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

Assessment of cytotoxicity, odontoblast-like differentiation, shear bond strength, and microhardness of four orthodontic adhesive composites

PURPOSE

To determine and compare the cytotoxicity, odontoblast-like differentiation, shear bond strength (SBS) and Vickers microhardness of four commercial light-cured orthodontic adhesives.

METHODS

The orthodontic resins selected were Transbond XT - GI, Transbond Plus Color Change - GII (both from 3M Unitek), Enlight - GIII and Blugloo - GIV (both from Ormco). Samples were prepared, and leached monomers were obtained. Cytotoxicity was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and deposited calcium was analyzed using Alizarin red staining (ARS). SBS and the adhesive remnant index (ARI) were determined using 120 human premolars. The Vickers microhardness test was performed on the resin discs.

RESULTS

All adhesives showed moderate to severe cytotoxicity (21-37%) and promoted similar formation of calcium deposits. A SBS of 6-8 MPa was achieved only by Blugloo (7.1 ± 2.4 MPa), and Enlight showed the lowest Vickers hardness score (40 ± 2.5 HV). Transbond Plus Color Change (score 0 = 42.9%) and Blugloo (score 0 = 46.4%) showed better ARI scores than Transbond XT (score 0 = 7.1%) and Enlight (score 0 = 3.6%).

CONCLUSION

On the basis of the properties evaluated, Blugloo seems to be the best option.

Antimicrobial and self-crosslinking potential of experimentally developed dioctadecyldimethyl ammonium bromide and riboflavin dentin adhesive

The aim of the study is to investigate a new formulation, based on dioctadecyldimethyl ammonium-bromide (QA) and riboflavin (RF), combining antimicrobial activities and protease inhibitory properties with collagen crosslinking without interference to bonding capabilities in a rabbit model. Quaternary ammonium riboflavin (QARF) experimental adhesives modified with dioctadecyldimethyl ammonium-bromide and riboflavin were bonded (0.5/1.0/2.0%) to rabbit dentin to investigate for pulpal-histology, interfacial-morphology, transmission electron microscopy, mechanical properties, collagen crosslinking, micro-Raman analysis, antimicrobial, and anti-protease activities. Collagen type-I molecules were generated using molecular-docking. Odontoblasts appeared with normal histology, were seen in controls with no inflammatory cells detected in 0.5% specimens at day 7 and mild inflammatory response at day 30. In QARF 2.0%, inflammatory cells were not detected at day 7 and 30 (p < .05). Dentinal tubules are seen with intact collagen surface in 1% specimens. Resin penetrated inside 1% adhesive specimens with few irregularly funnel-shaped tags. Transmission electron microscopy showed thinner collagen in all specimens except 1% QARF specimens. Biofilms were influenced by QARF adhesives. Elastic moduli were significantly higher in 1.0% and 2.0% QARF adhesive specimens with a significant increase in total crosslinks. Stable amide groups with anti-protease activity was observed in QARF groups. Charged residues were seen in the triple helix hCOL3A1, Gly489-Gly510 after stabilisation with formulation. The 1% QARF modified adhesives improved biochemical and biomechanical properties of rabbit dentin.

Influence of 2-hydroxyethyl methacrylate (HEMA) exposure on angiogenic differentiation of dental pulp stem cells (DPSCs)

OBJECTIVE

The angiogenic differentiation of dental pulp stem cells (DPSCs) is important for tissue homeostasis and wound healing. In this study the influence of 2-hydroxyethyl methacrylate (HEMA) on angiogenic differentiation was investigated.

METHODS

To evaluate HEMA effects on angiogenic differentiation, DPSCs were cultivated in angiogenic differentiation medium (ADM) in the presence or absence of non-toxic HEMA concentrations (0.1 mM and 0.5 mM). Subsequently, angiogenic differentiation was analyzed on the molecular level by qRT-PCR and protein profiler analyzes of angiogenic markers and flow cytometry of PECAM1. The influence of HEMA on angiogenic phenotypes was analyzed by cell migration and sprouting assays.

