Mucotoxicity of dental composite resins on a tissue-engineered human oral mucosal model

Polishing methods for composites restoration: the influence on human gingival fibroblasts behaviour

BACKGROUND

Carious/Non-carious cervical lesions with gingival recessions may require both dental and periodontal reconstructive therapy, where flaps/grafts may be placed in contact with a dental filling material. Human Gingival Fibroblasts (HGF-1) response during the early phase of healing could vary according to the procedures employed to cure the dental composite. Moreover, oxygen diffusion into dental composite inhibits the polymerization reaction, creating an oxygen-inhibited layer (OIL) that presents residual unreacted monomers. The aim of this study was to assess the effect of different polishing techniques and OIL on HGF-1.

METHODS

Composite discs polished with different techniques (diamond rubber, abrasive discs and tungsten carbide burr) were used. An additional not polished smooth group obtained with and without OIL was used as control. Samples were physically characterized through the analysis of their hydrophilicity and surface topography through contact angle measurement and SEM, respectively; afterwards the biologic response of HGF-1 when cultured on the different substrates was analyzed in terms of cytotoxicity and gene expression.

RESULTS

The finishing systems caused alterations to the wettability, even if without a proportional relation towards the results of the proliferation essay, from which emerges a greater proliferation on surfaces polished with one-step diamond rubber and with abrasive discs as well as a direct effect of the glycerin layer, confirming that surface roughness can heavily influence the biological response of HGF-1.

CONCLUSIONS

Surfaces wettability as well as cellular behavior seem to be affected by the selection of the finishing system used to lastly shape the restoration. Especially, the presence of OIL act as a negative factor in the regards of human gingival fibroblasts. The present study may provide the first clinical instruction regarding the best polishing system of composite material when the restoration is placed directly in contact with soft tissue cells. Understanding HGF-1 behavior can help identifying the polishing treatment for direct restoration of carious/non-carious cervical lesions associated with gingival recessions.

Comparative evaluation of six commercial adult toothpaste formulations reveals cytotoxicity and altered functions in a human oral melanocyte model: an in vitro study

This study aims to compare six commercial adult toothpaste (labeled as A, B, C, D, E, and F) for cytotoxicity and melanocyte function alterations in vitro using primary human epidermal melanocytes from a Caucasian donor (HEMn-LP cells) as a model of oral melanocytes. Cells were incubated with toothpaste extracts (50% w/v) in culture media at dilutions (1:25, 1:50, 1:100, 1:200, 1:500, 1:800, and 1:1000) for 24 h. MTS and LDH assays were used to assess cytotoxicity. The effects of noncytotoxic toothpaste concentrations on melanocyte functional endpoints were then examined using spectrophotometric methods. All toothpaste showed concentration-dependent cytotoxicity that was heterogeneous across toothpaste containing SLS detergent. IC50 values of cytotoxicity followed the order: A = E > C > B > D > F. To compare toothpaste, they were tested at 1:800 and 1:1000 dilutions that were noncytotoxic after 24 h. None of the toothpaste affected cellular melanin production. However, toothpaste A, C, and D suppressed tyrosinase activity at both dilutions, while toothpaste B suppressed tyrosinase activity only at 1:800 dilution. Toothpaste A, C, E, and F elevated ROS production at 1:800 dilution, with no change at 1:1000 dilution. Toothpaste has a heterogeneous effect on melanocytes. Toothpaste B, E, and F at 1:1000 dilution were the safest as they did not alter melanocyte functions at this dilution, although toothpaste F is the least cytotoxic of these. Future studies are necessary to expand these results in a physiological environment of oral tissue. The findings of this study provide novel insight into the biocompatibility studies of toothpaste on oral melanocytes. They can aid dental practitioners and consumers in selecting noncytotoxic toothpaste that do not contribute to ROS generation by melanocytes in the oral cavity or lead to cytotoxicity and impaired cellular function.

Microphysiological Modeling of Gingival Tissues and Host-Material Interactions Using Gingiva-on-Chip

Gingiva plays a crucial barrier role at the interface of teeth, tooth-supporting structures, microbiome, and external agents. To mimic this complex microenvironment, an in vitro microphysiological platform and biofabricated full-thickness gingival equivalents (gingiva-on-chip) within a vertically stacked microfluidic device is developed. This design allowed long-term and air-liquid interface culture, and host-material interactions under flow conditions. Compared to static cultures, dynamic cultures on-chip enabled the biofabrication of gingival equivalents with stable mucosal matrix, improved epithelial morphogenesis, and barrier features. Additionally, a diseased state with disrupted barrier function representative of gingival/oral mucosal ulcers is modeled. The apical flow feature is utilized to emulate the mechanical action of mouth rinse and integrate the assessment of host-material interactions and transmucosal permeation of oral-care formulations in both healthy and diseased states. Although the gingiva-on-chip cultures have thicker and more mature epithelium, the flow of oral-care formulations induced increased tissue disruption and cytotoxic features compared to static conditions. The realistic emulation of mouth rinsing action facilitated a more physiological assessment of mucosal irritation potential. Overall, this microphysiological system enables biofabrication of human gingiva equivalents in intact and ulcerated states, providing a miniaturized and integrated platform for downstream host-material and host-microbiome applications in gingival and oral mucosa research.

