Dentine as a bioactive extracellular matrix

Treatment of Pulpectomized Teeth With Trypsin Prior to Transplantation of Mobilized Dental Pulp Stem Cells Enhances Pulp Regeneration in Aged Dogs

There is an age-dependent decline of pulp regeneration, due to the decline of migration, proliferation, and cell survival of resident stem cells. Trypsin is a proteolytic enzyme clinically used for tissue repair. Here, we investigated the effects of trypsin pretreatment of pulpectomized teeth prior to cell transplantation on pulp regeneration in aged dogs. The amount of regenerated pulp was significantly higher in trypsin-pretreated teeth compared to untreated teeth. Trypsin pretreatment increased the number of cells attached to the dentinal wall that differentiated into odontoblast-like cells. The trypsin receptor, PAR2, was higher in vitro expression in the periodontal ligament cells (PDLCs) from aged dogs compared to those from young. The direct effects of trypsin on aged PDLCs were increased expression of genes related to immunomodulation, cell survival, and extracellular matrix degradation. To examine the indirect effects on microenvironment, highly extracted proteins from aged cementum were identified by proteomic analyses. Western blotting demonstrated that significantly increased fibronectin was released by the trypsin treatment of aged cementum compared to young cementum. The aged cementum extract (CE) and dentin extract (DE) by trypsin treatment increased angiogenesis, neurite extension and migration activities as elicited by fibronectin. Furthermore, the DE significantly increased the mRNA expression of immunomodulatory factors and pulp markers in the aged DPSCs. These results demonstrated the effects of trypsin on the microenvironment in addition to the resident cells including PDLCs in the aged teeth. In conclusion, the potential utility of trypsin pretreatment to stimulate pulp regeneration in aged teeth and the underlying mechanisms were demonstrated.

Periostin and matrix stiffness combine to regulate myofibroblast differentiation and fibronectin synthesis during palatal healing

Although the matricellular protein periostin is prominently upregulated in skin and gingival healing, it plays contrasting roles in myofibroblast differentiation and matrix synthesis respectively. Palatal healing is associated with scarring that can alter or restrict maxilla growth, but the expression pattern and contribution of periostin in palatal healing is unknown. Using periostin-knockout (Postn^-/-) and wild-type (WT) mice, the contribution of periostin to palatal healing was investigated through 1.5 mm full-thickness excisional wounds in the hard palate. In WT mice, periostin was upregulated 6 days post-wounding, with mRNA levels peaking at day 12. Genetic deletion of periostin significantly reduced wound closure rates compared to WT mice. Absence of periostin reduced mRNA levels of pivotal genes in wound repair, including α-SMA/acta2, fibronectin and βigh3. Recruitment of fibroblasts and inflammatory cells, as visualized by immunofluorescent staining for fibroblast specific factor-1, vimentin, and macrophages markers Arginase-1 and iNOS was also impaired in Postn^-/-, but not WT mice. Palatal fibroblasts isolated from the hard palate of mice were cultured on collagen gels and prefabricated silicon substrates with varying stiffness. Postn^-/- fibroblasts showed a significantly reduced ability to contract a collagen gel, which was rescued by the exogenous addition of recombinant periostin. As the stiffness increased, Postn^-/- fibroblasts increasingly differentiated into myofibroblasts, but not to the same degree as the WT. Pharmacological inhibition of Rac rescued the deficient myofibroblastic phenotype of Postn^-/- cells. Low stiffness substrates (0.2 kPa) resulted in upregulation of fibronectin in WT cells, an effect which was significantly reduced in Postn^-/- cells. Quantification of immunostaining for vinculin and integrinβ1 adhesions revealed that Periostin is required for the formation of focal and fibrillar adhesions in mPFBs. Our results suggest that periostin modulates myofibroblast differentiation and contraction via integrinβ1/RhoA pathway, and fibronectin synthesis in an ECM stiffness dependent manner in palatal healing.

