N-acetylcysteine as a novel methacrylate-based resin cement component: effect on cell apoptosis and genotoxicity in human gingival fibroblasts.

BACKGROUND: N-acetylcysteine (NAC) reduces the cytotoxicity and genotoxicity induced by monomers leached from dental composite resins. Herein, we investigated the effects of methacrylate-based resin cement used in dental implant restoration on apoptosis and genotoxicity, as well as the antiapoptotic and antigenotoxic capabilities of its component, NAC. METHODS: The antioxidant NAC (0.1 or 1 wt.%) was experimentally incorporated into the methacrylate-based dental resin cement Premier®. The Premier® + NAC (0.1 or 1 wt.%) mixture was subsequently immersed into Dulbecco's modified Eagle's medium for 72 h, and used to treat human gingival fibroblasts (HGFs). The viability of HGFs was determined using the XTT assay. The formation of deoxyribonucleic acid (DNA) double-strand breaks (DNA-DSBs) was determined using a γ-H2AX assay. Reactive oxygen species (ROS), apoptosis, necrosis, and cell cycles were detected and analyzed using flow cytometry. RESULTS: The eluate of Premier® significantly inhibited HGF proliferation in vitro by promoting a G1-phase cell cycle arrest, resulting in cell apoptosis. Significant ROS production and DNA-DSB induction were also found in HGFs exposed to the eluate. Incorporating NAC (1 wt.%) into Premier® was found to reduce cell cytotoxicity, the percentage of G1-phase cells, cell apoptosis, ROS production, and DNA-DSB induction. CONCLUSION: Incorporating NAC (1 wt.%) into methacrylate-based resin cement Premier® decreases the cell cytotoxicity, ROS production, and DNA-DSBs associated with resin use, and further offers protective effects against the early stages of cell apoptosis and G1-phase cell cycle arrest in HGFs. Overall, our in vitro results indicate that the addition of NAC into methacrylate-based resin cements may have clinically beneficial effects on the cytotoxicity and genotoxicity of these materials.

Toxicity assessment of core-shell and superabsorbent polymers in cell-based systems.

The identification of health risks arising from occupational exposure to submicron/nanoscale materials is of particular interest and toxicological investigations designed to assess their hazardous properties can provide valuable insights. The core-shell polymers poly (methyl methacrylate)@poly (methacrylic acid-co-ethylene glycol dimethacrylate) [PMMA@P (MAA-co-EGDMA)] and poly (n-butyl methacrylate-co-ethylene glycol dimethacrylate)@poly (methyl methacrylate) [P (nBMA-co-EGDMA)@PMMA] could be utilized for the debonding of coatings and for the encapsulation and targeted delivery of various compounds. The hybrid superabsorbent core-shell polymers poly (methacrylic acid-co-ethylene glycol dimethacrylate)@silicon dioxide [P (MAA-co-EGDMA)@SiO2] could be utilized as internal curing agents in cementitious materials. Therefore, the characterization of their toxicological profile is essential to ensure their safety throughout manufacturing and the life cycle of the final products. Based on the above, the purpose of the present study was to assess the acute toxic effects of the above mentioned polymers on cell viability and on cellular redox state in EA. hy926 human endothelial cells and in RAW264.7 mouse macrophages. According to our results, the examined polymers did not cause any acute toxic effects on cell viability after any administration. However, the thorough evaluation of a panel of redox biomarkers revealed that they affected cellular redox state in a cell-specific manner. As regards EA. hy926 cells, the polymers disrupted redox homeostasis and promoted protein carbonylation. Concerning RAW264.7 cells, P (nBMA-co-EGDMA)@PMMA caused disturbances in redox equilibrium and special emphasis was placed on the triphasic dose-response effect detected in lipid peroxidation. Finally, P (MAA-co-EGDMA)@SiO2 activated cellular adaptive mechanisms in order to prevent from oxidative damage.

Evidential requirements for the regulatory hazard and risk assessment of respiratory sensitisers: methyl methacrylate as an example.

