The induction of micronuclei in vitro by unpolymerized resin monomers

Cytotoxicity of resin composites containing bioactive glass fillers

OBJECTIVE

To determine the in vitro cytotoxicity of dental composites containing bioactive glass fillers.

METHODS

Dental composites (50:50 Bis-GMA/TEGDMA resin: 72.5wt% filler, 67.5%Sr-glass and 5% OX50) containing different concentrations (0, 5, 10 and 15wt%) of two sol-gel bioactive glasses, BAG65 (65mole% SiO2, 31mole% CaO, 4mole% P2O5) and BAG61 (3mole% F added) were evaluated for cytotoxicity using Alamar Blue assay. First, composite extracts were obtained from 7 day incubations of composites in cell culture medium at 37°C. Undifferentiated pulp cells (OD-21) were exposed to dilutions of the original extracts for 3, 5, and 7 days. Then freshly cured composite disks were incubated with OD-21 cells (n=5) for 2 days. Subsequently, fresh composite disks were incubated in culture medium at 37°C for 7 days, and then the extracted disks were incubated with OD-21 cells for 2 days. Finally, fresh composites disks were light cured for 3, 5, and 20s and incubated with OD-21 cells (n=5) for 1, 3, 5, and 7 days. To verify that the three different curing modes produced different levels of degree of conversion (DC), the DC of each composite was determined by FTIR. Groups (n=5) were compared with ANOVA/Tukey's (α≤0.05).

RESULTS

Extracts from all composites significantly reduced cell viability until a dilution of 1:8 or lower, where the extract became equal to the control. All freshly-cured composites showed significantly reduced cell viability at two days. However, no reduction in cell viability was observed for any composite that had been previously soaked in media before exposure to the cells. Composites with reduced DC (3s vs. 20s cure), as verified by FTIR, showed significantly reduced cell viability.

SIGNIFICANCE

The results show that the composites, independent of composition, had equivalent potency in terms of reducing the viability of the cells in culture. Soaking the composites for 7 days before exposing them to the cells suggested that the "toxic" components had been extracted and the materials were no longer cytotoxic. The results demonstrate that the cytotoxicity of composites with and without BAG must predominantly be attributed to the release of residual monomers, and not to the presence of the BAG.

In vitro cytotoxicity of self-curing acrylic resins of different colors

Objective

The aim of this study was to assess the in vitro cytotoxicity of acrylic resins of different colors over time.

Methods

Specimens were divided into 4 groups (n = 6) according to the color of the acrylic resin (Orto Class, Clássico, Campinas, São Paulo, Brazil): Group 1: clear acrylic resin; group 2: pink acrylic resin; group 3: blue acrylic resin and group 4: green acrylic resin. All specimens were fabricated according to the mass manipulation technique and submitted to mechanical polishing protocol. The control was performed with an amalgam specimen (C+), a glass specimen (C-) and cell control (CC). Specimens were immersed in Minimum Eagle's Medium (MEM) and incubated for 24 h at 37ºC. The extracts from the experimental material were filtered and mixed with L929 fibroblast. Cytotoxicity was evaluated at 4 different times, 24, 48, 72 and 168 h. After contact, cells were incubated for 24 h and added to 100 µ of 0.01% neutral red dye. The cells were incubated for 3 h for pigment incorporation and fixed. Cells viability was determined by a spectroscopic (BioTek, Winooski, Vermont, USA) with a 492-nm wavelength λ=492 nm).

Results

There were no statistical differences between the experimental groups and the CC and C- groups.

Conclusion

Clear, pink, blue and green self-curing acrylic resins fabricated by means of the mass manipulation technique and mechanically polished are not cytotoxic. Neither the pigment added to the self-curing acrylic resin nor the factor of time influenced the cytotoxicity of the material.

Evaluation of the genotoxicity and cytotoxicity in the buccal epithelial cells of patients undergoing orthodontic treatment with three light-cured bonding composites by using micronucleus testing

Objective

This study evaluated the cytotoxicity and genotoxicity of fixed orthodontic treatment with three different light-cured orthodontic bonding composites by analyzing micronucleus (MN) formation in the buccal mucosa during a 6-month period.

