The induction of micronuclei in vitro by unpolymerized resin monomers

N-acetyl cysteine (NAC)-assisted detoxification of PMMA resin

Despite its proven cytotoxicity, poly-methyl methacrylate (PMMA) resin is one of the most frequently and extensively used materials in dental practice. This study hypothesized that an anti-oxidant amino acid, N-acetyl cysteine (NAC), has the potential to detoxify this material. Ten percent of the rat dental pulp cells were viable when cultured on the PMMA resin for 24 hours, while over 70% of the cells were viable on the NAC-added resin. Nearly all suppressed alkaline phosphatase activity, matrix mineralizing capability, and odontoblastic gene expression, such as dentin sialoprotein, on the untreated control resin was recovered by NAC in a concentration-dependent manner. A Ca/P ratio of 1.65 was found in the extracellular matrix of cultures on NAC-added resin, while that in the untreated resin culture was 0.70. The addition of NAC to PMMA resin significantly ameliorated its cytotoxicity to the dental pulp cells and restored their odontoblast-like cell phenotype to a biologically significant degree.

A partially aromatic urethane dimethacrylate as a new substitute for Bis-GMA in restorative composites

OBJECTIVES

The objective of this study was to investigate the use of a new, partially aromatic urethane dimethacrylate in visible-light cured resin-based composite restoratives. Selected mechanical properties, such as flexural strength and flexural modulus of elasticity, of model monomer mixtures and composites containing the new urethane dimethacrylate were investigated and compared to the properties of materials that are based on Bis-GMA, at present the most frequently used cross-linker in restorative composites. In addition, the polymerization shrinkage and the water sorption of selected composites were determined.

METHODS

The flexural strength, flexural modulus of elasticity, and the water sorption were determined according to ISO 4049:2000. Test specimens (rods: 2 mmx2 mmx25 mm; discs: d=15 mm and h=1 mm) of the investigated composites were prepared in stainless steel molds and light-cured (150 mW/cm2, 2x180 s). The flexural strength and flexural modulus of rods were measured after the samples had been stored under dry conditions or in water for 24 h at 37 degrees C as well as after they had been stored in water for 7 days at 37 degrees C. The water sorption was determined with discs. The polymerization shrinkage was calculated from the densities of the uncured composite pastes and cured composites.

RESULTS

Visible light cured mixtures of dimethacrylate diluents with the new urethane dimethacrylate and composites based on these mixtures show a reactivity, flexural strength, flexural modulus of elasticity, polymerization shrinkage and water sorption similar to those of materials that are based on Bis-GMA. The composites did not show any strong deterioration of the mechanical properties after water storage.

Micronucleus rate of buccal mucosal epithelial cells in relation to oral hygiene and dental factors

Carcinogenesis of squamous cell carcinomas in the upper aero-digestive tract (UADT) is a multi-stage process. Since 1937, micronuclei (MN) have been considered a marker for genome damage in the initiation stage. By help of the micronucleus test, carcinogenic exposure can be proven in the mucosa area of the UADT. The hypothesis to be tested was that individual oral hygiene and the dental status, respectively - just like alcohol and tobacco abuse - are associated with the micronucleus rate in cytological preparations of the buccal mucosa. In a prospective clinical observation study, we determined in 100 probands the micronucleus frequency per 1000 mucosa epithelial cells. Study participants with a high number of missing teeth (M/T index, p=0.037), a below-average papillary bleeding index (PBI, p=0.032) and periodontal status, respectively (PSI, p=0.042) possessed a higher micronucleus number in comparison with restored dental conditions. Probands with composite restorations displayed a higher MN rate (p=0.006) compared to those with amalgam. However, we could not detect any significant relation with the prosthetic status (p> or =0.075). An adjustment was made according to alcohol and tobacco. We therefore conclude that subgingival plaque and synthetic dental materials in addition to chronic alcohol and tobacco consumption might have genotoxic relevance in the oral cavity.

In vitro and in vivo studies on the toxicity of dental resin components: a review

In vitro and in vivo studies have clearly identified that some components of restorative composite resins, adhesives, and resin-modified glass ionomer cements are toxic. The mechanisms of cytotoxicity are related firstly to the short-term release of free monomers occurring during the monomer-polymer conversion. Secondly, long-term release of leachable substances is generated by erosion and degradation over time. In addition, ion release and proliferation of bacteria located at the interface between the restorative material and dental tissues are also implicated in the tissue response. Molecular mechanisms involve glutathione depletion and reactive oxygen species (ROS) production as key factors leading to pulp or gingival cell apoptosis. Experimental animal approaches substantiate the occurrence of allergic reactions. There is a large gap between the results published by research laboratories and clinical reports.

