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Digital light processing (DLP) three‐dimensional printing has the advantages of both high printing resolution and efficiency and has been used to manufacture high‐precision, small, and complex shaped ceramic parts. One of the challenges of DLP is to develop photosensitive ceramic slurries with high solid content and low viscosity, especially for non‐oxide ceramics such as silicon nitride due to the dispersion and light absorption problem. This study mainly explores the dispersibility of silicon nitride in ultraviolet (UV)‐cured resins and the photocured properties of the slurry. Rheological measurements were utilized to characterize and screen different dispersants in the resin. It was found that DISPERMP is an effective dispersant. In order to improve the curing depth of Si3N4 photosensitive paste, the surface of silicon nitride powder was treated by oxidation, and organic compounds with different refractive indices were also introduced to increase the light penetration depth. It was found that glycerol with a refractive index of 1.474 resulted in the greatest improvement in the curing depth of Si3N4 photosensitive paste. Finally, a proposed slurry composition was developed to successfully print silicon nitride ceramics through UV‐curing molding technology. [ABSTRACT FROM AUTHOR]

High-strength alumina (Al2O3 ) was utilized as a reinforcing phase to improve the strength of hydroxyapatite (HA), a bioactive material, but the HA-Al2O3 ceramics prepared by traditional hydrothermal method could not achieve the precise control of pore size and porosity, whereas the light curing additive manufacturing technology could achieve the high precision molding of HA-Al2O3 ceramics through the high-performance photocurable slurry. The state of HA-Al2O3 slurry is adjusted by the addition of dispersant, photoinitiator, and photoabsorbent to alleviate the severe scattering effect caused by the refractive index mismatch between HA powder, Al2O3 powder, and photosensitive resin. In this study, the effects of the type and content of photoinitiator and dispersant on the slurry were explored. The rheological and curing properties of the slurry are first improved and then weakened with the addition of both, and the optimal dosages of photoinitiator and dispersant are 0. 5% and 4% (mass fraction), respectively. The effects of two light absorbers, graphite and methyl yellow, on improving the printing accuracy were compared. Although graphite improves the printing accuracy and rheology of the slurry, it reduces the printing quality, so the dosage of 5.0 x 10-5 methyl yellow is determined, and finally HA-Al2O3 slurries suitable for high precision printing are obtained. [ABSTRACT FROM AUTHOR]

Interparticle photo-cross-linkable ZrO2 slurry which can be photo-cured by near-infrared (nIR) light irradiation was successfully designed by mixing small amounts of multifunctional acrylate (MA), photo radical initiator, and nIR- absorbing dye into a concentrated ZrO2 slurry stabilized by a partial complex of polyethyleneimine and oleic acid. The reaction of MA to PEI-OA modified ZrO2 particles induced by nIR light irradiation was confirmed through the FTIR and TGA analysis of ZrO2 particles collected from the slurry before and after light irradiation as well as the microstructure investigation of photocured bodies using FE-SEM. Compared to the ultraviolet light-responsive interparticle photo-cross-linkable ZrO2 slurries, the designed nIR-responsive slurry found to possess large curing depth which enabled the shaping of complex structured ZrO2 green bodies through a simple photocuring process in a mold. [ABSTRACT FROM AUTHOR]

Fabrication of silicon carbide (SiC) ceramics by digital light processing (DLP) technology is difficult owing to high refractive index and high ultraviolet (UV) absorptivity of SiC powders. The surface of the SiC powders can be coated with silicon oxide (SiO2) with low refractive index and low UV absorptivity via high-temperature oxidation, reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics. However, it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders. Therefore, the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper. The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation, effectively reducing the UV absorptivity and the surface refractive index (nʹ) of the SiC powders. When the oxidation temperature is 1300 ℃, compared with that of unoxidized SiC powders, the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654, and a curing depth of SiC slurry increases from 22±4 to 59±4 μm. Finally, SiC green bodies are successfully prepared by the DLP with the the oxidized powders, and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000 ℃ without any sintering aid.

Dense hydroxyapatite (HA) bars were fabricated using digital light processing. The roles of HA median particle size (MPS), curing depth-to-layer thickness ratio (CD/LT), and debinding process on the printing/debinding flaws and flexural strength of the sintered parts were investigated. Commercial HA was milled for different times to provide powders with an MPS ranging from 0.3 to 2.7 µm. Thermal debinding led to delamination and vertical cracks, which decreased with increasing MPS; the minimum value required to fabricate specimens with appreciable flexural strength was 0.9 µm. At a given MPS (2.7 µm), the CD/LT varied between 1.4 and 3.3, indicating a progressive disappearance of the above major flaws. Finally, the positive effect of water debinding prior to thermal debinding on reducing crack formation was demonstrated. After optimisation, the bars achieved a flexural strength greater than 100 MPa, which is the highest value among dense HA fabricated using lithography-based techniques. [ABSTRACT FROM AUTHOR]

