Cytotoxicity of current adhesive systems: In vitro testing on cell cultures of primary murine macrophages

Comparative cell viability of dentin-bonding adhesive systems on human dental pulp stem cells: time-dependent analysis

BACKGROUND

Restorative materials are in prolonged contact with living tissues such as oral mucosa, dentin, pulp, periodontal, and periapical tissues. Therefore, the potentially harmful effects of these materials and their components on oral tissues should be evaluated before clinical use. This study aimed to compare the cell viability of different adhesive systems (ASs) on human dental pulp stem cells (hDPSCs).

METHODS

Three ASs that combining methacryloyloxydecyl dihydrogen phosphate (MDP) monomer with new hydrophilic amide monomers [Clearfil Universal Bond Quick(CUBQ), Kuraray Noritake], self-reinforcing 3D monomer [Bond Force II(BFII), Tokuyama)], and dual-cure property [Futurabond DC(FBDC), VOCO] were used. Three (n = 3) samples were prepared for each group. Dental pulp stem cells were isolated from ten patients' extracted third molar teeth. Samples were incubated in Dulbecco's modified Eagle's medium (DMEM) for 24 h (h), 72 h, and 7 days (d) to obtain extracts. For the control group, cells were cultured without DBA samples. Cell viability of ASs extracts was measured using a cell proliferation detection kit (WST-1, Roche). Statistical analysis was performed using two-way ANOVA and post-hoc (Duncan) tests (p < 0.05).

RESULTS

At 24 and 72 h statistically significant differences were determined between control and BFII, control and FBDC groups (p < 0.05), while no differences between control and CUBQ groups (p > 0.05). On the 7th d, statistically significant differences were found between the control and experimental groups (p < 0.05), while no differences between experimental groups (p > 0.05). A statistically significant difference was detected for the BFII group over the three-time interval (p < 0.05). The lowest cell viability was observed for the FBDC group at 24 h, and the difference was statistically significant when compared with 72 h and 7th d (p < 0.05).

CONCLUSION

All ASs showed different cell viability values at various exposure times. It should be taken into consideration that pH values, as well as the contents of ASs, have a significant effect on the cell viability.

Novel resin-based material containing β-tricalcium phosphate nanoparticles for the reduction of dentin permeability

OBJECTIVES

To synthesize and characterize a novel dentin adhesive containing Beta-Tricalcium Phosphate (β-TCP) nanoparticles and test its ability to reduce dentin permeability (dP).

METHODS

Experimental adhesives were prepared by mixing Bis-GMA, TEGDMA, HEMA (50/25/25 wt.%), photo-initiators, and inhibitors. The following groups were tested: Experimental adhesives without β-TCP (Exp.); with 10 wt.% β-TCP (Exp.10 wt.% β-TCP); with 15 wt.% β-TCP (Exp.15 wt.% β-TCP), Scotchbond Multi-Purpose (SBMP) and Clearfil SE Protect Bond (CFPB). Degree of conversion (DC%, 10 and 20 s); Flexural Strength (FS), Knoop Hardness (KHN), and Cell Viability (OD%) tests were performed. dP was evaluated by hydraulic conductance, using human dentin disks (n=12), at three-time intervals: post-EDTA (T0); post-treatment (T1); and post-erosion/abrasion cycling (T2). Data were statistically analyzed (α=0.05).

RESULTS

For all groups, exposure time for 20 s presented a higher DC% than for 10 s. For FS, filled adhesives did not differ from unfilled and from CFPB. Experimental adhesives did not differ among them and showed lower KHN than the commercial products. Cell viability did not differ among adhesives, except Exp. 15 wt.%, which showed lower OD% than Exp., Exp. 10% and, CFPB. For dP, only Exp.10 and 15 wt.% β-TCP did not present difference between the times T1 and T2. After cycling, Exp.10 wt.% β-TCP presented lower permeability than Exp. and CFPB.

CONCLUSIONS

The incorporation of 10 wt.% β-TCP nanoparticles into the resin-based dental material did not affect its mechanical properties and biocompatibility, and promoted the greatest reduction in dentin permeability, sustaining this effect under erosive/abrasive challenges.

CLINICAL SIGNIFICANCE

A novel resin-based dental material containing β-TCP nanoparticles was able to reduce dentin permeability, maintaining its efficacy after erosive/abrasive challenges. The synthesized material did not affect dental pulp cell viability and might be promising for other conditions that require dental remineralization, such as tooth wear and dental caries.

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.

Effect of Time and Temperature of Air Jet on the Mechanical and Biological Behavior of a Universal Adhesive System

OBJECTIVES

To evaluate the influence of heat application on the degree of conversion (DC) of the 3M Single Bond Universal Adhesive System, as well as its transdentinal cytotoxicity and microtensile bond strength to dentin.

METHODS

Experimental groups were established according to the time and temperature of the air jet: G1: 5 seconds-25°C; G2: 10 seconds-25°C; G3: 20 seconds-25°C; G4: 5 seconds-50°C; G5: 10 seconds-50°C; G6: 20 seconds-50°C. In control group (G7), no treatment was performed. The DC was assessed using the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. For the transdentinal cytotoxicity test, dentin discs fitted in artificial pulp chambers (APC) received the application of the adhesive system and the air jets. For the microtensile bond strength, healthy molars were restored and submitted to the microtensile test after 24 hours and 6 months, respectively.