Cytotoxicity of contemporary resin-based dental materials in contact with dentin

In this study, the cytotoxicity of different combinations of contemporary resin-based restoratives (adhesives, composites, luting agents) against human keratinocytes (HaCaT) was evaluated under two conditions, whether materials were applied to dentin or not. Adhesives (3-step etch-and-rinse/3ER: OptiBond FL; 2-step self-etch/2SE Clearfil SE Bond; Single Bond Universal/UNI), composites (conventional composite resin/CCR: Filtek Z350XT; flowable/FCR: Filtek Z350XT Flow; self-adhesive composite resin/SACR: Dyad Flow), and luting agents (conventional luting agent/CLA: Variolink-II; self-adhesive luting agent/SLA: RelyXU200) were combined according to their clinical use. Eluates from polymerized specimens applied to dentin were placed in contact with cells grown for 1 and 7 d. The controls were defined by cells without material contact. Cell viability was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] assay. C=C conversion was investigated using Fourier-transform infrared spectroscopy. After 1 d of incubation, when dentin was not present, 2SE yielded the highest cell viability, whereas 3ER, UNI, and SACR showed higher cell viability in the presence of dentin. After 7 d, when dentin was absent, 2SE and CLA achieved significantly higher cell viability. The presence of dentin resulted in a drastically higher cell viability for all materials, except 2SE and CLA. UNI had the lowest C=C conversion. The presence of dentin was a significant factor, which resulted in higher cell viability than what was seen for the material specimens per se. All materials resulted in a lower viability of HaCaT than what was seen under the no-material control conditions, with effects mainly limited to the first 24 h.

The Effects of Intracanal Irrigants and Medicaments on Dental-Derived Stem Cells Fate in Regenerative Endodontics: An update

Regenerative endodontics is a biologically based treatment designed for immature permanent teeth with necrotic pulp to replace dentin and root structures, as well as dental pulp cells. This procedure has become a part of novel modality in endodontics therapeutic manner, and it is considered as an alternative to apexification. In the last decade, numerous case reports, which describe this procedure, have been published. This therapeutic approach succeeded due to its lower financial cost and ease of performance. Although the clinical protocol of this procedure is not standardized and the effects of irrigants and medicaments on dental stem cells fate remain somewhat ambiguous, however when successful, it is an improvement of endodontics treatment protocols which leads to continued root development, increased dentinal wall thickness, and apical closure of immature teeth. To ensure a successful regenerative procedure, it is essential to investigate the appropriate disinfection protocols and the use of biocompatible molecules in order to control the release of growth factors and the differentiation of stem cells. This is the first review in the literature to summarize the present knowledge regarding the effect of intracanal irrigants and medicaments on the dental derived stem cells fate in regenerative endodontic procedures.

Effect of parathyroid hormone-related protein on odontogenic differentiation in human dental pulp cells

BACKGROUND

Parathyroid hormone-related protein (PTHrP) plays an important role in many physiological processes, including bone regeneration. The function of PTHrP is similar to PTH. It promotes osteogenic differentiation in MC3T3-E1 cells. The aim of this study was to investigate whether PTHrP might have odontogenic differentiation ability in human dental pulp cells (hDPCs).

METHODS

The viability of hDPCs after stimulation with PTHrP was measured. Real-time polymerase chain reaction and Western blot analysis were performed to evaluate the expression levels of odontogenic markers and activation of protein kinase B (PKB/AKT), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). To evaluate mineralized nodule formation, alkaline phosphatase (ALP) staining and alizarin red S staining were performed.

RESULTS

PTHrP promoted odontogenic differentiation as evidenced by the formation of mineralized nodules, the induction of ALP activity, and the upregulation of odontogenic markers (dentin sialophosphoprotein and dentin matrix protein-1). The phosphorylation of AKT, ERK, JNK, and p38 was increased by PTHrP. However, an AKT inhibitor (LY294002), an ERK inhibitor (U0126), a JNK inhibitor (SP600125), and a p38 inhibitor (SB203580) inhibited the increase of mineralization induced by PTHrP.

CONCLUSION

The present study revealed that PTHrP could promote odontogenic differentiation and mineralization through activating the AKT, ERK, JNK, and p38 signaling pathways. These results provide novel insights into the odontogenic action of PTHrP.

Transforming Growth Factor Beta 1 Distribution and Content in the Root Dentin of Young Mature and Immature Human Premolars

INTRODUCTION

Transforming growth factor beta 1 (TGF-β1) is a key morphogen in regenerative endodontics; yet, its location within the hard tissue phase of dentin and its availability in mature roots have not been fully elucidated.

METHODS

Young mature (n = 8) and immature (n = 11) roots from sound premolars were obtained from 13 orthodontic patients aged 17 ± 1 and 12 ± 1 years, respectively. Roots were cleaned of organic remnants in 5% sodium hypochlorite. The width of the minor foramen was measured using a digital microscope. TGF-β1 distribution was assessed in 3 roots per group by immunostaining combined with confocal laser scanning microscopy. The root dentin of the remaining 13 roots was powdered and decalcified in 17% EDTA to determine the overall levels of hard tissue-embedded TGF-β1 by enzyme-linked immunosorbent assay. Data were compared between groups using the Student t test (α = .05).

RESULTS

The minor foramen was 168 ± 49 μm versus 557 ± 295 μm in mature compared with immature roots (P < .05). TGF-β1 was highly stainable toward the pulp space in both groups. It was clearly associated with peritubular dentin and apparently absent in nontubular outer dentin. TGF-β1 content was 115 ± 31 pg and 74 ± 35 pg/100 mg mature versus immature root dentin, respectively (P > .05).