RESULTS

Treatment with 0.5 mM HEMA during differentiation can lead to a slight reduction of angiogenic markers on mRNA level. HEMA also seems to slightly reduce the quantity of angiogenic cytokines (not significant). However, these HEMA concentrations have no detectable influence on cell migration, the abundance of PECAM1 and the formation of capillaries. Higher concentrations caused primary cytotoxic effects in angiogenic differentiation experiments conducted for longer periods than 72 h.

SIGNIFICANCE

Non-cytotoxic HEMA concentrations seem to have a minor impact on the expression of angiogenic markers, essentially on the mRNA level, without affecting the angiogenic differentiation process itself on a detectable level.

Cytotoxicity evaluation of eluates from universal adhesives by real-time cell analysis

The aim of this study was to evaluate the cytotoxicity of universal adhesives on L929 mouse fibroblast cell line by using a real-time cell analysis. In order to obtain extract, six different cured dental adhesives were immersed in Dulbecco's Modified Eagle's Medium (DMEM) at 37°C for 24 h. A real-time cell analysis system was used to assess cytotoxicity of the dental adhesives. After seeding 25,000 cells/300 μL/well cell suspensions into the wells of an e-plate, fibroblasts were exposed to extracts of tested adhesives at varying dilutions (1:1, 1:2, and 1:10) and observed at every 30 min intervals for 72 h. Three-way ANOVA one factor repeated measures were used to analyze the results (α=0.05). All tested adhesives induced cell viability loss, cell morphology alteration, and cell death depending on extract concentration and time. Cell viability of L929 cells to between 44 and 10% for 1:1 diluted extracts, at 72 h, when compared to the negative control.

Solvent and HEMA Increase Adhesive Toxicity and Cytokine Release from Dental Pulp Cells

The aim of the present study was to evaluate the effect of the hydroxyethyl-methacrylate (HEMA) concentration and solvent content of dental adhesives on cell viability and cytokine (IL-1b, IL-6, IL-10, TNF-α) release by human dental pulp cells (HDPCs). HDPCs were obtained from fresh extracted human third molars. Experimental adhesives were prepared containing different concentrations of HEMA (0%, 10%, and 20%) with and without solvent (ethanol 10%). Cylindrical specimens were immersed on culture medium during 24 h to obtain the extracts. The cells were incubated with extracts (culture medium + components leached from the adhesives) of different adhesives, and cell viability and cytokine release were evaluated after 6 and 24 h of exposure. Adhesives containing HEMA promoted high cell viability reduction after 6 h of exposure; but after 24 h, the results were similar to the ones found among control group cells. These effects on cell viability were prominently increased with the addition of solvent. Although IL-1b release was not affected by exposure to eluates, other cytokines (IL-10, IL-6, TNF-α) were modulated by the different experiment conditions, directly influenced by the HEMA concentration and presence of solvent. Higher HEMA concentrations, combined with the presence of solvent, can promote significant reduction on HDPC viability, increasing the release of anti- and pro-inflammatory mediators.

In-vitro transdentinal diffusion of monomers from adhesives

OBJECTIVES

Biocompatibility of adhesives is important since adhesives may be applied on dentin near the pulp. Accurate knowledge of the quantity of monomers reaching the pulp is important to determine potential side effects. The aim of this study was to assess the transdentinal diffusion of residual monomers from dental adhesive systems using an in-vitro pulp chamber model.

METHODS

Dentin disks with a thickness of 300 μm were produced from human third molars. These disks were fixed between two open glass tubes, representing an in-vitro pulp chamber. The etch-and-rinse adhesive OptiBond FL and the self-etch adhesive Clearfil SE Bond were applied to the dentin side of the disks, while on in the pulpal side, the glass tube was filled with 600 μl water. The transdentinal diffusion of different monomers was quantified using ultra-performance liquid chromatography-tandem mass spectrometry.

