Patterns of cell death induced by eluates from denture base acrylic resins in U-937 human monoblastoid cells

Influence of Test Specimen Geometry and Water Soaking on the In Vitro Cytotoxicity of Orthocryl®, Orthocryl® LC, Loctite® EA 9483 and Polypropylene

Depending on their composition, plastics have a cytotoxic potential that needs to be evaluated before they are used in dentistry, e.g., as orthodontic removable appliances. Relevant guidelines set out requirements that a potential new resin in the medical field must meet, with a wide scope for experimental design. In the present study, test specimens of different geometries consisting of varying polymers (Orthocryl^®, Orthocryl^® LC, Loctite^® EA 9483, Polypropylene) were soaked for different periods of time, then transferred to cell culture medium for 24 h, which was subsequently used for 24-h cultivation of A549 cells, followed by cytotoxicity assays (WST-1, Annexin V-FITC-propidium iodide (PI) flow cytometry). In this context, a reduction in the cytotoxic effect of the eluates of test specimens prepared from Orthocryl^® LC and Loctite^® EA 9483 was particularly evident in the Annexin V-FITC-PI assay when the soaking time was extended to 48 h and 168 h, respectively. Consistent with this, a reduced release of potentially toxic monomers into the cell culture medium, as measured by gas chromatography-mass spectrometry, was observed when the prior soaking time of test specimens of all geometries was extended. Remarkably, a significant increase in cytotoxic effect was observed in the WST-1 assay, which was accompanied by a higher release of monomers when the thickness of the test sample was increased from 0.5 to 1.0 mm, although an elution volume adapted to the surface area was used. However, further increasing the thickness to 3.0 mm did not lead to an increase in the observed cytotoxicity or monomer release. Test specimens made of polypropylene showed no toxicity under all test specimen sizes and soaking time conditions. Overall, it is recommended to perform toxicity studies of test specimens using different geometries and soaking times. Thereby, the influence of the different specimen thicknesses should also be considered. Finally, an extension of the test protocols proposed in ISO 10993-5:2009 should be considered, e.g., by flow cytometry or monomer analysis as well as fixed soaking times.

Evaluation of the In-Vitro cytotoxicity of heat cure denture base resin modified with recycled PMMA-Based denture base resin

Aim:

The aim of the present study was to evaluate the in-vitro cytotoxicity of heat-cure denture base resin (PMMA) modified with recycled denture base resin at 10%, 20%, 30%, 40%, and 50% (w/w) concentration.

Materials and Methods:

A total of 30 disk-shaped specimens were prepared and divided into six groups (n = 5). The Control group (R₀) consisted of unmodified processed denture base resin, the experimental group consisted of denture base resin processed with substitution of 10% 20%, 30%, 40%, and 50% (w/w) of recycled denture base resin (R₁₀, R_20, R_30, R₄₀, and R₅₀). Eluates were prepared using five sterile specimens of each group. The mouse fibroblast cell line (L929) was seeded in a 96-well cell plate system at a concentration of 1 × 10⁴ cells/well in the DMEM medium with 1× antibiotic and antimycotic solution and 10% fetal bovine serum at 37°C with 5% CO₂ and incubated in a CO₂ incubator for 48 h. MTT assay was applied and the absorbance was measured at 570 nm using a microplate reader to assess the in-vitro cytotoxicity. One-way analysis of variance (ANOVA) along with post hoc Scheffe test was used to statistically compare the mean optical density (OD) values and cell survival/viability % amongst the groups.

Results:

No statistically significant difference was observed in the mean and standard deviation of the optical density and cell viability % of the test groups that were compared.

Conclusion:

Modification of denture base resin using recycled PMMA does not have a cytotoxic effect on the mouse fibroblast cell line L929.

