Research Articles

Stereolithography Printing and Mechanical Properties of Polyethylene Glycol Diacrylate/Hexagonal Boron Nitride Ceramic Composites

To enhance the mechanical properties of bioceramic composite bone scaffolds, a composite paste of polyethylene glycol diacrylate (PEGDA) and hexagonal boron nitride (h‐BN) with a solid content of up to 42 wt% was developed in this study. The part was produced using stereolithography (SLA). The SLA printing parameters and material ratios of the paste were optimized through a homogeneous design and mechanical property tests. The results indicate that the single‐line curing width of the PEGDA/h‐BN paste in the XY plane ranged from 172 to 209 μm, while the curing depth of a single layer along the Z‐axis ranged from 99 to 154 μm. Laser power was identified as the primary factor influencing both the width and depth of curing. The compressive strength of the printed sample of PEGDA/h‐BN ceramic composite paste was measured at 222.4 ± 5.6 MPa, which is 61 times greater than the compressive strength of a pure PEGDA structure and comparable to that of cortical bone (100‐230 MPa). Finally, the superior biocompatibility of PEGDA/h‐BN ceramics was confirmed through cytotoxicity experiments. Consequently, PEGDA/h‐BN ceramic composites meet the mechanical properties and biocompatibility requirements necessary for bone tissue applications, indicating promising potential in the field of bone tissue engineering.

Depth of Cure of Resin-Based Composites Irradiated With Three Types of Light-Curing Units at Different Output Intensities

Depth of Cure of Resin-Based Composites Irradiated With Three Types of Light-Curing Units at Different Output Intensities

The Effect of Inorganic Filler Content on the Properties of BPA-Free Bulk-Fill Dental Resin Composites.

This study aimed to enhance the performance of dental resin composites (DRCs) by increasing the content of inorganic fillers while addressing potential health risks associated with Bisphenol A (BPA). To achieve this, the BPA-based resin monomer Bis-GMA was replaced with BPA-free Bis-EFMA. The study then explored the impact of varying inorganic filler contents on the physiochemical properties of Bis-EFMA-based bulk-fill dental resin composites (BF-DRCs). Four distinct Bis-EFMA-based BF-DRCs were formulated, each with different inorganic filler contents ranging from 70 wt% to 76 wt%. The study tested the depth of cure (DOC), double-bond conversion (DC), water sorption (WS), solubility (SL), and cytotoxicity of the system. It notably investigated the effects of increasing filler content on mechanical properties through flexural strength (FS), flexural modulus (FM), Vickers microhardness (VHN), and wear resistance, as well as the impact on polymerization shrinkage, including volumetric shrinkage (VS) and shrinkage stress (SS). To assess the commercial application potential of Bis-EFMA-based BF-DRC, the research used the commercially available BF-DRC Filtek Bulk-Fill Posterior (FBF) as a control. The results indicated that a higher filler content did not affect the DOC of Bis-EFMA-based BF-DRCs. Inorganic fillers at higher concentrations significantly enhanced overall mechanical properties while significantly reducing volumetric shrinkage (VS; p < 0.05). When the concentration of inorganic fillers in the resin system reached 76 wt%, most of the performance of the Bis-EFMA-based BF-DRC surpassed that of the commercial control FBF, except for FS, FM, and SS. These findings highlight the potential of Bis-EFMA-based BF-DRC as a long-term restorative material for dental applications.

PMMA light channels facilitate the additive manufacturing of complex-structured SiC reflector mirrors

The rapid manufacturing of lightweight SiC reflector mirrors has always posed a formidable challenge. We have successfully solved the problem of SiC slurry’s difficulty in vat photopolymerization by using highly transparent organic particles to construct the light channels for the first time. Through the integration of digital light processing with reaction sintering, we manufactured complex-structured SiC/Si reflector mirrors. Utilizing the light channels constructed with PMMA, ultraviolet light can effectively penetrate SiC slurry, thereby significantly enhancing the curing depth. During subsequent reaction sintering, PMMA particles induce the formation of numerous spherical silicon through dissolution-precipitation mechanism, alleviating stress concentration in the matrix and enhancing the flexural strength of SiC/Si ceramics. The method achieves significantly higher curing depth for SiC slurry and greater flexural strength for ceramic compared to similar materials. Extending the success above further, we have demonstrated their potential as high-quality products for practical applications.

