Novel coronavirus (COVID-19) and dentistry–A comprehensive review of literature

The novel coronavirus (COVID-19) pandemic has become a real challenge for healthcare providers around the world and has significantly affected the dental professionals in practices, universities and research institutions. The aim of this article was to review the available literature on the relevant aspects of dentistry in relation to COVID-19 and to discuss potential impacts of COVID-19 outbreak on clinical dentistry, dental education and research. Although the coronavirus pandemic has caused many difficulties for provision of clinical dentistry, there would be an opportunity for the dental educators to modernize their teaching approaches using novel digital concepts in teaching of clinical skills and by enhancement of online communication and learning platforms. This pandemic has also highlighted some of the major gaps in dental research and the need for new relevant knowledge to manage the current crisis and minimize the impact of such outbreaks on dentistry in the future. In conclusion, COVID-19 has had many immediate complications for dentistry of which some may have further long-term impacts on clinical practice, dental education and dental research

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

Effects of electronic cigarette liquid on monolayer and 3D tissue-engineered models of human gingival mucosa

Background. There is limited data available on potential biological effects of E-cigarettes on human oral tissues. The aim of this study was to evaluate the effects of E-cigarette liquid on the proliferation of normal and cancerous monolayer and 3D models of human oral mucosa and oral wound healing after short-term and medium-term exposure. Methods. Normal human oral fibroblasts (NOF), immortalized OKF6-TERET-2 human oral keratinocytes, and cancerous TR146 keratinocyte monolayer cultures and 3D tissue engineered oral mucosal models were exposed to different concentrations (0.1%, 1%, 5% and 10%) of E-cigarette liquid (12 mg/ml nicotine) for 1 hour daily for three days and for 7 days. Tissue viability was monitored using the PrestoBlue assay. Wounds were also produced in the middle surface of the monolayer systems vertically using a disposable cell scraper. The alterations in the cell morphology and wound healing were visualized using light microscopy and histological examination. Results. Statistical analysis showed medium-term exposure of TR146 keratinocytes to 5% and 10% E-liquid concentrations significantly increased the viability of the cancer cells compared to the negative control. Short-term exposure of NOFs to 10% E-liquid significantly reduced the cell viability, whereas medium-term exposure to all E-liquid concentrations significantly reduced the NOF cells’ viability. OKF6 cells exhibited significantly lower viability following short-term and mediumterm exposure to all E-cigarette concentrations compared to the negative control. 3D oral mucosal model containing normal oral fibroblasts and keratinocytes showed significant reduction in tissue viability after exposure to 10% E-liquid, whereas medium-term exposure resulted in significantly lower viability in 5% and 10% concentration groups compared to the negative control. There was a statistically significant difference in wound healing times of both NOF and OKF6 cells after exposure to 1%, 5% and 10% E-cigarette liquid. Conclusion. Medium-term exposure to high concentrations of the E-cigarette liquid had cytotoxic effects on normal human oral fibroblasts and OKF6 keratinocytes, but a stimulatory cumulative effect on the growth of cancerous TR146 keratinocyte cells as assessed by the PrestoBlue assay and histological evaluation of 3D oral mucosal models. In addition, E-liquid exposure prolonged the wound healing of NOF and OKF6 oral mucosa cells

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

The sealing ability of biodentine and MTA as a root sealer in the management of open apices of permanent teeth

Introduction: The root seal should provide an impermeable seal in different environments to prevent the egress of bacteria from the canal into the peri-radicular tissues and the ingress of periradicular fluid into the canal. Aim: The aim of this pilot study is to assess, by means of an in-vitro investigation using micro-CT and an optical microscope, the quality of the root apical seal achieved with either MTA® or Biodentine™ when placed in a moist environment that simulates the various clinical periapical wet environments. Materials and methods: A total of thirty-six freshly extracted human teeth were randomly allocated to 2 groups: MTA® and Biodentine™. Each group was subdivided into 3 subgroups containing 6 teeth each. Materials insertion and packing occurred while the teeth were immersed in the environmental fluids (Dry, SBF and Acid), following the standard apical divergence and instrumentation. Then 3 mm of the materials were scanned and analysed using the micro-CT scan (MCT) and an optical microscope was used to investigate the integrity of the root-apex at the surface interface seal. Results: The mean porosity percentage of MTA® and Biodentine™ in the 3 different environments; Dry: 24.08% and 45.42%, SBF: 38.28% and 56.03%, Acid: 46.78% and 50.43% subsequently. There was not any statistically significant difference between the three environments at a P-value=0.16. Conclusion: Moisture and acidic environment do not have a statistically significant effect on the sealing ability of both materials MTA® and Biodentine™. But they generate morphological changes in both materials

Development of a clinically relevant index for tooth wear treatment needs

Background: This study aimed to develop a tooth wear classification system that combined the extent, severity, and aesthetic impact of tooth wear and correlated them with the most appropriate clinical management strategy. Methods: Three hundred photographs were used to develop a classification tool that contained four levels of severity and aesthetic impact (0, 1, 2, and 3) in three age groups of patients. Ten examiners assessed and classified the cases using validated forms. Additionally, they selected the recommended treatment modality for each level. The analysis was conducted using a coefficient correlation test. Results: The coefficient correlation for the severity was 0.81, 0.82 in the upper anterior and posterior segments, and 0.85 and 0.77 for the lower anterior and posterior segments, respectively. The aesthetic impact correlation coefficient was 0.84. Examiners had agreed that minor cases required monitoring or simple restorative interventions. The moderate-level cases had variety in the recommended management options depending on the aim of treatment. The severe level cases often required rehabilitation at an increased occlusal vertical dimension. Conclusion: Within the limitations of this preliminary study, a good agreement between the examiners was found using the provided tools. More strict criteria in the classification part of the tool can further improve the examiners’ agreement