RESULTS

Significant reduction in viability of Mouse Dental Papilla Cell-23 (MDPC-23), which exhibited morphological changes, was observed in all experimental groups compared to control (p<0.05). Although all tested protocols resulted in transdentinal diffusion of 2-hydroxyethyl methacrylate (HEMA), the group G6 presented the highest degree of monomeric conversion and the lowest cytotoxic effect, with higher dentin bond strength values in comparison to group G1 (p<0.05).

CONCLUSIONS

Applying an air blast at 50°C for 20 seconds increases the DC and microtensile bond strength of the 3M Single Bond Universal Adhesive System to dentin, as well as reduces the transdentinal cytotoxicity of the material to pulp cells.

Recent update on potential cytotoxicity, biocompatibility and preventive measures of biomaterials used in dentistry

Dental treatment is provided for a wide variety of oral health problems like dental caries, periodontal diseases, periapical infections, replacement of missing teeth and orthodontic problems. Various biomaterials, like composite resins, amalgam, glass ionomer cement, acrylic resins, metal alloys, impression materials, bone grafts, membranes, local anaesthetics, etc., are used for dental applications. The physical and chemical characteristics of these materials influence the outcome of dental treatment. It also impacts on the biological, allergic and toxic potential of biomaterials. With innovations in science and their positive results, there is also a need for awareness about the biological risks of these biomaterials. The aim of dental treatment is to have effective, yet safe, and long-lasting results for the benefit of patients. For this, it is important to have a thorough understanding of biomaterials and their effects on local and systemic health. Materials used in dentistry undergo a series of analyses before their oral applications. To the best of our knowledge, this is the first and original review that discusses the reasons for and studies on the toxicity of commonly used biomaterials for applications in dentistry. It will help clinicians to formulate a methodical approach for the selection of dental biomaterials, thus providing an awareness for forecasting their risk of toxic reactions.

Effect of heat treatment on cytotoxicity and polymerization of universal adhesives

To assess, in vitro, the influence of heat air treatment on cytotoxicity and degree of conversion (DC) of universal self-etch adhesives (Ambar Universal APS, Scotchbond Universal Adhesive, and Tetric N-Bond Universal) in an NIH/3T3 fibroblast cell culture. Samples were divided into three groups: 1) no heat treatment (control), 2) 37°C and 3) 60°C heat treatment before photopolymerization. Cytotoxicity was analyzed by MTT assay and the DC by FTIR. All adhesives heated at 60°C showed reduced cytotoxicity levels when compared with those heated at 37°C. In general, DC of Ambar Universal APS presented the highest DC than Scotchbond Universal Adhesive and Tetric N-Bond Universal, and the hot air treatment do not influence the conversion. Heat treatment at 60°C was able to reduce the cytotoxicity of universal self-etch adhesives, even, the heat treatment does not enhances the DC.

Morpho-functional effects of different universal dental adhesives on human gingival fibroblasts: an in vitro study

To analyze the effects of four universal adhesives (Optibond Solo Plus—OB, Universal Bond—UB, Prime&Bond Active—PBA, FuturaBond M + —FB) on human gingival fibroblasts in terms of cytotoxicity, morphology and function. After in vitro exposure for up to 48 h, fibroblast viability was determined by the MTT assay determined, morphology by phase-contrast microscopy and migration by the scratch wound assay. Expression levels of IL1β, IL6, IL8, IL10, TNFα and VEGF genes were assessed by RT-PCR and their protein production by Western blot analysis. Apoptosis and cell cycle were analyzed by flow cytometry. OB and UB induced early morphological changes on fibroblasts (3 h) with extended cell death at 24 h/48 h. Gene expression of collagen type I and fibronectin increased fivefold compared with controls, elastin disappeared and elastase increased threefold, indicating gingival tissue tended to become fibrotic. Only UB and OB increased gene expression of inflammatory markers: IL1β at 3 and 48 h (up to about three times), IL6 and IL8 at 3 h (up to almost four times) which corresponded to the increase of the activated form NF-kB. All adhesives showed an effect on the functionality of fibroblasts with cytotoxic effect time and concentration dependent. Among all the OB and UB adhesives, they showed the greatest cell damage. The in-depth analysis of the effects of universal adhesives and possible functional effects represents an important information for the clinician towards choosing the most suitable adhesive system.

Cytotoxicity of Self-Etch Versus Etch-and-Rinse Dentin Adhesives: A Screening Study

Six dentin adhesives were tested in vitro regarding their cytotoxicity on human fibroblasts. The adhesives Hybrid Bond, One-up Bond F Plus, AdheSE, Clearfil SE Bond, Optibond Solo Plus and Syntac were eluted with culture medium as single or sequentially applied adhesive part for 24 h. 75 Petri dishes were produced per group. They were evaluated triangulated, comprising the quantitative evaluation (105 ones) to determine “viable”, “dead” and “debris” cells with the use of a cell-counter and the reactivity index was also identified based on the qualitative assessment (420 ones). One-up Bond F Plus, AdheSE and Clearfil SE Bond showed a statistical difference of viable cells to the cell control. For One-up Bond F Plus, statistically, differences compared to hybrid bond and Syntac were also found. All the adhesives except One-up Bond F Plus showed significant differences between single and sequentially applied adhesive part regarding the quantitative evaluation. The test material showed a moderate grade of cytotoxicity. As a result, a statistically significant difference of the cytotoxicity between the self-etch and etch-and-rinse adhesives cannot be demonstrated regarding the qualitative evaluation and the reactivity index, but the differences between sequentially applied and single applied components can be proved.