Contour Analysis of Three-Dimensional Peri-Implant Mucosal Model as an Endpoint Analysis of Photofunctionalization Effects on Implant Abutment Materials

INTRODUCTION

The objective of this study was to examine the effect of photofunctionalization on the soft-tissue contour formed at the interface of various abutment materials using end-point analyses obtained from the three-dimensional oral mucosal model (3D-OMMs).

METHODS

Commercially pure titanium (CPTi), alumina-toughened zirconia (ATZ), and yttria-stabilized zirconia (YSZ) made into discs shapes were classified into two groups: UV-treated (PTx) and non-treated (NTx). The materials in PTx groups were exposed to UV light for 12 min. Human gingival fibroblasts and TR146 epithelial cell lines co-cultured on the acellular dermal membrane were used to construct the 3D-OMM. After 4 days of culture, the discs were inserted into the holes prepared within the membrane of 3D-OMMs. The contour formed by the tissue was evaluated after 14 days of culture.

RESULTS

The UV treatment of abutment materials resulted in the formation of more non-pocket-tissue types among the PTx group (p = 0.002). Of all materials tested, soft tissue contour around YSZ showed higher scores for the non-pocket type in both non- and UV-treated groups.

CONCLUSIONS

The non-pocket type of tissue attachment was frequently found in all surfaces modified by photofunctionalization, particularly zirconia. The 3D-OMM can be used to evaluate the biological endpoints of implant surface modifications.

Expression of Interleukin-1β and Histological Changes of the Three-Dimensional Oral Mucosal Model in Response to Yttria-Stabilized Nanozirconia

Over the years, advancement in ceramic-based dental restorative materials has led to the development of monolithic zirconia with increased translucency. The monolithic zirconia fabricated from nano-sized zirconia powders is shown to be superior in physical properties and more translucent for anterior dental restorations. Most in vitro studies on monolithic zirconia have focused mainly on the effect of surface treatment or the wear of the material, while the nanotoxicity of this material is yet to be explored. Hence, this research aimed to assess the biocompatibility of yttria-stabilized nanozirconia (3-YZP) on the three-dimensional oral mucosal models (3D-OMM). The 3D-OMMs were constructed using human gingival fibroblast (HGF) and immortalized human oral keratinocyte cell line (OKF6/TERT-2), co-cultured on an acellular dermal matrix. On day 12, the tissue models were exposed to 3-YZP (test) and inCoris TZI (IC) (reference material). The growth media were collected at 24 and 48 h of exposure to materials and assessed for IL-1β released. The 3D-OMMs were fixed with 10% formalin for the histopathological assessments. The concentration of the IL-1β was not statistically different between the two materials for 24 and 48 h of exposure (p = 0.892). Histologically, stratification of epithelial cells was formed without evidence of cytotoxic damage and the epithelial thickness measured was the same for all model tissues. The excellent biocompatibility of nanozirconia, as evidenced by the multiple endpoint analyses of the 3D-OMM, may indicate the potential of its clinical application as a restorative material.

Influence of the Polymerization Modes on the Methacrylic Acid Release from Dental Light-Cured Materials-In Vitro Study

The study focuses on the problem of lowering the pH around a composite filling concerning the polymerization modes and methacrylic acid release, which may affect not only the oral health but also the whole organism. A total of 90 specimens (30 of each: Filtek Bulk Fill, Evetric and Riva LC) were placed in 90 sterile hermetic polyethene containers with saline and incubated at 37 °C. Ten samples of each material were light-cured for 40 s with one of the three curing modes: full power mode (FPM), ramping mode (RM) and pulse mode (PM). The pH and methacrylic acid release evaluation were performed at the following time points: after 2 h and after 3, 7, 21 and 42 days from the specimen preparation. Regardless of light-curing mode, all used materials were characterized by a gradual elevation in methacrylic acid concentration. Only for Filtek Bulk Fill, increased methacrylic acid release was closely associated with lower pH. The choice of the polymerization mode has no significant influence on the methacrylic acid release. However, further research about composite light-curing is necessary to create the procedure algorithm, reducing the local and systemic complications associated with composite fillings.

Characterisation of Microparticle Waste from Dental Resin-Based Composites

Clinical applications of resin-based composite (RBC) generate environmental pollution in the form of microparticulate waste. Methods: SEM, particle size and specific surface area analysis, FT-IR and potentiometric titrations were used to characterise microparticles arising from grinding commercial and control RBCs as a function of time, at time of generation and after 12 months ageing in water. The RBCs were tested in two states: (i) direct-placement materials polymerised to simulate routine clinical use and (ii) pre-polymerised CAD/CAM ingots milled using CAD/CAM technology. Results: The maximum specific surface area of the direct-placement commercial RBC was seen after 360 s of agitation and was 1290 m²/kg compared with 1017 m²/kg for the control material. The median diameter of the direct-placement commercial RBC was 6.39 μm at 360 s agitation and 9.55 μm for the control material. FTIR analysis confirmed that microparticles were sufficiently unique to be identified after 12 months ageing and consistent alteration of the outermost surfaces of particles was observed. Protonation-deprotonation behaviour and the pH of zero proton charge (pH_zpc) ≈ 5–6 indicated that the particles are negatively charged at neutral pH7. Conclusion: The large surface area of RBC microparticles allows elution of constituent monomers with potential environmental impacts. Characterisation of this waste is key to understanding potential mitigation strategies.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

