Lipid peroxidation as a possible cause of benzoyl peroxide toxicity in rabbit dental pulp--a microsomal lipid peroxidation in vitro

Bio-functional strontium-containing photocrosslinked alginate hydrogels for promoting the osteogenic behaviors

In recent years, photocrosslinked alginate hydrogel has been widely studied in bone tissue engineering, owing to its numerous advantages. However, there are still some shortcomings like insufficient mechanical strength and lack of bone induction. To compensate for these deficiencies, in this work, a novel doped strontium (Sr) photocrosslinked methacrylated alginate (Sr-PMA) hydrogel was developed. Photocrosslinked alginate hydrogel fabricated via crosslinking methacrylate-modified alginate under ultraviolet (UV) light was placed into strontium solutions to prepare Sr-PMA gel by chelating reaction. The chemical structures, swelling behaviors, degradation profiles, elastic moduli, Sr²⁺ ion release and surface morphology of the Sr-PMA hydrogel were characterized, and we found that physical properties of the gels can be tailored by varying concentration of Sr²⁺ ions. And MC3T3-E1 cell viability, proliferation and mineralization outside the hydrogel were also investigated. Further research on cell survival, multiplication, osteogenic differentiation of the cells encapsulated in Sr-PMA hydrogels were explored. In vitro studies of biological properties revealed that incorporation of Sr²⁺ into photocrosslinked alginate gels significantly improved osteogenic differentiation capabilities and mineralization via stimulating expression of osteogenesis related genes and proteins of the cells compared to strontium-free photocrosslinked alginate gels. The research demonstrates that the innovative Sr-PMA hydrogels possessing adjustable physical performances, excellent biocompatibility and osteogenic differentiation capabilities could be potentially applied to bone tissue engineering and regenerative medicine. Meanwhile, it also provides a reference for the modification of biological properties of biomaterials.

Dental resin monomers induce early and potent oxidative damage on human odontoblast-like cells

Resin-based dental materials consist of filler particles and different monomers that are light cured in situ to re-establish dental function and aesthetics. Due to the degree of conversion of adhesive polymers, the monomers triethyleneglycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are released in relatively high amounts and are susceptible to degradation, acting as bioactive compounds and affecting cell and tissues. This study aimed to assess the effect of HEMA and TEGDMA exposure on metabolic activity, membrane integrity, and cell survival of human odontoblast-like cell (hOLCs). Exposure to resin monomers for 24 h induced major changes in cell membrane integrity, metabolic activity, and survival, which were measured by the calcein method and lactate dehydrogenase release. Increased and early reactive oxygen species (ROS) production was observed leading to degradative oxidation of membrane lipids identified as malondialdehyde production. Severe alteration in mitochondria occurred due to transmembrane mitochondrial potential collapse, possibly inducing activation of apoptotic cell death. hOLCs exposure to resin monomers modified the cell redox potential, with consequences on membrane permeability and integrity, including mitochondrial function. Lipid peroxidation appears to be a key phenomenon for the membrane structures oxidation after HEMA and TEGDMA exposure, leading to cell death and cytotoxicity. hOLCs respond early by differential induction of adaptive mechanisms to maintain cell homeostasis. Modulation of oxidative stress-induced response involves the regulation of genes that encode for antioxidant proteins such as catalase and heme oxygenase-1; regulation that functions as a critical protection mechanism against oxidative cell damage induced by HEMA and TEGDMA. Ascorbic acid as an antioxidant substance mitigates the oxidative damage associated with exposure to monomers.

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.

Cytotoxicity of Light-Cured Dental Materials according to Different Sample Preparation Methods

Dental light-cured resins can undergo different degrees of polymerization when applied in vivo. When polymerization is incomplete, toxic monomers may be released into the oral cavity. The present study assessed the cytotoxicity of different materials, using sample preparation methods that mirror clinical conditions. Composite and bonding resins were used and divided into four groups according to sample preparation method: uncured; directly cured samples, which were cured after being placed on solidified agar; post-cured samples were polymerized before being placed on agar; and “removed unreacted layer” samples had their oxygen-inhibition layer removed after polymerization. Cytotoxicity was evaluated using an agar diffusion test, MTT assay, and confocal microscopy. Uncured samples were the most cytotoxic, while removed unreacted layer samples were the least cytotoxic (p < 0.05). In the MTT assay, cell viability increased significantly in every group as the concentration of the extracts decreased (p < 0.05). Extracts from post-cured and removed unreacted layer samples of bonding resin were less toxic than post-cured and removed unreacted layer samples of composite resin. Removal of the oxygen-inhibition layer resulted in the lowest cytotoxicity. Clinicians should remove unreacted monomers on the resin surface immediately after restoring teeth with light-curing resin to improve the restoration biocompatibility.