Patterns of cell death and cell cycle profiles of cultured WEHI 13 var fibroblasts exposed to eluates of composite resins used for direct and indirect restorations

Previous studies have shown that in vitro exposure to single compounds released from composite resins may induce cell death. In the present study the effects of eluates from commercially available composite resins used for direct or indirect restorations were evaluated on the cell cycle progression and type of cell death of cultured WEHI 13 var fibroblasts. Cells exposed to eluates of the materials were assessed for cytotoxicity by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for cell death, for cell cycle profiles by flow cytometry, for caspase-3 biochemically and by immunocytochemistry, and for morphological changes by fluorescence microscopy with acridine orange. The direct composite resin eluates induced extensive apoptosis, followed by secondary necrosis. This was accompanied by cell enlargement, micromultinucleation, chromatin disintegration, cell cycle arrest at different phases, and caspase-3 activation. The composites for indirect restorations were much less cytotoxic at all biological end-points investigated. The findings suggest that composite resins used for direct and indirect dental restorations differ in their cytotoxic potential and their ability to affect basic cellular functions. This underlines the impact of improved polymerization with respect to their biologic behavior.

Effect of light curing type on cytotoxicity of dentine-bonding agents

AIM

To compare the cytotoxic effects of dentine-bonding agents (DBAs) polymerized with two different curing units at 24 h and 72 h on L-929 cells.

METHODOLOGY

Disc-shaped test samples of light-activated DBAs were prepared according to manufacturers' instructions and cured with either conventional quartz tungsten halogen or light-emitting diode light curing units (LCUs). After curing, the samples were transferred into a culture medium for 24 h. Eluates were obtained and pipetted onto L-929 mouse fibroblast cultures (3 x 10(4) cells per well), incubated for evaluation after 24 and 72 h. After both incubation periods, measurements were performed by an dimethylthiazol diphenyltetrazolium assay. The degree of cytotoxicity for each sample was determined according to the reference value represented by the cells with a control (culture without sample). Statistical significance was determined by a three-way analysis of variance followed by the Mann-Whitney U-test.

RESULTS

No significant three-factor interaction occurred amongst LCUs, DBAs and time factors (P = 0.955). LCUs and DBAs had a significant two-factor interaction (P < 0.001). In general, the test materials cured with the light-emitting diode LCU demonstrated higher cell survival rates when compared with the those cured with the quartz tungsten halogen.

CONCLUSIONS

Differential toxic effects of the DBAs cured with the quartz tungsten halogen or the light-emitting diode on the fibroblast cells may prove to be very important when suitable DBAs or LCUs are used for operative restorations.

Genotoxicity evaluation of five different dentin bonding agents by chromosomal aberration analysis

Dentin bonding agents became unavoidable in today's aesthetic restorative dentistry. Nevertheless, more and more evidences on their possible cytotoxicity and/or genotoxicity emerge. Still, only limited number of studies has been published on that issue. In our work we evaluated possible genotoxicity of five different adhesives: Adper Single Bond, Adper Single Bond 2 with nanofiller, Excite, OptiBond Solo Plus and Prompt L-pop. Genotoxicity assessment was carried out on human lymphocytes in vitro, using chromosomal aberration analysis. Polymerized adhesives were tested at three different dilutions of the 0.5 g mL(-1) eluate stock (2.5 x 1:10(6), 1:10(6) and 1:10(5)) after 1 h, 24 h and 5 days of elution. Slight but significant increase in the number of chromatid breaks was observed after 24-h elution period, for adhesives Adper Single Bond 2, Excite, and OptiBond Solo Plus at dilutions of 1:10(6) and 1:10(5), and for other two only at dilution of 1:10(5). First three adhesives also appeared to be slightly genotoxic after 1 h of elution but only at 1:10(5). As a bonding agent remains in close contact with living dental tissue over a long period of time, information on their possible genotoxicity and carcinogenicity should be more clearly clarified in the near future.