In vitro three-dimensional organotypic culture models of the oral mucosa

Three-dimensional, organotypic models of the oral mucosa have been developed to study a wide variety of phenomena occurring in the oral cavity. Although a number of models have been developed in academic research labs, only a few models have been commercialized. Models from academic groups offer a broader range of phenotypes while the commercial models are more focused on the oral and gingival mucosa. The commercialized models are manufactured under highly controlled conditions and meet the requirements of quality standards, which leads to high levels of reproducibility. These in vitro models have been used to evaluate the irritancy of oral care products such as toothpastes, mouthwashes, and mucoadhesives. The effects of cigarette smoke on oral cavity tissues have been studied and compared to those of e-cigarettes. Oral tissue models have facilitated investigation of the mechanisms of oral mucositis and oral candidiasis and have been used to examine transbuccal drug delivery rates and the absorption of nanoparticles. Infection studies have investigated the effects of HIV-1 along with the effects of commensal and pathogenic bacteria. More recently, a differentiated oral tissue model has been shown to express the ACE2 receptor, which is known to be important for the receptor-mediated entry of the SARS-CoV-2 coronavirus into human cells and tissues. Hence, oral mucosal models may find application in determining whether viral infection of the oral mucosa is possible and whether such infection has implications vis-a-vis the current COVID-19 pandemic. As is apparent, these models are used in a broad variety of applications and often offer advantages versus animal models in terms of reproducibility, avoiding species extrapolation, and the ethical concerns related to human and animal experimentation. The goals of this paper are to review commercially available models of the human buccal and gingival mucosa and highlight their use to gain a better understanding of a broad range of phenomena affecting tissues in the oral cavity.

Construction of Vascularized Oral Mucosa Equivalents Using a Layer-by-Layer Cell Coating Technology

There have been many advances in tissue engineering with respect to in vitro and in vivo models of oral mucosa equivalents (OMEs). To apply in vitro reconstructed oral mucosa models to regenerative medicine and alternatives to animal testing, it is necessary to develop the technology of reconstructing different types of oral tissues, such as control of epithelial differentiation and introduction of appendages. We previously reported that functional three-dimensional (3D) tissue models could be quickly constructed by using a layer-by-layer (LbL) cell coating technique that assembles extracellular matrix (ECM) nanofilms to a cell surface. In this study, 3D human OMEs composed of lamina-propria, keratinized or non-keratinized epithelium, and blood capillaries were constructed by using the LbL cell coating technology. Human oral mucosal fibroblasts (HOMFs) were coated with ECM nanofilms and accumulated for the construction of oral mucosal lamina-propria. To construct OMEs with keratinized or non-keratinized epithelium, human oral keratinocytes isolated from gingiva (human oral gingival keratinocytes: HOGKs) or human oral keratinocytes isolated from oral mucosa (human oral mucosal keratinocytes: HOMKs) were used in this study. We further studied the construction of epithelialized OMEs with density- and size-controlled blood capillary networks by using human umbilical vein endothelial cells (HUVECs). It was revealed that these constructions had barrier functions in accordance with their histological characterization. The OMEs with keratinization (K-OMEs) showed higher transepithelial electrical resistance (TEER) values compared with OMEs with non-keratinization (N-OMEs). The constructed epithelialized OMEs with blood capillaries are useful for in vitro/ex vivo research models and regenerative medicine as in oral tissue regeneration. The results suggest that OMEs with oral tissue appendages are more promising alternatives to animal testing and can be applied to the design of in vitro oral models that mimic human tissue organs.

Influence of resveratrol application with pulp-capping materials on the genetic expression levels of stem cells

AIM

To evaluate in a laboratory setting the response of human mesenchymal stem cells (MSCs) to pulp-capping materials with and without resveratrol (RSV).

METHODOLOGY

Five materials, Calcimol LC, Life, TheraCal LC, ProRoot MTA and Biodentine, were prepared according to the manufacturers' instructions. Human MSCs were then exposed to these materials, with and without RSV, for 24 h (n = 8). Cell viability was evaluated using the MTT assay, and total cell death was quantified by annexin V-FITC staining with flow cytometry. The expression levels of the IL-8, IL-10, HBD-2 and BCL-2 genes were investigated using real-time polymerase chain reaction (RT-PCR). Data obtained from MTT test were analysed using one-way anova, and Tukey's multiple-comparison test. The paired Student t test was employed to compare the effects of materials on gene expression (significance level of 5%).

RESULTS

The group cell viabilities were Calcimol LC 53%, Life 43%, TheraCal LC 78%, ProRoot MTA 75% and Biodentine 78%. Calcimol LC and Life exhibited significant differences compared with the control groups (P < 0.05). The percentages of necrotic/late apoptotic cells associated with Calcimol LC and TheraCal LC were greater than in the other materials. However, when RSV was added to wells containing materials, cell viability increased to Calcimol LC 63%, Life 52%, TheraCal LC 82%, ProRoot MTA 91% and Biodentine 96%, and the percentages of early apoptotic and late apoptotic/necrotic cells decreased. Calcimol LC + RSV and Life + RSV differed significantly from the control group (P < 0.05). The expression of IL-8 gene was high for all materials, ProRoot MTA caused significant overexpression, and the addition of RSV reduced the expression of IL-8 in the Calcimol LC, TheraCal LC and ProRoot MTA groups and led to increased expression of IL-10 in the Calcimol LC, Life and Biodentine groups. HBD-2 and BCL-2 exhibited increased expression in ProRoot MTA with RSV (P < 0.05).

