Effect of dentin bonding agents on the secretion of inflammatory mediators from macrophages

The Role of Cellular Metabolism in Maintaining the Function of the Dentine-Pulp Complex: A Narrative Review

The cellular metabolic processes ensure the physiological integrity of the dentine-pulp complex. Odontoblasts and odontoblast-like cells are responsible for the defence mechanisms in the form of tertiary dentine formation. In turn, the main defence reaction of the pulp is the development of inflammation, during which the metabolic and signalling pathways of the cells are significantly altered. The selected dental procedures, such as orthodontic treatment, resin infiltration, resin restorations or dental bleaching, can impact the cellular metabolism in the dental pulp. Among systemic metabolic diseases, diabetes mellitus causes the most consequences for the cellular metabolism of the dentine-pulp complex. Similarly, ageing processes present a proven effect on the metabolic functioning of the odontoblasts and the pulp cells. In the literature, several potential metabolic mediators demonstrating anti-inflammatory properties on inflamed dental pulp are mentioned. Moreover, the pulp stem cells exhibit the regenerative potential essential for maintaining the function of the dentine-pulp complex.

Efficacy of Three Commercially Available Desensitizers in Reducing Post-Operative Sensitivity Following Composite Restorations: A Randomized Controlled Clinical Trial

One of the most widely used esthetic restorations in dentistry is composite. The widespread application of composites can be related to advancements in biomaterials. However, due to various factors, composites are commonly associated with dental sensitivity. Hence, the present study evaluates and compares the effectiveness of three desensitizing agents in reducing post-treatment sensitivity for Class I composite restoration. Eighty subjects with Class I cavities were selected according to the inclusion criteria, and a randomized, double-blind, controlled clinical trial was carried out. Twenty patients were randomly assigned to four groups: Group C (Control group), Group GL (Gluma group), Group SF (Shield Force Plus group), and Group TC (Telio CS group). The desensitizers were applied after Class 1 cavity preparation and acid etching in all the groups, except the Control group, and thereafter, composite restoration was completed in a conventional manner. Questionnaires were provided to all the participants to record the post-operative pain/sensitivity level according to the visual analogue scale (VAS) on intake of cold drinks, intake of hot drinks, and intake of sugar for different periods of time. Significant variation was observed between the three desensitizers for all three stimuli. However, no significant variations were seen with the various age groups and between the maxillary and the mandibular teeth at the different time periods. Group GL performed better than Group SF and Group TC. It can be proposed that the application of the desensitizers reduced the post-restorative sensitivity in the composite restorations and improved acceptance.

Cytotoxicity of two self-adhesive resin cements and their interference in the phagocytic activity of murine macrophages

Objectives

This study aimed to evaluate in vitro the effects of the self-adhesive resin cements RelyX U200 (3M ESPE) and seT PP (SDI Limited) on murine macrophages and the interference of the photoactivation.

Materials and Methods

Cell viability assays, cell adherence, yeast phagocytosis of Saccharomyces boulardii and production of reactive oxygen species (ROS) were performed in the presence of capillaries containing the respective self-adhesive cement when photoactivated or not.

Results

After long periods of contact, both types of cements, when not photoactivated, are more cytotoxic for macrophages. The seT PP cement when only chemically activated seems to interfere more negatively in the process of phagocytosis of yeasts S. boulardii. Both types of cements interfere in the cell adhesion process, independent of photoactivation. None of the types of cements tested was able to induce the production of ROS.

Conclusions

Our results highlight the great importance of the photoactivation of self-adhesive resin cements in the dental clinic, since RelyX U200, when photoactivated, presented the best results within the evaluated parameters.

Genotoxic and cytotoxic potential of methacrylate-based orthodontic adhesives

Objectives

The biocompatibility of methacrylate-based adhesives is a topic that is intensively discussed in dentistry. Since only limited evidence concerning the cyto- and genotoxicity of orthodontic adhesives is available, the aim of this study was to measure the genotoxic potential of seven orthodontic methacrylate-based adhesives.

Materials and methods

The XTT assay was utilized to determine the cytotoxicity of Assure Plus, Assure Bonding Resin, ExciTE F, OptiBond Solo Plus, Scotchbond Universal Adhesive, Transbond MIP, and Transbond XT after an incubation period of 24 h on human gingival fibroblasts. We also performed the γH2AX assay to explore the genotoxic potential of the adhesives within cytotoxic dose ranges after an incubation period of 6 h.

Results

The XTT assay showed a concentration-dependent reduction in cell viability. The decrease in cellular viability was in the same dose range most significant for Assure Plus, rendering it the adhesive material with the highest cytotoxicity. Employing the γH2AX assay, a concentration-dependent increase in H2AX phosphorylation was detected, indicating induction of DNA damage.

Conclusions

For most products, a linear correlation between the material concentration and γH2AX foci was observed. The most severe effect on γH2AX focus induction was found for Transbond MIP, which was the only adhesive in the test group containing the co-initiator diphenyliodonium hexafluorophosphate (DPIHP).

Clinical relevance

The data indicate that orthodontic adhesives, notably Transbond MIP, bear a genotoxic potential. Since the study was performed with in vitro cultivated cells, a direct translation of the findings to in vivo exposure conditions should be considered with great diligence.

Molecular Response of Pulp Fibroblasts after Stimulation with Pulp Capping Materials

This in vitro study evaluated cell viability and metabolism, nitric oxide release and production of two chemokines and one cytokine by cultured human dental pulp fibroblasts (HDPF) in contact with two glass ionomer cements (Ketac Molar-KM and Vitrebond-VB), Single Bond (SB) and calcium hydroxide (Dycal-DY). Cultures of HDPF were established by means of an explant technique. The specimens were prepared under sterile conditions and in disks measuring 5 mm x 2 mm obtained from a prefabricated mold and placed on a permeable membrane to avoid direct contact with the cells. Cytotoxicity was assessed by Trypan Blue exclusion method and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Nitric oxide release in cell supernatant was detected by the Griess Method whereas stromal derived factor-1 alpha (SDF-1α or CXCL12), chemokine (C-X-C motif) ligand 8 [Interleukin 8 (IL-8 or CXCL8)] and interleukin-6 (IL-6) were detected by ELISA. RT-qPCR was employed for gene expression analysis. Statistical analyses were performed by One-way ANOVA followed by Tukey's post hoc test for materials independent of the time, and Two-way ANOVA followed by Bonferroni correction test for the comparisons between materials and experimental time (p<0.05). Cytotoxic tests showed significant differences only for DY. Protein levels and mRNA expression were significantly increased for IL-8 for both periods of time. IL-6 production increased when fibroblasts were stimulated by KM. SDF-1α protein production and mRNA expression were not affected by any of the materials. There was a decrease in nitrate/nitrite levels only for KM. Although DY caused intense cell death and did not stimulate the production of the inflammatory mediators evaluated in this work, it is known that this event seems to be fundamental for the process of repair of the pulp tissue and formation of mineralized barrier. KM and VB increased production of proteins related to the inflammatory process, thus favoring tissue repair. Therefore, although these glass ionomer cements did not lead to large cell death, they should be used with caution.

