Novel Biological and Technological Platforms for Dental Clinical Use

A New Landscape of Human Dental Aging: Causes, Consequences, and Intervention Avenues

Aging is accompanied by physical dysfunction and physiologic degeneration that occurs over an individual's lifetime. Human teeth, like many other organs, inevitably undergo chronological aging and age-related changes throughout the lifespan, resulting in a substantial need for preventive, restorative as well as periodontal dental care. This is particularly the case for seniors at 65 years of age and those older but economically disadvantaged. Dental aging not only interferes with normal chewing and digestion, but also affects daily appearance and interpersonal communications. Further dental aging can incur the case of multiple disorders such as oral cancer, encephalitis, and other systemic diseases. In the next decades or even hundreds of years, the proportion of the elderly in the global population will continue to rise, a tendency that attracts increasing attention across multiple scientific and medical disciplines. Dental aging will bring a variety of problems to the elderly themselves and poses serious challenges to the medical profession and social system. A reduced, but functional dentition comprising 20 teeth in occlusion has been proposed as a measurement index of successful dental aging. Healthy dental aging is critical to healthy aging, from both medical and social perspectives. To date, biomedical research on the causes, processes and regulatory mechanisms of dental aging is still in its infancy. In this article, updated insights into typical manifestations, associated pathologies, preventive strategies and molecular changes of dental aging are provided, with future research directions largely projected.

Kidney capsule transplantation of chemically treated embryonic murine tooth germs

Subcapsular transplantation of developing tissues and organs into the richly vascularized murine kidney provides the necessary trophic support, thus ensuring proper completion of their growth.1,2,3 Here, we provide a protocol for kidney capsule transplantation that allows the full differentiation of embryonic teeth previously exposed to chemicals. We describe steps for dissection and in vitro culture of embryonic teeth, followed by transplantation of tooth germs. We then detail harvesting of kidneys for further analysis. For complete details on the use and execution of this protocol, please refer to Mitsiadis et al.4.

Novel trends, challenges and new perspectives for enamel repair and regeneration to treat dental defects

Dental enamel is the hardest tissue in the human body, providing external protection for the tooth against masticatory forces, temperature changes and chemical stimuli. Once enamel is damaged/altered by genetic defects, dental caries, trauma, and/or dental wear, it cannot repair itself due to the loss of enamel producing cells following the tooth eruption. The current restorative dental materials are unable to replicate physico-mechanical, esthetic features and crystal structures of the native enamel. Thus, development of alternative approaches to repair and regenerate enamel defects is much needed but remains challenging due to the structural and functional complexities involved. This review paper summarizes the clinical aspects to be taken into consideration for the development of optimal therapeutic approaches to tackle dental enamel defects. It also provides a comprehensive overview of the emerging acellular and cellular approaches proposed for enamel remineralization and regeneration. Acellular approaches aim to artificially synthesize or re-mineralize enamel, whereas cell-based strategies aim to mimic the natural process of enamel development given that epithelial cells can be stimulated to produce enamel postnatally during the adult life. The key issues and current challenges are also discussed here, along with new perspectives for future research to advance the field of regenerative dentistry.

Hypes and Hopes of Stem Cell Therapies in Dentistry: a Review

One of the most exciting advances in life science research is the development of 3D cell culture systems to obtain complex structures called organoids and spheroids. These 3D cultures closely mimic in vivo conditions, where cells can grow and interact with their surroundings. This allows us to better study the spatio-temporal dynamics of organogenesis and organ function. Furthermore, physiologically relevant organoids cultures can be used for basic research, medical research, and drug discovery. Although most of the research thus far focuses on the development of heart, liver, kidney, and brain organoids, to name a few, most recently, these structures were obtained using dental stem cells to study in vitro tooth regeneration. This review aims to present the most up-to-date research showing how dental stem cells can be grown on specific biomaterials to induce their differentiation in 3D. The possibility of combining engineering and biology principles to replicate and/or increase tissue function has been an emerging and exciting field in medicine. The use of this methodology in dentistry has already yielded many interesting results paving the way for the improvement of dental care and successful therapies.

Sinking Our Teeth in Getting Dental Stem Cells to Clinics for Bone Regeneration

Dental stem cells have been isolated from the medical waste of various dental tissues. They have been characterized by numerous markers, which are evaluated herein and differentiated into multiple cell types. They can also be used to generate cell lines and iPSCs for long-term in vitro research. Methods for utilizing these stem cells including cellular systems such as organoids or cell sheets, cell-free systems such as exosomes, and scaffold-based approaches with and without drug release concepts are reported in this review and presented with new pictures for clarification. These in vitro applications can be deployed in disease modeling and subsequent pharmaceutical research and also pave the way for tissue regeneration. The main focus herein is on the potential of dental stem cells for hard tissue regeneration, especially bone, by evaluating their potential for osteogenesis and angiogenesis, and the regulation of these two processes by growth factors and environmental stimulators. Current in vitro and in vivo publications show numerous benefits of using dental stem cells for research purposes and hard tissue regeneration. However, only a few clinical trials currently exist. The goal of this review is to pinpoint this imbalance and encourage scientists to pick up this research and proceed one step further to translation.

