Effects of dentin bonding agents on macrophage mitochondrial activity

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.

Quantification of Macrophage Viability and Inflammatory Response to Dental Bonding Resins

This study presented a well-characterized biocompatibility profile of dental bonding agents in a mouse macrophage in vitro model. The cellular response to four different formulations of dental bonding resins and the cell viability was determined. Materials were prepared by photopolymerization and the unreacted monomers were extracted in a buffered medium. Murine macrophages were incubated in the extract medium for 24 h. Cellular viability was assessed by fluorescence microscopy and Wst-1 assay, while flow cytometry was used to quantify the apoptotic response. As an indicator of inflammatory responses, real-time polymerase chain reaction was utilized to quantify elevated cytokine production. These responses were monitored by quantifying the levels of tumor necrosis factor alpha (TNFα) and interleukin-1 β (IL-1β) produced by the cells. Murine macrophage cells exposed to the unfilled resin systems containing glycidyl ether of bisphenol A (Bis-GMA) and 2-hydroxyethyl methacrylate (HEMA) had the most adverse response and cells exposed to the filled Bis-GMA and HEMA resin system were the most viable at photopolymerization times. Other resin systems displayed intermediate levels of viability when compared with the untreated control. The levels of IL-1β were significantly elevated in all samples.

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.

Filtek™ Silorane and Filtek™ Supreme XT resins: tissue reaction after subcutaneous implantation in isogenic mice

The aim of this study was to evaluate the tissue compatibility of a silorane-based resin system (Filtek™ Silorane) and a methacrylate-based nanoparticle resin (Filtek™ Supreme XT) after implantation in the subcutaneous connective tissue of isogenic mice. One hundred and thirty five male isogenic BALB/c mice were randomly assigned to 12 experimental and 3 control groups, according to the implanted material and the experimental period of 7, 21 and 63 days. At the end of each period, the animals were killed and the tubes with the surrounding tissues were removed and processed for microscopic analysis. Samples were subjected to a descriptive and a semi-quantitative analyses using a 4-point scoring system (0-3) to evaluate the collagen fiber formation and inflammatory infiltrate. Data were statistically analyzed using the Kruskal Wallis test (α=0.05). The results showed that there was no significant difference between the experimental and control groups considering the three evaluation periods (p>0.05). The silorane-based and the methacrylate-based nanoparticle resins presented similar tissue response to that of the empty tube (control group) after subcutaneous implantation in isogenic mice.

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.

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.

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.

Effects of HEMA on type I collagen protein in human gingival fibroblasts

The cytotoxicity of dental composites has been attributed to the release of residual monomers from polymerized adhesive systems due to degradation processes or the incomplete polymerization of materials. 2-Hydroxyethyl methacrylate (HEMA) is one of the major components released from dental adhesives. Cytotoxic effects due to high concentrations of HEMA have already been investigated, but the influence of minor toxic concentrations on specific proteins such as type I collagen has not been studied in depth. The objective of this project was to study the effect of minor toxic concentrations of HEMA on human gingival fibroblasts (HGFs), investigating modification in cell morphology, cell viability, and the influence on type I collagen protein. Primary lines of human gingival fibroblasts were exposed to 3 mmol/L HEMA for different periods of time (24 h, 72 h, 96 h). The cell vitality was determined by MTT assay, and high-resolution scanning electron microscopy analysis was performed to evaluate differences in cell morphology before and after treatment. The presence and localization of type I collagen was determined by immunofluorescence in HGFs treated with HEMA for the same period of time. The vitality of the cells decreased after 72 h of exposure. The HGFs grown in monolayer and observed by field emission in-lens scanning electron microscopy demonstrated a preserved surface morphology after 24 h of treatment, while they showed an altered morphology after 96 h of treatment. Immunofluorescence demonstrated a reduction of type I collagen due to HEMA exposure after 96 h. From these results, we conclude that low concentrations of HEMA can significantly alter the morphology of human gingival fibroblasts and interfere with the presence of type I collagen protein.