For a specified ink formulation and a printer equipped with a particular light source, an optimal curing depth exists, which can be empirically determined. This depth is critical for maintaining shape fidelity of the printed object. In multilayered prints, each successive layer undergoes multiple exposures, collectively referred to as the cumulative exposure time. Consequently, when fabricating components of varying thicknesses, precise adjustment of exposure time is required to ensure that each layer fulfils the optimum cumulative exposure time criterion This can be achieved by increasing the exposure period for layers with thicknesses below the curing depth or by altering the printing orientation (to increase the number of the sliced layers, if applicable). [Display omitted] 3D printing, also known as additive manufacturing, continues to reshape manufacturing paradigms in healthcare by providing customized on-demand object fabrication. However, stereolithography-based 3D printers encounter a conflict between optimizing printing parameters, requiring more time, and print efficiency, requiring less time. Moreover, commonly used metrics to assess shape fidelity of 3D printed hydrogel materials like 'circularity' and 'printability' are limited by the soft nature of hydrogels, that can cause irregularities in their boundary. To unlock the full potential of 3D printing of biomaterials, it is also necessary to understand correlation between printing parameters and ink properties. In this work, a method based on curing depth, overcuring (cumulative cure), and print thickness was developed, which enables a time-efficient and reliable determination of printing conditions for complex geometries using gelatin methacrylate hydrogel biomaterial ink. We also examined the impact of printing direction on the print quality in terms of object/print thickness and aspect ratio. Moreover, the effects of dye concentration, exposure time, and layer thickness on print quality were evaluated, with discussions focused on the correlation between print dimension to layer thickness. Further evaluation was achieved by successfully printing bioinspired corneal stroma-like scaffold and delicate structures like a contact lens and a model eyeball, substantially expanding the scope of this method in producing high-quality prints with intricate details. We also demonstrate the effectiveness of 'Feret ratio,' another measure of object shape, in assessing the shape fidelity of different prints. Overall, the results highlight the practical potential of this method in enhancing the speed and reliability of the 3D printing processes involving complex geometries using a low-cost 3D printers. [ABSTRACT FROM AUTHOR]

Statement of the Problem: One of the problems with light-cured composite resins is the limitation and inadequate depth of curing and polymerization, resulting in low surface microhardness and restoration failure. Purpose: The present study aimed to compare the surface microhardness of two different bulk-fill composite resins and one conventional composite resin using the Vickers microhardness test. Materials and Method: In the present in vitro study, 108 samples from two different bulk-fill composite resins (Tetric N Ceram and Xtrafil) and one conventional composite resin (Filtek Z250) were prepared in metallic molds (2×4×10 mm) (n=36 for each composite resin). Six samples from each composite resin (n=6) underwent a hardness measurement test at specific depths (0.1, 1, 2, 3, 4 and 5mm). The samples were then stored at 37ºC for 24 hours, followed by a microhardness test at the depths mentioned above. Results: In all the composite resin samples, microhardness decreased with an increase in depth. The highest microhardness was recorded in Filtek Z250, followed by Xtrafil, with no significant difference. The lowest microhardness was recorded in Tetric N Ceram bulk-fill. Both bulk-fill composite resins at all the depths exhibited depth-to-surface standard microhardness (>80%). Conclusion: According to the results, both evaluated bulk-fill composite resins exhibited favorable surface microhardness up to a depth of 5 mm.

Lead-free piezoelectric materials are essential for our healthy future but offer lower performance than lead-based materials. Different material combinations are explored to improve the performance of lead-free materials. By filling the UV light curable photopolymer resin with 30 vol.% lead-free piezoelectric ceramics and with up to 0.4 wt.% conductive nanofillers, thin and flexible piezoelectric 0-0-3 composites are formed. Two particle sizes of Potassium Sodium Niobate (KNN) and Barium Titanate (BTO) ceramics were used with four conductive nanofillers: Graphene Nanoplatelets (GNPs), Multi-Walled Carbon Nanotubes (MWCNTs), and two types of Graphene Oxide (GO). Resulting high viscosity suspensions are tape-cast in a mold as thin layers and subsequently exposing them to UV light, piezoelectric composite sensors are formed in 80 s. Even low nanofiller concentrations increase relative permittivities, however, they strongly reduce curing depth and increase undesirable dielectric losses. Non-homogeneous dispersion of nanofillers is observed. In total, 36 different compositions were mixed and characterized. Only six selected material compositions were investigated further by measuring mechanical, dielectric, and piezoelectric properties. Results show KNN composite performance as piezoelectric sensors is almost six times higher than BTO composite performance. [ABSTRACT FROM AUTHOR]

