In vitro evaluation of dental materials

Effects of Novel Nanoparticulate Bioceramic Endodontic Material on Human Dental Pulp Stem Cells In Vitro

OBJECTIVES

This study aimed to investigate the in vitro effects of root canal filling and repair paste (nRoot BP) on human dental pulp stem cells (hDPSCs).

METHODS

The effects of nRoot BP and iRoot BP Plus on the adhesion, proliferation, migration, and differentiation of hDPSCs were examined in vitro for 72 hours. The adhesion of cells was observed using immunofluorescence rhodamine ghost pen cyclic peptide staining and scanning electron microscopy (SEM). Cell density and changes in migration area were measured under a fluorescence inverted microscope. Fluorescent quantitative PCR was performed to detect genes related to odontogenesis and osteogenesis.

RESULTS

Cells adhering to the surfaces of nRoot BP and iRoot BP Plus exhibited similar irregular polygonal morphologies, with cells extending irregular pseudopods to adhere to the materials. CCK-8 results indicated that the density of living cells for nRoot BP and iRoot BP Plus was lower than that of the blank control group at 3 and 5 days of culture. There was no significant difference in cell migration between the groups (P > .05). The migration ability of iRoot BP Plus and nRoot BP was similar to that of the control group. Both nRoot BP and iRoot BP Plus increased the expression of the RUNX2 gene, but there was no significant difference between the groups (P < .05). Furthermore, both nRoot BP and iRoot BP Plus downregulated the expression of the DSPP gene, with no significant difference between them (P > .05).

CONCLUSIONS

nRoot BP exhibited a slight inhibition of hDPSC proliferation but did not affect the adhesion and migration of hDPSCs. The impact of nRoot BP on the osteogenic and odontogenic differentiation of hDPSCs was similar to that of iRoot BP Plus.

Light Transmission Characteristics and Cytotoxicity within A Dental Composite Color Palette

Modern light-cured, resin-based composites are offered in a wide range of shades and translucencies. This large variation, created by varying the amount and type of pigmentation and opacifiers, is essential to enable an esthetic restoration in each patient situation, but may affect light transmission in the deeper layers during curing. We quantified optical parameters and their real-time variation during curing for a 13-shade composite palette of identical chemical composition and microstructure. Incident irradiance and real-time light transmission through 2 mm thick samples were recorded to calculate absorbance, transmittance, and the kinetic of transmitted irradiance. Data were supplemented by the characterization of cellular toxicity to human gingival fibroblasts up to 3 months. The study highlights a strong dependence of light transmission and its kinetic as a function of shade, with the largest changes occurring within the first second of exposure; the faster changes, the darker and more opaque the material. Transmission differences within progressively darker shades of a pigmentation type (hue) followed a hue-specific, non-linear relationship. Shades with similar transmittance but belonging to different hues were identified, while the corresponding kinetic was identical only up to a transmittance threshold. A slight drop in absorbance was registered with increasing wavelength. None of the shades were cytotoxic.

Cytotoxic, Elastic-Plastic and Viscoelastic Behavior of Aged, Modern Resin-Based Dental Composites

The development of resin-based composites (RBCs) is a delicate balance of antagonistic properties with direct clinical implications. The clear trend toward reducing filler size in modern RBCs solves esthetic deficiencies but reduces mechanical properties due to lower filler content and increases susceptibility to degradation due to larger filler-matrix interface. We evaluated a range of nano- and nano-hybrid RBCs, along with materials attempting to address shrinkage stress issues by implementing an Ormocer matrix or pre-polymerized fillers, and materials aiming to provide caries-protective benefit by incorporating bioactive fillers. The cytotoxic response of human gingival fibroblast (HGF) cells after exposure to the RBC eluates, which were collected for up to six months, was analyzed using a WST-1 assay. The microstructural features were characterized using a scanning electron microscopy and were related to the macroscopic and microscopic mechanical behaviors. The elastic-plastic and viscoelastic material behaviors were evaluated at the macroscopic and microscopic levels. The data were supplemented with fractography, Weibull analysis, and aging behavioral analysis. The results indicate that all RBCs are non-cytotoxic at adequate exposure. The amount of inorganic filler affects the elastic modulus, while only to a limited extent the flexural strength, and is well below the theoretical estimates. The nanoparticles and the agglomeration of nanoparticles in the RBCs help generate good mechanical properties and excellent reliability, but they are more prone to deterioration with aging. The pre-polymerized fillers lower the initial mechanical properties but are less sensitive to aging. Only the Ormocer retains its damping ability after aging. The strength and modulus of elasticity on the one hand and the damping capacity on the other are mutually exclusive and indicate the direction in which the RBCs should be further developed.

