Dentinogenic effects of extracted dentin matrix components digested with matrix metalloproteinases

Progress in Dentin-Derived Bone Graft Materials: A New Xenogeneic Dentin-Derived Material with Retained Organic Component Allows for Broader and Easier Application

The optimal repair of rigid mineralized tissues, such as bone, in cases of fracture, surgical resection, or prosthetic placement, is a complex process often necessitating the use of bone graft materials. Autogenous bone from the patient is generally the gold standard in terms of outcomes but also has disadvantages, which have resulted in extensive research in the field of tissue engineering to develop better and more convenient alternatives. In the dental field, several initiatives have demonstrated that the dentin material derived from extracted teeth produces excellent results in terms of repairing bone defects and supporting dental implants. Dentin is acellular and thus, in contrast to autogenous bone, cannot provide osteoblasts or other cellular elements to the grafted region, but it does contain growth and differentiation factors, and has other properties that make it an impressive material for bone repair. In this review, the beneficial properties of dentin and the ways it interacts with the host bone are described in the context of bone graft materials. Autogenous tooth material has limitations, particularly in terms of the need for tooth extraction and the limited amount available, which currently restrict its use to particular dental procedures. The development of a xenograft dentin-derived material, which retains the properties of autogenous dentin, is described. Such a material could potentially enable the use of dentin-derived material more widely, particularly in orthopedic indications where its properties may be advantageous.

Resolvin D2-induced reparative dentin and pulp stem cells after pulpotomy in a rat model

Introduction

Vital pulp therapy (VPT) is performed to preserve dental pulp. However, the biocompatibility of the existing materials is of concern. Therefore, novel materials that can induce pulp healing without adverse effects need to be developed. Resolvin D2 (RvD2), one of specialized pro-resolving mediators, can resolve inflammation and promote the healing of periapical lesions. Therefore, RvD2 may be suitable for use in VPT. In the present study, we evaluated the efficacy of RvD2 against VPT using in vivo and in vitro models.

Methods

First molars of eight-week-old male Sprague-Dawley rats were used for pulpotomy. They were then divided into three treatment groups: RvD2, phosphate-buffered saline, and calcium hydroxide groups. Treatment results were assessed using radiological, histological, and immunohistochemical (GPR18, TNF-α, Ki67, VEGF, TGF-β, CD44, CD90, and TRPA1) analyses. Dental pulp-derived cells were treated with RvD2 in vitro and analyzed using cell-proliferation and cell-migration assays, real-time PCR (Gpr18, Tnf-α, Il-1β, Tgf-β, Vegf, Nanog, and Trpa1), ELISA (VEGF and TGF-β), immunocytochemistry (TRPA1), and flow cytometry (dental pulp stem cells: DPSCs).

Results

The formation of calcified tissue in the pulp was observed in the RvD2 and calcium hydroxide groups. RvD2 inhibited inflammation in dental pulp cells. RvD2 promoted cell proliferation and migration and the expression of TGF-β and VEGF in vitro and in vivo. RvD2 increased the number of DPSCs. In addition, RvD2 suppressed TRPA1 expression as a pain receptor.

Conclusion

RvD2 induced the formation of reparative dentin, anti-inflammatory effects, and decreased pain, along with the proliferation of DPSCs via the expression of VEGF and TGF-β, on the pulp surface in pulpotomy models.

The Reparative Function of MMP13 in Tertiary Reactionary Dentinogenesis after Tooth Injury

MMP13 gene expression increases up to 2000-fold in mineralizing dental pulp cells (DPCs), with research previously demonstrating that global MMP13 deletion resulted in critical alterations in the dentine phenotype, affecting dentine-tubule regularity, the odontoblast palisade, and significantly reducing the dentine volume. Global MMP13-KO and wild-type mice of a range of ages had their molar teeth injured to stimulate reactionary tertiary dentinogenesis. The response was measured qualitatively and quantitatively using histology, immunohistochemistry, micro-CT, and qRT-PCR in order to assess changes in the nature and volume of dentine deposited as well as mechanistic links. MMP13 loss affected the reactionary tertiary dentine quality and volume after cuspal injury and reduced Nestin expression in a non-exposure injury model, as well as mechanistic links between MMP13 and the Wnt-responsive gene Axin2. Acute pulpal injury and pulp exposure to oral fluids in mice teeth showed upregulation of the MMP13 in vivo, with an increase in the gene expression of Mmp8, Mmp9, and Mmp13 evident. These results indicate that MMP13 is involved in tertiary reactionary dentine formation after tooth injury in vivo, potentially acting as a key molecule in the dental pulp during dentine-pulp repair processes.

Epigenetic therapeutics in dental pulp treatment: Hopes, challenges and concerns for the development of next-generation biomaterials

This opinion-led review paper highlights the need for novel translational research in vital-pulp-treatment (VPT), but also discusses the challenges in translating evidence to clinics. Traditional dentistry is expensive, invasive and relies on an outmoded mechanical understanding of dental disease, rather than employing a biological perspective that harnesses cell activity and the regenerative-capacity. Recent research has focussed on developing minimally-invasive biologically-based 'fillings' that preserve the dental pulp; research that is shifting the paradigm from expensive high-technology dentistry, with high failure rates, to smart restorations targeted at biological processes. Current VPTs promote repair by recruiting odontoblast-like cells in a material-dependent process. Therefore, exciting opportunities exist for development of next-generation biomaterials targeted at regenerative processes in the dentin-pulp complex. This article analyses recent research using pharmacological-inhibitors to therapeutically-target histone-deacetylase (HDAC) enzymes in dental-pulp-cells (DPCs) that stimulate pro-regenerative effects with limited loss of viability. Consequently, HDAC-inhibitors have the potential to enhance biomaterial-driven tissue responses at low concentration by influencing the cellular processes with minimal side-effects, providing an opportunity to develop a topically-placed, inexpensive bio-inductive pulp-capping material. Despite positive results, clinical translation of these innovations requires enterprise to counteract regulatory obstacles, dental-industry priorities and to develop strong academic/industry partnerships. The aim of this opinion-led review paper is to discuss the potential role of therapeutically-targeting epigenetic modifications as part of a topical VPT strategy in the treatment of the damaged dental pulp, while considering the next steps, material considerations, challenges and future for the clinical development of epigenetic therapeutics or other 'smart' restorations in VPT.