This review addresses the need for a framework to increase the consistency, objectivity and transparency in the regulatory assessment of respiratory sensitisers and associated uncertainties. Principal issues are considered and illustrated through a case study (with methyl methacrylate). In the absence of test methods validated for regulatory use, formal documentation of the weight-of-evidence for hazard classification both at the level of integration of individual studies within lines of evidence and across a broad range of data streams was agreed to be critical for such a framework. An integrated approach is proposed to include not only occupational studies and clinical evidence for the regulatory assessment of respiratory sensitisers, but also information on structure and physical and chemical factors, predictive approaches such as structure activity analysis and in vitro and in vivo mechanistic and toxicokinetic findings. A weight-of-evidence protocol, incorporating integration of these sources of data based on predefined considerations, would contribute to transparency and consistency in the outcome of the assessment. In those cases where a decision may need to be taken on the basis of occupational findings alone, conclusions should be based on transparent weighting of relevant data on the observed prevalence of occupational asthma in various studies taking into account all relevant information including the range and nature of workplace exposures to the substance of interest, co-exposure to other chemicals and study quality.

Challenges in the classification of chemical respiratory allergens based on human data: Case studies of 2-hydroxyethylmethacrylate (HEMA) and 2-hydroxypropylmethacrylate (HPMA).

Occupational asthma resulting from workplace exposure to chemical respiratory allergens is an important disease. No widely accepted or formally validated tests for the identification of chemical respiratory sensitizers. Consequently, there is a heavy reliance on human data from clinical examinations. Unfortunately, however, although such investigations are critical for the diagnosis of occupational asthma, and in guiding remedial actions, they do not reliably identify specific chemicals within the workplace that are the causative agents. There are several reasons for this, including the fact that specific inhalation tests conducted as part of clinical investigations are frequently performed with complex mixtures rather than single substances, that sometimes inhalation challenges are conducted at concentrations above the OEL and STEL, where effects may be confounded by irritation, and that involvement of immune mechanisms cannot be assumed from the observation of late asthmatic reactions. Further, caution should be taken when implicating substances on lists of "recognised" asthmagens unless they have undergone a formal weight of evidence assessment. Here the limitations of clinical investigations as currently performed for the purposes of regulatory classification and decision making are explored by reference to previously published case studies that implicate 2-hydroxyethylmethacrylate (HEMA) and/or 2-hydroxypropylmethacrylate (HPMA) as respiratory allergens.

Methacrylate Ester Monomers.

The Expert Panel for Cosmetic Ingredient Safety reviewed newly available studies since their original assessment in 2005, along with updated information regarding product types and concentrations of use, and confirmed that these 22 methacrylate ester monomers are safe as used in nail enhancement products in the practices of use and concentration as described in this report, when skin contact is avoided.

Toxicity of resin-matrix cements in contact with fibroblast or mesenchymal cells.

The main aim of this study was to perform an integrative review on the toxic effects of resin-matrix cements and their products in contact with fibroblasts or mesenchymal cells. A bibliographic search was performed on PubMed using the following search terms: "cytotoxicity" AND "fibroblast" OR "epithelial" OR "mesenchymal" AND "polymerization" OR "degree of conversion" OR "methacrylate" OR "monomer" AND "resin cement" OR "resin-based cement". The initial search in the available database yielded a total of 277 articles of which 21 articles were included in this review. A decrease in the viability of mouse fibroblasts ranged between 13 and 15% that was recorded for different resin-matrix cements after light curing exposure for 20 s. The viability of human fibroblasts was recorded at 83.11% after light curing for 20 s that increased up to 90.9% after light curing exposure for 40 s. Most of the studies linked the highest toxicity levels when the cells were in contact with Bis-GMA followed by UDMA, TEGDMA and HEMA. Resin-matrix cements cause a cytotoxic reaction when in contact with fibroblasts or mesenchymal cells due to the release of monomers from the polymeric matrix. The amount of monomers released from the resin matrix and their cytotoxicity depends on the polymerization parameters.