CONCLUSIONS

TGF-β1 is deposited into the peritubular dentin. It should be possible to release this molecule in regenerative endodontic procedures from young mature roots as well as immature roots.

Expression of BSP-GFPtpz Transgene during Osteogenesis and Reparative Dentinogenesis

Bone sialoprotein (BSP) is a member of the SIBLING family with essential roles in skeletogenesis. In the developing teeth, although the expression and function of BSP in the formation of acellular cementum and periodontal attachment are well documented, there are uncertainties regarding the expression and function of BSP by odontoblasts and dentin. Reporter mice are valuable animal models for biological research, providing a gene expression readout that can contribute to cellular characterization within the context of a developmental process. In the present study, we examined the expression of a BSP-GFPtpz reporter mouse line during odontoblast differentiation, reparative dentinogenesis, and bone. In the developing teeth, BSP-GFPtpz was expressed at high levels in cementoblasts but not in odontoblasts or dentin. In bones, the transgene was highly expressed in osteoblasts at an early stage of differentiation. Interestingly, despite its lack of expression in odontoblasts and dental pulp during tooth development, the BSP-GFPtpz transgene was detected during in vitro mineralization of primary pulp cultures and during reparative dentinogenesis following pulp exposures. Importantly, under these experimental contexts, the expression of BSP-GFPtpz was still exclusive to DSPP-Cerulean, an odontoblast-specific reporter gene. This suggests that the combinatorial use of BSP-GFPtpz and DSPP-Cerulean can be a valuable experimental tool to distinguish osteogenic from dentinogenic cells, thereby providing an avenue to investigate mechanisms that distinctly regulate the lineage progression of progenitors into odontoblasts versus osteoblasts.

The effect of three different pulp capping cements on mineralization of dental pulp stem cells

This study evaluated the osteogenic differentiation of human dental pulp stem cells in response to substances released by the pulp capping agents, Biodentine (BD), mineral trioxide aggregate (MTA) and two-paste calcium hydroxide cement (CHC), along with their physicochemical characteristics. The dimensional stability test showed that of the materials studied, only BD met the standards recommended by the International Organization for Standardization (ISO) for pulp capping materials and thus can be used safely. In the chemical tests, BD was the most stable material. In the Alizarin red S test, BD formed the higher amount of mineralized nodules in the mineralizing medium and also formed mineralized nodules in a non-mineralizing medium. BD releases substances that can significantly induce formation of the human dental pulp stem cell-mineralized extracellular matrix, with physicochemical characteristics that are more conducive to pulp repair than those of MTA and CHC.

Molecular Mechanisms of Dentine-Pulp Complex Response Induced by Microbiome of Deep Caries

Deep caries progress is associated with tertiary dentin formation and additional reversible or irreversible dental pulp inflammation. It seems that some particular signs of pain in irreversible pulpitis are associated to a particular caries microflora. Streptococcus species, Parvimonas micra and Dialister invisus are prevailing in cases of throbbing pain while Streptococcus mutans is incriminated in sensitivity to vertical percussion of tooth. Continuous pain is thought to be the clinical outcome of Lactobacillus implication. A better understanding of molecular signals and mechanisms induced by microbiome of deep caries that orchestrate the modulation of dental pulp complex response toward tertiary dentinogenesis or pulp inflammation it is supposed to improve diagnosis and conservative therapies of vital pulp.

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.

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.

Differential Protein Expression in Human Dental Pulp: Comparison of Healthy, Inflamed, and Traumatic Pulp

Trauma or injury to the dental pulp causes inflammation. This study compared the proteome of healthy pulp with inflamed pulp and traumatic pulp to identify the differentially expressed proteins in the diseased state. Five participants were grouped based on the pulpal status of the teeth: healthy, inflamed, or traumatic pulp. Pulp was extirpated and stored immediately in liquid nitrogen. Pulp tissues were subjected to 2-dimensional gel electrophoresis, and spot selection was performed. The selected spots were analyzed using liquid chromatography-tandem mass spectrometry and identified by correlating mass spectra to the proteomic databases. Fifteen spots showed increased expression in the inflamed and traumatic pulp. Annexin V, type II keratin, and hemoglobin levels were increased two-fold in the inflamed and traumatic pulp group and annexin V, mutant beta-actin, and hemoglobin were increased by ten-fold in the inflamed or traumatic pulp group, compared to levels in the healthy pulp group. Annexin V constituted two out of fifteen protein spots, and seemed to play a critical role in inhibiting inflammation and promoting the immune reaction. Further studies on this protein concerning its role in pulp repair are necessary to elucidate the underlying mechanisms.