Cytotoxic assessment of 3D printed photoinitiated prosthodontic resins versus heat polymerized acrylic resin (In-Vitro Study).. [DOI: 10.21203/rs.3.rs-1948364/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Background: Although 3D printed photoinitiated resins are among the many materials utilized in prosthetic appliances today, biocompatibility for photocuring 3D printing materials for direct and long-term contacting with living body remain scarce. The purpose of this in vitro study was to evaluate the cell viability of human gingival fibroblasts after the exposure to two different 3D printed photoinitiated resins and compare it to the traditionally used heat polymerized acrylic resin for up to 7 days.Methods: This comparative in vitro study of sample size (n= 96), where the 3D printed resin disc samples (n= 64), were divided into two test groups, test group 1 (TG1) for NextDent Base resin (n= 32) and test group 2 (TG2) for Dental LT clear resin (n= 32), to be compared to Heat polymerized acrylic resin samples (Reference group (RG)) (n= 32). Human gingival fibroblasts were extracted from attached keratinized gingival tissues collected from healthy patient undergoing clinical crown lengthening procedure, cellular viability using MTT assay in response to TG1, TG2 and RG samples was assessed throughout four-time intervals (24, 48, 72 and 168 hours). The One-Way ANOVA test followed by Tukey’s post hoc test and Repeated Measures ANOVA test were used for statistical analyses, statistically significant different at P value ≤ 0.05Results: Throughout time intervals, there was a decrease in cell viability of all groups but with favorable cell viability which was more that 90% denoting non cytotoxicity. It was found to be significant among RG (P< 0.0001). The highest cell viability was found after 24 hours among all groups; however, the least viability was found after 48 hours among TG1 and RG, and among TG2 after 72 hours. After 168 hours, there was a non-statistical significant change in cell viability between groups (P= 0.526). there was significant increase in optical density for all groups throughout time intervals (P< 0.0001).Conclusion: Photoinitiated resins are comparable to traditionally used heat polymerized acrylic resin with equivalent cytotoxic effect for long term use. 3D printed photoinitiated resins are biocompatible and suggested for long term intraoral use.

A critical analysis of research methods and experimental models to study biocompatibility of endodontic materials

Materials used for endodontics and with direct contact to tissues have a wide range of indications, from vital pulpal treatments to root filling materials and those used in endodontic surgery. In principle, interaction with dental materials may result in damage to tissues locally or systemically. Thus, a great variety of test methods are applied to evaluate a materials' potential risk of adverse biological effects to ensure their biocompatibility before commercialization. However, the results of biocompatibility evaluations are dependent on not only the tested materials but also the test methods due to the diversity of these effects and numerous variables involved. In addition, diverse biological effects require equally diverse assessments on a structured and planned approach. Such a structured assessment of the materials consists of four phases: general toxicity, local tissue irritation, pre‐clinical tests and clinical evaluations. Various types of screening assays are available; it is imperative to understand their advantages and limitations to recognize their appropriateness and for an accurate interpretation of their results. Recent scientific advances are rapidly introducing new materials to endodontics including nanomaterials, gene therapy and tissue engineering biomaterials. These new modalities open a new era to restore and regenerate dental tissues; however, all these new technologies can also present new hazards to patients. Before any clinical usage, new materials must be proven to be safe and not hazardous to health. Certain international standards exist for safety evaluation of dental materials (ISO 10993 series, ISO 7405 and ISO 14155‐1), but researchers often fail to follow these standards due to lack of access to standards, limitation of the guidelines and complexity of new experimental methods, which may cause technical errors. Moreover, many laboratories have developed their testing strategy for biocompatibility, which makes any comparison between findings more difficult. The purpose of this review was to discuss the concept of biocompatibility, structured test programmes and international standards for testing the biocompatibility of endodontic material biocompatibility. The text will further detail current test methods for evaluating the biocompatibility of endodontic materials, and their advantages and limitations.