Cytotoxic and biological effects of bulk fill composites on rat cortical neuron cells

The aim of this study was to investigate potential cellular responses and biological effects of new generation dental composites on cortical neuron cells in two different exposure times. The study group included five different bulk-fill flow able composites; Surefil SDR Flow, X-tra Base Flow, Venus Bulk Flow, Filtek Bulk Flow and Tetric-Evo Flow. They were filled in Teflon molds (Height: 4 mm, Width: 6 mm) and irradiated for 20 s. Cortical neuron cells were inoculated into 24-well plates. After 80% of the wells were coated, the 3 µm membrane was inserted and dental filling materials were added. The experiment was continued for 24 and 72 h. Cell viability measured by MTT assay test, total antioxidant and total oxidant status were examined using real assay diagnostic kits. The patterns of cell death (apoptosis) were analyzed using annexin V-FITC staining with flow cytometry. Β-defensins were quantitatively assessed by RT-PCR. IL-6, IL-8 and IL-10 cytokines were measured from the supernatants. All composites significantly affected analyses parameters during the exposure durations. Our data provide evidence that all dental materials tested are cytotoxic in acute phase and these effects are induced cellular death after different exposure periods. Significant cytotoxicity was detected in TE, XB, SS, FBF and VBF groups at 24 and 72 h, respectively.

Novel endodontic sealers induce cell cytotoxicity and apoptosis in a dose-dependent behavior and favorable response in mice subcutaneous tissue

OBJECTIVES

The objective of the present study is to evaluate the in vitro cytotoxicity and in vivo biocompatibility of two novel endodontic sealers: RealSeal XT1 and Sealapex Xpress on the subcutaneous connective tissue of mice.

MATERIALS AND METHODS

The cytotoxicity was assessed by cell viability using the MTT assay (one-way ANOVA), trypan blue test (Mann-Whitney) and cell apoptosis by flow cytometer. For the subcutaneous study, polyethylene tubes filled with the sealers were implanted in 70 BALB/c mice: 6 experimental groups (n = 10/group) and 2 control groups with empty tubes (n = 5/group). At the end of experimental periods (7, 21, and 63 days), the tissue was removed and histotechnically processed. Angioblastic proliferation and edema (Fisher's exact test) were evaluated, besides thickness measurement (μm) of the reactionary granulomatous tissue and neutrophil counts (Kruskal-Wallis and Dunn's post test; Mann-Whitney) (α = 0.05).

RESULTS

MTT assay, trypan blue, and analysis of apoptotic cells showed a dose-dependent direct effect: the more diluted the sealer, the less cytotoxic. Regarding the angioblastic proliferation and edema, difference between the sealers at 7 and 63 days occurred (p < 0.05). Both endodontic sealers initially promoted perimaterial tissue reaction as a foreign body granuloma and thus stimulated favorable tissue responses.

CONCLUSIONS

Both sealers showed a dose-dependent effect and promoted satisfactory subcutaneous tissue response; the sealer Sealapex Xpress was less cytotoxic and more biocompatible than RealSeal XT.

CLINICAL RELEVANCE

The step of root canal filling during endodontic treatment is highly important for the preservation of the periapical tissue integrity. Subcutaneous reaction to endodontic sealers enables scientific basis for clinical use.

Cytotoxicity and cytokine expression induced by silorane and methacrylate-based composite resins

OBJECTIVE

The aim of this study was to evaluate cytotoxicity and cytokine production induced by light-cured or non-light-cured methacrylate-based and silorane composite resins in RAW 264.7 macrophages.

MATERIAL AND METHODS

Cells were stimulated with the extracts from light-cured or non-light-cured composite resins. After incubation for 24 h, cytotoxicity was assessed with the lactate dehydrogenase (LDH) and methyl thiazolyl tetrazolium (MTT) assays, and total protein was quantified using the Lowry method. TNF-α detection was examined with an enzyme-linked immunosorbent assay (ELISA) conducted with cell supernatants after cell stimulation for 6, 12, and 24 h. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc test (α=0.05).

RESULTS

KaloreTM and FiltekTM Silorane were cytotoxic with or without light curing (p<0.05) after 24 h of incubation. KaloreTM stimulated the early production of TNF-α in comparison with control (p<0.05), whereas FiltekTM Silorane did not affect TNF-α levels after 6 and 12 h (p>0.05). However, after 24 h FiltekTM Silorane inhibited the production of TNF-α (p<0.05).

CONCLUSIONS

KaloreTM and FiltekTM Silorane were cytotoxic regardless of light curing. The extract obtained from KaloreTM after 15 days of incubation stimulated the production of TNF-α, unlike that obtained from FiltekTM Silorane.

Resin monomers act as adjuvants in Ni-induced allergic dermatitis in vivo

Resin monomers (RMs) are inflammatory agents and are thought to cause allergic contact dermatitis (ACD). However, mouse models are lacking, possibly because of the weak antigenicities of RMs. We previously reported that inflammatory substances can promote the allergic dermatitis (AD) induced by intradermally injected nickel (Ni-AD) in mice. Here, we examined the effects of RMs on Ni-AD. To sensitize mice to Ni, a mixture containing non-toxic concentrations of NiCl2 and an RM [either methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA)] was injected intraperitoneally or into ear-pinnae intradermally. Ten days later, a mixture containing various concentrations of NiCl2 and/or an RM was intradermally injected into ear-pinnae, and ear-swelling was measured. In adoptive transfer experiments, spleen cells from sensitized mice were transferred intravenously into non-sensitized recipients, and 24 h later NiCl2 was challenged to ear-pinnae. Whether injected intraperitoneally or intradermally, RM plus NiCl2 mixtures were effective in sensitizing mice to Ni. AD-inducing Ni concentrations were greatly reduced in the presence of MMA or HEMA (at the sensitization step from 10 mM to 5 or 50 µM, respectively, and at the elicitation step from 10 µM to 10 or 100 nM, respectively). These effects of RMs were weaker in IL-1-knockout mice and in macrophage-depleted mice. Cell-transfer experiments in IL-1-knockout mice indicated that both the sensitization and elicitation steps depended on IL-1. Challenge with an RM alone did not induce allergic ear-swelling in mice given the same RM + NiCl2 10 days before the challenge. These results suggest that RMs act as adjuvants, not as antigens, to promote Ni-AD by reducing the AD-inducing concentration of Ni, and that IL-1 and macrophages are critically important for the adjuvant effects. We speculate that what were previously thought of as "RM-ACD" might include ACD caused by antigens other than RMs that have undergone promotion by the adjuvant effects of RMs.