Effect of processing methods on the cytotoxicity of methyl methacrylate-based ocular prostheses: An in vitro study

The study evaluated the influence of cycles and methods of an ocular prosthesis resin on cytotoxicity toward human conjunctival cells. Resins were polymerized by water bath (WB, 74 °C or 100 °C for 30 min to 9 h), microwave (MW, 1200 W, 3 to 14 min and 30 s at 0 to 720 W), or autopolymerization (AP, room temperature for 20 min ± 60 °C for 30 min). Degree of conversion (DC), cytotoxicity, level of inflammatory mediators, gene expression of different markers, and apoptosis were evaluated. Data were submitted to ANOVA and Tukey test (p < 0.05). WB with longer processing time at higher temperature had highest DC (85.6%) and higher TGF β1-gene expression (1.39); long cycle low power MW showed lowest DC (69.6%), lower cell proliferation (85.4%, MTT), and large IL-2 release (39,297 ng/mL). AP with additional processing time showed lower cell proliferation (75.3%, Alamar Blue), and AP polymerized at room temperature showed higher CASP 9-gene expression (1.21). AP methods showed higher IL-6 release (>277 pg/mL). Short cycle medium power MW had higher IL-23 release (534.2 pg/mL). MW (long and short cycles) and AP polymerizations have triggered a more intense inflammatory response. Among methods recommended by the manufacturer, WB showed high DC and less cytotoxicity.

Response of two gingival cell lines to CAD/CAM composite blocks

OBJECTIVE

This study aimed to investigate the influence of CAD/CAM composite materials on human gingival fibroblasts (HGF) and gingival keratinocytes (HGK).

METHODS

Four materials were investigated: two resin-composite blocks (RCB), Grandio Blocs (GR) and Block HC (HC); one polymer-infiltrated ceramic network (PICN) (Enamic, EN); and one conventional resin-composite, Grandioso (GND). HGF and HGK were cultured as per the supplier's protocol (ATCC, UK). Cell proliferation and cytotoxicity were evaluated at 1, 3, 5 and 10 days using LDH and Alamar Blue assays. Indirect immunostaining was used to assess the Caspase-3 activity. Data were analysed via two-way ANOVA, one-way ANOVA and Tukey's post hoc test (α = 0.05 for all tests).

RESULTS

There was significant difference in cell proliferation of the HGK and HGF cells in contact with different composite materials but no significant differences in their cytotoxicity. There was a significant effect on cell proliferation and cytotoxicity with different exposure times, for each type of resin-composite. HGF cell proliferation was higher than HGK with almost all investigated materials and at all time points. No Caspase-3 activity was detected in either cell lines.

SIGNIFICANCE

HGK proliferation and cytotoxicity appeared to be more influenced by composite materials compared to HGF, demonstrating EN cytotoxic effects in HGK. Different manufacturing techniques of resin-composites (photo curing versus heat/pressure curing) had no significant effect on their biocompatibility.

TEGDMA Causes Apoptosis in Primary Human Gingival Fibroblasts

Previous in vivo studies have revealed that resins may generate a persistent inflammation of oral tissues and cell death as well. Apoptosis is an important regulated process that results in rapid cell death. This study tested the hypothesis that the comonomer triethyleneglycol-dimethacrylate (TEGDMA) causes apoptosis. The effects of TEGDMA on proliferation and apoptosis in primary oral fibroblasts were analyzed by light microscopy and flow cytometry (FACS; Annexin V-assay). TEGDMA at 5 and 7.5 mM inhibited proliferation after 24 hrs. No increased frequency of apoptosis or necrosis was observed with 1 mM or 2.5 mM TEGDMA after 24 hrs. Apoptosis and Annexin V-positive cells were observed with 5 mM and 7.5 mM TEGDMA by light microscopy after 24 hrs. A dramatic increase in apoptotic cells was detected by FACS after 24 hrs with 7.5 mM TEGDMA. Thus, TEGDMA was cytotoxic and “apoptotic” in a dose- and time-dependent manner.