Experimental EDX analysis of different periodontal splinting systems

Physiological/normal tooth mobility may be defined as the slight displacement of the clinical crown of a tooth, which is allowed by the resilience of an intact and healthy periodontium, under the application of a moderate force. The factors influencing the success and longevity of dental splinting are the type of material used for the splint, the type of composite resin, the number and location of the dental units included for splinting (maxillary or mandibular arch). In periodontology, the term 'splint' is defined as the joining of two or more teeth into a rigid unit through restorations or fixed or removable devices. The purpose of using periodontal splints for tooth immobilization is to provide a period of rest in the areas where the healing process has begun and to allow normal functioning there where the tissues alone would not be able to withstand occlusal forces. The aim of the present study was to evaluate comparatively, by means of energy dispersive electron spectrometry (EDX), the chemical composition in the case of in vitro samples that structurally reproduce direct periodontal immobilization systems using fiberglass strips and fluid composite resins. The differences in the chemical composition of the investigated materials can influence their physiochemical properties, but also their biological and toxicological reliability. Elements such as C, O, Al, Si and Ba were identified as common elements among the resins tested in the present study. The only difference in terms of the component elements was found in the case of the fluid composite Clearfil Majesty ES Flow, which, apart from the elements mentioned, also presented Co in its structure.

3D Bioprinting in Tissue Engineering for Medical Applications: The Classic and the Hybrid

Three-dimensional (3D) printing, as one of the most popular recent additive manufacturing processes, has shown strong potential for the fabrication of biostructures in the field of tissue engineering, most notably for bones, orthopedic tissues, and associated organs. Desirable biological, structural, and mechanical properties can be achieved for 3D-printed constructs with a proper selection of biomaterials and compatible bioprinting methods, possibly even while combining additive and conventional manufacturing (AM and CM) procedures. However, challenges remain in the need for improved printing resolution (especially at the nanometer level), speed, and biomaterial compatibilities, and a broader range of suitable 3D-printed materials. This review provides an overview of recent advances in the development of 3D bioprinting techniques, particularly new hybrid 3D bioprinting technologies for combining the strengths of both AM and CM, along with a comprehensive set of material selection principles, promising medical applications, and limitations and future prospects.

Cytotoxic effects of different self-adhesive resin cements: Cell viability and induction of apoptosis

PURPOSE

The effects of four different self-adhesive resin cement materials on cell viability and apoptosis after direct and indirect exposure were evaluated using different cell culture techniques.

MATERIALS AND METHODS

Self-adhesive cements were applied to NIH/3T3 mouse fibroblasts by the extract test method, cell culture inserts, and dentin barrier test method. After exposure periods of 24 h and 72 h, the cytotoxicity of these self-adhesive materials was evaluated using the MTT assay (viability) and the Annexin-V-FITC/PI staining (apoptosis).

RESULTS

The lowest cell viability was found in cells exposed to BeautiCem SA for 24 h in the extract test method. Cell viability was reduced to 70.6% compared to negative controls. After the 72 h exposure period, viability rate of cell cultures exposed to BeautiCem SA decreased more than 2- fold (29.5%) while cells exposed to RelyX U200 showed the highest viability rate of 71.4%. In the dentin barrier test method, BeautiCem SA induced the highest number of cells in apoptosis after a 24 h exposure (4.1%). Panavia SA Cement Plus was the material that caused the lowest number of cells in apoptosis (1.5%).

CONCLUSION

The used self-adhesive cements have showed different cytotoxic effects based on the evaluation method. As exposure time increased, the materials showed more cytotoxic and apoptotic effects. BeautiCem SA caused significantly more severe cytotoxic and apoptotic effects than other cements tested. Moreover, cements other than BeautiCem SA have caused necrotic cell death rather than apoptotic cell death.