Genetic and cellular toxicology of dental resin monomers

Monomers are released from dental resin materials, and thus cause adverse biological effects in mammalian cells. Cytotoxicity and genotoxicity of some of these methacrylates have been identified in a vast number of investigations during the last decade. It has been well-established that the co-monomer triethylene glycol dimethacrylate (TEGDMA) causes gene mutations in vitro. The formation of micronuclei is indicative of chromosomal damage and the induction of DNA strand breaks detected with monomers like TEGDMA and 2-hydroxyethyl methacrylate (HEMA). As a consequence of DNA damage, the mammalian cell cycle was delayed in both G1 and G2/M phases, depending on the concentrations of the monomers. Yet, the mechanisms underlying the genetic and cellular toxicology of resin monomers have remained obscure until recently. New findings indicate that increased oxidative stress results in an impairment of the cellular pro- and anti-oxidant redox balance caused by monomers. It has been demonstrated that monomers reduced the levels of the natural radical scavenger glutathione (GSH), which protects cell structures from damage caused by reactive oxygen species (ROS). Depletion of the intracellular GSH pool may then significantly contribute to cytotoxicity, because a related increase in ROS levels can activate pathways leading to apoptosis. Complementary, cytotoxic, and genotoxic effects of TEGDMA and HEMA are inhibited in the presence of ROS scavengers like N-acetylcysteine (NAC), ascorbate, and Trolox (vitamin E). Elevated intracellular levels of ROS can also activate a complex network of redox-responsive macromolecules, including redox-sensitive transcription factors like nuclear factor kappaB (NF-kappaB). It has been shown that NF-kappaB is activated probably to counteract HEMA-induced apoptosis. The induction of apoptosis by TEGDMA in human pulp cells has been associated with an inhibition of the phosphatidylinositol 3-kinase (PI3-K) cell-survival signaling pathway. Although the details of the mechanisms leading to cell death, genotoxicity, and cell-cycle delay are not completely understood, resin monomers may be able to alter the functions of the cells of the oral cavity. Pathways regulating cellular homeostasis, dentinogenesis, or tissue repair may be modified by monomers at concentrations well below those which cause acute cytotoxicity.

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.

Induction of micronuclei and other nuclear abnormalities in mussels exposed to bisphenol A, diallyl phthalate and tetrabromodiphenyl ether-47

Analysis of micronuclei, nuclear buds, bi-polynucleated and fragmented-apoptotic cells was performed in gills of blue mussels exposed for 3 weeks to sublethal concentrations of bisphenol A, diallyl phthalate (for the both nominal concentration 50 ppb) and to tetrabromodiphenyl ether-47 (nominal concentration 5 ppb). Fourteen specimens from each treatment and control group were used for the analysis. Our results demonstrated a significant increase in micronuclei frequency after the treatment with bisphenol A (P=0.0243), diallyl phthalate (P=0.0005) and tetrabromodiphenyl ether-47 (P<0.0001; Mann-Whitney U-test). Induction of bi-nucleated (P=0.0028), fragmented-apoptotic (P=0.0004) cells and nuclear buds (P=0.0101) was found in mussels exposed to tetrabromodiphenyl ether-47 while treatment with diallyl phthalate increased the level of fragmented-apoptotic cells (P=0.0283). Bisphenol A was the only agent that resulted only in induction of micronuclei but not any other kind of nuclear injuries.

Effect of N-acetyl-l-cysteine on ROS production and cell death caused by HEMA in human primary gingival fibroblasts

Previous investigations have shown that 2-hydroxyethyl methacrylate (HEMA) causes reactive oxygen species (ROS) production, which in turn affects cell survival and cell death. The purpose of this study was to evaluate the effects of the antioxidant N-acetyl-L-cysteine (NAC) on HEMA-induced toxicity in human primary gingival fibroblasts (HGF). HGF were treated with various concentrations of HEMA (0-12 mm) in the absence and presence of NAC (1, 5, and 10 mm). The 3-(4,5 dimethyiazol-2-1)-2-5-diphenyl tetrazolium bromide (MTT) assay was used to evaluate the mitochondrial dehydrogenase activity after HEMA exposure. Viability and cell death were determined by flow cytometry using Annexin V and PI staining. ROS production was detected by the increasing fluorescence of the oxidation-sensitive dye 2',7'-dichlorofluorescein diacetate (DCFH-DA) after HEMA treatment. After a 24h incubation period, HEMA concentrations higher then 10mm caused a decrease of cell viability, mitochondrial activity, and an increase of cell death. HEMA concentrations of 4-12 mm markedly increased ROS levels in a dose-dependent manner. High NAC concentrations (5 and 10 mm) significantly reduced cell death, and restored the mitochondrial activity after a 24 h co-treatment, but 1 mm NAC increased HEMA toxicity (p<0.05). All NAC concentrations significantly reduced ROS levels induced by HEMA after a 2 h exposure (p<0.05), but no such reduction was observed after a 4 h treatment. Furthermore, treatment with 10 mm HEMA and 1 mm NAC for 6h caused an increase in ROS levels compared to 10 mm HEMA alone (p<0.05). In conclusion, our results suggest that high NAC concentrations protect HGF against HEMA cytotoxicity by reducing the induced ROS levels.