Dentin Degradation: From Tissue Breakdown to Possibilities for Therapeutic Intervention

Purpose of the Review

Presently, dental materials science is driven by the search for new and improved materials that can trigger specific reactions from the affected tissue to stimulate repair or regeneration while interacting with the oral environment to promote or maintain oral health. In parallel, evidence from the past decades has challenged the exclusive role of bacteria in dentin tissue degradation in caries, questioning our understanding of caries etiopathogenesis. The goal of this review is to recapitulate the current evidence on the host and bacterial contributions to degradation, inflammation, and repair of the dentin-pulp complex in caries.

Recent Findings

Contrasting findings attribute dentin breakdown to the activity of endogenous enzymes, such as matrix metalloproteinases (MMPs) and cathepsins, while the role of bacteria and their by-products in the destruction of dentin organic matrix and pulp inflammation has been for decades supported as an incontestable paradigm. Aiming to better understand the mechanisms involved in collagen degradation by host enzymes in caries, studies have showed that these proteinases are expressed in the mature dentin (i.e., after dentin formation) and become activated by the low pH in the acidic environment resulted by bacterial metabolism in caries. However, different host sources other than dentin-bound proteinases seem to also contribute to caries progression, such as saliva and pulp. Interestingly, studies evaluating pulp responses to bacteria invasion and inflammation in caries report higher levels of MMPs and cathepsins in inflamed tissue, but also showed MMP potential to resolve inflammation and stimulate wound healing. Notably, as reported for other tissues, MMPs exert dual roles in the dentin-pulp complex in caries, participating or regulating both degradative and reparative mechanisms.

Summary

The specific roles of host and bacteria and their by-products in caries progression have yet to be clarified. The complex interactions between inflammation and repair in caries pose challenges to a clear understanding of the dentin-pulp complex responses and changes to bacteria invasion. However, it opens new venues for the development of novel therapies and dental biomaterials based on the modulation of specific mechanisms to favor tissue repair and healing.

Multivariate prognostic analysis of direct pulp capping using a bioceramic material in mature permanent teeth with carious pulp exposure: a retrospective cohort study

OBJECTIVES

On the basis of a large sample size and a long follow-up period, the objectives of this study were to evaluate the outcomes of direct pulp capping (DPC) in mature permanent teeth with carious pulp exposure using a kind of bioaggregate putty (BP) which commercially named iRoot BP Plus (Innovative Bioceramix, Inc., Vancouver, Canada) and to analyze the potential prognostic factors.

MATERIALS AND METHODS

The design of this research was retrospective regarding treatment procedures and prospective regarding the assessment of outcomes. The preoperative diagnosis of the teeth was either normal pulp or reversible pulpitis. Results were assessed based on clinical and radiographic examinations with at least 12 months of follow-up after DPC. No symptoms or signs, a positive response to electric pulp testing, a normal response to cold pulp testing and radiographs showing no abnormalities were considered to indicate success. Kaplan-Meier survival analysis was used to calculate the cumulative survival of teeth after DPC. Univariate and multivariate Cox proportional hazard regressions were used to analyze potential prognostic factors.

RESULTS

Three hundred thirty-four patients, including a total of 354 teeth, were available for the final clinical examination. The follow-up period ranged from 12 to 85 months, with an average of 27.0 ± 0.8 months. The total success rate was 85% (302/354), and the cumulative survival rates at 1, 2, 3, 4, and 5 years were 92%, 87%, 83%, 76%, and 72%, respectively. Univariate analysis indicated a significantly increased risk of failure in patients aged above 40 years and those treated by resident operators (P ≤ 0.01), with hazard ratios of 2.18 and 2.27, respectively.

CONCLUSIONS

Under appropriate indication selection and treatment procedures, long-term success is possible in mature permanent teeth with carious pulp exposure by DPC using iRoot BP Plus. Patient age and operator experience are potential prognostic factors.

CLINICAL RELEVANCE

Clinical data on iRoot BP Plus as a pulp capping medicament in mature permanent teeth with carious pulp exposure is lacking. This study indicated the efficacy of BP in DPC. Younger patient and sophisticated operator are beneficial for the outcome of DPC.

Novel Functional Peptide for Next-Generation Vital Pulp Therapy

Although vital pulp therapy should be performed by promoting the wound-healing capacity of dental pulp, existing pulp-capping materials were not developed with a focus on the pulpal repair process. In previous investigations of wound healing in dental pulp, we found that organic dentin matrix components (DMCs) were degraded by matrix metalloproteinase-20, and DMC degradation products containing protein S100A7 (S100A7) and protein S100A8 (S100A8) promoted the pulpal wound-healing process. However, the direct use of recombinant proteins as pulp-capping materials may cause clinical problems or lead to high medical costs. Thus, we hypothesized that functional peptides derived from recombinant proteins could solve the problems associated with direct use of such proteins. In this study, we identified functional peptides derived from the protein S100 family and investigated their effects on dental pulp tissue. We first performed amino acid sequence alignments of protein S100 family members from several mammalian sources, then identified candidate peptides. Next, we used a peptide array method that involved human dental pulp stem cells (hDPSCs) to evaluate the mineralization-inducing ability of each peptide. Our results supported the selection of 4 candidate functional peptides derived from proteins S100A8 and S100A9. Direct pulp-capping experiments in a rat model demonstrated that 1 S100A8-derived peptide induced greater tertiary dentin formation compared with the other peptides. To investigate the mechanism underlying this induction effect, we performed liquid chromatography-tandem mass spectrometry analysis using hDPSCs and the S100A8-derived peptide; the results suggested that this peptide promotes tertiary dentin formation by inhibiting inflammatory responses. In addition, this peptide was located in a hairpin region on the surface of S100A8 and could function by direct interaction with other molecules. In summary, this study demonstrated that a S100A8-derived functional peptide promoted wound healing in dental pulp; our findings provide insights for the development of next-generation biological vital pulp therapies.

