Involvement of oxidative stress in mutagenicity and apoptosis caused by dental resin monomers in cell cultures

OBJECTIVE: This investigation studied the possibility that apoptosis as well as mutagenicity induced by resin monomers are mediated by oxidative stress. METHODS: A range of dilutions of three resin monomers (GMA, TEGDMA, and HEMA) was added to culture medium (DMEM/10% FBS), of V79-4 fibroblasts and RPC-C2A pulp cells for 24 h. Their cytotoxic effects were measured by a colorimetric functional assay (MTT). Chromosomal aberration induced by the resin monomers was investigated by counting micronuclei in V79-4 cells. The effects of the resin monomers on DNA fragmentation were viewed by agarose gel electrophoresis of DNA, isolated from RPC-C2A pulp cells that were treated by resin compounds. Resin monomer-induced apoptosis was further confirmed by flow cytometry (staining with both annexin V-FITC and PI). RESULTS: All monomers exhibited a dose-dependent cytotoxic effect, and the ranking of the cytotoxicity based on TC50 was GMA > TEGDMA > HEMA. The resin monomer-induced cytotoxicity was significantly decreased by co-treatment with N-acetylcystein (NAC), an antioxidant. The authors also confirmed a dose-dependent genotoxicity of the resin monomers that had induced micronucleated cells in V79-4 fibroblasts. Similar to the effects on cytotoxicity, NAC reduced the numbers of micronuclei in comparison with those generated by the resin monomers. The preventive effects of NAC were also observed in monomer-induced apoptosis in RPC-C2A cells. A DNA ladder pattern, characteristic of apoptosis, was shown at cytotoxic concentrations, but NAC blocked the resin monomer-mediated DNA fragmentation. The preventive effects of NAC on apoptosis were confirmed by Annexin V staining. Cells exposed to 300 microM GMA, 7 mM TEGDMA, or 14 mM HEMA for 24 h showed a significant increase in apoptotic cells, while NAC co-treatment caused a reduction in apoptotic cells compared to controls. SIGNIFICANCE: These findings suggest that glutathione depletion and oxidative stress are responsible for GMA, TEGDMA, and HEMA-induced mutagenicity and apoptosis.     

Inhibition of TEGDMA and HEMA-induced genotoxicity and cell cycle arrest by N-acetylcysteine.

OBJECTIVES: Dental resin monomers like triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are able to cause an imbalance of the redox state in mammalian cells. The resulting oxidative stress originating from reactive oxygen species (ROS) has been associated with cytotoxicity. We hypothesized that ROS might contribute to the generation of genotoxicity by TEGDMA and HEMA as well. Therefore, we examined the formation of micronuclei in V79 cells by both resin monomers in the presence of the antioxidant N-acetylcysteine (NAC), which scavenges ROS. In addition, we analyzed the effects of TEGDMA and HEMA on the normal cell cycle in the presence of NAC. METHODS: V79 fibroblasts were exposed to increasing concentrations of TEGDMA and HEMA in the presence and absence of NAC for 24h. Genotoxicity was indicated by the formation of micronuclei. The modification of the normal cell cycle was analyzed by flow cytometry (FACS). RESULTS: A dose-related increase in the number of micronuclei in V79 cells-induced by TEGDMA and HEMA indicated genotoxicity of both chemicals. However, the formation of micronuclei was reduced in the presence of 10 mmol/L NAC, indicating its protective role. A cell cycle delay in G2 phase caused by TEGDMA was absent when cells were co-treated with NAC. Similarly, the presence of NAC led to a reversion of the cell cycle delay in HEMA-treated cell cultures. SIGNIFICANCE: Our results suggest that genotoxic effects and the modification of the cell cycle caused by TEGDMA and HEMA are mediated, at least in part, by oxidative stress.     

