Ethyl 4-dimethylaminobenzoate Research Articles

Advancing photopolymerization and 3D printing: High-Performance NiII complexes bearing N2O2 Schiff-base ligands as photocatalysts

New high-performance photocatalysts based on metal structures are being developed for polymerization. However, using low-cost metals while ensuring effectiveness is challenging. In this study, two NiII complexes NiL1 and NiL2 were synthesized using N2O2 Schiff-base ligands bearing π-extended rings (naphthaldehyde (H2L1) and phenylsalicylaldehyde (H2L2) groups), respectively. These complexes were characterized by FTIR, UV–Vis and 1H NMR spectroscopy, elemental analysis, cyclic voltammetry, and MALDI-TOF mass spectrometry. NiL1 and NiL2 were evaluated in photoinitiating system as new photocatalysts for the Free Radical Photopolymerization of Ethoxylated (3) Trimethylolpropane Triacrylate (TMPETA) for violet and green light. Three-component systems were employed in the presence of Di-tert-butyl-diphenyl iodonium hexafluorophosphate (Iod) and ethyl dimethylaminobenzoate (EDB). The absorption, luminescence, and redox properties of nickel complexes and ligands were explored and compared for a better understanding of their structure/reactivity relationship. The designed nickel complexes showed good photoinitiation abilities. NiL2 exhibited the highest monomer conversion, and it was investigated in the on–off process under green light irradiation, demonstrating the efficiency of the system in reactivating the polymerization process. An oxidative pathway mechanism was proposed based on free energy, steady state photolysis and electron spin resonance spin trapping experiments. The best system was successfully applied in cationic photopolymerization and 3D printing.

Salivary levels of eluents during Invisalign™ treatment with attachments: an in vivo investigation

BackgroundThe aim of the present study was to investigate qualitatively and quantitatively the elution of substances from polyester-urethane (Invisalign™) aligners and resin composite attachments (Tetric EvoFlow) in vivo.MethodsPatients (n = 11) treated with the aligners and attachments (16 per patient, without other composite restorations) for an average of 20 months, who were planned for attachment removed were enrolled in the study. Patients were instructed to rinse with 50 mL of distilled water upon entry and the rinsing solution was collected (before removal). Then, the attachments were removed with low-speed tungsten carbide burs for adhesive residue removal, a thorough water rinsing was performed immediately after the grinding process to discard grinding particle residues, and subsequently, after a second water-rinsing the solution was collected for analysis (after removal). The rinsing solutions were analyzed for targeted (LC-MS/MS: Bis-GMA, DCDMA, UDMA, BPA) and untargeted (LC-HRMS: screening of leached species and their degradation products) compounds.ResultsTargeted analysis revealed a significant reduction in BPA after attachment removal (4 times lower). Bis-GMA, DCDMA, UDMA were below the detection limit before removal but were all detectable after removal with Bis-GMA and UDMA at quantifiable levels. Untargeted analysis reviled the presence of mono-methacrylate transformation products of Bis-GMA (Bis-GMA-M1) and UDMA (UDMA-M1), UDMA without methacrylate moieties (UDMA-M2), and 4-(dimethylamino) benzoic acid (DMAB), the degradation product of the photo-initiator ethyl-4-(dimethylamino) benzoate (EDMAB), all after attachment removal. Several amino acids and endogenous metabolites were also found both before and after removal.ConclusionsElevated levels of BPA were traced instantaneously in patients treated with Invisalign™ and flowable resin composite attachments for the testing period. BPA was reduced after attachment removal, but residual monomers and resin degradation products were found after removal. Alternative resin formulations and attachment materials may be utilized to reduce eluents.

Role of Nanotitania Ceramic Particulate Filler on Mechanical and Wear Behaviour of Dental Composite