NF-κB Protection against Apoptosis Induced by HEMA

The cytotoxicity of dental monomers has been widely investigated, but the underlying mechanisms have not been elucidated. We studied the molecular mechanisms involved in cell death induced by HEMA. In human primary fibroblasts, HEMA induced a dose-dependent apoptosis that was confirmed by the activation of caspases-8, -9, and -3. We found an increase of reactive oxygen species (ROS) and NF-κB activation after HEMA exposure. Blocking of ROS production by anti-oxidants had no direct influence on apoptosis caused by HEMA, but inhibition of NF-κB increased the fraction of apoptotic cells. Accordingly, mouse embryonic fibroblasts (MEF) from p65−/− mice were more susceptible to HEMA-induced apoptosis than were wild-type controls. Our results indicate that exposure to HEMA triggers apoptosis and that this mechanism is not directly dependent upon redox signaling. Nevertheless, ROS induction by HEMA activates NF-κB, which exerts a protective role in counteracting apoptosis.

In Vitro Therapeutic Potential of Tio2 Nanoparticles Against Human Cervical Carcinoma Cells

Cellular and physiological responses to the degradation products of titanium implants are key indicators to determine the quality of biocompatibility of implant devices. The present study investigated titanium dioxide (TiO2) nanoparticle-induced cytotoxicity, apoptotic morphological modification, and apoptotic-related gene expressions in the human cervical carcinoma cells. TiO2 nanoparticle-induced cytotoxicity on cancer cells was determined by the sulphorhodamine-B assay. Apoptotic morphological modification such as nuclear fragmentation, rounding, cytoplasm shrinkage, loss of adhesion, and reduced cell volume were observed by an inverted, fluorescence, and confocal laser scanning microscope (CLSM). The DNA fragmentation study showed the occurrence of necrosis and apoptosis in nanoparticle-treated cells. The qPCR study showed the increased p53 and bax mRNA expression in the nanoparticle-treated cells compared to control. In addition, caspase 3 activity was increased in nanoparticle-treated cells, which indicates the increased auto-catalysis. Taking all these data together, it may suggest that TiO2 nanoparticle could inhibit the growth of HeLa cells.

Time and Concentration-Dependent Therapeutic Potential of Silver Nanoparticles in Cervical Carcinoma Cells

Silver nanoparticles (AgNPs) have well-known anti-bacterial properties and have been widely used in daily life as various medical and general products. There is limited information available on the cytotoxicity of AgNPs. Therefore, the present study aimed to investigate the cytotoxicity of AgNPs in HeLa cells. Cytotoxicity and apoptosis have been observed in the AgNPs treated in the HeLa cells. Sulphorhodamine-B assay (SRB assay) showed the cytotoxic effect in the AgNP-treated HeLa cells. Inverted microscope, fluorescence microscope, and confocal laser scanning microscope (CLSM) analyses showed the apoptosis-induced morphological changes such as rounding in shape, nuclear fragmentation, cytoplasm reduction, loss of adhesion, and reduced cell volume. Necrosis and apoptosis were observed in the AgNP-treated HeLa cells by DNA fragmentation study. Mitochondria-derived reactive oxygen species (ROS) have increased in AgNP-treated HeLa cells. Up-regulation of messenger RNA (mRNA) expression of p53, bax, and caspase 3 were found in AgNP-treated HeLa cells. Caspase 3 enzyme activity was found to increase in AgNP-treated HeLa cells. The AgNPs showed the right cytotoxic effect in cervical carcinoma cells. Our results suggest that metal-based nanoparticles might be a potential candidate for the treatment of cervical cancer.

Allergic effects of the residual monomer used in denture base acrylic resins

Denture base resins are extensively used in dentistry for a variety of purposes. These materials can be classified as chemical, heat, light, and microwave polymerization materials depending upon the factor which starts the polymerization reaction. Their applications include use during denture base construction, relining existing dentures, and for fabrication of orthodontic removable appliances. There have been increased concerns regarding the safe clinical application of these materials as their biodegradation in the oral environment leads to harmful effects. Along with local side effects, the materials have certain occupational hazards, and numerous studies can be found in the literature mentioning those. The purpose of this article is to outline the cytotoxic consequences of denture base acrylic resins and clinical recommendations for their use.