Methods

Thirty healthy volunteers were selected from consecutive patients referred for orthodontic treatment. Equilibrium 2 brackets and molar tubes (Dentaurum) were bonded with three different light-cured orthodontic bonding composites-Transbond XT (3M Unitek), Kurasper F (Kuraray Europe), or GrenGloo (Ormco Corporation)- to all teeth in both arches. Exfoliated buccal epithelial cells were scraped from the middle part of the inner cheeks with sterile cement spatulas before treatment and at 1, 3, and 6 months after treatment. MNs and nuclear alterations, such as karyorrhexis (KR), karyolysis (KL), and binucleated cells (BNs), were scored under a light microscope. Repeated measure ANOVA was used to calculate statistical differences in degenerative nuclear abnormalities.

Results

MN rates did not significantly differ among different time points within the same cell type (p > 0.05). In contrast, the number of BNs in buccal epithelial cells significantly increased in all composite groups (p < 0.01, Transbond XT; p < 0.001, Kurasper F and GrenGloo). KL frequency significantly increased between the beginning and end of the study in the Kurasfer F (0.80 ± 0.79 to 1.90 ± 1.10; p < 0.05) and GrenGloo (1.30 ± 1.06 to 2.40 ± 1.08; p < 0.05) groups.

Conclusions

After 6 months of fixed orthodontic treatment with different light-cured composites, morphological signs of cytotoxicity were observed but genotoxic effects were absent.

Effect of extraction media and storage time on the elution of monomers from four contemporary resin composite materials

Introduction:

The purpose of this study was to examine the effect of different extraction media, including culture media, as well as storage times on the elution of monomers from modern dental composites.

Materials and Methods:

Four contemporary composite materials were tested: (a) Clearfil Majesty Esthetic (Kuraray), (b) Esthet X (DENTSPLY), (c) Filtek Silorane (3M ESPE), and (d) Admira (Voco). Forty-eight specimens were made. The specimens were stored in 1 ml of (a) artificial saliva, (b) Dulbecco's Modified Eagle Medium (DMEM), (c) DMEM plus 10% fetal bovine serum (FBS), and (d) ethanol 75%. The specimens were analyzed after 24 hours and after 1 week of storage. HPLC Liquid Chromatography was performed to analyze the extracted solutions. The statistical package SPSS 18 was used for the statistical analysis of the results.

Results:

All the materials tested released monomers that were consistent with the base composition of their resin matrix. Bisphenol-A (BPA) was detected in Clearfil Esthetic and EsthetX when ethanol 75% was used for storage. TEGDMA was released at a faster rate compared to the other monomers with most of the monomer eluted in the first 24 hours. The effect of storage solution and storage time on the elution of the same monomers varied between materials.

Conclusions:

There was a significant effect of time, storage solution, and material on the elution of the detectable unbound monomers. Unbound monomers were detected in culture media, which may lead to false-negative results in cytotoxicity tests of resin composite materials. BPA was detected in two of the tested materials.

Residual HEMA and TEGDMA release and cytotoxicity evaluation of resin-modified glass ionomer cement and compomers cured with different light sources

The purpose of this study was first to evaluate the elution of 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) monomers from resin-modified glass ionomer cement (RMGIC) and compomers cured with halogen and light-emitting diode (LED) light-curing units (LCUs). The effect of cured materials on the viability of L929 fibroblast cells was also evaluated. One RMGIC (Ketac N100) and two compomers (Dyract Extra and Twinkystar) were tested. Materials were prepared in teflon disks and light-cured with LED or halogen LCUs. The residual monomers of resin materials in solution were identified using high-performance liquid chromatography. The fibroblast cells' viability was analyzed using MTT assay. The type of LCU did not have a significant effect on the elution of HEMA and TEGDMA. A greater amount of HEMA than TEGMDA was eluted. The amount of TEGDMA eluted from Twinkystar was greater than Dyract Extra (P < 0.05) when cured with a halogen LCU. All material-LCU combinations decreased the fibroblast cells' viability more than the control group (P < 0.01), except for Dyract Extra cured with a halogen LCU (P > 0.05). Curing with the LED LCU decreased the cells' viability more than curing with the halogen LCU for compomers. For Ketac N100, the halogen LCU decreased the cells' viability more than the LED LCU.