Nanotitania is a well-acceptable material in biomedical applications due to its excellent biocompatibility. However, its other performances in terms of physical properties, mechanical properties and specific wear rate have been the keen interest of researchers. The study aims to modify dental composite formulation by adding nanotitania filler in different mass fractions and study to investigate its influence on physical and mechanical properties. A conventional monomer matrix consisting of Bisphenol A-Glycidyl methacrylate (BisGMA), Urethane dimethacrylate (UDMA), Triethylene glycol dimethacrylate (TEGDMA), Camphor Quinone (CO), Ethyl-4-dimethylaminobenzoate (EDMAB) was first added and modified with varying nanotitania filler fractions (0,0.5,1,1.5 wt. %). The performance of newly formulated composites was investigated in four major parameters like apparent porosity, hardness, compressive strength and specific wear rate. All tests are performed as per ISO4049 standard which are requirements for fabrication, characterization, direct/indirect restoration of dental composite, inlays, onlays, veneers, crowns and bridges. Specific wear rate was estimated using pin on disk tribometer under constant load of 20N. Due to its extremely hard and brittle nature, the micro-hardness and compressive strength of resin composite on adding 0.5 wt.-% of nanotitania filler fraction (DC0.5TiO2) were increased by 68% and 16% respectively. Using a pin on disc tribometer, a wear assessment has been performed and it was found that under constant wear parameters and distilled water environmental conditions, the specific wear rate was decreased by 26 % on adding 0.5 wt.-% mass fraction of nanotitania. Nanotitania indicated excellent performance based on mechanical and wear properties and hence, it can be suggested to use nanotitania as a novel filler of dental composite for the replacement of other non-biocompatible ceramic filler.

Monitoring of photoinitiators in food products from Turkey

Photoinitiators (PIs) are the potential contaminants that may migrate from the packaging material to the food. These migrants could be a potential risk to human health. A total of 115 samples including 67 snack foods, 3 noodles, 10 milk samples, 8 baby foods, 9 fruit juices, 5 butter samples, and 13 kinds of cereal and their based-foodstuffs were analyzed for screening the occurrence of 15 photoinitiator residues including 4,4′-Dihydroxybenzophenone (44-DHBP), 2,4-Dihydroxybenzophenone (24-DHBP), 2,2′-Dihydroxy-4-methoxybenzophenone (DHBP), benzophenone (BP), 2-Hydroxy-4-methoxybenzophenone (OXBP), 2-Hydroxy-4-n-Octoxybenzophenone (2H4OBP), 2-Hydroxy-4-n-hexyloxybenzophenone (2H4HBP), 4-Isopropylthioxanthone (ITX), 4-Hydroxybenzophenone (4-HBP), 4-Methylbenzophenone (4-MBP), 4-Morpholinobenzaldehyde (44-MB), Ethyl 4-dimethylaminobenzoate (EDMAB), 2-Isopropylthioxanthone (2-ITX), 4,4′-Bis(diethylamino)-benzophenone (DEAB) and 2-Ethylanthraquinone (EA). BP was the most detected PI in different food categories. The highest BP concentration was 30.2 ppb in snack foods. Seven snack food samples had high concentrations of 44-DHBP, 4-MBP, ITX, and 2-ITX and their concentrations exceeded the relevant specific migration limit (SML) values. The other positive samples did not exceed the SML values recommended by the European Commission. Another predominant PI, namely ITX, was detected in all different food categories except baby foods. The highest ITX concentrations were in snack foods (17.2 ppb) and fruit juices (15 ppb).

Ethyl-2-(tosylmethyl)acrylate: A promising chain transfer agent for the development of low-shrinkage dental composites.

To evaluate the potential of ethyl-2-(tosylmethyl)acrylate (ASEE) as chain transfer agent for the development of low-shrinkage photopolymerizable dental composites. Composites containing 10, 20 and 30mol% of ASEE in their organic matrix were formulated. Camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDAB) (0.33wt%/0.60wt%), CQ/EDAB/Ivocerin® (0.33wt%/0.60wt%/0.10, 0.25 or 0.50wt%), CQ/EDAB/SpeedCure 938 (SC-938) (0.33wt%/0.60wt%/0.30, 0.50 or 1.00wt%) and Ivocerin® (0.50wt%) were used as photoinitiator systems. The glass transition temperature (Tg) and the crosslink density were determined by DMTA measurements. The flexural strength/modulus and ambient light working time were assessed according to ISO 4049. The shrinkage force was evaluated using a universal testing machine. The double bond conversion (DBC) was determined by NIR spectroscopy. DBC, flexural strength and modulus were measured after the storage of the specimens in deionized water at 37°C for 24h. The DBC, flexural strength and modulus data were analyzed by one-way ANOVA with p=0.05 as significance level. ASEE-based composites containing the classical initiator system CQ/EDAB exhibited low mechanical properties (flexural strength/modulus) and DBC. The screening of various photoinitiator systems showed that composites based on CQ/EDAB/Ivocerin® (0.33wt%/0.60wt%/0.50wt%), Ivocerin® (0.50wt%) or CQ/EDAB/SC-938 (0.33wt%/0.60wt%/1.00wt%) were particularly attractive. Indeed, the use of these photoinitiator systems enabled the formulation of composites containing up to 30mol% ASEE exhibiting excellent mechanical properties, high DBC, good network homogeneity and low shrinkage force values. Interestingly, the addition of SC-938 did not impair the ambient light working time of the uncured composites, whereas the incorporation of 0.50wt% Ivocerin® resulted in a strong decrease of this value. The addition of the allyl sulfone ASEE in combination with the initiator system CQ/EDAB/SC-938 (0.33wt%/ 0.60wt%/ 1.00wt%) is a promising strategy to develop low-shrinkage dental composites which exhibit excellent mechanical properties, low shrinkage force, high DBC and suitable ambient light working time.