Treated Dentin Matrix in Tissue Regeneration: Recent Advances

Tissue engineering is a new therapeutic strategy used to repair serious damage caused by trauma, a tumor or other major diseases, either for vital organs or tissues sited in the oral cavity. Scaffold materials are an indispensable part of this. As an extracellular-matrix-based bio-material, treated dentin matrixes have become promising tissue engineering scaffolds due to their unique natural structure, astonishing biological induction activity and benign bio-compatibility. Furthermore, it is important to note that besides its high bio-activity, a treated dentin matrix can also serve as a carrier and release controller for drug molecules and bio-active agents to contribute to tissue regeneration and immunomodulation processes. This paper describes the research advances of treated dentin matrixes in tissue regeneration from the aspects of its vital properties, biologically inductive abilities and application explorations. Furthermore, we present the concerning challenges of signaling mechanisms, source extension, individualized 3D printing and drug delivery system construction during our investigation into the treated dentin matrix. This paper is expected to provide a reference for further research on treated dentin matrixes in tissue regeneration and better promote the development of relevant disease treatment approaches.

Dentin Matrix Metalloproteinases: A Futuristic Approach Toward Dentin Repair and Regeneration

Matrix metalloproteinases (MMPs) have been linked to modulating healing during the production of tertiary dentin, as well as the liberation of physiologically active molecules and the control of developmental processes. Although efforts to protect dentin have mostly centered on preventing these proteases from doing their jobs, their role is actually much more intricate and crucial for dentin healing than anticipated. The role of MMPs as bioactive dentin matrix components involved in dentin production, repair, and regeneration is examined in the current review. The mechanical characteristics of dentin, especially those of reparative and reactionary dentin, and the established functions of MMPs in dentin production are given particular attention. Because they are essential parts of the dentin matrix, MMPs should be regarded as leading applicants for dentin regeneration.

Matrix Metalloproteinases in Dental and Periodontal Tissues and Their Current Inhibitors: Developmental, Degradational and Pathological Aspects

Objectives: This review article aims to describe some of the roles of Matrix metalloproteinases (MMPs) in enamel, dentine, dental caries, hybrid layer degradation, pulp and periodontal tissues, throwing light on their current inhibitors. The article addresses the potential of MMPs to serve as biomarkers with diagnostic and therapeutic value. Design: The sections of this review discuss MMPs’ involvement in developmental, remodeling, degradational and turnover aspects of dental and periodontal tissues as well as their signals in the pathogenesis, progress of different lesions and wound healing of these tissues. The literature was searched for original research articles, review articles and theses. The literature search was conducted in PubMed and MEDLINE for articles published in the last 20 years. Results: 119 published papers, two textbooks and two doctoral theses were selected for preparing the current review. Conclusions: MMPs are significant proteases, of evident contribution in dental and periapical tissue development, health and disease processes, with promising potential for use as diagnostic and prognostic disease biomarkers. Continuing understanding of their role in pathogenesis and progress of different dental, periapical and periodontal lesions, as well as in dentine-pulp wound healing could be a keystone to future diagnostic and therapeutic regimens.

The Critical Role of MMP13 in Regulating Tooth Development and Reactionary Dentinogenesis Repair Through the Wnt Signaling Pathway

Matrix-metalloproteinase-13 (MMP13) is important for bone formation and remodeling; however, its role in tooth development remains unknown. To investigate this, MMP13-knockout (Mmp13^−/−) mice were used to analyze phenotypic changes in the dentin–pulp complex, mineralization-associated marker-expression, and mechanistic interactions. Immunohistochemistry demonstrated high MMP13-expression in pulp-tissue, ameloblasts, odontoblasts, and dentin in developing WT-molars, which reduced in adults, with human-DPC cultures demonstrating a >2000-fold increase in Mmp13-expression during mineralization. Morphologically, Mmp13^−/− molars displayed critical alterations in the dentin-phenotype, affecting dentin-tubule regularity, the odontoblast-palisade and predentin-definition with significantly reduced dentin volume (∼30% incisor; 13% molar), and enamel and dentin mineral-density. Reactionary-tertiary-dentin in response to injury was reduced at Mmp13^−/− molar cusp-tips but with significantly more dystrophic pulpal mineralization in MMP13-null samples. Odontoblast differentiation-markers, nestin and DSP, reduced in expression after MMP13-loss in vivo, with reduced calcium deposition in MMP13-null DPC cultures. RNA-sequencing analysis of WT and Mmp13^−/− pulp highlighted 5,020 transcripts to have significantly >2.0-fold change, with pathway-analysis indicating downregulation of the Wnt-signaling pathway, supported by reduced in vivo expression of the Wnt-responsive gene Axin2. Mmp13 interaction with Axin2 could be partly responsible for the loss of odontoblastic activity and alteration to the tooth phenotype and volume which is evident in this study. Overall, our novel findings indicate MMP13 as critical for tooth development and mineralization processes, highlighting mechanistic interaction with the Wnt-signaling pathway.