Cytotoxic and genotoxic effects of resin monomers in human salivary gland tissue and lymphocytes as assessed by the single cell microgel electrophoresis (Comet) assay

Malignant tumors of the three major pairs and the numerous minor salivary glands in humans are rare, and little is known about their various etiologies. Considering the fact that resin monomers from dental restorative materials are released into the saliva and diffuse into the tooth pulp or gingiva, mucosa, and salivary glands, this may potentially contribute to tumorigenesis. Resin monomers may also be reabsorbed and reach the circulating blood as well. Whereas the cytotoxic potential of some components has been clearly documented, data on genotoxicity in human target cells require further investigation. In the present study, genotoxic and cytotoxic effects of three common methacrylates are investigated in human samples of salivary glands and peripheral lymphocytes. The Comet assay was used to quantify DNA single strand breaks, alkali labile and incomplete excision repair sites in salivary gland probes and lymphocytes of 10 volunteers. The xenobiotics investigated were triethyleneglycoldimethacrylate (TEGDMA), urethanedimethacrylate (UDMA), and 2-hydroxyethylmethacrylate (HEMA), with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and dimethyl sulfoxide (DMSO) as controls. DNA migration was analyzed using the tail moment according to Olive (OTM). Cytotoxicity was monitored using trypan blue staining. With TEGDMA concentrations at 10(-5)m (10(-3)m), UDMA at 10(-7)m (10(-7)m), and HEMA at 10(-3)m (10(-5)m) significant enhancements of DNA migration were achieved in tissue cells (lymphocytes) as compared to the negative controls. At higher concentrations of up to 2.5x10(-2)m, induced DNA migration was expressed by OTM at 10.7 for TEGDMA in tissue cells (8.7 in lymphocytes), 10.5 for UDMA (6.4), and 9.7 for HEMA (6.1). The viability of the cell systems was not affected as concerns the threshold level for the assay of 75% viable cells except for the highest concentration tested for TEGDMA and UDMA in tissue cells. At higher concentration levels, all tested substances induced significant enhancement of DNA migration in the Comet assay as a possible sign for genotoxic effects in human salivary glands and lymphocytes. These data add to the results of prior studies in human peripheral lymphocytes and give evidence of a possible risk factor for tumor initiation in human salivary glands.

The effect of triethylene glycol dimethacrylate on the cell cycle of mammalian cells

The induction of DNA damage by a genotoxic agent is a signal leading to cell cycle delay, and thereby enables and induces DNA repair prior to cell cycle progression. Triethylene glycol dimethacrylate (TEGDMA), a monomer of dental resinous materials, caused mutagenic effects in mammalian cells probably as a consequence of DNA damage. Therefore, we hypothesized that TEGDMA will induce a cell cycle delay in mammalian cells. Here, cell lines deficient and proficient of a functional p53 tumor suppressor protein were used to study the effects of TEGDMA on the various phases of the cell cycle. V79 Chinese hamster lung fibroblasts (p53 deficient), N1 human skin fibroblasts (p53 proficient), and primary human pulp fibroblasts (p53 proficient) were exposed to increasing TEGDMA concentrations (0-3 mmol/l). Cell survival and vitality were determined after a 24-h exposure period and a 24-h recovery period, and the distribution of cells between the phases of the cell cycle in untreated and TEGDMA-treated cultures was analyzed by flow cytometry. The majority of the TEGDMA-treated V79 cells accumulated in G2 phase. In contrast, about 30% of human N1 fibroblasts were reversibly blocked in G1 phase by 0.5-3.0 mmol/l TEGDMA. The fraction of G2-phase cells was increased only by high TEGDMA concentrations. The percentage of human pulp cells in G1 phase increased very slightly with 1 mmol/l TEGDMA, but cell numbers in G1 phase were reduced by 10-20% by 1.5-3 mmol/l TEGDMA. The percentage of pulp cells in G2 phase increased about 2-fold without any obvious effect of a 24-h recovery period. Therefore, TEGDMA caused cell cycle delays through p53-dependent and independent pathways in the various cell lines. From these results, we conclude that TEGDMA may influence physiological processes like cell growth and differentiation of human pulp cells in vivo.

