Bone marrow combined with dental bud cells promotes tooth regeneration in miniature pig model

Animal models and related techniques for dentin study

The intricate and protracted process of dentin formation has been extensively explored, thanks to the significant advancements facilitated by the use of animal models and related techniques. Despite variations in their effectiveness, taking into account factors such as sensitivity, visibility, and reliability, these models or techniques are indispensable tools for investigating the complexities of dentin formation. This article focuses on the latest advances in animal models and related technologies, shedding light on the key molecular mechanisms that are essential in dentin formation. A deeper understanding of this phenomenon enables the careful selection of appropriate animal models, considering their suitability in unraveling the underlying molecular intricacies. These insights are crucial for the advancement of clinical drugs targeting dentin-related ailments and the development of comprehensive treatment strategies throughout the duration of the disease.

Current Trends, Advances, and Challenges of Tissue Engineering-Based Approaches of Tooth Regeneration: A Review of the Literature

INTRODUCTION

Tooth loss is a significant health issue. Currently, this situation is often treated with the use of synthetic materials such as implants and prostheses. However, these treatment modalities do not fully meet patients' biological and mechanical needs and have limited longevity. Regenerative medicine focuses on the restoration of patients' natural tissues via tissue engineering techniques instead of rehabilitating with artificial appliances. Therefore, a tissue-engineered tooth regeneration strategy seems like a promising option to treat tooth loss.

OBJECTIVE

This review aims to demonstrate recent advances in tooth regeneration strategies and discoveries about underlying mechanisms and pathways of tooth formation.

RESULTS AND DISCUSSION

Whole tooth regeneration, tooth root formation, and dentin-pulp organoid generation have been achieved by using different seed cells and various materials for scaffold production. Bioactive agents are critical elements for the induction of cells into odontoblast or ameloblast lineage. Some substantial pathways enrolled in tooth development have been figured out, helping researchers design their experiments more effectively and aligned with the natural process of tooth formation.

CONCLUSION

According to current knowledge, tooth regeneration is possible in case of proper selection of stem cells, appropriate design and manufacturing of a biocompatible scaffold, and meticulous application of bioactive agents for odontogenic induction. Understanding innate odontogenesis pathways play a crucial role in accurately planning regenerative therapeutic interventions in order to reproduce teeth.

The cell re-association-based whole-tooth regeneration strategies in large animal, Sus scrofa

OBJECTIVES

Whole-tooth regeneration for tooth loss has long been a goal of dentistry. There is also an increasing demand to carry out pre-clinical in vitro and in vivo research methods in large animal model similar to human. The miniature pig has proven to be an alternative as a large mammal model owing to its many similarities to human. However, whole-tooth regeneration in large animal remains a challenge. Here, we investigated the feasibility of cell re-association-based whole-tooth regeneration in miniature pigs.

MATERIALS AND METHODS

Single cells from the forth deciduous molar germs (p4) of pig were reconstituted to bioengineered tooth bud using different treatment for in vitro culture and in vivo transplantation in mouse subrenal capsules and jawbones.

RESULTS

The bioengineered tooth bud from re-aggregated epithelial to mesenchymal single cells with and without compartmentalization restored the morphogenesis, interactions or self-sorting between 2 cells in vitro culture. The pig bioengineered tooth bud transplanted in mouse subrenal capsules and jawbones restored odontogenesis and developed into large size tooth.

CONCLUSIONS

We characterized the morphogenesis and interaction of single-tooth germ cells in vitro, and first addressed efficient long-term survival and growth through transplantation of pig bioengineered tooth bud under mouse subrenal capsules or in mouse jawbones, where it can develop into large size tooth. Our study extends the feasibility of whole-tooth regeneration in large animal.

Efficient induction of functional ameloblasts from human keratinocyte stem cells

Background

Although adult human tissue-derived epidermal stem cells are capable of differentiating into enamel-secreting ameloblasts and forming teeth with regenerated enamel when recombined with mouse dental mesenchyme that possesses odontogenic potential, the induction rate is relatively low. In addition, whether the regenerated enamel retains a running pattern of prism identical to and acquires mechanical properties comparable with human enamel indeed warrants further study.

Methods

Cultured human keratinocyte stem cells (hKSCs) were treated with fibroblast growth factor 8 (FGF8) and Sonic hedgehog (SHH) for 18 h or 36 h prior to being recombined with E13.5 mouse dental mesenchyme with implantation of FGF8 and SHH-soaked agarose beads into reconstructed chimeric tooth germs. Recombinant tooth germs were subjected to kidney capsule culture in nude mice. Harvested samples at various time points were processed for histological, immunohistochemical, TUNEL, and western blot analysis. Scanning electronic microscopy and a nanoindentation test were further employed to analyze the prism running pattern and mechanical properties of the regenerated enamel.

Results

Treatment of hKSCs with both FGF8 and SHH prior to tissue recombination greatly enhanced the rate of tooth-like structure formation to about 70%. FGF8 and SHH dramatically enhanced stemness of cultured hKSCs. Scanning electron microscopic analysis revealed the running pattern of intact prisms of regenerated enamel is similar to that of human enamel. The nanoindentation test indicated that, although much softer than human child and adult mouse enamel, mechanical properties of the regenerated enamel improved as the culture time was extended.