Migration behavior of photoinitiators in polyethylene-coated paper for takeaway fast food

The migration of photoinitiators (PIs): benzophenone (BP), ethyl 4-dimethylaminobenzoate (EDAB), and 4-chlorobenzophenone (CBP), from polyethylene (PE)-coated paper to 4% (v/v) acetic acid and 10% (v/v) salt-simulated food solution was quantitatively analyzed using gas chromatography–mass spectrometry. The migration behavior of the three PIs was studied under three specific working conditions: conventional heating, microwave power, and random vibration level. The migration rate of the three PIs in acidic food simulants was ranked from BP > EDAB > CBP under the specific working conditions. The mobility of the three PIs increased with increasing temperature, microwave power, and random vibration acceleration in 4% (v/v) acetic acid by 10, 10, and 15%, respectively. The experimental migration data of three PIs in PE-coated paper under different temperatures and microwave powers were used to establish the Crank monolayer migration model according to Fick’s second law. The diffusion coefficient D increased with an increase in experimental conditions. According to the migration data under the condition of random vibration level, a mathematical model conforming to the Fick model was established, fitting the migration process. These results showed that conventional heating, microwave heating, and vibration could affect the food safety of PE-coated paper.

Strength of Fiber Posts with Experimental TiO2 and ZrO2 Particle Bonding—An SEM, EDX, Rheometric and Push-Out Strength Study

The present study aimed to prepare experimental adhesives (EAs): 5 wt.% titanium dioxide (TiO2) adhesive; and 5 wt.% zirconium oxide (ZrO2) adhesive; and analyze their impact on bond integrity of fiber posts to root dentin, and viscosity. The EA was composed of: bisphenol A glycol dimethacrylate (BisGMA); triethylene glycol dimethacrylate (TEGDMA); 2-hydroxyethyl methacrylate (HEMA); and ethyl 4-dimethylamino benzoate and camphorquinone. TiO2 and ZrO2 particles were individually incorporated into the EA at 5 wt.%, to form two groups (5% TiO2 and 5% ZrO2). The adhesives, with particles, were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The bonded interface was evaluated for adhesive–dentin penetration at the interface, using SEM. The study adhesive groups (EA, 5% TiO2 and 5% ZrO2) were analyzed for rheology and push-out bond strength of the fiber post to root dentin. Data were analyzed using analysis of variance and post hoc comparison. Both TiO2 and ZrO2 particles had irregular, non-uniform shapes. The EDX mapping showed the elemental presence of Ti (TiO2), Zr (ZrO2) and oxygen in formulated adhesives. The 5% TiO2 and 5% ZrO2 adhesives showed a decrease in viscosity, compared with the EA. Bond strength among the 5% TiO2 and 5% ZrO2 adhesives was statistically comparable (p > 0.05), but higher than the control group (10.57 ± 1.45 MPa) (p < 0.05). Reinforcement of the experimental dentin adhesive with 5% TiO2 or 5% ZrO2 increased the push-out bond strength of the fiber post to root dentin, in comparison with the EA. Particle-incorporated adhesives (5% TiO2 and 5% ZrO2) displayed decreased viscosity, compared with the EA (without particles).

Influence of TiO2 and ZrO2 Nanoparticles on Adhesive Bond Strength and Viscosity of Dentin Polymer: A Physical and Chemical Evaluation.