Cytogenetic abnormality in exfoliated cells of buccal mucosa in head and neck cancer patients in the Tunisian population: impact of different exposure sources

Chromosome/DNA instability could be one of the primary causes of malignant cell transformation. The objective of the present study was to evaluate the spontaneous genetic damages in exfoliated cells of buccal mucosa of head and neck cancer (HNC) by counting micronucleus (MN) and binucleated (BN) cells frequencies. MN and BN frequencies were significantly increased in HNC patients compared with controls (5.53 ± 3.09/1000 cells, 5.63 ± 2.99/1000 cells versus 2.36 ± 2.11/1000 cells, 3.09 ± 1.82/1000 cells, P < 0.001). Regarding the gender and the age, the frequencies of the MN and BN were significantly higher than those of controls (P < 0.01). The evaluation of the MN and BN frequencies revealed a significant increase (P < 0.001) in the cases in relation to the control group after controlling the risk factors (tobacco smoking and chewing and occupational exposure) of HNC. Moreover, MN and BN frequencies were significantly increased in smokers and chewers compared with nonsmokers and nonchewers among patients (P < 0.05). MN frequency was significantly (P = 0.014) different between patients occupationally exposed (6.99 ± 3.40/1000 cells) and nonexposed (4.70 ± 2.48/1000 cells) among HNC group. The logistic regression model illustrated that HNC was significantly associated with frequencies of MN (OR = 8.63, P < 0.0001) and BN (OR = 5.62, P = 0.001). Our results suggest that increased chromosome/DNA instabilities may be associated with HNC.

Genotoxic biomonitoring of flowable and non-flowable composite resins in peripheral blood leukocytes

OBJECTIVE

Composite restorative materials represent one of the most important groups of materials in contemporary dental practice. However, their incomplete polymerization may lead to monomer-induced genotoxicity. The objective of this study was to evaluate the genotoxicity of three flowable (Filtek Supreme XT Flow, Tetric EvoFlow, Gradia Direct Flo) and three non-flowable dental composite materials (Filtek Z250, Tetric EvoCeram, Gradia Direct Posterior).

MATERIALS AND METHODS

Genotoxicity assessment of composite materials was carried out in vitro in human peripheral blood leukocytes using the alkaline single-cell gel electrophoresis technique (comet assay). Prepared materials were eluted in saline solution for 1 h, 1 day and 5 days. Thereafter leukocyte cultures were treated with different concentrations of eluates obtained from each of the tested dental composite materials. Kruskall-Wallis non-parametric test was used for statistical analysis (p < 0.05).

RESULTS

The tested materials did not show genotoxic effects after exposure of leucocytes to 1 h eluates. Culture treated with 1 day eluates of all tested materials, only at a highest concentration (10(-2)), affected the measured cytogenetic parameters. Of all tested materials, only Filtek Z250 and Filtek Supreme XT Flow did not exhibit a genotoxic effect in cultures that were under the influence of 5 day eluates.

CONCLUSION

Tested materials exhibited limited genotoxic activity in peripheral blood leukocytes. Since the effect was observed only in leukocyte cultures treated by 1-day eluates at the highest concentration (10(-2)) and it decreases in cultures exposed to 5 day eluates, it should not pose a significant risk to the human genome.

Effect of 2-hydroxyethyl methacrylate on antioxidant responsive element-mediated transcription: a possible indication of its cytotoxicity

BACKGROUND

The resin monomer 2-hydroxyethyl methacrylate (HEMA) is known to be more cytotoxic than methyl methacrylate (MMA). Using a luciferase reporter assay system, we previously showed that MMA activates the glutathione S-transferase alpha 1 gene (Gsta1) promoter through the anti-oxidant responsive element (ARE). However, it is not known whether HEMA induces ARE-mediated transcription.