RESULTS

The monomers HEMA, CQ, BisGMA, GPDM, 10-MDP and UDMA eluted from the dental materials and were able to diffuse through the dentin disks to a certain extent. Compounds with a lower molecular weight (uncured group: HEMA 7850 nmol and CQ 78.2 nmol) were more likely to elute and diffuse compared to monomers with a higher molecular weight (uncured group: BisGMA 0.42 nmol). When the adhesives were left uncured, diffusion was up to 10 times higher compared to the cured conditions.

CONCLUSIONS

This in-vitro research resulted in the quantification of various monomers able to diffuse through dentin and therefore contributes to a more detailed understanding about the potential exposure of the dental pulp to monomers from dental adhesives.

CLINICAL SIGNIFICANCE

Biocompatibility of adhesives is important since adhesives may be applied on dentin near the pulp, where tubular density and diameter are greatest.

Evaluation of HEMA released from four different adhesive systems by HPLC

PURPOSE

This study evaluated the elution of 2-hydroxyethyl methacrylate (HEMA) from 4 different adhesives, using high-performance liquid chromatography (HPLC).

MATERIALS AND METHODS

The adhesives were applied on a bovine dentin surface and polymerized using an LED curing unit (n=5). After polymerization, specimens were stored in 75% ethanol solution (6 mL). Residual HEMA that was eluted from adhesives (after 10 minutes, 1 hour, 24 hours, 7 days and 30 days) was analyzed using HPLC. Statistical analyses were performed using 1-way ANOVA, Tukey HSD test and paired 2-sample t-test.

RESULTS

There were statistically significant differences among adhesive systems for the cumulative released HEMA and among the time periods (p&lt;0.05). Clearfil SE Bond showed the highest amount of HEMA released, while Easy Bond showed the lowest. Among the time periods, the highest eluted HEMA value was detected in 10 minutes for all adhesives, and elution continued for up to 30 days.

CONCLUSIONS

The HEMA eluted from adhesives was in different amounts, and the elution continued for a long time. The amount of eluted HEMA from adhesives used in this study was not viewed as critical for toxic reactions in biological tissues.

Experimental self-etching HEMA-free adhesive systems: cytotoxicity and degree of conversion

The aim of this study was to evaluate the effect of replacing 2-hydroxyethyl methacrylate (HEMA) by methacrylate surfactant monomers on the cytotoxicity and degree of conversion of two-step self-etching dentin adhesive systems. Five HEMA-free adhesive systems were tested: Bis-EMA 10, Bis-EMA 30, PEG400, PEG400UDMA, PEG1000, and a HEMA group was used as positive control. The cytotoxicity of the experimental primers, with different monomer concentrations (2 or 20 wt%), and bond resins, containing 25 wt% surfactant, was assessed using murine fibroblast cell line 3T3 and the tetrazolium assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)). The degree of conversion of the bond resins was analyzed using Fourier transform infrared spectroscopy. The data were submitted to statistical analysis using level of significance set at P < 0.05. The PEG 1000 group obtained higher cell viability in comparison with HEMA in the 2 % primer. The cell survival rate using 20 % primer showed that PEG1000 and BIS-EMA 10 were less cytotoxic than HEMA. With regard to the eluate from bond resin, the data showed that the groups BIS-EMA 10, BIS-EMA 30 and PEG400UDMA were less cytotoxic than HEMA. No statistically significant difference was found among degrees of conversion of the experimental groups and HEMA. PEG 1000, BIS-EMA 10 and 30 monomers showed the biological potential for use in new adhesive system formulations since they showed lower cytotoxicity and similar degree of conversion when compared with the HEMA-containing group.