Genotoxicity and cytotoxicity of dental materials in human lymphocytes as assessed by the single cell microgel electrophoresis (comet) assay

OBJECTIVES: Resin monomers may be released from restorative dental materials and can diffuse into the tooth pulp or the gingiva, and can reach the saliva and the circulating blood. Whereas the cytotoxic potential of some components has been clearly documented, possible genotoxicity in human target cells demands further investigation. METHODS: The Comet assay was used to quantify DNA single strand breaks, alkali labile and incomplete excision repair sites in lymphocytes of 10 volunteers. The xenobiotics investigated were 2-hydroxyethylmethacrylate (HEMA), triethyleneglycoldimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A-glycidyl methacrylate (Bis-GMA) with N-methyl-N'-nitro-N-nitrosoguanidine and dimethyl sulfoxide as controls. DNA migration was quantified using the tail moment according to Olive (OTM) and DNA migration was considered to be elevated at OTM levels above 2. Cytotoxicity was monitored using trypan blue. RESULTS: In the negative controls, OTM ranged between 1.0 and 1.2. With HEMA concentrations above 10(-6)M, TEGDMA 10(-3)M, Bis-GMA 10(-4)M, and UDMA above 10(-6)M relevant enhancements of DNA migration (OTM>2) were achieved. At higher concentrations of up to 2.5x10(-2) induced DNA migration was expressed by OTM of 3.3 for HEMA, 4.5 for TEGDMA, 7.4 for Bis-GMA, and 2.8 for UDMA. Relevant cytotoxic effects were also seen but vitality levels were at a critical range of 71% for Bis-GMA and 73% for TEGDMA, only. SIGNIFICANCE: In higher concentration levels, all tested substances induced significant but minor enhancement of DNA migration in the Comet assay as a possible sign for limited genotoxic effects. However, with the highest levels of DNA migration being combined with elevated cytotoxic effects, a low in vivo genotoxic strain appears to be posed by the resin components.     

Pattern of cell death after in vitro exposure to GDMA, TEGDMA, HEMA and two compomer extracts.

OBJECTIVES: In vitro exposure to chemical compounds in dental materials may cause cell death by apoptosis, necrosis or a combination of both. The aim of this paper was to evaluate aqueous extracts of freshly cured compomers Freedom (SDI) and F2000 (3M ESPE), and constituents identified in the extracts, GDMA (glycerol dimethacrylate), TEGDMA (triethylene glycol dimethacrylate) and HEMA (2-hydroxyethyl methacrylate) for their ability to induce necrosis and apoptosis in primary rat alveolar macrophages and the J744A1 macrophage cell line. METHODS: The cells were exposed to either extracts of freshly cured samples of the products or to one of the constituents identified in the extracts. Cytotoxicity and necrosis were assayed by MTT test and fluorescence microscopy, respectively. Apoptosis was assayed by fluorescence microscopy and flow cytometry. RESULTS: Concentration-related apoptosis and necrosis were found in both cell types after exposure to extracts from Freedom and F2000. GDMA appeared to be the most cytotoxic of the tested constituents in the J744A1 cell line as evaluated by the MTT test. TEGDMA was more cytotoxic than HEMA using the MTT test and fluorescence microscopy, whereas HEMA caused a greater accumulation of apoptotic cells seen by fluorescence microscopy and flow cytometry. For various concentrations of HEMA and TEGDMA, the extent of apoptosis appeared inversely related to the cytotoxicity evaluated by the MTT test. SIGNIFICANCE: As an apoptotic response elicits less inflammatory response in the surrounding tissues than a necrotic process, the role of cell death pattern could be important for the evaluation of the biocompatibility of dental materials.     

Apoptosis induced by the monomers HEMA and TEGDMA involves formation of ROS and differential activation of the MAP-kinases p38, JNK and ERK.

OBJECTIVES: Cytotoxic methacrylate monomers have been identified in aqueous extracts of freshly cured compomers. Some of these compounds, including HEMA and TEGDMA, induce apoptosis and necrosis in vitro. The aim of the present study was to elucidate possible signaling pathways involved in apoptosis following exposure to HEMA or TEGDMA in a salivary gland cell line. METHODS: The cells were exposed to various concentrations of HEMA or TEGDMA. ROS formation was determined by dichlorofluorescein assay. Phosphorylated MAP-kinases ERK1/2, p38 and JNK, as well as specific caspases were identified by Western blotting. Apoptosis was assayed by fluorescence microscopy. RESULTS: HEMA or TEGDMA exposure resulted in ROS formation and concentration-dependent apoptosis as well as phosphorylation of ERK. Phosphorylation of JNK and p38 was induced by HEMA. Selective inhibitors of ERK and JNK modified the apoptotic response after HEMA and TEGDMA exposure, whereas p38 inhibition modified the apoptotic response only after HEMA exposure. Vitamin C reduced HEMA-induced apoptosis. SIGNIFICANCE: ROS formation and differential MAP kinase activation appear to be involved in the apoptotic response following exposure to HEMA and TEGDMA.     