Four piezoelectric ceramic materials with varying particle sizes and geometries are added up to 30 vol.% to a photopolymer resin to form UV-curable piezoelectric composites. Such composites solidify in a few minutes, can be used in UV-curing-based 3D printing processes, and can achieve improved sensor performance. The particle dispersion with ultrasonication shows the most homogeneous particle dispersion with ethanol, while two other solvents produced similar results. The viscosities of the prepared suspensions show some dependency on the particle size. The curing depth results show a strong dependency on the ceramic particle size, the difference in refractive index, and the particle size distribution, whereby composites filled with PZT produced the worst results and composites filled with KNN produced the highest curing depths. The SEM images show a homogeneous dispersion of ceramic particles. The highest dielectric properties are also shown by KNN-filled composites, while BTO and PZT produced mixed results of dielectric constants and dielectric losses. KNN-filled composites seem to be very promising for further 3D-printable, lead-free piezoelectric composite development. [ABSTRACT FROM AUTHOR]

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Statement of the Problem: One of the problems with light-cured composite resins is the limitation and inadequate depth of curing and polymerization, resulting in low surface microhardness and restoration failure. Purpose: The present study aimed to compare the surface microhardness of two different bulk-fill composite resins and one conventional composite resin using the Vickers microhardness test. Materials and Method: In the present in vitro study, 108 samples from two different bulkfill composite resins (Tetric N Ceram and Xtrafil) and one conventional composite resin (Filtek Z250) were prepared in metallic molds (2×4×10 mm) (n=36 for each composite resin). Six samples from each composite resin (n=6) underwent a hardness measurement test at specific depths (0.1, 1, 2, 3, 4 and 5mm). The samples were then stored at 37ºC for 24 hours, followed by a microhardness test at the depths mentioned above. Results: In all the composite resin samples, microhardness decreased with an increase in depth. The highest microhardness was recorded in Filtek Z250, followed by Xtrafil, with no significant difference. The lowest microhardness was recorded in Tetric N Ceram bulk-fill. Both bulk-fill composite resins at all the depths exhibited depth-to-surface standard microhardness (>80%). Conclusion: According to the results, both evaluated bulk-fill composite resins exhibited favorable surface microhardness up to a depth of 5 mm. [ABSTRACT FROM AUTHOR]

Traditional ceramic processing technology has high cost, long cycle and many defects, which makes it difficult to produce high-performance ceramics. The refractive index (n = 2.1) of pure Si3N4 powder is quite different from that of resin (n = 1.49), and the light scattering is serious, which leads to the lower curing depth of the ceramic paste. It is difficult to directly use stereolithography technology to form Si3N4 ceramic parts. In order to solve the problem that Si3N4 powder is difficult to be cured, two methods of surface coating and surface oxidation were used to modify Si3N4 powder, and the influence of the two methods on the light curing characteristics of Si3N4 powder was compared. The results show that the organic monomer uniformly attaches to the surface of Si3N4 powder after a certain reaction time; after being oxidized at 800 °C for 4 h, amorphous SiO2 layer is formed on the surface of Si3N4 powder, which is uniformly attached to the surface of Si3N4 powder. The curing depth of original Si3N4 powder is merely 20 µm, and the curing depth of Si3N4 powder after coating modification and oxidation modification increase to 40 µm and 50 µm, respectively. Both methods effectively improve the curing depth of original Si3N4 powder. [ABSTRACT FROM AUTHOR]

In this paper, we study the optimal photoinitiator (camphorquinone, CQ) concentration for light-cured dental resins by combining such properties as the degree of conversion, mechanical properties, and curing depth (the depth at which the hardness is 80% of the surface hardness). The material properties of the light-cured dental resins (Bis-GMA/TEGDMA in a mass ratio of 70:30) are characterized by in-situ near-infrared (NIR) spectroscopy and nanoindentation tests. Experimental results indicate that the degree of conversion (DC) and mechanical properties such as elastic modulus and hardness increase, while the curing depth decreases with the increase of CQ concentration. However, above a certain concentration (~0.5 wt%), these properties do not benefit from the further increasing CQ concentration because of potential self-annihilation between free radicals. The presented study offers a method to determine the optimal photoinitiator concentration for light-cured resins and establishes the correlations between the photoinitiators, polymerization kinetics, and mechanical properties of the light-cured resins.