Evaluation of the responses of MHC class II molecule-expressing cells and macrophages to epoxy resin-based and 4-META-containing, methacrylate resin-based root canal sealers in rat subcutaneous tissue

Major histocompatibility complex (MHC) class II molecule-expressing cells and macrophages play a pivotal role in mediating the host tissue response to biomaterials. This study investigated the responses of these cells to epoxy resin-based and 4-META-containing, methacrylate resin-based endodontic sealers (AH Plus and MetaSEAL respectively) in rat connective tissue. Silicone tubes loaded with one of the sealers or solid silicone rods (control) were subcutaneously implanted in male Wistar rats for three time periods of 7, 14, or 28 days. Tissue specimens were immunoperoxidase-stained for MHC class II molecules and CD68 (a general macrophage marker). Results showed that AH Plus-implanted tissue displayed significantly more MHC class II-positive cells than the control at 14 and 28 days, whereas MetaSEAL-implanted tissue showed significantly more CD68-positive cells than both AH Plus-implanted tissue and the control at all time periods. It was concluded that the epoxy resin-based sealer induced the infiltration of MHC class II molecule-expressing cells, whereas 4-META-containing, methacrylate resin-based sealer elicited macrophage infiltration.

Pulpal and Periapical Response After Restoration of Deep Cavities in Dogs' Teeth With Filtek Silorane and Filtek Supreme XT Systems

Objective:

This study evaluated, histopathologically, the pulpal and periapical response to a silorane-based resin (Filtek Silorane) and a methacrylate-based nanoparticle resin (Filtek Supreme XT) in deep cavities in dogs, having zinc oxide and eugenol-based cement (ZOE) as a control.

Methods:

The tooth/bone blocks were collected after 10 and 90 days and processed for microscopic analysis of the dentin, pulp, and periapical tissues using a score system. Data were analyzed statistically by Kruskal-Wallis and Dunn post-test (α=0.05).

Results:

At 10 days, the pulp, connective tissue, and periodontal ligament showed normal characteristics. No resorption areas were observed. Both resins caused significantly less (p&lt;0.05) periapical and pulpal inflammatory response than ZOE. At 90 days, for all materials, the connective pulp tissue was healthy and dense, with a normal blood vessel system. The apical and periapical region had normal structure and thickness.

Conclusions:

The use of the Filtek Silorane and the Filtek Supreme XT resins caused no adverse pulpal and periapical reactions after restoration of deep dentin cavities in vivo.

Biocompatibility of Root Canal Filling Materials: Differences between Vitality and Functionality Tests

Biocompatibility of root canal filling materials is of great interest because they can come into permanent contact with the living periapical tissue, and induce mild or severe inflammatory responses. Usually biocompatibility tests only determine non-cytotoxic effects of dental materials, even if their functional interactions with cells also play a role in the host responses. The purpose of this study is to evaluate peripheral blood monocyte (PBM) vitality and functionality after contact with 5 different root canal filling materials: Thermafil (gutta-percha), Real Seal and Real Seal 1 (methacrylic resins), AureoSeal (MTA) and SuperSeal (EBA). Cellular vitality was determined by MTT test and cellular functionality by Chemiluminescence (CL) technique. Dishes of the materials were covered with cell culture medium (0.5 cm2/mL) and incubated for 24 h. The extracts were added to PBMs and the latter, after 2 h of incubation, were analysed by MTT and by Chemiluminescence (CL). All results are expressed as mean ± SEM. The group means were compared by analysis of variance. Results showed that SuperSeal and AuroSeal exhibited a moderate cytotoxic effect, while the toxicity induced by RealSeal, RealSeal 1 and Thermafil was lower. SuperSeal and AuroSeal induced a significant decrease of both oxidative burst and basal reactive oxygen species (ROS) production. RealSeal 1 caused a doubling of basal ROS production in respect to control. The results demonstrate that a low cytotoxic effect does not guarantee a total integrity of cellular functionality and more differences among biocompatibility of root canal materials can be detected when a functionality test is used.

Inflammatory suppression by endodontic sealers after aging 12 weeks In vitro

Dental endodontic sealers are in intimate contact with tissues around the root apex (periapical area) for extended periods. New endodontic sealers have been developed in the past decade, but the biological responses to many new products are not well documented. In this study, we assessed in vitro monocytic cytotoxic and inflammatory responses to several contemporary endodontic sealers. AH-Plus (AH), Pulp Canal Sealer (PC), Epiphany (EPH), Endo-Rez (ER), and an experimental Endo-Rez (ERx) were initially placed in buffered-saline for 12 weeks to simulate in vivo use. After "aging," specimens were placed in direct contact with THP1 monocytes for 72 h and their cytotoxicity (mitochondrial response; MTT) or ability to trigger or suppress cytokine secretion (ELISA; TNFalpha, IL1beta, IL=6; +/- lipopolysaccharide (LPS) exposure) were measured relative to Teflon (Tf) negative controls. Cellular responses among conditions were compared with ANOVA and Tukey post-hoc analysis (alpha = 0.05). Two of the five sealers, EPH and PC, still suppressed cell mitochondrial activity by 70% or more after 12 weeks of conditioning in saline. No sealer alone activated monocytic TNFalpha, IL1beta, or IL6 secretion (p > 0.05 vs. +LPS controls). When THP1 were activated by LPS after exposure to the sealers, differential suppression of TNFalpha, IL1beta, and IL6 secretion was observed for two of the five sealers tested. (EPH and PC) This data suggest that common endodontic sealers do not activate monocytic TNFalpha, IL1beta, and IL6 secretion in vitro by themselves, but degradation products of the sealers may suppress activation of monocytes.

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

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

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

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

Effects of filler type and content on mechanical properties of photopolymerizable composites measured across two-dimensional combinatorial arrays

Multicomponent formulations coupled with complex processing conditions govern the final properties of photopolymerizable dental composites. In this study, a single test substrate was fabricated to support multiple formulations with a gradient in degree of conversion (DC), allowing the evaluation of multiple processing conditions and formulations on one specimen. Mechanical properties and damage response were evaluated as a function of filler type/content and irradiation. DC, surface roughness, modulus, hardness, scratch deformation and cytotoxicity were quantified using techniques including near-infrared spectroscopy, laser confocal scanning microscopy, depth-sensing indentation, scratch testing and cell viability. Scratch parameters (depth, width, percent recovery) were correlated to composite modulus and hardness. Total filler content, nanofiller and irradiation time/intensity all affected the final properties, with the dominant factor for improved properties being a higher DC. This combinatorial platform accelerates the screening of dental composites through the direct comparison of properties and processing conditions across the same sample.

Biocompatibility of resin composites subcutaneously implanted in rats with experimentally induced arthritis

OBJECTIVE

To evaluate the biocompatibility of resin composite specimens with different curing efficiency, subcutaneously implanted in rats with experimentally induced arthritis.

