Toxicokinetic of HEMA in guinea pigs

A Novel Role of Ascorbic Acid in Anti-Inflammatory Pathway and ROS Generation in HEMA Treated Dental Pulp Stem Cells

Resin (co)monomers issued from restorative dental materials are able to distribute in the dental pulp or the gingiva, to get to the saliva and to the flowing blood. Many authors have recently shown that methacrylate-based resins, in particular 2-hydroxyethylmethacrylate (HEMA), are responsible of inflammatory and autophagic processes in human dental pulp stem cells (hDPSCs) while ascorbic acid (AS), an antioxidant molecule, can assume a protective role in cell homeostasis. The purpose of the current work was to study if 50 µg/mL AS can affect the inflammatory status induced by 2 mM HEMA in hDPSCs, a tissue–specific cell population. Cell proliferation, cytokine release, morphological arrangement and reactive oxygen species (ROS) formation were determined respectively by MTT, ELISA, morphological analysis and dichlorofluorescein assay. The hDPSCs exposed to HEMA let to an increment of ROS formation and in the expression of high levels of inflammatory mediators such as nuclear factor-κB (NFkB), inflammatory cytokines such as interleukin IL6, IL8, interferon (IFN)ɣ and monocyte chemoattractant protein (MCP)1. Moreover, HEMA induced the up-regulation of pospho-extracellular signal–regulated kinases (pERK)/ERK signaling pathway associated to the nuclear translocation. AS treatment significantly down-regulated the levels of pro-inflammatory mediators. Then, the natural product AS reduced the detrimental result promoted by methacrylates in clinical dentistry, in fact restore cell proliferation, reduce the pro-inflammatory cytokine, downregulate ROS production and of NFkB/pERK/ERK signaling path. In synthesis, AS, could improve the quality of dental care and play a strategic role as innovative endodontic compound easy to use and with reasonable cost.

Load-dependent surface nanomechanical properties of poly-HEMA hydrogels in aqueous medium

The mechanical properties of hydrogels are of importance in many applications, including scaffolds and drug delivery vehicles where the release of drugs is controlled by water transport. While the macroscopic mechanical properties of hydrogels have been reported frequently, there are less studies devoted to the equally important nanomechanical response to local load and shear. Scanning probe methods offer the possibility to gain insight on surface nanomechanical properties with high spatial resolution, and thereby provide fundamental insights on local material property variations. In this work, we investigate the local response to load and shear of poly(2-hydroxyethyl methacrylate) hydrogels with two different cross-linking densities submerged in aqueous solution. The response of the hydrogels to purely normal loads, as well as the combined action of load and shear, was found to be complex due to viscoelastic effects. Our results show that the surface stiffness of the hydrogel samples increased with increasing load, while the tip-hydrogel adhesion was strongly affected by the load only when the cross-linking density was low. The combined action of load and shear results in the formation of a temporary sub-micrometer hill in front of the laterally moving tip. As the tip pushes against such hills, a pronounced stick-slip effect is observed for the hydrogel with low cross-linking density. No plastic deformation or permanent wear scar was found under our experimental conditions.

Wear of dental materials: Clinical significance and laboratory wear simulation methods -A review

This review focusses on tribological aspects of teeth during function, the clinical significance of wear, wear of natural teeth and restorative materials and laboratory methods to simulate wear of restorative materials. Ceramic, metal alloy and amalgam show low material wear, whereas resin-based materials demonstrate substantial wear in the long term. The clinical wear shows a high variability with the patient factor accounts for about 50% of the variability. Wear as such seldomly compromises the function of the stomatognath system or individual teeth and is in most cases an esthetic problem. Particles that are ingested due to attrition and abrasion wear may pose a health risk to the patient, especially those from composite resin materials. However, systematic clinical studies on that issue are not available. For laboratory research many wear simulation devices and methods have been developed but only few are validated and have a moderate correlation with clinical wear.

Antioxidants as a novel dental resin-composite component: Effect on elution and degree of conversion

OBJECTIVE

Ascorbic acid (Asc) and N-acetylcysteine (NAC) were reported to reduce genotoxicity induced by dental (co)monomers and their epoxy metabolites. The aim of the present study was to investigate Asc or NAC as novel components in light-curable methacrylate based dental composites regarding their effects on degree of conversion (DC) and elution of composite components. Additionally, the release of Asc or NAC was determined.