Loss of IκBζ Drives Dentin Formation via Altered H3K4me3 Status

Enforced enrichment of the active promoter marks trimethylation of histone H3 lysine 4 (H3K4me3) and acetylation of histone H3 lysine 27 (H3K27ac) by inhibiting histone demethylases and deacetylases is positively associated with hard tissue formation through the induction of osteo/odontogenic differentiation. However, the key endogenous epigenetic modulator of odontoblasts to regulate the expression of genes coding dentin extracellular matrix (ECM) proteins has not been identified. We focused on nuclear factor (NF)-κB inhibitor ζ (IκBζ), which was originally identified as the transcriptional regulator of NF-κB and recently regarded as the NF-κB-independent epigenetic modulator, and found that IκBζ null mice exhibit a thicker dentin width and narrower pulp chamber, with aged mice having more marked phenotypes. At 6 mo of age, dentin fluorescent labeling revealed significantly accelerated dentin synthesis in the incisors of IκBζ null mice. In the molars of IκBζ null mice, marked tertiary dentin formation adjacent to the pulp horn was observed. Mechanistically, the expression of COL1A2 and COL1A1 collagen genes increased more in the odontoblast-rich fraction of IκBζ null mice than in wild type in vivo, similar to human odontoblast-like cells transfected with small interfering RNA for IκBζ compared with cells transfected with control siRNA in vitro. Furthermore, the direct binding of IκBζ to the COL1A2 promoter suppressed COL1A2 expression and the local active chromatin status marked by H3K4me3. Based on whole-genome identification of H3K4me3 enrichment, ECM and ECM organization-related gene loci were selectively activated by the knockdown of IκBζ, which consistently resulted in the upregulation of these genes. Collectively, this study suggested that IκBζ is the key negative regulator of dentin formation in odontoblasts by inhibiting dentin ECM- and ECM organization-related gene expression through an altered local chromatin status marked by H3K4me3. Therefore, IκBζ is a potential target for epigenetically improving the clinical outcomes of dentin regeneration therapies such as pulp capping.

Present status and future directions - Vital pulp treatment and pulp preservation strategies

Therapeutic strategies focussed on the pulp preservation, are important when managing vital teeth with deep caries and an exposed pulp. These vital pulp treatments (VPTs); however, are not new, with indirect and direct pulp capping procedures being described as a therapy for carious teeth for over a century. As a result of unpredictable outcomes, the traditional indications for VPT particularly when the pulp was exposed were limited to the treatment of immature teeth with incomplete root formation. Over the last 20 years, the advent of regenerative endodontics and the promotion of biologically based therapies aimed at reducing intervention have reinvigorated VPT with new waves of basic science and clinical research indicating a role for VPT not only in mature cariously affected teeth, but also in teeth with signs and symptoms indicative of irreversible pulpitis. Driven by new materials such as hydraulic calcium silicate cements, a better understanding of pulpal immunity and biology as well and improved tissue handling, VPT has been at the forefront of treatment recommendations made by global Cariology and Endodontic organizations. Care must be exercised, however, as key gaps in scientific knowledge remain alongside severe limitations in educational dissemination amongst dentists. Although research has highlighted that carious injury to the dentine–pulp complex stimulates a wide range of responses and that the interaction between infection, inflammation and repair will eventually impact on the outcome of pulpitis, our ability to accurately and objectively diagnose the true inflammatory state of the pulp remains poor. An overreliance on symptoms leaves clinicians with subjective, crude diagnostic tools by which to inform treatment planning and decision‐making, which results in large variations in the treatments offered to patients. Not only is there an urgent need to develop preoperative and intraoperative diagnostic tools, but there is also a paucity of the high‐quality comparative evidence required to answer the most important questions and justify treatment options. The aim of this review was to consider the current status of VPT and to discuss the principle problems that are hindering clinical acceptance of these techniques. Potential solutions and opportunities are offered to suggest ways that VPT may become a more consistently prescribed evidenced‐based treatment in dental practice.

Inert to bioactive - A multidimensional spectrum

OBJECTIVE

To clarify the terminology and its application in the context of materials placed in contact with tissues in living systems.

METHODS

Review the nature of both the biological and chemical reactions occurring in such contexts with a view to a classification of types of behaviour and thus types of material.

RESULTS

A range of types of behaviour was identified with clear diagnostic characteristics. Materials could thus be classified accordingly, with the possibility of more than one type of behaviour being exhibited. 'Bioactivity' was concluded to depend solely on the modulation of a natural biological process, but excluding pharmaceutical action.

SIGNIFICANCE

Clarity in the characterisation and labelling of materials and their behaviours in biological systems will benefit the interpretation of the literature, the design of experiments, and future research directions.

Extracellular Matrix in Human Craniofacial Development

The extracellular matrix (ECM) is a highly dynamic amalgamation of structural and signaling molecules whose quantitative and qualitative modifications drive the distinct programmed morphologic changes required for tissues to mature into their functional forms. The craniofacial complex houses a diverse array of tissues, including sensory organs, glands, and components of the musculoskeletal, neural, and vascular systems, alongside several other highly specialized tissues to form the most complex part of the vertebrate body. Through cell-ECM interactions, the ECM coordinates the cell movements, shape changes, differentiation, gene expression changes, and other behaviors that sculpt developing organs. In this review, we focus on several common key roles of the ECM to shape developing craniofacial organs and tissues. We summarize recent advances in our understanding of the ability of the ECM to biochemically and biomechanically orchestrate major events of craniofacial development, and we discuss how dysregulated ECM dynamics contributes to disease and disorders. As we expand our understanding of organ-specific matrix functionality and composition, we will improve our ability to rationally modify matrices to promote regeneration and/or prevent degenerative outcomes in vitro and in vivo.