Effect of Different Curing Time on Degree of Conversion and Depth of Curing of Supra-Nano Filled Resin Composite Compared to a Conventional One

Effect of Different Curing Time on Degree of Conversion and Depth of Curing of Supra-Nano Filled Resin Composite Compared to a Conventional One

Depth of Cure, Surface Characteristics, Hardness, and Brushing Wear of 4 Direct Restorative Materials in Paediatric Dentistry

Aim: The study aimed to compare the depth of cure, hardness, surface roughness, and wear resistance of four restorative materials used in pediatric dentistry: FUJI IX GP FAST, RivaSilver, SDR flow+, and Vertise Flow. Materials and Methods: The depth of cure was measured per ISO 4049 standards using a digital caliper, with 15 samples of each material. Hardness was evaluated using a Vickers indenter under a 10 N load for 20 s. Surface roughness was assessed before and after acid exposure using an optical profilometer according to ISO 4288. Brushing wear resistance was analyzed by subjecting samples to 20 and 60 min of brushing, followed by roughness measurements. Statistical analysis was performed using independent sample t-tests to determine the significance of differences between the materials, with p-values &lt; 0.05 considered significant. Results: SDR flow+ exhibited the highest depth of cure with an average of 3.5 mm (±0.2 mm), significantly higher than Vertise Flow at 2.8 mm (±0.3 mm) (p &lt; 0.001). Hardness testing revealed SDR flow+ had the highest average hardness (85 HV ± 4 HV), while Vertise Flow had the lowest (72 HV ± 5 HV) (p &lt; 0.001). Surface roughness increased significantly after acid exposure for RivaSilver (from 1.2 μm ± 0.12 μm to 1.6 μm ± 0.15 μm, p = 0.007) and for SDR flow+ (from 0.85 μm ± 0.08 μm to 1.3 μm ± 0.14 μm, p = 0.001). Brushing wear resistance was highest in RivaSilver (Ra increase from 1.2 μm to 1.4 μm ± 0.11 μm) and lowest in FUJI IX GP FAST (Ra increase from 1.5 μm to 1.9 μm ± 0.15 μm, p &lt; 0.001). Conclusions: The study demonstrates significant differences in performance among the tested materials. SDR flow+ showed a superior depth of cure and hardness, making it suitable for high-stress applications. However, all materials displayed increased surface roughness following acid exposure and brushing, with FUJI IX GP FAST showing the highest wear. These findings highlight the need to select restorative materials based on the specific clinical demands of pediatric patients, considering both their mechanical properties and resistance to wear and acid.

Effect of SiO2/AlOOH double-coated SiC powders on the properties of SiC ceramics by vat photopolymerization

Vat Photopolymerization (VPP) technology is expected to address the challenges of preparing high-strength, precise, and complex SiC ceramics. However, the poor printability of SiC powders and the low strength of the resulting SiC ceramics remain significant obstacles. To overcome these issues, this study proposes a SiO2/AlOOH double-coating method for modifying SiC powders. The effects of AlOOH content in the double coating on the properties of SiC powders, slurries, and ceramics were investigated. Additionally, the impact of sintering additives on the densification behavior and mechanical properties of SiC ceramics was examined. The results indicated that increasing the AlOOH content in the double coating decreased the UV absorption of the powders and increased the curing depth of the slurries, but also increased the viscosity of the pastes. Moreover, while increasing the AlOOH content in the double coating improved the densification and flexural strength of the ceramics, the effect was significantly less compared to optimizing the sintering additive. Using SiO2/AlOOH double-coated SiC powders containing 2.5 wt% AlOOH and 10 wt% Al2O3-Y2O3-MgO (mass ratio 1:8:1) sintering additives, SiC ceramics were prepared with a relative density of 91.1 ± 3.5 %, a Vickers hardness of 1685.6 ± 86.4 HV, and a flexural strength of 281.7 ± 14.4 MPa, much higher than that of other SiC ceramic prepared using the same process. This represents the highest flexural strength of SiC ceramics prepared by VPP technology to date, providing a new method for the preparation of high-strength SiC ceramics via VPP.

