Cytotoxicity and genotoxicity of a low-shrinkage monomer and monoacylphosphine oxide photoinitiator: Comparative analyses of individual toxicity and combination effects in mixtures

Impact of bisphenol A and analogues eluted from resin-based dental materials on cellular and molecular processes: An insight on underlying toxicity mechanisms

Dental resin systems, used for artificial replacement of teeth and their surrounding structures, have gained popularity due to the Food and Drug Administration's (FDA) recommendation to reduce dental amalgam use in high-risk populations and medical circumstances. Bisphenol A (BPA), an endocrine-disrupting chemical, is an essential monomer within dental resin in the form of various analogues and derivatives. Leaching of monomers from resins results in toxicity, affecting hormone metabolism and causing long-term health risks. Understanding cellular-level toxicity profiles of bisphenol derivatives is crucial for conducting toxicity studies in in vivo models. This review provides insights into the unique expression patterns of BPA and its analogues among different cell types and their underlying toxicity mechanisms. Lack of a consistent cell line for toxic effects necessitates exploring various cell lines. Among the individual monomers, BisGMA was found to be the most toxic; however, BisDMA and BADGE generates BPA endogenously and found to elicit severe adverse reactions. In correlating in vitro data with in vivo findings, further research is necessary to classify the elutes as human carcinogens or xenoestrogens. Though the basic mechanisms underlying toxicity were believed to be the production of intracellular reactive oxygen species and a corresponding decline in glutathione levels, several underlying mechanisms were identified to stimulate cellular responses at low concentrations. The review calls for further research to assess the synergistic interactions of co-monomers and other components in dental resins. The review emphasizes the clinical relevance of these findings, highlighting the necessity for safer dental materials and underscoring the potential health risks associated with current dental resin systems.

Light-Mediated Polymerization Catalyzed by Carbon Nanomaterials

Carbon nanomaterials, specifically carbon dots and carbon nitrides, play a crucial role as heterogeneous photoinitiators in both radical and cationic polymerization processes. These recently introduced materials offer promising solutions to the limitations of current homogeneous systems, presenting a novel approach to photopolymerization. This review highlights the preparation and photocatalytic performance of these nanomaterials, emphasizing their application in various polymerization techniques, including photoinduced i) free radical, ii) RAFT, iii) ATRP, and iv) cationic photopolymerization. Additionally, it discusses their potential in addressing contemporary challenges and explores prospects in this field. Moreover, carbon nitrides, in particular, exhibit exceptional oxygen tolerance, underscoring their significance in radical polymerization processes and allowing their applications such as 3D printing, surface modification of coatings, and hydrogel engineering.

Evaluation of the toxic potential of Bisphenol-A glycidylmethacrylate (BisGMA) on the third instar larvae of transgenic Drosophila

Introduction

In the present study the cytotoxic and genotoxic effects of Bisphenol-A glycidyl methacrylate (BisGMA) was studied on the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg9.

Materials and methods

The concentration of BisGMA i.e. 0.005, 0.010, 0.015 and 0.020 M were established in diet and the larvae were allowed to feed on it for 24 h.

Results

A dose dependent significant increase in the activity of β-galactosidase was observed compared to control. A significant dose dependent tissue damage was observed in the larvae exposed to 0.010, 0.015 and 0.020 M of BisGMA compared to control. A dose dependent significant increase in the Oxidative stress markers was observed compared to control. BisGMA also exhibit significant DNA damaged in the third instar larvae of transgenic D. melanogaster (hsp70-lacZ)Bg9 at the doses of 0.010, 0.015 and 0.020 M compared to control.

Conclusion

BisGMA at 0.010, 0.015 and 0.020 M was found to be cytotoxic for the third instar larvae of transgenic D. melanogaster (hsp70-lacZ) Bg9.