Assessment of Mechanical/Chemical Properties and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Sr/F-Bioactive Glass Nanoparticles and Methacrylate Functionalized Polyacids.

This study prepared low-toxicity, elemental-releasing resin-modified glass ionomer cements (RMGICs). The effect of 2-hydroxyethyl methacrylate (HEMA, 0 or 5 wt%) and Sr/F-bioactive glass nanoparticles (Sr/F-BGNPs, 5 or 10 wt%) on chemical/mechanical properties and cytotoxicity were examined. Commercial RMGIC (Vitrebond, VB) and calcium silicate cement (Theracal LC, TC) were used as comparisons. Adding HEMA and increasing Sr/F-BGNPs concentration decreased monomer conversion and enhanced elemental release but without significant effect on cytotoxicity. Rising Sr/F-BGNPs reduced the strength of the materials. The degree of monomer conversion of VB (96%) was much higher than that of the experimental RMGICs (21-51%) and TC (28%). The highest biaxial flexural strength of experimental materials (31 MPa) was significantly lower than VB (46 MPa) (p < 0.01) but higher than TC (24 MPa). The RMGICs with 5 wt% HEMA showed higher cumulative fluoride release (137 ppm) than VB (88 ppm) (p < 0.01). Unlike VB, all experimental RMGICs showed Ca, P, and Sr release. Cell viability in the presence of extracts from experimental RMGICs (89-98%) and TC (93%) was significantly higher than for VB (4%). Experimental RMGICs showed desirable physical/mechanical properties with lower toxicity than the commercial material.

Incorporation of dimethyl sulfoxide into experimental hydrophilic and hydrophobic adhesive resins: evaluation of cytotoxic activities.

This study evaluated the cytotoxicity of methacrylate-based resins containing dimethyl sulfoxide (DMSO). DMSO was incorporated into hydrophobic (R2) and hydrophilic (R5) resins at weight concentrations of 0, 0.01, 0.1, 1, 5, or 10 w/w %. Resin discs (n = 10/group) were prepared. Human gingival fibroblasts (HGF-1) were exposed to resin eluates for 24 h. Furthermore, dentin barrier test was performed using 3-D cultures of odontoblast-like cells (SV40 transfected pulp derived cells) with dentin slices of 400 µm thickness (n = 8). After acid etching of dentin, DMSO-modified resins were applied into the cavity part of the device and light-cured for 20 s. Cell viability (%) was assessed by MTT and analyzed spectrometrically. Data were analyzed by ANOVA and Tukey test (α = 0.05). Resin eluates showed statistically significantly lower % cell viability for all neat and DMSO-modified resins than seen for the negative control. Moreover, DMSO-R5 eluates resulted in significantly lower % cell viability than DMSO-R2 emulates. The dentin barrier test showed that DMSO-R2 did not result in significantly lower % cell viability, whereas incorporation of 1-10 w/w % DMSO into R5 resulted in significantly lower % of cell viability. Incorporating DMSO into hydrophilic self-etching resins may increase cytotoxicity. The biocompatibility is not influenced by the addition of DMSO into hydrophobic resin.

The activity of methacrylate esters in skin sensitisation test methods II. A review of complementary and additional analyses.

Allergic contact dermatitis is an important occupational health issue, and there is a need to identify accurately those chemicals that have the potential to induce skin sensitisation. Hazard identification was performed initially using animal (guinea pig and mouse) models. More recently, as a result of the drive towards non-animal methods, alternative in vitro and in silico approaches have been developed. Some of these new in vitro methods have been formally validated and have been assigned OECD Test Guideline status. The performance of some of these recently developed in vitro methods, and of 2 quantitative structure-activity relationships (QSAR) approaches, with a series of methacrylate esters has been reviewed and reported previously. In this article that first review has been extended further with additional data and complementary analyses. Results obtained using in vitro methods (Direct Peptide Reactivity Assay, DPRA; ARE-Nrf2 luciferase test methods, KeratinoSens and LuSens; Epidermal Sensitisation Assay, EpiSensA; human Cell Line Activation Test, h-CLAT, and the myeloid U937 Skin Sensitisation test, U-SENS), and 2 QSAR approaches (DEREK™-nexus and TIMES-SS), with 11 methacrylate esters and methacrylic acid are reported here, and compared with existing data from the guinea pig maximisation test and the local lymph node assay. With this series of chemicals it was found that some in vitro tests (DPRA and ARE-Nrf2 luciferase) performed well in comparison with animal test results and available human skin sensitisation data. Other in vitro tests (EpiSensA and h-CLAT) proved rather more problematic. Results with DEREK™-nexus and TIMES-SS failed to reflect accurately the skin sensitisation potential of the methacrylate esters. The implications for assessment of skin sensitising activity are discussed.