This in vitro study investigated the depth of cure of a microhybrid composite resin when cured with reduced times of exposure to three commercially available curing lights. Different sample thicknesses (1, 2, and 3 mm) were light cured in high intensity polymerization mode (2,400 mW/cm2 for 5, 10, 15, and 20 seconds; 1,100 mW/cm2 for 10, 20, 30, and 40 seconds; and 1,100 mW/cm2 for 10, 20, 30, and 40 seconds, respectively). The degree of conversion (%) at the bottom of each sample was measured by Attenuated Total Reflection Fourier Transform Infrared (ATR F-TIR) analysis after each polymerization step. Data were analyzed by ANOVA for repeated measures, showing the degree of conversion was not influenced by the curing light employed (P = .622) but was significantly influenced by the thickness of composite resin (P < .05). Variations in the degree of conversion vs the shorter irradiation time permitted (T1) were not significant among different lamps but were significant among different thicknesses. The depth of cure of microhybrid composite resin appears not to be influenced by the curing light employed. Increased irradiation time significantly increases the degree of conversion. Thickness strongly influences depth of cure. (Quintessence Int 2011;42:e89-e95) [ABSTRACT FROM AUTHOR]

To compare the depth of cure (DoC) of a colored polyacid-modified composite resin (PAM-C) with a traditional PAM-C and a fine hybrid composite resin using different light-curing units and different radiant energies. Method and Materials: The DoC of the PAM-C Twinky Star (Voco, all shades), the PAM-C Glasiosite (Voco), and the composite resin Z100 (3M ESPE) shades A2 and A4 was determined using a penetrometer test method. The materials were cured in bulk using a halogen-based unit (Elipar Trilight, E = 18 J/cm² and E = 32 J/cm²; 3M ESPE) and an LED curing unit (Elipar Freelight 2, E = 20 J/cm²; 3M ESPE) in split stainless steel molds. Immediately after curing, the height (mm) of the cured material was measured and taken as the DoC. Ranking of means was performed by Student-Newman-Keuls multiple comparison test, and statistically significant differences among mean values were detected with ANOVA. Results: Mean DoC for all materials and shades varied as follows: 4.705 to 8.870 mm (E = 32 J/cm²); 3.672 to 8.050 mm (E = 20 J/cm²); and 4.090 to 7.357 mm (E = 18 J/cm²). Two-way ANOVA revealed that the DoC depended significantly (P < .001) on the shade of the material and the curing device. Moreover, there was a significant interaction (P < .001) between the latter, indicating that the effect of the energy densities differed quantitatively among the shades. Conclusions: In this study, DoC differed significantly among the materials and the shades. Twinky Star shade blue showed the highest DoC compared to Glasiosite and Z100 shades A2 and A4. The curing device with the highest energy density exhibited the highest curing depths. [ABSTRACT FROM AUTHOR]

Objectives: To determine the hardness versus depth profile of several polyacid-modified composite resins (PAM-Cs) as a function of shade (A2, A4) and compare the depth of cure (DoC) based on these profiles with that previously obtained with the scraping and penetrometer methods. Method and Materials: Samples of 6 PAM-Cs (Hytac, 3M ESPE; F2000, 3M ESPE; Glasiosite, Voco; Dyract, Dentsply DeTrey; Dyract AP, Dentsply DeTrey; Compoglass F, Vivadent) and 3 composite resins (Herculite Enamel XRV, Kerr; Z100, 3M ESPE; Durafill VS, Heraeus Kulzer) with shades A2 and A4 were light-cured in bulk in split stainless steel molds (thickness ranging from 0.5 to 3.5 mm in steps of 0.5 mm). The Knoop hardness of the irradiated top (KHNsurface) and nonirradiated bottom (KHNbottom) surfaces was determined as a function of sample thickness using a microhardness tester. Results: Regression analysis demonstrated that for a given material, KHNbottom equals KHNsurface up to a specific depth (= DoC) depending on the material and shade and then decreases linearly with increasing depth. The decrease of the KHN per unit depth differs significantly among materials and shades. According to a regression analysis, the scraping and penetrometer methods overestimate the DoC of PAM-Cs compared to the method based on the change of the hardness indentation with depth. Conclusions: Shade A2 results in greater values of DoC than shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-Cs do not reach a DoC of 2 mm, a layer recommended to be applied in the incremental technique. The DoC as determined according to ISO 4049:2000 apparently is based on a lower degree of polymerization corresponding to a KHN of 80% of the irradiated surface. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the curing efficiency, through tooth slices (0, 1.2, 1.5 and 2.0 mm), of three different light sources. Materials and Methods: Three caries-free mandibular 3rd molars were used. After the roots were cut from the coronal portions, slices of different thickness (1.2 mm, 1.5 mm, 2.0 mm) were made by cutting the buccal face of the dental crowns. Then, samples were made in a metallic mold (4 mm diameter and 2 mm thickness) with a microhybrid composite resin (Charisma; Heraeus-Kulzer). The samples (n = 140) were divided into 3 groups: group I - halogen LCU for 20 and 40 s; group II - argon laser LCU for 20 and 40 s; group III - LEDs LCU for 20, 40, and 60 s. The samples were cured either directly (no tooth slice intervening; control), or indirectly (through tooth slices of different thickness). The samples were stored dry at 37°C for 24 h, and then Vickers microhardness testing was performed. Results: The data were submitted to ANOVA (p < 0.05). Standard deviation values from the microhardness measurements were less than 1% of the mean and showed a statistically significant difference among the light curing units and the cure through the tooth slices of different thicknesses. Conclusion: In the indirect photoactivation technique, it was necessary to increase the exposure time independent of the LCUs used mainly for the bottom surface. Under these experimental conditions, the LED curing unit promoted the lower microhardness values when compared to the halogen and argon laser LCUs. [ABSTRACT FROM AUTHOR]