3D Micro-CT and O-PTIR Spectroscopy Bring New Understanding of the Influence of Filler Content in Dental Resin Composites

BackgroundDental resin composites' performance is intricately linked to their polymerisation shrinkage characteristics. This study compares polymerisation shrinkage using advanced 3D micro-computed tomography (micro-CT) and traditional 2D linear assessments. It delves into the crucial role of filler content on shrinkage and the degree of conversion in dental resin composites, providing valuable insights for the field. MethodsFive experimental dental composite materials were prepared with increasing filler contents (55-75wt%) and analysed using either 3D micro-CT for volumetric shrinkage or a custom-designed linometer for 2D linear shrinkage. The degree of conversion was assessed using Optical Photothermal Infrared (O-PTIR) and Fourier-Transform Infrared (FTIR) spectroscopy. Light transmittance through a 2-mm layer was evaluated using a NIST-calibrated spectrometer. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) examined surface morphology and elemental distribution. Correlation between the investigated parameters was determined using Spearman correlation analyses. ResultsThe study found significant differences in polymerisation-related properties among different filler content categories, with volumetric shrinkage consistently demonstrating higher mean values than linear shrinkage across most groups. Volumetric shrinkage decreased with increasing curing depth, showing no direct correlation between filler content and shrinkage levels at different curing depths. The results highlighted a strong negative correlation between filler content and degree of conversion, volumetric and linear shrinkage, as well as maximum shrinkage rate. Light transmittance showed a moderate correlation with the filler content and a weak correlation with other tested parameters. ConclusionsThis study underscores the importance of considering both volumetric and linear shrinkage in the design and analysis of dental composite materials. The findings advocate optimising filler content to minimise shrinkage and enhance material performance. Integrating micro-CT and O-PTIR techniques offers novel insights into dental composites' polymerisation behaviour, providing a foundation for future research to develop materials with improved clinical outcomes.

Simulation of UV curing of photosensitive resins with phase change materials

Based on the mechanism of the resin polymerization reaction and free radical diffusion under UV irradiation, here, a mathematical model of the curing process was established for the mixture of photosensitive resin (PAA) and polyethylene glycol (PEG, as the phase change material), and the factor influencing the mechanical performance of the cured samples was analyzed. The yield stress (σs) of the pure resin sample can reach 50 MPa when the monolayer curing depth is 5 mm. σs decreases with the increase in the PEG content and monolayer curing depth. With increasing the monolayer exposure time, the yield stress increases and then decreases, and there is an optimum value. The material has the maximum stress at the monolayer exposure time of 13.5 s when the resin content is 50 %.

Correlation between Dental Composite Filler Percentage and Strength, Modulus, Shrinkage Stress, Translucency, Depth of Cure and Radiopacity.