Hepatoprotective and antineoplastic potencial of red propolis produced by the bees Apis mellifera in the semiarid of Rio Grande do Norte, Brazil

ABSTRACT: The objective of this study was to evaluate the hepatoprotective effect of the honey bee Apis mellifera ethanolic extract of the red propolis, obtained in four municipalities of the Rio Grande do Norte semi-arid region, through an in vitro evaluation of the antineoplastic potential in human hepatic carcinoma (HepG2) and normal cell lines (L929), and from the comet assay in hepatic cell lines (ZF-L hepatocytes) to evaluate the genoprotective potential of the extract. The hepatoprotective effect was also evaluated in vivo by the induction of chronic experimental hepatic lesions in rodents (Rattus norvegicus Berkenhout, 1769), Wistar line, by intraperitoneal administration of thioacetamide (TAA) at the dose of 0.2g/kg. The animals were distributed in the following experimental groups: G1 (control), G2 (treated with 500mg/kg ethanolic extract of propolis), G3 (treated with 500mg/kg of ethanolic extract and TAA) and G4 (treated with TAA). All rats were submitted to serum biochemical, macroscopic, histological and stereological biochemical exams of the liver. It was verified the genoprotective effect of red propolis since the mean damages promoted to DNA in cells tested with the extract were significantly lower than the mean of the positive control damage (hydrogen peroxide). The red propolis extract did not present cytotoxic activity to the tumor cells of human liver cancer, as well as to normal ones. The absence of cytotoxicity in normal cells may indicate safety in the use of the propolis extract. The results of the serum biochemical evaluation showed that the serum levels of the aminotransferase enzymes (AST) did not differ significantly between G1, G2 and G3 when compared to each other. G4 showed significant increase in levels compared to the other groups, indicating that the administration of the extract did not cause liver toxicity, as well as exerted hepatoprotective effect against the hepatic damage induced by TAA. The G3 and G4 animals developed cirrhosis, but in G3 the livers were characterized by the presence of small regenerative nodules and level with the surface of the organ, whereas in G4 the livers showed large regenerative nodules. The livers of the G1 and G2 animals presented normal histological appearance, whereas the livers of the G3 animals showed regenerative nodules surrounded by thin septa of connective tissue, and in G4 the regenerative nodules were surrounded by thick septa fibrous connective tissue. The analysis of the hepatic tissues by means of stereology showed that there was no statistical difference between the percentage of hepatocytes, sinusoids, and collagens in G1 and G2. In G3 the percentage of hepatocytes, sinusoids, and collagen did not differ significantly from the other groups. It was concluded that the ethanolic extract of the red propolis exerted a hepatoprotective effect, because it promoted in vitro reduction of the damage to the DNA of liver cells, antineoplastic activity in human hepatocellular carcinoma cell line (HepG2) and did not exert cytotoxic effect in normal cells or was able to reduce liver enzyme activity and the severity of cirrhosis induced by TAA in vivo.

In Vitro Cytotoxicity of Self-Adhesive Dual-Cured Resin Cement Polymerized Beneath Three Different Cusp Inclinations of Zirconia

The aim of the present study was to evaluate the in vitro cytotoxicity of self-adhesive dual-cured resin cement (SADRC) polymerized beneath three different cusp inclinations of zirconia with different light curing time. A commercial SADRC (Multilink Speed) was polymerized beneath zirconia (ZrO₂) with three different cusp inclinations (0°, 20°, and 30°) for 20 s or 40 s. After being stored in light-proof box for 24 h, the ZrO₂-SADRC specimens were immersed in DMEM for 72 h and then we got the extract solution, cultured the human gingival fibroblasts (HGF, 8 × 10³ per well) with 100% or 50% concentrations of the extract solution for 24 h, 72 h, and 120 h, respectively, and evaluated cytotoxicity of the polymerized SADRC with CCK-8 assay in optical density (OD) values, relative growth rates (RGR), and cytotoxicity grades. Statistical analysis was conducted using a two-way ANOVA followed by post hoc Student–Newman–Keuls test. The OD values varied from 0.8930 to 3.2920, the RGR varied from 33.93% to 98.68%, and the cytotoxicity grades varied from 0 to 2. There was significant difference in the OD values among the different cusp inclinations of zirconia (P < 0.001), and there was significant difference in the OD values between the different light curing times in some situations (P < 0.05). The cusp inclination of zirconia affects the in vitro cytotoxicity of SADRC. Prolonging the light curing time from 20 s to 40 s can reduce the in vitro cytotoxicity of SADRC when the cusp inclination of zirconia is smaller than 20°.