Enhanced Bonding to Caries-Affected Dentin Using an Isocyanate-Based Primer

Dental caries is the most common oral disease and the most common cause of resin restorations. In minimally invasive dentistry, the principle behind cavity preparation is to remove external caries-infected dentin (CID) and preserve internal caries-affected dentin (CAD) and sound dentin (SD). The cavity floor is mainly composed of CAD, but the poor bonding performance of CAD has become a widespread concern. This study evaluated the performance of a new collagen-reactive monomer (ITCM) used as a primer to improve the bonding performance of CAD. The experimental specimens were grouped as follows: SD, CAD, and ITCM-pretreated CAD (CAD-ITCM). Dentin slices were obtained for attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis. The bonded samples were subjected to microtensile bond strength analysis after 24 h of water storage or aging by thermocycling, and the bonding interface quality was evaluated by nanoleakage assessment, interfacial nanoindentation testing, and in situ zymography. Cytotoxicity experiments with ITCM were performed. ATR-FTIR showed that the isocyanate groups in ITCM can covalently bind and form hydrogen bonds with the collagen in CAD to mediate chemical bonding. ITCM pretreatment significantly improved the bond strength of CAD (P < 0.05), reduced interfacial nanoleakage, improved the sealing of the bonding interface, enhanced the homogeneity of the hybrid layer, and inhibited matrix metalloproteinase activity. In addition, ITCM presented acceptable biocompatibility for dental restorative application. Taken together, this study reported the application of ITCM to induce collagen-based chemical bonding in the CAD bonding system, which fills the gap in strategies to improve the bonding performance of CAD immediately and after aging and has important clinical application prospects.

Release of Monomers from Dental Composite Materials into Saliva and the Possibility of Reducing the Toxic Risk for the Patient

Background and Objectives: The objective of this study was (1) to measure the amount of monomers released into the saliva depending on the time elapsed after the hardening of the composite and on the type of monomer used; and (2) with the prolongation of the light-curing procedure, to publish information on whether it would be possible to influence the level of leached monomers. Materials and Methods: HPLC technique was used to monitor the levels of the unpolymerized monomers Bis-GMA, Bis/EMA, TEGDMA, and UDMA from the four commonly used composite materials, released into the saliva of a volunteer with intact dentition. The levels were monitored in 3 time periods during 24 h after composite hardening. From every composite material, 4 samples were formed and cured with an LED lamp for 10 s, 20 s, 40 s, and 60 s. After the light curing, the same polishing procedure was used and the samples were leached in blank saliva samples. Results: We observed that every monitored composite material eluted monomers into the saliva after its application. The amount of monomers depended on the time elapsed after the curing of the composite and on the type of composite used. A 40 s LED curing procedure can reduce the amount of leached monomers in comparison with the standard 20 s procedure, especially for monomers of higher molecular weight. Conclusions: Our study confirmed the hypothesis that the release of monomers gradually decreases with increasing time after the hardening of the composite filling.

Co-initiators of polymerization can modulate the inflammatory cytokine release without major cytotoxic effects in human dental pulp cells

To evaluate the cytotoxicity of co-initiators of polymerization and its influence on cytokine release from human dental pulp cells (hDPCs). Cells were isolated from the dental pulp of sound human third molars. The co-initiators dimethylaminoethyl amine benzoate-(EDAB), 2-(dimethylamino)ethyl methacrylate (DMAEMA); 2-Ethylhexyl 4-(dimethylamino)benzoate (EHA) and bis(4-methyl phenyl)iodonium hexafluorophosphate (BPI) were diluted in dimethylsulfoxide (DMSO) at different concentrations. In this way, experimental groups and one control (without treatment) were obtained. hDPCs (10 × 10⁴ cell per well) were seeded on 96 well plates and incubated at 37°C and 5% CO₂ for 48 h. After this, the cells were exposed to different concentrations of co-initiators cited for 24 h. After this time, the culture medium was removed, and the mitochondrial metabolism was evaluated by MTT assay, cell death by flow cytometry, and cytokine released (IL-1β, IL6, IL-8, IL-10, and TNF-α) was analyzed by MAGPIX assay. The data were analyzed by ANOVA one-way and Tukey's test. EHA, DMAEMA, and EDAB did not reduce the mitochondrial metabolism. BPI presented high toxicity with remarkable reduction (80%) after exposure to 1 mM. The cell death of all test groups was similar to control. After 24 h treatment, the IL-8 was up-regulated by all compounds, while IL-6 was upregulated after exposure to EHA and downregulated after DMAEMA stimulation. BPI, EHA, EDAB, and DMAEMA can trigger an initial inflammatory response, upregulating the IL-8 secretion in hDPCs in a compound-concentration-dependent manner; however, this was not accompanied by major cytotoxic effects at cell death or mitochondrial-metabolism levels.