Filler content in dental composites is credited for affecting its physical and mechanical properties. This study evaluated the correlation between the filler percentage and strength, modulus, shrinkage stress, depth of cure, translucency and radiopacity of commercially available high- and low-viscosity dental composites. Filler weight percentage (wt%) was determined through the burned ash technique (800 °C for 15 min). Three-point bend flexural strength and modulus were measured according to ISO 4049 with 2 mm × 2 mm × 25 mm bars. Shrinkage stress was evaluated using a universal testing machine in which composite was polymerized through two transparent acrylic rods 2 mm apart. Shrinkage was measured from the maximum force following 500 s. The translucency parameter (TP) was measured as the difference in color (ΔE00) of 1 mm thick specimens against white and black tiles. The depth of cure was measured according to ISO 4049 in a cylindrical metal mold (4 mm diameter) with a 10 s cure. Radiopacity was measured by taking a digital X-ray (70 kVp for 0.32 s at 400 mm distance) of 1 mm thick specimens and comparing the radiopacity to an aluminum step wedge using image analysis software. The correlation between the filler wt% and properties was measured by Pearson's correlation coefficient using SPSS. There was a positive linear correlation between the filler wt% and modulus (r = 0.78, p < 0.01), flexural strength (r = 0.46, p < 0.01) and radiopacity (r = 0.36, p < 0.01) and negative correlation with translucency (r = -0.29, p < 0.01). Filler wt% best predicts the modulus and strength and, to a lesser extent, the radiopacity and translucency. All but two of the high- and low-viscosity composites from the same manufacturer had statistically equivalent strengths as each other; however, the high-viscosity materials almost always had a statistically higher modulus. For two of the flowable composites measured from the same manufacturer (3M and Dentsply), there was a lower shrinkage stress in the bulk-fill version of the material but not for the other two manufacturers (Ivoclar and Tokuyama). All flowable bulk-fill composites achieved a deeper depth of cure than the flowable composite from the same manufacturer other than Omnichroma Flow Bulk.

Effect of ZrO2 content on mechanical properties of SiC ceramics prepared based on digital light processing

Digital light processing (DLP) technology shows promise in addressing the challenges of preparing high-strength, precise, and complex SiC ceramic structural parts. However, the low strength of DLP-printed SiC ceramic parts remains a persistent issue. To address this, a nano-ZrO2 particle enhancement strategy is proposed. This study systematically investigates the effects of ZrO2 content on slurry viscosity, curing depth, microscopic morphology, and the mechanical properties of SiC ceramics. The results indicate that increasing the ZrO2 content raises the viscosity of the SiC slurry and decreases the curing depth, which can adversely affect the printing quality of SiC ceramic green bodies. However, a higher ZrO2 content significantly reduces pore defects in the sintered parts, improving densification and mechanical properties. This underscores the importance of optimizing ZrO2 content. The SiC sintered parts reinforced with ZrO2 particles exhibited outstanding properties, including a relative density of 91.1 ± 3.2 %, Vickers hardness of 996.4 ± 93.8 HV, and a flexural strength of 201.5 ± 11.4 MPa. This study provides a straightforward and effective method for producing high-strength SiC ceramics via DLP.

Particle grading and debinding process of zirconia ceramic based on digital light process

Digital light processing technology has the advantages of high molding accuracy and the ability to prepare complex structures, which is commonly used in the preparation of resin or ceramics. By mixing two particle sizes of zirconia powders, this paper successfully prepared a 60 vol% slurry with a low viscosity of 1.28 Pa s at shear rate was 50 s−1. By systematically studying the rheological properties of the mixed slurry, the curing depth was exceeding 100 μm at exposure time of 3 s. Furthermore, by investigating the debinding process of the printed sample, it is found that the sintering sample after debinding in vacuum has the highest density. This work has a positive significance for the preparation and debinding process of high solid loading ceramic slurry.