Evaluation of antibacterial and remineralizing nanocomposite and adhesive in rat tooth cavity model

Antibacterial and remineralizing dental composites and adhesives were recently developed to inhibit biofilm acids and combat secondary caries. It is not clear what effect these materials will have on dental pulps in vivo. The objectives of this study were to investigate the antibacterial and remineralizing restorations in a rat tooth cavity model, and determine pulpal inflammatory response and tertiary dentin formation. Nanoparticles of amorphous calcium phosphate (NACP) and antibacterial dimethylaminododecyl methacrylate (DMADDM) were synthesized and incorporated into a composite and an adhesive. Occlusal cavities were prepared in the first molars of rats and restored with four types of restoration: control composite and adhesive; control plus DMADDM; control plus NACP; and control plus both DMADDM and NACP. At 8 or 30days, rat molars were harvested for histological analysis. For inflammatory cell response, regardless of time periods, the NACP group and the DMADDM+NACP group showed lower scores (better biocompatibility) than the control group (p=0.014 for 8days, p=0.018 for 30days). For tissue disorganization, NACP and DMADDM+NACP had better scores than the control (p=0.027) at 30days. At 8days, restorations containing NACP had a tertiary dentin thickness (TDT) that was five- to six-fold that of the control. At 30days, restorations containing NACP had a TDT that was four- to six-fold that of the control. In conclusion, novel antibacterial and remineralizing restorations were tested in rat teeth in vivo for the first time. Composite and adhesive containing NACP and DMADDM exhibited milder pulpal inflammation and much greater tertiary dentin formation than the control adhesive and composite. Therefore, the novel composite and adhesive containing NACP and DMADDM are promising as a new therapeutic restorative system to not only combat oral pathogens and biofilm acids as shown previously, but also facilitate the healing of the dentin-pulp complex.

The effect of glutathione on 2-hydroxyethylmethacrylate cytotoxicity and on resin-dentine bond strength

AIM

To evaluate the influence of reduced glutathione (GSH) application on 2-hydroxyethylmethacrylate (HEMA) cytotoxicity on rat pulpal cells and evaluate the effect of etched-dentine treatment with GSH on the immediate microtensile bond strength (μTBS) of etch-and-rinse adhesive.

METHODOLOGY

The cytotoxicity of 10 mmol L(-1) HEMA, 10 mmol L(-1) HEMA + 1 mmol L(-1) GSH, 10 mmol L(-1) HEMA + 5 mmol L(-1) GSH and 10 mmol L(-1) HEMA + 10 mmol L(-1) GSH was compared (6 h and 24 h). Cells viability was measured by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, followed by morphological observation of cells. Etched-dentine surfaces were rinsed and treated with one of the following solutions: 2% GSH, 5% GSH or 10% GSH, bonded with Adper Single Bond Plus (3M, ESPE, St. Paul, MN, USA) and restored with resin composite. The control group received no GSH treatment. After 1 day of water-storage at 37 °C, the specimens were subjected to μTBS testing. Cytotoxicity and μTBS data were analysed by one-way anova and Tukey post hoc tests (P < 0.05).

RESULTS

There were significant differences between the groups. HEMA elicited a remarkable toxic effect. 10 mmol L(-1) GSH prevented HEMA-induced damage at both exposure times. Whilst 5 mmol L(-1) GSH lost its protective effect at 24-h exposure time and 1 mmol L(-1) GSH showed no protective effect at both exposure times, GSH had no significant effect on the immediate μTBS; however, 5% GSH had higher bond strength value when compared to 10% GSH (P = 0.003).

CONCLUSION

Controlled concentrations of GSH had a protective effect against HEMA cytotoxicity. GSH had neither positive nor negative influence on μTBS.