Alterations of energy metabolism and glutathione levels of HL-60 cells induced by methacrylates present in composite resins

OBJECTIVES: Methacrylic compounds such as 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA) and bisphenol A glycerolate (1 glycerol/phenol) dimethacrylate (Bis-GMA) are largely present in auto- or photopolymerizable composite resins. Since the polymerization reaction is never complete, these molecules are released into the oral cavity tissues and biological fluids where they could cause local adverse effects. The aim of this work was to verify the hypothesis that the biological effects of HEMA, TEGDMA and Bis-GMA - at a non-cytotoxic concentration - depend on the interaction with mitochondria and exert consequent alterations of energy metabolism, GSH levels and the related pathways in human promyelocytic cell line (HL-60). METHODS: The biological effects of methacrylic monomers were determined by analyzing the following parameters: GSH concentration, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione reductase (GR) activity, oxygen and glucose consumption and lactate production along with cell differentiation and proliferation. RESULTS: All monomers induced both cellular differentiation and decrease in oxygen consumption. Cells treated with TEGDMA and Bis-GMA showed a significant enhancement of glucose consumption and lactate production. TEGDMA and HEMA induced GSH depletion stimulating G6PDH and GR activity. CONCLUSIONS: All the monomers under study affect the metabolism of HL-60 cells and show differentiating activity. Since alterations in cellular metabolism occurred at compound concentrations well below cytotoxic levels, the changes in energy metabolism and glutathione redox balance could be considered as potential mechanisms for inducing clinical and sub-clinical adverse effects and thus providing useful parameters when testing biocompatibility of dental materials.     

Quantitative analysis of TEGDMA and HEMA eluted into saliva from two dental composites by use of GC/MS and tailor-made internal standards.

OBJECTIVES: The use of resin-based dental restorative materials is rapidly increasing, concurrently the biocompatibility of the materials is under investigation. Attention has been placed on studies addressing the cytotoxic, genotoxic and estrogenic potential of these materials. Therefore, the degree of exposure to eluted compounds from the dental materials is of high interest. The aim of this study was to assess the amounts of 2-hydroxyethyl methacrylate (HEMA) and triethyleneglycol dimethacrylate (TEGDMA), released from two composites, eluting into human saliva. To improve the method of quantification, three tailor-made internal standards were synthesized. METHODS: Specimens made from two composites (Tetric EvoCeram and Filtek Z250) were polymerized and immersed in human saliva for 24h. Eluted TEGDMA and HEMA were identified and quantified. The quantitative analyses were performed by use of combined gas chromatography-mass spectrometry (GC/MS) with tailor-made internal standards synthesized by dissolving HEMA or TEGDMA in methanol and reducing the double bond of the methacrylate group by hydrogenation with 1H2 and 2H2 (D2) gas. RESULTS: HEMA was released from both materials, whereas TEGDMA eluted from Filtek Z250 only. Full scan GC-MS analysis of each tailor-made internal standard demonstrated one peak only, which was well separated from the corresponding analyte's peak and with no traces of HEMA or TEGDMA. SIGNIFICANCE: The quantification method seems well suited for in vivo analysis, and the three standards synthesized represent an improved tool for quantification of the eluted monomers. The synthesis may be applied to other methacrylate monomers to produce tailor-made standards for quantification.     