Acellular biomaterial strategies for endodontic regeneration

Dental decay is treated by removing infected dental tissues such as dentine and restoring the tooth with a material. However, the vast majority of these materials have been designed to be mechanically robust and bioinert, whereas the potential regenerative properties of a biomaterial have not been considered. In endodontics for example, materials are used to seal the pulp cavity to avoid bacterial colonisation of the tooth and prevent further infection. While these treatments are effective in the short term, many of these materials have not been designed to interface with the pulp tissue in a biocompatible manner and are often cytotoxic. This can lead to less favourable long-term outcomes such as devitalisation of the tooth via root-canal therapy or extraction of the tooth. Clinical outcomes could be improved if regenerative approaches were followed whereby the biology of the tooth is engineered for repair and regeneration often with the support of a biomaterial. Within these, acellular or cell homing approaches are particularly interesting, as some regulatory hurdles associated with cellular therapies could be circumvented which may aid their clinical translation. In this review, we highlight progress in regenerative dentistry and focus on exciting developments using acellular biomaterials for regenerating dental tissues.

Neurotrophic Proteins in Dentin and Their Effect on Trigeminal Sensory Neurons

INTRODUCTION

A plethora of bioactive molecules present during tooth formation become sequestered in the mineralized dentin matrix and can be released into the pulp tissue after demineralization from carious lesions. However, neurotrophic factors are differentially expressed and secreted during various stages of odontogenesis. Thus, the aims of this study were (1) to investigate their presence and relative abundance in crown and root dentin and (2) to evaluate the bioactivity of dentin-derived proteins on neuronal cells.

METHODS

Dentin matrix proteins (DMPs) were isolated from matched roots and crowns of extracted healthy human third molars. The total protein amount as well as the concentration of growth factors and neurotrophic proteins were quantified. The impact on neuritogenesis was determined with mouse trigeminal neurons in vitro and by a hydrogel implant model in vivo. Transient receptor potential cation channel subfamily V member 1 (TRPV1) sensitization of DMP-conditioned neurons was evaluated by single-cell calcium imaging.

RESULTS

The relative concentration of neurotrophic molecules revealed that nerve growth factor is the most abundant neurotrophin with 3-fold increased expression in radicular dentin. Similarly, brain-derived neurotrophic factor and neurotrophin 3 are more abundant in radicular than coronal dentin. Conversely, glial cell line-derived neurotrophic factor is more abundant in coronal dentin, whereas neurotrophin 4 is equally distributed. Dentin matrix proteins promoted neurite outgrowth in vitro and axonal targeting in vivo, with a greater effect observed by radicular dentin extracts. Furthermore, DMPs sensitized TRPV1 responses in mouse trigeminal neurons with greater activity seen with extracts from root dentin.

CONCLUSIONS

Neurotrophic factors are differentially distributed between coronal and radicular dentin with different effects of dentin-derived proteins on axonal growth and targeting as well as the sensitization of TRPV1. Thus, extracellular proteins from the dentin matrix are likely involved in neurogenic responses to caries and could be exploited in clinical regenerative endodontics to promote reinnervation and enhance tissue regeneration.

Shotgun Proteomics of Human Dentin with Different Prefractionation Methods

Human dentin is not only a composite material of a collagenous matrix and mineral to provide strength and elasticity to teeth, but also a precious reservoir full of bioactive proteins. They are released after demineralization caused by bacterial acids in carious lesions, by decalcifying irrigants or dental materials and they modulate tissue responses in the underlying dental pulp. This work describes a first-time analysis of the proteome of human dentin using a shotgun proteomic approach that combines three different protein fractionation methods. Dentin matrix proteins were extracted by EDTA and separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), OFFGEL isoelectric focusing (IEF) or strong cation exchange chromatography (SCX). Liquid chromatography tandem mass spectrometry (LC-MS/MS) identified 813 human proteins with high confidence, however, isoelectric focusing turned out to be the most beneficial prefractionation method. All Proteins were categorized based on the PANTHER system and representation analysis revealed 31 classes and subclasses to be overrepresented. The acquired knowledge provides a comprehensive insight into the number of proteins in human dentin as well as their physiological and pathological functions. Thus, the data presented paves the way to the analysis of specific functions of dentin matrix proteins in vivo and their potential in tissue engineering approaches to regenerate dental pulp.