The present study aimed to formulate an experimental adhesive (EA) and reinforce it with 5 wt.% titanium dioxide (TiO2) or zirconium oxide (ZrO2) to yield 5% TiO2 and 5% ZrO2 adhesives, respectively, and then analyze the impact of this reinforcement on various mechanical properties of the adhesives. The EA contained a blend of monomers such as bisphenol A glycol dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and ethyl 4-dimethylamino benzoate and camphorquinone. The EA included ethyl 4-dimethylamino benzoate and camphorquinone photo-initiators, and diphenyliodonium hexafluorophosphate (DPIHP) was also included to act as an electron initiator. The TiO2 and ZrO2 nanoparticles were incorporated into the EA post-synthesis. To characterize the filler nanoparticles, scanning electron microscopy (SEM) and line-energy dispersive X-ray (EDX) spectroscopy were performed. The adhesives were characterized by analyzing their rheological properties, shear-bond strength (SBS), and interfacial failure types. Further, the resin–dentin interface was also analyzed via SEM. The TiO2 nanoparticles were spherically shaped on the SEM micrographs, while the ZrO2 nanoparticles were seen as non-uniformly shaped agglomerates. The EDX mapping demonstrated the presence of Ti and oxygen for TiO2 and Zr and oxygen for the ZrO2 nanoparticles. Both 5% TiO2 and 5% ZrO2 adhesives revealed decreased viscosity as compared with the EA. The 5% TiO2 adhesive demonstrated higher SBS values for both non-thermocycled (NTC) and thermocycled samples (NTC: 25.35 ± 1.53, TC: 23.89 ± 1.95 MPa), followed by the 5% ZrO2 adhesive group (NTC: 23.10 ± 2.22, TC: 20.72 ± 1.32 MPa). The bulk of the failures (>70%) were of adhesive type in all groups. The SEM analysis of the resin–dentin interface revealed the development of a hybrid layer and resin tags (of variable depth) for the EA and 5% TiO2 groups. However, for the 5% ZrO2 group, the hybrid layer and resin tag establishment appeared compromised. Reinforcement of the EA with TiO2 or ZrO2 caused an increase in the adhesive’s SBS (with the 5% TiO2 group demonstrating the highest values) in comparison with the EA (without nanoparticles). However, both nanoparticle-containing adhesives revealed decreased viscosity compared with the EA (without nanoparticles). Further studies investigating the impact of diverse filler concentrations on the properties of adhesives are suggested.

In situ generation of Ag nanoparticles during photopolymerization by using newly developed dyes‐based three‐component photoinitiating systems and the related 3D printing applications and their shape change behavior

AbstractSilver nanoparticles (AgNPs) play a crucial role in biology and medical research as their extensive and efficient antibacterial activity and high electrical and thermal conductivity. However, the generation of them with a certain morphology under mild conditions (under air, solvent‐free, room temperature, etc.,) is still a huge challenge. Herein, a simple one‐step method is proposed to generate AgNPs in situ at room temperature under air by combining the photopolymerization process with the formation process of AgNPs within a few minutes. In detailed, 12 different dyes based on 2,5‐diethylene‐cyclopentan‐1‐one were first synthesized and used as high‐performance type II photoinitiator. When using in conjunction of bis‐(4‐tert‐butylphenyl) iodonium hexafluorophosphate (Iod) and ethyl 4‐dimethylaminobenzoate (EDB), they can effectively boost the free radical photopolymerization (FRP) of polyethylene glycol diacrylate (PEG‐DA) and the cationic photopolymerization (CP) of 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate (EPOX) upon irradiation with LED@405 nm. Furthermore, all the formulations containing/without AgNPs can be successfully used to perform the direct laser write experiment. However, even if all of the obtained 3D patterns exhibited reversible swelling performance and shape‐memory effects caused by swelling and dehydration for the access to 4D printing, the presence of AgNPs will affect these properties.