Cytotoxicity of universal dental adhesive systems: Assessment in vitro assays on human gingival fibroblasts

Universal adhesives are the most important innovation in restorative dentistry. They are composed of different monomers, solvents and fillers. The potential cytotoxic effect of these materials is an important scientific aspect in recent literature. The aim of this study was to determine, using different in vitro techniques, the cytotoxicity evaluation of seven universal enamel-dental adhesives on human gingival fibroblasts. For this purpose, seven universal dental enamel adhesives have been evaluated by in vitro cytotoxicity tests using direct contact tests (an unpolymerized and a polymerized method) and an indirect contact test: preparation of extracts. The polymerized method showed a cytotoxicity range from 36% (G-PremioBond, GPB) to 79% (FuturaBond M+, FB). With the unpolymerized direct methods the range was from 4% (Prime&Bond Active, PBA) to 40% (Ibond Universal, IB) for undiluted adhesives; generally passing to the major dilutions the test showed a strong inhibitory activity by all the adhesives. Whereas with the indirect method by diluting the extracts of all dental adhesives the cell viability increased. The data obtained from the work has shown a lower cytotoxic effect of Optibond Solo Plus (OB) and Adhesive Universal (AU) with more reliable results with the extracts technique. The choice of reliable in vitro cytotoxic technique could represent, in dental practice, an important aid for clinical procedures in the use of adhesive systems.

Flow Cytometry Analysis of Antibacterial Effects of Universal Dentin Bonding Agents on Streptococcus mutans

There is no consensus on the antibacterial activity of dentin bonding systems (DBS). Many study models have been used to evaluate the antimicrobial activity of dental materials. In this study, a novel detection method, flow cytometry, was introduced. It allows for evaluation of the antibacterial activity of DBS, based on assessment of the disruption of the bacterial physical membrane induced by DBS. The aim of the study was to evaluate the antibacterial properties of selected dentin bonding systems against Streptococcus mutans. The highest antibacterial activity against S. mutans was observed for Adhese Universal (99.68% dead cells) and was comparable to that of Prime&Bond Universal, OptiBond Universal, or Clearfil Universal Bond Quick (p > 0.05). The lowest activity of all tested systems was displayed by the multi-mode adhesive, Universal Bond (12.68% dead bacteria cells), followed by the self-etch adhesive, OptiBond FL (15.58% dead bacteria cells). The present study showed that in the case of two-component DBS, the primer exhibited higher antimicrobial activity than the adhesive (or bond) itself.

The Dawn of Thiol-Yne Triazine Triones Thermosets as a New Material Platform Suited for Hard Tissue Repair

The identification of a unique set of advanced materials that can bear extraordinary loads for use in bone and tooth repair will inevitably unlock unlimited opportunities for clinical use. Herein, the design of high-performance thermosets is reported based on triazine-trione (TATO) monomers using light-initiated thiol-yne coupling (TYC) chemistry as a polymerization strategy. In comparison to traditional thiol-ene coupling (TEC) systems, TYC chemistry has yielded highly dense networks with unprecedented mechanical properties. The most promising system notes 4.6 GPa in flexural modulus and 160 MPa in flexural strength, an increase of 84% in modulus and 191% in strength when compared to the corresponding TATO system based on TEC chemistry. Remarkably, the mechanical properties exceed those of polylactide (PLA) and challenge poly(ether ether ketone) PEEK and today's methacrylate-based dental resin composites. All the materials display excellent biocompatibility, in vitro, and are successfully: i) molded into medical devices for fracture repair, and ii) used as bone adhesive for fracture fixation and as tooth fillers with the outstanding bond strength that outperform methacrylate systems used today in dental restoration application. Collectively, a new era of advanced TYC materials is unfolded that can fulfill the preconditions as bone fixating implants and for tooth restorations.

Antibacterial effects and cytotoxicity of an adhesive containing low concentration of silver nanoparticles

OBJECTIVES

To evaluate the antibacterial effects, cytotoxicity and microtensile bond strength of an adhesive containing low concentrations of silver nanoparticles (NAg).

METHODS

Various concentrations of NAg (50, 100, 150, 200 and 250 ppm) were incorporated into the primer of the Scotchbond Multi-Purpose adhesive system (SBMP). Antibacterial activity was examined using a broth microdilution assay to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), agar diffusion assay and the MTT assay was used to examine the biofilm metabolic activity (S. mutans). The Microtensile Bond Test (μTBS) was performed after 24 h, followed by 6-months storage in distilled water. Cytotoxicity was assessed with an MTT reduction assay in human dental pulp stem cells viability after exposure to Nag-conditioned culture media during 0, 24, 48, and 72 h. The results were statistically analyzed (α ≤ 0.05).

RESULTS

MIC was found between NAg 25 and 50 ppm MBC was determined at 50 ppm of NAg. Bacterial activity inhibition was higher than control in all NAg groups compared to control in agar diffusion assay. Biofilm inhibition was statistically higher in 250 ppm NAg than control. All NAg groups and SBMP presented similar cytotoxicity in each period. Adhesives with NAg 200 and 250 ppm and SBMP (control) presented the highest μTBS values, similar to that of SBMP control, in both instances (24 h and 6 months) (p > 0.05).

CONCLUSIONS

The commercial primer containing NAg 250 ppm showed both antibacterial effect and reliable bond strength with no cytotoxicity increase. The addition of NAg to primers seems promising for the improvement of conventional dental adhesives efficacy.