Relative survivability of human osteoblasts is enhanced by 39 °C and ascorbic acid after exposure to photopolymerization ingredients

Photopolymerizable hydrogels offer great potential in cartilage tissue engineering due to their ability to conform to irregular defect shapes and be applied in a potentially minimally invasive manner. An important process requirement in the use of photopolymerizable hydrogels is the ability of the suspended cells to withstand low intensity ultraviolet light (UV) exposure (4-5 mW/cm(2)) and photoinitiator concentrations. For cartilage integration with underlying subchondral bone tissue, robust localized osteoblast activity is necessary. Yet, while it is known that osteoblasts do not respond well to UV light, limited work has been conducted to improve their survivability. In this study, we evaluated the cellular cytotoxicity of five different human cell sources at different UV exposure times, with and without a commercially used photoinitiator. We were able to confirm that human osteoblasts were the least tolerant to varying UV exposure times in comparison to bone marrow stem cell, periodontal ligament cell, smooth muscle and endothelial cell lineages. Moreover osteoblasts cultured at 39 °C did not deteriorate in terms of alkaline phosphatase expression or calcium deposition within the extracellular matrix (ECM), but did reduce cell proliferation. We believe however that the lower proliferation diminished osteoblast sensitivity to UV and the photoinitiator. In fact, the relative survivability of osteoblasts was found to be augmented by the combination of a biochemical factor and an elevated incubation temperature; specifically, the use of 50 mg/l of the anti-oxidant, ascorbic acid significantly (P < 0.05) increased the survivability of osteoblasts when cultured at 39 °C. We conclude that ascorbic acid at an incubation temperature of 39 °C can be included in in vitro protocols used to assess cartilage integration with bone ECM. Such inclusion will enhance conditions of the engineered tissue model system in recapitulating in vivo osteoblast activity.

Radical-scavenging activity of dietary phytophenols in combination with co-antioxidants using the induction period method

The radical-scavenging activity of dietary phytophenols has been investigated by many researches due to their antioxidant, anti-inflammatory and anticancer property but the radical-scavenging effect of 2-phytophenol and the phytophenol:co-antioxidants, vitamin C and thiol combination under nearly anaerobic conditions still remains unknown. The radical-scavenging activity for seventeen phytophenols and for six synthetic phenols (positive controls) was investigated using the induction period method in the polymerization of methyl methacrylates (MMA) initiated by thermal decomposition of benzoyl peroxide (BPO) by monitoring differential scanning calorimetery (DSC). The k_inh for the phytophenols was likely with the range 0.5 × 10³ M⁻¹s⁻¹−2.2 × 10³ M⁻¹s⁻¹, whereas that for synthetic phenols, hydroquinone and galvinoxyl, was with the range 7 × 10³ M⁻¹s⁻¹−8 × 10³ M⁻¹s⁻¹. Also, the additive scavenging effect of the (−)-epigallocatechin (EGC):(−)-epicatechin (EC) and the (+)-catechin:epicatechin (EC) combination was observed at 1:1 molar ratio, whereas that of the EC:quercetin combination showed the cancel (prooxidative) effect. Furthermore, the EGC:ASDB (L-ascorbyl 2,6-dibutylate) or 2-ME (2-mercaptoethanol) combination showed the prooxidative effect. Such enhancement of prooxidation in the combination may increase their toxic effects due to their cooxidation. Also, the synergic, additive or cancel effects of the flavonoid:vitamins E combination on the induction period in the BPO (a PhCOO* radical) and 2,2′-azobisisobutyronitrile (AIBN, an R* radical) systems are discussed.

Medium osmolarity and pericellular matrix development improves chondrocyte survival when photoencapsulated in poly(ethylene glycol) hydrogels at low densities

The ability to encapsulate cells over a range of cell densities is important toward mimicking cell densities of native tissues and rationally designing strategies where cell source and/or cell numbers are clinically limited. Our preliminary findings demonstrate that survival of freshly isolated adult bovine chondrocytes dramatically decreases when photoencapsulated in poly(ethylene glycol) hydrogels at low densities (4 million cells/mL). During enzymatic digestion of cartilage, chondrocytes undergo a harsh change in their microenvironment. We hypothesize that the absence of exogenous antioxidants, the hyposmotic environment, and the loss of a protective pericellular matrix (PCM) increase chondrocytes' susceptibility to free radical damage during photoencapsulation. Incorporation of antioxidants and serum into the encapsulation medium improved cell survival twofold compared to phosphate-buffered saline. Increasing medium osmolarity from 330 to 400 mOsm (physiological) improved cell survival by 40% and resulted in approximately 2-fold increase in adenosine triphosphate (ATP) production 24 h postencapsulation. However, cell survival was only temporary. Allowing cells to reproduce some PCM before photoencapsulation in 400 mOsm medium resulted in superior cell survival during and postencapsulation for up to 15 days. In summary, the combination of antioxidants, physiological osmolarity, and the development of some PCM result in an improved robustness against free radical damage during photoencapsulation.