METHODS

Asc or NAC (1, 0.1, 0.01 or 0 wt%) was experimentally incorporated into the composites Venus^®, Grandio^® and Filtek^TM Supreme XTE and polymerized according to the instruction of manufacturers. The samples were elussted in methanol and water. For each composite-antioxidant mixture and elution medium four samples (n = 4) were prepared. The eluates were analyzed by gas chromatography/mass spectrometry (GC/MS), high-performance liquid chromatography/ultraviolett/diode array detection (HPLC/UV/DAD) and high-performance liquid chromatography/fluorescence detection (HPLC/FLD). DC of composite-antioxidant mixtures was measured in real-time with Fourier transform infrared spectroscopy (FTIR).

RESULTS

The highest concentrations of eluted Asc were 313.98 μM (Venus^®-1 wt% Asc; 1 day; methanol) and 245.34 μM (Filtek^TM Supreme XTE-1 wt% Asc; 5 min; water). The highest concentrations of eluted NAC were 42.99 μM (1 day; Filtek^™ Supreme XTE-1 wt% NAC; 1 day; methanol) and 108.11 μM (Filtek^™ Supreme XTE-1 wt% NAC; 7 day; water). Triethylene glycol dimethacrylate (TEGDMA) elution was significantly increased in Venus^®-1 wt% Asc and Grandio^®-1 wt% Asc (1 day and 7 day methanol/water), compared to control. No significant difference was found for TEGDMA elution in Filtek^™ Supreme XTE-1 wt% Asc/NAC. DC was significantly decreased compared to control (= composite without antioxidant) in Grandio^® and Filtek^™ Supreme XTE after 1, 0.1 and 0.01 wt% Asc incorporation and in Venus^® after 1 and 0.1 wt% Asc incorporation. For composite-NAC mixtures, only DC of Grandio^®-1 wt% NAC was significantly reduced.

SIGNIFICANCE

Incorporation of NAC (1 wt%), as a novel composite component, into Filtek^™ Supreme XTE, had no effect on DC and composite component elution, and supplies sufficient amount of antioxidant which may reduce toxicity. Therefore, it represents a beneficial mixture.

NAC ameliorates dental composite-induced DNA double-strand breaks and chromatin condensation

Released (co)monomers from dental composite components can induce DNA damage of which DNA double-strand breaks (DSBs) threaten genome integrity. Here, we tested whether the administration of the antioxidant N-acetylcysteine (NAC) is able to reduce the dental composite-induced DSBs in primary human gingiva fibroblasts. The dental composites Bis-GMA (bisphenol-A-glycerolate dimethacrylate), GMA (glycidyl methacrylate), HEMA (2-hydroxyethyl methacrylate) and TEGDMA (triethyleneglycol dimethacrylate) were found to induce co-localizing microscopic nuclear foci numbers of the DSB markers γ-H2AX and 53BP1 per cell in the order: GMA>Bis-GMA>TEGDMA>HEMA. Supplementation of (co)monomer-containing culture medium with NAC led to a significant reduction of resin-induced DSBs as well as to an amelioration of dental monomer-induced nuclear chromatin condensation in gingival fibroblasts. Thus, antioxidant treatment can reduce radical-induced chromatin and DNA damage and open avenues to mitigate genotoxic effects of dental composite compounds.

Effects of antioxidants on DNA double-strand breaks in human gingival fibroblasts exposed to dental resin co-monomer epoxy metabolites

OBJECTIVE

Eluted dental resin co-monomers can be metabolized to intermediate methacrylic acid (MA) and, further, to epoxy metabolites. Antioxidants have been studied previously, with the intention of decreasing the DNA double-strand breaks (DNA-DSBs) in human gingival fibroblasts (HGFs). In this study, the effects of the antioxidants, ascorbic acid (Asc) and N-acetylcysteine (NAC), were investigated on co-monomer metabolite-induced DNA-DSBs.

METHODS

HGFs were incubated with MA, 2,3-epoxy-2-methyl-propionicacid-methylester (EMPME) and 2,3-epoxy-2-methylpropionic acid (EMPA), respectively, in the presence or absence of antioxidants (Asc or NAC). EC₅₀ Values were obtained from an XTT-based viability assay. DNA-DSBs were determined using a γ-H2AX assay.