High-performance sunlight induced polymerization using novel push-pull dyes with high light absorption properties

In this article, a series of three-component photoinitiating systems (PISs) based on push–pull dyes are proposed. The systems are composed of the newly synthesized push-pull dyes and different co-initiators, namely an iodonium salt and a tertiary amine (ethyl dimethylaminobenzoate EDB). Photoinitiation abilities and photochemical properties of the different investigated photoinitiating systems were studied in detail. Notably, the mechanisms related to the polymerization efficiencies were determined using different techniques such as UV–visible absorption and fluorescence spectroscopy. Moreover, the photoinitiation abilities of the three-component systems for the sunlight-induced polymerization processes were also examined, indicating that sunlight can act as an effective light source for photopolymerization. Finally, 3D patterns with a spatial resolution were successfully produced by the direct laser writing (DLW) approach, even with photosensitive resins containing silica fillers.

N-ethyl carbazole-1-allylidene-based push-pull dyes as efficient light harvesting photoinitiators for sunlight induced polymerization

In this article, the free radical polymerization of acrylates was successfully achieved with a series of twelve push-pull chromophores comprising the N-ethyl carbazole-1-allylidene group as the electron-donating group. Using this strong donor, the resulting dyes, never synthesized before, could efficiently initiate the free radical photopolymerization of acrylates upon mild irradiation conditions e.g. using sunlight. These novel multi-component systems comprising the above mentioned push-pull dyes, a tertiary amine (ethyl dimethylaminobenzoate EDB) and an iodonium salt could act as efficient photoinitiating systems (PISs) in free radical polymerization (FRP), leading to the formation of 3D patterns with precise shapes under the direct laser write (DLW) approach. Among these new PISs, dyes 3, 6, 7 and 8 were selected due to their efficient photoinitiation performances for chemical mechanism studies including steady state photolysis, fluorescence quenching measurements, electron spin resonance (ESR) spin-trapping experiments and cyclic voltammetry. Markedly, their excellent photochemical reactivities prompted us to investigate the performance of these multi-component photoinitiating systems upon sunlight as an ecofriendly approach. As a result, this research proved that sunlight could be used as a potential light source that can advantageously replace LEDs when highly reactive push-pull dyes are used as photosensitizers for the free radical photopolymerization of acrylate resins. Finally, 3D patterns could be prepared with the new photocomposites, and silica fillers could be even incorporated within the photosensitive resins so that a gradient of resolution could be successfully demonstrated.

Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing

This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. The different coumarin derivatives can also be employed in three component photoinitiating systems with a Iod/amine (ethyl 4-dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)) couple for FRP upon irradiation with an LED @ 405 nm. These compounds showed excellent photoinitiating abilities, and high polymerization rates and final conversions (FC) were obtained. The originality of this work relies on the comparison of the photoinitiating abilities of monofunctional (Coum1 and Coum2) vs. difunctional (Coum3) compounds. Coum3 is a combined structure of Coum1 and Coum2, leading to a sterically hindered chemical structure with a relatively high molecular weight. As a general rule, a high molecular weight should reduce the migration of initiating molecules and favor photochemical properties such as photobleaching of the final polymer. As attempted, from the efficiency point of view, Coum3 can initiate the FRP, but a low reactivity was observed compared to the monofunctional compound (Coum1 and Coum2). Indeed, to study the photochemical and photophysical properties of these compounds, different parameters were taken into account, e.g., the light absorption and emission properties, steady state photolysis, and fluorescence quenching. To examine these different points, several techniques were used including UV-visible spectroscopy, real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), fluorescence spectroscopy, and cyclic voltammetry. The photochemical mechanism involved in the polymerization process is also detailed. The best coumarins investigated in this work were used for laser writing (3D printing) experiments and also for photocomposite synthesis containing glass fibers.

Novel Push–Pull Dyes Derived from 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as Versatile Photoinitiators for Photopolymerization and Their Related Applications: 3D Printing and Fabrication of Photocomposites