Influences of curing depth and layer thickness on forming accuracy and mechanical properties of biphasic calcium phosphate bioceramics fabricated by vat photopolymerization

Vat photopolymerization (VPP) is a high potential and efficient method for fabricating advanced ceramics. However, the selection of printing strategy importantly determines the geometrical accuracy and mechanical strength of ceramic parts prepared by VPP. In this study, the effects of the curing depth (Cd) to layer thickness (Lt) ratio and Lt on forming accuracy, microstructures, mechanical properties, surface roughness of biphasic calcium phosphate (BCP) bioceramic green bodies and sintered bodies were investigated. When the Cd/Lt ratio was smaller than 4.0, and the Lt was not over 50 μm, the green bodies presented high forming accuracy (the dimension errors ˂ 3.50 %). Inappropriate Cd/Lt and Lt caused lots of defects including different types of cracks and delamination on green bodies and sintered bodies, and impaired their mechanical strength. The optimal Cd/Lt ratio and Lt were obtained to be 4.0 and 50 μm, in which parameters there were few cracks and delamination on the sintered BCP bioceramics. The flexural strength and the fracture toughness of sintered BCP increased when the Cd/Lt ratio increased from 3.0 to 4.0. However, the flexural strength and the fracture toughness decreased when the Cd/Lt ratio further increased to 5.0. The flexural strength of sintered BCP increased at first and then decreased when the Lt increased from 25 μm to 50 μm, and the fracture toughness and hardness of BCP decreased continually. The flexural strength of sintered BCP showed a maximum value of 113.21 MPa, and the maximum fracture toughness was 0.71 MPa∙m1/2. The elastic modulus and hardness of sintered BCP also reached 24.16 GPa and 3.04 GPa, respectively. The printing surface roughness of BCP bioceramics decreased when the Cd/Lt ratio or Lt increased. The lateral surface roughness decreased with the increase of Cd/Lt ratio, and increased with the increase of Lt. This new result provides a clear printing strategy for fabricating ceramics with high geometrical accuracy and mechanical properties by VPP technique.

Effect of a 3-second Off-label Exposure on the Depth of Cure of Eight Resin-based Composites.

This study evaluated the depth of cure (DoC) of eight resin-based composites (RBCs) photocured using one multipeak light-curing unit (LCU) on the standard output setting for the manufacturer's RBC recommended exposure time and at a higher irradiance for 3 seconds. Three conventional RBCs: Tetric EvoCeram (Evo), Tetric N-Ceram (Cer), Tetric Prime (Pri); and five bulk-fill: Tetric N-Ceram Bulk Fill (CerBF), Opus Bulk Fill APS (OpusBF), Opus Bulk Fill Flow APS (OpusF), Tetric PowerFill (PFill) and Tetric PowerFlow (PFlow) were examined. Only PFill and PFlow are formulated to be photocured in 3 seconds. The RBCs were packed into a metal mold and photocured using a Bluephase PowerCure LCU for the RBC manufacturer's recommended exposure time on the standard mode and using the 3-second high irradiance mode. After photocuring, the specimens were immersed in a solvent for 1 hour. The length of the remaining RBC was measured and divided by 2. Data were analyzed using two-way analysis of variance (ANOVA) followed by the Tukey post hoc multiple comparison test (α=0.05). There was no significant difference in the DoC values for PFill and PFlow when photocured using the 3-second high irradiance protocol compared to the lower irradiance standard mode protocol. All other RBCs had significantly lower DoC values (p<0.001) when photocured off-label using the 3-second high irradiance mode. Of the eight RBCs tested, only PFill and PFlow achieved the same DoC when the high irradiance 3-second curing method was used compared to when their longer lower irradiance protocol was used.

ZrO2 reinforced porous Si3N4-based ceramics with improved mechanical properties fabricated via vat photopolymerization (VPP)