RESULTS

The cytotoxicity of the compounds could be ranked in the following order (mean±SEM; n=4): EMPA>EMPME>MA. The average number of DSBs-foci/cell induced by each substance at EC₅₀-concentration could be ranked in the following order (mean±SD; n=4): EMPA>EMPME>MA. EMPA (1.72mM) and EMPME (2.58mM) induced the highest number of DSBs-foci, that is 21-fold and 13-fold, respectively, compared to control (0.48±0.08 foci/cell). The addition of Asc (50; 100; 200μM) or NAC (50; 100; 200; 500μM) to MA (15.64; 5.21mM), EMPME (2.58mM), and EMPA (1.72; 0.57mM) significantly reduced the number of foci/cell in HGFs. The highest reduction could be found in HGFs with 1.72mM EMPA, the addition of NAC (50; 100; 200; 500μM) induced a 15-fold, 17-fold, 14-fold and 14-fold lower number of DSBs-foci/cell, respectively.

SIGNIFICANCE

Dental co-monomer epoxy metabolites, EMPME and EMPA, can induce DNA-DSBs. The addition of antioxidants (Asc or NAC) leads to reduction of DNA-DSBs, and NAC leads to more prominent reduction of DNA-DSBs compared to Asc.

Own brand label restorative materials-A false bargain?

OBJECTIVES

This study aims at evaluating and comparing mechanical, chemical, and cytotoxicological parameters of a commercial brand name composite material against two 'own brand label' (OBL) composites.

METHODS

Parameters included depth of cure, flexural strength, degree of conversion, polymerization shrinkage, filler particle morphology and elemental analyzes, Vickers hardness, surface roughness parameters after abrasion, monomer elution, and cytotoxicity.

RESULTS

The conventional composite outperformed the OBLS in terms of depth of cure (p<0.001), degree of cure at the first and last time intervals (p<0.001), hardness (p<0.001), and post-abrasion roughness (p<0.05). The polymerization volumetric shrinkage ranged from 2.86% to 4.13%, with the highest shrinkage seen among the OBLs. Both Monomer elution from the OBLs was statistically significantly higher (p<0.001). Statistically significantly higher cytotoxicity combined with altered morphology and loss of confluence was detected in the cells exposed to extracts from the OBLs.

CONCLUSIONS

The OBLs were in general outdone by the conventional composite.

CLINICAL SIGNIFICANCE

OBLs restorative materials have become pervasive in the dental market. Manufacturers often promise equal or better characteristics than existing brand-name composites, but at a lower price. Dentists are highly recommended to reconsider utilization of OBLs lacking sound scientific scrutiny, and our findings underscore this recommendation.

Dental composite components induce DNA-damage and altered nuclear morphology in gingiva fibroblasts

OBJECTIVE

Released dental composite components can damage human gingival fibroblasts (HGFs) and their DNA. The cytotoxicity, chromatin condensation and the induction of DNA double strand breaks (DSBs) by different compounds of dental composites was investigated using an improved γ-H2AX focus assay.

METHODS

HGFs were incubated with the monomers: bisphenol-A-ethoxylate-dimethacrylate (Bis-DMA), bisphenol-A-glycerolate-dimethacrylate (BisGMA), ethyltriethylen glycol methacrylate (ETEGMA), glycidyl methacrylate (GMA), 1,6-hexandiol-dimethycrylate (HDDMA), trimethylolpropane ethoxylate triacrylate (TMPTA), and acrylamide (ACR). DSBs were determined by enumerating γ-H2AX and 53BP1 foci colocalized at DSBs.

RESULTS

A concentration-dependent induction of DSBs was found in the order: GMA>BisGMA>ACR>Bis-DMA>HDDMA>TMPTA>ETEGMA. HGFs exposure to GMA (0.3mM) and to BisGMA (0.09mM) induced the highest rate of DSB foci, i.e. 12-fold and 8-fold, respectively, relative to control (0.33 DSB foci/cell). At the highest concentrations (EC50) prominent changes in the chromatin morphology of HGF cell nuclei, i.e. compaction of nuclear chromatin and reduction of the area covered by the ovoid fibroblast nuclei, were observed. Nuclear condensation was significantly induced by GMA (1.7-fold at 0.3mM) and BisGMA (1.6-fold at 0.09mM), which correlated with the highest numbers of induced DSB foci (GMA, BisGMA, 3.9 and 2.6 foci/cell, respectively).