Genotoxic and cytotoxic potential of methacrylate-based orthodontic adhesives.

OBJECTIVES: The biocompatibility of methacrylate-based adhesives is a topic that is intensively discussed in dentistry. Since only limited evidence concerning the cyto- and genotoxicity of orthodontic adhesives is available, the aim of this study was to measure the genotoxic potential of seven orthodontic methacrylate-based adhesives. MATERIALS AND METHODS: The XTT assay was utilized to determine the cytotoxicity of Assure Plus, Assure Bonding Resin, ExciTE F, OptiBond Solo Plus, Scotchbond Universal Adhesive, Transbond MIP, and Transbond XT after an incubation period of 24 h on human gingival fibroblasts. We also performed the γH2AX assay to explore the genotoxic potential of the adhesives within cytotoxic dose ranges after an incubation period of 6 h. RESULTS: The XTT assay showed a concentration-dependent reduction in cell viability. The decrease in cellular viability was in the same dose range most significant for Assure Plus, rendering it the adhesive material with the highest cytotoxicity. Employing the γH2AX assay, a concentration-dependent increase in H2AX phosphorylation was detected, indicating induction of DNA damage. CONCLUSIONS: For most products, a linear correlation between the material concentration and γH2AX foci was observed. The most severe effect on γH2AX focus induction was found for Transbond MIP, which was the only adhesive in the test group containing the co-initiator diphenyliodonium hexafluorophosphate (DPIHP). CLINICAL RELEVANCE: The data indicate that orthodontic adhesives, notably Transbond MIP, bear a genotoxic potential. Since the study was performed with in vitro cultivated cells, a direct translation of the findings to in vivo exposure conditions should be considered with great diligence.

Illuminating the cellular and molecular mechanism of the potential toxicity of methacrylate monomers used in biomaterials.

The cytotoxicity of methacrylate-based biopolymers crosslinked by in situ photopolymerization has been attributed mainly to residual methacrylate monomers released due to incomplete polymerization. The residual monomers, primarily triethyleneglycol dimethacrylate or 2-hydroxyethyl methacrylate, may irritate adjacent tissue, or be released into the bloodstream and reach practically all tissues. Increased production of reactive oxygen species, which may be connected to concomitant glutathione depletion, has been the most noticeable effect observed in vitro following the exposure of cells to methacrylates. Radical scavengers such as glutathione or N-acetylcysteine represent the most important cellular strategy against methacrylate-induced toxicity by direct adduct formation, resulting in monomer detoxification. Reactive oxygen species may participate in methacrylate-induced genotoxic or pro-apoptotic effects and cell-cycle arrest via induction of corresponding molecular pathways in cells. A deeper understanding of the biological mechanisms and effects of methacrylates widely used in various bioapplications may enable a better estimation of potential risks and thus, selection of a more appropriate composition of polymer material to eliminate potentially harmful substances such as triethyleneglycol dimethacrylate.

Toxicological alert: Exposure to glycidyl methacrylate and cancer risk.

Glycidyl methacrylate (GMA; CAS no. 106-91-2) is a chemical monomer used in the manufacture of dental resins, can coatings and polymers. GMA has demonstrated toxicity to the ocular, digestive, respiratory and dermal systems. Human exposure occurs mainly in the workplace, but it can also happen through food. Although there were no available data on carcinogenicity of GMA, carcinogenic potential in the nasal cavity is highly expected. Further studies are needed to assess GMA exposure in humans. This study provides an alert of GMA human exposure and its genotoxic and carcinogenic potential.

