Dentin extracellular matrix molecules implanted into exposed pulps generate reparative dentin: a novel strategy in regenerative dentistry

Harnessing the Regenerative Potential of Purified Bovine Dental Pulp and Dentin Extracellular Matrices in a Chitosan/Alginate Hydrogel

When a tooth is diseased or damaged through caries, bioactive molecules are liberated from the pulp and dentin as part of the natural response to injury and these are key molecules for stimulating stem cell responses for tissue repair. Incorporation of these extracellular-matrix (ECM)-derived molecules into a hydrogel model can mimic in vivo conditions to enable dentin-pulp complex regeneration. Here, a chitosan/alginate (C/A) hydrogel is developed to sequester bovine ECM extracts. Human dental pulp cells (hDPCs) are cultured with these constructs and proliferation and cytotoxicity assays confirm that these C/A hydrogels are bioactive. Sequential z-axis fluorescent imaging visualizes hDPCs protruding into the hydrogel as it degraded. Alizarin red S staining shows that hDPCs cultured with the hydrogels display increased calcium-ion deposition, with dentin ECM stimulating the highest levels. Alkaline phosphatase activity is increased, as is expression of transforming growth factor-beta as demonstrated using immunocytochemistry. Directional analysis following phase contrast kinetic image capture demonstrates that both dentin and pulp ECM molecules act as chemoattractants for hDPCs. Data from this study demonstrate that purified ECM from dental pulp and dentin when delivered in a C/A hydrogel stimulates dental tissue repair processes in vitro.

Periostin Is a Candidate Regulator of the Host Microenvironment in Regeneration of Pulp and Dentin Complex and Periodontal Ligament in Transplantation with Stem Cell-Conditioned Medium

Purpose

The microenvironment is required for tissues to maintain their properties in vivo. This microenvironment encompasses the types and three-dimensional arrangement of cells forming the tissues, and their interactions with neighboring cells and extracellular matrices, as represented by the stem cell niche. Tissue regeneration depends not on the original tissue source of the transplanted cells, but on the microenvironment in which they are transplanted. We have previously reported pulp regeneration in a heterotopic root graft model by transplantation of conditioned medium alone, which suggests that host-derived cells expressing receptors for migration factors in conditioned medium migrate into the root canal and cause pulp regeneration. Regenerative medicine is needed to restore the original function of complex tissues. To achieve this, it is necessary to reproduce the changes in the microenvironment of the host tissue that accompany the regenerative response. Therefore, it is important to reproduce the microenvironment in vivo for further development of tissue regeneration therapy. Periostin is also found in the epithelial-mesenchymal junction, with expression sites that differ depending on the mineralized matrix stage, and is involved in regulation of calcification.

Methods

We investigate whether periostin contributes to microenvironmental changes in regenerated pulp tissue. Dental pulp stem cells were induced into dentin, and gene expression of DSPP, nestin, DMP1, Runx2, and periostin was analyzed by qPCR and protein expression by IHC. Similarly, gene expression was analyzed using qPCR and protein expression using IHC in regenerated dental pulp obtained by ectopic transplantation.

Results

Since these regenerated tissues were observable on the same slice, it was possible to understand changes in the microenvironment within the tissues.

Conclusions

Periostin promoted proliferation of pulp stem cells, migration in type I collagen, and calcification in regenerated pulp, which strongly suggests that periostin is a promising candidate as a factor that contributes to the microenvironment of regenerated pulp.

Development of cobalt-incorporated chitosan scaffold for regenerative potential in human dental pulp stem cells: An in vitro study

The aim of the study was to comparatively evaluate chitosan and Cobalt incorporated chitosan (CoCH) scaffold at varying concentrations in terms of their material characteristics, cytotoxicity and cell adhesion potential. In the present study, cobalt incorporated chitosan scaffolds at varying concentrations were prepared and dried. The synthesised scaffolds were characterised using XRD, FTIR, SEM-EDX and BET which revealed amorphous, porous surface of CoCH scaffolds and FTIR analysis showed the complexation confirming the chelation of cobalt with chitosan. The experimental scaffolds proved to be non-cytotoxic when compared to chitosan scaffolds on XTT analysis. Cell-seeding assay revealed enhanced adherence of hDPSCs to CoCH scaffold at 1:1 ratio in the concentration of 100 mL of 100 μmol/L cobalt chloride solution in 100mL of 2% chitosan solution, when compared to other groups. The results highlighted that 100 μmol/L concentration of cobalt chloride when incorporated in 1:1 ratio into 2 % CH solution yields a promising porous, biocompatible scaffold with enhanced cellular adhesion for dentin-pulp regeneration.