CONCLUSIONS

The addition of RSV exerted a protective effect on MSCs and regulated the inflammatory process by altering the expression levels of pro- and anti-inflammatory genes.

Implant Soft-Tissue Attachment Using 3D Oral Mucosal Models-A Pilot Study

PURPOSE

The aim of this study was to investigate soft-tissue attachment to different metal, ceramic, and polymer implant surfaces using an inflamed, three-dimensional (3D), tissue-engineered, human oral mucosal model, as well as multiple-endpoint qualitative and quantitative biological approaches.

METHODS

Normal human oral fibroblasts, OKF6/TERT-2 keratinocytes and THP-1 monocytes were cultured, and full-thickness, 3D oral mucosal models were engineered inside tissue culture inserts. Sand-blasted and acid-etched (SLA) and machined (M) titanium-zirconium alloy (TiZr; commercially known as Roxolid; Institut Straumann AG, Switzerland), ceramic (ZrO2), and polyether ether ketone (PEEK) rods (Ø 4 mm × 8 mm) were inserted into the center of tissue-engineered oral mucosa following a Ø 4mm punch biopsy. Inflammation was simulated with addition of the lipopolysaccharide (LPS) of Escherichia coli (E. coli) and tumor necrosis factor (TNF)-alpha to the culture medium. Implant soft-tissue attachment was assessed using histology, an implant pull-test with PrestoBlue assay, and scanning electron microscopy (SEM).

RESULTS

Inflamed, full-thickness, 3D human oral mucosal models with inserted implants were successfully engineered and histologically characterized. The implant pull-test with PrestoBlue assay showed higher viability of the tissue that remained attached to the TiZr-SLA surface compared to the other test groups. This difference was statistically significant (p < 0.05). SEM analysis showed evidence of epithelial cell attachment on different implant surfaces.

CONCLUSIONS

The inflamed, 3D, oral mucosal model has the potential to be used as a suitable in vitro test system for visualization and quantification of implant soft-tissue attachment. The results of our study indicate greater soft tissue attachment to TiZr-SLA compared to TiZr-M, ceramic, and PEEK surfaces.

The effects of the dental methacrylates TEGDMA, Bis-GMA, and UDMA on neutrophils in vitro

Objectives

The prevalent usage of methacrylates in modern dentistry demands good knowledge of their biological impacts. While there have been several studies demonstrating the effects of different methacrylic monomers on mononuclear white blood cells, very little is known about the effects caused by these monomers on neutrophilic granulocytes. The objective of this study was to add novel knowledge about how neutrophils are affected by exposure to triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A glycol dimethacrylate (Bis‐GMA) alone or in combinations.

Materials and Methods

Isolated neutrophils were cultured in the presence or absence of methacrylates. The IL‐8 release was measured using a DuoSet ELISA development kit. Apoptosis and necrosis were analyzed using flow cytometry. The formation of neutrophil extracellular traps (NETs) was investigated using Sytox green DNA staining combined with microscopically examination of released DNA and myeloperoxidase (MPO).

Results

The release of IL‐8 was significantly increased after exposure to TEGDMA, Bis‐GMA, UDMA, or TEGDMA in combination with Bis‐GMA or UDMA compared to the unstimulated controls. Exposure to TEGDMA, UDMA, and Bis‐GMA for 24 hr separately or in combination did not affect apoptosis or necrosis of the exposed neutrophils. NET structures were formed by neutrophils after exposure to the different combinations of the methacrylates.

Conclusion

The combination of TEGDMA and Bis‐GMA had a synergistic proinflammatory effect on neutrophils by increasing the release of IL‐8 and the formation of NET structures. The changes in the normal functions of neutrophils caused by methacrylate exposure may lead to altered inflammatory response and relate to previously reported adverse immune reactions caused by these substances.

Biomodification of a Class-V Restorative Material by Incorporation of Bioactive Agents

Restoring subgingival class-V cavities successfully, demand special biological properties from a restorative material. This study aimed to assess the effects of incorporating bioactive materials to glass ionomer cement (GIC) on its mechanical and biological properties. Hydroxyapatite, chitosan, chondroitin sulphate, bioglass, gelatine and processed bovine dentin were incorporated into a GIC restorative material. Compressive strength, biaxial flexural strength (BFS), hardness, setting and working time measurements were investigated. Biocompatibility of the new materials was assessed using both monolayer cell cultures of normal oral fibroblasts (NOF) and TR146 keratinocytes, and a 3D-tissue engineered human oral mucosa model (3D-OMM) using presto-blue tissue viability assay and histological examination. Significant reduction in the compressive strength and BFS of gelatine-modified discs was observed, while chondroitin sulphate-modified discs had reduced BFS only (p value > 0.05). For hardness, working and setting times, only bioglass caused significant increase in the working time. NOF viability was significantly increased when exposed to GIC-modified with bovine dentine, bioglass and chitosan. Histological examination showed curling and growth of the epithelial layer toward the disc space, except for the GIC modified with gelatine. This study has highlighted the potential for clinical application of the modified GICs with hydroxyapatite, chitosan, bioglass and bovine dentine in subgingival class-V restorations.