METHODS

The amount of remaining CC bonds (%RDB) of hybrid resin composite specimens photopolymerized for 10s and 40s exposure time (n=3) was measured by micro-attenuated total reflectance Fourier transform infrared spectroscopy. Male Wistar rats (n=36) were classified in two groups (n=18) of healthy animals and of animals with experimentally induced arthritis. Resin composite specimens irradiated for 10s and 40s and calcium hydroxide control specimens were implanted subcutaneously in each animals' dorsum. Following 2-, 4- and 9-week periods the animals were sacrificed. The development of arthritis was defined by biochemical analysis and the changes in the relative weight of animals' organs (spleen, thymus, adrenals). Tissue reactions were examined histologically.

RESULTS

%RDB per site and exposure time showed statistically significant differences. Lowest %RDB values were recorded on 40s exposed specimens. Biochemical indices and relative organ weights demonstrated statistically significant differences between healthy animals and animals with arthritis. The health status of the animals and the materials used did not influence tissue response. First and second periods of sacrifice showed reduced propensity of connective tissue development in comparison to the third period. The same applied for the second period regarding the presence of giant cells.

SIGNIFICANCE

The materials tested and the animals' health status did not result in altered tissue response compared to control group. The period of sacrifice was associated with different tissue responses.

Cytotoxicity of one-step dentin-bonding agents toward dental pulp and odontoblast-like cells

The purpose of this study was to compare the cytotoxicity of five one-step dentin-bonding agents on human dental pulp and odontoblast-like cells (MDPC-23). Photopolymerized and unpolymerized samples of these dentin-bonding agents were prepared and incubated with dental pulp or MDPC-23 cells. After 24 or 72 h of incubation, the number of unstained cells with trypan blue was counted. The staining of cells with trypan blue stands for a cytotoxicity. The pulp cell and MDPC-23 cytotoxicity of polymerized sample treatment increased in the order of AQ Bond Plus (AQ)<Clearfil Tri-S Bond (TS)=G-bond (GB)<Absolute (AB)<Adper Prompt (AP) for 24 and 72 h. The pulp cell cytotoxicity of unpolymerized sample treatment for 24 h increased in the order of AQ<GB = AB<TS<AP. The MDPC-23 cytotoxicity of unpolymerized sample treatment for 24 h increased in the order of AQ<GB<TS = AB<AP. Whether polymerized or unpolymerized, AQ was the least cytotoxic agent, while AP was the strongest. All polymerized dentin-bonding agents exhibited lower cytotoxicity by 2-65% than their unpolymerized counterparts. The appearance of the cytotoxicity of dentin-bonding agents was time-dependent, and cell viability was lower at 72 h by 2-46% than at 24 h. The cytotoxicity to MDPC-23 cells was about 5-24% higher than that to pulp cells. These results indicate that one-step dentin-bonding agents differ markedly in their cytotoxicity. Differential cytotoxic effects of one-step dentin-bonding agents should be considered during clinical application of operative restoration.

Dose-dependent effects of Ni (II) ions on production of three inflammatory cytokines (TNF-alpha, IL-1beta and IL-6), superoxide dismutase (SOD) and free radical NO by murine macrophage-like RAW264 cells with or without LPS-stimulation

The effect of Ni (II) ions on macrophages is not well understood. The purpose of this study was to examine the dose-dependent effects of Ni (II) ions up to 1,000 micromol/L on production of three inflammatory cytokines (TNF-alpha, IL-1beta and IL-6), superoxide dismutase (SOD) and nitric oxide (NO) by murine macrophage-like RAW264 cells with (+) or without (-) lipopolysaccharide (LPS) -stimulation. Ni (II) ions caused LPS (-) RAW264 cells to slightly increase production of TNF-alpha and IL-6, proportionally to the Ni (II) ion concentration while IL-1beta was not produced, and to slightly increase production of SOD and NO. It can be concluded that Ni (II) ions dose-dependently increased the inflammatory and oxidative stress conditions of LPS (-) RAW264 cells. LPS-stimulation caused RAW264 cells to produce in abundance the three inflammatory cytokines, SOD and NO. Ni (II) ions dose-dependently reduced the three cytokine quantities and NO amounts in LPS (+) RAW264 cells, while dose-independently increasing SOD amounts. It was noted that Ni (II) ions dose-dependently reduce the resistance power against bacteria of LPS (+) macrophages, because the production of volatile NO--bacteria killer is diminished proportionally to the Ni (II) ion concentration.

Accumulation of bisphenol A in hemodialysis patients

Bisphenol A [BPA, 2,2-bis(4-hydoxyphenyl)propane], an industrial chemical used in the production of polycarbonate, epoxide resin, and polyarylate, is considered to be an endocrine-disrupting chemical. BPA may be present in some hollow-fiber dialyzers used in hemodialysis. In this study, we tested the amounts of BPA eluted from various hollow fibers. Furthermore, we measured the BPA concentration in the sera of 22 renal disease predialysis patients, as well as 15 patients who were receiving hemodialysis, to see if there is BPA accumulation in these patients. The elution test of BPA showed that a much larger amount of BPA was eluted from polysulfone (PS), and polyester-polymeralloy hollow fibers. Among renal disease patients who had not undergone hemodialysis, the serum BPA concentration increased as the renal function deteriorated, showing a significant negative association. In a crossover test between PS and cellulose (Ce) dialyzers, the predialysis serum BPA concentration of PS dialyzer users decreased after changing to a Ce dialyzer, and the serum BPA increased again after switching back to PS dialyzers. In patients who were using PS dialyzers, the BPA level significantly increased after a dialysis session. However, in the Ce dialyzer users, the BPA level decreased. Since accumulation of BPA could affect the endocrine or metabolic system of the human body, it is important to perform further investigations on dialysis patients.

In vitro cytotoxicity of dental composites based on new and traditional polymerization chemistries

The biological response to dental restorative polymer composites is mediated by the release of unpolymerized residual monomers. Several new composite formulations claim to reduce unpolymerized residual mass. The current study assessed the cytotoxic responses to several of these new formations and compared them with more traditional formulations. Our hypothesis predicted that if these new polymerization chemistries reduce unpolymerized residual mass, the cytotoxicity of these materials also should be reduced relative to traditional formulations.

METHODS

Materials (HerculiteXRV, Premise, Filtek Supreme, CeramxDuo, Hermes, and Quixfil) were tested in vitro in direct contact with Balb mouse fibroblasts, initially, then after aging in artificial saliva for 0, 1, 3, 5, or 8 weeks. The toxicity was determined by using the MTT assay to the estimate SDH activity. Knoop hardness of the materials also was measured at 0 and 8 weeks to determine whether surface breakdown of the materials in artificial saliva contributed to cytotoxic responses.