SIGNIFICANCE

The improved γ-H2AX/53BP1 focus assay revealed a concentration-dependent increase in DSBs for all tested substances. Furthermore, concentration-dependent changes in HGF cell nucleus morphology was noted, demonstrating genotoxic effects of the substances tested.

Genotoxic effects of camphorquinone and DMT on human oral and intestinal cells

OBJECTIVE

Released components of oral biomaterials can leach into the oral cavity and may subsequently reach the gastrointestinal tract. Camphorquinone (CQ) is the most common used photoinitiator in resinous restorative materials and is often combined with the co-initiator N,N-dimethyl-p-toluidine (DMT). It has been shown that CQ exerts cytotoxic effects, at least partially due to the generation of reactive oxygen species (ROS). Objective of this study was to examine the cytotoxic and genotoxic potential of CQ in human oral keratinocytes (OKF6/TERT2) and immortalized epithelial colorectal adenocarcinoma cells (Caco-2). Furthermore, the effects of visible-light irradiation and the co-initiator DMT were investigated as well as the generation of ROS, the potential protective effect of glutathione (GSH) and a recovery period of CQ-treated Caco-2 cells.

METHODS

The alkaline comet assay was used to determine DNA damage. Additionally, an enzyme modified comet assay was applied, which detects 7,8-dihydro-8-oxoguanine (8-oxoguanine), a reliable marker for oxidative stress.

RESULTS

Our data revealed that high concentrations of CQ induced DNA lesions in OKF6/TERT2 cells. This DNA damage is at least partly caused by the generation of 8-oxoguanine. In addition, CQ and DMT increased ROS formation and induced DNA damage in Caco-2 cells. CQ-treatment resulted in generation of 8-oxoguanine. The antioxidant GSH efficiently prevented CQ-associated DNA damage. Furthermore, a recovery following CQ-treatment significantly reduced DNA damage.

SIGNIFICANCE

We conclude that CQ-induced DNA damage is caused by oxidative stress in oral and intestinal cells. These lesions can be prevented and possibly repaired by GSH-treatment and recovery of cells after the photoinitiator is removed from cultures.

Restorative materials in the primary dentition of poli-caries patients

BACKGROUND

Despite an overall caries decline in children, still 50-60% of carious primary teeth of 6-year-olds remain untreated, in 3-year-olds 13%. There are an increasing number of poli-caries patients with insufficiently treated primary teeth. Therefore, early treatment is fundamental.

REVIEW

The assessment and indication for the use of restorative materials can be summarized as follows: Glass ionomer cements (GIC) are associated with easy handling and high fluoride release. This makes them attractive especially for Class I cavities in uncooperative children. However, low flexural strength causes high fracture rates in Class II cavities. Further developments (viscous and resin-modified GIC) have improved handling characteristics, but conventional non-resin-modified GIC are still prone to fracture. Compomers exhibit a clear potential as an alternative to amalgam. Long-term results are good even in stress-bearing areas. The compliance of the child should at least last long enough for adhesive application. Resin composites are still the most time-consuming alternative. Under a correct application protocol, resin composites behave in a similar manner to compomers. Therefore, the effort has to be judged individually. Finally, especially in severely decayed teeth and after endodontic treatment, preformed metal crowns should be taken into account as a last and appropriate alternative to direct restorations.

CONCLUSION

Based on the high clinical success rates, compomers with self-etch adhesives can be recommended for restorative therapy in anterior and posterior primary teeth.

Distribution and Excretion of BisGMA in Guinea Pigs

Bisphenol-A-glycidyldimethacrylate (BisGMA) is used in many resin-based dental materials. It was shown in vitro that BisGMA was released into the adjacent biophase from such materials during the first days after placement. In this study, the uptake, distribution, and excretion of [14C]BisGMA applied via gastric and intravenous administration (at dose levels well above those encountered in dental care) were examined in vivo in guinea pigs to test the hypothesis that BisGMA reaches cytotoxic levels in mammalian tissues. [14C]BisGMA was taken up rapidly from the stomach and intestine after gastric administration and was widely distributed in the body following administration by each route. Most [14C] was excreted within one day as 14CO2. The peak equivalent BisGMA levels in guinea pig tissues examined were at least 1000-fold less than known toxic levels. The peak urine level in guinea pigs that received well in excess of the body-weight-adjusted dose expected in humans was also below known toxic levels. The study therefore did not support the hypothesis.