Cytotoxic and mutagenic effects of dental composite materials

Mutagenicity of single compounds of dental resinous materials has been investigated on many occasions before, but the induction of mutagenic effects by extracts of clinically used composites is still unknown. Here, cytotoxic effects and the formation of micronuclei were determined in V79 fibroblasts after exposure to extracts of modern composite filling materials (Solitaire, Solitaire 2, Tetric Ceram, Dyract AP, Definite). For cytotoxicity testing, test specimens were aged for various time periods (0, 24, and 168 h), and V79 cells were then exposed to dilutions of the original extracts for 24, 48, and 72 h. The ranking of the cytotoxic effects of the composites according to EC50 values after a 24-h exposure period was as follows: Solitaire (most toxic)=Solitaire 2<Tetric Ceram<Dyract AP<Definite (least toxic). Cytotoxicity was independent of the period of aging for each composite, but varied with exposure periods. The cytotoxic effect of Solitaire increased about two-fold between exposure periods of 24, 48, and 72 h, no changes were observed with Solitaire 2, and cytotoxicity of Tetric Ceram, Dyract AP, and Definite was reduced. Even eight-fold diluted original extracts of freshly mixed Solitaire test specimens increased the numbers of micronuclei about 10-fold, and Solitaire 2 was slightly less effective. The mutagenic effects of these materials were reduced in the presence of a rat liver homogenate (S9). Weak increases of the numbers of micronuclei were detected only with undiluted extracts of Tetric Ceram and Dyract AP, but Definite was not effective. Our findings suggest that mutagenic components of biologically active composite resins should be replaced by more biocompatible substances to avoid risk factors for the health of patients and dental personnel.

Leachability of plasticizer and residual monomer from commercial temporary restorative resins

OBJECTIVES

This study was performed to determine the compositions of commercial temporary restorative resins and to evaluate the leachability of plasticizer and residual monomer from them.

METHODS

The chemicals in four commercial temporary restorative resins (Dura Seal, Fit Seal, Plast Seal Quick, and Poly Seal) were detected by GCMS and HPLC. The amounts of plasticizers and residual monomers that leached from cured resin samples immersed in ethanol for 1 h to 14 d were determined by HPLC.

RESULTS

Phthalate esters used as plasticizers contained 40-55 wt% either di-n-butyl phthalate (DBP) or butyl phthalyl butyl glycolate. The resin monomer included methyl methacrylate (MMA) or a mixture of MMA and 2-hydroxyethyl methacrylate (HEMA); 1,3-butanediol dimethacrylate was added as a cross-linking agent. Each resin contained 40-60 wt% monomer. The amounts of phthalate esters leached increased with immersion time up to 7 d, reaching 120-190 microg/mg, and did not change subsequently. The residual monomers leached gradually for up to 3d and did not change subsequently. The amount of leached residual monomer (MMA, HEMA) was 20-90 microg/mg after 3d storage. More than 50% of the leachable plasticizers and monomers were eluted from the cured resins within 24 and 3 h, respectively.

CONCLUSIONS

The amounts of leached plasticizers and residual monomers were extremely large compared with the concentrations of endocrine disrupters and their potentially genotoxic effects. Therefore, it is very important to evaluate the leachability of these compounds from temporary restorative resins.

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.

Toxicity of methyl methacrylate in dentistry

Methyl methacrylate (MMA), a monomer of acrylic resin, has a wide variety of dental, medical and industrial applications. Concerns have been raised regarding its potential toxicity in dental use, both for the patient and also in the workplace. Dental patients are also exposed to MMA leached from some dental appliances and the effects, at least in vitro, appear toxic to cells and may cause local mucosal irritation or even an allergic reaction. When exposed to MMA in the dental clinic, dentists and other dental staff appear to occasionally suffer hypersensitivity, asthmatic reactions, local neurological symptoms, irritant and local dermatological reactions. The integrity of latex gloves may also be compromised after exposure to MMA during dental procedures. MMA is not thought to be carcinogenic to humans under normal conditions of use. Techniques should be employed to reduce patients' exposure to MMA during dental procedures in order to reduce the risks of possible complications. Dental staff should avoid direct contact with MMA and room ventilation should be optimised.

Components of dentinal adhesives modulate heat shock protein 72 expression in heat-stressed THP-1 human monocytes at sublethal concentrations

Few studies have investigated the ability of dental resins to induce cellular stress at sublethal concentrations. Cellular stress, especially in immune cells such as monocytes, may modulate the biological response to materials or the host's ability to respond to bacterially mediated inflammation. The current study examined the ability of sublethal concentrations of 2-hydroxylethylmethacrylate (HEMA) and triethyleneglycol dimethacrylate (TEGDMA) to induce heat shock protein 72 (HSP72) in human monocytes. HEMA and TEGDMA significantly suppressed heat-induced HSP72 expression, even at sublethal levels, but did not induce HSP72 by themselves. The results of the current study suggest that components released from dental resin could modulate the HSP stress response without altering cellular metabolic activity.