Genotoxicity of dental resin polymerization initiators in vitro

The polymerization initiators for resins cured using visible light usually consist of a photosensitizer, primarily camphorquinone (CQ), and a reducing agent, which is often a tertiary amine (DMPT, DMAEMA), while the initiator used for self-curing resins consists of benzoyl peroxide (BPO) and a tertiary amine (DMPT). The genotoxicities of camphorquinone (CQ), benzoyl peroxide (BPO), dimethyl-para-toluidine (DMPT), 2-dimethylamino-ethyl-methacrylate (DMAEMA), and 1-allyl-2-thiourea (ATU) were examined using the bioluminescent bacterial genotoxicity test. 4-Nitroquinoline-N-oxide (4NQO) was prepared for comparison with these chemicals. Acetone solutions of the five polymerization initiators and 4NQO were prepared. Benzoyl peroxide (BPO), dimethyl-para-toluidine (DMPT), and 1-allyl-2-thiourea (ATU) showed significant genotoxic activity at 24 h in the bioluminescent bacterial genotoxicity test, at concentrations of approximately 5 microM, 4 mM, and 1 mM, respectively. 2-Dimethyloamino-ethyl-methacrylate (DMAEMA) did not have genotoxic activity and CQ had questionable genotoxic activity. In comparison, 4NQO had strong genotoxicity, at 4 microM, roughly the same as that of BPO. Therefore, BPO should be used carefully in clinical dentistry.

Cell death effects of resin-based dental material compounds and mercurials in human gingival fibroblasts

In order to test the hypothesis that released dental restorative materials can reach toxic levels in human oral tissues, the cytotoxicities of the resin-based dental (co)monomers hydroxyethylmethacrylate (HEMA), triethyleneglycoldimethacrylate (TEGDMA), urethanedimethacrylate (UDMA), and bisglycidylmethacrylate (BisGMA) compared with methyl mercury chloride (MeHgCl) and the amalgam component mercuric chloride (HgCl2) were investigated on human gingival fibroblasts (HGF) using two different test systems: (1) the modified XTT-test and (2) the modified H 33342 staining assay. The HGF were exposed to various concentrations of the test-substances in all test systems for 24 h. All tested (co)monomers and mercury compounds significantly (P<0.05) decreased the formazan formation in the XTT-test. EC50 values in the XTT assay were obtained as half-maximum-effect concentrations from fitted curves. Following EC50 values were found (mean [mmol/l]; s.e.m. in parentheses; n=12; * significantly different to HEMA): HEMA 11.530 (0.600); TEGDMA* 3.460 (0.200); UDMA* 0.106 (0.005); BisGMA* 0.087 (0.001); HgCl2* 0.013 (0.001); MeHgCl* 0.005 (0.001). Following relative toxicities were found: HEMA 1; TEGDMA 3; UDMA 109; BisGMA 133; HgCl2 887; MeHgCl 2306. A significant (P<0.05) increase of the toxicity of (co)monomers and mercurials was found in the XTT-test in the following order: HEMA < TEGDMA < UDMA < BisGMA < HgCl2 < MeHgCl. TEGDMA and MeHgCl induced mainly apoptotic cell death. HEMA, UDMA, BisGMA, and HgCl2 induced mainly necrotic cell death. The results of this study indicate that resin composite components have a lower toxicity than mercury from amalgam in HGF. HEMA, BisGMA, UDMA, and HgCl2 induced mainly necrosis, but it is rather unlikely that eluted substances (solely) can reach concentrations, which might induce necrotic cell death in the human physiological situation, indicating that other (additional) factors may be involved in the induction of tissue (pulp) inflammation effects after dental restauration.

Variable cytocompatibility of six cell lines with photoinitiators used for polymerizing hydrogels and cell encapsulation

The development of biocompatible photopolymerizing polymers for biomedical and tissue engineering applications has the potential to reduce the invasiveness and cost of biomaterial implants designed to repair or augment tissues. However, more information is needed about the cellular toxicity of the compounds and initiators used in these systems. The current study evaluates the cellular toxicity of three ultraviolet sensitive photoinitiators on six different cell populations that are used for engineering numerous tissues. The photoinitiator 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) caused minimal toxicity (cell death) over a broad range of mammalian cell types and species. It was also demonstrated that different cell types have variable responses to identical concentrations of the same photoinitiator. While inherent differences in the cell lines may contribute to the variable cytotoxicity, a correlation between cellular proliferation rate (population doubling time) and increased cytotoxicity of the photoinitiator was observed. Cell lines that divided more quickly were more sensitive to photoinitiator-induced cell death. In summary, the photoinitiator Irgacure 2959 is well tolerated by many cell types over a range of mammalian species. Cell photoencapsulation strategies may be optimized to improve cell survival by manipulating proliferation rate.

Resin composite monomers alter MTT and LDH activity of human gingival fibroblasts in vitro

OBJECTIVES

Substances such as monomers may be released from composite resin systems and may induce adverse effects in biological tissues. The aim of this study is to investigate the cytotoxic concentrations of resin composite monomers on cultures of human gingival fibroblasts.

METHODS

A range of dilutions of five resin composite monomers (HEMA, HPMA, DMAEMA, TEGDMA, and Bis-GMA) were added to the culture medium of human gingival fibroblasts for 24 h. Their cytotoxic effects were measured by using two colorimetric functional assays, mitochondrial dehydrogenase activity (MTT) and lactate dehydrogenase activity (LDH) assay. The logP values (water/octanol partition) of test monomers were also calculated computationally.

RESULTS

Mitochondrial reducing activity assessed with the MTT test was inhibited by all monomers and all the monomers increased the LDH release in a reproducible dose dependent manner. A wide range of TC 50 values (concentrations altering MTT and LDH activity by 50%) (0.32-5.8 mM by MTT assay and 0.36-6.7 mM by LDH assay) was observed. Ranking of composite resin monomer cytotoxicities (TC 50) were similar for both the MTT and LDH assays, (Bis-GMA>TEGDMA>DMAEMA>HPMA >HEMA). However, the MTT assay was found to be more sensitive than the LDH assay, particularly when lower doses of the tested monomers were determined. The ranking of TC 50 concentrations correlated with the calculated logP values.