Challenges especially in the minimal invasive restorative treatment of teeth require further developments of composite polymerization techniques. These include, among others, the securing of a complete polymerization with moderate thermal stress for the pulp. The aim of this study is to compare current light curing sources with a blue diode laser regarding curing depth and heat generation during the polymerization process. A diode laser (445 nm), a LED, and a halogen lamp were used for polymerizing composite resins. The curing depth was determined according to the norm ISO 4049. Laser output powers of 0.1, 0.5, 1, and 2 W were chosen. The laser beam diameter was adapted to the glass rod of the LED and the halogen lamp (8 mm). The irradiation time was fixed at 40 s. To ascertain ΔT values, the surface and ground area temperatures of the cavities were simultaneously determined during the curing via a thermography camera and a thermocouple. The curing depths for the LED (3.3 mm), halogen lamp (3.1 mm) and laser(0.5/1 W) (3/3.3 mm) showed no significant differences (p < 0.05). The values of ΔTsurface as well as ΔTground also showed no significant differences among LED, halogen lamp, and laser(1 W). The ΔTsurface values were 4.1LED, 4.3halogen lamp, and 4.5 °C for the laser while the ΔTground values were 2.7LED, 2.6halogen lamp, and 2.9 °C for the laser. The results indicate that the blue diode laser (445 nm) is a feasible alternative for photopolymerization of complex composite resin restorations in dentistry by the use of selected laser parameters. [ABSTRACT FROM AUTHOR]

The fabricated photoinitiator ID-HA with green indole as electron donor displays high migration stability, efficient photobleaching, and photoinitiation. [Display omitted] • Six photoinitiators IDs are fabricated with green indole as electron donor. • IDs displays a fast completely fading. • Double bond conversion is as high as 81% initiated by ID-HA. • ID-HA exhibits high migration stability. • The colorless polymer columns and bleaching ratios reach 47 mm and 96.8 %. Six symmetric D-π-A-π-D indole derivatives (IDs) have been investigated as visible light photoinitiators (PIs). The IDs, with different indole as the electron donor (D), C = C bond as the π-bridge and carbonyl group as the electron acceptor (A), are type II PIs owning to their intermolecular hydrogen abstraction. In the process of generating free radicals, the carbonyl transformed to hydroxyl alkyl radicals, which disrupted the large conjugation systems and resulted in the color fading. Real time infrared (RT-IR) indicated that IDs and ID/N-methyldiethanolamine (MDEA) effectively initiated the photopolymerization of 1, 6-hexanediol diacrylate under illumination. ID-HA containing acrylate double bonds is expected to be served as not only a PI but also a crosslinker with extremely high migration stability. The extraction rate of ID-HA from the polymer films following 30 min of illumination was 1.0 %. ID-HA has a lower energy in the excited triplet state (DFT calculations), which is favorable for electron transfer and radical generation. Therefore, the color of ID-HA in acetonitrile solution completely faded within 15 s under illumination, demonstrating the best photobleaching behavior. Meanwhile, the polymerization conversion initiated by it alone could reach as high as 81 %. Furthermore, 47 mm high (with 96.8 % whiteness bleaching ratio) and 55 mm high (with 94.5 % whiteness bleaching ratio) polymer columns were obtained respectively, by using ID-HA and ID-HA/MDEA as PI. Thus, their outstanding photobleaching performance, migration stability and thermal stability endow IDs potential applications in deep photopolymerization, food packaging and biomedicine. [ABSTRACT FROM AUTHOR]

The effect of altering the distance between light tip and outer layer of composite (DLR) on the depth of composite cure with a range of low to high light intensity curing lamps and with different types of light unit is of interest. Three LED units (T= Freelight,U = Ultrablue IS, V = Coltolux LED, one PAC unit (S=PAC) and three halogen light-curing units (P = XL2500, Q = HelioluxVL, R = Visiolux) were analyzed. A human molar tooth that was separated mesio-distally to buccal and lingual halves was used to create a natural tooth sample. Data shows that the depth of cure for the composite material decreased as the distance between the repair and the light source increased. There was no appreciable difference in performance between the LEDs and the other kinds of curing lamps as the distance between them grew., (© 2023 Biomedical Informatics.)