CLINICAL SIGNIFICANCE

The addition of low concentrations of NAg (250 ppm) to primers were effective to improve antibacterial effect preserving the bond strength and the biocompatibility of the commercial product. NAg/primer association could protect the tooth-adhesive interface increasing dental restoration longevity.

Effects of two disinfection/sterilization methods for dentin specimens on dentin permeability

OBJECTIVES

To investigate the effects of two disinfection/sterilization methods on the permeability of dentin specimens.

MATERIALS AND METHODS

Forty intact human third molars were freshly extracted and cut, close to the pulp chamber, into dentin disks with a 500-μm thickness. The disks were randomized (n = 20 each) into a 70% ethanol group (acid-etched dentin disks soaked in 70% ethanol for 15 min) and a steam autoclaving group (acid-etched dentin disks autoclaved for 25 min). The permeability (Lp) of each dentin disk was measured before and after either treatment using a hydraulic device, and intra- and inter-group differences in values before and after treatment were analyzed using t tests. Field emission scanning electron microscopy (FE-SEM) micrographs of the dentin surface were acquired and examined. FE-SEM samples were prepared using the critical point drying (CPD) method.

RESULTS

Immersion in 70% ethanol increased the Lp values of dentin specimens by 17%, which was not statistically significant. Steam autoclaving significantly reduced dentin permeability by 66% because the dentin collagen mesh became compact and collapsed, as detected by FE-SEM.

CONCLUSIONS

The disinfection of acid-etched dentin disks using 70% ethanol for 15 min does not significantly affect dentin permeability, whereas sterilization of acid-etched dentin disks via autoclaving significantly reduces dentin permeability.

CLINICAL RELEVANCE

Considering the influences of dentin permeability by disinfection/sterilization methods, the disinfection of the acid-etched dentin disks using 70% ethanol for 15 min could be used for the study related to dentin permeability, while the sterilization of autoclaving could not.

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.

Porous zirconia ceramic as an alternative to dentin for in vitro dentin barriers cytotoxicity test

OBJECTIVES

This study assessed the potential of porous zirconia ceramic as an alternative to dentin via an in vitro dentin barrier cytotoxicity test.

METHODS

The permeability of dentin and porous zirconia ceramic was measured using a hydraulic-conductance system, and their permeability was divided into two groups: high and low. Using an in vitro dentin barrier test, the cytotoxicity of dental materials by dentin and porous zirconia ceramic was compared within the same permeability group. The L-929 cell viability was assessed by MTT assay.

RESULTS

The mean (SD) permeability of the high and low group for dentin was 0.334 (0.0873) and 0.147 (0.0377) μl min^-1 cm^-2 cm H₂O^-1 and for zirconia porous ceramic was 0.336 (0.0609) and 0.146 (0.0340) μl min^-1 cm^-2 cm H₂O^-1. The cell viability of experimental groups which are the low permeability group was higher than that of the high permeability group for both dentin and porous zirconia ceramic as a barrier except for Maxcem Elite^™ by porous zirconia ceramic. There was no significant difference between dentin and porous zirconia ceramic in cell viability, within either the high or low permeability group for all materials. The SD for cell viability of the porous zirconia ceramic was less than that of the dentin, across all materials within each permeability group, except for Maxcem Elite^™ in the high permeability group.

CONCLUSIONS

Porous zirconia ceramic, having similar permeability to dentin at the same thickness, can be used as an alternative to dentin for in vitro dentin barrier cytotoxicity tests.

CLINICAL RELEVANCE

In vitro dentin barrier cytotoxicity tests when a standardized porous zirconia ceramic was used as a barrier could be useful for assessing the potential toxicity of new dental materials applied to dentin before applying in clinical and may resolve the issue of procuring human teeth when testing proceeds.

Biocompatibility Evaluation of Four Dentin Adhesives Used as Indirect Pulp Capping Materials

BACKGROUND

In many cases, the indirect pulp treatment (IPT) is an acceptable treatment for deciduous teeth with reversible pulp inflammation. Various medicaments have been used for IPT, ranging from calcium hydroxide and glass ionomers to dentin adhesives.

OBJECTIVE

This in vitro trial aimed to measure cytotoxicity in a cell culture, comparing the following four adhesives: Xeno® V (XE), Excite® F DSC (EX), Adhese® OneF (AD) and Prime & Bond NT (PB).

MATERIALS AND METHODS

The adhesives were prepared according to the manufacturer's instructions. After 24 hours of exposure, the cell viability was evaluated using a photometrical test (MTT test). Data were subjected to analysis of variance (ANOVA).

RESULTS

Adhesives, the main component of which was 2-hydroxyethyl methacrylate (HEMA), were found to be less cytotoxic, while those that included the monomer urethane dimethacrylate (UDMA were the most cytotoxic) in their composition. The effects on cell viability assay varied between the adhesives assayed with statistically significant differences.

CONCLUSIONS

The results may support the argument that Adhese® OneF is the least cytotoxic of the adhesives assayed, and may be considered as an adhesive agent for indirect pulp treatment. However, Prime and Bond NT showed a reduced biocompatibility under the same conditions.

In vitro dentin barrier cytotoxicity testing of some dental restorative materials

OBJECTIVES

To investigate the cytotoxicity of four dental restorative materials in three-dimensional (3D) L929 cell cultures using a dentin barrier test.