Dentine matrix metalloproteinases as potential mediators of dentine regeneration

Matrix metalloproteinases (MMPs) have been implicated not only in the regulation of developmental processes but also in the release of biologically active molecules and in the modulation of repair during tertiary dentine formation. Although efforts to preserve dentine have focused on inhibiting the activity of these proteases, their function is much more complex and necessary for dentine repair than expected. The present review explores the role of MMPs as bioactive components of the dentine matrix involved in dentine formation, repair and regeneration. Special consideration is given to the mechanical properties of dentine, including those of reactionary and reparative dentine, and the known roles of MMPs in their formation. MMPs are critical components of the dentine matrix and should be considered as important candidates in dentine regeneration.

Biomineralization of Dental Tissues Treated with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is a dental biomaterial used to arrest dental caries. To better understand SDF's mechanism of action, we examined the localization of silver within the tissues of SDF-treated teeth. Carious primary teeth fixed within 2 min of SDF application (SDF-minutes, n = 3), at 3 wk after SDF application in vivo (SDF-weeks, n = 4), and at 2 y after multiple SDF applications in vivo (SDF-multiple, n = 1) were investigated in this study. Carious primary teeth without SDF application (no-SDF, n = 3) served as controls. Mineral density and structural analyses were performed via micro-X-ray computed tomography and scanning electron microscopy. Elemental analyses were performed through X-ray fluorescence microprobe and energy-dispersive X-ray spectroscopic techniques. SDF-treated teeth revealed higher X-ray-attenuated surface and subsurface regions within carious lesions, and similar regions were not present in no-SDF teeth. Regions of higher mineral density correlated with regions of silver abundance in SDF-treated teeth. The SDF penetration depth was approximated to 0.5 ± 0.02 mm and 0.6 ± 0.05 mm (mean ± SD) for SDF-minutes and SDF-weeks specimens, respectively. A higher percentage of dentin tubular occlusion by silver or calcium phosphate particles was observed in primary teeth treated with SDF-weeks as compared with SDF-minutes. Elemental analysis also revealed zinc abundance in carious lesions and around the pulp chamber. SDF-weeks teeth had significantly increased tertiary dentin than SDF-minutes and no-SDF teeth. These results suggest that SDF treatment on primary teeth affected by caries promotes pathologic biomineralization by altering their physicochemical properties, occluding dentin tubules, and increasing tertiary dentin volume. These seemingly serendipitous effects collectively contribute to the cariostatic activity of SDF.

Manifestation and Mechanisms of Abnormal Mineralization in Teeth

Tooth biomineralization is a dynamic and complicated process influenced by local and systemic factors. Abnormal mineralization in teeth occurs when factors related to physiologic mineralization are altered during tooth formation and after tooth maturation, resulting in microscopic and macroscopic manifestations. The present Review provides timely information on the mechanisms and structural alterations of different forms of pathological tooth mineralization. A comprehensive study of these alterations benefits diagnosis and biomimetic treatment of abnormal mineralization in patients.

Bioactivity—Symphony or Cacophony? A Personal View of a Tangled Field

In the pursuit of better treatments, the concept of a chemically-active material, responding to local conditions by causing reactions, or reacting to produce substances that are deemed beneficial, seems laudable. Ultimately, the goal appears to be to recruit natural biological processes such that a natural ‘repair’ is effected. This goal seems to be the reason for prefixing “bio-” to many terms with a view to advertising the desire, yet without presenting evidence that it has occurred, or indeed that it is capable of occurring, relying instead on non-biological processes to justify the claims. The dogma is such that all work where local ‘responsive’ chemistry is involved must receive the label “bioactive” to legitimize and promote. Nevertheless, the primary evidence adduced is flawed, and the claim must fail. A rethink to restore scientific sense and confidence in the endeavour is essential if real progress is to be made.

Notoginsenoside R1 functionalized gelatin hydrogels to promote reparative dentinogenesis

Pulp-capping materials are commonly adopted in the clinic to form reparative dentin and thus protect dental pulp tissues from cases of deep caries, accidentally exposed pulps or partial pulpotomy. Some traditional pulp capping materials used in the clinic include calcium hydroxide and mineral trioxide aggregates. However, there are limitations to thin restorative dentin, and a long period of time is needed to cause degenerative changes in dental pulp. In this paper, injectable colloidal gels were developed to induce the formation of reparative dentin through a simple UV method from methacrylic acid functionalized gelatin loaded with notoginsenoside R1 (Gel-MA/NGR1). The results of the physicochemical property examinations showed that the prepared Gel-MA/NGR1 hydrogel possessed an appropriate interconnected porous microarchitecture with a pore size of 10.5 micrometres and suitable mechanical properties with a modulus of 50-60 kPa, enabling cell adhesion and proliferation. The hydrogel remained hydrophilic with sustained drug release performance. In addition, Gel-MA/NGR1 significantly enhanced the odontogenetic differentiation of mouse dental papilla cells by elevating the expression levels of the dentinogenic markers ALP and OCN and extracellular matrix mineralization. In vivo stimulation was carried out by injecting the precursors into the predrilled alveolar cavity of Sprague-Dawley rats followed by immediate in situ UV crosslinking. The results showed that Gel-MA/NGR1 has a strong capacity to promote reparative dentin formation. Haematoxylin& eosin, Masson, and immunohistochemical staining (DMP-1, DSPP, OCN and RUNX2) and micro-CT were employed to illustrate the effectiveness of dentinogenesis, and the relative volumes of calcification were found to have increased ~175-fold. All of the results showed that the Gel-MA/NGR1 hydrogel promoted reparative dentin formation, which suggests that this hydrogel provides great potential as a pulp-capping material to induce dentin formation.