Effect of monomer composition and filler fraction on surface microhardness and depth of cure of experimental resin composites

This study evaluated microhardness profiles and calculated depths of cure at 80% of the surface microhardness of experimental dental resin composites having different base monomer compositions and different filler fractions. Composites were prepared using four different base monomers (bisphenol A-glycidyl methacrylate [Bis-GMA], urethane dimethacrylate [UDMA], ethoxylated bisphenol-A dimethacrylate [Bis-EMA], and Fit-852) with triethylene glycol dimethacrylate (TEGDMA) used as a co-monomer at three filler:resin matrix weight percent fractions (50:50, 60:40, and 70:30). Uncured material was placed in 3D printed molds and light cured for 40 s from the top surface only. Knoop microhardness was measured at the top of the specimen, and at every 0.5 mm up to 4 mm in depth. Microhardness at the surface increased in all experimental composites as the filler fraction increased. When comparing base monomers, microhardness was the highest in UDMA-based composites, while Bis-GMA-based composites showed the lowest values. When comparing depth of cure as a function of base monomer type, both Bis-GMA and Bis-EMA showed significantly lower values than UDMA or Fit-852. Composites having 50 wt% filler showed a significantly higher depth of cure than those with 60 and 70 wt% filler. Base monomer and filler fraction significantly influence microhardness and depth of cure in these experimental composites.

Cytotoxicity of 3D printed resin materials for temporary restorations on human periodontal ligament (PDL-hTERT) cells

OBJECTIVES

Various dental resin materials are available for the fabrication of temporary restorations using modern additive printing methods. Albeit these materials are placed for several months in intimate contact with dental hard and soft tissues, including the gingival crevice, there exists only insufficient evidence on the biocompatibility of these materials. This in vitro study aimed to delineate the biocompatibility of 3D printable materials on periodontal ligament cells (PDL-hTERTs).

METHODS

Samples of four dental resin materials for additive fabrication of temporary restorations using 3D printing (MFH, Nextdent; GC Temp, GC; Freeprint temp, Detax; 3Delta temp, Deltamed), one material for subtractive fabrication (Grandio disc, Voco) and one conventional temporary material (Luxatemp, DMG) were prepared with a standardized size according to the manufacturer's instructions. Human PDL-hTERTs were exposed to resin specimens or eluates of the material for 1, 2, 3, 6 and 9 days. For determination of cell viability, XTT assays were performed. In addition, the expression of the proinflammatory cytokines interleukin 6 and 8 (IL-6 and 8) was assessed in the supernatants with ELISA. Cell viability and the expression of IL-6 and 8 in presence of the resin material or their eluates was compared with untreated controls. Immunofluorescence staining for IL-6 and IL-8, as well as scanning electron microscopy of the discs after culturing, were performed. Differences between groups were analyzed with Student´s t-test for unpaired samples.

RESULTS

Compared to untreated control samples, the exposure against the resin specimen induced strong reduction of cell viability in case of the conventional material Luxatemp (p < 0.001) and the additive material 3Delta temp (p < 0.001) irrespective of the observation period. On the contrary, the presence of eluates of the various materials induced only minor changes in cell viability. Considering IL-6 (day 2: p = 0.001; day 6 and 9: p < 0.001) and IL-8 (day 1: p = 0.001; day 2, 3, 6, 9: p < 0.001) their expression was strongly reduced in presence of the eluate of Luxatemp. Except for IL-6 at day 1 and 6 also the material 3Delta temp caused significant reduction of both proinflammatory mediators at any time point.

SIGNIFICANCE

The conventional material Luxatemp and the additive material 3Delta temp appear to severely affect cell viability when in direct contact with PDL-hTERTs. The other tested materials of this new category of additive materials and the subtractive material Grandio seem to induce only minor changes in direct contact with these cells. Therefore, they could serve as a viable alternative in the fabrication of temporary restorations.

A Pilot Study on Monomer and Bisphenol A (BPA) Release from UDMA-Based and Conventional Indirect Veneering Composites

This study aimed to investigate the release of common monomers from conventional (Dialog Vario, Enamel Plus HFO) and UDMA-based indirect veneering composites (VITA VM LC, GC Gradia). Ten cylindrical samples of each material were prepared (n = 40), immersed in HPLC grade water, and incubated for 24 h in an incubation shaker at 37 °C and 112 rpm. Extraction was performed following ISO 10993-12 and monomers were detected and quantified by HPLC-MS/MS. In all the samples, urethane dimethacrylate (UDMA) and bisphenol A (BPA) were quantifiable. Compared to water blanks, BPA levels were only elevated in the eluates from conventional composites. In all other samples, concentrations were in the range of extraneous BPA and were therefore clinically irrelevant. Low concentrations of Bisphenol A-glycidyl methacrylate (BisGMA) were found in one BPA-free composite and in both conventional materials. Statistical analyses showed that BPA-free materials released significantly less BisGMA and no BPA, while UDMA elution was comparable to elution from conventional materials. All measured concentrations were below reported effective cytotoxic concentrations. Considering these results, the substitution of BPA-derivatives with UDMA might be beneficial since BPA-associated adverse effects are ruled out. Further studies should be enrolled to test the biocompatibility of UDMA on cells of the oral environment.