Novel Human Full-Thickness Three-Dimensional Nonkeratinized Mucous Membrane Model for Pharmacological Studies in Wound Healing

INTRODUCTION

Efforts are increasingly aiming to develop in vitro models that can provide effective alternatives to in vivo experiments. The main aim of this study was the establishment of an in vitro model of the nonkeratinized mucous membrane that can be used as a standardized tool to evaluate biological and therapeutic effects of pharmaceuticals for mucosal wound healing.

METHODS

We established a full-thickness in vitro model of the nonkeratinized mucous membrane. While histological examination was performed to assess morphological characteristics, we utilized gene expression profiling using microarray and qRT-PCR analyses to identify molecular effects of treatment with a dexpanthenol-containing ointment after laser wounding.

RESULTS

Performing histological and immunofluorescence analyses we proved that our model mimics the two distinctive layers of the mucous membrane - the stratified squamous epithelium and the lamina propria. We used this model to investigate molecular effects of a dexpanthenol-containing ointment that is commonly used for the wound treatment of mucous membranes. For that purpose, our model exhibits a unique feature in that dexpanthenol and proliferation-enhancing additives that may interfere with our studies are not required for the maintenance of the model culture. After setting standardized lesions with a nonsequential fractional ultrapulsed CO2 laser, topical treatment with the dexpanthenol-containing ointment enhanced wound closure in the model compared to placebo and untreated controls. Furthermore, microarray analysis revealed that the treatment of the laser-wounded model with the dexpanthenol-containing ointment evoked an upregulated expression of various genes related to accelerated wound healing.

CONCLUSION

Overall, we verified that this novel mucous membrane model can be utilized in future to monitor ex vivo effects of various topical therapies on mucosa morphology, physiology, and gene expression. Our findings confirm the potential of the model as an in vitro tool for the replacement of pharmacological in vivo studies regarding mucosal wound healing.

Assessing the effect of triethyleneglycol dimethacrylate on tissue repair in 3D organotypic cultures

Leachables from dental restoratives induce toxicity in gingival and pulp tissues and affect tissue regeneration/healing. Appropriate testing of these materials requires a platform that mimics the in vivo environment and allows the architectural self-assembly of cells into tissue constructs. In this study, we employ a new 3D model to assess the impact of triethyleneglycol dimethacrylate (TEGDMA) on early organization and advanced recruitment/accumulation of immortalized mouse gingival fibroblasts (GFs) and dental papilla mesenchymal cells (DPMCs) in extracellular matrix. We hypothesize that TEGDMA (1) interferes with the developmental architecture of GFs and DPMCs, and (2) inhibits the deposition of mineral. To test these hypotheses, GFs and DPMCs were incubated with the soluble TEGDMA at concentrations (0-2.5) mmol/L. Diameter and thickness of the constructs were determined by microscopic analysis. Cell differentiation was assessed by immunocytochemistry and the secreted mineral detected by alizarin-red staining. TEGDMA interfered with the development of GFs and/or DPMCs microtissues in a dose-dependent manner by inhibiting growth of inter-spherical cell layers and decreasing spheroid size (four to six times). At low/moderate TEGDMA levels, GFs organoids retained their structures while reducing thickness up to 21%. In contrast, at low TEGDMA doses, architecture of DPMC organoids was altered and thickness decreased almost twofold. Overall, developmental ability of TEGDMA-exposed GFs and DPMCs depended on TEGDMA level. GFs constructs were more resistant to structural modifications. The employed 3D platform was proven as an efficient tool for quantifying the effects of leachables on tissue repair capacities of gingiva and dental pulp.

In vitro Cytokeratin Expression Profiling of Human Oral Mucosa Substitutes Developed by Tissue Engineering

In this work we performed a study of cytokeratin (CK) expression profiling on human artificial oral mucosa developed in vitro by tissue engineering at different stages of maturation (from immature to well-developed stages) at the protein and mRNA levels. Human artificial oral mucosa was generated in the laboratory using fibrin-agarose biomaterials. As controls, we used human native normal oral mucosa and embryonic oral tissues. Our results demonstrated that human embryonic oral tissues tended to express CK8 and CK19. In contrast, monolayered bioengineered oral mucosa did not show any CK expression by immunohistochemistry whereas bilayered and multilayered artificial oral mucosa showed several markers of stratified epithelia, but did not express CK10. These results suggest that the CK expression pattern is strongly dependent on the maturation state of the artificial tissues and that the CK expression profile of our model of artificial oral mucosa was partially similar to that of the non-keratinized human adult oral mucosa. However, the expression of CK8 by the artificial oral mucosa suggests that these samples correspond to an early stage of development while kept in vitro.

Triethylene glycol dimethacrylate: adjuvant properties and effect on cytokine production

Objective: Leakage of monomers from dental fillings due to incomplete curing is very common. The objective of the present study was to examine the cytokine profile in cells exposed to triethyleneglycol dimethacrylate (TEGDMA) and the adjuvant properties of TEGDMA.

Materials and methods: Human peripheral blood mononuclear cells were exposed to TEGDMA (500 and 1000 μM) for 24 h in vitro. Bio-Plex Pro™ assays were used for analysis and detection of cytokines. In vivo, BALB/c mice were immunized subcutaneously in the base of the tail with TEGDMA in combination with ovalbumin (OVA).

Results: The cytokine levels of IL-8, IL-18, GRO-α and MCP-1 were significantly increased for both concentrations. IL-1β, IL-6 and TNF-α was only significantly increased in cultures exposed to 500 μM TEGDMA. The concentration of TNF-α was significantly decreased in cultures exposed to 1000 μM TEGDMA. Animals immunized with OVA co-administrated with TEGDMA had a significantly higher IgE and IgG anti-OVA antibody levels in blood than animals immunized with OVA only.