Role and application of stem cells in dental regeneration: A comprehensive overview

Recently, a growing attention has been observed toward potential advantages of stem cell (SC)-based therapies in regenerative treatments. Mesenchymal stem/stromal cells (MSCs) are now considered excellent candidates for tissue replacement therapies and tissue engineering. Autologous MSCs importantly contribute to the state-of-the-art clinical strategies for SC-based alveolar bone regeneration. The donor cells and immune cells play a prominent role in determining the clinical success of MSCs therapy. In line with the promising future that stem cell therapy has shown for tissue engineering applications, dental stem cells have also attracted the attention of the relevant researchers in recent years. The current literature review aims to survey the variety and extension of SC-application in tissue-regenerative dentistry. In this regard, the relevant English written literature was searched using keywords: "tissue engineering", "stem cells", "dental stem cells", and "dentistry strategies". According to the available database, SCs application has become increasingly widespread because of its accessibility, plasticity, and high proliferative ability. Among the growing recognized niches and tissues containing higher SCs, dental tissues are evidenced to be rich sources of MSCs. According to the literature, dental SCs are mostly present in the dental pulp, periodontal ligament, and dental follicle tissues. In this regard, the present review has described the recent findings on the potential of dental stem cells to be used in tissue regeneration.

Exploiting teeth as a model to study basic features of signaling pathways

Teeth constitute a classical model for the study of signaling pathways and their roles in mediating interactions between cells and tissues in organ development, homeostasis and regeneration. Rodent teeth are mostly used as experimental models. Rodent molars have proved fundamental in the study of epithelial–mesenchymal interactions and embryonic organ morphogenesis, as well as to faithfully model human diseases affecting dental tissues. The continuously growing rodent incisor is an excellent tool for the investigation of the mechanisms regulating stem cells dynamics in homeostasis and regeneration. In this review, we discuss the use of teeth as a model to investigate signaling pathways, providing an overview of the many unique experimental approaches offered by this organ. We discuss how complex networks of signaling pathways modulate the various aspects of tooth biology, and the models used to obtain this knowledge. Finally, we introduce new experimental approaches that allow the study of more complex interactions, such as the crosstalk between dental tissues, innervation and vascularization.

Dental cell type atlas reveals stem and differentiated cell types in mouse and human teeth

Understanding cell types and mechanisms of dental growth is essential for reconstruction and engineering of teeth. Therefore, we investigated cellular composition of growing and non-growing mouse and human teeth. As a result, we report an unappreciated cellular complexity of the continuously-growing mouse incisor, which suggests a coherent model of cell dynamics enabling unarrested growth. This model relies on spatially-restricted stem, progenitor and differentiated populations in the epithelial and mesenchymal compartments underlying the coordinated expansion of two major branches of pulpal cells and diverse epithelial subtypes. Further comparisons of human and mouse teeth yield both parallelisms and differences in tissue heterogeneity and highlight the specifics behind growing and non-growing modes. Despite being similar at a coarse level, mouse and human teeth reveal molecular differences and species-specific cell subtypes suggesting possible evolutionary divergence. Overall, here we provide an atlas of human and mouse teeth with a focus on growth and differentiation.

Human dental pulp stem cells exhibit enhanced properties in comparison to human bone marrow stem cells on neurites outgrowth

Mesenchymal stem cells (MSCs) have the capacity to self-renew and differentiate into specific cell types and are, therefore, key players during tissue repair and regeneration. The use of MSCs for the regeneration of tissues in vivo is increasingly being explored and already constitutes a promising alternative to existing clinical treatments. MSCs also exert paracrine and trophic functions, including the promotion of innervation that plays fundamental roles in regeneration and in restoration of the function of organs. Human bone marrow stem cells (hBMSCs) and human dental pulp stem cells (hDPSCs) have been used in studies that aimed at the repair and/or regeneration of bone or other tissues of the craniofacial complex. However, the capabilities of hBMSCs and hDPSCs to elicit the growth of specific axons in order to reestablish functional innervation of the healing tissues are not known. Here, we compared the neurotrophic effects of hDPSCs and hBMSCs on trigeminal and dorsal root ganglia neurons using microfluidic organs-on-chips devices. We found that hDPSCs express significantly higher levels of neurotrophins than hBMSCs and consequently neurons cocultured with hDPSCs develop longer axons in the microfluidic co-culture system when compared to neurons cocultured with hBMSCs. Moreover, hDPSCs elicited the formation of extensive axonal networks and established close contacts with neurons, a phenomenon not observed in presence of hBMSCs. Taken together, these findings indicate that hDPSCs constitute a superior option for restoring the functionality of damaged craniofacial tissues, as they are able to support and promote extensive trigeminal innervation.

Comparative models for human nasal infections and immunity

The human olfactory system is a mucosal surface and a major portal of entry for respiratory and neurotropic pathogens into the body. Understanding how the human nasopharynx-associated lymphoid tissue (NALT) halts the progression of pathogens into the lower respiratory tract or the central nervous system is key for developing effective cures. Although traditionally mice have been used as the gold-standard model for the study of human nasal diseases, mouse models present important caveats due to major anatomical and functional differences of the human and murine olfactory system and NALT. We summarize the NALT anatomy of different animal groups that have thus far been used to study host-pathogen interactions at the olfactory mucosa and to test nasal vaccines. The goal of this review is to highlight the strengths and limitations of each animal model of nasal immunity and to identify the areas of research that require further investigation to advance human health.