Effects of advanced glycation end products on dental pulp calcification

OBJECTIVE

The main aim of this study was to elucidate the effects of advanced glycation end products (AGEs) on the calcification of cultured rat dental pulp cells (RDPCs) and to investigate the crystallisation ability of glycated collagen.

MATERIALS AND METHODS

AGEs were prepared via non-enzymatic glycation of a dish coated with type I collagen using dl-glyceraldehyde. To investigate the effects of AGEs on RDPCs, we performed WST-1 and lactate dehydrogenase assays; alkaline phosphatase, Alizarin Red S and immunohistochemical staining; and real-time quantitative reverse transcription PCR. In addition, we performed crystallisation experiments on glycated collagen. All microstructures were analysed using scanning electron microscopy/energy-dispersive X-ray spectroscopy and transmission electron microscopy/diffraction pattern analysis.

RESULTS

AGEs did not affect the proliferation or differentiation of RDPCs, but enhanced the calcification rate and cytotoxicity. No major calcification-related genes or proteins were involved in these calcifications, and glycated collagen was found to exhibit a negative polarity and form calcium phosphate crystals. Cytotoxicity due to drastic changes in the concentration of pericellular ions led to dystrophic calcification, assumed to represent an aspect of diabetic pulp calcifications.

CONCLUSION

Glycated collagen-containing AGEs provide a nurturing environment for crystallisation and have a significant effect on the early calcification of RDPCs.

Immunohistochemical study of dental pulp cells with 3D collagen type I gel in demineralized dentin tubules in vivo

Dental pulp cells (DPCs) represent good candidates for the regeneration of dental tissue. This study aimed to evaluate the growth and differentiation potential of DPCs cultured inside demineralized dentin tubules in vivo. Six green fluorescent protein-transgenic rats (body weight 100 g each) and thirty-two Sprague-Dawley (SD) male rats (body weight 250 g each) were used for DPC collection and dentin tubules preparation and transplantation, respectively. Third-passage DPCs with or without collagen gels were loaded into demineralized dentin tubules. Both types of grafts were transplanted into the rectus abdominis muscles of SD rats and were harvested after 21 days. The expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), osteopontin (OPN), nestin, and dentin sialoprotein (DSP) was analyzed by immunohistochemistry. Histological analysis showed that DPCs in the collagen gel formed an osteodentin-like hard tissue matrix after 21 days. Increased positive immunoreactivity for ALP, BSP, OPN, nestin, and DSP was observed in experimental groups compared with control. Our results demonstrate that DPCs in collagen gel inside demineralized dentin tubules show increased growth and differentiation.

Equivalence of human and bovine dentin matrix molecules for dental pulp regeneration: proteomic analysis and biological function

OBJECTIVE

To compare proteomics and biological function of human dentin matrix molecules (hDMMs) and bovine dentin matrix molecules (bDMMs).

DESIGN

Dentin powder from human or bovine teeth (n = 4) was demineralized in 10% (v/v) ethylenediaminetetraacetic acid for 7 days. The extracts were dialyzed, lyophilized and proteins were characterized using liquid chromatography-tandem mass spectrometry and shotgun proteomic analysis. To study biological function, mouse-derived undifferentiated dental pulp cells (OD21) were treated with 0.01, 0.1 or 1 μg/mL of hDMMs or bDMMs and proliferation was measured after 24 hours and 48 hours using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell migration was assessed after 24 hours using a Boyden chamber. Alizarin Red S staining was used to evaluate mineral formation.

RESULTS

There were 307 proteins identified, of which 93 proteins were common to both species. Gene Ontology functional analysis demonstrated similar pattern of biological process in both species which consisted mainly of tissue development and biomineralization. hDMMs and bDMMs both enhanced cell proliferation. After 24 hours, all concentrations of bDMMs promoted cell proliferation (p ≤ 0.05), while hDMMs did not affect proliferation. After 48 hours, groups with 1μg/mL of bDMMs and 0.01μg/mL of hDMMs had increased cell proliferation compared to control (p ≤ 0.0001). All concentrations of hDMMs and bDMMs enhanced cell migration and mineralization (p ≤ 0.0001).

CONCLUSION

bDMMs has similar biological functions as hDMMs. Moreover, bDMMs stimulated cell proliferation, migration and differentiation similar to hDMMs.

Controlled release of odontogenic exosomes from a biodegradable vehicle mediates dentinogenesis as a novel biomimetic pulp capping therapy

Mineralized enamel and dentin provide protection to the dental pulp, which is vital tissue rich with cells, vasculature, and nerves in the inner tooth. Dental caries left untreated threaten exposure of the dental pulp, providing facile access for bacteria to cause severe infection both in the pulp and systemically. Dental materials which stimulate the formation of a protective dentin bridge after insult are necessary to seal the pulp chamber in an effort to maintain natural dentition and prevent pulpal infection. Dental materials to date including calcium hydroxide paste, mineral trioxide aggregate, and glass ionomer resin, are used with mixed results. Herein we exploited the cell-cell communicative properties of exosomes, extracellular vesicles derived from both mineralizing primary human dental pulp stem cells (hDPSCs) and an immortalized murine odontoblast cell line (MDPC-23), to catalyze the formation of a reactionary dentin bridge by recruiting endogenous stem cells of the dental pulp, through an easy-to-handle delivery vehicle which allows for their therapeutic controlled delivery at the pulp interface. Exosomes derived from both hDPSCs and MDPCs upregulated odontogenic gene expression and increased mineralization in vitro. We designed an amphiphilic synthetic polymeric vehicle from a triblock copolymer which encapsulates exosomes by polymeric self-assembly and maintains their biologic integrity throughout release up to 8-12 weeks. The controlled release of odontogenic exosomes resulted in a reparative dentin bridge formation, superior to glass-ionomer cement alone in vivo, in a rat molar pulpotomy model after six weeks. We have developed a platform for the encapsulation and controlled, tunable release of cell-derived exosomes, which maintains their advantageous physiologic properties reflective of the donor cells. This platform is used to modulate downstream recipient cells towards a designed dentinogenic trajectory in vitro and in vivo. Additionally, we have demonstrated the utility of an immortalized cell line to produce a high yield of exosomes with cross-species efficacy.