Quality of Cure in Depth of Commercially Available Bulk-fill Composites: A Layer-by-layer Mechanical and Biological Evaluation

Despite their popularity, the use of bulk-fill composites remains controversial, both in terms of their properties and their in-depth development. The objectives of the present work were (1) to provide a more comprehensive evaluation of the quality of cure in depth of commercially available bulk-fill composites by combining various key mechanical and biological characterization methods, (2) to evaluate the inter-material differences when optimally cured, and (3) to evaluate the efficiency of an antioxidant-N-acetyl-cysteine (NAC)-to restrain the adverse effects of the leached components on cell viability. Nine bulk-fill composites (including flowable and high-viscosity materials) were investigated and compared to two conventional resin-based composites, one flowable and one high-viscosity restorative material. The materials were injected or packed into Teflon molds of various configurations, up to 6 mm material thickness. They were then light-cured from the top for 20 seconds with Bluephase G2 (Ivoclar Vivadent, irradiance = 1050 mW/cm2). The following physicomechanical properties were measured for the upper (0-2 mm), intermediate (2-4 mm), and lower (4-6 mm) layers: degree of conversion using Raman Spectrometry (DC, in %), microhardness using a Vickers micro-indenter before (VHN dry) and after 24 hours of storage in ethanol (VHN EtOH), and flexural strength (in MPa) and flexural modulus (in GPa) using a three-point bend test. Each composite layer and an uncured layer were also stored for one week in a standard cell growth medium to generate conditioned media. Human dental pulp cells were then cultured for 24 hours with the latter and cell viability was measured using an MTS assay. A similar experiment was repeated with conditioned media produced in contact with uncured composites, with and without the addition of 4 mM NAC. The data were subjected to a Shapiro-Wilk test, then one-way ANOVA or Kruskal-Wallis test, followed either by Tukey's test (inter-material comparison) or by Dunnett's or Dunn's test (comparison between layers relative to the upper one). The level of statistical significance was set at 0.05. Some materials (EverX, X-traF, VenusBF, X-traB) did not show any significant differences (p>0.05) for any of the properties considered between the intermediate layers compared to the upper one (considered as reference). Others displayed significant differences, at least for some properties, highlighting the value of combining various key mechanical and biological characterization methods when investigating the quality of cure in depth. Significant inter-material differences (p<0.05) were observed when comparing the properties of their upper layer, considered as "optimally" polymerized. Hence, one needs to consider the absolute property values, not only their relative evolution concerning layer thickness. Finally, the use of NAC appeared as beneficial to reduce the risk of harmful effects to dental pulp cells, especially in case of excessive thickness use, and may therefore be of potential interest as an additive to composites in the future.

Characteristics of a novel photoinitiator aceanthrenequinone-initiated polymerization and cytocompatibility of its triggered polymer

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AATQ is a novel photosensitizer with high-photoinitiating conversion efficiency at a relatively low concentration under 455 nm-blue light.

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Cytotoxicity of AATQ to different tissue types of cells is much lower than widely used-BAPO.

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Cytocompatibility of AATQ-initiated polymer is significantly superior to PANQ, but inferior to CQ.

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AATQ offers an alternative in industrial or biomedical areas, especially in the required low concentration of photoinitiators.

A number of photoinitiators are available in chemical industry, but less of them in biomedicine or clinical therapy due to the limitation of their cytotoxicity and biocompatibility. Thus, it is urgently necessary to find non-toxic or low-toxic photoinitiators to meet clinical demands. Aceanthrenequinone (AATQ) is a novel photosensitizer with high-photoinitiating ability, but no reports contribute, to date, to its cytotoxicity and biocompatibility. Here, primary cells and various cell lines were exposed to different concentrations of AATQ with or without irradiation. AATQ had the similar photoinitiating conversion efficiency to the extensively used bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO) and higher one than 9,10-phenanthrenequinone (PANQ) with the similar extent of polymerization in depth within a certain range, but displayed much lower cytotoxicity than BAPO under non-irradiation or irradiation. The biocompatibility of BisGMA/TEGDMA polymer prepared by AATQ was superior to that of PANQ, but inferior to that of camphorquinone (CQ) although the far lower dose of AATQ is enough to initiate polymerization of monomer than that of CQ. Hence, AATQ offers a valuable alternative in applications of industrial or biomedical areas.