Functional role of apoptosis in oral diseases: An update

Cell death appears to be a basic biological phenomenon which is maintained by the human body. The term apoptosis, also known as programmed cell death, is characterized by several unique morphological and biochemical features. Apoptosis and its different forms are essential for tissue homeostasis. Alteration in molecular mechanisms involved in apoptotic signaling contributes to a vast range of oral diseases. An understanding of the regulation of apoptosis has led to the development of many therapeutic approaches and better management of oral diseases. The review updates us the correlation between apoptosis in normal oral tissues and oral diseases.

Biocompatibility of a titanium dioxide-coating method for denture base acrylic resin

OBJECTIVES

Ease of denture cleaning is of paramount importance in geriatric patients and those with limited dexterity. We have previously investigated methods of coating dentures with titanium dioxide (TiO₂ ) and reported the effects (self-cleaning and antibacterial) of such treatments in in vitro studies. This study was to verify the biocompatibility of a TiO₂ -coated acrylic resin produced by the new coating method with spray-coating technique.

METHODS

Specimens were prepared from denture base acrylic resin and polished up to grit #1000. The TiO₂ -coating agent was sprayed onto the specimens using an airbrush gun. Specimens were then divided into 'polymethyl methacrylate (PMMA)', 'primer-coated PMMA' and 'TiO₂ -coated PMMA' groups to be evaluated for biological safety using a hamster oral mucosa irritation test, a guinea pig skin sensitisation test and a rabbit intracutaneous test. The biological reaction was scored.

RESULTS

Reaction scores were considerably <1.0, the acceptable limit set by the ISO, in all three tests. Indeed, in most samples, there was no deleterious effect at all.

CONCLUSION

These results tested on animals demonstrate that denture base resin coated with TiO₂ by this method does not cause irritation or sensitisation of the oral mucosa, skin or intracutaneous tissue and is therefore good biocompatibility for use in close proximity to oral mucosa and skin.

Investigation of flexural strength and cytotoxicity of acrylic resin copolymers by using different polymerization methods

PURPOSE

The aim of this study was to appraise the some mechanical properties of polymethyl methacrylate based denture base resin polymerized by copolymerization mechanism, and to investigate the cytotoxic effect of these copolymer resins.

MATERIALS AND METHODS

2-hydroxyethyl methacrylate (HEMA) and isobutyl methacrylate (IBMA) were added to monomers of conventional heat polymerized and injection-molded poly methyl methacrylate (PMMA) resin contents of 2%, 3%, and 5% by volume and polymerization was carried out. Three-point bending test was performed to detect flexural strength and the elasticity modulus of the resins. To determine the statistical differences between the study groups, the Kruskall-Wallis test was performed. Then pairwise comparisons were performed between significant groups by Mann-Whitney U test. Agar-overlay test was performed to determine cytotoxic effect of copolymer resins. Chemical analysis was determined by FTIR spectrum.

RESULTS

Synthesis of the copolymer was approved by FTIR spectroscopy. Within the conventional heat-polymerized group maximum transverse strength had been seen in the HEMA 2% concentration; however, when the concentration ratio increased, the strength decreased. In the injection-molded group, maximum transverse strength had been seen in the IBMA 2% concentration; also as the concentration ratio increased, the strength decreased. Only IBMA showed no cytotoxic effect at low concentrations when both two polymerization methods applied while HEMA showed cytotoxic effect in the injection-molded resins.

CONCLUSION

Within the limitations of this study, it may be concluded that IBMA and HEMA may be used in low concentration and at high temperature to obtain non-cytotoxic and durable copolymer structure.

Effects of soft denture liners on L929 fibroblasts, HaCaT keratinocytes, and RAW 264.7 macrophages

The effects of six soft liners (Ufi Gel P (UG), Sofreliner S (SR), Durabase Soft (D), Trusoft (T), Coe Comfort (CC), and Softone (ST)) on L929, HaCat, and RAW 264.7 cells were investigated. Eluates (24 and 48 h) from the materials were applied on the cells and the viability, type of cell death, and morphology were evaluated. Cells were also seeded on the specimens' surfaces (direct contact) and incubated (24 or 48 h), and viability was analyzed. Controls were cells in culture medium without eluates or specimens. For cell viability, no significant differences were found among materials or between extraction periods, and the liners were noncytotoxic or slightly cytotoxic. Morphology of RAW 264.7 cells was altered by the 24 h eluates from CC and D and the 48 h eluates from SR, CC, and D. The 24 and 48 h eluates from all materials (except T) increased the percentages of L929 necrotic cells. For direct contact tests, the lowest cytotoxicity was observed for UG and SR. Although eluates did not reduce viability, morphology alterations and increase in necrosis were seen. Moreover, in the direct contact, effects on viability were more pronounced, particularly for D, T, CC and ST. Thus, the use of UG and SR might reduce the risk of adverse effects.

Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

OBJECTIVES

Residual methyl methacrylate (MMA) may leach from the acrylic resin denture bases and have adverse effects on the oral mucosa. This in vitro study evaluated and correlated the effect of the leaching residual MMA concentrations ([MMA]r) on in vitro cytotoxicity of L-929 fibroblasts.

MATERIAL AND METHODS

A total of 144 heat-polymerized acrylic resin specimens were fabricated using 4 different polymerization cycles: (1) at 74ºC for 9 h, (2) at 74ºC for 9 h and terminal boiling (at 100ºC) for 30 min, (3) at 74ºC for 9 h and terminal boiling for 3 h, (4) at 74ºC for 30 min and terminal boiling for 30 min. Specimens were eluted in a complete cell culture medium at 37ºC for 1, 2, 5 and 7 days. [MMA]r in eluates was measured using high-performance liquid chromatography. In vitro cytotoxicity of eluates on L-929 fibroblasts was evaluated by means of cell proliferation using a tetrazolium salt XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) assay. Differences in [MMA]r of eluates and cell proliferation values between polymerization cycles were statistically analyzed by Kruskal-Wallis, Friedman and Dunn's multiple comparison tests. The correlation between [MMA]r of eluates and cell proliferation was analyzed by Pearson's correlation test (p<0.05).

RESULTS

[MMA]r was significantly (p<0.001) higher in eluates of specimens polymerized with cycle without terminal boiling after elution of 1 and 2 days. Cell proliferation values for all cycles were significantly (p<0.01) lower in eluates of 1 day than those of 2 days. The correlation between [MMA]r and cell proliferation values was negative after all elution periods, showing significance (p<0.05) for elution of 1 and 2 days. MMA continued to leach from acrylic resin throughout 7 days and leaching concentrations markedly reduced after elution of 1 and 2 days.

CONCLUSION

Due to reduction of leaching residual MMA concentrations, use of terminal boiling in the polymerization process for at least 30 min and water storage of the heat-polymerized denture bases for at least 1 to 2 days before denture delivery is clinically recommended for minimizing the residual MMA and possible cytotoxic effects.

Testing of residual monomer content reduction possibility on acrilic resins quality

Poly (methyl methacrylate) (PMMA) is material widely used in dentistry. Despite the various methods used to initiate the polymerization of acrylic resins, the conversion of monomer to polymer is not complete thus leaving some unreacted methyl methacrylate (MMA), known as residual monomer (RM), in denture structure. RM in dental acrylic resins has deleterious effects on their mechanical properties and their biocompatibility. The objective of the work was to test the residual monomer reduction possibility by applying the appropriate postpolymerization treatment as well as to determine the effects of this reduction on pressure yields stress and surface structure characteristics of the acrylic resins. Postpolymerization treatments and water storage induced reduction of RM amount in cold-polymerized acrylic resins improved their mechanical properties and the homogenized surface structure. After the polymerization of heat-polymerized acrylic resins the post-polymerization treatments for improving the quality of this material type are not necessary.

Effect of post-polymerization heat treatments on the cytotoxicity of two denture base acrylic resins

INTRODUCTION

Most denture base acrylic resins have polymethylmethacrylate in their composition. Several authors have discussed the polymerization process involved in converting monomer into polymer because adequate polymerization is a crucial factor in optimizing the physical properties and biocompatibility of denture base acrylic resins. To ensure the safety of these materials, in vitro cytotoxicity assays have been developed as preliminary screening tests to evaluate material biocompatibility. (3)H-thymidine incorporation test, which measures the number of cells synthesizing DNA, is one of the biological assays suggested for cytotoxicity testing.