Approaches to vital pulp therapies

Tooth decay, which leads to pulpal inflammation due to the pulp's response to bacterial components and byproducts is the most common infectious disease. The main goals of clinical management are to eliminate sources of infection, to facilitate healing by regulating inflammation indental tissue, and to replace lost tissues. A variety of novel approaches from tissue engineering based on stem cells, bioactive molecules, and extracellular matrix-like scaffold structures to therapeutic applications, or a combination of all these are present in the literature. Shortcomings of existing conventional materials for pulp capping and the novel approches aiming to preserve pulp vitality highligted the need for developing new targeted dental materials. This review looks at the novel approches for vital pulp treatments after briefly addresing the conventional vital pulp treatment as well as the regenerative and self defense capabilities of the pulp. A narrative review focusing on the current and future approaches for pulp preservation was performed after surveying the relevant papers on vital pulp therapies including pulp capping, pulpotomy, and potential approaches for facilitating dentin-pulp complex regeneration in PubMed, Medline, and Scopus databases.

Mutations Causing X-Linked Amelogenesis Imperfecta Alter miRNA Formation from Amelogenin Exon4

Amelogenin plays a crucial role in tooth enamel formation, and mutations on X-chromosomal amelogenin cause X-linked amelogenesis imperfecta (AI). Amelogenin pre-messenger RNA (mRNA) is highly alternatively spliced, and during alternative splicing, exon4 is mostly skipped, leading to the formation of a microRNA (miR-exon4) that has been suggested to function in enamel and bone formation. While delivering the functional variation of amelogenin proteins, alternative splicing of exon4 is the decisive first step to producing miR-exon4. However, the factors that regulate the splicing of exon4 are not well understood. This study aimed to investigate the association between known mutations in exon4 and exon5 of X chromosome amelogenin that causes X-linked AI, the splicing of exon4, and miR-exon4 formation. Our results showed mutations in exon4 and exon5 of the amelogenin gene, including c.120T>C, c.152C>T, c.155C>G, and c.155delC, significantly affected the splicing of exon4 and subsequent miR-exon4 production. Using an amelogenin minigene transfected in HEK-293 cells, we observed increased inclusion of exon4 in amelogenin mRNA and reduced miR-exon4 production with these mutations. In silico analysis predicted that Ser/Arg-rich RNA splicing factor (SRSF) 2 and SRSF5 were the regulatory factors for exon4 and exon5 splicing, respectively. Electrophoretic mobility shift assay confirmed that SRSF2 binds to exon4 and SRSF5 binds to exon5, and mutations in each exon can alter SRSF binding. Transfection of the amelogenin minigene to LS8 ameloblastic cells suppressed expression of the known miR-exon4 direct targets, Nfia and Prkch, related to multiple pathways. Given the mutations on the minigene, the expression of Prkch has been significantly upregulated with c.155C>G and c.155delC mutations. Together, we confirmed that exon4 splicing is critical for miR-exon4 production, and mutations causing X-linked AI in exon4 and exon5 significantly affect exon4 splicing and following miR-exon4 production. The change in miR-exon4 would be an additional etiology of enamel defects seen in some X-linked AI.

Biodegradation of an injectable treated dentin matrix hydrogel as a novel pulp capping agent for dentin regeneration

BACKGROUND

A novel injectable mixture termed treated dentin matrix hydrogel (TDMH) has been introduced for restoring dentin defect in DPC. However, no study evaluated its physiological biodegradation. Therefore, the present study aimed to assess scaffold homogeneity, mechanical properties and biodegradability in vitro and in vivo and the regenerated dentin induced by TDMH as a novel pulp capping agent in human permanent teeth.

METHODS

Three TDMH discs were weighted, and dry/wet ratios were calculated in four slices from each disc to evaluate homogeneity. Hydrogel discs were also analyzed in triplicate to measure the compressive strength using a universal testing machine. The in vitro degradation behavior of hydrogel in PBS at 37 °C for 2 months was also investigated by monitoring the percent weight change. Moreover, 20 intact fully erupted premolars were included for assessment of TDMH in vivo biodegradation when used as a novel injectable pulp capping agent. The capped teeth were divided into four equal groups according to extraction interval after 2-, 8-, 12- and 16-weeks, stained with hematoxylin-eosin for histological and histomorphometric evaluation. Statistical analysis was performed using F test (ANOVA) and post hoc test (p = 0.05).

RESULTS

No statistical differences among hydrogel slices were detected with (p = 0.192) according to homogeneity. TDMH compression modulus was (30.45 ± 1.11 kPa). Hydrogel retained its shape well up to 4 weeks and after 8 weeks completely degraded. Histological analysis after 16 weeks showed a significant reduction in TDMH area and a simultaneous significant increase in the new dentin area. The mean values of TDMH were 58.8% ± 5.9 and 9.8% ± 3.3 at 2 and 16 weeks, while the new dentin occupied 9.5% ± 2.8 at 2 weeks and 82.9% ± 3.8 at 16 weeks.