A comparative in vitro study on monomer release from bisphenol A-free and conventional temporary crown and bridge materials

This study aimed to investigate the release of common monomers from two conventional and two bisphenol A (BPA)-free temporary crown and bridge materials. Cylindrical samples of all materials were prepared (N = 90; five samples for each material and cycle of analysis). All samples were immersed in high-performance liquid chromatography (HPLC)-grade water and incubated for 1 h, 12 h, 24 h, and 7 days in an incubation shaker at 37°C and 112 rpm. Extraction was performed in accordance with ISO 10993-12. Eluted monomers were detected and quantified by HPLC coupled with ultraviolet-visible spectroscopy and mass spectrometry (HPLC-UV/Vis-MS). Analysis of BPA was performed by HPLC coupled with ultraviolet-visible spectroscopy (HPLC-UV/Vis) and positive results were verified by HPLC-tandem mass spectrometry (HPLC-MS/MS). Neither bisphenol A-glycidyl methacrylate (Bis-GMA) nor BPA was quantifiable in any of the crown and bridge samples investigated in the present study. However, all samples contained triethylene glycol dimethacrylate (TEGDMA) and/or urethane dimethacrylate (UDMA) after 24 h of incubation. Statistical analysis showed that significantly more UDMA was released from the BPA-free materials than from the conventional materials. All concentrations of UDMA measured were below the effective cytotoxic concentrations previously reported. However, for a few materials, especially BPA-free temporary crown and bridge materials, the levels of UDMA were above previously reported potentially harmful concentrations for local cells. As BPA-free materials were introduced as being more biocompatible than materials containing BPA, substitution of Bis-GMA with UDMA should be further investigated.

Electrospun poly (L-lactic acid)/gelatine membranes loaded with doxorubicin for effective suppression of glioblastoma cell growth in vitro and in vivo

Electrospun membranes are attracting interest as a drug delivery system because of their material composition flexibility and versatile drug loading. In this study, the electrospun membrane was loaded with doxorubicin (DOX) via electrostatic adsorption for long-term drug delivery. DOX loading process was optimized by varying temperature, time, drug concentration, pH and ionic strength of solutions. The loading process did not impair the structural properties of the membrane. Next, we investigated the drug release kinetics using spectroscopic techniques. The composite membranes released 22% of the adsorbed DOX over the first 48 h, followed by a slower and sustained release over 4 weeks. The DOX release was sensitive to acidic solutions that the release rate at pH 6.0 was 1.27 times as that at pH 7.4. The DOX-loaded membranes were found to be cytotoxic to U-87 MG cells in vitro that decreased the cell viability from 82.92% to 25.49% from 24 to 72 h of co-incubation. These membranes showed strong efficacy in suppressing tumour growth in vivo in glioblastoma-bearing mice that decreased the tumour volume by 77.33% compared with blank membrane-treated group on Day 20. In conclusion, we have developed an effective approach to load DOX within a clinically approved poly (L-lactic acid)/gelatine membrane for local and long-term delivery of DOX for the treatment of glioblastoma.

Cytotoxic and cytocompatible comparison among seven photoinitiators-triggered polymers in different tissue cells

Photoinitiators (PIs) are widely used for photopolymerization in industrial area and recently paid close attention to in biomedical field. However, there are few reports on their toxicity to human health. Here we explored cytotoxicity and cytocompatibilty of seven commercial and industrial-used PIs for developing their potential clinical application. Phenylbis(acyl) phosphine oxides (BAPO), 2-Benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone (369), 4,4'-Bis(diethylamino) benzophenone (EMK), Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO), and 2-Isopropylthioxanthone (ITX) caused different extent cytotoxicities to four tissue types of cells at the concentrations of 1 to 50 μM under a non-irradiation condition, of which the BAPO cytotoxicity was the highest, whereas Ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate (TPOL) and Methyl benzoylformate (MBF) displayed the lowest cellular toxicity. The cell lines and primary cells appeared highly sensitive to BAPO toxicity, the primary lymphocytes relatively to photoinitiator 369 (369) and EMK toxicities, LO2 cells to EMK and TPO toxicities, the primary lymphocytes and HUVEC-12 cells to MBF toxicity, but only HEK293T cells not to 369 toxicity. Furthermore, these PIs led to increasing cytotoxicity to different extents after exposure to 455 nm blue light, which is consistent with non-irradiation tendency. All the cells presented low sensitivity to TPOL and MBF, of which TPOL-triggered polymer is dramatically superior in its cytocompatibility to MBF, and in its transparency to clinically exclusively-used camphorquinone (CQ). The novel findings indicate that BAPO is the most toxic among the seven PIs, but TPOL and MBF are the least toxic, directing their development and application. Combined their triggered polymer cytocompatibility and color with reported deep curing efficiency, TPOL is more promising to be applied especially to clinical practice.