SIGNIFICANCE

Monomers used in dental restorative materials show a variety of toxic effects on gingival fibroblasts. A combination approach using MTT and LDH assays provides valuable information about their toxic effects.

Effects of subtoxic concentrations of benzoyl peroxide on cell lipid metabolism

Benzoyl peroxide (BP), a tumor promoter, has been shown to cause free-radical-induced lipid peroxidation and membrane damage at toxic concentrations. However, its effects on lipid metabolism at concentrations that were not overtly toxic have not been investigated. The purpose of the current study was to examine the effects of BP and its final degradation product, benzoic acid (BA), on lipid metabolism. Two cell lines, hamster cheek pouch (HCP) and human monocytes (THP-1), were used to determine the effects of BP, BA, and BP combined with FeCl2 on cell lipid metabolism. Cells were exposed to BP and 14C acetate for 24 h, or cells with prelabeled lipids were harvested, and the lipids were extracted and separated with the use of thin-layer chromatography. Lipid metabolism of some neutral lipids such as triglycerides was altered for both cell types in response to BP. Also, cholesterol content was reduced in THP-1 cells and a phospholipid, phosphatidylethanolamine (PE), was reduced in HCP cells. The final degradation product of BP, BA, failed to elicit any response in lipid metabolism. Subtoxic concentrations of BP induced changes in neutral lipids such as triglycerides and cholesterol. The metabolism of major phospholipids except PE remained unchanged. The effects were related to BP and its degradation and varied with the cell type.

Identification of organic eluates from four polymer-based dental filling materials

Elution from polymer-based dental filling materials may have a potential impact on the biocompatibility of the materials. Since information from the manufacturers about ingredients in the materials often is incomplete, analyses of eluates from the materials are necessary for a better knowledge about possible harmful compounds. The aim of this study was to identify organic eluates from polymerized samples of two composites, one compomer and one resin-reinforced glass ionomer cement. Samples were immersed in ethanol or Ringer's solution. Organic leachables were analyzed by gas chromatography-mass spectrometry. Identification was confirmed with reference substances, if available. Among components detected were monomers, co-monomers, initiators, stabilizers, decomposition products and contaminants. Thirty-two substances were identified and 17 were confirmed with reference substances. From elution in Ringer's we identified 13 eluates from Tetric Ceram, 10 from Z250, 21 from Dyract and six from Fuji II LC; HEMA, HC and CQ were found in all samples. From elution in ethanol 12 eluates from Tetric Ceram, 18 eluates from Z250, 19 from Dyract and 10 from Fuji II LC were identified. The diversity of eluates from the four materials under study is demonstrated. Owing to variation between the materials, the biocompatibility including the allergenic potential may be different.

Chemical-Biological Interactions of the resin monomer triethyleneglycol-dimethacrylate (TEGDMA)

Most dental resinous materials contain high quantities of the diluent monomer triethyleneglycol-dimethacrylate (TEGDMA). Due to its 'hydrophilic' nature, significant amounts of this substance leach into an aqueous environment, such as the oral cavity. Therefore, it is hypothesized that TEGDMA frequently interferes with oral and/or systemic tissues. In vitro studies revealed that TEGDMA is considerably cytotoxic in various cell cultures. It has also been observed that TEGDMA can easily penetrate membranes and subsequently may react with intracellular molecules. The formation of glutathione-TEGDMA adducts is of specific interest, since the nearly complete exhaustion of this molecule significantly reduces its cellular detoxifying potency. Large deletions of DNA sequences were caused by TEGDMA, resulting in high mutation frequency. In addition, TEGDMA has been identified as an important resinous sensitizer in patients and professionals. Taken together, available in vitro information, in vivo studies with animals, and clinical data as well indicate that TEGDMA may contribute considerably to local and systemic adverse effects caused by dental resins.

The relationship between leachability of polymerization initiator and degree of conversion of visible light-cured resin

Recently, polymerization-initiator-induced radicals have been identified as a biohazard as well as residual monomers. The present investigation was conducted to clarify the leaching behavior of the polymerization initiator and to measure the relationship between the leached amount of polymerization initiator and the degree of conversion of visible light (VL)-cured resin. Moreover, determining a suitable ratio of polymerization initiator to the base monomer according to the above relationship was carried out. The base monomer (UDMA/TEGDMA) was activated with varying concentrations of polymerization initiator (CQ/DMPT, CQ/DMAEMA) from 0.3-0.9 wt%, respectively, which were exposed to light for 40 s. Gas chromatograph mass spectrometry (GCMS) was carried out to evaluate the leached amount of polymerization initiator. The degree of conversion (DC) of the cured sample was estimated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. As the result, it was recognized that the leachability of the polymerization initiator (CQ, DMPT, and DMAEMA) depended on the degree of conversion of the VL-cured resin. Therefore, the optimal concentration of polymerization initiator can be determined from the relation between the degree of conversion and the leached amount of polymerization initiator, which is about 0.6 wt% for CQ/DMPT (1:1 in weight) and 0.5 wt% for CQ/DMAEMA (1:1 in weight) relative to the UDMA/TEGDMA (1:1 in weight) monomer.