Cytotoxicity evaluation of an antibacterial dentin adhesive system on established cell lines

Clearfil Protect Bond is a new dental bonding agent recently introduced into clinical practice. It contains an antibacterial monomer that contributes to its antibacterial profile. The aim of the present study was to evaluate cytotoxic effect of Clearfil Protect Bond against three established fibroblastic cell lines, in comparison with four commonly used adhesive materials (Adper Scotchbond 1, Excite, Tyrian SPE, and One Step plus). The experiments were performed using RPC-C2A, BHK21/C13, and MRC5 cell lines. Test specimens, either cured or uncured, were placed in a culture medium and the extraction media were used as experimental material. The effect of the bonding materials was assessed by a modified sulforhodamine-B assay after 24 and 48 h of exposure. All tested agents exhibited an antiproliferative effect on cells, the effect on RPC-C2A being the most marked. Extraction media from the uncured materials were without exception highly cytotoxic. In the experiments performed using extraction medium from cured material, Clearfil Protect Bond appeared to be the least toxic material, followed by Tyrian SPE and One Step plus. Adper Scotchbond 1 and Excite exhibited the strongest cytotoxic effect. The cell survival percentage ranged between 66 and 97% for Clearfil Protect bond, 15 and 82% for Tyrian SPE, 28 and 58% for One Step plus, 2 and 28% for Excite, and 1 and 6% for Adper Scotchbond 1. Taking into consideration the limitations of an in vitro study, our results indicate that the new antibacterial dental adhesive system is suitable for clinical application.

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.

HEMA diffusion from dentin bonding agents in young and old primary molars in vitro

OBJECTIVE

The objective of this study was to evaluate and compare amounts of HEMA diffusion from three dentin bonding systems in young and old primary molars at a remaining dentin thickness (RDT) of 1 mm.

METHODS

Occlusal cavities were prepared with RDT of 1 mm in young and old primary molars. Chambers that contain 1 ml of distilled water were attached to each tooth. The groups were treated with Total Etch+Syntac Single Component, Syntac Single Component and Clearfil SE Bond. Water eluates were analyzed by HPLC at 4 min, 24 h and 72 h.

RESULTS

The cumulative HEMA release amounts were significantly different among all groups (p<0.05). Acid-etching significantly increased pulpward diffusion of HEMA and young primary teeth presented higher dentin permeability.

SIGNIFICANCE

Acid-etching significantly increases pulpward release of HEMA from dentin bonding systems in primary molar teeth. Young primary molars have higher dentin permeability; so the pulp should be protected with cavity liners in deep cavities. However, the dentin bonding systems can be considered safe for clinical use in primary teeth, even in deep cavities, since the released HEMA amounts are below the level of cytotoxicity.

Adverse effects of human pulps after direct pulp capping with the different components from a total-etch, three-step adhesive system

OBJECTIVES

The objective was to evaluate the response of human pulps capped with different components from a total-etch three-step adhesive system.

METHODS

Direct pulp capping was performed in 25 caries-free human premolars scheduled for extraction due to orthodontic treatment. The teeth were randomly divided in five groups, and capped with the following materials: Group 1-acid+primer+adhesive were used as recommended; Group 2-only primer was applied; Group 3-only bonding resin (light-cured for 10s); Group 4-only composite resin (light-cured for 40s); Group 5-calcium hydroxide. After capping, all teeth were restored with ScotchBond Multi Purpose Plus and Z-100 was placed incrementally. After 60 days, the teeth were extracted and processed for light microscopic examination (H/E) according to a histological score system. These were subjected to non-parametric tests (alpha<0.05).

RESULTS

Overall, the histological features showed that groups 1-4 were quite similar and inferior to group 5. In groups 1-4 the pulp response varied from acute inflammatory cell infiltrate with varying degrees to necrosis. The groups 3 and 4 showed a trend towards better pulp response, since a normal connective tissue could be observed in more than half of the sample. All teeth from group 5 showed normal connective tissue below an amorphous dentin bridge.

SIGNIFICANCE

Adhesive components (primer or adhesive) as well as a composite should be avoided for pulp capping. Ca(OH)(2) should be the first choice for pulp capping.

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.