Conclusions: TEGDMA affects production of proinflammatory cytokines IL-1β, IL-6, IL-8, IL-18 and TNF-α. This inflammatogenic capacity renders TEGDMAs adjuvant properties, which may interfere with the homeostasis between the immune system and the indigenous microflora in the oral cavity.

Effects of the methacrylate/acrylate monomers HEMA, TEGDMA, DEGDA, and EMA on the immune system

Incomplete curing of dental fillings may lead to leakage of methacrylate/acrylate monomers, which may come in contact with different cells of the immune system in oral tissues. Very little is known about the different immunologic effects caused by these methacrylates/acrylates. The objective of the present study was to study if and how the methacrylate/acrylate monomers ethyl methacrylate (EMA) and diethylene glycol diacrylate (DEGDA) affect the immune system in vivo and in vitro in comparison to 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA). Human peripheral blood mononuclear cells were exposed to the different monomers (500 and 1000 μM) for 24 hr in vitro. BioPlex Pro™ assays were used for cytokine analysis. In vivo, BALB/c mice were immunized subcutaneously at the base of the tail with HEMA, TEGDMA, EMA, or DEGDA in combination with ovalbumin (OVA) in order to study adjuvant properties of the 4 monomers. Peripheral blood mononuclear cells exposed to DEGDA had viability less than 50% of the cells. A pattern was observed where the levels of most cytokines were elevated after exposure to HEMA or TEGDMA. Since that, many cells died after DEGDA-exposure, the only observed cytokine secretion was a significantly increased production of interleukin-18. In the in vivo experiments, all mice immunized with DEGDA died after the booster injection. Mice receiving OVA in combination with HEMA, TEGDMA, or EMA developed a higher immunoglobulin G anti-OVA antibody levels compared to the group immunized with OVA alone. We could not demonstrate any significant difference in antibody levels among the mice receiving the various methacrylate/acrylate monomers. The different monomers affected the production, increase and decrease, of different cytokines in vitro but resulted also in vivo in increased antibody production and T-cell activity.

* Ethical Issues in the Use of Animal Models for Tissue Engineering: Reflections on Legal Aspects, Moral Theory, Three Rs Strategies, and Harm-Benefit Analysis

Animal experimentation requires a solid and rational moral foundation. Objective and emphatic decision-making and protocol evaluation by researchers and ethics committees remain a difficult and sensitive matter. This article presents three perspectives that facilitate a consideration of the minimally acceptable standard for animal experiments, in particular, in tissue engineering (TE) and regenerative medicine. First, we review the boundaries provided by law and public opinion in America and Europe. Second, we review contemporary moral theory to introduce the Neo-Rawlsian contractarian theory to objectively evaluate the ethics of animal experiments. Third, we introduce the importance of available reduction, replacement, and refinement strategies, which should be accounted for in moral decision-making and protocol evaluation of animal experiments. The three perspectives are integrated into an algorithmic and graphic harm-benefit analysis tool based on the most relevant aspects of animal models in TE. We conclude with a consideration of future avenues to improve animal experiments.

Biological evaluation of enamel sealants in an organotypic model of the human gingiva

OBJECTIVES

Various sealant materials have been suggested to decrease decalcification during orthodontic treatment. However, only a few in vitro studies on the cytotoxicity of resinous pit and fissure sealants have been published, and to the best of our knowledge no similar studies are available for the enamel sealants used in orthodontics. Therefore, we aimed to characterize the possible adverse effects of enamel sealants, especially on the gingival epithelium.

METHODS

Organotypic cultures of the human gingival mucosa were used to assess the possible impact of six enamel sealants. Differentiation and apoptosis were determined by immunofluorescent staining. The pro-inflammatory cytokines IL-1β and IL-6 were quantified by ELISA. Cytotoxicity was measured using MTS assays in monolayer cultures of human gingival fibroblasts. Leaching of monomers from enamel sealants was quantified using HPLC.

RESULTS

The differentiation of the organotypic gingival mucosa remained unaffected. All under-cured and several standard-cured sealants (Light Bond™ Sealant, Light Bond™ Filled Sealant, and L.E.D. Pro Seal®) significantly induced apoptosis in the organotypic model. Light Bond™ Sealant, Light Bond™ Filled Sealant, and L.E.D. Pro Seal® caused a significant induction of pro-inflammatory cytokines. Reducing curing time had an influence on cytotoxicity in monolayer cultures of primary human oral cells. All resin-based sealants leached monomers.

SIGNIFICANCE

Enamel sealants might exert adverse effects on the gingival epithelium. Due to the vicinity of the enamel sealant to the gingival epithelium, and the large surface area of applied sealants, these materials should be carefully applied and sufficiently cured.