Porous Si3N4 ceramics are widely applied in many fields owing to their excellent properties such as high electromagnetic wave permeability, oxidation resistance, and wear resistance. Besides, the vat photopolymerization (VPP) technique can fabricate porous Si3N4-based ceramics with complex shapes and high precision. Nevertheless, The high absorptivity and refractive index of Si3N4 to ultraviolet light make it difficult to form porous Si3N4-based ceramics with the VPP technique. In this work, the addition of ZrO2 simultaneously improved the printability of Si3N4 slurries and the performance of Si3N4 ceramics via VPP technology. Rheological behavior and curing properties of the slurries were investigated, and the influence of ZrO2 content on the mechanical properties of printed Si3N4-based ceramics was investigated systematically. The addition of ZrO2 decreased the UV absorptivity of composite powder, thus improving the curing depth from 25.2 ± 2.6 μm to 64.8 ± 3.7 μm. XRD analysis revealed that ZrO2 in the composite ceramics mainly exists as the phase of yttria-stabilized tetragonal zirconia (Zr0.92Y0.08O1.96), which could ensure the effect of phase transformation toughening. With the increase of ZrO2 content, flexural strength and fracture toughness of porous Si3N4-based ceramics exhibited a trend of increase first and then decrease. As ZrO2 content increased to 10 wt%, the flexural strength and fracture toughness of porous Si3N4-based ceramics were improved from 214.7 MPa and 4.23 MPa·m1/2 to 345.0 MPa and 5.69 MPa·m1/2, respectively. Therefore, this work provided an important reference for the fabrication of high-performance porous Si3N4-based ceramic components with complex structures.

Ultra-lightweight silicon nitride truss-based structures fabricated via UV-assisted robot direct ink writing

Additive manufacturing techniques have gone beyond their reputation for rapid prototype production and are increasingly adopted for the manufacture of functional components comprising high-end materials and intricate lattice structures. Silicon nitride, renowned for its exceptional mechanical properties and thermal stability, has emerged as a promising candidate for lightweight structural applications. Nonetheless, its high refractive index and density have limited the fabrication of highly complex structures using extrusion and photopolymerization based techniques. In this work, a highly reactive silicon nitride-based ink with high solid loading is developed for the fabrication of ultra-lightweight, truss-based structures. By employing a robot UV-assisted direct ink writing process, it is possible to control the printing head orientation, thus overcoming the limited curing depth of silicon nitride-based inks. The failure behavior of the sintered lattice beam structures under 4-point bending loading has been modeled by applying a linear elastic fracture mechanics (LEFM) based approach to the results of finite element (FE) simulations.

Mechanical and dielectric properties of Si3N4/β-SiAlON composite ceramics fabricated by vat photopolymerization 3D printing technology

Vat photopolymerization 3D printing provides a novel approach for preparing broadband wave-transparent Si3N4/β-SiAlON composite ceramics. This paper oxidized raw powder to introduce low dielectric phases (SiO2) and overcome the low curing depth of α-Si3N4. The solid content of oxidized α-Si3N4 was increased to 50 vol% for the first time by modification with dispersant. The selected print thickness of 50 μm was the highest known for Si3N4 vat photopolymerization 3D printing, greatly improving printing efficiency. Finally, Si3N4/β-SiAlON composite ceramics were sintered in the range of 1600-1800 °C, and the mechanical and dielectric properties were systematically studied. The composite ceramics sintering at 1780 °C had a maximum bending strength of 236 ± 16 MPa, and the real permittivity was 4.83. At 1800 °C the porosity increased resulting in bending strength decreased to 109 ± 4 MPa, and the real permittivity to 3.23. This study filled the gap in the post-treatment of oxidized α-Si3N4 and guided the application of Si3N4/β-SiAlON composite ceramics in the field of wave-transparent.

Low-migration, deep photocuring thiobarbituric acid-based one-component visible photoinitiators for high-efficiency photopolymerization