AIM

The purpose of this study was to investigate, using (3)H-thymidine incorporation test, the effect of microwave and water-bath post-polymerization heat treatments on the cytotoxicity of two denture base acrylic resins.

MATERIALS AND METHODS

Nine disc-shaped specimens (10 x 1 mm) of each denture base resin (Lucitone 550 and QC 20) were prepared according to the manufacturers' recommendations and stored in distilled water at 37 degrees C for 48 h. The specimens were assigned to 3 groups: 1) post-polymerization in a microwave oven for 3 min at 500 W; 2) post-polymerization in water-bath at 55 degrees C for 60 min; and 3) without post-polymerization. For preparation of eluates, 3 discs were placed into a sterile glass vial with 9 mL of Eagle's medium and incubated at 37 degrees C for 24 h. The cytotoxic effect of the eluates was evaluated by (3)H-thymidine incorporation.

RESULTS

The results showed that the components leached from the resins were cytotoxic to L929 cells, except for the specimens heat treated in water bath (p<0.05). Compared to the group with no heat treatment, water-bath decreased the cytotoxicity of the denture base acrylic resins.

CONCLUSION

The in vitro cytotoxicity of the tested denture base materials was not influenced by microwave post-polymerization heat treatment.

Induction of cell death by TiO2 nanoparticles: studies on a human monoblastoid cell line

The cellular responses to degradation products from titanium (Ti) implants are important indicators for the biocompatibility of these widely used implantable medical devices. The potential toxicity of nanoparticulate matter released from implants has been scarcely studied. The aim of this study was to investigate the potential of TiO2 nanoparticles to induce modifications characteristic for death by apoptosis and/or necrosis in U937 human monoblastoid cells. Suspensions of TiO2 nanoparticles with a diameter <100nm were prepared in RPMI cell culture medium at concentrations that covered a range (0.005-4mg/ml) corresponding to concentrations found in blood, plasma, or in tissues surrounding Ti implants. The cells were exposed to the nanoparticulate suspensions for 24 and 48h and the responses were evaluated by flow cytometry and transmission electron microscopy. TiO2 nanoparticles induced both apoptotic and necrotic modifications in U937 cells.

Effect of denture base resin extracts on HeLa cells growth in vitro

Growth of HeLa cell culture in vitro was examined, in different concentrations of four resin materials extracts which are used for denture base making. Cell growth was evaluated through density, invert microscope counting, after 48 hours of incubation and through metabolic MTT test after 3 days. Extract was taken by incubation of material sample on 37 ?C in physiological solution, for 72 hours. It is given weaker growth, reduction of adherent cells count and phenotypic changes of cells grown in presence of extracts from all examined materials. Extracts of examined materials increase number of phyllopodic extensions on dose dependent manner.

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.

Apoptosis in normal and diseased oral tissues

Apoptotic cell death plays an important role in maintenance of the normal physiological state and in the pathogenesis of diseases in the body. Over the last three decades the molecular mechanisms of apoptosis have been unravelled leading to development of novel therapeutic approaches. This paper aims to present current knowledge of the role of apoptosis in normal oral tissues and in the development of oral diseases.

The coinitiator DMABEE induces death by apoptosis and necrosis in human monoblastoid cells

4-N,N-Dimethyl amino benzoic acid ethylester (DMABEE), a leachable lipophilic component of polymer-based dental-filling materials, has been shown to interact with cell membrane phospholipids, such as phosphatidylcholine and phosphatidylserine (PS). One marker of cellular death by apoptosis is the change in architecture of the plasma membrane involving the translocation of the negatively charged PS from the inner to the outer leaflet of the cell membrane. We therefore hypothesized that DMABEE has the potential to induce apoptosis. The necrosis inducing potential was also investigated. To test our hypothesis human monoblastoid U-937 cells were exposed to 10, 20, 40, 80, 120, 160, and 200 microM of DMABEE for 24, 48, and 72 h. At the culture end-points apoptotic and necrotic cells were detected by flow cytometry. DMABEE enhanced cell death by apoptosis and necrosis in U-937 cells in a dose-dependent fashion. The data support our hypothesis that DMABEE triggers death-signaling pathways.