Expression of Neurotrophic Factors in Human Dentin and Their Regulation of Trigeminal Neurite Outgrowth

INTRODUCTION

Neurotrophic factors play a significant role in the innervation of the pulp-dentin complex during and after organogenesis. There have been numerous bioactive molecules identified in the dentin extracellular matrix; however, the expression of neurotrophic factors in the dentin matrix and their biological activity are largely unknown. The purpose of this study was to characterize the relative expression of neurotrophic factors in human dentin matrix proteins (DMPs) and their effect on neurite outgrowth of trigeminal (TG) neurons.

METHODS

Dentin was powdered in liquid nitrogen from noncarious human third molar teeth. DMPs were solubilized through an EDTA extraction method, dialyzed, and lyophilized until use. The relative expression of nerve growth factor, brain-derived neurotrophic factor, glial cell-line derived neurotrophic factor, neurotrophin 3, and neurotrophin 4/5 was determined by the enzyme-linked immunosorbent assay. Rat TG neurons were cultured and exposed to different concentrations of DMPs (1-10⁵ ng/mL) or vehicle, and a quantitative neurite outgrowth assay was performed.

RESULTS

Human DMPs contained all of the tested neurotrophic factors, with glial cell-line derived neurotrophic factor and neurotrophin 4/5 found at the highest levels. DMPs were able to promote the neurite outgrowth of rat TG neurons at an optimum concentration of 10-10² ng/mL, whereas the effect was partially inhibited at higher concentrations (>10³ ng/mL).

CONCLUSIONS

The human dentin extracellular matrix is a rich reservoir for neurotrophic factors that are key components for neuronal homeostasis, differentiation, and regeneration. These data suggest that neurotrophins in DMPs could play an important role as signaling molecules for the innervation of the pulp-dentin complex during the processes of tooth formation, repair, and regeneration.

Effect of Dentin Matrix Components on the Mineralization of Human Mesenchymal Stromal Cells

IMPACT STATEMENT

This research has been conducted with the aim to contribute to the development of treatment modalities for the reconstruction of lost/damaged mineralized tissues. Currently, determining the most appropriate stromal cell population and signaling cues stands at the core of developing effective treatments. We provide new insights into the effect of innate inductive cues found in human dentin matrix components, on the osteogenic differentiation of various human stromal cell types. The effects of dentin extracellular matrix components on umbilical cord mesenchymal stromal cells have not been investigated before. The findings of this study could underpin translational research based on the development of techniques for mineralized tissue engineering and will be of great interest for the readership of Tissue Engineering Part A.

Dentinogenic effects of extracted dentin matrix components digested with matrix metalloproteinases

Dentin is primarily composed of hydroxyapatite crystals within a rich organic matrix. The organic matrix comprises collagenous structural components, within which a variety of bioactive molecules are sequestered. During caries progression, dentin is degraded by acids and enzymes derived from various sources, which can release bioactive molecules with potential reparative activity towards the dentin-pulp complex. While these molecules’ repair activities in other tissues are already known, their biological effects are unclear in relation to degradation events during disease in the dentin-pulp complex. This study was undertaken to investigate the effects of dentin matrix components (DMCs) that are partially digested by matrix metalloproteinases (MMPs) in vitro and in vivo during wound healing of the dentin-pulp complex. DMCs were initially isolated from healthy dentin and treated with recombinant MMPs. Subsequently, their effects on the behaviour of primary pulp cells were investigated in vitro and in vivo. Digested DMCs modulated a range of pulp cell functions in vitro. In addition, DMCs partially digested with MMP-20 stimulated tertiary dentin formation in vivo, which exhibited a more regular tubular structure than that induced by treatment with other MMPs. Our results indicate that MMP-20 may be especially effective in stimulating wound healing of the dentin-pulp complex.

Zn-containing polymer nanogels promote cervical dentin remineralization

OBJECTIVE

Nanogels designing for effective treatment of eroded cervical dentin lesions.

MATERIALS AND METHODS

Polymethylmetacrylate-based nanoparticles (NPs) were doxycycline (D), calcium, or zinc loaded. They were applied on eroded cervical dentin. Treated surfaces were characterized morphologically by atomic force and scanning electron microscopy, mechanically probed by a nanoindenter to test nanohardness and Young's modulus, and chemically analyzed by Raman spectroscopy at 24 h and 7 days of storage. Data were submitted to ANOVA and Student-Newman-Keuls multiple comparisons tests.

RESULTS

Dentin treated with Zn-NPs attained the highest nanomechanical properties, mineralization, and crystallinity among groups. Nanoroughness was lower in Zn-treated surfaces in comparison to dentin treated with undoped gels. Dentin treated with Ca-NPs created the minimal calcification at the surface and showed the lowest Young's modulus at peritubular dentin. Intertubular dentin appeared remineralized. Dentinal tubules were empty in samples treated with D-NPs, partially occluded in cervical dentin treated with undoped NPs and Ca-NPs, and mineral covered when specimens were treated with Zn-NPs.