Preparation and Characterization of Natural Bleaching Gels Used in Cosmetic Dentistry

The novelty of this study consists of the formulation and characterization of three experimental bleaching gels with hydroxylapatite oxides and fluorine (G28®, G29®, G30®) based on natural fruit extracts compared to the commercial Opalescence 15% (GC, Ultradent, South Jordan, UT, USA). Studies have been conducted on the effect that the experimental bleaching gels have on the color and morphology of different restorative materials (Nanofill®-Schulzer, P.L. Superior Dental Materials GmbH, Hamburg, Germany, and experimental nanocomposites (P11®, P31®, P61®)), immersed in coffee and artificial saliva (for 10 days and 30 days). The study also includes a cytotoxicity test on the gels and nanocomposites after bleaching, with ISO 109993-5 protocols on human dental follicle stem cells. UV-VIS spectroscopy, computerized measurement, and fluorescence spectrometry were used in order to observe the color changes, while the microstructure of the surface was investigated by Scanning Electron Microscopy (SEM). All of the samples immersed in coffee showed the highest color shift in comparison to the baseline. The color difference ΔE values obtained using the two methods (UV-Vis, computerized based on digital images) both after coloring and bleaching, respectively, were different for all four types of nanocomposites stored in the coffee, while no difference was observed in those stored in artificial saliva. The studied experimental gels and nanocomposites had a low cytotoxic effect on cell cultures after bleaching.

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.

Comparison of cytotoxicity test models for evaluating resin-based composites

OBJECTIVES

This study compared different cytotoxicity test models for evaluating resin-based composites (RBCs) and assessed the biocompatibility of standard and bulk-fill RBCs.

METHODS

A standard (spectrum TPH) and a bulk-fill (smart dentin replacement (SDR)) RBC were selected. Disc-shaped specimens (7 mm diameter) of 2 and 4 mm thickness were polymerized for 20 s with a LED curing light of 700 mW/cm² irradiance. The specimens ( n = 5) were subjected to micro-hardness testing and three cytotoxicity test models (direct contact, indirect contact and extract tests) with the established L-929 cell line. Hardness ratios of top and bottom surfaces of specimens were computed to assess the effectiveness of cure. For the direct and indirect contact tests, the cells were stained and zones of inhibition were analyzed after material contact for 24 h. For the extract test, cells were exposed to extracts for 24 h, and cell viability was measured. Data was analyzed using analysis of variance/Scheffe's post hoc test and Pearson's correlation ( p < 0.05).

RESULTS

The lowest mean hardness ratio and highest cytotoxicity were observed for TPH at 4 mm. At 4-mm thickness, SDR was found to be biocompatible with all three models. Correlations between hardness ratio and cell viability ranged from r = 0.89-0.96 for the various tests. A significant correlation ( r = 0.97) was also observed between the three test models.

CONCLUSION

Our data indicated consistency between direct contact, indirect contact and extract test models for cytotoxicity testing of RBCs. Bulk placement and curing at 4 mm for the bulk-fill RBC evaluated did not result in undue cytotoxicity.

In Vitro Cytotoxicity of Calcium Silicate-Based Endodontic Cement as Root-End Filling Materials

The aim of this study was to evaluate the cytotoxicity of three types of calcium silicate-based endodontic cement after different incubation periods with human periodontal ligament fibroblasts. Human periodontal ligament fibroblasts were cultured from extracted third molars and seeded in 96-well plates. MTA, calcium enriched mixture (CEM) cement, and Biodentine were prepared and added to culture insert plates which were immediately placed into 96-well plates containing cultured cells. After incubation periods of 24, 48, and 72 hours, cell viability was determined with WST-1 assay. Data were analysed statistically by ANOVA with repeated measures and Bonferroni tests. There was no significant difference in cell viability amongst the test materials after each incubation period (P > 0.05). MTA and CEM presented more than 90% cell viability after 24 and 48 hours of incubation and showed statistically significant decrease in cell viability after 72 hours of incubation (P < 0.05). Biodentine showed significantly less cell viability (73%) after 24 hours of incubation, whereas more than 90% cell viability was seen after 48 and 72 hours of incubation (P < 0.05). Despite the significant changes in cell viability over time, materials presented similar cytotoxicity profile. Biodentine and CEM can be considered as alternative materials for root-end surgery procedures.

Evaluation of Cytotoxicity of Dentin Desensitizing Products

Objectives

To evaluate the cytotoxic effects of the dentin desensitizing products (DDPs) used in the treatment of dentin hypersensitivity on cultured human gingival and pulpal fibroblast cells.