Saliva improves Streptococcus mitis protective effect on human gingival fibroblasts in presence of 2-hydroxyethyl-methacrylate

This study aimed to investigate the effect of saliva on Streptococcus mitis free cells and on S. mitis/human gingival fibroblasts (HGFs) co-culture model, in presence of 2-hydroxyethyl-methacrylate (HEMA). The bacterial aggregation both in the planktonic phase and on HGFs, as well as the apoptotic and necrotic eukaryotic cells amount were analyzed, in presence of saliva and/or HEMA. The aggregation test revealed a significant saliva aggregation effect on S. mitis strains compared to the untreated sample. No significant differences were recorded in the amount of culturable bacteria in all studied conditions; however, from microscopy images, the saliva/HEMA combining effect induced a significant bacterial aggregation and adhesion on HGFs. HEMA treatment decreased viable eukaryotic cell number with a parallel increment of necrotic cells, but when saliva was added to the co-culture, the viable cells percentage increased to a value comparable to the control sample.

Biocompatibility of various dental materials in contemporary dentistry: a narrative insight

In the past few decades, there has been an increase in demand for safety evaluation and control of dental materials used daily in dentistry; however, this task is difficult and cumbersome. Dental materials that are passive and do not react with the oral environment will be more stable and have superior durability. It is expected that dental materials will be universally accepted and will not cause harm or injury to the surrounding structures in the oral cavity. This is an entirely negative approach to the material tolerance and biocompatibility, and hides the possibility that some positive gains can be achieved. Side-effects of dental materials are believed to be rare, and generally, those that have been reported are mild. There are wide varieties of materials used in dentistry, which include liners, irrigants, intracanal filling materials, intracanal medicaments, prosthetic materials, restorative materials, subgingival implants, and mouth rinses. Therefore, in this study, the biocompatibility of various commonly-used clinical materials used in contemporary dentistry was discussed.

Influence of thicknesses of smear layer on the transdentinal cytotoxicity and bond strength of a resin-modified glass-ionomer cement

This study evaluated the transdentinal cytotoxicity (TC) and the bond strength (BS) of a resin-modified glass-ionomer cement (RMGIC) applied to dentin covered with smear layer (SL) of different thicknesses. Forty dentin discs had thick (TSL) or thin (THSL) smear layer created on their occlusal side. In artificial pulp chambers, MDPC-23 cells were seeded on the pulpal side of the dentin discs and divided into five groups: G1TC: no treatment (control); G2TC: TSL + RMGIC; G3TC: THSL + RMGIC; G4TC: TSL removal + RMGIC; G5TC: THSL removal + RMGIC. After 24 h, cell metabolism and morphology were evaluated by the methyltetrazolium (MTT) assay and by scanning electron microscopy (SEM), respectively. For BS, the following groups were determined: G1BS: TSL removal + RMGIC; G2BS: THSL removal + RMGIC; G3BS: TSL + RMGIC; G4BS: THSL + RMGIC. Shear bond strength was tested to failure in a mechanical testing machine MTS (0.5 mm/min). Statistically significant difference was observed only between the control and experimental groups (Kruskal-Wallis, p<0.05). The metabolic activity of the viable MDPC-23 cells in G2TC, G3TC, G4TC and G5TC decreased by 54.85%, 60.79%, 64.12% and 62.51%, respectively. Mean shear bond strength values for G1BS, G2BS, G3BS and G4BS were 7.5, 7.4, 6.4 and 6.7 MPa, respectively, without significant difference among them (ANOVA, p>0.05). RMGIC presented moderate transdentinal cytotoxic effects. Maintenance or removal of smear layer did not affect the bond strength of RMGIC to dentin substrate.

The effects of hyaluronic acid, calcium hydroxide, and dentin adhesive on rat odontoblasts and fibroblasts

The aim of this study was to investigate the effects and efficiency of pulp capping preparations based on hyaluronic acid, calcium hydroxide, and dentin adhesive on the pulp tissue of Sprague-Dawley rats. The rats were killed and extracted teeth sectioned transversely through the pulp. The slices were placed in a RPMI 1640 cell culture medium supplemented with 10 % foetal calf serum. During 14 days of cultivation cultures were treated with preparations that contained hyaluronic acid (Gengigel Prof®), and calcium hydroxide (ApexCal®), or with dentin adhesive (Excite®). Cellularity and viability of fibroblasts and odontoblasts was analysed using a haemocytometer. Hyaluronic acid proved most efficient and the least toxic for direct pulp capping. Even though calcium hydroxide and dentin adhesive demonstrated a higher degree of cytotoxicity, their effects were still acceptable in terms of biocompatibility.