Metabolic effects of dental resin components in vitro detected by NMR spectroscopy

Earlier studies have shown that the comonomer triethyleneglycol-dimethacrylate (TEGDMA) and the photostabilizer 2-hydroxy-4-methoxybenzophenone (HMBP) are cytotoxic and inhibit cell growth. It was the aim of this study to elucidate the underlying metabolic effects of TEGDMA and HMBP on immortal contact-inhibited Swiss albino mouse embryo cells (3T3 fibroblasts) by nuclear magnetic resonance (NMR) spectroscopy. Cell extracts and culture media were analyzed by NMR spectroscopy for metabolic changes after incubation for 24 hours with ED20-concentrations of TEGDMA and HMBP. TEGDMA could be detected in all fractions (cytosol, lipid fractions, and culture media) of 3T3 cells, while HMBP was found only in the lipid fraction accumulated at a maximum rate (51 nmol/mg DNA) compared with TEGDMA (27 nmol/mg DNA). TEGDMA increased the concentration of phosphomonoesters to 180+/-36% and decreased the phosphodiesters to 65+/-5% of controls (control = 100%). Thus, the turnover of phospholipids was enhanced, whereas content and composition of phospholipids of membranes did not alter markedly. Additionally, TEGDMA changed the metabolic state of cells, indicated by slight decreases of nucleoside triphosphates and an increase in the ratio of nucleoside diphosphates to nucleoside triphosphates, while HMBP had no effect. The most remarkable effect of TEGDMA was a nearly complete decline of the intracellular glutathione levels. Analysis of our data shows that NMR spectroscopy of cell-material interactions may reveal metabolic effects of organic test substances which are not detectable by standard in vitro assays. The comonomer TEGDMA affected the metabolism of the cells on different levels, while HMBP accumulated in the lipid fraction and induced significantly fewer effects on cell metabolism.

Effects of BisGMA and TEGDMA on proliferation, migration, and tenascin expression of human fibroblasts and keratinocytes

Previous studies have documented a marked cytotoxic potency of BisGMA and TEGDMA. The purpose of this investigation was to determine if these substances also affect proliferation, migration, and tenascin expression of primary human gingival fibroblasts (HGF) and immortalized human keratinocytes (HaCaT). These parameters play an important role in healing wounds. HGF and HaCaT cultures were incubated with TEGDMA and BisGMA. Cell proliferation (BrdU-assay) and migration (Boyden method) were determined 24 h after incubation. Tenascin expression was investigated four and seven days after treatment. Results were statistically evaluated by ANOVA using the Wilcoxon-Mann-Whitney test (p < 0.05). Proliferation of both cell types was significantly inhibited at concentrations > or = 0.25 mM (TEGDMA) or > or = 0.01 mM (BisGMA). Migration of HaCaT was significantly increased after incubation with BisGMA for 24 h. TEGDMA did not alter migration of HGF and HaCaT. In addition, TEGDMA had no effect on tenascin expression of both cell cultures. After 4 days of incubation, BisGMA (at a concentration of 0.01 mM) significantly reduced tenascin production of HaCaT cultures related to cell number. However, 7 days after treatment, BisGMA significantly increased tenascin expression of HGF and HaCaT cultures. Altogether, our results indicate that BisGMA can affect migration of keratinocytes and alters the expression of the extracellular matrix component tenascin. Thus, BisGMA may significantly influence the healing of injured oral tissues.

Biocompatibility of resin-modified filling materials

Increasing numbers of resin-based dental restorations have been placed over the past decade. During this same period, the public interest in the local and especially systemic adverse effects caused by dental materials has increased significantly. It has been found that each resin-based material releases several components into the oral environment. In particular, the comonomer, triethyleneglycol di-methacrylate (TEGDMA), and the 'hydrophilic' monomer, 2-hydroxy-ethyl-methacrylate (HEMA), are leached out from various composite resins and 'adhesive' materials (e.g., resin-modified glass-ionomer cements [GICs] and dentin adhesives) in considerable amounts during the first 24 hours after polymerization. Numerous unbound resin components may leach into saliva during the initial phase after polymerization, and later, due to degradation or erosion of the resinous restoration. Those substances may be systemically distributed and could potentially cause adverse systemic effects in patients. In addition, absorption of organic substances from unpolymerized material, through unprotected skin, due to manual contact may pose a special risk for dental personnel. This is borne out by the increasing numbers of dental nurses, technicians, and dentists who present with allergic reactions to one or more resin components, like HEMA, glutaraldehyde, ethyleneglycol di-methacrylate (EGDMA), and dibenzoyl peroxide (DPO). However, it must be emphasized that, except for conventional composite resins, data reported on the release of substances from resin-based materials are scarce. There is very little reliable information with respect to the biological interactions between resin components and various tissues. Those interactions may be either protective, like absorption to dentin, or detrimental, e.g., inflammatory reactions of soft tissues. Microbial effects have also been observed which may contribute indirectly to caries and irritation of the pulp. Therefore, it is critical, both for our patients and for the profession, that the biological effects of resin-based filling materials be clarified in the near future.