METHODS

The cytotoxicities of light-cured glass ionomer cement (Vitrebond), total-etching adhesive (GLUMA Bond5), and two self-etching adhesives (GLUMA Self Etch and Single Bond Universal) were evaluated. The permeabilities of human dentin disks with thicknesses of 300, 500, and 1000μm were standardized using a hydraulic device. Test materials and controls were applied to the occlusal side of human dentin disks. The 3D-cell scaffolds were placed beneath the dentin disks. After a 24-h contact with the dentin barrier test device, cell viabilities were measured by performing MTT assays. Statistical analysis was performed using the Mann-Whitney U test.

RESULTS

The mean (SD) permeabilities of the 300-μm, 500-μm, and 1000-μm dentin disks were 0.626 (0.214), 0.219 (0.0387) and 0.089 (0.028) μlmin^-1cm^-2cm H₂O^-1. Vitrebond was severely cytotoxic, reducing the cell viability to 10% (300-μm disk), 17% (500μm), and 18% (1000μm). GLUMA Bond5 reduced the cell viability to 40% (300μm), 83% (500μm), and 86% (1000μm), showing moderate cytotoxicity (300-μm) and non-cytotoxicity (500-μm and 1000-μm). Single Bond Universal and GLUMA Self Etch did not significantly reduce cell viability, regardless of the dentin thicknesses, which characterized them as non-cytotoxic.

CONCLUSIONS

Cytotoxicity varied with the materials tested and the thicknesses of the dentin disks.

CLINICAL SIGNIFICANCE

The tested cytotoxicity of materials applied on 300-, 500-, and 1000-μm dentin disks indicates that the clinical use of the test materials (excepting self-etching adhesives) in deep cavities poses a potential risk of damage to the pulp tissues to an extent, depending on the thickness of the remaining dentin.

Citotoxicity evaluation of three dental adhesives on vero cells in vitro

BACKGROUND

To evaluate, in vitro, the potential cytotoxicity of three different dental adhesives systems (Adper Single Bond 2 -SB, Silorane System Adhesive Bond -SSAB and Single Bond Universal -SBU) on cultivated Vero cells after different contact times.

MATERIAL AND METHODS

The cells were cultured in a concentration of 2 x 105 cells/mL for 24h and grown to sub-confluent monolayers. VERO cells were exposed to 25µl of conditioned extracts obtained from 24h, 48h and 72h immersion of adhesive samples in culture medium (DMEM), immediately after polymerization. Fresh DMEM was used as negative control. Cell metabolism was evaluated by the MTT assay (3-(4,5-dimethylthiazol-2-yl)-2, 5diphenyl-tetrazolium bromide). The data were analyzed statistically by ANOVA, considering a significance of 5%.

RESULTS

The values of cell viability ranged from 94.2% at 72h (SBU) to 109.6% at 48h (SB). The mean percentage of viability after exposure to the extracts of SB, SSAB and SBU were 103.2%, 100.63% and 97.43%, respectively. There was no statistically significant difference (p= 0.342) between the experimental and negative control groups.

CONCLUSIONS

At all exposure times, all adhesives tested in this study presented no cytotoxicity to Vero cells in vitro. Key words:Biocompatibility, cytotoxicity, dental adhesives, Vero cells.

The influence of intrinsic water permeation on different dentin bonded interfaces formation

OBJECTIVES

To determine the effects of intrinsic wetness on the formation of dentin bonding interfaces of four resin cement systems bonded to dentin under different pulpal pressures.

METHODS

Thirty-six freshly extracted third molars were selected and processed for dentin μTBS. The teeth were randomly assigned into 12 experimental groups, according to the adhesive luting system [Adper Single Bond Plus (3M ESPE) combined with two luting agents RelyX ARC (3M ESPE) and heated Filtek Z250 Universal Restorative (3M ESPE), Clearfil CD Bond (Kuraray) combined with Clearfil Esthetic Cement (Kuraray), and RelyX Unicem 2 Automix (3M ESPE)] and pulpal pressure (0, 5, and 20 cm of simulated pulpal pressure). Leucite-reinforced glass-ceramic slabs (IPS Empress CAD, Ivoclar Vivadent) of 3mm thickness were bonded to dentin. The samples were stored in distilled water for 24h and then sectioned in X/Y directions across the adhesive interface to obtain specimens with a cross section of 0.8 ± 0.2mm(2). All sticks were fractured by tension at a crosshead speed of 1.0mm/min and the data were submitted to Kruskal-Wallis and Mann-Whitney Tests (α=0.05). Ultrastructural analysis of the interfaces was performed using Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM).

RESULTS

The statistical analyses showed that pulpal pressure decreased μTBS for all groups. Significantly higher μTBS values were obtained in heated Z250 group restored without any pulpal pressure. CLSM showed that the uptake of water through the dentin tubuli and their anastomosis of lateral branches during the adhesive luting procedures prevented adequate formation of the dentin bonding interfaces. SEM showed that the luting film created is material- dependent and all adhesive failure occurred at the resin-dentin interface.

CONCLUSION

The constant intrinsic wetness replenishment prevents adequate formation of the hybrid layer.