Methods and Materials

The cytotoxic effects of DDPs (Smart Protect, Systemp Desensitizer, Seal & Protect, Aqua-Prep F, Isodan, Gluma, BisBlock, D/Sense Crystal, UltraEZ, Colgate Sensitive Pro-Relief, Topex, and Clinpro White Varnish) on cultured human gingival- and pulp-derived fibroblast cells were evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test (Serva, Heidelberg, Germany) under two different conditions. In the first test, different dilutions of the DDPs were directly applied onto cultured gingival fibroblast cells, and in the second test, the products were applied onto different-thickness dentin discs (0.5 and 1 mm) placed above cell culture medium, which contained pulp fibroblast cells.

Results

According to the cytotoxicity evaluations of gingival fibroblast cells, the cytotoxicity of all of the DDPs was very high at 50% concentrations (p&lt;0.05). Colgate Sensitive Pro-Relief, Clinpro White Varnish, and Topex showed higher cytotoxicity than did the other products (p&lt;0.05), decreasing with further dilutions, and these products were found to be less cytotoxic to both types of cells (p&lt;0.05) than were the other products with further dilutions. The cytotoxicity to human gingival and pulpal fibroblast cells of Systemp Desensitizer, Aqua-Prep F, Isodan, and Gluma did not show any decrease with further dilutions, and these products were found to be more cytotoxic than the other products (p&lt;0.05).

Conclusions

According to the findings of this study, Colgate Sensitive Pro-Relief, Topex, and Clinpro White Varnish were less cytotoxic than the other DDPs used in this study.

Evaluation of Cytotoxicity of Silorane and Methacrylate based Dental Composites using Human Gingival Fibroblasts

AIM

The effects of leached substances from the restorative dental materials may induce local and systemic adverse effects. Thus the biological and toxic properties of the restorative dental materials must be compatible with the oral tissues or with general health. Therefore, the need for biocompatible restorative dental material implies the necessity of toxicity testing. It was the purpose of this investigation to determine and compare the possible toxic effect of silorane based composite (Filtek P90) on human gingival fibroblast (HGF) in vitro using cytotoxicity measuring parameters (MTT assay) in comparison with its methacrylate counterpart (Z100) for their viability, proliferation rate.

MATERIALS AND METHODS

Fresh healthy biopsy specimens of human gingival tissue of patients were obtained. For HGF, cells were cultured in Dulbecco's modified Eagle medium and grown to sub confluent monolayers. After attaining confluence, cells were treated with different doses of the Filtek P90 or Z 100 for different time point. HGF cells were observed for their proliferation, viability by MTT assay.

RESULTS

The results of the cytotoxicity assay showed that, the percentage of viable cells was very good in the first 24h and marginally decreased in the next 48h period in all groups. However, the proliferation rate was never below 84% in all the groups, at any given concentration. Filtek P90 and Z100 treated cells exhibited insignificant decrease in the cell proliferation both in 24h and 48h exposure when compared to significant decrease in the cell survival rate in the positive control (Mitomycin C 250 μg/ml).) Comparison of the toxicity between Filtek P90 and Z100 in 24h & 48h separately showed that there was no significant difference (p<0.05) between these two composites in 24h and 48h' time period at all concentrations of the composites.

CONCLUSION

To conclude, the new silorane based restorative composite showed comparable cytotoxic characteristics to clinically successful dimethacrylate composites suggesting the non-toxic nature in the oral environment and hence contributing to clinical success of these new restorative materials.

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.

Toxicity evaluation of two dental composites: three-dimensional confocal laser scanning microscopy time-lapse imaging of cell behavior

The purpose of this study was to investigate the in vitro biocompatibility of two dental composites (namely A and B) with similar chemical composition used for direct restoration using three-dimensional confocal laser scanning microscopy (CLSM) time-lapse imaging. Time-lapse imaging was performed on cultured human HGF-1 fibroblast-like cells after staining using Live/Dead®. Image analysis showed a higher mortality rate in the presence of composite A than composite B. The viability rate decreased in a time-dependent manner during the 5 h of exposure. Morphological alterations were associated with toxic effects; cells were enlarged and more rounded in the presence of composite A as shown by F-actin and cell nuclei staining. Resazurin assay was used to confirm the active potential of composites in cell metabolism; results showed severe cytotoxic effects in the presence of both no light-curing composites after 24 h of direct contact. However, extracts of polymerized composites induced a moderate decrease in cell metabolism after the same incubation period. Composite B was significantly better tolerated than composite A at all investigated end points and all time points. The finding confirmed that the used CLSM method was sufficiently sensitive to differentiate the biocompatibility behavior of two composites based on similar methacrylate monomers.