CONCLUSIONS

TDMH was homogenous and exhibited significant stability and almost completely recovered after excessive compression. TDMH generally maintained their bulk geometry throughout 7 weeks. The in vivo response to TDMH was characterized by extensive degradation of the hydrogel and dentin matrix particles and abundant formation of new dentin. The degradation rate of TDMH matched the rate of new dentin formation.

TRIAL REGISTRATION

PACTR201901866476410: 30/1/2019.

Odontogenesis by Endocytosis of Peptide Embedding Bioactive Glass Composite

Limited therapeutic options are available for treating deep caries. Those materials with potential of a dual effect to remineralize hard tissue and regenerate defective dentin tissues could be used as a new strategy for deep caries treatment. However, the application of the single component remains a challenge mainly because they lack calcium and phosphorus, are easily degraded, and are difficult to retain in the intricate body fluid environment. Considering the abundant source of calcium and phosphorus as well as the delivery performance of mesoporous bioactive glass (MBG), an amelogenin-derived peptide (QP5), which has a significant role in hard tissue remineralization, was loaded to fabricate a novel composite. After the synthesis of highly ordered MBG using a sol-gel method, the QP5 peptide was loaded increasingly by its extensive porous structure and enhanced electrostatic absorption. When used in an acidic environment, the MBG/QP5 composite presented pH-responsiveness, releasing therapeutic ions and functional peptides in a sequential cascade, and eventually adjusted the pH to a neutral state. The composite was internalized by dental pulp cells through a clathrin-mediated pathway and influenced by cell membrane lipid raft regulation. It could be also transported through the macro-pinocytotic pathway. Compared to the single treatment of peptide QP5 in 48 h, the composite facilitated a higher level of retention of the intracellular peptides. The composite further promoted migration and odontogenesis of dental pulp cells, including the improved activity of alkaline phosphatase, increased formation of mineralized nodules, and upregulated expression of mineralization-related genes compared to using MBG or QP5 alone. The composite further induced the dentin-like layer in a rat pulp capping model. The results suggested that this intelligent material with pH-responsiveness provides a promising alternative treatment method for biomimetic restoration of deep caries.

Facilitating Reparative Dentin Formation Using Apigenin Local Delivery in the Exposed Pulp Cavity

Apigenin, a natural product belonging to the flavone class, affects various cell physiologies, such as cell signaling, inflammation, proliferation, migration, and protease production. In this study, apigenin was applied to mouse molar pulp after mechanically pulpal exposure to examine the detailed function of apigenin in regulating pulpal inflammation and tertiary dentin formation. In vitro cell cultivation using human dental pulp stem cells (hDPSCs) and in vivo mice model experiments were employed to examine the effect of apigenin in the pulp and dentin regeneration. In vitro cultivation of hDPSCs with apigenin treatment upregulated bone morphogenetic protein (BMP)- and osteogenesis-related signaling molecules such as BMP2, BMP4, BMP7, bone sialoprotein (BSP), runt-related transcription factor 2 (RUNX2), and osteocalcin (OCN) after 14 days. After apigenin local delivery in the mice pulpal cavity, histology and cellular physiology, such as the modulation of inflammation and differentiation, were examined using histology and immunostainings. Apigenin-treated specimens showed period-altered immunolocalization patterns of tumor necrosis factor (TNF)-α, myeloperoxidase (MPO), NESTIN, and transforming growth factor (TGF)-β1 at 3 and 5 days. Moreover, the apigenin-treated group showed a facilitated dentin-bridge formation with few irregular tubules after 42 days from pulpal cavity preparation. Micro-CT images confirmed obvious dentin-bridge structures in the apigenin-treated specimens compared with the control. Apigenin facilitated the reparative dentin formation through the modulation of inflammation and the activation of signaling regulations. Therefore, apigenin would be a potential therapeutic agent for regenerating dentin in exposed pulp caused by dental caries and traumatic injury.

Dental stem cells: The role of biomaterials and scaffolds in developing novel therapeutic strategies

Dental stem cells (DSCs) are self-renewable cells that can be obtained easily from dental tissues, and are a desirable source of autologous stem cells. The use of DSCs for stem cell transplantation therapeutic approaches is attractive due to their simple isolation, high plasticity, immunomodulatory properties, and multipotential abilities. Using appropriate scaffolds loaded with favorable biomolecules, such as growth factors, and cytokines, can improve the proliferation, differentiation, migration, and functional capacity of DSCs and can optimize the cellular morphology to build tissue constructs for specific purposes. An enormous variety of scaffolds have been used for tissue engineering with DSCs. Of these, the scaffolds that particularly mimic tissue-specific micromilieu and loaded with biomolecules favorably regulate angiogenesis, cell-matrix interactions, degradation of extracellular matrix, organized matrix formation, and the mineralization abilities of DSCs in both in vitro and in vivo conditions. DSCs represent a promising cell source for tissue engineering, especially for tooth, bone, and neural tissue restoration. The purpose of the present review is to summarize the current developments in the major scaffolding approaches as crucial guidelines for tissue engineering using DSCs and compare their effects in tissue and organ regeneration.