Biophysical and Fluoride Release Properties of a Resin Modified Glass Ionomer Cement Enriched with Bioactive Glasses

The aim of this study was to evaluate the bond strength, microleakage, cytotoxicity, cell migration and fluoride ion release over time from a resin-modified glass-ionomer cement (RMGIC) enriched with bioactive glasses (BAGs) and a nanohybrid restorative polymer resin agent used as adhesion material in the cemented brackets. One hundred and twenty bovine lower incisors were divided into three groups: (Transbond Plus Self Etching Primer (TSEP)/Transbond XT (TXT), TSEP/ACTIVA, orthophosphoric acid gel/ACTIVA) and brackets were bonded. A bond strength test and microleakage test were applied. A fluoride release test was applied after 60 days for the TXT and ACTIVA group. To evaluate cytotoxicity and cell migration, a cell viability and scratch migration assay were done for each group. p values < 0.05 were considered significant. Regarding bond strength and microleakage test, no significant differences were found between TSEP/TXT and TSEP/ACTIVA. At 6.4 pH, ACTIVA showed a higher degree of fluoride ion release, which increased with acid pH (3.5), with a maximum fluoride secretion at 30 days. MTT assay revealed that TXT reduces the viability of gingival cells with significant differences (p < 0.001) compared to the untreated cells (control group). ACTIVA provides optimal adhesive and microfiltration properties, releases substantial amounts of fluoride ions in both acid and neutral media, and its biocompatibility is greater than that of traditional composite resin adhesive systems.

The Development of a Novel Device Based on Loss of Guidewire Resistance to Identify Epidural Space in a Porcine Model

Background

The application of additive manufacturing (3D printing) has been recently expanded to various medical fields. The new technique named loss of guide wire resistance (LOGR) was developed via 3D printing for the detection of epidural space using a guide wire instead of air or saline used in the loss of resistance (LOR) technique.

Methods

The prototype model of epidural space finder consists of a polyactic acid (PLA) or a resin. It was manufactured with 3D printing. Biocompatibility test (eluate and sterility tests) was performed in both products. The advantage of the newly developed device was compared with conventional loss of resistance (LOR) technique in a porcine model.

Results

Eluate and sterility tests revealed that the PLA was more biocompatible than the resin. The LOGR technique facilitated rapid access to epidural space compared with the LOR technique (41.64 ± 32.18 vs. 92.28 ± 61.46 seconds, N = 14, p=0.0102, paired sample t-test), without any differences in success rate (87.5%).

Conclusion

We conclude that LOGR technique is comparable to LOR technique to access the epidural space, although the advantage of either technique in terms of complications such as dural puncture or epidural hematoma is unknown. We demonstrated the potential benefit of 3D printer for the development of a new medical device for anesthesia.

The Photoinitiator Lithium Phenyl (2,4,6-Trimethylbenzoyl) Phosphinate with Exposure to 405 nm Light Is Cytotoxic to Mammalian Cells but Not Mutagenic in Bacterial Reverse Mutation Assays

Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP) is a free radical photo-initiator used to initiate free radical chain polymerization upon light exposure, and is combined with gelatin methacryloyl (GelMA) to produce a photopolymer used in bioprinting. The free radicals produced under bioprinting conditions are potentially cytotoxic and mutagenic. Since these photo-generated free radicals are highly-reactive but short-lived, toxicity assessments should be conducted with light exposure. In this study, photorheology determined that 10 min exposure to 9.6 mW/cm2 405 nm light from an LED light source fully crosslinked 10 wt % GelMA with >3.4 mmol/L LAP, conditions that were used for subsequent cytotoxicity and mutagenicity assessments. These conditions were cytotoxic to M-1 mouse kidney collecting duct cells, a cell type susceptible to lithium toxicity. Exposure to ≤17 mmol/L (0.5 wt %) LAP without light was not cytotoxic; however, concurrent exposure to ≥3.4 mmol/L LAP and light was cytotoxic. No condition of LAP and/or light exposure evaluated was mutagenic in bacterial reverse mutation assays using S. typhimurium strains TA98, TA100 and E. coli WP2 uvrA. These data indicate that the combination of LAP and free radicals generated from photo-excited LAP is cytotoxic, but mutagenicity was not observed in bacteria under typical bioprinting conditions.