RESULTS

Materials with traditional methacrylate chemistries (Herculite, Premise, Filtek Supreme) were severely (>50%) cytotoxic throughout the 8-week interval, but materials with newer chemistries or filling strategies (Hermes, CeramXDuo, and Quixfil) improved over time of aging in artificial saliva. Hermes showed the least cytotoxicity at 8 weeks, and was statistically equivalent to Teflon negative controls. Hardness of the materials was unaffected by exposure to artificial saliva.

CONCLUSIONS

Newer polymerization and filling strategies for dental composites show promise for reducing the release of unpolymerized components and cytotoxicity.

Macrophage response to methacrylate conversion using a gradient approach

Incomplete conversion, an ongoing challenge facing photopolymerized methacrylate-based polymers, affects leachables as well as the resulting polymer network. As novel polymers and composites are developed, methods to efficiently screen cell response to these materials and their properties, including conversion, are needed. In this study, an in vitro screening methodology was developed to assess cells cultured directly on cross-linked polymer networks. A gradient in methacrylate double bond conversion was used to increase the experimental throughput. A substrate of 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl] propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) was prepared with a conversion ranging from 43.0% to 61.2%. Substrates aged for 7 days had no significant differences in surface roughness or hydrophilicity as a function of conversion. Leachables were detectable for at least 7 days using UV absorption, but their global cytotoxicity was insignificant after 5 days of aging. Thus, RAW 264.7 macrophage-like cells were cultured on aged substrates to evaluate the cell response to conversion, with possible contributions from the polymer network and local leachables. Conversions of 45% and 50% decreased viability (via calcein/ethidium staining) and increased apoptosis (via annexin-V staining). No significant changes (p>0.05) in tumor necrosis factor-alpha and interleukin-1beta gene expression, as measured by quantitative, real-time reverse transcription-polymerase chain reaction, were seen as conversion increased. Thus, conversions greater than 50% are recommended for equimolar BisGMA/TEGDMA. The ability to distinguish cell response as a function of conversion is useful as an initial biological screening platform to optimize dental polymers.

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.

Radicals produced by blue-light–resin interactions alter the redox status of THP1 human monocytes

Resin composites are widely used in dentistry, and are polymerized in situ using a blue-light activated, free-radical polymerization mechanism. Blue light (400-500nm) is used to activate camphoroquinone (CQ), which decomposes to form free radicals that are stabilized by dimethyl-p-toludine (DMPT). CQ and DMPT are applied near tooth pulpal tissues and are irradiated during restorative procedures, suggesting that pulpal cells are exposed to free radicals. Because glutathione is a major component of the cellular redox management system, we tested the hypothesis that blue light irradiation would shift cellular glutathione redox balance of cells exposed to CQ and DMPT. We also measured NFkappaB activation, a redox-sensitive transcription factor that regulates inflammatory responses and glutathione synthetic enzyme levels. THP1 human monocytes were exposed to sublethal levels of CQ (0.4 mM) or DMPT (1.0 mM), with or without blue light exposure (25 J/cm(2)) from a quartz-tungsten-halogen source. The ratio of reduced to oxidized glutathione was measured using as assay based on 5,5'-dithio-bis(2-nitrobenszoic acid). NFkappaB transactivation was measured by transfection of an NFkappaB-containing plasmid linked to a luciferase reporter. Our results showed that blue light, CQ, or DMPT alone had no significant effect on cellular glutathione redox balance, but that the combination of these agents induced a marked oxidative bias, and reduced total glutathione levels up to 50%. On the other hand, light, CQ, and DMPT alone or in combination suppressed NFkappaB transactivation by >70%. Our results suggest that CQ and DMPT pose risks to pulpal tissues with or without blue light irradiation, and that multiple, interacting mechanisms shape the response to these agents.

Cytotoxicity of Epiphany�and Resilon�with a root model

AIM

To record the cytotoxicity of Resilon and Epiphany (Pentron clinical technologies, Wallingford, CT, USA) using a root model.

METHODOLOGY

Thirty teeth with single roots were sectioned at the enamel-cementum junction, the root canals prepared and each root then sterilized before filling with the lateral condensation technique using one of three filling materials (n = 10 per group): Resilon and Epiphany, Sealite (Septodont, Pierre Rolland, Merignac, France) and gutta-percha, Roekoseal Automix (Coltène/Whaledent, Langenau, Germany) and gutta-percha. The roots were stored at 37 degrees C in an incubator to allow for setting of the root filling materials. The apices of the roots were dipped in 1 mL of MEM culture medium for 1, 2, 7 and 30 days renewing the medium every day. After 24 h contact between the medium and the filled roots, the medium was used to measure the cytotoxicity on mouse fibroblasts L 929 with the MTT assay that recorded the mitochondrial activity of the target cells. An additional test according to ISO 10993-5 standards was undertaken to compare Resilon and Epiphany.

RESULTS

The root model showed no statistically significant differences between the sealers at 7 and 30 days (NS). Epiphany and Resilon were the most cytotoxic materials at 1 and 2 days (P < 0.001). Unlike Epiphany, Resilon was not cytotoxic when tested according to ISO 10993-5 standards.

CONCLUSIONS

The cytotoxicity of Resilon + Epiphany, due mainly to Epiphany, decreased after 2 days to reach a level comparable with commonly used root canal sealers.

Cytotoxicity of materials used in perforation repair tested using the V79 fibroblast cell line and the granulocyte-macrophage progenitor cells

AIM

To compare the cytotoxicity of materials used to repair perforations using permanent V79 fibroblasts and murine granulocyte-macrophage progenitor cells (CFU-GM).

METHODOLOGY

Set specimens from amalgam, glass-ionomer, SuperEBA, N-Rickert, MTA and gutta-percha were eluted with culture medium for 72 h and their cytotoxicities were assessed by incubating the extracts with V79 and bone marrow-derived progenitors for 24 h and 7 days, respectively. Cytotoxicity on V79 cells was judged using the total nucleic acid content (NAC), neutral red uptake (NRU) and reduction of the tetrazolium salt (MTT). The number of bone marrow CFU-GM colonies determined in clonal cultures stimulated with recombinant murine granulocyte-macrophage colony-stimulating factor was used to assess cytotoxicity to progenitor cells. Statistical analyses were conducted using the one-way analysis of variance and Tukey's test where appropriate.

RESULTS

All materials were cytotoxic in both cell systems; however, CFU-GM was more sensitive to the extracts than V79 cells. A similar rank order of toxicity was observed in V79 cells using the NAC and the MTT assays: glass-ionomer > N-Rickert congruent with SuperEBA > gutta-percha > amalgam congruent with MTA (P < 0.05). In contrast, the NRU test exhibited a lower sensitivity to MTA, gutta-percha and amalgam extracts. In the clonal culture assay, the toxicity was less pronounced in the presence of gutta-percha, SuperEBA and MTA. Similar cellular responses were found by placing the set specimens directly in the clonal culture dishes.