METHODOLOGY/PRINCIPAL FINDINGS

We further developed the reporter system and studied the concentration-dependent effect of HEMA on ARE enhancer activity. The revised system employed HepG2 cells stably transfected with a destabilized luciferase reporter vector carrying 2 copies of the 41-bp ARE region of Gsta1. In this system, MMA increased ARE activity by 244-fold at 30 mM; HEMA augmented ARE activity at 3 mM more intensely than MMA (36-fold versus 11-fold) and was equipotent as MMA at 10 mM (56-fold activation); however, HEMA failed to increase ARE activity at 30 mM. In HepG2 cells, HEMA detectably lowered the cellular glutathione levels at 10 mM and cell viability at 30 mM, but MMA did not.

CONCLUSIONS

These results suggest that the low-concentration effect of HEMA on ARE activity reflects its cytotoxicity. Our reporter system used to examine ARE activity may be useful for evaluating cytotoxicities of resin monomers at concentrations lower than those for which cell viabilities are reduced.

Genotoxicity evaluation of dental restoration nanocomposite using comet assay and chromosome aberration test

Nanocomposite is used as a dental filling to restore the affected tooth, especially in dental caries. The dental nanocomposite (KelFil) for tooth restoration used in this study was produced by the School of Dental Sciences, Universiti Sains Malaysia, Malaysia and is incorporated with monodispersed, spherical nanosilica fillers. The aim of the study was to determine the genotoxic effect of KelFil using in vitro genotoxicity tests. The cytotoxicity and genotoxicity of KelFil was evaluated using MTT assay, comet assay and chromosome aberration tests with or without the addition of a metabolic activation system (S9 mix), using the human lung fibroblast cell line (MRC-5). Concurrent negative and positive controls were included. In the comet assay, no comet formation was found in the KelFil groups. There was a significant difference in tail moment between KelFil groups and positive control (p < 0.05). Similarly, no significant aberrations in chromosomes were noticed in KelFil groups. The mitotic indices of treatment groups and negative control were significantly different from positive controls. Hence, it can be concluded that the locally produced dental restoration nanocomposite (KelFil) is non-genotoxic under the present test conditions.

2-Hydroxyethyl methacrylate inflammatory effects in human gingival fibroblasts

AIM

To investigate the inflammatory response in human gingival fibroblasts (HGFs) treated with a relatively low 2-hydroxyethyl methacrylate (HEMA) concentration by studying reactive oxygen species (ROS) production, cyclooxygenase-2 (COX-2) and tumour necrosis factor-alpha (TNF-α) gene expression, and prostaglandin E2 (PGE₂) release.

METHODOLOGY

Cultured HGFs were exposed to 3 mmol L⁻¹ HEMA for 0, 24 or 96 h. ROS production was investigated by flow cytometry; TNF-α and COX-2 gene expression was determined by RT-PCR, and prostaglandin E2 production was detected by an enzyme immunoassay.

RESULTS

After 24- or 96-h HEMA incubation, ROS levels were approximately eightfold and elevenfold higher than controls, whilst COX-2 gene expression was approximately twofold or fourfold higher than controls, respectively. Twenty-four-hour exposure enhanced TNF-α mRNA levels by approximately 66%, whilst after 96-h incubation, TNF-α gene expression was fivefold higher than controls. Ninety-six-hour HEMA treatment increased PGE₂ concentration in the culture medium by around 17% compared with controls.

CONCLUSIONS

2-Hydroxyethyl methacrylate treatment (3 mmol L⁻¹) induced an inflammatory response in HGFs modulated by ROS production, as well as by the increase in TNF-α and COX-2 gene expression and by PGE₂ release.

The effects of cytotoxicity and genotoxicity induced by 2,2-bis[4-(acryloxypropoxy)phenyl]propane via caspases in human gingival fibroblasts

The toxicity of dental materials has raised public concern over the past years. One of the most commonly used methacrylic monomers for building the three-dimensional structure of the dental resin composites is 2,2-bis[4-(acryloxypropoxy)phenyl]propane (BAPP). The purpose of this study is to evaluate the potential toxicological implication of BAPP on human gingival fibroblasts (HGFs). Flow cytometric, fluorometric, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assays were used to detect the mode of cell death, caspase activities, and cell viability, respectively. In addition, alkaline single-cell gel electrophoresis (COMET) and cytokinesis block micronucleus (MN) assays were applied to evaluate the genotoxicity. According to the results BAPP demonstrated a cytotoxic effect on HGFs in a dose- and time-dependent manner. With increasing concentrations of BAPP, the mode of cell death shifted from apoptosis to necrosis, and the activities of caspases 3, 8, and 9 were also significantly induced. Moreover, a dose-related increase in the number of micronucleus and DNA strand breaks hinted at the expression of genotoxicity by BAPP. In conclusion, the results gathered from this study had demonstrated that BAPP-induced cytotoxicity and genotoxicity on HGFs were mediated by DNA damage and the activation of caspases 3, 8, and 9.