A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 nm. Notably, polymerization reactions could be initiated with light-emitting diodes (LEDs) which constitute a unique opportunity to promote the free radical polymerization under mild conditions, i.e., low light intensity (e.g., sunlight) and under air. Photopolymerization is an active research field, and push–pull dyes have already been investigated for this purpose. Besides, it remains of crucial interest to investigate new reactive structures capable of efficiently initiating photopolymerization reactions. The plausible potential of these structures to act as efficient photoinitiators in vat photopolymerization (or 3D printing) and fabrication of photocomposites prompts us to select eleven new push–pull dyes to design multi-component photoinitiating systems activable with LEDs emitting at 405 nm. Precisely, a tertiary amine, i.e., ethyl dimethylaminobenzoate (EDB) used as an electron/hydrogen donor and an iodonium salt used as an electron acceptor were selected to behave as powerful co-initiators to construct three-component photoinitiating systems (PISs) with the different push–pull dyes. Among these new PISs, dye 8 and 9-based PISs could efficiently promote the free radical photopolymerization of acrylates upon exposure to a LED emitting at 405 nm also upon sunlight irradiation, highlighting their huge performance. Photoinitiating abilities could be explained on the basis of steady state photolysis experiments. Fluorescence measurements and electron spin resonance (ESR) spin-trapping experiments were also performed to obtain a deeper insight into the chemical mechanisms supporting the polymerization reaction and determine the way the initiating species, i.e., the radicals, are observed. Finally, two investigated dye-based PISs were applied to the fabrications of photocomposites. Three-dimensional patterns with excellent spatial resolutions were generated by the laser writing technique to identify the effects of photopolymerization of acrylates both in the absence and presence of fillers (silica). Interestingly, comparison between the 3D objects fabricated by the PISs/monomer systems and the PISs/monomer/filler photocomposites indicates that the newly designed photocomposites are suitable for practical applications.

Effect of curing-light attenuation on color stability and physical and chemical properties of resin cements containing different photoinitiators

This study aimed to evaluate the effect of light attenuation by ceramic veneers on the degree of conversion (DC), flexural strength (FS) and color change (CC) of resin cements containing different photoinitiators. Thus, samples included resin cements containing different photoinitiators: (a) camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDMAB); (b) CQ/4-(N,N-dimethylamino) phenethyl alcohol (DMPOH); (c) CQ/2(dimethylamino) ethyl methacrylate (DMAEMA); (d) CQ/ethyl 4-(dimethylamino)benzoate (EDMAB) + diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO); (e) TPO; and (f) phenylbis(2.4.6-trimethylbenzoyl)phosphine oxide (BAPO). Ceramic veneers (10 × 10 mm) were 0.4 mm, 0.7 mm, 1.0 mm or 1.5 mm thick. The light irradiance of a multiple-peak LED through ceramic veneers was measured (n = 5) using a spectrometer. DC (micro-Raman spectrometer) and FS (Bar-shaped specimens) were tested in cements with and without the veneers. Color change was evaluated before and after UV artificial aging. Data were submitted to ANOVA and Tukey's test (α = 0.05). The violet spectrum showed the lowest irradiance values through the veneer, considering all thicknesses. BAPO had the highest DC values for all veneers. CQ/EDMAB + TPO, CQ + EDMAB, and CQ + DMPOH showed similar DC values concerning all thicknesses. TPO (1.0 mm) showed the lowest DC and FS values. CQ + TPO and CQ/amines showed similar FS values. CQ + EDMAB and CQ + DMAEMA showed the highest color change values while TPO showed the lowest. It was concluded that the physical and chemical properties of the resin cement were improved with BAPO. CQ/EDMAB + TPO showed the greatest color stability, considering all veneer groups and control, without affecting the other properties assessed.

Bis(4-methyl phenyl)iodonium as an alternative component to diphenyliodonium in camphorquinone-based ternary initiating systems

ObjectiveTo evaluate the influence of different co-initiators (diphenyliodonium hexafluorophosphate - DPI - and bis(4-methyl phenyl)iodonium hexafluorophosphate – BPI) on chemical and mechanical properties of resins. MethodsNine experimental resins (50% Bis-GMA and 50% TEGDMA, w/w) with 60 wt% filler particles were formulated. The initiating system used was camphorquinone (CQ-1 mol%) and ethyl dimethylaminobenzoate (EDAB-2 mol%). Experimental groups were established according to DPI and BPI quantities (0.25, 0.5, 0.75, and 1 mol%). The control group was a resin containing only CQ-EDAB. Light transmission through the resin during polymerisation was analysed with a UV–vis spectrophotometer. Real-time polymerisation of the systems was evaluated using an FTIR spectrometer. Real-time polymerisation shrinkage strain was evaluated, and the flexural strength and modulus of materials were obtained by 3-point bending. Experimental groups were statistically analysed by Analysis of Variance and Tukey’s test (α = 0.05). Dunnett’s test was applied to compare experimental groups with control. ResultsLight transmission rapidly increased initially for resins containing DPI or BPI. After 30 s cure, the irradiance on the lower surface of resin specimens was similar for all groups. After 10 s of light irradiation, groups containing DPI and BPI had higher conversion than the control. However, conversion after 120 s post-irradiation was similar for all groups. The rate of polymerisation, shrinkage strain, and the maximum strain rate were higher for groups containing DPI/BPI. The use of iodonium salts increased the flexural strength and flexural moduli of resins. SignificanceDPI and BPI increased resin reactivity similarly. Increased rate of polymerization influenced light transmission through the resin in the first seconds of polymerisation and increased resin shrinkage and rate of shrinkage, as well as flexural strength and moduli.

Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems

The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm LED prompts us to develop new dyes based on push–pull structures. In the present paper, we chose two series of new dyes which possess indane-1,3-dione and 1H-cyclopenta naphthalene-1,3-dione groups as the electron-withdrawing groups, since they have the great potential to behave as sensitive and remarkable photoinitiators in vat photopolymerization/3D printing. When incorporated with a tertiary amine (ethyl dimethylaminobenzoate EDB, used as electron/hydrogen donor) and an iodonium salt (used as electron acceptor) as the three-component photoinitiating systems (PISs), and among a series of 21 dyes, 10 of them could efficiently promote the free radical photopolymerization of acrylates. Interestingly, steady state photolysis experiments revealed different behaviors of the dyes. Fluorescence experiments and free energy change calculations for redox processes were also carried out to investigate the relevant chemical mechanisms. Additionally, the formation of radicals from the investigated PISs was clearly observed by electron spin resonance (ESR) spin-trapping experiments. Finally, stereoscopic 3D patterns were successfully fabricated by the laser writing technique. In this work, the use of push–pull dyes based on the naphthalene scaffold as photoinitiators of polymerization is reported for the first time in a systematic study aiming at investigating the structure–performance relationship for irradiation carried out at 405 nm. By carefully selecting the electron donors used in the two series of push–pull dyes, novel and high-performance photoinitiating systems operating at 405 nm are thus proposed.

Naphthoquinone derivatives: Naturally derived molecules as blue-light-sensitive photoinitiators of photopolymerization

Two naphthoquinone derivatives, i.e. 5-hydroxy-1,4-naphthoquinone (5HNQ) and 2-hydroxy-1,4-naphthoquinone (2HNQ), combined with different additives such as diphenyliodonium hexafluorophosphate (Iod), N-vinylcarbazole (NVK), phenacyl bromide (R-Br), N-phenyl glycine (NPG) and ethyl 4-dimethylamino benzoate (EDB), are investigated as photoinitiating systems (PISs) for free radical polymerization of trimethylolpropane triacrylate (TMPTA) and cationic polymerization of triethyleneglycol divinyl ether (DVE-3). The photopolymerization of the thiol-ene system trimethylolpropane tris(3-mercaptopropionate) (Trithiol)/DVE-3 with 5HNQ or 2HNQ based PISs are also investigated. 5HNQ shows maximum absorption in visible light region (blue light) which thus has the potential to perform under the irradiation of blue LED light. For the free radical polymerization of TMPTA, 5HNQ/Iod/NPG shows the highest photoinitiating ability among all the naphthoquinone derivative-based PISs, while 2HNQ-based systems are inefficient. The addition of Trithiol to TMPTA can significantly increase the double bond conversion of TMPTA during the photopolymerization. For the cationic photopolymerization of DVE-3, 2HNQ/Iod shows the highest photoinitiating ability among all the naphthoquinone derivative-based photoinitiating systems. 5HNQ-based systems also demonstrate good photoinitiation ability for DVE-3, but with slower polymerization rate compared to 2HNQ-based systems. In thiol-ene photopolymerization, 5HNQ PISs shows better photoinitiation ability than 2HNQ PIs systems. The results illustrate that the position of hydroxyl group in 1,4-naphthoquinone molecules plays an important role on photoinitiation ability of naphthoquinone derivatives. Steady state photolysis and electron spin resonance trapping experiments are also carried out to evaluate the relevant photochemical mechanism.