On permeability of methyl methacrylate, 2-hydroxyethyl methacrylate and triethyleneglycol dimethacrylate through protective gloves in dentistry

Continuous glove use is more common in dentistry than in most other occupations, and the glove should offer protection against blood-borne infections, skin irritants and contact allergens. Methacrylate monomers are potent contact allergens, and it is known that these substances may penetrate the glove materials commonly used. The aim of this study was to assess the permeability of various types of gloves to methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA) and triethyleneglycol dimethacrylate (TEGDMA) with special reference to combinations with ethanol or acetone. The permeation rate and time lag breakthrough (lag-BT) for MMA (neat, or diluted to 30% in ethanol or acetone), HEMA (30% in water, ethanol, or acetone) and TEGDMA (30% in ethanol or acetone) were investigated for different protective gloves. Nine different types of gloves were tested for one or several of these methacrylates. The lag-BT for neat MMA was 相似文献   

Bonding of light-cured glass ionomer cement to polycarbonate resin treated with experimental primers

The effect of experimental primers on the shear bond strength of polycarbonate composite resin with light-cured glass ionomer cements was investigated. Mixtures of methylmethacrylate (MMA) with the comonomers 2-hydroxyethyl methacrylate (HEMA), triethyleneglycol methacrylate (TEGDMA), and bisphenol-A-glycidymethacrylate (bisGMA) were used as primers. Polycarbonate composite resin rods of circular cross section and plates were bonded, with and without precured and nonprecured primers, using 2 light-cured glass ionomer cements (commercially available [LC] and experimental [EX]). In addition, commercial polycarbonate composite resin brackets with precured 50% TEGDMA/MMA primer were bonded to etched human enamel with both cements. Shear bond strengths were measured. Results were compared by ANOVA and Scheffe's tests at P = .05. The 30% HEMA/MMA, 50% TEGDMA/ MMA, 10% bisGMA/MMA, and 30% bisGMA/MMA primers produced the higher shear bond strengths (9.5 to 20.8 MPa) with LC and EX to polycarbonate composite resin. The 50% TEGDMA/MMA primer was most effective in improving the shear bond strengths of both LC and EX. Precured 50% TEGDMA/ MMA primer on a commercial resin bracket was effective in providing good shear bond strength to enamel.     

Effects of three resin monomers on the cellular glutathione concentration of cultured human gingival fibroblasts.

OBJECTIVES: Oral and systemic cells are permanently exposed to various types of xenobiotics, such as dental restorative materials, which may subsequently cause adverse effects. Objective of the present investigation was to analyze the effects of three important resin monomers on the glutathione metabolism of human gingival fibroblasts after an incubation period of 4h. METHODS: Cells were exposed to various concentrations of 2-hydroxyethyl methacrylate (HEMA; 0.1-10 mM), triethylene-glycol dimethacrylate (TEGDMA; 0.05-2.5 mM), and urethane dimethacrylate (UDMA; 0.005-0.25 mM). Subsequently, cellular glutathione (GSH) concentrations were determined after a treatment period of 4h using the monobromobimane assay. Data were statistically evaluated using Tukey ANOVA with p<0.05. RESULTS: GSH depletion was dependent on the type of the resin monomer: UDMA>TEGDMA>HEMA. The concentrations for a 50%-reduction of cellular GSH varied between 0.1 mM (0.05 mM) (UDMA), 0.33 mM (0.09 mM) (TEGDMA), and 1.6 mM (0.8 mM) (HEMA). Simultaneously, no decrease of cell numbers was found at any tested concentration. SIGNIFICANCE: These data indicate that the investigated resins may cause cell damage due to depletion of intracellular GSH level even at low concentrations within a short period of time. The decrease of GSH is an early reaction, which is triggered prior to other cytotoxic alterations.     

Cytotoxicity of dental composite components and mercury compounds in lung cells.