Effects of the iron-chelating agent deferoxamine on triethylene glycol dimethacrylate, 2-hydroxylethyl methacrylate, hydrogen peroxide-induced cytotoxicity

Triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxylethyl methacrylate (HEMA) are known to deplete glutathione in mammalian cells, generate reactive oxygen species (ROS), and cause oxidative stress. In this study, we investigated whether hydroxyl radicals (·OH), the most lethal and genotoxic ROS, and the Fenton reaction are involved in the cytotoxicity of resin monomers to four different cell types, namely MC3T3-E1 preosteoblasts, human dental pulp cells (HDPCs), human gingival fibroblasts, and L929 mouse fibroblasts. Deferoxamine (DFO), an iron chelating agent, effectively protected MC3T3-E1 cells from resin monomer-induced cytotoxicity, indicating that cytotoxicity was caused primarily by hydroxyl radicals. However, DFO only had a protective effect against relatively high concentrations of TEGDMA and HEMA in HDPCs and human gingival fibroblasts, and resin monomer-induced cytotoxicity in L929 was not attenuated by DFO. A labile iron pool (LIP) was detectable only in MC3T3-E1 cells among the four cell types. This indicates that the generation of hydroxyl radicals induced by resin monomers is likely dependent on LIP levels. In contrast to resin monomers, hydrogen peroxide (H(2)O(2))-induced cytotoxicity was not prevented by DFO in any of the cell types examined, although hydroxyl radicals were detected in MC3T3-E1 cells and HDPCs on exposure to exogenous H(2)O(2). This result suggests that generation of hydroxyl radicals is not always the primary cause of cytotoxicity in H(2)O(2)-treated cells.

Methyl methacrylate and respiratory sensitization: a critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants. The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer.

Cytotoxicity and degree of conversion of orthodontic adhesives

OBJECTIVES

To test the hypothesis that there is no difference in the cytotoxicity related to the modes of polymerization of five commercially available orthodontic bonding resins, with and without an oxygen-inhibited layer (OIL), and to evaluate the degree of conversion (DC) of these resins and correlate this to cytotoxicity.

MATERIALS AND METHODS

Five commercially available orthodontic bonding resins were tested for cytotoxicity and DC. Thirty-six disks of standardized dimensions, for each resin, were used for cytotoxicity assessment. Half of them were washed with 99% acetone to remove the OIL (washed resins), and the remaining disks were left intact (intact resins). Glass disks were used as a control. Vero cells were exposed to intact and washed resins on day 1. Cell viability was determined by tetrazolium bromide reduction assay 1, 3, and 6 days after exposure. The DC of the adhesive specimens of each resin, prepared with a procedure identical to the clinical bonding process, was assessed by Fourier transform infrared spectroscopy.

RESULTS

Single-cured systems were comparatively less cytotoxic than dual-cured systems. With removal of the OIL, increased cell viability was noted only with two resins on all three days. Resins tested showed differences in DC. A positive correlation was demonstrated by two resins.

CONCLUSION

The hypothesis is rejected. Single-cured systems are superior to dual-cured systems in exhibiting comparatively less toxicity and higher DC. A significant positive correlation was not established between cytotoxicity and DC.