Evaluation of Osteogenic and Cementogenic Potential of Periodontal Ligament Fibroblast Spheroids Using a Three-Dimensional In Vitro

The aim of this study was to develop a three-dimensional in vitro model of periodontium to investigate the osteogenic and cementogenic differentiation potential of the periodontal ligament fibroblast (PDLF) spheroids within a dentin-membrane complex. PDLFs were cultured in both spheroid forms and monolayers and were seeded onto two biological collagen-based and synthetic membranes. Cell-membrane composites were then transferred onto dentin slices with fibroblasts facing the dentin surface and further cultured for 20 days. The composites were then processed for histology and immunohistochemical analyses for osteocalcin, Runx2, periostin, and cementum attachment protein (CAP). Both membranes seeded with PDLF-derived cells adhered to dentin and fibroblasts were present at the dentin interface and spread within both membranes. All membrane-cell-dentine composites showed positive staining for osteocalcin, Runx2, and periostin. However, CAP was not expressed by any of the tissue composites. It can be concluded that PDLFs exhibited some osteogenic potential when cultured in a 3D matrix in the presence of dentin as shown by the expression of osteocalcin. However the interaction of cells and dentin in this study was unable to stimulate cementum formation. The type of membrane did not have a significant effect upon differentiation, but fibroblast seeded-PGA membrane demonstrated better attachment to dentin than the collagen membrane

Characterization of multi-layered tissue engineered human alveolar bone and gingival mucosa

Advances in tissue engineering have permitted assembly of multi-layered composite tissue constructs for potential applications in the treatment of combined hard and soft tissue defects and as an alternative in vitro test model to animal experimental systems. The aim of this study was to develop and characterize a novel three-dimensional combined human alveolar bone and gingival mucosal model based on primary cells isolated from the oral tissues. Bone component of the model was engineered by seeding primary human alveolar osteoblasts (HAOBs) into a hydroxyapatite/tricalcium phosphate (HA/TCP) scaffold and culturing in a spinner bioreactor. The engineered bone was then laminated, using an adhesive tissue sealant, with tissue engineered gingival mucosa consisting of air/liquid interface-cultured normal human gingival keratinocytes on oral fibroblast-populated collagen gel scaffold. Histological characterization revealed a structure consisting of established epithelial, connective tissue, and bone layers closely comparable to normal oral tissue architecture. The mucosal component demonstrated a mature epithelium undergoing terminal differentiation similar to that characteristic of native buccal mucosa, as confirmed using cytokeratin 13 (CK13) and cytokeratin 14 (CK14) immunohistochemistry. Ultrastructural analysis confirmed the presence of desmosomes and hemi-desmosomes in the epithelial layer, a continuous basement membrane and newly synthesized collagen in the connective tissue layer. Quantitative PCR (qPCR) assessment of osteogenesis-related gene expression showed a higher expression of genes encoded Collagen I (COL1) and Osteonectin (ON) compared with Osteocalcin (OC), Osteopontin (OPN), and Alkaline phosphatase (ALP). ELISA quantification of COL1, ON, and OC confirmed a pattern of secretion which paralleled the model’s gene expression profile. We demonstrate here that replicating the anatomical setting between oral mucosa and the underlying alveolar bone is feasible and the developed model showed characteristics similar to those of normal tissue counterparts. This tri-layered model therefore offers great scope as an advanced, and anatomically-representative tissue-engineered alternative to animal models

3D-printed membrane for guided tissue regeneration

Three-dimensional (3D) printing is currently being intensely studied for a diverse set of applications, including the development of bioengineered tissues, as well as the production of functional biomedical materials and devices for dental and orthopedic applications. The aim of this study was to develop and characterize a 3D-printed hybrid construct that can be potentially suitable for guided tissue regeneration (GTR). For this purpose, the rheology analyses have been performed on different bioinks and a specific solution comprising 8% gelatin, 2% elastin and 0.5% sodium hyaluronate has been selected as the most suitable composition for printing a structured membrane for GTR application. Each membrane is composed of 6 layers with strand angles from the first layer to the last layer of 45, 135, 0, 90, 0 and 90°. Confirmed by 3D Laser Measuring imaging, the membrane has small pores on one side and large pores on the other to be able to accommodate different cells like osteoblasts, fibroblasts and keratinocytes on different sides. The ultimate cross-linked product is a 150 μm thick flexible and bendable membrane with easy surgical handling. Static and dynamic mechanical testing revealed static tensile modules of 1.95 ± 0.55 MPa and a dynamic tensile storage modulus of 314 ± 50 kPa. Through seeding the membranes with fibroblast and keratinocyte cells, the results of in vitro tests, including histological analysis, tissue viability examinations and DAPI staining, indicated that the membrane has desirable in vitro biocompatibility. The membrane has demonstrated the barrier function of a GTR membrane by thorough separation of the oral epithelial layer from the underlying tissues. In conclusion, we have characterized a biocompatible and bio-resorbable 3D-printed structured gelatin/elastin/sodium hyaluronate membrane with optimal biostability, mechanical strength and surgical handling characteristics in terms of suturability for potential application in GTR procedures

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 (pHzpc) ≈ 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