Biocompatibility of Resin-based Dental Materials

Oral and mucosal adverse reactions to resin-based dental materials have been reported. Numerous studies have examined the biocompatibility of restorative dental materials and their components, and a wide range of test systems for the evaluation of the biological effects of these materials have been developed. This article reviews the biological aspects of resin-based dental materials and discusses the conventional as well as the new techniques used for biocompatibility assessment of dental materials.

Biocompatibility of dental materials

With the long history of use of many materials in dental surgery, biocompatibility concerns are not as great a concern as other issues, such as long-term degradation, mechanical strength problems, and prevention of secondary caries. It is important, however, not to forget that the potential exists for adverse tissue responses to synthetic materials used in repair, augmentation, and repair of natural tissue structures. As new materials and repair techniques become available and the sophistication of cell-level and subcellular response evaluations increases, the concerns to be addressed and the methods to be used may change. The advent of tissue-engineered medical products may mean that new questions must be addressed.

Cytotoxicity of resin monomers on human gingival fibroblasts and HaCaT keratinocytes

OBJECTIVES

The aim of this study was to evaluate and compare the biological effects of three resin monomers on three human gingival fibroblast (HGF) cell lines and immortalised human keratinocytes.

METHODS

Primary HGFs and HaCaT keratinocytes were cultured for 24h and grown to sub-confluent monolayers. Resin monomers were dissolved in dimethyl sulphoxide (DMSO) and diluted with culture medium. Cultures were exposed to different concentrations of monomers (10(-2) to 10mM) for 24h. Cell viability measured by Alamar Blue assay, and cell culture supernatant was examined for the presence of human interlukin-1beta (IL-1beta) using sandwich enzyme-linked immunosorbant assay (ELISA). TC50 values were calculated from fitted dose-response curves.

RESULTS

All monomers showed toxic effects on the HGFs and HaCaT cells and inhibited chemical reduction of Alamar Blue in high concentrations. Statistical analysis of TC50 values by one-way ANOVA followed by Tukey's analysis showed that there is a significant difference in TC50 values between the cell lines (p<0.05), although the rank order of monomer toxicity remained the same for different cell lines. None of these monomers-induced IL-1beta release from HGFs and HaCaT cells.

SIGNIFICANCE

Dental resin monomers are toxic to human gingival fibroblasts and HaCaT keratinocytes. However, they cannot induce IL-1beta release from these cells by themselves. Alamar Blue assay is a sensitive method for the evaluation of cytotoxicity and it can detect different sensitivities of different cell lines to the resin monomers.

Effects of root-end filling materials and eugenol on mitochondrial dehydrogenase activity and cytotoxicity to human periodontal ligament fibroblasts

Various root-end filling materials have been used to prevent the entry of root-canal pathogens into periapical regions. Five root-end filling materials were compared regarding the cytotoxicity, apoptosis, and mitochondrial dehydrogenase (MDH) activities of human periodontal ligament (PDL) fibroblasts, with the use of a novel transwell culture system. Exposure to IRM (a ZnO eugenol-based intermediate restorative material), a 2-ethoxybenzoic acid cement (Super EBA), and amalgam for 3 days inhibited the MDH activity of PDL fibroblasts as indicated by decrease in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction by 97%, 95%, and 51%, respectively. Evident suppression of MTT reduction by amalgam and glass ionomer cement (GIC) was noted after 5 days of exposure, with 73% and 46% of inhibition, respectively. Mineral trioxide aggregates (MTA) showed little effect on MDH activity. IRM and Super EBA were cytotoxic to PDL fibroblasts as indicated by a trypan blue dye exclusion technique. GIC and amalgam showed mild cytotoxicity. IRM, GIC, and amalgam further induced apoptosis of PDL cells, as revealed by the presence of sub-G0/G1 DNA content in flow cytometric histogram. Twenty-four-hour exposure to IRM and Super EBA elevated the MDH activities to 156% and 117%, correspondingly, of that of control. Eugenol, a phenolic ingredient in Super EBA and IRM, also increases MDH activity of PDL fibroblasts by 45% and 51%, at concentrations of 0.5 and 1 mM. However, at concentrations higher than 0.5 mM, eugenol decreased the number of viable PDL fibroblasts. These results suggest that MTA is a biocompatible root-end filling material, followed by self-curing Fuji II GIC and amalgam. IRM and Super EBA ingredients induced marked cytotoxicity and transiently stimulate MDH activities, which is possibly due to their content of eugenol and induction of cellular adaptive response.

