Immunohistochemical expression of fibrillin-1 and fibrillin-2 during tooth development

Semaphorin-RhoA signaling regulates HERS maintenance by acting against TGF-β-induced EMT

BACKGROUND AND OBJECTIVES

Hertwig's epithelial root sheath (HERS) plays a role in root dentin formation. It produces the epithelial rests of Malassez (ERM) for the induction of periodontal tissue development during root formation. Although ERM is thought to be caused by epithelial-mesenchymal transition (EMT), the mechanism by which HERS is maintained as epithelium is unknown. Here, we aimed to elucidate the molecular mechanisms regulating the relationship between HERS maintenance and ERM development.

METHODS

To understand the relationship between HERS and ERM development during root formation, we observed the developing molar root using cytokeratin14 (CK14) Cre/tdTomato mice via stereomicroscopy. The relationship between semaphorin and transforming growth factor (TGF) signaling in the maintenance of HERS and ERM development was examined using CK14cre/R26-tdTomato mice and a HERS cell line.

RESULTS

tdTomato-positive cells were observed on HERS and the migrating cells from HERS. The migrating cells showed reduced E-cadherin expression. In contrast, HERS cells expressed semaphorin receptors and active RhoA. Semaphorin signaling was associated with RhoA activation and cell-cell adhesion, while TGF-β induced decreased E-cadherin and active RhoA expression, and consequently enhanced cell migration.

CONCLUSION

HERS induces root formation by controlling epithelial maintenance and EMT through the opposing effects of semaphorin and TGF-β signaling.

Fibrillin protein, a candidate for creating a suitable scaffold in PDL regeneration while avoiding ankylosis

The tooth is stabilized by fiber-rich tissue called the periodontal ligament (PDL). The narrow space of the PDL does not calcify in the physiological state even thought it exists between two calcified tissues, namely, the cementum of the root and alveolar bone. Two situations that require PDL regeneration are periodontitis and dental trauma. Periodontitis induces the loss of PDL and alveolar bone due to inflammation related to infection. Conversely, in PDLs damaged by dental trauma, accelerating bone formation as an overreaction of the healing process is induced, thereby inducing dentoalveolar ankylosis at the tooth root surface. PDL regeneration following dental trauma must therefore be considered separately from periodontitis. Therefore, PDL regeneration in dental trauma must be considered separately from periodontitis. This review focuses on the components involved in avoiding dentoalveolar ankylosis, including oxytalan fibers, aggregated microfibrils, epithelial cell rests of Malassez (ERM), and TGF-β signaling. During root development, oxytalan fibers produced by PDL cells work in collaboration with the epithelial components in the PDL (e.g., Hertwig's root sheath [HERS] and ERM). We herein describe the functions of oxytalan fibers, ERM, and TGF-β signals which are involved in the avoidance of bone formation.

A Review of In Vivo and Clinical Studies Applying Scaffolds and Cell Sheet Technology for Periodontal Ligament Regeneration

Different approaches to develop engineered scaffolds for periodontal tissues regeneration have been proposed. In this review, innovations in stem cell technology and scaffolds engineering focused primarily on Periodontal Ligament (PDL) regeneration are discussed and analyzed based on results from pre-clinical in vivo studies and clinical trials. Most of those developments include the use of polymeric materials with different patterning and surface nanotopography and printing of complex and sophisticated multiphasic composite scaffolds with different compartments to accomodate for the different periodontal tissues' architecture. Despite the increased effort in producing these scaffolds and their undoubtable efficiency to guide and support tissue regeneration, appropriate source of cells is also needed to provide new tissue formation and various biological and mechanochemical cues from the Extraccellular Matrix (ECM) to provide biophysical stimuli for cell growth and differentiation. Cell sheet engineering is a novel promising technique that allows obtaining cells in a sheet format while preserving ECM components. The right combination of those factors has not been discovered yet and efforts are still needed to ameliorate regenerative outcomes towards the functional organisation of the developed tissues.

Expression of proteins of elastic fibers and collagen type I in orthodontically rotated teeth in rats

INTRODUCTION

The aims of this study were to investigate the expression of proteins of elastic fibers and collagen type I in the supra-alveolar structure of orthodontically rotated teeth in rats and to elucidate whether circumferential supracrestal fiberotomy diminishes relapse.

METHODS

The rats' maxillary left first molars were rotated by couple of force. Specimens were divided into groups according to different orthodontic procedures. A1-3 and B1-3 were blank control groups and operation control groups. Group C underwent rotation only, and group D was treated with rotation and retention. Groups E and F were treated with rotation, retention, and release of retention; additionally, circumferential supracrestal fiberotomy was performed in group F before the release of retention. The animals were killed, and the jaws were processed for histologic evaluation using the immunohistochemical method to evaluate the protein expressions of elastin, fibrillin-1, fibrillin-2, and collagen type I in supra-alveolar structures (around and below the gingival sulcus) between the maxillary left first and second molars. The degree and percentage of relapse were measured by a series of impressions.

RESULTS

The degree and percentage of relapse in group F were much lower than those in group E (P <0.05). Collagen type I was increased in group C (P <0.05) and at normal levels in groups D, E, and F. Elastin below the gingival sulcus and fibrillin-1 showed the same patterns of expression and were consistently elevated in groups C, D, E, and F (P <0.05). No positive staining for elastin was found around the gingival sulcus in any specimen. The difference in the expression of fibrillin-2 between the experimental groups (C, D, E, and F) and their matching control groups was not statistically significant (P >0.05).

CONCLUSIONS

Circumferential supracrestal fiberotomy can alleviate the relapse of rotated teeth. Collagen fibers of supra-alveolar structures might contribute to relapse in a short time, whereas elastic fibers may be the reason that rotated teeth relapse to their original positions after retention.

Bioengineered Tooth Buds Exhibit Features of Natural Tooth Buds

Tooth loss is a significant health issue currently affecting millions of people worldwide. Artificial dental implants, the current gold standard tooth replacement therapy, do not exhibit many properties of natural teeth and can be associated with complications leading to implant failure. Here we propose bioengineered tooth buds as a superior alternative tooth replacement therapy. We describe improved methods to create highly cellularized bioengineered tooth bud constructs that formed hallmark features that resemble natural tooth buds such as the dental epithelial stem cell niche, enamel knot signaling centers, transient amplifying cells, and mineralized dental tissue formation. These constructs were composed of postnatal dental cells encapsulated within a hydrogel material that were implanted subcutaneously into immunocompromised rats. To our knowledge, this is the first report describing the use of postnatal dental cells to create bioengineered tooth buds that exhibit evidence of these features of natural tooth development. We propose future bioengineered tooth buds as a promising, clinically relevant tooth replacement therapy.