Aims: To study the effect of different curing modes of Light emitting diodes (LED) curing unit on the depth of cure (DOC) of composite resin with light and dark shades and compare the results with conventional curing method by the use of halogen curing light. Materials and Methods: A total of 40 cylindrical composite resin samples (4mm diameter and 6mm height) were prepared, 20 of light shade and 20 of dark shade. They were subjected to four curing modes (n=5 for each group): conventional halogen light, and three modes related to the LED light curing unit (LCU) which were: Fast (F); Ramped (R); and Pulsed (P). The samples were irradiated to the time required by the manufacturer for each curing mode, and a digital micrometer was used to measure the depth of cure according to scraping method described in ISO 4049:2000. Data were collected and analyzed for comparison. Results: No significant difference was found in the DOC of composite irradiated by LED curing light for all of the three curing modes or shade. However, the LED produced significantly greater depths of cure when compared with conventional halogen curing unit for both shades. The lighter shade was cured to a significantly greater depth than dark one when considering halogen LCU. Conclusions: All curing modes of the LED light can produce similar DOC regardless of composite shade when irradiated to the time recommended by the manufacturer. However, Curing with conventional halogen curing unit yielded the least DOC values for light or dark shades when compared with LED units. Longer irradiation times are needed to cure dark shades by the use of halogen LCUs.

[Display omitted] • Two of carbazole-indenedione photobleachable photoinitiators were synthesized. • Piperidine group in the ortho -position of the double bond is a key to improve initiating efficiency. • Six minutes visible LED irradiation provides a colorless IPN polymer as thick as 5.8 mm. In order to investigate the properties of carbazole-indenedione based photoinitiators for photopolymerization, two visible light-sensitive photoinitiators (CAs) were designed and synthesized. Their structures were confirmed by nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HR-MS). Additionally, their properties concerned photophysical/photochemical and photoinitiating were determined by electron paramagnetic resonance (EPR), UV–vis spectrophotometer and real-time FT-IR spectroscopy. The results have showed that CA-2 could be regarded as an effective one-component photobleachable photoinitiator for free-radical polymerization (FRP). Meanwhile, its photoinitiating property could be enhanced or optimized by adding the additional hydrogen donor or iodonium salt, and the interpenetrated polymer networks (IPN) were synthesized by the hybrid polymerization of TMPTA (trimethylolpropane triacrylate)/EPOX (3,4-epoxycyclohexylmethyl 3,4-epoxycycohexanecarboxylate) initiated by two-component CA-2/Iod (iodonium salt). The results of theoretical calculation experiments showed that it is also an effective way to improve the photoinitiating efficiency by the introduction of the electron-donating piperidine group in the ortho -position of the double bond on carbazole skeleton. The curing depth experiments showed that the photobleaching performance could be enhanced by introduction of Iod in acrylic/epoxy resin and a colorless polymer with the thickness of 5.8 mm was obtained under visible LED light irradiation for 6 min. Thus, the carbazole-indenedione based photobleachable dye CA-2 has great potential in deep curing materials (e.g. dental materials, biomedical materials and 3D printing). [ABSTRACT FROM AUTHOR]

With the aim to prepare Bis-GMA-free bulk-filled dental resin composite (DRC), Bis-GMA-free resin matrix was prepared by mixing Bis-EFMA with TEGDMA at two mass ratios (Bis-EFMA/TEGDMA = 50 wt/50 wt and 60 wt/40 wt), and the bulk-filled resin composites were then obtained by mixing resin matrix with silanated glass fillers at a mass ratio of 30 wt/70 wt. Bis-GMA based resin composites were used as control. Refractive indexes of resin matrixes were measured. Besides the depth of cure mentioned in ISO standard, double bond conversion (DC) and bottom/top Vickers hardness (VHN) ratio of resin composites were investigated to evaluate the curing depth. Physicochemical properties, such as flexural properties, volumetric shrinkage (VS), shrinkage stress (SS), water sorption (WS) and solubility (SL), and cytotoxicity of resin composites were tested and statistically analyzed (ANOVA, Tukey's, p = 0.05). The results showed that Bis-EFMA/TEGDMA resin matrixes had higher refractive indexes than Bis-GMA/TEGDMA resin matrixes. Viscosities of Bis-EFMA based DRCs were higher than Bis-GMA based DRCs. Bis-EFMA-based (50/50) DRC had comparable depth of cure, DC, and VHN as Bis-GMA-based (50/50) DRC (p > 0.05). Though Bis-EFMA/TEGDMA (60/40) had the highest refractive index in all resin matrix, the corresponding DRCs had the lowest depth of cure, DC, and bottom/top VHN ratio in all groups (p < 0.05). Replacing Bis-GMA with Bis-EFMA had no negative effect on flexural properties, WS and SL of DRCs, and could reduce VS and SS of DRCs. Results of CCK8 assay showed that all of DRCs had the same cytotoxicity (p > 0.05), and the thickness of sample had no influence on the cytotoxicity (p > 0.05). All the results indicated that Bis-EFMA could be used to replace Bis-GMA to prepare bulk-filled dental resin composites. According to the results of depth of cure, DC, and bottom/top VHN ratio, 50 wt/50 wt was more appropriate than 60 wt/40 wt as the mass ratio of Bis-EFMA and TEGDMA in the resin matrix for bulk-filled dental resin composites. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The aim of this study is to investigate depth dependent changes of polymerization process and kinetics of visible light-curing (VLC) dental composites in real-time. The measured quantity – “ion viscosity” determined by dielectric analysis (DEA) – provides the depth dependent reaction rate which is correlated to the light intensity available in the corresponding depths derived from light transmission measurements. Methods: The ion viscosity curves of two composites (VOCO Arabesk Top and Grandio) were determined during irradiation of 40s with a light-curing unit (LCU) in specimen depths of 0.5/0.75/1.0/1.25/1.5/1.75 and 2.0mm using a dielectric cure analyzer (NETZSCH DEA 231 with Mini IDEX sensors). The thickness dependent light transmission was measured by irradiation composite specimens of various thicknesses on top of a radiometer setup. Results: The shape of the ion viscosity curves depends strongly on the specimen thickness above the sensor. All curves exhibit a range of linear time dependency of the ion viscosity after a certain initiation time. The determined initiation times, the slopes of the linear part of the curves, and the ion viscosities at the end of the irradiation differ significantly with depth within the specimen. The slopes of the ion viscosity curves as well as the light intensity values decrease with depth and fit to the Lambert–Beer law. The corresponding attenuation coefficients are determined for Arabesk Top OA2 to 1.39mm−1 and 1.48mm−1, respectively, and for Grandio OA2 with 1.17 and 1.39mm−1, respectively. For thicknesses exceeding 1.5mm a change in polymerization behavior is observed as the ion viscosity increases subsequent to the linear range indicating some kind of reaction acceleration. Significance: The two VLC composites and different specimen thicknesses discriminate significantly in their ion viscosity evolution allowing for a precise characterization of the curing process even with respect to the polymerization mechanism. [Copyright &y& Elsevier]