CLINICAL SIGNIFICANCE

Intrinsic moisture during adhesive luting procedures significantly affects the interaction between luting materials and dentin subtract and decreases the quality and bonding strength of the resin-dentin bond.

Cytotoxic effects of one-step self-etching adhesives on an odontoblast cell line

The aim of this study was to evaluate the cytotoxic effects of one-step self-etching adhesives. Cells from an immortalized mouse odontoblast cell line (MDPC-23) were cultured with six different dental adhesive systems (diluted to concentrations of 0.5% for 4 h): Adper Easy Bond (EB), Xeno V (XV), iBond (IB), AdheSE One (AO), Clearfil SE primer (CS), and Adper Single Bond 2 (SB). MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and flow cytometric apoptosis assays were used to evaluate cell viability and the rate of apoptosis. The odontoblasts were also examined under a scanning electron microscope. While all of the cultures with adhesives showed reduced viability, the viabilities in the IB and SB groups were not significantly different from the control group. Although increased apoptosis rates were observed in all of the cultures with adhesives, the rate in the SB group was not significantly different from the rate in the control. The control group showed the lowest apoptosis rate followed by the SB, AO, IB, EB, XV, and CS groups. When examined under a scanning electron microscope, control odontoblasts and the SB group exhibited relatively large cytoplasmic extensions. In contrast, in the EB and CS groups, fewer fibroblasts remained adhered to the plate surface. Cytoplasmic membrane shrinkage and cell-free areas with residual membrane fragments from dead cells were observed. In conclusion, all cultures with one-step self-etching adhesives showed increased apoptotic activity. SB, an etch-and-rinse adhesive, was comparable to the control group, and CS and EB showed the lowest odontoblast viabilities according to the MTT assay.

Toxicity of a dental adhesive compared with ionizing radiation and zoledronic acid

Background

To determine the toxicity of aqueous dilutions of a universal self-priming dental adhesive (DA) and comparing these with those elicited by exposure to ionizing radiation (IR), Zoledronic acid (Z) treatment and the synergic effects of the combined treatment with IR+Z.

Material and Methods

The genotoxic effect of DA was determined by the increase in the frequency of micronuclei in cytokinesis-blocked in cultured human lymphocytes before and after exposure to 2Gy of X-rays. The cytotoxic effect was studied by using the MTT cell viability test in normal prostate cell lines (PNT2) after exposure to different X-ray doses (0Gy-20Gy). The cell lines divided into different groups and treated with different test substances: DA in presence of O2, DA in absence of O2, Z-treated and control.

Results

An in vitro dose-dependent and time-dependent cytotoxic effect of DA, Z and IR on PNT2 cells (p>0.001) was demonstrated. DA without-O2, following the recommendations of manufacturers, had a more pronounced effect of increasing cell death than DA with-O2 (p<0.001). In the genotoxicity assay, DA at 25% of its original concentration significantly increased chromosome damage (p<0.001). The samples studied were found to be toxic, and the samples photo-polymerized in absence of O2 showed a bigger cytotoxic effect comparable to the additive toxic effect showed by the combined treatment of IR+Z.

Conclusions

Additional effort should be carried out to develop adhesives, which would reduce the release of hazardous substances; since toxic effects are similar to that reported by other agents whose clinical use is controlled by the health authorities.

Key words: Micronucleus, toxicity, dental adhesive, zolendronic acid, radiation effects.

Cytotoxicity of universal, self-etching and etch-and-rinse adhesive systems according to the polymerization time

This in vitro study evaluated in fibroblast cultures the direct cytotoxicity of universal, self-etching and etch-and-rinse adhesive systems according to the polymerization time. Paper discs were impregnated with adhesives and light-cured (10, 20 or 40 s). The discs were then immersed in culture medium to obtain the eluates for the experimental groups (A1-Single Bond 2; A2-Scotchbond Multi-purpose; A3-Clearfil SE Bond; A4 Scotchbond Universal). As a negative control, paper discs were immersed in culture medium only. After 24 h or 7 days, the eluate obtained was applied on fibroblast culture. Cell viability, cell morphology, membrane damage and the presence of residual monomers were evaluated by MTT assay, SEM, flow cytometry and high-performance liquid chromatography (HPLC), respectively. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (=0.05). All adhesive systems significantly reduced 33-51% cell metabolism when compared to the negative control, regardless of polymerization time, storage period and adhesive system. Moreover, the adhesives caused intense morphological alterations and cell membrane damage. Toxicity was directly related to the presence of residual monomers in the eluates. Residual monomers and additional components are capable of reducing mitochondrial activity, causing morphological alterations and disruption of the cell membrane in fibroblasts, regardless of the polymerization time. This study highlights that despite the more complex composition of the universal adhesive system, its biological response was not more toxic when compared with other systems, even when the shortest polymerization time was tested in cell culture.

Influence of light-curing mode on the cytotoxicity of resin-based surface sealants

Background

Surface sealants have been successfully used in the prevention of erosive tooth wear. However, when multiple tooth surfaces should be sealed, the light-curing procedure is very time-consuming. Therefore, the aim of this study was to investigate whether reduced light-curing time (while maintaining similar energy density) has an influence on resin-based surface sealant cytotoxicity.