CONCLUSIONS

The sensitivity of toxicity depended on the choice of the endpoint and the cell-culture system. Nevertheless, MTA was ranked as the least cytotoxic cement in both cell systems.

Alteration of monocytic cell oxidative burst caused by methacrylic monomers present in dental materials: a chemiluminescence study

Methacrylates are present in dental composite resins used in clinical practice. Methacrylates are photo-polymerized, but this reaction is never complete, so release of uncured monomers in the periapical tissues and in biological fluids may happen and, potentially, alter the repair of pulpal and of periapical lesions by interfering with local phagocytes. The aim of this study was the evaluation of the functional activity of the monocyte-macrophage system after incubation with methacrylic monomers. The oxidative burst of two cellular systems was analysed using the chemiluminescence technique. Data were collected and statistically analysed. Monomers were found to reduce the in vitro oxidative burst of phagocytes independently from their cytotoxicity. These findings demand further evaluation of the effects of oxidative burst alteration in monocyte-macrophage function and may prompt the inclusion of the described chemiluminescence test in biocompatibility preliminary studies of dental materials.

Anti-rheumatic gold compounds as sublethal modulators of monocytic LPS-induced cytokine secretion

The objective of this study was to quantify the ability of sublethal concentrations of several gold compounds to differentially modulate the monocytic secretion of key cytokines that are important in the etiology of rheumatic diseases. Human THP1 monocytic cells were exposed to the anti-rheumatic drugs auranofin (AF), gold sodium thiomalate (GSTM) or HAuCl4 (Au(III)) for 24-72 h. Succinate dehydrogenase (SDH) activity of the monocytes was used to determine sublethal concentrations. Monocytes were then exposed to sublethal concentrations of gold compounds for 72 h, and the activator lipopolysaccharide (LPS) was added (or not) to cultures for the last 6h. The secretion of IL6, IL8, IL10, and TNFalpha were measured in cell supernatants using ELISA. Cytokine secretion was compared among concentrations and gold compounds. SDH experiments established a sublethal concentration range of 0-75 microM for GSTM and Au(III) and 0-0.5 microM for AF. In cytokine experiments, none of the compounds alone activated secretion of any of the cytokines, but all differentially (50-440%, p<0.05) increased LPS-induced secretion of IL6 and IL8 over TNFalpha and IL10. In conclusion, sublethal concentrations of AF, GSTM, and Au(III) all may differentially modulate activation of monocytic cells, and this differential modulation may be important in the mechanisms of action of these compounds.

Polymerized bonding agents and the differentiation in vitro of human pulp cells into odontoblast-like cells

OBJECTIVES

Odontoblasts are highly differentiated post-mitotic cells, which under pathological conditions such as carious lesions and dental injuries may degenerate and be replaced by other pulp cells. We have recently shown that this physiological event can be reproduced in an in vitro assay system, but is highly modified by the presence of unpolymerized resinous monomers. Our hypothesis was that the photopolymerization of the monomers in the bonding agents might abolish these negative effects. The purpose of this study was to evaluate the effects of polymerized dentin bonding agents, through dentin slices, on odontoblast differentiation in vitro.

METHODS

Pulp cells were obtained from human third molars. They were used to study the effects of four dentin bonding agents through 0.7 mm dentin slices which served as a barrier between the bonding agents and the culture medium. The media containing the bonding agents' extracts were added at non-toxic concentrations onto the cultured cells. Immunohistochemistry was performed to study the differentiation of pulp fibroblasts into odontoblasts under these conditions by evaluating the expression of several odontoblast specific genes.

RESULTS

Pulp fibroblasts cultivated under these conditions synthesized type I collagen, osteonectin, dentin sialoprotein and nestin at the same level as in control cultures. Moreover, pulp cells synthesized a mineralized nodular extracellular matrix. Expression of these proteins was higher in the cells contributing to the nodule formation. In addition, except nestin, all these proteins were expressed in the mineral nodules.

SIGNIFICANCE

This work shows the lack of effects of photopolymerized bonding agents, through dentin slices, on cytodifferentiation of secondary odontoblasts.

Bisphenol A-induced downregulation of murine macrophage activities in vitro and ex vivo

Bisphenol A (BPA) is known to have detrimental effects on the reproductive system, but the toxicity of BPA on immune responses has not been systematically investigated. We investigated the effects of BPA exposure on the activities of murine peritoneal macrophages through evaluation of BPA-induced alteration of nitric oxide (NO) production, tumor necrosis factor-α (TNF-α) synthesis, and expression of co-stimulatory molecules B7. Macrophages were examined ex vivo from mice orally treated with various doses of BPA for 5 consecutive days per week for 4 weeks followed by culture for 2 or 4 days in the presence of lipopolysaccharides (LPS). Macrophages from naive mice were also stimulated with LPS ± BPA for 2 or 4 days. NO production was decreased with the in vitro exposure to 1, 10 and 100μM BPA. NO production was lower in the BPA-exposed mice than the control mice with all doses. In vitro, BPA suppressed TNF-α secretion with significant reduction at 10 and 100μM BPA. Similar findings were observed with the macrophages from the BPA-exposed mice. This study provides the substantial evidence on BPA-induced alteration in macrophage activity.

BIOLOGICAL RISKS OF RESIN-BASED MATERIALS TO THE DENTIN-PULP COMPLEX

Over the past 30 years, restorative dentistry has seen a revolution in materials, restorative techniques, and patient priorities. This revolution has been made possible with the development of new resin-based materials which can be bonded to the tooth structure. Not all of these changes have been without controversy or concern, and some have raised questions about the biological safety of these new materials and techniques. It is the purpose of this review to present recent and relevant information about the biological risks and consequences of resin-tooth bonding and how these risks are affected by the material, its clinical properties, and its manipulation by the practitioner. These biological risks are complex and interactive, and are still incompletely defined. In broad terms, these risks can be divided into those stemming from the toxicological properties of the materials themselves (direct biological risks) and those stemming from microbiological leakage (indirect biological risks).

Influence of resinous monomers on the differentiation in vitro of human pulp cells into odontoblasts

Odontoblasts are highly differentiated postmitotic cells, which under pathological conditions such as carious lesions and dental injuries may degenerate and be replaced by other pulp cells. A recent work showed that this physiological event can be reproduced in an in vitro assay system. The purpose of the present study was to evaluate the effects of resinous monomers on odontoblast differentiation in vitro. Pulp cores from extracted human third molars were cultured with beta-glycerophosphate (2 mM) and used to evaluate the effects of TEGDMA, HEMA, UDMA, and Bis-GMA on the differentiation of pulp fibroblasts into odontoblasts. The effect of the monomers was studied by evaluating the expression of several odontoblast specific genes. In the absence of monomers, mineral nodule formation was observed. Pulp cells contributing to the nodule formation synthesized type I collagen, osteonectin, and dentin sialoprotein (DSP). In addition, Fourier transform infrared microspectroscopy showed that the mineral and organic composition of the nodules were characteristic of dentin. When the monomers were added at nontoxic concentrations, the effects of HEMA and Bis-GMA were more evident than that of TEGDMA and UDMA on collagen 1, osteonectin, and DSP expression. However, all monomers significantly decreased DSP expression and completely inhibited the mineral nodule formation.