N-acetyl cysteine directed detoxification of 2-hydroxyethyl methacrylate by adduct formation

Cytotoxicity of the dental resin monomer 2-hydroxyethyl methacrylate (HEMA) and the protective effects of N-acetyl cysteine (NAC) on monomer-induced cell damage are well demonstrated. The aim of our study was to analyze the hypothesis that the protection of NAC from HEMA cytotoxicity might be due to direct NAC adduct formation. To this end, using HPLC we first measured the actual intracellular HEMA concentrations able to cause toxic effects on 3T3-fibroblasts and then determined the decrease in intracellular and extracellular HEMA levels in the presence of NAC. In addition, by capillary electrophoresis coupled with mass spectrometry analysis (CE-MS), we evaluated NAC-HEMA adduct formation. HEMA reduced 3T3 cell vitality in a dose- and time-dependent manner. The concentration of HEMA inside the cells was 15-20 times lower than that added to the culture medium for cell treatment (0-8 mmol/L). In the presence of 10 mmol/L NAC, both intracellular and extracellular HEMA concentrations greatly decreased in conjunction with cytotoxicity. NAC-HEMA adducts were detected both in the presence and absence of cells. Our findings suggest that the in vitro detoxification ability of NAC against HEMA-induced cell damage occurs through NAC adduct formation. Moreover, we provide evidence that the actual intracellular concentration of HEMA able to cause cytotoxic effects is at least one magnitude lower than that applied extracellularly.

Genotoxicity of urethane dimethacrylate, a tooth restoration component

Urethane dimethacrylate (UDMA) is used in dental restorative materials in its polymeric form. However, the process of polymerization is usually incomplete and the monomers of UDMA can diffuse into the oral cavity and the pulp, reaching millimolar concentrations. In the present work we showed that UDMA at 0.1 and 1.0 mM decreased the viability of and induced DNA damage in lymphocytes in a concentration dependent manner, but it did not affect a plasmid DNA in vitro. UDMA at 1mM induced apoptosis in lymphocytes. The lymphocytes exposed to UDMA were able to repair their DNA within 60 min. Analysis with DNA repair enzymes Endo III and Fpg showed that UDMA induced mainly oxidative DNA lesions. Vitamin C and chitosan decreased genotoxic effect of UDMA. Our results show that monomers of UDMA may exert pronounced cyto- and genotoxic effects in human lymphocytes and chitosan can be considered as a protection against such effects.

Molecular toxicology of substances released from resin-based dental restorative materials

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites' molecular toxicology and to give implications for possible improvements concerning their biocompatibility.

HEMA down-regulates procollagen alpha1 type I in human gingival fibroblasts

2-Hydroxyethyl methacrylate (HEMA) can be released from restorative materials and diffused into the tooth pulp over long periods of time. Although cytotoxicity due to high concentrations of monomers has been well studied, little is known about the risk of chronic toxicity resulting from low concentrations. The purpose of the study was to evaluate the effects of a minor toxic concentration of HEMA in the synthesis and expression of procollagen alpha1 type I produced by human gingival fibroblasts (HGF). HGF were exposed to 3 mM HEMA from 24 to 96 h. An MTT assay was performed to evaluate cell viability while reverse-transcriptase polymerase chain reaction (RT-PCR), real-time polymerase chain reaction (real-time PCR), and Western-blot analysis were carried out to evaluate the variability in the expression and synthesis of procollagen alpha1. Immunofluorescence was performed to detect the protein inside the cells. The results showed that there was a strong reduction of procollagen alpha 1 type I expression at 72 and 96 h. These findings demonstrate that, even if it does not reduce cell viability, 3 mM HEMA interferes both with the synthesis of the procollagen alpha 1 type I protein and its mRNA expression, suggesting that normal cell production and activity are modified by HEMA at concentrations below those which cause acute cytotoxicity.

The effects of one-step self-etch adhesives on the induction of oxidative stress and production of TGF-beta1 and BMP-2 by human gingival fibroblasts

The aim of this study was to evaluate and compare the effects of two self-etch adhesive materials on the induction of oxidative stress and production of transforming growth factor-beta1 (TGF-beta1) and bone morphogenetic protein-2 (BMP-2) by cultured human gingival fibroblasts (HGF). Inflammation-free attached gingiva was obtained from healthy donors under informed consent. Following 24- and 72-h exposure of HGF to two different elutes of the test materials, cell viability was determined using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Lipid peroxidation, a major indicator of oxidative stress, was measured by the thiobarbituric acid reactive substance (TBARS) assay. TGF-beta1 and BMP-2 levels in cell-free culture media were determined by enzyme-linked immunosorbent assay (ELISA). Cell viability of the test groups was significantly lower than those of control at 24 and 72 h (P < 0.001), but showed an increase at 72 h (P < 0.001). The TBARS levels of both test groups were significantly greater than that of control (P < 0.05), and displayed similar values at 72 h (P > 0.05). For both materials, the levels of TGF-beta1 and BMP-2 were significantly greater than that of control (P < 0.05). Both test groups showed increased TGF-beta1 levels. These results indicate that the tested self-etch adhesives might be capable of inducing production of TGF-beta1 and BMP-2 in cultured HGF, despite their cytotoxic and oxidative stress-producing potential.