Aim: Light-emitting diode light curing units (LED LCUs) have become more popular than halogen LCUs in routine dental restorative treatment. The aim of the study was to compare the effects of two conventional halogen (Hilux Plus and VIP) and two LED (Elipar FreeLight 2 and Smart Lite) light curing units on the depth of cure and the microhardness of various esthetic restorative materials. Materials and Methods: The curing depth and microhardness of a compomer (Dyract Extra), a resin-modified glass ionomer (Vitremer), a packable composite (Sculpt It), an ormocer (Admira), a hybrid composite (Tetric Ceram), two microhybrid composites (Miris and Clearfil Photo Posterior) and, a nanofil composite (Filtek Supreme) were determined using a scraping method and a hardness tester. A total of 320 samples were prepared using the eight different materials (n = 10 samples for each subgroup). The scraping test was based on ISO 4049:2000. Vicker’s microhardness testing was carried out using hardness tester (Zwick 3212). Data were analyzed using one-way analysis of variance (ANOVA), Bonferroni and the Kolmogorov–Smirnov tests. Results: Best microhardness results were obtained with the LED light curing units and Tetric EvoCeram and Filtek Supreme achieved the highest hardness values. The nanofil composite, Filtek Supreme, showed the best curing depth results in all the tested light curing systems. Conclusions: The LEDs were found to be more successful than the halogen units with respect to both curing depth and microhardness properties. [ABSTRACT FROM AUTHOR]

Objectives: The present study aimed to compare the curing depth of polyacid-modified composite resins (PAM-C) and some representative composite resins as a function of shade and post-cure using a scraping method and a penetrometer.Methods: The curing depth of the PAM-C Hytac, F2000, Glasiosite, Dyract, Dyract AP, and Compoglass F and of the composite resins Durafill VS and Z100 were determined for shade A2 and A4 using a scraping method based on ISO 4049:2000 and a digital penetrometer. Samples were light-cured (800 mW/cm2 at 40 s) in bulk in split stainless steel molds. Immediately after light-curing or after a 24 h post-cure, the height of the cylinder of cured material was measured and taken as the curing depth.Results: For both test methods, the curing depth was independent of post-cure (P≥0.05), but differed significantly among materials and shade (P<0.001). Moreover, there was a significant interaction between the latter (P<0.001). Regression analysis generally demonstrated that there was no significant systematic or proportional difference between the test methods. The curing depths of the PAM-C F2000 and Glasiosite were comparable to that of the hybrid composite Z100, but greater than the curing depth of the microfilled composite Durafill VS. The PAM-C Dyract AP, Dyract, Compoglass F and Hytac had a curing depth smaller than that of the microfilled composite.Significance: The scraping method based on ISO 4049:2000 and a digital penetrometer give comparable curing depths for PAM-C. The curing depth greatly varies among the materials and can be considerably smaller than that of a microfilled composite resin. Shade A2 results in significantly greater values for the curing depth compared to shade A4, the effect depending quantitatively on the formulation of the material. [Copyright &y& Elsevier]