Cytotoxicity of dental composite components and mercury compounds in pulmonary cells

The cytotoxic potentials of the dental composite components triethyleneglycoldimethacrylate (TEGDMA) and 2-hydroxy-ethylmethacrylate (HEMA) as well as mercuric chloride (HgCl2) and methyl mercury chloride (MeHgCl) were investigated. Proliferating A549 and L2 cell monolayers were cultured in the absence or presence of composite components or mercurials. Twenty-four hours later the tetrazolium salt XTT (sodium 3'-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) was added. Formazan formation was quantified using a microtiter plate reader. EC50 values were obtained as half-maximum-effect concentrations from fitted curves. EC50 values were in A549 cells (mean values +/- standard deviation; n = 12; micromol/l); HEMA 8854+/-1882; TEGDMA 1821+/-529; HgCl2 41+/-7 and MeHgCl 27+/-3. EC50 values in L2 cells were: HEMA 191+/-28; TEGDMA 112+/-16; HgCl2 25+/-6 and MeHgCl 8+/-6. All tested substances induced a dose-dependent loss of viability in A549 and L2 cells after 24 h. The EC50 values of both mercurials were significantly (p < 0.05) lower compared to the values of both composite components. TEGDMA was about 5-fold (A549 cells) and about 2-fold (L2 cells) more toxic compared to HEMA. It is to be assumed that the risk of lung cell damage by dental composite components is even more unlikely.

The effect of heat- and auto-polymerized denture base polymers on clonogenicity, apoptosis, and necrosis in fibroblasts: denture base polymers induce apoptosis and necrosis

Eluates from poly(methyl methacrylate)-based denture base polymers have recently been found to enhance death by apoptosis and necrosis in U-937 human monoblastoid cells. The present study investigated the potential of such polymers to induce apoptosis and/or necrosis and to alter clonogenicity in L929 murine fibroblasts. A fibroblast cell line was chosen because the impairment of fibroblasts subjacent to denture bases may result in a weaker or more permeable mucosa. Two aspects were addressed: the effect of direct contact with the denture base polymers and the effect of eluates extracted from the polymers. For this purpose L929 fibroblasts were seeded on disks manufactured from three heat-polymerized and four autopolymerized denture base polymers or in different concentrations of their eluates. The effects were evaluated by light, fluorescent, confocal and electron microscopy, counting of colonies, and flow cytometry. Disks and eluates of all polymers enhanced cell death by apoptosis and necrosis in L929 cells and decreased their clonogenic potential in a dose-dependent manner. Apoptosis was the main form of cell death. In general, the deleterious effects were stronger when cells were plated directly on the polymer disks than in the eluates. The autopolymerized polymers, except one, yielded higher percentages of apoptosis and necrosis than the heat-polymerized polymers. The results of the study indicated that poly(methyl methacrylate)-based denture base polymers trigger death-signals in L929 fibroblasts and open doors for possible modulation of the cell/biomaterial interaction.

Cytotoxicity of 35 dental resin composite monomers/additives in permanent 3T3 and three human primary fibroblast cultures

It was the purpose of this investigation to determine the cytotoxic effects (ED50 concentrations) of 35 monomers or additives identified in commercial dental resin composites. Monolayers of permanent 3T3 cells and three primary human fibroblast types derived from oral tissues (gingiva, pulp, and periodontal ligament) were used as test systems. All substances were tested in concentrations ranging from 0.01 to 5.0 mM. In general, ED50 values varied from 0.06 to > 5 mM. Within the groups of co(monomers), initiators, and cointiators, severe (e.g., Bis-GMA, UDMA, DMBZ, and DMDTA) or moderate (HEMA, BEMA, CQ, DMPT, and DMAPE) cytotoxic effects could be evaluated. Within the group of reaction/decomposition products, only moderate or slight effects were found (ED50: 0.7 to > 5 mM). The inhibitor BHT, the contaminant TPSb, and the photostabilizer HMBP, however, were highly cytotoxic in all cell cultures. In addition, the ED50 values of DBPO and HMBP significantly varied (0.43-3.8 mM, respectively, and 0.44-3.07 mM) with the applied cell culture. Our comprehensive screening shows that for several of the highly cytotoxic composite components, less cytotoxic alternatives are available. Furthermore, there was no cell type identified which was consistently less or more sensitive to the toxic effects of the tested compounds than the others. Primary human periodontal ligament and pulp fibroblasts, however, were found to be more sensitive than 3T3 and gingival fibroblasts to alterations from most tested substances.