The effect of hyaluronic acid hydrogels on dental pulp stem cells behavior

Dental caries and trauma, particularly in childhood, are among the most prevalent teeth problems, which result in the creation of cavities and probably tooth loss. Thus, novel regenerative approaches with high efficiency and less toxicity are required. Stem cell therapy along with the implementation of scaffolds has provided excellent opportunities in the regeneration of teeth structure. Hyaluronic acid (HA) hydrogels have enticed great attention in the field of regenerative medicine. The unique chemical and structural properties of HA and its derivatives have enabled their application in tissue engineering. Several factors such as the location and type of the lesion, teeth age, the type of capping materials determine the success rate of pulp therapy. HA hydrogels have been considered as biocompatible and safe scaffold supports in human dental cell therapies.

Effect of Liquid Platelet-rich Fibrin and Platelet-rich Plasma on the Regenerative Potential of Dental Pulp Cells Cultured under Inflammatory Conditions: A Comparative Analysis

INTRODUCTION

Platelet-rich plasma (PRP) has been widely used in regenerative dentistry for over 2 decades. Nevertheless, previous studies have shown that its growth factor content is released over a short time period, and the application of anticoagulants limits its regenerative potential. Therefore, a second-generation platelet concentrate (liquid platelet-rich fibrin [PRF]) was developed without the use of anticoagulants and with shorter centrifugation times. The purpose of the present study was to compare the cellular regenerative activity of human dental pulp cells (hDPCs) when cultured with either liquid PRF or traditional PRP.

METHODS

The regenerative potential of hDPCs isolated from healthy human third molars (18-22 years, n = 5) was investigated in both normal and inflammatorylike conditions (lipopolysaccharide [LPS]) and assessed for their potential for dentin repair. The effects of liquid PRF and PRP were assessed for cellular migration, proliferation, and odontoblastic differentiation using a transwell assay, scratch assay, proliferation assay, alkaline phosphatase assay, alizarin red staining, and real-time polymerase chain reaction for genes encoding collagen type 1 alpha 1, dentin sialophosphoprotein, and dentin matrix protein 1, respectively. The effects of both platelet concentrates were also assessed for their ability to influence nuclear translocation of nuclear factor kappa B (p65) by immunofluorescence, and reverse-transcription polymerase chain reaction for genes encoding interleukin-1β, tumor necrosis factor alpha, and nuclear factor kappa B (p65) during an inflammatory condition.

RESULTS

Both PRP and liquid PRF increased the migration and proliferation of hDPCs when compared with the control group, whereas liquid PRF showed a notable significant increase in migration when compared with PRP. Furthermore, liquid PRF induced significantly greater alkaline phosphatase activity, alizarin red staining, and a messenger RNA expression of genes encoding collagen type 1 alpha 1, dentin sialophosphoprotein, and dentin matrix protein 1 when compared with PRP. When hDPCs were cultured with LPS to stimulate an inflammatory environment, a marked decrease in dentin-related repair was observed. When liquid PRF was cultured within this inflammatory environment, the reduced regenerative potential in this LPS-produced environment was significantly and markedly improved, facilitating hDPC regeneration. The messenger RNA expression of inflammatory markers including tumor necrosis factor alpha, interleukin-1β, and p65 were all significantly decreased in the presence of liquid PRF, and, furthermore, liquid PRF also inhibited the transport of p65 to the nucleus in hDPCs (suggesting a reduced inflammatory condition).

CONCLUSIONS

The findings from the present study suggest that liquid PRF promoted greater regeneration potential of hDPCs when compared with traditional PRP. Furthermore, liquid PRF also attenuated the inflammatory condition created by LPS and maintained a supportive regenerative ability for the stimulation of odontoblastic differentiation and reparative dentin in hDPCs.