Performance of a Biodegradable Composite with Hydroxyapatite as a Scaffold in Pulp Tissue Repair

Vital pulp therapy is an important endodontic treatment. Strategies using growth factors and biological molecules are effective in developing pulp capping materials based on wound healing by the dentin-pulp complex. Our group developed biodegradable viscoelastic polymer materials for tissue-engineered medical devices. The polymer contents help overcome the poor fracture toughness of hydroxyapatite (HAp)-facilitated osteogenic differentiation of pulp cells. However, the composition of this novel polymer remained unclear. This study evaluated a novel polymer composite, P(CL-co-DLLA) and HAp, as a direct pulp capping carrier for biological molecules. The biocompatibility of the novel polymer composite was evaluated by determining the cytotoxicity and proliferation of human dental stem cells in vitro. The novel polymer composite with BMP-2, which reportedly induced tertiary dentin, was tested as a direct pulp capping material in a rat model. Cytotoxicity and proliferation assays revealed that the biocompatibility of the novel polymer composite was similar to that of the control. The novel polymer composite with BMP-2-induced tertiary dentin, similar to hydraulic calcium-silicate cement, in the direct pulp capping model. The BMP-2 composite upregulated wound healing-related gene expression compared to the novel polymer composite alone. Therefore, we suggest that novel polymer composites could be effective carriers for pulp capping.

Surface Pre-Reacted Glass Filler Contributes to Tertiary Dentin Formation through a Mechanism Different Than That of Hydraulic Calcium-Silicate Cement

The induction of tissue mineralization and the mechanism by which surface pre-reacted glass-ionomer (S-PRG) cement influences pulpal healing remain unclear. We evaluated S-PRG cement-induced tertiary dentin formation in vivo, and its effect on the pulp cell healing process in vitro. Induced tertiary dentin formation was evaluated with micro-computed tomography (μCT) and scanning electron microscopy (SEM). The distribution of elements from the S-PRG cement in pulpal tissue was confirmed by micro-X-ray fluorescence (μXRF). The effects of S-PRG cement on cytotoxicity, proliferation, formation of mineralized nodules, and gene expression in human dental pulp stem cells (hDPSCs) were assessed in vitro. μCT and SEM revealed that S-PRG induced tertiary dentin formation with similar characteristics to that induced by hydraulic calcium-silicate cement (ProRoot mineral trioxide aggregate (MTA)). μXRF showed Sr and Si ion transfer into pulpal tissue from S-PRG cement. Notably, S-PRG cement and MTA showed similar biocompatibility. A co-culture of hDPSCs and S-PRG discs promoted mineralized nodule formation on surrounding cells. Additionally, S-PRG cement regulated the expression of genes related to osteo/dentinogenic differentiation. MTA and S-PRG regulated gene expression in hDPSCs, but the patterns of regulation differed. S-PRG cement upregulated CXCL-12 and TGF-β1 gene expression. These findings showed that S-PRG and MTA exhibit similar effects on dental pulp through different mechanisms.

Remineralization, Regeneration, and Repair of Natural Tooth Structure: Influences on the Future of Restorative Dentistry Practice

Currently, the principal strategy for the treatment of carious defects involves cavity preparations followed by the restoration of natural tooth structure with a synthetic material of inferior biomechanical and esthetic qualities and with questionable long-term clinical reliability of the interfacial bonds. Consequently, prevention and minimally invasive dentistry are considered basic approaches for the preservation of sound tooth structure. Moreover, conventional periodontal therapies do not always ensure predictable outcomes or completely restore the integrity of the periodontal ligament complex that has been lost due to periodontitis. Much effort and comprehensive research have been undertaken to mimic the natural development and biomineralization of teeth to regenerate and repair natural hard dental tissues and restore the integrity of the periodontium. Regeneration of the dentin-pulp tissue has faced several challenges, starting with the basic concerns of clinical applicability. Recent technologies and multidisciplinary approaches in tissue engineering and nanotechnology, as well as the use of modern strategies for stem cell recruitment, synthesis of effective biodegradable scaffolds, molecular signaling, gene therapy, and 3D bioprinting, have resulted in impressive outcomes that may revolutionize the practice of restorative dentistry. This Review covers the current approaches and technologies for remineralization, regeneration, and repair of natural tooth structure.

Protein S100-A7 Derived from Digested Dentin Is a Critical Molecule for Dentin Pulp Regeneration

Dentin consists of inorganic hard tissue and organic dentin matrix components (DMCs). Various kinds of bioactive molecules are included in DMCs and some of them can be released after digestion by endogenous matrix metalloproteinases (MMPs) in the caries region. Digested DMCs induced by MMP20 have been reported to promote pulpal wound healing processes, but the released critical molecules responsible for this phenomenon are unclear. Here, we identified protein S100-A7 as a critical molecule for pulpal healing in digested DMCs by comprehensive proteomic approaches and following pulp capping experiments in rat molars. In addition, immunohistochemical results indicated the specific distribution of S100-A7 and receptor for advanced glycation end-products (RAGE) as receptor for S100-A7 in the early stage of the pulpal healing process, and following accumulation of CD146-positive stem cells in wounded pulp. Our findings indicate that protein S100-A7 released from dentin by MMP20 might play a key role in dentin pulp regeneration.