Effect of variations from the recommended powder/liquid ratio on some properties of resin-modified cements

OBJECTIVES

The powder and liquid contents of cements are mixed in accordance with the recommended mixing ratio, but discrepancies occur despite the use of proportioning scoops. Little is known about powder/liquid ratio variations on certain properties of resin-modified cements.

METHODS

Two resin-modified glass ionomer cements (RMGIC) were mixed using various powder/liquid ratios: (a) Recommended ratio: Fuji Plus: powder/liquid 2:1; ProTecCEM p/l 2.25:1. (b) Maximal variation arising using proportioning aids (17% liquid surplus): Fuji Plus 1.66:1, ProTecCEM 1.875:1. Limits of mixing and specimen construction: either (c) both groups with more liquid (1.5:1) or (d) more powder (3:1). Flexural strength was determined using a 3-point bending test (after 24 h) and wear using a 3-body abrasion device. The extent of cure reaction was characterized using differential thermal analysis (DTA).

RESULTS

While higher powder content did not significantly affect the flexural strength of Fuji Plus and ProTecCEM, it considerably reduced wear of Fuji Plus. Increasing liquid content reduced flexural strength. A substantial increase in wear for Fuji Plus 1.5:1, and ProTecCEM 1.875:1 and 1.5:1 mixtures was observed. DTA demonstrated that a higher liquid content resulted in incomplete setting reactions, which could be detected even after 24 h of cure.

CONCLUSIONS

If RMGICs are mixed with powder/liquid variations, given the inaccuracy of proportioning aids the properties of RMGIC will change slightly and may be disregarded. If set with higher powder/liquid variations, a surplus of powder has less influence on the properties than a surplus of liquid.

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.

Application of HEMA on intact mouse skin - effects on the immune system

Previously, we have shown that 2-hydroxyethylmethacrylate (HEMA) can bind to protein and that autoantibodies were induced in mice by immunization with a self-protein in vitro conjugated with HEMA. The present study aimed to develop a model for HEMA-induced sensitivity by the application of the substance on intact skin. Female BALB/c mice were painted on the dorsum of each ear with 50% HEMA in vehicle twice a week for 6 weeks. The anti-CD3epsilon-stimulated lymph node production and the spontaneous spleen-cell production of the cytokines interleukin (IL)-2, IL-4, IL-6, IL-10 and interferon-gamma were assessed by enzyme-linked immunosorbent assay. In another experiment, the cytokines were followed after subcutaneous HEMA injections. Animals painted with HEMA had a significantly higher IL-6 production by anti-CD3epsilon-stimulated lymph node cells and significantly suppressed IL-10 production by spleen cells compared to vehicle-treated mice. This correlated to some extent with the spontaneous spleen-cell production induced by subcutaneously administered HEMA. An injection of 20 micromol of HEMA induced an increased production of IL-6, while injection of 40 micromol depressed both IL-6 and IL-10 production. Although there was no sign of inflammation on the ears, findings suggest that HEMA had penetrated the skin and induced a reaction in the immune system.

Identification of 2,3-epoxymethacrylic acid as an intermediate in the metabolism of dental materials in human liver microsomes

OBJECTIVES

In previous studies it could be demonstrated that methacrylic acid (MA) is an intermediate in the metabolism of unpolymerized dental comonomers, released from dental restorative materials. This study was performed to identify the possible dental material intermediate 2,3-epoxymethacrylic acid (2,3-EMA) from MA in human liver microsomes. Most epoxy compounds are regarded as highly toxic substances.

METHODS

The formation and hydrolysis were studied in defined systems containing only MA and human liver microsomes at 37 degrees C. Hydrolysis was inhibited by cyclohexene oxide, a competitive inhibitor of epoxide hydrolase. The reaction product 2,3-EMA was analyzed by the headspace gas chromatography-mass spectrometry. After 5, 30, and 60 min samples were taken and analyzed.