Cytotoxic effects of dental resin liquids on primary gingival fibroblasts and periodontal ligament cellsin vitro

Cytotoxic effects of resin liquids of three in situ relining dental polymers, Alike, Kooliner, and Tokuso Rebase, and their major components, methyl methacrylate (MMA), isobutyl methacrylate (IBMA), and 1,6-hexanediol dimethacrylate (1,6-HDMA) were investigated. The concentrations of major monomers in these resin liquids were determined by high-performance liquid chromatography. Cellular viability of human gingival fibroblasts (GF) and periodontal ligament (PDL) cells were evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide assay. Moreover, patterns of cell death were analysed using annexin V/propidium iodide staining with flow cytometry. The results indicated that Alike liquid contained 91.3% MMA, Kooliner liquid contained 94.5% IBMA, and Tokuso Rebase liquid contained 65.8% 1,6-HDMA. All materials examined had cytotoxic effects on GF and PDL cells in dose-dependent manners. Tokuso Rebase liquid appeared to be the most cytotoxic among the various resin liquids examined. The effects of Kooliner and Tokuso Rebase liquids may have resulted from IBMA and 1,6-HDMA, respectively. Furthermore, the majority of treated cells died from necrosis; whereas a small portion of cells died from apoptosis. In conclusion, the results demonstrated that these liquid forms of dental polymers and their major monomers cause cytotoxic reactions. The direct relining procedure that cures these materials in situ should be used cautiously.

Effects of BisGMA on glutathione metabolism and apoptosis in human gingival fibroblasts in vitro

Aim of this study was to investigate the effects of the resin monomer BisGMA on the glutathione concentration (monobromobimane assay) and apoptosis (Annexin V/PI-assay) of cultured primary human gingival fibroblasts. Cells were treated for up to 24h with 0.001-0.25 mM BisGMA to determine growth curves using the DNA stain H33342. Subsequent Annexin V/PI-assays revealed that fibroblasts exposed to concentrations of 0.005-0.01 mM (non-cytotoxic) and 0.05 mM (ED(10)-concentration) showed no increase of the share of apoptotic cells compared to non-treated controls (5-8%), while 0.1 mM BisGMA (approximately ED(50)-concentration) caused a significant increase of the percentage of apoptotic cells (50%). Simultaneously to the induction of apoptosis, 0.1 and 0.25 mM of BisGMA caused a significant depletion of the intracellular GSH content after 18 h of incubation. Our results indicate that BisGMA at concentrations >0.1 mM causes an extreme depletion of the intracellular GSH pool as well as apoptosis.

Residual methyl methacrylate monomer, water sorption, and water solubility of hypoallergenic denture base materials

STATEMENT OF PROBLEM

Denture base materials have the potential to cause irritation and allergic reaction to the oral mucosa. Water sorption and water solubility of denture base resins affect dimensional behavior and denture stability. A correlation between residual monomer and water sorption exists.

PURPOSE

This in vitro study compared the amount of residual monomer, quantity of water sorption, and solubility of 4 denture base materials purported to be hypoallergenic with those of a polymethyl methacrylate-based (PMMA) heat-polymerizing acrylic resin.

MATERIAL AND METHODS

The denture base resins Sinomer (heat-polymerized, modified methacrylate), Polyan (thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), and Microbase (microwave polymerized, polyurethane-based), which are purported to be hypoallergenic, and Paladon 65 (heat-polymerized, methacrylate, control group) were examined. Specimens of each material were tested for residual methyl methacrylate (MMA) monomer (% wt, n=3), amount of water sorption (microg/mm3, n=5) and water solubility (microg/mm3, n=5), according to ISO 1567:2000. The residual MMA monomer concentrations were determined by gas chromatography (GC). The data were analyzed with 1-way ANOVA and the Bonferroni-Dunn multiple comparisons post hoc analysis for each test variable (alpha=.05).