Resin viscosity determines the condition for a valid exposure reciprocity law in dental composites

ObjectiveTo provide conditions for the validity of the exposure reciprocity law as it pertains to the photopolymerization of dimethacrylate-based dental composites. MethodsComposites made from different mass ratios of resin blends (Bis-GMA/TEGDMA and UDMA/TEGDMA) and silanized micro-sized glass fillers were used. All the composites used camphorquinone and ethyl 4-dimethylaminobenzoate as the photo initiator system. A cantilever beam-based instrument (NIST SRI 6005) coupled with NIR spectroscopy and a microprobe thermocouple was used to simultaneously measure the degree of conversion (DC), the polymerization stress (PS) due to the shrinkage, and the temperature change (TC) in real time during the photocuring process. The instrument has an integrated LED light curing unit providing irradiances ranging from 0.01W/cm2 to 4W/cm2 at a peak wavelength of 460nm (blue light). Vickers hardness of the composites was also measured. ResultsFor every dental composite there exists a minimum radiant exposure required for an adequate polymerization (i.e., insignificant increase in polymerization with any further increase in the radiant exposure). This minimum predominantly depends on the resin viscosity of composite and can be predicted using an empirical equation established based on the test results. If the radiant exposure is above this minimum, the exposure reciprocity law is valid with respect to DC for high-fill composites (filler contents >50% by mass) while invalid for low-fill composites (that are clinically irrelevant). SignificanceThe study promotes better understanding on the applicability of the exposure reciprocity law for dental composites. It also provides a guidance for altering the radiant exposure, with the clinically available curing light unit, needed to adequately cure the dental composite in question.

Photo-curing kinetics of hydroxyethyl acrylate (HEA): synergetic effect of dye/amine photoinitiator systems

The aim of this study is to examine and evaluate several dye/amine systems as photoinitiators for photopolymerization of 2-hydroxyethyl acrylate (HEA) monomer under visible light conditions. For this purpose, a series of dye/amine photoinitiators were formed using methylene blue (MB) or acridine orange (AO) as photosensitizers, and triethanolamine (TEOA), ethyl 4-(dimethylamino) benzoate (EDMAB), trioctylamine (TOA), and N,N-diméthylallylamine (DMAA) as co-initiators. The photopolymerization kinetic of the HEA monomer in the presence of proposed dye/amine systems was performed using Fourier-transform infrared spectroscopy (FTIR) analysis and the synergetic effect of the dye/amine photoinitiators systems on the photopolymerization efficiency was examined. Interestingly, (MB/EDMAB) system shows the better reactivity with a total conversion of HEA monomer.

Evaluation of alternative photoinitiator systems in two-step self-etch adhesive systems

ObjectiveThe aim of this study was to evaluate the effect of different photoinitiator systems on the cell viability and physico-chemical properties of an experimental adhesive resin of a two-step self-etch adhesive system. MethodsEight photoinitiators and coinitiators were evaluated, camphorquinone (CQ); ethyl-dimethylamino benzoate (EDAB); diphenyliodonium hexafluorophosphate (DPIHFP); 1,3-benzodioxole (BDO); piperonyl alcohol (AP); 1,3-diethyl-2-thiobarbituric acid (TBA); bisphenyl phosphinic oxide (BAPO); and diphenyl phosphinic oxide (TPO). Seven experimental adhesive resins (Bis-GMA:TEGDMA – 1:1 by wt%) were formulated by varying the initiation systems: RCQ+EDAB (control), RCQ+EDAB+DPHFP, RCQ+BDO, RCQ+AP, RCQ+TBA, RBAPO and RTPO. The cell viability of the different photoinitiators in their isolated form and after being incorporated into the adhesive resins was evaluated using the MTT assay. The degree of conversion within the hybrid layer (DC in situ) was evaluated by micro-Raman spectroscopy; the polymerization kinetics, by FTIR spectroscopy. The water sorption (Wsp) and solubility (Wsl) were calculated by using percentage of gain and loss of mass. Data were analyzed using One-way ANOVA and Kruskal-Wallis tests (α=0.05). ResultsWhen evaluated in their isolated form, the DPIHFP was considered cytotoxic in all concentrations evaluated. When incorporated into and adhesive resin, RCQ+TBA presented higher cell viability values than control and the highest values of DC in situ (p<0.05). Additionally, the use of CQ+TBA showed a higher cell viability when compared with the conventional CQ+EDAB system. SignificanceThe pair CQ+TBA could be potentially useful in the development of materials with improved biocompatibility.