Present and future of tissue engineering scaffolds for dentin-pulp complex regeneration

More than two thirds of the global population suffers from tooth decay, which results in cavities with various levels of lesion severity. Clinical interventions to treat tooth decay range from simple coronal fillings to invasive root canal treatment. Pulp capping is the only available clinical option to maintain the pulp vitality in deep lesions, but irreversible pulp inflammation and reinfection are frequent outcomes for this treatment. When affected pulp involvement is beyond repair, the dentist has to perform endodontic therapy leaving the tooth non-vital and brittle. On-going research strategies have failed to overcome the limitations of existing pulp capping materials so that healthy and progressive regeneration of the injured tissues is attained. Preserving pulp vitality is crucial for tooth homeostasis and durability, and thus, there is a critical need for clinical interventions that enable regeneration of the dentin-pulp complex to rescue millions of teeth annually. The identification and development of appropriate biomaterials for dentin-pulp scaffolds are necessary to optimize clinical approaches to regenerate these hybrid dental tissues. Likewise, a deep understanding of the interactions between the micro-environment, growth factors, and progenitor cells will provide design basis for the most fitting scaffolds for this purpose. In this review, we first introduce the long-lasting clinical dental problem of rescuing diseased tooth vitality, the limitations of current clinical therapies and interventions to restore the damaged tissues, and the need for new strategies to fully revitalize the tooth. Then, we comprehensively report on the characteristics of the main materials of naturally-derived and synthetically-engineered polymers, ceramics, and composite scaffolds as well as their use in dentin-pulp complex regeneration strategies. Finally, we present a series of innovative smart polymeric biomaterials with potential to overcome dentin-pulp complex regeneration challenges.

Treated dentin matrix paste as a novel pulp capping agent for dentin regeneration

Regenerating dentin and preserving pulp vitality are the two key targets for the treatment of dental pulp exposure. Calcium hydroxide (CH), the widely used capping agent, may induce potential tunnel defect in reparative dentin and cause inflammation or even necrosis in pulp tissues. This study aimed to produce a novel pulp capping agent with better bioactivities. Treated dentin matrix (TDM) paste (TDMP) was fabricated consisting of TDM powder and aqueous TDM extract. The chemical and biological characteristics of TDMP were investigated, and its effect on the odontogenic differentiation of dental pulp stem cells explored at gene and protein level; the therapeutic effect for pulp exposure in miniature swine was further verified. TDMP possessed better biocompatibility with neutral pH value, significantly promoted the proliferation of dental pulp stem cells, and enhanced the gene and protein expressions of alkaline phosphatase, bone sialoprotein, dentin sialoprotein etc., compared with CH. In vivo pulp capping using TDMP presented the formation of continuous reparative dentin bridge thicker and denser than CH group. Moreover, pulp tissues under TDMP capping sites showed relatively slight angiectasis than those induced by CH. TDMP could achieve both dentin regeneration and vital pulp conservation, and might serve as a feasible substitute for CH in dental pulp repair procedure. Copyright © 2017 John Wiley & Sons, Ltd.

Could the application of bioactive molecules improve vital pulp therapy success? A systematic review

This study aimed to systematically review the literature of animal studies to evaluate whether bioactive dentin proteins could improve vital pulp therapy success. The review is reported in accordance with the PRISMA Statement. Two reviewers independently conducted a literature search of seven databases: PubMed (Medline), Lilacs, IBECS, BBO, Web of Science, Scopus, and SciELO. Animal experiments in which bioactive dentin proteins were applied directly or indirectly to the pulp tissue were included. Data regarding the characteristics of the proteins evaluated, the delivery systems used and the main findings from each study were tabulated to assess the outcomes of interest (tertiary dentin formation, inflammatory response, intratubular mineralization). After screening, 32 papers were subjected to qualitative analysis. In 75% of the studies, direct pulp capping was performed. Additionally, the most studied proteins were BMP-7, TGF-β1, and extracted soluble dentin matrix proteins. In conclusion, there is evidence in the literature suggesting that bioactive dentin molecules could enhance tertiary dentin formation with fewer initial inflammatory responses in direct and indirect pulp therapy in animal models. There are potential areas to be explored for novel therapeutic approaches for dental tissue repair and regeneration with bioactive materials. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 941-956, 2017.

EDTA soluble chemical components and the conditioned medium from mobilized dental pulp stem cells contain an inductive microenvironment, promoting cell proliferation, migration, and odontoblastic differentiation

Background

The critical challenge in tissue engineering is to establish an optimal combination of stem cells, signaling morphogenetic molecules, and extracellular matrix scaffold/microenvironment. The extracellular matrix components of teeth may be reconstituted as an inductive microenvironment in an ectopic tooth transplantation bioassay. Thus, the isolation and identification of the chemical components of the inductive microenvironment in pulp/dentin regeneration will accelerate progress towards the goal of tissue engineering of the tooth.