CONCLUSIONS

Zn-loaded NPs permit functional remineralization of eroded cervical dentin. Based on the tested nanomechanical and chemical properties, Zn-based nanogels are suitable for dentin remineralization.

CLINICAL RELEVANCE

The ability of zinc-loaded nanogels to promote dentin mineralization may offer new strategies for regeneration of eroded cervical dentin and effective treatment of dentin hypersensitivity.

Liposomal Delivery of Demineralized Dentin Matrix for Dental Tissue Regeneration

Current dental restorations have short longevity, and consequently, there is a need for novel tissue engineering strategies that aim to regenerate the dentin-pulp complex. Dentin matrix contains a myriad of bioactive growth factors and extracellular matrix proteins associated with the recruitment, proliferation, and differentiation of dental pulp progenitor cells. In this study, we show that demineralized dentin matrix (DDM), from noncarious dentine, can be encapsulated into liposomes for delivery to dental tissue to promote regeneration. Liposomes were formulated to encapsulate 0-100 μg/mL DDM, lysed with Triton X, and used in vascular endothelial growth factor (VEGF) and transforming growth factor-β1 (TGF-β1) enzyme-linked immunosorbent assays to quantify release. The encapsulation efficiencies were calculated to be 25.9% and 28.8% (VEGF/TGF-β1) for 50 μg/mL DDM liposomes and 39% and 146.7% (VEGF/TGF-β1) for 100 μg/mL DDM liposomes. All liposome formulations had no cytotoxic effects on a dental pulp stem cell (DPSC) clone, as shown by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium bromide), Caspase 3/7 assays, and cell counts. The ability of the liposomes to stimulate DPSC chemotactic recruitment was tested by Boyden chamber chemotaxis assays. Unloaded liposomes alone stimulated significant progenitor cell recruitment, while DDM-loaded liposomes further promoted chemotactic recruitment in a dose-dependent manner. DDM liposomes promoted the upregulation of "osteodentin" markers osteocalcin and RUNX2 (Runt-related transcription factor 2) in DPSCs after 9 days of treatment, determined by real-time quantitative PCR. Furthermore, Alizarin Red S staining showed that unloaded liposomes alone induced biomineralization of DPSCs, and DDM liposomes further increased the amount of mineralization observed. DDM liposomes were more effective than free DDM (10 μg/mL) at activating recruitment and osteogenic differentiation of DPSC, which are key events in the endogenous repair of the dentin-pulp complex. The study has highlighted the therapeutic potential of bioactive DDM liposomes in activating dental tissue repair in vitro, suggesting that liposomal delivery from biomaterials could be a valuable tool for reparative dentistry and hard-tissue engineering applications.

Regenerative endodontics: a comprehensive review

The European Society of Endodontology and the American Association for Endodontists have released position statements and clinical considerations for regenerative endodontics. There is increasing literature on this field since the initial reports of Iwaya et al. (Dental Traumatology, 17, 2001, 185) and Banchs & Trope (Journal of Endodontics, 30, 2004, 196). Endogenous stem cells from an induced periapical bleeding and scaffolds using blood clot, platelet rich plasma or platelet-rich fibrin have been utilized in regenerative endodontics. This approach has been described as a 'paradigm shift' and considered the first treatment option for immature teeth with pulp necrosis. There are three treatment outcomes of regenerative endodontics; (i) resolution of clinical signs and symptoms; (ii) further root maturation; and (iii) return of neurogenesis. It is known that results are variable for these objectives, and true regeneration of the pulp/dentine complex is not achieved. Repair derived primarily from the periodontal and osseous tissues has been shown histologically. It is hoped that with the concept of tissue engineering, namely stem cells, scaffolds and signalling molecules, that true pulp regeneration is an achievable goal. This review discusses current knowledge as well as future directions for regenerative endodontics. Patient-centred outcomes such as tooth discolouration and possibly more appointments with the potential for adverse effects needs to be discussed with patients and parents. Based on the classification of Cvek (Endodontics and Dental Traumatology, 8, 1992, 45), it is proposed that regenerative endodontics should be considered for teeth with incomplete root formation although teeth with near or complete root formation may be more suited for conventional endodontic therapy or MTA barrier techniques. However, much is still not known about clinical and biological aspects of regenerative endodontics.

Bone morphogenetic protein 7 promotes odontogenic differentiation of dental pulp stem cells in vitro

AIMS

in vitro effects of bone morphogenetic protein 7 (BMP-7) on proliferation and differentiation of dental pulp stem cells (DPSCs) have not been investigated, nor has an appropriate dose been established.