OBJECTIVE: The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA), as well as mercuric chloride (HgCl2) and methylmercury chloride (MeHgCl) was investigated on the release of lactatedehydrogenase (LDH) from alveolar epithelial lung cell lines in vitro. METHODS: The confluent cell layers from the A549 (human, malignant) and the L2 cells (rat) were incubated with various concentrations of HEMA, TEGDMA, MeHgCl and HgCl2 at 37 degrees C in 2% (v/v) CO2 atmosphere for 8h. In further experiments the L2 cells were incubated with the same compounds for 6-48 h. LDH release was measured and the values were expressed as percentage of the LDH content. The values were plotted on a concentration log-scale and the substance concentration at the maximum slope was assessed as effective concentration (EC50). RESULTS: A significant (p<0.05) increase in the LDH release was found in the L2 cells after 8-h incubation with HEMA (4 mmol/l), TEGDMA (2 mmol/l), MeHgCl (0.01 mmol/l) and HgCl2 (0.015 mmol/l), and in A549 cells with HEMA (14 mmol/l), TEGDMA (15 mmol/l), MeHgCl (0.15 mmol/l) and HgCl2 (0.05 mmol/l), compared to controls. The EC50 values from compounds in the L2 cells are shown in the following table (mean; sem in parentheses; n=3-6; #n=1): [see text]. SIGNIFICANCE: The toxic effect of HgCl2 and MeHgCl from the L2 cells was about 100-700-fold higher than of the dental composite components. A significant (p<0.05) time dependent increase of toxicity was observed with TEGDMA, HEMA and MeHgCl.     

Antioxidative vitamins decrease cytotoxicity of HEMA and TEGDMA in cultured cell lines

OBJECTIVES AND METHODS: In a previous study it was postulated that toxicity of 2-hydroxyethylmethacrylate (HEMA) and triethleneglycoldimethacrylate (TEGDMA) is based on oxidative metabolites. In this study the influence of antioxidative vitamins (including uric acid) on the toxicity of HEMA or TEGDMA was tested. Toxicity of HEMA and TEGDMA was determined in rat alveolar epithelial L2, human malignant A549, and human fibroblast-like 11Lu cells by inhibition of methionine incorporation (as a marker of protein synthesis inhibition) and by determination of glutathione depletion, as well as by measurement of GSSG increase. RESULTS: Toxicity of the composite components HEMA and TEGDMA was demonstrated by GSH depletion as the most sensitive method. Five hundred micromoles per litre Vitamin C or 250 micromol/l Vitamin E were mostly able to decrease toxicity of HEMA and TEGDMA in the cell lines tested. In addition, 250 micromol/l Vitamin A was only effective in L2 cells impairing HEMA toxicity and 250 micromol/l uric acid impairing TEGDMA toxicity as assessed by decreased GSH depletion. In A549 cells only methionine incorporation inhibition but not GSH depletion was significantly affected. By contrast, in 11Lu cells methionine incorporation inhibition was not significantly changed, but GSH depletion was. CONCLUSIONS: The postulated mechanism of HEMA or TEGDMA toxicity based on radical metabolites is supported by the effectivity of the antioxidative substances tested in mitigating toxicity and by the greater susceptibility of the glutathione redox system as compared to protein synthesis inhibition in assessing toxicity.     

Responses of L929 mouse fibroblasts, primary and immortalized bovine dental papilla-derived cell lines to dental resin components.

OBJECTIVE: The use of adequate target cells for cytotoxicity testing of dental restorative materials has often been experimentally assessed with respect to the clinical relevance of the test results. In the present study, the responses in primary bovine dental papilla-derived cells (pulp cells) were compared with those in transformed dental papilla-derived cell lines and L929 mouse fibroblasts after exposure to various dental resin compounds. METHODS: Primary bovine dental papilla-derived cells (CPC), tCPC B (CPC cells transformed with SV40 T-antigen), tCPC E (CPC cells transformed with E6/E7 oncogen), and L929 mouse fibroblast cells were exposed to various compounds of dental resin materials for 24 h, and cytotoxicity was determined using the MTT assay. Bis-GMA, UDMA, 1,6 hexane diol dimethacrylate (HDDM), TEGDMA, HEMA, MMA, camphorquinone (CQ), bisphenol A (BPA), and glycidyl methacrylate (GMA) were tested. Concentrations leading to 50% cell survival (TC50 values) were calculated from fitted dose-response curves. RESULTS: The simple ranking of the cytotoxic effects of the dental resin compounds in the four cell types was identical, and TC50 values determined in L929 cells here were consistent with findings by other authors using continuous cell lines. However, the concentrations of the resin compounds necessary for eliciting cytotoxic responses in the various cells were clearly different. The analyses of TC50 values of the resin compounds revealed a linear correlation between cell lines, and the overall sensitivities increased as follows: CPC=tCPC B相似文献   