Methods

The teeth demineralized in 0.6 M hydrochloric acid were sequentially extracted by 4.0 M guanidine hydrochloride (GdnHCl), pH 7.4, and 0.5 M ethylenediaminetetraacetic acid (EDTA), pH 7.4. The extracted teeth were transplanted into an ectopic site in severe combined immunodeficiency (SCID) mice with mobilized dental pulp stem cells (MDPSCs). The unextracted tooth served as a positive control. Furthermore, the soluble components for the inductive microenvironment, the GdnHCl extracts, or the EDTA extracts together with or without MDPSC conditioned medium (CM) were reconstituted systematically with autoclaved teeth in which the chemical components were completely inactivated and only the physical microenvironment was preserved. Their pulp/dentin regenerative potential and angiogenic potential were compared 28 days after ectopic tooth transplantation by histomorphometry and real-time RT-PCR analysis.

Results

Expression of an odontoblastic marker, enamelysin, and a pulp marker, thyrotropin-releasing hormone degrading enzyme (TRH-DE), was lower, and expression of a periodontal cell marker, anti-asporin/periodontal ligament-associated protein 1 (PLAP-1), was higher in the transplant of the EDTA-extracted teeth compared with the GdnHCl-extracted teeth. The autoclaved teeth reconstituted with the GdnHCl extracts or the EDTA extracts have weak regenerative potential and minimal angiogenic potential, and the CM significantly increased this potential. Combinatorial effects of the EDTA extracts and the CM on pulp/dentin regeneration were demonstrated in vivo, consistent with their in-vitro effects on enhanced proliferation, migration, and odontoblastic differentiation.

Conclusions

The EDTA-extracted teeth demonstrated significantly lower pulp/dentin regenerative potential compared with the GdnHCl-extracted teeth. The EDTA soluble chemical components when reconstituted with the physical structure of autoclaved teeth serve as an inductive microenvironment for pulp/dentin regeneration, promoting cell proliferation, migration, and odontoblastic differentiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0334-z) contains supplementary material, which is available to authorized users.

Wnt Acts as a Prosurvival Signal to Enhance Dentin Regeneration

Wnt proteins are lipid-modified, short-range signals that control stem cell self-renewal and tissue regeneration. We identified a population of Wnt responsive cells in the pulp cavity, characterized their function, and then created a pulp injury. The repair response was evaluated over time using molecular, cellular, and quantitative assays. We tested how healing was impacted by wound environments in which Wnt signaling was amplified. We found that a Wnt-amplified environment was associated with superior pulp healing. Although cell death was still rampant, the number of cells undergoing apoptosis was significantly reduced. This resulted in significantly better survival of injured pulp cells, and resulted in the formation of more tertiary dentin. We engineered a liposome-reconstituted form of WNT3A then tested whether this biomimetic compound could activate cells in the injured tooth pulp and stimulate dentin regeneration. Pulp cells responded to the elevated Wnt stimulus by differentiating into secretory odontoblasts. Thus, transiently amplifying the body's natural Wnt response resulted in improved pulp vitality. These data have direct clinical implications for treating dental caries, the most prevalent disease affecting mankind.

Distribution of the amelogenin protein in developing, injured and carious human teeth

Amelogenin is the major enamel matrix protein with key roles in amelogenesis. Although for many decades amelogenin was considered to be exclusively expressed by ameloblasts, more recent studies have shown that amelogenin is also expressed in other dental and no-dental cells. However, amelogenin expression in human tissues remains unclear. Here, we show that amelogenin protein is not only expressed during human embryonic development but also in pathological conditions such as carious lesions and injuries after dental cavity preparation. In developing embryonic teeth, amelogenin stage-specific expression is found in all dental epithelia cell populations but with different intensities. In the different layers of enamel matrix, waves of positive vs. negative immunostaining for amelogenin are detected suggesting that the secretion of amelogenin protein is orchestrated by a biological clock. Amelogenin is also expressed transiently in differentiating odontoblasts during predentin formation, but was absent in mature functional odontoblasts. In intact adult teeth, amelogenin was not present in dental pulp, odontoblasts, and dentin. However, in injured and carious adult human teeth amelogenin is strongly re-expressed in newly differentiated odontoblasts and is distributed in the dentinal tubuli under the lesion site. In an in vitro culture system, amelogenin is expressed preferentially in human dental pulp cells that start differentiating into odontoblast-like cells and form mineralization nodules. These data suggest that amelogenin plays important roles not only during cytodifferentiation, but also during tooth repair processes in humans.

Matricellular proteins and biomaterials

Biomaterials are essential to modern medicine as components of reconstructive implants, implantable sensors, and vehicles for localized drug delivery. Advances in biomaterials have led to progression from simply making implants that are nontoxic to making implants that are specifically designed to elicit particular functions within the host. The interaction of implants and the extracellular matrix during the foreign body response is a growing area of concern for the field of biomaterials, because it can lead to implant failure. Expression of matricellular proteins is modulated during the foreign body response and these proteins interact with biomaterials. The design of biomaterials to specifically alter the levels of matricellular proteins surrounding implants provides a new avenue for the design and fabrication of biomimetic biomaterials.