Cytotoxicity of photosensitizers camphorquinone and 9-fluorenone with visible light irradiation on a human submandibular-duct cell line in vitro

The cytotoxic effect of two types of photosensitizers (camphorquinone, CQ, a widely used aliphatic type and 9-fluorenone, 9F, an aromatic type) in the presence of 2-dimethylaminoethyl methacrylate (DM) as a reducing agent with exposure to visible light (350-550 nm) was examined in a human cell line. Cytotoxicity was evaluated in terms of the percentage of cell survival, and the production of reactive oxygen in living single cells was measured with an adherent cell analysis and sorting laser cytometer and a peroxide indicator. The amount of reactive oxygen generated in the cells irradiated in the 9F (1 mM-3 min) system was about 9-fold greater than under the same conditions in the CQ system. Similarly, the decrease in cell survival in the 9F system was about 10-fold greater than in the CQ. Both the production of reactive oxygen in the cells and the decrease in cell survival paralleled the concentration of photosensitizers and the irradiation time. Although the cell-damaging effects with the CQ system were mild, at a higher dose (10 mM) and longer irradiation time (24 min) it produced cell survival equal to that in the 9F (1 mM-3 min) system. These results suggest that in the case of irradiated photosensitizer systems, 9F was much more damaging to the cells than CQ, which damage probably occurred via free radicals involving reactive oxygen generation.

Effects of an aminomethacrylate on epithelial cell lipid metabolism

Methacrylates can affect cell functions by surfactant-like effects or by altering cell lipid composition. Dimethylaminoethyl methacrylate (DMAEMA), an activator widely used in visible-light polymerized dental resins has been shown to elute readily into aqueous environments. The current study examined the metabolism of this material by oral epithelial cells (HCP) and its subsequent effects on cell lipids. Cells were plated in culture medium, then exposed to DMAEMA in the presence of 14C-acetate, a precursor which labeled the cell lipids. Other cultures were prelabeled with radioisotope, then exposed to DMAEMA. After incubation, the cell lipids were extracted and separated by TLC. Radioactive lipids were located and quantitated. Exposure of the cells to DMAEMA resulted in decreased synthesis of cholesterol with a concomitant increase in sterol precursors. Cholesterol esters and triacylglycerides also increased. Among the polar lipids, phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) decreased in response to DMAEMA. However, dimethylphosphatidyl ethanolamine (DMPE), a precursor of PC not detectable in control cultures, accumulated to a significant extent in cells exposed to DMAEMA. Furthermore, changes in PC and DMPE levels persisted in the cells for at least 48 h after removal of the DMAEMA. The results indicate that DMAEMA produces alterations in the relative amounts of several cellular neutral and polar lipids. Such alterations, especially of the normal phospholipid composition, along with an alteration in cellular cholesterol, could result in altered membrane-associated cell functions.

Benzoyl peroxide cytotoxicity evaluated in vitro with the human keratinocyte cell line, RHEK-1

The human keratinocyte cell line, RHEK-1, was used to evaluate the cytotoxicity of benzoyl peroxide (BZP). As determined with the neutral red (NR) cytotoxicity assay, the 24-h midpoint (NR50) toxicity values, in mM, were 0.11 for BZP and 29.5 for benzoic acid, the stable metabolite of BZP. Irreversible cytotoxicity occurred after a 1-h exposure to 0.15 mM BZP and greater. When exposed to BZP for 7 days, a lag in growth kinetics was first observed at 0.06 mM BZP. Damage to the integrity of the plasma membrane was evident, as leakage of lactic acid dehydrogenase occurred during a 4-h exposure to BZP at 0.05 mM and greater. Intracellular membranes were also affected, as extensive vacuolization, initially perinuclear but then spreading throughout the cytoplasm, was noted in BZP-stressed cells. The generation of reactive free radicals from BZP was suggested by the following: the intracellular content of glutathione was lowered in cells exposed to BZP; cells pretreated with the glutathione-depleting agent, chlorodinitrobenzene, were hypersensitive to a subsequent challenge with BZP; lipid peroxidation by BZP was inducible in the presence of Fe2+; and cells previously maintained in a medium amended with vitamin E, an antioxidant, were more resistant to BZP, showed less lipid peroxidation in the presence of BZP+Fe2+ and did not develop the extensive intracellular vacuolization as compared to non-vitamin E maintained cells.

Responses of oral epithelial cells to dental resin components

The light-polymerized resins used in dentistry and their various constituents have been shown to produce significant levels of cytotoxicity, depending upon the material and the cell type exposed to it. These responses include altered cell growth and macromolecule synthesis. The current study examined the effects of several resin components on growth and lipid metabolism of oral epithelial cells. Resin discs were fabricated from triethyleneglycol dimethacrylate (TEGDMA) as received from the manufacturer and after removal of the stabilizer methyl ether hydroquinone (MEHQ). Some discs also contained the initiators benzoyl peroxide (BPO) and camphoroquinone (CQ), and/or an activator, dimethylaminoethyl methacrylate (DMAEMA). After polymerization, the ability of components to elute from the discs and alter cell growth and lipid synthesis were assayed by a colorimetric method and thin layer chromatography respectively. Purified TEGDMA had little effect on the cells' growth or lipid metabolism, while TEGDMA containing MEHQ did inhibit growth as well as total polar lipid synthesis. Eluates from discs containing DMAEMA inhibited cell growth as well as decreasing polar lipid formation. However, this same material produced increased synthesis of diglycerides and cholesterol esters. Eluates from BPO-containing discs, as well as those with CQ, with or without DMAEMA resulted in increased levels of diglycerides. These results demonstrate that even after polymerization, components used in dental resins may elute into the immediate environment and alter various cell metabolic processes.