Development of an oral mucosa model to study host-microbiome interactions during wound healing

Crosstalk between the human host and its microbiota is reported to influence various diseases such as mucositis. Fundamental research in this area is however complicated by the time frame restrictions during which host-microbe interactions can be studied in vitro. The model proposed in this paper, consisting of an oral epithelium and biofilm, can be used to study microbe-host crosstalk in vitro in non-infectious conditions up to 72 h. Microbiota derived from oral swabs were cultured on an agar/mucin layer and challenged with monolayers of keratinocytes grown on plastic or collagen type I layers embedded with fibroblasts. The overall microbial biofilm composition in terms of diversity remained representative for the oral microbiome, whilst the epithelial cell morphology and viability were unaffected. Applying the model to investigate wound healing revealed a reduced healing of 30 % in the presence of microbiota, which was not caused by a reduction of the proliferation index (52.1-61.5) or a significantly increased number of apoptotic (1-1.13) or necrotic (32-30.5 %) cells. Since the model allows the separate study of the microbial and cellular exometabolome, the biofilm and epithelial characteristics after co-culturing, it is applicable for investigations within fundamental research and for the discovery and development of agents that promote wound healing.

Cytotoxicity of low-shrink composites with new monomer technology on bovine dental pulp-derived cells

Objectives:

The aim of this study was to evaluate the cytotoxicity of four low-shrink composites with new monomer technology on the bovine dental pulp-derived cells (bDPCs).

Materials and methods:

Ten samples were prepared for each group composites, and the samples were immersed in 7 mL of culture medium for 72 h at 37°C to extract residual monomer or cytotoxic substances. The culture medium containing the material extracts was sterile filtered for use on the cell cultures. Materials were incubated in medium with serum for 72 h. bDPCs were maintained in a medium with serum. A real-time cell analyzer was used to evaluate cell survival. After seeding 200 mL of the cell suspensions into the wells (10,000 cells/well) of the E-plate 96, bDPCs were treated with bioactive components released by the composite materials (1:1 and 1:2 dilutions) and monitored every 15 min for 50 h.

Results:

According to analysis of variance, there were significant differences between the cell indexes of the control and GC kalore ( p < 0.05) and Bisco Reflexions ( p < 0.001) groups for the 1:1 dilutions at 25 h. When evaluated at 50 h, 1:1 dilutions of GC Kalore ( p < 0.01) and Bisco Reflexions ( p < 0.001) reduced cell survival significantly.

Conclusions:

Although composites resins are being advanced, their cytotoxic effects have been proceeding till this time. However, two of the four materials tested significantly reduced cell viability when compared with control.

Clinical relevance:

Research should focus on the cytotoxicity of composites in addition to their mechanical properties.

The biological seal of the implant-soft tissue interface evaluated in a tissue-engineered oral mucosal model

For dental implants, it is vital that an initial soft tissue seal is achieved as this helps to stabilize and preserve the peri-implant tissues during the restorative stages following placement. The study of the implant-soft tissue interface is usually undertaken in animal models. We have developed an in vitro three-dimensional tissue-engineered oral mucosal model (3D OMM), which lends itself to the study of the implant-soft tissue interface as it has been shown that cells from the three-dimensional OMM attach onto titanium (Ti) surfaces forming a biological seal (BS). This study compares the quality of the BS achieved using the three-dimensional OMM for four types of Ti surfaces: polished, machined, sandblasted and anodized (TiUnite). The BS was evaluated quantitatively by permeability and cell attachment tests. Tritiated water (HTO) was used as the tracing agent for the permeability test. At the end of the permeability test, the Ti discs were removed from the three-dimensional OMM and an Alamar Blue assay was used for the measurement of residual cells attached to the Ti discs. The penetration of the HTO through the BS for the four types of Ti surfaces was not significantly different, and there was no significant difference in the viability of residual cells that attached to the Ti surfaces. The BS of the tissue-engineered oral mucosa around the four types of Ti surface topographies was not significantly different.

Tissue-engineered oral mucosa

Advances in tissue engineering have permitted the three-dimensional (3D) reconstruction of human oral mucosa for various in vivo and in vitro applications. Tissue-engineered oral mucosa have been further optimized in recent years for clinical applications as a suitable graft material for intra-oral and extra-oral repair and treatment of soft-tissue defects. Novel 3D in vitro models of oral diseases such as cancer, Candida, and bacterial invasion have been developed as alternatives to animal models for investigation of disease phenomena, their progression, and treatment, including evaluation of drug delivery systems. The introduction of 3D oral mucosal reconstructs has had a significant impact on the approaches to biocompatibility evaluation of dental materials and oral healthcare products as well as the study of implant-soft tissue interfaces. This review article discusses the recent advances in tissue engineering and applications of tissue-engineered human oral mucosa.

Base-metal dental casting alloy biocompatibility assessment using a human-derived three-dimensional oral mucosal model

Nickel-chromium (Ni-Cr) alloys used in fixed prosthodontics have been associated with type IV Ni-induced hypersensitivity. We hypothesised that the full-thickness human-derived oral mucosa model employed for biocompatibility testing of base-metal dental alloys would provide insights into the mechanisms of Ni-induced toxicity. Primary oral keratinocytes and gingival fibroblasts were seeded onto Alloderm™ and maintained until full thickness was achieved prior to Ni-Cr and cobalt-chromium (Co-Cr) alloy disc exposure (2-72 h). Biocompatibility assessment involved histological analyses with cell viability measurements, oxidative stress responses, inflammatory cytokine expression and cellular toxicity analyses. Inductively coupled plasma mass spectrometry analysis determined elemental ion release levels. We detected adverse morphology with significant reductions in cell viability, significant increases in oxidative stress, inflammatory cytokine expression and cellular toxicity for the Ni-Cr alloy-treated oral mucosal models compared with untreated oral mucosal models, and adverse effects were increased for the Ni-Cr alloy that leached the most Ni. Co-Cr demonstrated significantly enhanced biocompatibility compared with Ni-Cr alloy-treated oral mucosal models. The human-derived full-thickness oral mucosal model discriminated between dental alloys and provided insights into the mechanisms of Ni-induced toxicity, highlighting potential clinical relevance.