Streptococcus mitis/human gingival fibroblasts co-culture: the best natural association in answer to the 2-hydroxyethyl methacrylate release

One of the major components of dental polymerized resin-based restorative materials is 2-hydroxyethyl methacrylate (HEMA) and its release in monomeric form interferes with the oral cavity environment. This study aimed to evaluate HEMA monomeric effects on the co-culture of Streptococcus mitis and human gingival fibroblasts (HGFs). Streptococcus mitis DS12 and S. mitis ATCC 6249 were co-cultivated with HGF in the presence of HEMA (3 mM), for 48 and 72 h; the amount of sessile and planktonic cells, as well as the prokaryotic and eukaryotic cell viability were analyzed in treated and untreated samples. The treatment of S. mitis/HGFs with HEMA did not produce significant effects on the bacterial adhesion and induced an increase in planktonic S. mitis ATCC 6249 population after 48 and 72 h. HEMA increased significantly the planktonic S. mitis ATCC 6249 viability when co-cultured with HGFs, while a cytotoxic effect on HGFs, without bacteria, was recorded. An increase of bacterial aggregation on HGFs was also detected with HEMA. Data obtained in this study suggest that HEMA exhibits a toxic effect mainly on eukaryotic cells and this effect can be modulated by co-cultivation with the S. mitis cells which, in the presence of the monomer, enhance their aggregation rate on HGFs.

Suppression of procollagen {alpha}1 type 1 by long-term low-dose exposure to 2-hydroxyethylmethacrylate in human gingival fibroblasts in vitro

The purpose of this study was to evaluate the cytotoxicity of low doses and long-term exposure to 2-hydroxyethylmethacrylate (HEMA) on the protein expression of human gingival fibroblasts (HGFs). Human gingival fibroblasts were exposed to different concentrations of HEMA ranging from 0.5 mmol/L to 3 mmol/L for periods of time from 72 hours to 2 weeks. A significant decrease in the expression of procollagen α1 type I protein was observed 72 hours after treatment of cells with 3 mmol/L HEMA. Although low concentrations of the monomer after 2 weeks of exposure to HEMA did not appear to induce any marked changes in the morphology or viability of cells, the expression of procollagen α1 type I protein and its messenger RNA (mRNA) markedly decreased. In conclusion, our data demonstrated that cell viability and morphology assays could be deficient parameters in evaluating the biocompatibility of dental resin materials.

The effect of dentine-bonding agents on substance P release in human dental pulp

AIM

To quantify the effect of dentine-bonding agents on Substance P (SP) release in healthy human dental pulp tissue.

METHODOLOGY

Forty pulp samples were obtained from healthy pre-molars where extraction was indicated for orthodontic reasons. In thirty of these pre-molars, a standardized Class V cavity preparation was performed, and teeth were divided equally into three groups: (i) Unetched-cavity control group: Class V cavities only; (ii) Experimental Group I: 'One-step' self-etch bonding agent was placed in the cavity; and (iii) Experimental Group II: 'Two-step' total-etch bonding agent was placed in the cavity. The remaining ten healthy pre-molars where extracted without treatment and served as an intact-teeth control group. SP was measured by radioimmunoassay.

RESULTS

Greater SP release was found in the 'one-step' bonding agent group, followed by the 'two-step' bonding agent group and the unetched-cavity control group. The lower SP values were for the intact-teeth control group. anova showed statistically significant differences between groups (P = 0.0001). Tukey HSD post hoc tests showed statistically significant differences in SP release between the intact-teeth control group and the three other groups (P < 0.01) and between the unetched-cavity control group and the 'one-step' bonding agent group (P < 0.05). No significant difference was found between the 'two-step' bonding agent and the unetched-cavity control group.