Occurrence of multiple classes of emerging photoinitiators in indoor dust from E-waste recycling facilities and adjacent communities in South China and implications for human exposure

Photoinitiators (PIs) are indispensable additives in photopolymerization. PI-containing consumables, such as adhesives, coatings, UV-cured inks and light-sensitive materials, are widely used in various electronic products. Nevertheless, there is no information concerning the identification of PIs as emerging contaminants from e-waste recycling. In this study, 25 PIs, including 9 benzophenones (BZPs), 8 amine coinitiators (ACIs), 4 thioxanthones (TXs) and 4 phosphine oxides (POs), were analyzed in indoor dust from typical e-waste recycling facilities and adjacent rural communities, as well as from control urban communities. All 25 target PIs were detected in e-waste dust, while only 17 and 15 of the 25 target PIs were detected in local home dust and urban home dust, respectively. The PIs detected in all dust samples were dominated by BZPs and POs, followed by ACIs and TXs. Most PIs exhibited significantly higher levels in e-waste dust than local or urban home dust. The influence of PI contamination on the local household environment by dust diffusion and transport from near e-waste recycling facilities may be lower due to the low volatility of most PIs. Characteristic composition profiles of PIs for indoor dust from the e-waste recycling area were identified and compared to those from the control area. Significant correlations were found among almost all the frequently detected PIs in the e-waste dust, indicating their similar application in electronic products and common emission from e-waste recycling. The estimated daily intakes of PIs via dust ingestion for the e-waste dismantling workers, as determined by using Monte Carlo analysis, were several times higher than those for the local adult residents and the general urban adult residents, which should be an emerging concern. To the best of our knowledge, this is the first report showing that e-waste dismantling/recycling activities lead to largely common releases of a wide range of multiple classes of PIs.

Influence of the degree of conversion and Bis-GMA residues of bulk fill resins on tissue toxicity in an subcutaneous model in rats

AIM

To analyse the influence of the degree of conversion (DC) and light curing residues of different bulk fills (BFs) composites on the inflammatory profile in the subcutaneous tissue of rats.

MATERIALS AND METHODS

Resin disks of BF-resins and their active conventional resins (CR; 3M®, Ivoclar®, and Kerr®) were light-cured at 2 mm (BF-superficial) and 4 mm (BF-deep) thicknesses and analyzed by infrared spectroscopy (FTIR; n = 3/group; DC and light curing residues). Then, the disks were implanted in four quadrants in the subcutaneous tissue of Wistar rats (sham, CR, BF-superficial and RF-deep), and after 7, 14, and 28 days, the animals (n = 6/day) were euthanized for histological analysis of the intensity of the inflammatory process (scores 0-3). Kruskal-Wallis/Dunn and ANOVA/Bonferroni tests were used (p < 0.05, Graph Pad Prism 5.0).

RESULTS

The DC of CR 3M® did not differ significantly compared to BF-superficial and BF-deep resins (p = 0.235). The Ivoclar® and Kerr® resins showed a higher DC with CR and BF-superficial compared to the BF-deep (p = 0.005 and p = 0.011, rctively). Kerr® resins showed a higher Bis-GMA/UDMA ratio, especially in BF-deep resin (p < 0.05). 3M® and Ivoclar resins did not show high inflammation scores, but for Kerr® BF resins (superficial and deep), the inflammatory process was significantly higher than that in the CR and sham quadrants (p = 0.031).

CONCLUSION

The tissue inflammatory response after resin inoculation depends on the DC and light curing residues of Bis-GMA.