Advances in regeneration of dental pulp--a literature review

This review summarizes the biological response of dentin-pulp complexes to a variety of stimuli and responses to current treatment therapies and reviews the role of tissue engineering and its application in regenerative endodontics. An electronic search was undertaken based on keywords using Medline/PubMed, Embase, Web of Science and Ovid database resources up to March 2012 to identify appropriate articles, supplemented by a manual search using reference lists from relevant articles. Inclusion criteria were mainly based on different combinations of keywords and restricted to articles published in English language only. Biological approaches based on tissue engineering principles were found to offer the possibility of restoring natural tooth vitality, with distinct evidence that regeneration of lost dental tissues is possible. Studies to formulate an ideal restorative material with regenerative properties, however, are still under way. Further research with supporting clinical studies is required to identify the most effective and safe treatment therapy.

The chicken or the egg: PHEX, FGF23 and SIBLINGs unscrambled

The eggshell is an ancient innovation that helped the vertebrates' transition from the oceans and gain dominion over the land. Coincident with this conquest, several new eggshell and noncollagenous bone-matrix proteins (NCPs) emerged. The protein ovocleidin-116 is one of these proteins with an ancestry stretching back to the Triassic. Ovocleidin-116 is an avian homolog of Matrix Extracellular Phosphoglycoprotein (MEPE) and belongs to a group of proteins called Small Integrin-Binding Ligand Interacting Glycoproteins (SIBLINGs). The genes for these NCPs are all clustered on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of the SIBLING proteins is an Acidic Serine Aspartate-Rich MEPE (ASARM)-associated motif. The ASARM motif and the released ASARM peptide play roles in mineralization, bone turnover, mechanotransduction, phosphate regulation and energy metabolism. ASARM peptides and motifs are physiological substrates for phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), a Zn metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets. PHEX interacts with another ASARM motif containing SIBLING protein, Dentin Matrix Protein-1 (DMP1). DMP1 mutations cause bone-renal defects that are identical with the defects caused by loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both X-linked hypophosphatemic rickets and ARHR, increased fibroblast growth factor 23 (FGF23) expression occurs, and activating mutations in FGF23 cause autosomal dominant hypophosphatemic rickets (ADHR). ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. This review will discuss the evidence for a new integrative pathway involved in bone formation, bone-renal mineralization, renal phosphate homeostasis and energy metabolism in disease and health.

Regulation of bone-renal mineral and energy metabolism: the PHEX, FGF23, DMP1, MEPE ASARM pathway

More than 300 million years ago, vertebrates emerged from the vast oceans to conquer gravity and the dry land. With this transition, new adaptations occurred that included ingenious changes in reproduction, waste secretion, and bone physiology. One new innovation, the egg shell, contained an ancestral protein (ovocleidin-116) that likely first appeared with the dinosaurs and was preserved through the theropod lineage in modern birds and reptiles. Ovocleidin-116 is an avian homolog of matrix extracellular phosphoglycoprotein (MEPE) and belongs to a group of proteins called short integrin-binding ligand-interacting glycoproteins (SIBLINGs). These proteins are all localized to a defined region on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of SIBLING proteins is an acidic serine aspartate-rich MEPE-associated motif (ASARM). Recent research has shown that the ASARM motif and the released ASARM peptide have regulatory roles in mineralization (bone and teeth), phosphate regulation, vascularization, soft-tissue calcification, osteoclastogenesis, mechanotransduction, and fat energy metabolism. The MEPE ASARM motif and peptide are physiological substrates for PHEX, a zinc metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets (HYP). There is evidence that PHEX interacts with another ASARM motif containing SIBLING protein, dentin matrix protein-1 (DMP1). DMP1 mutations cause bone and renal defects that are identical with the defects caused by a loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both HYP and ARHR, increased FGF23 expression plays a major role in the disease and in autosomal dominant hypophosphatemic rickets (ADHR), FGF23 half-life is increased by activating mutations. ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. FGF23 is a member of the fibroblast growth factor (FGF) family of cytokines, which surfaced 500 million years ago with the boney fish (i.e., teleosts) that do not contain SIBLING proteins. In terrestrial vertebrates, FGF23, like SIBLING proteins, is expressed in the osteocyte. The boney fish, however, are an-osteocytic, so a physiological bone-renal link with FGF23 and the SIBLINGs was cemented when life ventured from the oceans to the land during the Triassic period, approximately 300 million years ago. This link has been revealed by recent research that indicates a competitive displacement of a PHEX-DMP1 interaction by an ASARM peptide that leads to increased FGF23 expression. This review discusses the new discoveries that reveal a novel PHEX, DMP1, MEPE, ASARM peptide, and FGF23 bone-renal pathway. This pathway impacts not only bone formation, bone-renal mineralization, and renal phosphate homeostasis but also energy metabolism. The study of this new pathway is relevant for developing therapies for several diseases: bone-teeth mineral loss disorders, renal osteodystrophy, chronic kidney disease and bone mineralization disorders (CKD-MBD), end-stage renal diseases, ectopic arterial-calcification, cardiovascular disease renal calcification, diabetes, and obesity.