CONCLUSION

Dentine-bonding agents placed over Class V cavity preparations increased SP release. One-step dentine-bonding agents increased SP release most.

Genotoxicity of urethane dimethacrylate, a tooth restoration component

Urethane dimethacrylate (UDMA) is used in dental restorative materials in its polymeric form. However, the process of polymerization is usually incomplete and the monomers of UDMA can diffuse into the oral cavity and the pulp, reaching millimolar concentrations. In the present work we showed that UDMA at 0.1 and 1.0 mM decreased the viability of and induced DNA damage in lymphocytes in a concentration dependent manner, but it did not affect a plasmid DNA in vitro. UDMA at 1mM induced apoptosis in lymphocytes. The lymphocytes exposed to UDMA were able to repair their DNA within 60 min. Analysis with DNA repair enzymes Endo III and Fpg showed that UDMA induced mainly oxidative DNA lesions. Vitamin C and chitosan decreased genotoxic effect of UDMA. Our results show that monomers of UDMA may exert pronounced cyto- and genotoxic effects in human lymphocytes and chitosan can be considered as a protection against such effects.

HEMA down-regulates procollagen alpha1 type I in human gingival fibroblasts

2-Hydroxyethyl methacrylate (HEMA) can be released from restorative materials and diffused into the tooth pulp over long periods of time. Although cytotoxicity due to high concentrations of monomers has been well studied, little is known about the risk of chronic toxicity resulting from low concentrations. The purpose of the study was to evaluate the effects of a minor toxic concentration of HEMA in the synthesis and expression of procollagen alpha1 type I produced by human gingival fibroblasts (HGF). HGF were exposed to 3 mM HEMA from 24 to 96 h. An MTT assay was performed to evaluate cell viability while reverse-transcriptase polymerase chain reaction (RT-PCR), real-time polymerase chain reaction (real-time PCR), and Western-blot analysis were carried out to evaluate the variability in the expression and synthesis of procollagen alpha1. Immunofluorescence was performed to detect the protein inside the cells. The results showed that there was a strong reduction of procollagen alpha 1 type I expression at 72 and 96 h. These findings demonstrate that, even if it does not reduce cell viability, 3 mM HEMA interferes both with the synthesis of the procollagen alpha 1 type I protein and its mRNA expression, suggesting that normal cell production and activity are modified by HEMA at concentrations below those which cause acute cytotoxicity.

In vitro potential cytotoxicity of an adhesive system to alveolar macrophages

The purpose of this study was to evaluate the potential cytotoxicity of Adper Single Bond 2 (SB) simplified etch-and-rinse adhesive system in alveolar macrophage cultures, as a function of the post-polymerization time and duration of immersion in the culture medium for preparation of extracts, by observing the levels of nitric oxide (NO) release and cell survival rate (MTT assay). Wistar rat alveolar macrophages were exposed to 200 μL of extracts obtained from 24- or 72-h immersion of adhesive samples in culture medium (RPMI), immediately or 24 h after polymerization. Fresh RPMI and E. coli lipopolysaccharides were used as negative and positive controls, respectively. The cells were placed in a humidified incubator for 24 h. The results were analyzed by the Student's-t test (α=5%). The amount of NO produced and viable cells were significantly different (p<0.05) between the experimental and the control groups, showing that, irrespective of the post-polymerization time and duration of immersion in the culture medium, the adhesive system caused intense cytotoxicity to the macrophages. The cytotoxic effects were not statistically different (p<0.05) among the experimental groups. In conclusion, chemical components released from SB in aqueous environment were highly toxic to cell culture and thus an inflammatory pulpal response should be considered during the clinical application of dental adhesives.

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.