MAIN METHODS

Human DPSCs obtained from healthy volunteers were cultured with BMP-7 at 25, 50, and 100 ng/ml. Cell viability was measured by Cell Counting Kit-8 assay. Expression profiles of selected odontogenic differentiation-related markers in DPSCs were evaluated using quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunocytochemistry, and western blot analysis. Mineralization of DPSCs was evaluated by alizarin red staining. The Smad5 signaling pathway was examined by qRT-PCR and western blot analysis.

KEY FINDINGS

Diminished cell viability was found in DPSCs induced with 25, 50, and 100 ng/ml of BMP-7 for 7 days, showing a dose-response effect (P-trend = 0.03). DSPP, OCN, DMP-1, and RUNX2 were upregulated by BMP-7 induction after 7 and 14 days, especially at 50 and 100 ng/ml (P < 0.05). Immunocytochemical staining revealed strong expression of DSPP, DMP-1 and ALP in DPSCs induced by BMP-7, whereas null or weak expression in untreated cells. Western blot analysis confirmed over-expression of DSPP in cells induced by BMP-7. Alizarin red staining confirmed formation of mineralized nodules 4 weeks after BMP-7 induction. BMP-7 treated cells showed dose-dependently increased expression of BMPR1A, Smad5, and p-Smad5.

SIGNIFICANCE

Our data indicated that BMP-7 at 50 ng/ml and 100 ng/ml was capable to induce DPSCs toward odontogenic differentiation through the Smad5 signaling pathway and not dramatically halt cell proliferation in vitro.

Interactive effects of LPS and dentine matrix proteins on human dental pulp stem cells

AIM

To investigate the combinatorial effects of lipopolysaccharide (LPS) and extracted dentine matrix proteins (eDMP) on regenerative and inflammatory responses in human dental pulp stem cells (DPSCs).

METHODOLOGY

Culture media were supplemented with several concentrations of LPS, eDMP and combinations of both. Cell viability was assessed over 1 week by MTT assay; cell survival was evaluated after 24 h and 7 days by flow cytometry. The expression of mineralization-associated marker genes was determined by real-time quantitative polymerase chain reaction (RT-qPCR). To analyse the inflammatory response, secretion of interleukin 6 (IL-6) was quantified in the initial and the late phase of cell culture by enzyme-linked immunosorbent assay (ELISA). Data were treated nonparametrically and Mann-Whitney U-tests were performed to compare all experimental groups (α = 0.05).

RESULTS

Whereas LPS had no impact on viability, eDMP led to a concentration-dependent decrease, which was significant after 7 days (P ≤ 0.024). A moderate decline of cell survival induced by LPS was detected after 48 h (P ≤ 0.026), whereas eDMP was able to reverse this effect. eDMP alone caused increased expression of tested marker genes, LPS had no regulatory effect. Combined eDMP and LPS induced an upregulation of collagen type I and osteocalcin, whereas expression levels of dentine matrix acidic phosphoprotein and dentine sialophosphoprotein were similar to the control. IL-6-secretion was increased by LPS over time. eDMP markedly elevated initial production of IL-6 (P ≤ 0.002), but suppressed LPS-induced cytokine production in the later phase.

CONCLUSIONS

Lipopolysaccharide did not affect cell viability but interfered with odontoblast-like cell differentiation of DPSCs. Proteins from the dentine matrix may have a protective effect, attenuate the detrimental impact of LPS and thus play an important role during pulp repair.

Direct Pulp Capping: What is the Most Effective Therapy?-Systematic Review and Meta-Analysis

INTRODUCTION

Direct pulp capping therapies use biomaterials to protect exposed tissues, inducing repair through the production of a mineralized barrier. The purpose of this study was to compare the effectiveness of biomaterials and techniques by means of a systematic review and meta-analysis.

METHODS

The PubMed, Cochrane, and Embase databases were used to search the literature published from January 1, 1980 until August 31, 2017. Studies that met inclusion criteria were screened by 2 authors individually. The meta-analysis was performed on mineral trioxide aggregate (MTA) cement vs calcium hydroxide cement, tricalcium silicate cement vs MTA cement, and adhesive systems vs CaOH cement and evaluated the success rate, inflammatory response, and dentin bridge formation.

RESULTS

Forty-six studies were included in the systematic review, while 22 studies were included in the meta-analysis. There was no significant heterogeneity between the studies. MTA cements showed a significantly higher success rate, in all parameters, compared with calcium hydroxide cements (odds ratio = 2.72; 95% confidence interval [CI] = 1.90-3.90; P = 0.000). However, when compared with the tricalcium silicate cements, there were no statistically significant differences (odds ratio = 1.18; 95% CI = 0.53-2.65; P = 0.672). Adhesive systems showed a significantly lower success rate, in all parameters, compared with calcium hydroxide cements (odds ratio = 0.062; 95% CI = 0.024-0.157; P = 0.000).