Cellular inflammatory responses to direct restorative composite resins

As a result of shaping, finishing, or removal of dental composite resin restorations, resin particles may become trapped and embedded in oral tissues. However, tissue reactions induced by entrapped composite resin particles have not been thoroughly examined. To assess the soft tissue inflammatory response to composite restorative materials, three commercial dental composite resin suspensions were implanted subcutaneously in rats. Implantation resulted in a granulomatous inflammatory reaction that persisted 8 weeks after placement. The lesion was characterized by an influx of lymphocytes and the presence of fibroblasts and epithelioid cells. Composite resin particles have the potential to cause persistent inflammation if they are entrapped in oral tissues.

Ferric(III) ions inhibits copper(II)/hydrogen peroxide-catalyzing lipid peroxidation in human erythrocyte membranes

1. Effect of ferric ions (Fe3+) on the lipid peroxidation catalyzed by copper ions (Cu2+) and hydrogen peroxide (H2O2) was studied in human erythrocyte membranes. 2. The formation of thiobarbituric acid-reactive products elicited by CuCl2/H2O2 was inhibited by FeCl3 in a concentration-dependent manner; 0.25 mM FeCl3 were enough to cause 50% inhibition of the formation of peroxides. 3. The inhibitory effect of FeCl3 is not due to competition against Cu2+. 4. FeCl3 inhibited the initiation, but did not inhibit the propagation of Cu2+/H2O2-catalyzing lipid peroxidation. 5. In the heat- or trypsin-treated erythrocyte membranes, FeCl3 had no inhibitory effect on Cu2+/H2O2-catalyzing lipid peroxidation. 6. Sodium azide, an inhibitor of catalase, had no effect on the inhibitory effect of FeCl3. 7. These results suggest that a protein factor(s), which is not catalase, is involved in the inhibition of Cu2+/H2O2-catalyzing lipid peroxidation by Fe3+.

Cytotoxic effects of resin components on cultured mammalian fibroblasts

The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 mumol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 mumol/L, while the ID50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 mumol/L. The concentrations to which the cells and tissues are exposed in vivo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

Dental amalgam and mercury

This paper looks at the issues of the current amalgam controversy: the daily dose of mercury from amalgam, hypersensitivity to mercury, claims of adverse effects from amalgam mercury and alleged overnight "cures." In addition, the toxicity and allergenicity of the proposed alternative materials are examined with the same kind of scrutiny applied by the anti-amalgam group to dental amalgam.

Inhibitory effect of eugenol on Cu2+-catalyzed lipid peroxidation in human erythrocyte membranes

1. The effects of eugenol on lipid peroxidation catalyzed by hydrogen peroxide (H2O2) or benzoyl peroxide (BPO) in the presence of copper ions were studied in human erythrocyte membranes. 2. The production of hydroxyl radicals was suggested in the peroxidation system catalyzed by H2O2/Cu2+. 3. H2O2/Cu2+-dependent peroxidation was inhibited by eugenol in a concentration-dependent manner; peroxidation was inhibited 62% by 200 microM eugenol. 4. In the presence of eugenol, the peroxidation catalyzed by BPO/Cu2+ was inhibited in a concentration-dependent manner, and more than 100 microM eugenol completely inhibited peroxidation. 5. The inhibitory effect of eugenol was non-competitive against Cu2+ in H2O2/Cu2+- and BPO/Cu2+-dependent peroxidation. 6. It is suggested that eugenol inhibits formation of hydroxyl radicals.

Inhibition of benzoyl peroxide/Cu2+-dependent lipid peroxidation by manganese

1. Formation of peroxides by benxoyl peroxide (BPO) and CuCl2 was examined in the human red blood cell ghost. 2. Amounts of peroxides formed increased with the amount of the ghost solution added. 3. Of all the cations tested only manganese ion inhibited the formation of peroxides in BPO-CuCl2 reaction system. 4. The formation of peroxides was inhibited approx. 50% with 0.4 microM manganese. 5. The inhibitory manner of manganese was non-competitive against copper.

Effects of photoinitiators for the visible-light resin system on hemolysis of dog erythrocytes and lipid peroxidation of their components

The visible-light (VL) polymerizing resin system with photoinitiators (photosensitizer and reducing agent) is widely used in modern dentistry. In this system, polymerization is initiated by photochemical reactions between the photosensitizers (aromatic or aliphatic ketones) and reducing agents (tertiary amines) during VL irradiation. In order to simulate the VL resin-induced toxicity in dental pulps, the present investigation was conducted to determine whether hemolysis of dog erythrocytes and lipid peroxidation of their components occur on exposure to a VL resin system containing aromatic (9-fluorenone, benzil) or aliphatic ketones (camphoroquinone) plus tertiary amine [2-(dimethylamino) ethyl methacrylate]. It was demonstrated that the hemolysis and lipid peroxidation with aromatic ketones were markedly higher than with those of aliphatic ketones, even when the latter were used at higher concentrations. It was clear that peroxidation-induced hemolysis occurred and, further, that surface-active complexes between photosensitizers and reducing agents, which are formed by irradiation, promote hemolytic activity due to their hydrophobic interactions. VL resin-induced responses to dental pulps are probably promoted due to the double effects of unpolymerized monomers and of both radicals and surface-active complexes formed during irradiation.