Dental adhesive compounds alter glutathione levels but not glutathione redox balance in human THP-1 monocytic cells

The use of hydrophilic dental monomers in dentin bonding agents has vastly improved resin-dentin bond strengths, but incomplete polymerization of these monomers and their leaching into adjacent (pulpal) oral tissues has raised concerns about their biocompatibility. The sublethal effects of these resins are virtually unknown, but their electrophilic nature led to the hypothesis that they may alter cellular oxidative stress pathways. Glutathione balance between reduced (GSH) and oxidized (GSSG) is a major mechanism by which cells maintain redox balance and was therefore the focus of the current investigation. THP-1 human monocytic cells were exposed to hydroxyethyl methacrylate (HEMA), benzoyl peroxide (BPO), camphorquinone (CQ), or triethyelene glycol dimethacrylate (TEGDMA) for 24 h at sublethal doses, then GSH and GSSG levels were measured by means of Ellman's method adapted for cell culture. The results indicate that these dental resin compounds act at least partly via oxidative stress by increasing GSH levels at sublethal concentrations. However, the GSH-GSSG ratio was relatively unaffected. Only BPO altered the GSH-GSSG ratio at 24 h, again at sublethal levels (7.5-15 micromol/L). The results support the hypothesis that resin monomers act, at least in part, via oxidative stress, and that oxidative-stress pathways should be one focus of future investigations of monomer biocompatibility.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

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.

Response of human pulps following acid conditioning and application of a bonding agent in deep cavities

OBJECTIVES

The aim of this in vivo study was to evaluate the human dental pulp response when a one-bottle adhesive system was applied on etched or unetched deep dentine.

METHODS

Eighteen class V deep cavity preparations were divided in three groups: group 1-total etching + two coats of single bond (SB) + composite resin (Z-100); group 2-enamel etching + two coats of SB + Z-100; group 3-cavity floor lined with a calcium hydroxide liner (Dycal) + acid-etching of enamel and lateral walls + two coats of SB + Z-100. Two teeth were used as intact control group. After 30 days the teeth were extracted and processed through H and E, Masson's trichrome and Brown and Brenn staining techniques.

RESULTS

Moderate inflammatory response, disorganization of pulp tissue, as well as, deposition of thin layer of reactionary dentin were observed in group 1 teeth in which the remaining dentin thickness (RDT) was less than 300 microm. These histological findings appear to be related to long resin tags formation and bonding agent diffusion through dentinal tubules. In group 2, slight inflammatory response was observed only in one tooth in which the RDT was 162 microm. In group 3, all the teeth showed normal histological characteristics which were similar to the intact control group. Presence of bacteria was not correlated with the intensity of pulpal response. The patients reported no symptoms during the experiment. Radiographic evaluation showed no periapical pathology for any of the teeth.

SIGNIFICANCE AND CONCLUSIONS

Acid-etched deep dentin (RDT less than 300 microm) lined with SB causes more intense pulpal response than unetched deep dentin. Based on the results observed in the present study and the conditions in which it was carried out, we recommend the application of a biocompatible liner before etching deep dentin and applying SB.

Biocompatibility of resin-modified filling materials

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

Changes in cell phospholipid metabolism in vitro in the presence of HEMA and its degradation products

OBJECTIVES

Diacylglycerol-kinase (DAG-kinase) is an enzyme that phosphorylates diacylglycerol (DAG) to phosphatidic acid (PA), which serves as a precursor to phosphoglycerides involved in cell signaling or as cell membrane structural components. DAG-kinase can be inhibited by diacylethylene glycols (DAEG). We hypothesize that 2-hydroxyethyl methacrylate (HEMA) may alter phosphorylation of DAG to PA following intracellular formation of DAEG.

METHODS

Cultured rabbit kidney (RK13) epithelial cells were treated with HEMA, EG, or known inhibitors of DAG-kinase for 24 h, then exposed to [32P]O4- in the presence of a synthetic diacylglycerol for 2 h. Other cultures were radiolabeled with [3H]-oleic acid for 24 h, then exposed to HEMA for an additional 24 h. The cells were harvested and the lipids extracted. Radioactive lipids were separated by thin layer chromatography, located by autoradiography, and quantitated as cpm/ug protein. Cell cultures treated with HEMA were homogenized and the DAG-kinase activity was assayed and expressed as cpm/ug protein. Data were analyzed by one-way ANOVA and Newman-Keuls Multiple Comparison Test.