[Role of LINC00310 in the glycidyl methacrylate-induced malignant transformation of human bronchial epithelial cell].

OBJECTIVE: To investigate the expression and biological significance of LINC00310 in the malignant transformation of human bronchial epithelial cells(16 HBE) induced by glycidyl methacrylate(GMA). METHODS: The 16 HBE cells recovered successfully used 1 µg/mL dimethyl sulfoxide(DMSO) as the solvent control group, and the final concentration was 8 µg/mL GMA as the treatment group, and were subcultured after repeated exposure 3 times for 72 hours each time. The 10 th, 20 th and 30 th generation cells of the GMA treatment group and corresponding DMSO control group were collected. The LncRNA microarrays was used to analyze the expression changes of LINC00310 in different periods, and the target gene and function prediction was performed by NCBI and cBioPortal bioinformatics database, and real-time quantification PCR(qPCR) was used to detect the relative expression levels of LINC00310 and predicted target genes. RESULTS: The result of the microarray showed that LINC00310 in the GMA-treated group was down-regulated by 2. 02-fold, up-regulated by 6. 17-fold, and up-regulated by 2. 03-fold in the pre-transformation, mid-term, and late, respectively. The result of qPCR confirmed that the expression of LINC00310 relative expression level of 10 th, 20 th and 30 th generation cells was consistent with the microarray result, which were down-regulated by 2. 76-fold, up-regulated by 2. 68-fold, and up-regulated by 3. 09-fold. Consistently, the relative expression of the target gene C-Myc was statistically significant in 20 th and 30 th generation cells. CONCLUSION: LINC00310 induced low expression in the early stage of malignant transformation of 16 HBE cells induced by GMA, and was highly expressed in the middle and late stages. It indicated that LINC00310 may play a cancer-promoting role in the process of cell malignant transformation through C-Myc.

Cell-Membrane-Inspired Silicone Interfaces that Mitigate Proinflammatory Macrophage Activation and Bacterial Adhesion.

Biofouling on silicone implants causes serious complications such as fibrotic encapsulation, bacterial infection, and implant failure. Here we report the development of antifouling, antibacterial silicones through covalent grafting with a cell-membrane-inspired zwitterionic gel layer composed of 2-methacryolyl phosphorylcholine (MPC). To investigate how substrate properties influence cell adhesion, we cultured human-blood-derived macrophages and Escherichia coli on poly(dimethylsiloxane) (PDMS) and MPC gel surfaces with a range of 0.5-50 kPa in stiffness. Cells attach to glass, tissue culture polystyrene, and PDMS surfaces, but they fail to form stable adhesions on MPC gel surfaces due to their superhydrophilicity and resistance to biofouling. Cytokine secretion assays confirm that MPC gels have a much lower potential to trigger proinflammatory macrophage activation than PDMS. Finally, modification of the PDMS surface with a long-term stable hydrogel layer was achieved by the surface-initiated atom-transfer radical polymerization (SI-ATRP) of MPC and confirmed by the decrease in contact angle from 110 to 20° and the >70% decrease in the attachment of macrophages and bacteria. This study provides new insights into the design of antifouling and antibacterial interfaces to improve the long-term biocompatibility of medical implants.

Bioinspired Surface Functionalization of Titanium Alloy for Enhanced Lubrication and Bacterial Resistance.