RESULTS

For the reaction of MA to 2,3-EMA the average conversion rate was about 5% within 1h. It was found that without cyclohexene oxide the rate constant of enzymatic hydrolysis at pH 7.4 was about 10 times higher than the rate constant of the formation from MA in combination with cyclohexene oxide (k=8.3 versus 0.83 micromol/l min), indicating an instability and thus a high reactivity of 2,3-EMA. The formation of the MA intermediate 2,3-EMA was not observed when heat-inactivated liver microsomes were used (controls).

SIGNIFICANCE

It could be clearly demonstrated that 2,3-EMA is a product of dental material metabolisms in biological systems. Therefore, increased toxicity might occur on dental restorative materials which are able to release (co)monomers which can be metabolized to MA.

Inflammatogenic and adjuvant properties of HEMA in mice

2-Hydroxyethylmethacrylate (HEMA), a common constituent in dental materials, is known to cause hypersensitivity reactions. While the means by which this small molecule causes adverse responses has not been ascertained, we have previously demonstrated that it binds to protein and in mice induces the production of autoantibodies to HEMA-conjugated self-protein. The present study explores the inflammatory and adjuvant properties of HEMA in response to the subcutaneous injection of HEMA and a protein. Ovalbumin (OVA) was used as a 'reporter antigen', and mouse serum albumin (MSA), conjugated in vitro with HEMA (MSA(H)) to a low degree (0.5 molecules of HEMA per molecule of MSA on average), was used to mimic a possible in vivo situation. Inflammatory responses at injection sites were scored by using an ordinal scale, and immunoglobulin (Ig)G1, IgG2a, and IgE activities to OVA or MSA were assessed by enzyme-linked immunosorbent assay (ELISA). Injections of 20 micromol HEMA induced overt inflammatory skin responses, the severity of which was influenced by the co-administered substances. A significantly higher IgG1 and IgE response to OVA was induced by the presence of HEMA. Interestingly, injections with low conjugated MSA(H) only induced the production of autoantibodies if free HEMA was included at the time of immunization. These findings suggest that HEMA is an inflammatogenic substance with adjuvant properties.

In vitro embryotoxicity assessment with dental restorative materials

OBJECTIVES

Resin (co)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. Genotoxic potential of some dental composite components has been clearly documented. The genotoxic effects of xenobiotics can represent a possible step in tumor initiation and/or embryotoxicity/teratogenesis. A modified fluorescent mouse embryonic stem cell test (R.E.Tox) was used to test the embryotoxic potential of following dental restorative materials: Bisphenol A glycidylmethacrylate (BisGMA), urethanedimethacrylate (UDMA), hydroxyethylmethacrylate (HEMA), and triethyleneglycoldimethacrylate (TEGDMA), as well as some of their metabolic intermediates 2,3-epoxy-2-methyl-propionicacid-methylester (EMPME), methacrylic acid (MA), and 2,3-epoxy-2-methylpropionic acid (EMPA).

METHODS

Mouse embryonic stem (ES) cells stably transfected with a vector containing the gene for the green fluorescent protein under control of the cardiac alpha-myosin heavy chain promoter were differentiated in the presence of various concentrations of the test compounds for 12 days. Fluorescence was measured using the TECAN Safire and values were expressed as percent of control values. To distinguish between cytotoxic and embryotoxic effects, all compounds were tested in a standard MTT assay.

RESULTS

HEMA, TEGDMA and EMPME did not influence the differentiation process of ES cells towards cardiac myocytes. No cytotoxic effects were observed at any of the concentration levels tested. Exposure to BisGMA resulted in a 50% decrease in cell survival and a very strong inhibition of cell differentiation at 10(-5)M (p<0.01). Embryotoxic effects were also present at 10(-6) and 10(-7)M (p<0.05). EMPA induced a decrease in ES cell differentiation at 10(-5)M (p<0.01) without cytotoxic effects. No embryotoxic effects were induced at lower concentrations. Exposure to UDMA resulted in a slight decrease of cell differentiation at 10(-5)M (p<0.05). Exposure of cells to MA resulted in an increase of cardiac differentiation up to 150% (p<0.05) at 10(-5)M without cytotoxic effects.

CONCLUSIONS

BisGMA induced a significant high embryotoxic/teratogenic effect over a large range of concentration. Therefore attention should be focused on this dental monomer, which should be investigated further by in vivo experiments.