Identification of Photoinitiators, Including Novel Phosphine Oxides, and Their Transformation Products in Food Packaging Materials and Indoor Dust in Canada

Although photopolymerization is generally considered a green technology, the contamination of foodstuffs by photoinitiators (PIs), an essential component of photopolymerization systems, has recently attracted notice. Despite this interest, little attention has been paid to PI contamination in the environment. To date, only one study, performed in China, has reported the occurrence of PIs in the environment. In the present study, the occurrence of 25 PI additives with discrete molecular structures was investigated in food packaging materials and indoor dust. The PIs studied here include benzophenones (BZPs), thioxanthones (TXs), amine co-initiators (ACIs), and novel phosphine oxides (POs). Twenty-four PIs were detected in food packaging materials. Total concentrations of PIs (∑PIs) ranged between 122 and 44 113 ng/g, with a geometric mean (GM) of 3375 ng/g. The photodegradation of PIs in food packaging materials was investigated for the first time, and the half-lives of PIs in these materials were found to range from 32 to 289 h. These 24 PIs were also detected in indoor dust samples (GM of ∑PIs = 1483 ng/g). The relative abundances of different PIs were found to vary between the packaging materials and the indoor dust, which is attributed in part to the different stabilities of different PIs under simulated sunlight. Using standards synthesized in our lab, four TX transformation products (GM: 34.8 ng/g) were also detected in indoor dust. The concentrations of the transformation products were higher than the concentrations of the parent chemicals in indoor dust. Thus, further studies exploring human exposure to TXs should include these transformation products to avoid underestimation. This is the first report of PIs and relevant transformation products in the indoor environment in North America.

Cytotoxic and genotoxic potential of the type I photoinitiators BAPO and TPO on human oral keratinocytes and V79 fibroblasts

OBJECTIVES

Phenylbis(acyl) phosphine oxide (BAPO) and diphenyl(acyl) phosphine oxide (TPO) are alternative photoinitiators to camphorquinone (CQ) in dental resinous materials. Aim of this study was to investigate their cytotoxic/genotoxic potential in human oral keratinocytes (OKF6/Tert2) and Chinese hamster lung fibroblasts (V79) in comparison to CQ.

METHODS

Cells were exposed to different concentrations of BAPO and TPO (1-50μM). Cytotoxicity was evaluated using H33342 and MTT assay, cell proliferation by BrdU proliferation assay and microscopy. Effects on cellular redox homeostasis were assessed by detecting intracellular levels of reactive oxygen/nitrogen species (ROS/RNS) using the DCFH₂ assay and by quantification of mRNA expression of oxidatively regulated, cyto-protective enzymes. Genotoxic potential was determined by use of micronucleus (MN) assay.

RESULTS

BAPO and TPO induced a concentration-dependent decrease of cell number. BAPO and TPO showed 50- to 250-fold higher cytotoxicity than CQ. In contrast to CQ, both photoinitiators revealed no increase of intracellular ROS/RNS. However, BAPO (10μM) at least significantly induced mRNA-expression of redox-regulated proteins after 24h similar to 2.5mM CQ. Additionally, BAPO significantly raised the number of micronuclei, but only in V79 cells (10μM: 12±1, 2.5mM CQ: 15±1, medium control: 6±3). However, it also significantly decreased proliferation of these cells (10μM BAPO: 19.8%±7.3% compared to controls).

SIGNIFICANCE

BAPO and TPO revealed concentration-dependent cytotoxic effects in human oral keratinocytes and V79 cells. However, in contrast to CQ, no generation of intracellular ROS/RNS was found. Only BAPO induced genotoxicity in V79 cells.

Effect of the Bis-Dimethylamino Benzydrol Coinitiator on the Mechanical and Biological Properties of a Composite

To examine the effect of the alternative coinitiator 4,4'bis dimethylamino benzydrol (BZN) in degree of conversion (DC), mechanical and biological properties of experimental composites. The coinitiator BZN was used in three concentrations (0.2, 0.5 and 1.2%), and the coinitiator DMAEMA was used as control at the same concentrations as above. The molar concentration of camphorquinone (CQ) and coinitiators was kept constant (1:1). The composites were manipulated and submitted to microhardness test (VHN), flexural and compressive strength (in MPa), elastic modulus (GPa), DC (FT-IR) and in vitro cytotoxicity (against 3T3 fibroblastic cells) of the experimental resins. Data were subjected to two-way ANOVA and Tukey post-test (α=0.05). The experimental composite resin with BZN showed higher DC values compared to control DMAEMA groups. For the mechanical properties, microhardness values were higher in BZN groups; flexural strength and elastic modulus were similar between all the groups. Compressive strength for groups BZN0.5 and DMAEMA0.5 were not statistically different, being the lowest values attributed to group BZN0.2. The experimental resins with BZN and DMAEMA were considered nontoxic against 3T3 fibroblasts. The inclusion of the coinitiator BZN in experimental composites was considered nontoxic against 3T3 fibroblast cells, without compromising DC and mechanical properties.