In clinics it is extremely important for implanted devices to achieve the property of enhanced lubrication and bacterial resistance; however, such a strategy has rarely been reported in previous literature. In the present study, a surface functionalization method, motivated by articular cartilage-inspired superlubrication and mussel-inspired adhesion, was proposed to modify titanium alloy (Ti6Al4V) using the copolymer (DMA-MPC) synthesized via free radical copolymerization. The copolymer-coated Ti6Al4V (Ti6Al4V@DMA-MPC) was evaluated by X-ray photoelectron spectroscopy, water contact angle, and Raman spectra to confirm that the DMA-MPC copolymer was successfully coated onto the Ti6Al4V substrate. In addition, the tribological test, with the polystyrene microsphere and Ti6Al4V or Ti6Al4V@DMA-MPC as the tribopair, indicated that the friction coefficient was greatly reduced for Ti6Al4V@DMA-MPC. Furthermore, the bacterial resistance test showed that bacterial attachment was significantly inhibited for Ti6Al4V@DMA-MPC for the three types of bacteria tested. The enhanced lubrication and bacterial resistance of Ti6Al4V@DMA-MPC was due to the tenacious hydration shell formed surrounding the zwitterionic charges in the phosphorylcholine group of the DMA-MPC copolymer. In summary, a bioinspired surface functionalization strategy is developed in this study, which can act as a universal and promising method to achieve enhanced lubrication and bacterial resistance for biomedical implants.

Cytotoxic effects to mouse and human gingival fibroblasts of a nanohybrid ormocer versus dimethacrylate-based composites.

OBJECTIVES: Tooth-colored composites have emerged as a standard restorative material in caries therapy and have largely replaced materials such as silver amalgam or glass ionomer cements. In addition to their superior esthetics and desirable mechanical properties, composites also comprise negative characteristics, such as wear, shrinkage, and an adverse biocompatibility. Modifications of classic resin-based dental composites have been developed to overcome these shortcomings. For example, ormocers are innovative inorganic-organic hybrid polymers that form a siloxane network modified by the incorporation of organic groups. Recently, a new ormocer, Admira Fusion (VOCO), was introduced to composite technology. The absence of cytotoxic matrix monomers leads to the hypothesis that ormocers have improved biocompatibility compared to resin-based dental restorative materials. MATERIALS AND METHODS: The aim of this study was to compare the cytotoxic effects of Admira Fusion to a nanohybrid composite (GrandioSO, VOCO) and a nanofiller composite (Filtek Supreme XTE, 3M Espe) on the standard dermal mouse fibroblasts (L929) and human gingival fibroblasts (GF-1) via a Cell Counting Kit-8 (CCK-8) assay. RESULTS: Admira Fusion was significantly less cytotoxic than GrandioSO and Filtek Supreme XTE to both the standard mouse dermal fibroblasts (L929) and human gingival fibroblasts. CONCLUSIONS: Compared to other resin-based dental restorative materials, the ormocer (Admira Fusion) possesses a superior biocompatibility in vitro. Future research studies are needed to confirm our results. CLINICAL SIGNIFICANCE: Clinically, dental practitioners and their patients might benefit from Admira Fusion in terms of reduced adverse biologic reactions compared to resin-based dental restorative materials.

The Power of Shielding: Low Toxicity and High Transfection Performance of Cationic Graft Copolymers Containing Poly(2-oxazoline) Side Chains.

We show the potential of oligo(2-ethyl-2-oxazoline) (Oxn)-shielded graft copolymers of (2-aminoethyl)-methacrylate and N-methyl-(2-aminoethyl)-methacrylate for pDNA delivery in HEK cells. For the effect of grafting density and side chain length concerning improved transfection properties through the concept of shielding to be investigated, copolymers were synthesized via the macromonomer method using a combination of cationic ring opening polymerization and reversible addition-fragmentation chain transfer polymerization to vary the degree of grafting (DG = 10 and 30%) as well as the side chain degree of polymerization (DP = 5 and 20). Investigations of the polyplex formation, in vitro flow cytometry, and confocal laser scanning microscopy measurements on the copolymer library revealed classical shielding properties of the Ox side chains, including highly reduced cytotoxicity and a partial decrease in transfection efficiency, as also reported for polyethylene glycol shielding. In terms of the transfection efficiency, the best performing copolymers (A- g-Ox5(10) and M- g-Ox5(10)) revealed equal or better performances compared to those of the corresponding homopolymers. In particular, the graft copolymers with low DG and side chain DP transfected well with over 10-fold higher IC50 values. In contrast, a DG of 30% resulted in a loss of transfection efficiency due to missing ability for endosomal release, and a side chain DP of 20 hampered the cellular uptake.