In vitro genotoxicity of root canal sealers

AIM

To evaluate the effect of leakage on differences in genotoxicity of root canal sealers ex vivo according to their main components using two different cytogenetic assays.

METHODOLOGY

Six materials of different composition (GuttaFlow, Epiphany, Diaket, IRM, SuperEBA and Hermetic) were tested on human peripheral blood lymphocytes using the comet assay and chromosomal aberration analysis. Prepared materials were eluted in physiological solution for 1 h, 1 day, 5 and 30 days. Thereafter cultures were treated with 8 microg, 4 microg and 2 microg of each sealer. Frequencies of chromatide and chromosome breaks and accentric fragments were determined. Comet assay was used to evaluate primary DNA damage by measuring tail length and tail intensity. Chi-square, Fisher's PLSD (Protected Least Significant Difference) and Kruskall-Wallis non parametric tests were used for statistical analysis.

RESULTS

After 1-h elution only the highest dose of Diaket, Hermetic and SuperEBA significantly (P = 0.035, P = 0.048, P = 0.037 respectively) affected the measured cytogenetic parameters. The migration ability of DNA was more strongly affected than induction of chromosomal aberrations. After elutions longer than 24 h none of the tested sealers exhibited a genotoxic effect.

CONCLUSION

Under the conditions used in the study all sealers had acceptable biocompatibility in terms of genotoxicity.

Surgical applications of methyl methacrylate: a review of toxicity

Methyl methacrylate (MMA) is a monomer of acrylic resin widely used in a variety of medical, dental, and industrial applications. Its extensive use in surgery, particularly for arthroplasties, has often raised concerns regarding potential human toxicity for orthopaedic surgeons, surgical nurses, and other operating-room staff who are occupationally exposed to the compound. The main toxic effects of MMA exposure appear to involve the cardiovascular system. When exposed to MMA in the work environment, surgical staff have been reported to suffer from hypersensitivity, asthmatic reactions, local neurological symptoms, irritations and local dermatological reactions. The integrity of latex gloves may also be compromised following exposure to MMA during surgical procedures. At present, MMA is not thought to be carcinogenic to humans under normal conditions of use. Nevertheless, sound occupational hygiene practices should still be used to help reduce workplace exposure to MMA during orthopaedic and other medical procedures. Surgical staff should avoid direct contact with MMA mixtures wherever possible, and room ventilation and adequate airflow should also be optimized. In the present article, the authors review studies relating to MMA toxicity in surgical practice, updating in part a previous literature review and expanding on the toxicity of MMA within the surgical setting.

Methyl Methacrylate Activates the Gsta1 Promoter

Residual monomers in resin-based biomaterials cause cytotoxicity. We previously showed that methyl methacrylate (MMA) induced mRNA expression of the glutathione S-transferase alpha 1 gene ( Gsta1) located downstream of the cis-acting anti-oxidant responsive element (ARE). Herein, we tested the hypothesis that MMA activated the Gsta1 promoter through the ARE. HepG2 cells were transfected with a luciferase reporter vector containing the ARE and the Gsta1 promoter (−990 to +46 bp) and cultured for 12 hrs with MMA (initial concentration, 10 mM). Analysis of the expressed luciferase activity indicated that MMA activated the promoter 2.6-fold. MMA (from 1 to 30 mM) dose-dependently increased the promoter activity, which reached a plateau between 6 and 12 hrs. In HepG2 cells transfected with a reporter vector containing 2 AREs and a TATA-like promoter, 10 mM MMA increased the reporter expression 2.8-fold. These results suggest that MMA increases Gsta1 transcription through ARE-mediated promoter activation.