This study determined the depth of cure of different shades of a prosthetic composite material with the aim of evaluating the influence of shade variation on post-curing material properties. Four light shades having small tabs (A1, B1, C1 and D2) and four dark shades having higher tabs (A4, B4, C4 and D4) of a prosthetic composite (Artglass) for body paste based on the Vita Lumin Shade guide were selected. Specimens of each shade were exposed with the proprietary photo-curing unit (UniXS) for periods 20, 30, 60 and 90 s. The curing depth of the material for each shade was determined with a scraping technique described by the International Organization for Standardization (ISO 4049), and average values of groups of five specimens were compared using analysis of variance (ANOVA) and Scheffe’s S intervals (P < 0·05). The L*a*b* colour parameters of five specimens after 90 s exposure were measured using a small-area dental colorimeter (ShadeEye) in order to determine the colorimetric differences. Three-factor ANOVA revealed that the depth of cure was influenced by shade letter (A, B, C or D) and shade tab (1 and 2, or 4) as well as by the exposure period (P=0·05). Curing depth of the light shades was consistently greater than that of the dark shades. Among the eight shades selected, B1 shade demonstrated the greatest curing depth, while A4 shade exhibited the lowest curing depth. For all shades, longer exposure increased the depth of cure. All of the light shades exhibited higher L* values than any of the four dark shades. Curing depth of the composite material was found to be related to the Vita shade variation and the exposure period. [ABSTRACT FROM AUTHOR]

The aim of this study was to fabricate flowable resin composites, by incorporating Farnesol loaded Halloysite Nanotubes (Fa-HNT) as a filler and evaluate their physicochemical as well as biological properties. Chemical and morphological characterization of antibacterial filler, Fa-HNT were performed using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM). The antibacterial filler was mixed into composite material consisting of methacrylate monomers and dental glass fillers at concentrations of 1–20% (wt./wt.). It was observed that addition of mass fractions of Fa-HNT causes enhancement of compressive strength as well as flexural modulus of the composite. However, it significantly decreases flexural strength and degree of conversion. A significant antibacterial activity of dental composite was observed with increase in the area of zone of inhibition against the strains of Streptococcus mutans (S. mutans). There was no cytotoxicity observed by Fa-HNT resin composites on NIH-3T3 (mouse embryonic fibroblast cells) cell lines. A favourable integration of antibacterial filler with significant mechanical properties was achieved at concentrations from 7 to 13 wt% of Fa-HNT in dental composites, which is desirable in dentistry. Image 1 [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of three variables on the shear bond strength between a composite resin and dentin treated with a simplified Gluma system. Thickness of material (2 or 3 mm), distance between light guide and the surface of composite resin (0, 1, 3, or 5 mm) and irradiation time (10, 20, 40, or 60 s) were selected as variables. Thickness of material and distance between light guide and composite resin affected bond strength, but there was little influence of irradiation time under the conditions of the study. It is suggested that bond strength depends on the amount of light transmitted through the composite. [ABSTRACT FROM AUTHOR]

Kinetics and analytical formulas for radical-mediated thiol–ene photopolymerization were developed in this paper. The conversion efficacy of thiol–ene systems was studied for various propagation to chain transfer kinetic rate-ratio (RK), and thiol–ene concentration molar-ratio (RC). Numerical data were analyzed using analytical formulas and compared with the experimental data. We demonstrated that our model for a thiol–acrylate system with homopolymerization effects, and for a thiol–norbornene system with viscosity effects, fit much better with the measured data than a previous model excluding these effects. The general features for the roles of RK and RC on the conversion efficacy of thiol (CT) and ene (CV) are: (i) for RK = 1, CV and CT have the same temporal profiles, but have a reversed dependence on RC; (ii) for RK >> 1, CT are almost independent of RC; (iii) for RK << 1, CV and CT have the same profiles and both are decreasing functions of the homopolymerization effects defined by kCV; (iv) viscosity does not affect the efficacy in the case of RK >> 1, but reduces the efficacy of CV for other values of RK. For a fixed light dose, higher light intensity has a higher transient efficacy but a lower steady-state conversion, resulting from a bimolecular termination. In contrast, in type II unimolecular termination, the conversion is mainly governed by the light dose rather than its intensity. For optically thick polymers, the light intensity increases with time due to photoinitiator depletion, and thus the assumption of constant photoinitiator concentration (as in most previous models) suffers an error of 5% to 20% (underestimated) of the crosslink depth and the efficacy. Scaling law for the overall reaction order, defined by [A]m[B]n and governed by the types of ene and the rate ratio is discussed herein. The dual ratio (RK and RC) for various binary functional groups (thiol–vinyl, thiol–acrylate, and thiol–norbornene) may be tailored to minimize side effects for maximal monomer conversion or tunable degree of crosslinking. [ABSTRACT FROM AUTHOR]