Preparation and Characterization of Novel Dental Material with High Shear Bond Strength.

HPMA (hydroxypropyl methacrylate) and Bis-GMA (bisphenol A glycerolate dimethacrylate), the main ingredients, and styrene, TEGDMA (triethylene glycol dimethacrylate), BPO (benzoyl peroxide) and camphoroquinone, the photo-initiators, and BHT (butylated hydroxytoluene), the photocatalyst were mixed by different ratios and stirred to investigate the compatibility of dental materials with photoinitiators. The degree of polymerization was checked and determination of the most ideal ratio for photopolymerization was followed by establishing the basic combination of styrene, HPMA, Bis-GMA, BHT, TEGDMA and HEMA. The mixture made in accordance to the predetermined ratio was stirred for 24 hours and was polymerized at a wavelength of 440 to 480 nm for 40 secs. The physical properties of each combination were also evaluated to analyze the functionality of the prepared resin cement. And also, the cytotoxicity of the samples was tested, and as a result, the cell lysis rate was 0% in negative control and 100% in positive control and 0% in S-1 combination which indicates that it does not possess cytotoxicity against cultured cells. It is considered suitable for commercializing and will be highly applicable as high quality dental resin cement.

Toxicological assessment of lower alkyl methacrylate esters by a category approach.

Categories and read-across are essential tools for supplying information for assessments of endpoints without data while minimizing animal testing. This study is based on the guidance of ECHA in its Read-Across Framework (RAAF). A category of C1 - C8 alkyl methacrylate esters (methyl, ethyl, n-butyl, iso-butyl and 2-ethylhexyl) was constructed to fill in missing information for human health endpoints using read-across as a permitted adaptation under EU REACH. The esters form a series with common functional groups, small incremental changes of electrophilicity by molecular weight, and rapid hydrolysis by ester cleavage. Read-across is justified by two common specific modes of action, direct electrophilic reaction of the parent compounds and the potential inherent toxicities of the common metabolites methacrylic acid and the corresponding alcohols. The toxicological profile is very similar for all category members and not driven by the alcohol metabolites. Data gaps can be filled in with high confidence based on the number of studies available, the effects therein observed and the toxicological profiles of the hydrolysis products. The guidance provided by the RAAF enabled data gaps to be filled in a robust manner.

Qualitative and Quantitative Evaluation of Cytotoxicity of Five Different One-Step Self-Etching Adhesives.

PURPOSE: To qualitatively and quantitatively compare the cytotoxic potentials of five different one-step self-etching adhesives: Prime&Bond One-Select (PB-OS), Optibond All-in-One (OB-AIO), G-Bond (GB), Clearfil Universal Bond (CUB), Single Bond Universal (SBU). MATERIALS AND METHODS: During the first stage of the study, the cytotoxic activities of the test materials were evaluated qualitatively using the direct contact method. In this method, the test materials were placed directly into a monkey kidney epithelial cell culture medium. Reaction zones which occurred in the culture medium were evaluated, in addition to the density and changes in the morphology of the cells. During the second stage, the cytotoxic potential of four different dilutions (1%, 0.1%, 0.01%, 0.001%) of the test materials on L929 rat fibroblast cells was quantitatively evaluated at three different time periods (24 h, 48 h, 72 h) with the MTT tetrazolium-based assay. RESULTS: In the first stage, a zone exceeding 1 cm was observed around or below SBU, CUB, GB and OB-AIO. In PB-OS, the zone borders were approximately 1 cm. In the second stage after the MTT assay, CUB was the most cytotoxic after 24 h, GB and SBU after 48 h, and OB-AIO after 72 h. CONCLUSION: All adhesives tested showed different degrees of cytotoxicity, which statistically significantly increased with dose. Changes were seen related to time.