Tooth slice organ culture and established cell line culture models for cytotoxicity assessment of dental materials

The aim was to compare the use of different cell-material contact test methods with two different biological systems (cell line and tooth slice cultures) for cytotoxicity assessment of dental materials. Cytotoxicity of composites polymerized with two halogen-based and two light-emitting diode (LED) light-curing units (LCUs) served as the basis for comparison. Disk shaped specimens (7 x 2 mm) were fabricated using the four light sources. Composites were tested using L-929 cell line using direct/indirect/extract tests in accordance to standard protocols. Cytotoxicity was assessed using neutral red uptake. Tooth slice organ cultures were also employed to test the dental materials using direct/indirect test methods. Histomorphometric cell counting of intact odontoblasts and pulp fibroblasts and the use of tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were applied for cytotoxicity evaluation. Discrepancy in result presentation was observed in the different tests used with L-929. Sensitivity levels of the L-929 tests ranked as follows: extract test < direct contact test < indirect contact test. Tooth slice tests confirmed that L-929 direct contact test proved to be the most reliable test among the three. In conclusion, this study highlights the risk involved when relying on a single test method for cytotoxicity assessment. It would be advisable to test different culture models and then proceed using more clinically relevant biological system that stimulate the in vivo situation for confirmation.

Assessment of dental material degradation product toxicity using a bioluminescent bacterial assay

OBJECTIVES

This study examined dental material degradation product toxicity using the Microtox bacterial bioluminescence assay as well as the effects on toxicity of selective leaching, chelation with protein, the physical form of the products, and synergistic/antagonistic interactions among released ions.

METHODS

Polarization was used to produce ionically dissolved (ID) and precipitated corrosion products from Litecast B alloy specimens, which were then chemically analyzed to determine their composition and to identify metal valence states. Corrosion product toxicity, as well as that of the individual alloying elements, alone and in the presence of mucin, was analyzed using Microtox. A mathematical approach identified synergistic/antagonistic interactions and determined element contribution to product toxicity. The mechanism by which the Microtox test bacterium interacts with solid products was explored. The toxicity of methyl methacrylate (MMA) monomer was also examined.

RESULTS

Precipitated corrosion products were found to be more toxic than ID products. The metals in the precipitate have been shown to be available to the test bacterium. Be and Ni were the most toxic elements in the products and contributed significantly to their toxicity. Synergistic and slightly antagonistic interactions were observed in the ID and precipitated products, respectively. Mucin decreased toxicity of all elements except Be. MMA monomer toxicity was found to be low compared to metal toxicity.

SIGNIFICANCE

Microtox is useful for evaluating dental degradation product biocompatibility and has significant promise for use in other types of studies, such as determining the effectiveness of antimicrobial treatments.

Cytotoxicity testing with three-dimensional cultures of transfected pulp-derived cells

SV40 large T-antigen-transfected bovine pulp-derived cells were grown three-dimensionally on polyamide meshes. For optimal cell growth, various cell numbers and mesh coatings were tested. Next the three-dimensional cultures were used in a dentin barrier test device, and the system was evaluated by testing a set of dental filling materials. After 24 hr exposure with or without perfusion of the pulpal part of the test device, cell survival was evaluated using an MTT assay. In all experiments pulp-derived cells transfected with SV40 large T-antigen grew three-dimensionally on polyamide meshes and showed growth kinetics similar to those on cell culture plates with lag, log, and plateau phases (reached after about 14 days of incubation). Cross-sections of the three-dimensional cell cultures revealed about 15 to 20 cell layers. In vitro cytotoxicity tests resulted in cell survival rates which are in good agreement with in vivo data and with results obtained from cytotoxicity tests with three-dimensional cultures of human foreskin fibroblasts.