In vitro effect of light-cure dental adhesive on IL-6 release from LPS-stimulated and unstimulated macrophages

The objective of this study was to measure IL-6 release from LPS-stimulated and -unstimulated macrophages exposed to extracts from fresh and aged Scotchbond Multipurpose Plus adhesive disks (5 mm in diameter by 2 mm in thickness) light cured for 10, 20, or 40 s. One set of disks was aged for 16 weeks at 4 degrees C. Extracts were prepared by incubating three disks in 1 mL of serum-free culture medium for 72 h at 37 degrees C. Then macrophages (RAW 264.7) were exposed to the extracts (6.25-50 microL) for 72 h at 37 degrees C/5% CO(2). Supernatants were analyzed for cytokine levels (ELISA), and the monolayer of cells was assessed for viability (MTT assay). Unlike adhesive disk age, curing time affected cell viability. Disk extracts cured for 10 s were more cytotoxic (p < 0.05) than were extracts from 20- or 40-s cured disks. Macrophage release of IL-6 was stimulated significantly (p < 0.01) by extracts from fresh 10-s cured disks, up to 777 pg/mL and by 2 microg/mL of LPS (1174 pg/mL). The LPS response was significantly (p < 0.05) suppressed by 50 microL of extracts, which may be related to the enhanced cytotoxicity exhibited by LPS in combination with extracts. This study has demonstrated the possibility that IL-6 release is stimulated by light-cure dental adhesive applications using 10-s curings.

Sublethal, 2-week exposures of dental material components alter TNF-alpha secretion of THP-1 monocytes

OBJECTIVES

The aim of this study was to investigate the hypothesis that dental material components alter cytokine secretion from monocytes if applied for several weeks at sublethal doses. The current study significantly extended exposure times of monocytes to the components over times published in previous studies. These exposure times approached the estimated average life span of monocytes in the bloodstream.

METHODS

Human THP-1 monocytes were exposed to 2-hydroxyethylmethacrylate (HEMA, 0-1.2mmol/l), triethyleneglycoldimethacrylate (TEGDMA, 0-0.75mmol/l), Hg(2+) (0-2 micromol/l), or Ni(2+) (0-20 micromol/l) for 2 weeks. The cells were then collected and additionally incubated for 24h, with or without bacterial lipopolysaccharide (LPS), a common component of dental plaque. TNF-alpha secretion from THP-1 was determined using by enzyme-linked immunosorbent assay.

RESULTS

None of the dental material components induced TNF-alpha from THP-1 by themselves, but LPS alone strongly induced TNF-alpha secretion as expected. HEMA and TEGDMA significantly suppressed (40-70%) TNF-alpha secretion from cells stimulated with LPS. Hg(2+) at 2.0 micromol/l doubled TNF-alpha secretion from THP-1s stimulated with LPS over LPS alone. Ni(2+) did not significantly affect TNF-alpha secretion, with or without LPS exposure. Significance. The results in this study suggest that sublethal, 2-week exposures of some dental material components may alter TNF-alpha secretion from THP-1 monocytes when the cells are challenged. These alterations may influence the biological response of tissues to materials in an inflammatory intraoral environment.

In vitro biological response to core and flowable dental restorative materials

OBJECTIVES

In vitro cytotoxicities of commercially available core and flowable dental restorative materials were assessed and compared to traditional resin composites. Our hypothesis was that the increased resin diluents added to achieve higher flow in flowables would increase cytotoxicities, whereas the higher filler content of core materials would decrease cytotoxicities relative to traditional resin composites.

METHODS

Specimens were made under aseptic conditions, then extracted into an artificial saliva solution for 0-4 weeks, to assess the effect of aging on cytotoxicity. After extraction, specimens were tested for cytotoxicity in vitro using Balb/c fibroblasts in direct contact format. Cells were exposed to the materials for 48h, after which the mitochondrial activity of the cells was measured (MTT method). Cellular activity was normalized to Teflon negative controls.

RESULTS

Core materials were uniformly and severely (<50% of Teflon cellular activity) cytotoxic initially, but several materials (Corepaste, Definite core) improved somewhat with aging in artificial saliva. Flowable materials were uniformly and severely cytotoxic with no trend toward improvement with aging. The Definite-flow was the least cytotoxic of the flowable materials, but it too was severely cytotoxic.

SIGNIFICANCE

Commercially available core and flowable restorative materials showed severe in vitro cytotoxicities that are worse than some traditional composites and most dental casting alloys and amalgams used today. Of particular note was the persistent cytotoxicity of these materials after 4 weeks of extraction with artificial saliva. These cytotoxicities indicate a continuing release of mass from these materials at levels that have biological relevance in vitro. In vivo relevance of these cytotoxicities is less clear, but these results indicate a higher biological risk for these materials compared to traditional materials that exhibit less initial toxicity and improve with aging time.

Cytotoxicity of dentine-bonding agents on human pulp cells in vitro

AIM

To investigate the cytotoxicity of five different dentine-bonding agents on human pulp cells in vitro.

METHODOLOGY

Set specimens from Clearfil SE Bond (CB), Heliobond (HB), Prime & Bond NT (PB), Single Bond (SB), and Syntac Single Component (SC) were eluted with culture medium for 2 and 5 days. Cytotoxicity was judged using tetrazolium bromide reduction assay on human primary pulp cells.

RESULTS

Elutes from five dentine-bonding agents were cytotoxic to primary human pulp cells (P < 0.05). CB was the least toxic sealer amongst the chemicals tested. The cytotoxic response decreased in an order of SB > PB > SC > HB > CB.

CONCLUSIONS

The influence of the cytotoxicity depended on the materials tested. Dentine-bonding agents have significant potential for pulpal toxicity.

Low-dose, long-term exposures of dental material components alter human monocyte metabolism

The short-term degradation of dental polymers and alloys in biological environments has been well documented, but recent evidence indicates that oral tissues may be chronically exposed to low levels of these released components. The effect of these chronic exposures on the ability of cells to respond to a subsequent challenge is not known. To investigate this idea, we exposed human THP-1 monocytes to sublethal concentrations of HEMA, TEGDMA, Hg(2+), and Ni(2+) for 2 weeks and then assessed the monocytic response to subsequent 24-h challenge with the same components at higher concentrations. Chronic (2 week) exposures of monocytes to HEMA and both metal ions significantly altered monocyte response to short-term (24 h) secondary exposures, even when overt effects of the chronic exposures were not apparent. However, cellular responses were highly variable depending on the material and its concentrations. For TEGDMA, no effects were seen. These results demonstrate that the chronic effects of materials must be considered even when the chronic exposure has no initial overt effect. The effect on cells may only be apparent if the cell is challenged by a secondary exposure.