Monomer permeability of disposable dental gloves

STATEMENT OF PROBLEM: Studies have suggested that monomers may be able to permeate dental gloves. PURPOSE: This study examined the permeability of disposable dental gloves to 6 kinds of dental monomers. MATERIAL AND METHODS: The permeability of 6 kinds of dental monomers (methyl methacrylate [MMA], 2-hydroxyethyl methacrylate [HEMA], triethyleneglycol methacrylate [TEGDMA], ethyleneglycol dimethacrylate [EGDMA], urethane dimethacrylate [UDMA], and Bis-glycidyl methacrylate [Bis-GMA]) through 5 kinds of dental gloves (latex, powder-free latex, coated latex, polychloroprene, and polyvinyl chloride) was examined for up to 180 minutes at 37 degrees C. The fingers of unused gloves without pin holes were cut and used in the experiments. Five specimens per test group were examined. One type of monomer was poured into each finger and dipped in ethanol. The ethanol for extraction was measured by a spectrophotometer at a wavelength of 210 nm, and the results were analyzed by analysis of variance and the Kruskal-Wallis test (P<.05). RESULTS: Four of the monomers tested (MMA, HEMA, TEGDMA, and EGDMA) permeated the gloves tested, whereas 2 (UDMA and Bis-GMA) did not (P>.01). The amount of monomers permeating the latex in 10 minutes was 0.8 +/- 0.6, 0.6 +/- 0.6, 0.07 +/- 0.1, 0.07 +/- 0.1, 0.1 +/- 0.1 and 0.06 +/- 0.1 microL/mL for MMA, HEMA, EGDMA, TEGDMA, UDMA, and Bis-GMA, respectively. The amount of permeated monomer was then increased in relation to the examination time, and in MMA and HEMA, permeation occurred rapidly during the initial 60 minutes at 3 times the 10-minute values, then continued gradually and linearly. The polyvinyl chloride glove showed the greatest monomer permeability. Two-way analysis of variance showed significant correlations between MMA, HEMA, EGDMA or TEGDMA and UDMA or Bis-GMA (P<.01). Statistical significance was shown between polyvinyl chloride and latex, powder-free latex, coated latex or polychloroprene (P<.01). However, there was no significant relation between any kind of dental monomer and any kind of dental glove. CONCLUSION: Within the limitations of this study, 4 of the monomers tested permeated all of the gloves tested.     

Analysis of organic components in resin‐modified pulp capping materials: critical considerations

The purpose of this study was to elucidate the organic composition and eluates of three resin‐based pulp‐capping materials in relation to their indications and safety data sheets. Uncured samples of Theracal LC, Ultra‐Blend Plus, and Calcimol LC were investigated using gas chromatography–mass spectrometry (GC‐MS) and ultra‐performance liquid chromatography–mass spectrometry (UPLC‐MS). Identification/quantification of 7‐d leachables of cured samples was performed using GC‐MS for 2‐hydroxyethyl methacrylate (HEMA), 2‐(dimethylamino)ethyl methacrylate (DMAEMA), camphorquinone (CQ), ethylene glycol dimethacrylate (EGDMA), ethyl‐4‐(dimethylamino)benzoate (DMABEE), and triethylene glycol dimethacrylate (TEGDMA). A similar organic composition was found for Ultra‐Blend and Calcimol; however, only Ultra‐Blend is indicated for direct pulp‐capping. In contrast to the other materials analysed, Theracal contained substances of high molecular weight. The safety data sheets of all materials were incomplete. We detected HEMA, CQ, and TEGDMA in eluates from Ultra‐Blend and Calcimol, and it was considered that HEMA might have originated from decomposition of diurethane dimethacrylate (UDMA) in the GC‐injector. For Theracal, additives associated with light curing (DMABEE and CQ) were detected in higher amounts (4.11 and 19.95 μg mm^?2) than in the other materials. Pores were quantified in all samples by micro‐computed tomography (micro‐CT) analysis, which could influence leaching. The organic substances in the investigated materials might affect their clinical suitability as capping agents, especially for direct capping procedures.     