RESULTS

Cultures exposed to HEMA or known DAG-kinase inhibitors exhibited reduced incorporation of radioactivity in the PA fraction compared to control cultures. Direct assays of DAG-kinase activity from cells exposed to HEMA demonstrated decreased enzyme activity. Evaluation of cell phospholipid synthesis showed altered formation of phosphatidylethanolamine and phosphatidylcholine.

SIGNIFICANCE

Results suggest that HEMA impairs formation of PA, possibly by acylation of EG released by hydrolysis of the HEMA and resultant production of the inhibitor DAEG. The decreased availability of PA may alter PA-dependent cell structural lipid pathways and lipid-dependent signaling pathways, altering cell growth.

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.

Alterations in cell lipid metabolism by glycol methacrylate (HEMA)

Components of dental resins such as dimethylaminoethyl methacrylate (DMAEMA) can alter cell lipid composition, presumably by esterase-mediated hydrolysis. The resulting dimethylethanolamine is incorporated into cell phospholipids, while the methacrylic acid may alter several metabolic pathways. We hypothesize that HEMA is cleaved in a similar manner and the released ethylene glycol is incorporated into cell lipids, yielding phosphatidylethylene glycol (PtEG), and the methacrylic acid alters other lipid pathways in a manner similar to that of methacrylic acid released from hydrolysis of DMAEMA. Cultures of hamster buccal pouch (HCP) and rabbit kidney (RK13) epithelial cells were exposed to subtoxic concentrations of HEMA in the presence of [14C]-acetate or [3H]-oleic acid. Other cultures were prelabeled with [14C]-acetate followed by exposure to various concentrations of HEMA. Cell lipids were extracted by the method of Bligh and Dyer and separated by thin layer chromatography on silica gel K-6 plates or SG-81 silica gel loaded chromatography paper. The fate of the ethylene glycol was traced using [14C]-ethylene glycol. Radioactive lipids were located using autoradiography and known standard lipids and quantitated by liquid scintillation spectrometry. In the presence of HEMA several classes of lipids were altered. Among the neutral lipids, the most notable changes involved sterol precursors, triglycerides, fatty acids, and cholesterol esters, while phosphatidylcholine was affected among the phospholipids. The results differed quantitatively between the two cell types. Results also suggest that EG, including that released by hydrolysis of HEMA, is incorporated into cell phospholipids, producing PtEG. The changes in neutral lipid labeling may occur by alteration of lipid synthetic pathways utilizing acetyl Co-A as well as inhibition of enzymes involved in synthesis of cholesterol from sterol precursors and hydrolysis of cholesterol esters. Synthesis of PtEG may take place via phospholipase D-mediated headgroup exchange. Alterations in the cellular lipids may affect cell membrane properties and associated cell functions.

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

Dentin bonding agents (DBAs) have been proposed as substitutes for amalgam as root-end filling materials. The current study tested the hypothesis that certain components of DBAs could alter the secretion of cytokines from macrophages. Such alteration would likely be undesirable for healing of the periapical tissues. Human THP-1 macrophages were exposed to 2-hydroxyethyl methacrylate, 4-methacryloxyethyl trimelliate anhydride, bisphenol-gycidylmethacrylate, and urethane dimethacrylate. The secretion of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) were measured with or without challenge by lipopolysaccharide (LPS). Results showed that all DBA components completely suppressed LPS-induced IL-1 beta and TNF-alpha secretion at concentrations that suppressed mitochondrial activity by 50%. In addition, 4-methacryloxyethyl trimelliate anhydride induced secretion of IL-1 beta, but not TNF-alpha, without the LPS challenge. These results indicate that DBA components may alter normal macrophage-directed inflammatory responses if the macrophages are exposed to sufficiently high concentrations of these components.