RESULTS

Significantly lower residual MMA monomer was shown for Sinomer and Polyan compared to the PMMA control group (0.90 +/- 0.20% wt, P<.05). Sinomer contained 0.31% +/- 0.00% wt MMA monomer, and Polyan exhibited residual MMA monomer content of 0.44% +/- 0.01% wt. Promysan and Microbase did not contain detectable residual MMA. Water sorption of Promysan (16.21 +/- 0.96 microg/mm3) was significantly lower than Paladon 65 (23.04 +/- 3.13 microg/mm3, P<.0001), whereas water solubility of the hypoallergenic denture base materials (0.34-0.84 +/- 0.05-0.09 microg/mm3) was not significantly lower than the PMMA material (0.40 +/- 0.06 microg/mm3, P>.05). Except for Sinomer, the tested denture base resins passed the requirements of ISO 1567 regarding residual MMA monomer (<2.2% wt). Sinomer failed to comply with the requirements for residual MMA monomer because the manufacturer claimed that the material did not contain any MMA. The tested denture base materials fulfilled the requirements regarding water sorption (<32 microg/mm3) and solubility (<1.6 microg/mm3).

CONCLUSION

The tested hypoallergenic denture base materials exhibited significantly lower residual monomer content than PMMA. Promysan and Microbase showed no detectable residual MMA.

In vitro cell death induced by irradiation and chemicals relevant for dental applications; dose-response and potentiation effects

Resin-based dental materials polymerized using blue light are frequently used in dental practice and may come in contact with the oral mucosa. Remnants from oral hygiene product ingredients, such as sodium lauryl sulfate (SLS), add to the chemical exposure of the mucosa. The aim of the present in vitro study was to elucidate the cytotoxic effects in terms of apoptosis and necrosis after exposures to combinations of an adhesive (0.5% and 0.6%), SLS (concentration range 0.0025%-0.0075%), and irradiation from a dental curing lamp (radiant exposure of 8 J cm(-2)). The test system chosen was rat submandibular salivary gland acinar cells, and the cytotoxic effects were measured by fluorescence microscopy and flow cytometry methods. Cytotoxicity was observed as a result of irradiation. The most pronounced cytotoxic effects were seen in cells exposed to a combination of adhesive and SLS compared with those exposed to either agent alone. Necrosis was the dominating form of cell death for all exposures, except for the highest concentration of SLS. Apoptosis was dose-dependent on SLS in the rat submandibular acinar cells. Cytotoxic considerations of dental materials should include contributions from irradiation and other chemicals that might be present in the oral cavity.

Cytotoxicity of denture base acrylic resins: a literature review

Acrylic resins are widely used in the fabrication of denture bases and have been shown to be cytotoxic as a result of substances that leach from the resin. The primary eluate is residual monomer. Numerous reports suggest that residual monomer may be responsible for mucosal irritation and sensitization of tissues. This information is important, not only to assess the biologic effects of such materials, but also to enable a comparison among the different polymerization methods, thus assisting the clinician in selecting a material with minimal cytotoxicity. This article reviews the literature published from 1973 to 2000, selected by use of a Medline search, associated with cytotoxic effects usually ascribed to acrylic denture base materials.

Strategies for the in vitro testing of in situ polymers

In situ polymers are used by mixing two or more compounds that are then placed directly in tissues to form a unique product. This type of reaction can generate heat, reactive oxygen species, free radicals, and other by-products of unknown toxicities, but the polymer itself is biocompatible. Many regulatory agencies require in vitro testing, however, standard guidelines (ASTM, ISO, AAMI) test polymers in a final form prior to use as a medical device. To better estimate the cytotoxicity of these in situ polymers, various means of introducing the reacting material to cells in culture were explored. Coating the material on a sterile glass cover slip then adding the cover slip to the in vitro test system immediately provided reasonable cytotoxicity data that reflected actual use conditions. For in situ polymeric devices that are more viscous, such as dental materials and bone cements, a mold was used that was placed directly into cell culture. This approach in testing in situ polymers generated in vitro toxicity data that reflects the actual use of the material.