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.

Effects of DMAEMA and 4-methoxyphenol on gingival fibroblast growth, metabolism, and response to interleukin-1

Some components of resins used in restorative dentistry have been shown to alter metabolism in cultured oral epithelial cells. Here we have extended such studies to the underlying supportive tissue, composed of gingival fibroblasts (GF). Primary cultures of human GF were transferred to serum-free, defined medium and exposed to either 2-(dimethylamino)ethyl methacrylate (DMAEMA) or 4-methoxyphenol (MEHQ) for 24-72 h. At a DMAEMA concentration of 6.4 mM, which was well tolerated by epithelial cells, GF numbers, as estimated by crystal violet, and metabolic activity, as indicated by MTT, were reduced at least 60% within 24 h of exposure. Between 1.6 and 6.4 mM, there were dose-related reductions in cell numbers; however, at lower doses (0.32-0.64 mM), proliferation was stimulated. MEHQ, between 8 and 16 microM, did not stimulate cellular protein production. To examine the capacity of GF to respond to an inflammatory stimulus, interleukin-6 (IL-6) production by confluent cells was estimated without or with these compounds. DMAEMA (1.6- 6.4 mM) virtually eliminated the acute IL-6 response of these cells to an interleukin-1beta challenge; only at 0.32 mM DMAEMA was the response restored. MEHQ (1.6-16 microM) reduced the IL-6 response by >50%. In summary, both growth and the innate immune responsivity of GF were affected by DMAEMA and MEHQ in vitro; thus, these compounds deserve careful evaluation for biocompatibility.

Cytotoxicity of low pH dentin-bonding agents in a dentin barrier test in vitro

The reaction of three-dimensional cultures of pulp-derived cells in a dentin barrier test was recorded after exposure to All-Bond 2, Prime & Bond NT, Syntac SC, Syntac Classic, and Prompt L-Pop. The materials were applied on bovine dentin disks in a perfusion chamber, and the experiments were performed with (0.3 ml/h, 2 ml/h) and without perfusion of the pulpal part of the chamber. The cell reaction was recorded (MTT assay) and related to noncytotoxic controls. Bonding agents with low pH did not show any cytotoxicity. Syntac Classic decreased the cell activities to 38% to 72%, depending on different experimental conditions, and was more cytotoxic than Syntac SC. Perfusion (2 ml/h) reduced the cytotoxicity for Syntac Classic and increased cell activities from 52% to 72%. Because low pH bonding agents did not show toxic reactions in this dentin barrier test, pulp damage caused by the tested substance is unlikely if a dentin layer protects the pulp.

Principles of biocompatibility for dental practitioners

This article is an evidence-based tutorial on the principles of biocompatibility. Although the technical issues of biocompatibility may seem beyond the scope of most practicing dentists, knowledge of these issues is fundamentally important to ensure the health of patients, dental staff members (including laboratory personnel), and practitioners themselves. Furthermore, the legal liability of dentists is often linked to biocompatibility issues. The biocompatibility of a material is not absolute; it must be measured with regard to the way the material is used. Measuring biocompatibility is a complex process that involves in vitro and in vivo tests. These tests contribute to understanding biologic responses to a material but cannot define the material's biocompatibility with 100% certainty. Practitioners should understand enough about biocompatibility testing methods to critically judge advertising claims and ask relevant questions of manufacturers. Because there is no infallible way to assess biologic response to a material, decisions about the clinical use of a material ultimately must weigh the biologic risks of a material against its potential benefits.

Evidence for bacterial causation of adverse pulpal responses in resin-based dental restorations

The widespread use of resin and resin-monomers for bonding of dental restorations to dentin has occurred because of a fundamental shift in the view that injury to the pulp is induced by restorative procedures. While, for many years, the toxic effects of restorative materials were thought to be of crucial importance in the development of adverse pulpal responses, the key role of bacterial leakage at the restoration-tooth interface is now well-recognized. Consequently, if optimal conditions for the preservation of pulpal health are to be ensured, dental restorations should provide an impervious seal against the surrounding tooth structure. However, polymerization shrinkage and contraction stresses induced during setting, as well as a variety of technical difficulties encountered during the clinical operation, often produce less than perfect results. Therefore, modern restorative procedures involving resin and resin-bonded restoratives must still rely on the ability of the pulp to cope with the injurious elements to which it may be exposed during and after the procedure. This review examines factors that may govern the pulp's response to restorative procedures that involve adhesive technologies. An assessment is made of the risks involved as far as the continued vital function of the pulp is concerned. It is concluded that an intact, although thin, wall of primary dentin often enables the pulp to overcome both toxic material effects and the influences of bacterial leakage. In contrast, the pulp may not do equally well following capping of open exposures with resin composites. A dearth of controlled clinical studies in this area of dentistry calls for confirmation that pulpal health prevails over the long term following the use of total-etch and resin-bonding techniques.

Effects of long-term sub-lethal concentrations of dental monomers on THP-1 human monocytes

Studies have shown that monomers from dental resins are acutely cytotoxic, but little is known of their long-term effects at sub-lethal concentrations. The current study determined the long-term effects of sub-lethal concentrations of TEGDMA (triethyleneglycol dimethacrylate) and Bis-GMA (bisphenol-glycidylinethacrylate), two common dental monomers, on the in vitro cellular proliferation, succinic dehydrogenase activity, and total cellular protein production of monocytes. Human THP-1 monocytes were exposed to concentrations of 100, 200, and 400 micromol l(-1) of TEGDMA or 1, 5, and 25 micromol l(-1) Bis-GMA for 5 weeks. Controls received only vehicle solutions of ethanol. Each week cellular proliferation (hemocytometer), succinic dehydrogenase (SDH) activity (MTT) and total cellular protein (bicinchoninic acid) were assessed. The results were compared with ANOVA and Tukey intervals (alpha = 0.05). TEDGMA had no proliferative or cellular protein effects, but increased SDH activity 20-60% in week 1 (p < 0.05). SDH activity then decreased 40% in week 2, followed by a gradual increase of 30-40% over week 3-5 (p < 0.05). Bis-GMA reduced proliferation by 40-60% from 1-5 weeks exposure (p < 0.05). However, SDH activity and total protein per cell were not affected. There was some indication of increased SDH activity after 5 weeks (20-30%, p < 0.05). Sub-lethal concentrations of TEGDMA and Bis-GMA have significant long-term effects on monocytes at low-dose 5-week exposures in vitro. Each monomer acted differently.