Glutathione level and genotoxicity in human oral keratinocytes exposed to TEGDMA

Triethylene-glycol dimethacrylate (TEGDMA) is an important matrix comonomer used in many resin-modified dental materials. As the monomer-polymer conversion of these biomaterials is up to 80% at best, TEGDMA may leach into the oral cavity and the pulp in millimolar concentrations. Objective of this study was to evaluate whether TEGDMA is genotoxic in immortalized human oral keratinocytes (OKF6/TERT2), for example, due to formation of oxidative DNA-lesions. OKF6-TERT2 cells were exposed to TEGDMA at concentrations ranging from 0.5 mM to 5.0 mM. Cell viability was analyzed by the fluorescent probe propidium iodide (PI), intracellular levels of reactive oxygen species (ROS) were measured by 2',7'-dichlorofluorescein diacetate, whereas glutathione concentrations (GSH) were read using monobromobimane. Genotoxicity was determined quantitatively by the alkaline comet assay. To explore the presence of oxidized bases that could be produced by oxidative events during short-term treatment with TEGDMA, the 8-hydroxyguanine DNA-glycosylase 1 (hOGG1)-modified comet assay was used. TEGDMA induced an early and rapid GSH-depletion in a concentration-dependent manner (p < 0.05). A total of 5 mM TEGDMA reduced GSH to 57.8% ± 8.6% of control values already after 30 min. There was no significant reduction in cell viability during 6 h of incubation, and only moderate ROS-formation was detected after 4 h of treatment with TEGDMA. But after 24 h, TEGDMA-concentrations of ≥2.5 mM induced a significant reduction of total cell numbers and cells' viability. Furthermore, TEGDMA caused a concentration-dependent DNA damage in OKF6/TERT2 cultures, which was not associated with a detectable formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the cellular genome. In conclusion, our results show that TEGDMA influences the intracellular redox metabolism and may exhibit pronounced cyto- and genotoxic effects in human immortalized oral keratinocytes. However, it may be concluded that oxidative stress is not causative for TEGDMA-dependent genotoxicity in these cells.

Development of a novel model for the investigation of implant-soft tissue interface

BACKGROUND

In dental implant treatment, the long-term prognosis is dependent on the biologic seal formed by the soft tissue around the implant. The in vitro investigation of the implant-soft tissue interface is usually carried out using a monolayer cell-culture model that lacks a polarized-cell phenotype. This study developed a tissue-engineered three-dimensional oral mucosal model (3D OMM) to investigate the implant-soft tissue interface.

METHODS

A 3D OMM was constructed using primary human oral keratinocytes and fibroblasts cultured on a skin-derived scaffold at an air-liquid interface. A titanium implant was inserted into the engineered oral mucosa and further cultured to establish epithelial attachment. The 3D OMM was characterized using basic histology and immunostaining for cytokeratin (CK) 10 and CK13. Histomorphometric analyses of the implant-soft tissue interface were carried out using a light-microscopy (LM) examination of ground sections and semi-thin sections as well as scanning electron microscopy (SEM).

RESULTS

Immunohistochemistry analyses suggests that the engineered oral mucosa closely resembles the normal oral mucosa. The LM and SEM examinations reveal that the 3D OMM forms an epithelial attachment on the titanium surface.

CONCLUSION

The 3D OMM provided mimicking peri-implant features as seen in an in vivo model and has the potential to be used as a relevant alternative model to assess implant-soft tissue interactions.

Biologic assessment of antiseptic mouthwashes using a three-dimensional human oral mucosal model

BACKGROUND

The biologic safety profile of oral health care products is often assumed on the basis of simplistic test models such as monolayer cell culture systems. We developed and characterized a tissue-engineered human oral mucosal model, which was proven to represent a potentially more informative and more clinically relevant alternative for the biologic assessment of mouthwashes. The aim of this study was to evaluate the biologic effects of alcohol-containing mouthwashes on an engineered human oral mucosal model.

METHODS

Three-dimensional (3D) models were engineered by the air/liquid interface culture technique using human oral fibroblasts and keratinocytes. The models were exposed to phosphate buffered saline (negative control), triethylene glycol dimethacrylate (positive control), cola, and three types of alcohol-containing mouthwashes. The biologic response was recorded using basic histology; a cell proliferation assay; 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tissue-viability assay; transmission electron microscopy (TEM) analysis; and the measurement of release of interleukin (IL)-1beta by enzyme-linked immunosorbent assay.

RESULTS

Statistical analysis showed that there was no significant difference in tissue viability among the mouthwashes, cola, and negative control groups. However, exposure to the positive control significantly reduced the tissue viability and caused severe cytotoxic epithelial damage as confirmed by histology and TEM analysis. A significant increase of IL-1beta release was observed with the positive control and, to a lesser extent, with two of the tested mouthrinses.

CONCLUSIONS

The 3D human oral mucosal model can be a suitable model for the biologic testing of mouthwashes. The alcohol-containing mouthwashes tested in this study do not cause significant cytotoxic damage and may slightly stimulate IL-1beta release.

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.