Methods

Bovine dentine discs were treated as follows: group 1: untreated, groups 2–5: Seal&Protect and groups 6–9: experimental sealer. Groups 2 and 6 were light-cured (VALO LED light-curing device) for 40 s (1000 mW/cm²), groups 3 and 7 for 10 s (1000 mW/cm²), groups 4 and 8 for 7 s (1400 mW/cm²) and groups 5 and 9 for 3 s (3200 mW/cm²). Later, materials were extracted in culture medium for 24 h, and released lactate dehydrogenase (LDH) activity as a measure of cytotoxicity was determined photometrically after cells (dental pulp cells and gingival fibroblasts) were exposed to the extracts for 24 h. Three independent experiments, for both sample preparation and cytotoxicity testing, were performed.

Results

Overall, lowest cytotoxicity was observed for the unsealed control group. No significant influence of light-curing settings on the cytotoxicity was observed (p = 0.537 and 0.838 for pulp cells and gingival fibroblasts, respectively). No significant difference in the cytotoxicity of the two sealants was observed after light-curing with same light-curing settings (group 2 vs. 6, 3 vs. 7, 4 vs. 8 and 5 vs. 9: p > 0.05, respectively).

Conclusions

Shortening the light-curing time, while maintaining constant energy density, resulted in no higher cytotoxicity of the investigated sealants.

Cytotoxicity Test of One-Step Self-Etching Bonding Agents by Standardized Dentin Barrier Test Using Polyurethane Discs

This study was performed to standardize a dentin barrier test with the substitute and evaluate the cytotoxicity of one-step self-etching bonding agents. Each of the natural bovine dentin and polyurethane discs were 500-μm thick and were tested using a perfusion device. Following the treatment with 0.05% phenol on the natural bovine disc or three kinds of polyurethane discs—30, 40, and 50 pcf (pounds per cubic foot)—cell viability of L-929 was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and expressed as percentages of non-treated group, respectively. A substitute showing permeability similar to that of bovine dentin was determined based on this result. Cytotoxicity test of bonding agents was performed by the selected substitute, the results of which were expressed as percentages of the control. In addition, SEM images were taken after the tests. The cell viability by 40-pcf polyurethane disc was not statistically different from that by bovine dentin disc (P > 0.05). Futurabond DC resulted in the highest cell viability and Bond force the lowest by the 40-pcf polyurethane disc (P < 0.05). The adhesives on the 40-pcf polyurethane disc changed cellular morphology with different degrees on the SEM images. This standardized test might be useful for assessing the cytotoxicity of dental materials applied to dentin before clinical applications.

Cytotoxicity evaluation of three light-cured dentin adhesive materials on human gingival fibroblasts, ex vivo

PURPOSE

To evaluate the cytotoxic effects of three current light-cured dentin adhesives, in both uncured and post-cured conditions, on human gingival fibroblasts.

MATERIAL AND METHODS

The materials tested were Heliobond, Adper Single Bond 2 and Xeno V, which are characterized by various compositions and application procedures. Each agent, in volumes of 5 and 10 μL, was tested after polymerization, and those unpolymerized were diluted in DMEM to 10-3 and 10-5. The cytotoxicity of the adhesives was assessed on the basis of a test of cell viability in a culture of human gingival fibroblasts, with the use of tetrazolic salt (MTT assay).

RESULTS

The results showed that, among the adhesive/bonding systems tested, Xeno V was the least cytotoxic. There were statistically significant differences in cell survival between polymerized Xeno V, Adper Single Bond 2 and Heliobond in the amount of 5 μL as well as between the Xeno V and Adper Single Bond 2 in 10-5 dilutions. The tested adhesives were more toxic in the polymerized form than in the dilutions. Samples of 10 μL resulted in a lower survival percentage of fibroblasts compared to 5 μL.

CONCLUSION

All the tested adhesives demonstrated cytopathic effects towards human gingival fibroblasts, but varied in their cytotoxicity. This has clinical implications. Dentists should follow the rules of adhesive application, precisely dose them and not allow direct contact with the gums as, even after polymerization, adhesive agents exhibit potential cytotoxic activity.

Epigallocatechin-3-gallate (EGCG) enhances the therapeutic activity of a dental adhesive

OBJECTIVES

The purpose of this study was to evaluate the antibacterial potential and physicochemical properties of a dental adhesive incorporated with epigallocatechin-3-gallate (EGCG) in different concentration over time.

METHODS

EGCG was incorporated at a ratio of 100, 200, and 300 μg/ml into a dental adhesive. The effects of the cured adhesives on the growth of Streptococcus mutans were determined by direct contact test immediately or one month later and by scanning electron microscopy (SEM), respectively. Microtensile bond strength (μTBS) test was used to test the mechanical property of the adhesives immediately or six months later. The degree of conversion (DC) of the adhesives was evaluated by Fourier transform infrared spectroscopy (FTIR).

RESULTS

Compared with negative control, the 200 μg/ml and 300 μg/ml EGCG-incorporated dental adhesive were found to exhibit inhibitory effect on the growth of S. mutans. The μTBS of the EGCG-incorporated dental adhesive was higher than the control. The DC of the adhesive system was not affected by the addition of EGCG.

CONCLUSIONS

200 μg/ml EGCG incorporated dental adhesives could accomplish therapeutic goals that play in antimicrobial function whilst keeping the durability of resin-dentine bond.