Conclusions

Application of FGF8 and SHH proteins in cultured hKSCs improves stemness but does not facilitate odontogenic fate of hKSCs, resulting in an enhanced efficiency of ameloblastic differentiation of hKSCs and tooth formation in human–mouse chimeric tooth germs.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0822-4) contains supplementary material, which is available to authorized users.

Induction of Rhesus Keratinocytes into Functional Ameloblasts by Mouse Embryonic Dental Mesenchyme

Fast progresses in stem cell-based tooth tissue engineering have been achieved in recent years in several animal models including the mouse, rat, dog, and pig. Moreover, various postnatal mesenchymal stem cells of dental origin have been isolated and shown capable of differentiating into odontoblasts and generating dentin. Meanwhile, human keratinocyte stem/progenitor cells, gingival epithelial cells, and even iPSC-derived epithelium have been demonstrated to be able to differentiate into functional ameloblasts. Translational medicine studies in the nonhuman primate are irreplaceable steps towards clinical application of stem cell-based tissue engineering therapy. In the present study, we first examined the epithelial stem cell markers in the rhesus skin using immunostaining. Keratinocyte stem cells were then isolated from rhesus epidermis, cultured in vitro, and characterized by epithelial stem cell markers. Epithelial sheets of these cultured keratinocytes, which were recombined with E13.5 mouse dental mesenchyme that possesses odontogenic potential in the presence of exogenous FGF8, were induced to differentiate into enamel-secreting ameloblasts. Our results demonstrate that in the presence of appropriate odontogenic signals, rhesus keratinocytes can be induced to gain odontogenic competence and are capable of participating in odontogenesis, indicating that rhesus keratinocytes are an ideal epithelial cell source for further translational medicine study of tooth tissue engineering in nonhuman primates.

Animal models for periodontal regeneration and peri-implant responses

Translation of experimental data to the clinical setting requires the safety and efficacy of such data to be confirmed in animal systems before application in humans. In dental research, the animal species used is dependent largely on the research question or on the disease model. Periodontal disease and, by analogy, peri-implant disease, are complex infections that result in a tissue-degrading inflammatory response. It is impossible to explore the complex pathogenesis of periodontitis or peri-implantitis using only reductionist in-vitro methods. Both the disease process and healing of the periodontal and peri-implant tissues can be studied in animals. Regeneration (after periodontal surgery), in response to various biologic materials with potential for tissue engineering, is a continuous process involving various types of tissue, including epithelia, connective tissues and alveolar bone. The same principles apply to peri-implant healing. Given the complexity of the biology, animal models are necessary and serve as the standard for successful translation of regenerative materials and dental implants to the clinical setting. Smaller species of animal are more convenient for disease-associated research, whereas larger animals are more appropriate for studies that target tissue healing as the anatomy of larger animals more closely resembles human dento-alveolar architecture. This review focuses on the animal models available for the study of regeneration in periodontal research and implantology; the advantages and disadvantages of each animal model; the interpretation of data acquired; and future perspectives of animal research, with a discussion of possible nonanimal alternatives. Power calculations in such studies are crucial in order to use a sample size that is large enough to generate statistically useful data, whilst, at the same time, small enough to prevent the unnecessary use of animals.

Nanomaterials for Tissue Engineering In Dentistry

The tissue engineering (TE) of dental oral tissue is facing significant changes in clinical treatments in dentistry. TE is based on a stem cell, signaling molecule, and scaffold triad that must be known and calibrated with attention to specific sectors in dentistry. This review article shows a summary of micro- and nanomorphological characteristics of dental tissues, of stem cells available in the oral region, of signaling molecules usable in TE, and of scaffolds available to guide partial or total reconstruction of hard, soft, periodontal, and bone tissues. Some scaffoldless techniques used in TE are also presented. Then actual and future roles of nanotechnologies about TE in dentistry are presented.

Tooth Organ Bioengineering: Cell Sources and Innovative Approaches

Various treatment approaches for restoring missing teeth are being utilized nowadays by using artificial dental crowns/bridges or the use of dental implants. All aforementioned restorative modalities are considered to be the conventional way of treating such cases. Although these artificial therapies are commonly used for tooth loss rehabilitation, they are still less conservative, show less biocompatibility and fail to restore the natural biological and physiological function. Adding to that, they are considered to be costly due to the risk of failure and they also require regular maintenance. Regenerative dentistry is currently considered a novel therapeutic concept with high potential for a complete recovery of the natural function and esthetics of teeth. Biological-cell based dental therapies would involve replacement of teeth by using stem cells that will ultimately grow a bioengineered tooth, thereby restoring both the biological and physiological functions of the natural tooth, and are considered to be the ultimate goal in regenerative dentistry. In this review, various stem cell-based therapeutic approaches for tooth organ bioengineering will be discussed.

Bioengineering of a human whole tooth: progress and challenge

A major challenge in stem cell-based bioengineering of an implantable human tooth is to identify appropriate sources of postnatal stem cells that are odontogenic competent as the epithelial component due to the lack of enamel epithelial cells in adult teeth. In a recent issue (2013, 2:6) of Cell Regeneration, Cai and colleagues reported that epithelial sheets derived from human induced pluripotent stem cells (iPSCs) can functionally substitute for tooth germ epithelium to regenerate tooth-like structures, providing an appealing stem cell source for future human tooth regeneration.