Pulpal progenitors and dentin repair

Mesenchymal stem cells are present in the dental pulp. They have been shown to contribute to dentin-like tissue formation in vitro and to participate in bone repair after a mandibular lesion. However, their capacity to contribute efficiently to reparative dentin formation after pulp lesion has never been explored. After pulp exposure, we have identified proliferative cells within 3 zones. In the crown, zone I is near the cavity, and zone II corresponds to the isthmus between the mesial and central pulp. In the root, zone III, near the apex, at a distance from the inflammatory site, contains mitotic stromal cells which may represent a source of progenitor cells. Stem-cell-based strategies are promising treatments for tissue injury in dentistry. Our experiments focused on (1) location of stem cells induced to leave their quiescent state early after pulp injury and (2) implantation of pulp progenitors, a substitute for classic endodontic treatments, paving the way for pulp stem-cell-based therapies.

Pulp Healing and Regeneration

Differences between pulp repair and regeneration guide different strategic options. After mild carious dentin lesions, odontoblasts and Hoehl’s cells are implicated in the formation of reactionary dentin. Reparative dentin formation and/or pulp regeneration after partial degradation is under the control of pulp progenitors. A series of questions arise from recent researches on tissue engineering. In this series of questions, we compare the therapeutic potential of pluripotent embryonic and adult stem cells, both being used in cell-based dental therapies. Crucial questions arise on the origin of stem cells and the localization of niches of progenitors in adult teeth. Circulating progenitor cells may also be candidate for promoting pulp regeneration. Then, we focus on strategies allowing efficient progenitors recruitment. Along this line, we compare the potential of embryonic stem cells versus adult stem cells. Re-programming adult pulp cells to become induced pluripotent stem cells constitute another option. Genes, transcription factors and growth factors may be used to stimulate the differentiation cascade. Extracellular matrix molecules or some bioactive specific domains after enzymatic cleavage may also contribute to the formation of an artificial pulp and ultimately to its mineralization.

Biological approaches toward dental pulp regeneration by tissue engineering

Root canal therapy has been the predominant approach in endodontic treatment, wherein the entire pulp is cleaned out and replaced with a gutta-percha filling. However, living pulp is critical for the maintenance of tooth homeostasis and essential for tooth longevity. An ideal form of therapy, therefore, might consist of regenerative approaches in which diseased/necrotic pulp tissues are removed and replaced with regenerated pulp tissues to revitalize the teeth. Dental pulp regeneration presents one of the most challenging issues in regenerative dentistry due to the poor intrinsic ability of pulp tissues for self-healing and regrowth. With the advent of modern tissue engineering and the discovery of dental stem cells, biological therapies have paved the way to utilize stem cells, delivered or internally recruited, to generate dental pulp tissues, where growth factors and a series of dentine extracellular matrix molecules are key mediators that regulate the complex cascade of regeneration events to be faithfully fulfilled.

Can interaction of materials with the dentin-pulp complex contribute to dentin regeneration?

Understanding outcomes of the interaction between a dental material and tooth tissue is important in terms not only of biocompatibility but also of the potential for the material to modulate the response of the tissue. This interaction is influenced by many factors, including the chemistry of the material and any of its eluted components or degradation products, and the manner in which the tissue responds to these agents. Past studies of this interaction have primarily been aimed at identifying cytotoxic effects. More recently, investigations have focused on specific cellular responses, and in particular, on understanding how the materials themselves actually may contribute to regenerative processes in the tooth. Recent work has demonstrated the solubilization of proteins from dentin exposed to certain materials, such as calcium hydroxide, mineral trioxide aggregate, and acidic solutions that relate to those used in dentin bonding agents, with the subsequent modulation by these proteins of gene expression in odontoblast-like cells. This work suggests that dentin bridge formation under such materials may be stimulated through this process. Thus, there is much merit in examining both how new dental materials can be developed and how more traditional ones can be modified to preferentially stimulate regenerative processes when preferred. This review summarizes current knowledge about the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex, as well as potential future developments in this exciting field.