Dissecting dentine-pulp injury and wound healing responses: consequences for regenerative endodontics

A thorough understanding of the biology of the dentine-pulp complex is essential to underpin new treatment approaches and maximize clinical impact for regenerative endodontics and minimally invasive vital pulp treatment (VPT) strategies. Following traumatic and carious injury to dentine-pulp, a complex interplay between infection, inflammation and the host defence responses will occur, which is critical to tissue outcomes. Diagnostic procedures aim to inform treatment planning; however, these remain clinically subjective and have considerable limitations. As a consequence, significant effort has focussed on identification of diagnostic biomarkers, although these are also problematic due to difficulties in identifying appropriate diagnostic fluid sources and selecting reproducible biomarkers. This is further compounded by the link between inflammation and repair as many of the molecules involved exhibit significant multifunctionality. The tertiary dentine formed in response to dental injury has been purposefully termed reactionary and reparative dentine to enable focus on associated biological processes. Whilst reactionary dentine produced in response to milder injury is generated from surviving primary odontoblasts, reparative dentine, in response to more intense injury, requires the differentiation of new odontoblast-like cells derived from progenitor/stem cells recruited to the injury site. These two diverse processes result in very different outcomes in terms of the tertiary dentine produced and reflect the intensity rather than specific nature (nonexposure versus exposure) of the injury. The subsequent identification of the odontoblast-like cell phenotype remains challenging due to lack of unique molecular or morphological markers. Furthermore, the cells ultimately lining the newly deposited dentine provide only a snapshot of events. The specific source and plasticity of the progenitor cells giving rise to the odontoblast-like cell phenotype are also of significant debate. It is likely that improved characterization of tertiary dentine may better clarify the influence of cell derivation for odontoblast-like cells and their diversity. The field of regenerative endodontics offers exciting new treatment opportunities, and to maximize outcomes, we propose that the term regenerative endodontics should embrace the repair, replacement and regeneration of dentine-pulp.

Management of deep caries and the exposed pulp

Caries prevalence remains high throughout the world, with the burden of disease increasingly affecting older and socially disadvantaged groups in Western cultures. If left untreated, caries will advance through dentine stimulating pulpitis and eventually pulp infection and necrosis; however, if conservatively managed, pulpal recovery occurs even in deep carious lesions. Traditionally, deep caries management was destructive with nonselective (complete) removal of all carious dentine; however, the promotion of minimally invasive biologically based treatment strategies has been advocated for selective (partial) caries removal and a reduced risk of pulp exposure. Selective caries removal strategies can be one-visit as indirect pulp treatment or two-visit using a stepwise approach. Management strategies for the treatment of the cariously exposed pulp are also shifting with avoidance of pulpectomy and the re-emergence of vital pulp treatment (VPT) techniques such as partial and complete pulpotomy. These changes stem from an improved understanding of the pulp-dentine complex's defensive and reparative response to irritation, with harnessing the release of bioactive dentine matrix components and careful handling of the damaged tissue considered critical. Notably, the development of new pulp capping materials such as mineral trioxide aggregate, which although not an ideal material, has resulted in more predictable treatments from both a histological and a clinical perspective. Unfortunately, the changes in management are only supported by relatively weak evidence with case series, cohort studies and preliminary studies containing low patient numbers forming the bulk of the evidence. As a result, critical questions related to the superiority of one caries removal technique over another, the best pulp capping biomaterial or whether pulp exposure is a negative prognostic factor remain unanswered. There is an urgent need to promote minimally invasive treatment strategies in Operative Dentistry and Endodontology; however, the development of accurate diagnostic tools, evidence-based management strategies and education in management of the exposed pulp are critical in the future.

Effect of tissue inhibitor of metalloprotease 1 on human pulp cells in vitro and rat pulp tissue in vivo

AIM

To evaluate the dentinogenetic effects of tissue inhibitor of metalloprotease (TIMP1) on human pulp cells in vitro and rat pulp tissue in vivo.

METHODOLOGY

The effect of TIMP1 on pulp cell functions related to hard tissue formation as part of the wound healing process (i.e. biocompatibility, proliferation, differentiation and mineralized nodule formation) was evaluated in vitro and using a direct pulp capping experimental animal model in vivo. The effects of different-sized cavity preparations on hard tissue formation induced by ProRoot MTA at 2 weeks were evaluated using micro-computed tomography (micro-CT). Tertiary dentine formation quality and quantity after pulp capping using TIMP1, ProRoot MTA and phosphate-buffered saline (PBS) was also evaluated after 4 weeks using micro-CT in term of dentine volume (DV), dentine mineral density (DVD) and histological analysis. The data were evaluated by Student's t-test, one-way ANOVA with Tukey's post hoc test, the Kruskal-Wallis test or the Steel-Dwass test. P values < 0.05 were considered statistically significant.

RESULTS

TIMP1 significantly stimulated dental pulp stem cell proliferation, differentiation, and mineralization and was more biocompatible compared with the PBS control (P < 0.05). In the pulp capping model, the amount of tertiary dentine that formed was directly proportional to the size of the pulp exposure; greater amounts of tertiary dentine were observed in pulps with larger exposures after 2 weeks. 4-week samples of TIMP1 and ProRoot MTA had similar characteristics, but both sample significantly induced tertiary dentine formation beneath the cavity compared with PBS (P <  0.05) under standardized cavity preparations.

CONCLUSIONS

TIMP1 has an important role in pulpal wound healing, which makes it a potential biological pulp capping material and candidate molecule for regenerative endodontic therapy.