Vasodilatory effect of hydroxyethyl methacrylate and triethylene glycol dimethacrylate in rat aorta through calcium antagonistic action

Introduction

Resin-based dental materials contain various diluent monomers that can interfere with vascular function by causing vasodilation. In this study, we evaluated the vasoactive potential of hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) and the possible mechanism of their vascular action on isolated rat aorta.

Methods

Responses of thoracic aorta rings were recorded isometrically by using force displacement transducers. After precontracting aorta rings with phenylephrine, relaxations to HEMA and TEGDMA were recorded in the absence and presence of nitric oxide synthase inhibitor N^ω-nitro-L-arginine methyl ester, cyclooxygenase inhibitor indomethacin, and K⁺ channel inhibitors tetraethylammonium, glibenclamide, and 4-aminopyridine. To investigate the Ca²⁺-channel antagonistic effect of HEMA and TEGDMA in different aorta rings, concentration-response curves to CaCl₂ were obtained in the absence and presence of the test monomers.

Results

Both HEMA and TEGDMA elicited concentration-dependent relaxations. The vasorelaxant effect of HEMA and TEGDMA was not mediated via endothelium-dependent nitric oxide and prostanoid-dependent mechanisms or by K⁺ efflux through K⁺ channels. Both monomers significantly inhibited the contractions induced by CaCl₂.

Conclusions

Our results showed that HEMA and TEGDMA induce vasodilation via Ca²⁺-antagonistic action, whereas nitric oxide and cyclooxgenase pathway and K⁺ channels were not responsible for this vasoactive effect.     

Detection of leachables and cytotoxicity after exposure to methacrylate‐ and epoxy‐based root canal sealers in vitro

Root canal sealing materials may have toxic potential in vitro depending on the cell line, cytotoxicity assay, material chemistry, and degree of polymer curing. The aims of the present study were to detect leaching components from epoxy‐ or methacrylate‐based root canal sealers and to investigate the degree of cytotoxicity after exposure to extracts from these materials. Qualitative determination of substances released from the materials was performed by gas‐ and liquid chromatography/mass spectrometry. Submandibular salivary gland acinar cell death (apoptosis/necrosis) was determined using a fluorescence staining/microscopy technique. The major leachable monomer from the epoxy‐based material was bisphenol‐A diglycidyl ether (BADGE), whereas leachables from the methacrylate‐based materials were mainly triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), hydroxyethyl methacrylate (HEMA), and polyethyleneglycol dimethacrylate (PEGDMA). Exposure to diluted extracts of cured methacrylate‐based materials caused a postexposure time‐dependent increase in cell death. This effect was not demonstrated as a result of exposure to undiluted extract of cured epoxy‐based material. Extracts of all fresh materials induced apoptosis significantly, but at lower dilutions of the epoxy‐ than the methacrylate‐based materials. The degree of leaching, determined from the relative chromatogram peak heights of eluates from the methacrylate‐based sealer materials, corresponded with the degree of cell death induced by extracts of these materials.     

The induction of gene mutations and micronuclei by oxiranes and siloranes in mammalian cells in vitro

Oxiranes and siloranes are candidate molecules for the development of composite materials with low shrinkage. Since some of these molecules are highly reactive, they could lead to adverse biological effects from underlying genetic mechanisms. Therefore, we analyzed the formation of micronuclei (chromosomal aberrations) and the induction of gene mutations (HPRT assay) in mammalian cells. The numbers of micronuclei induced by the oxirane di(cyclohexene-epoxidemethyl)ether (Eth-Ep) at low concentrations (10 micro M) were about five-fold higher than controls. The related compound epoxy cyclohexyl methyl-epoxy cyclo-hexane carboxylate (Est-Ep) was less effective. The activity of diglycidylether of bisphenol A (BADGE) was even lower but similar to the most reactive silorane, di-3,4-epoxy cyclohexylmethyl-dimethyl-silane (DiMe-Sil). No induction of micronuclei was detected in the presence of a rat liver homogenate (S9). Est-Ep and Eth-Ep also induced gene mutations. Our analyses indicated low mutagenic potentials of siloranes; however, some oxiranes induced strong effects at two genetic endpoints.