The practical applications of thiobarbiturates in medicinal chemistry exemplifies their exceptional biosafety, which is crucial for developing high-efficiency photopolymerization and low-migration photoinitiators (PIs). In this study, five novel D-π-A visible PIs (ANs) were designed and synthesized via using aniline derivatives as the electron donor (D) and thiobarbituric acid as electron acceptor (A). EPR and steady-state photolysis display that the conjugated structure can be destroyed by intramolecular electron/proton transfer, leading to photobleaching. Real-time infrared (FT-IR) analyses have confirmed effective polymerization of 1,6-hexanediol diacrylate (HDDA) initiated by ANs and ANs/N-methyldiethanolamine (MDEA) under illumination. The experimental molar extinction coefficient (ε) aligns with the oscillator strength (f) calculated via DFT, while the high ε and f of AN-5 facilitate electron transfer and free radical generation, resulting in improved initiation efficiency. The conversion rate of independent initiating polymerization exhibits an impressive 78 %. Moreover, colorless polymer columns initiated by AN-5 and AN-5/MDEA display curing depths of 45 mm and 50 mm, along with photobleaching rates reaching up to 98.7 % and 100 %, respectively. Especially, AN-5 exhibits the mere 0.2 % extraction rate from polymerization films under illumination (60 min). These results indicated the great potential of thiobarbituric acid-based ANs in deep-curing materials, food packaging.

Selection strategy of curing depth for vat photopolymerization 3D printing of Al2O3 ceramics

Vat photopolymerization (VPP) 3D printing technology allows the fabrication of complex ceramic structure components through the layer-by-layer stacking strategy. The curing depth is a crucial parameter for the stacking process, as it directly impacts the printing quality. Furthermore, this parameter exerts a profound effect on the final quality of the printed part. However, there is currently a lack of comprehensive research on how the curing depth affects VPP ceramic 3D printing. This study aims to thoroughly evaluate the impact of curing depth parameters on critical aspects of the 3D printing process, including the forming accuracy, surface quality, monomer conversion, resin pyrolysis, interlayer defects, and mechanical properties. The results of our investigation clearly demonstrate the significant influence of curing depth on the precision and performance of VPP 3D printed ceramic parts. Ceramic samples produced with higher curing depth exhibited superior surface quality (Ra<1.6 μm) but lower forming accuracy. Increasing the curing depth improved interlayer adhesion but excessive depth led to a decreased monomer conversion content from 5.2 % to 2.0 % and an internal stress in the green body. Moreover, increasing the curing depth intensified the pyrolysis process and increased the propensity for cracks forming, as confirmed by simultaneous thermal analysis and microstructure observations. The flexural strength of the sintered samples reached its maximum value of 630 MPa at three times the printing layer thickness. This study provides valuable insights for selecting appropriate curing depth parameters in VPP ceramic 3D printing.

Effect of Preheating on Microhardness, Degree of Conversion, and Depth of Cure of Various Bulk-Fill Composites

Background: This study aims to evaluate the effect of preheating on microhardness, degree of conversion, and depth of cure of bulk-fill composites (Tetric EvoCeram Bulk-Fill, SonicFill2) and a conventional composite (Tetric EvoCeram). Methods: Layers of Tetric EvoCeram (2 mm), Tetric EvoCeram Bulk-Fill (4 mm), and SonicFill2 (5 mm) were placed in 4-mm diameter molds and polymerized at room temperature or heated to 55oC for 10 s with a total number of 60 samples. Then, the top surfaces of samples were polished. 30 samples’ Vickers microhardness was measured from the top and bottom surfaces. The other 30 samples were pulverized into a fine powder, and the composites’ degree of conversion was measured with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained data were analyzed statistically with a significance level of p&amp;lt;0.05. Results: The degree of conversion of Tetric EvoCeram was higher than the minimum rate of clinically acceptable value, which is 55%, but the scores of Tetric EvoCeram Bulk-Fill and SonicFill2 were below the threshold. Preheating increased the degree of conversion of Tetric EvoCeram Bulk-Fill and SonicFill2. In addition, preheating did not affect depth of cure of SonicFill2 but decreased the rate of Tetric EvoCeram Bulk-Fill. Conclusion: The results showed that the effect of preheating on the degree of conversion and depth of cure varied according to the material. Keywords: Preheating, bulk-fill composite, degree of conversion, depth of cure, microhardness.