CONCLUSIONS

MTA cements have a higher success rate, with a lower inflammatory response and a more predictable hard dentin barrier formation than calcium hydroxide cements. However, there were no differences, in these parameters, when MTA cement was compared with tricalcium silicate cements. Dental adhesives systems showed the lowest success rates.

Mechanism of bioactive molecular extraction from mineralized dentin by calcium hydroxide and tricalcium silicate cement

OBJECTIVES

The objective of the present study was to elucidate the mechanism of bioactive molecule extraction from mineralized dentin by calcium hydroxide (Ca(OH)₂) and tricalcium silicate cements (TSC).

METHODS AND RESULTS

Transmission electron microscopy was used to provide evidence for collagen degradation in dentin surfaces covered with Ca(OH)₂ or a set, hydrated TSC for 1-3 months. A one micron thick collagen degradation zone was observed on the dentin surface. Fourier transform-infrared spectroscopy was used to identify increases in apatite/collagen ratio in dentin exposed to Ca(OH)₂. Using three-point bending, dentin exposed to Ca(OH)₂ exhibited significant reduction in flexural strength. Using size exclusion chromatography, it was found that the small size of the hydroxyl ions derived from Ca(OH)₂ enabled those ions to infiltrate the intrafibrillar compartment of mineralized collagen and degrade the collagen fibrils without affecting the apatite minerals. Using ELISA, TGF-β1 was found to be extracted from dentin covered with Ca(OH)₂ for 3 months. Unlike acids that dissolve the mineral component of dentin to release bioactive molecules, alkaline materials such as Ca(OH)₂ or TSC released growth factors such as TGF-β1 via collagen degradation.

SIGNIFICANCE

The bioactive molecule extraction capacities of Ca(OH)₂ and TSC render these dental materials excellent for pulp capping and endodontic regeneration. These highly desirable properties, however, appear to be intertwined with the untoward effect of degradation of the collagen matrix within mineralized dentin, resulting in reduced flexural strength.

MMP-9 in Dentinal Fluid Correlates with Caries Lesion Depth

The analysis of molecular cues in dentinal fluid from an excavated cavity could improve diagnostics in the context of minimally invasive caries treatment. In the current clinical trial we assessed whether the dentinal fluid levels of MMP-9 (matrix metalloproteinase-9; neutrophil gelatinase) would increase with the progression of carious lesions. MMP-9 is associated with neutrophil-related tissue breakdown in the pulp. Absolute MMP-9 levels were contrasted against the levels of MMP-2, an enzyme related to normal tissue turnover. Dentinal fluid was collected below deep and shallow caries from molars and premolars within the same patients aged 18 years and older (n = 30, 1 tooth per group/patient). Experimental teeth were isolated under a rubber dam prior to excavation. Dentinal fluid was collected from the bottom of the cavity using a size 25 paper point. MMP levels were assessed using an enzyme-linked immunosorbent assay. Nonparametric methods were applied to test for differences between groups. Significantly more (p < 0.05, Wilcoxon test) MMP-9 was collected from the deep carious lesions than from the shallow counterparts. Pairwise comparison of MMP-9 values within patients revealed that there was more MMP-9 collected from deep lesions than from shallow counterparts in 27 of the 30 individuals under investigation (pairwise Wilcoxon test, p < 0.001). In contrast, no such difference existed for MMP-2. There was a high correlation between MMP-9 from deep and shallow lesions (Spearman's ρ = 0.72, p < 0.001), indicating that patients with more MMP-9 in the deep carious lesion also tended to have more MMP-9 in the shallow lesion.

Release of Growth Factors into Root Canal by Irrigations in Regenerative Endodontics

INTRODUCTION

The aim of this study was to investigate the release of growth factors into root canal space after the irrigation procedure of regenerative endodontic procedure.

METHODS

Sixty standardized root segments were prepared from extracted single-root teeth. Nail varnish was applied to all surfaces except the root canal surface. Root segments were irrigated with 1.5% NaOCl + 17% EDTA, 2.5% NaOCl + 17% EDTA, 17% EDTA, or deionized water. The profile of growth factors that were released after irrigation was studied by growth factor array. Enzyme-linked immunosorbent assay was used to validate the release of transforming growth factor (TGF)-β1 and basic fibroblast growth factor (bFGF) at 4 hours, 1 day, and 3 days after irrigation. The final concentrations were calculated on the basis of the root canal volume measured by cone-beam computed tomography. Dental pulp stem cell migration on growth factors released from root segments was measured by using Transwell assay.

RESULTS

Total of 11 of 41 growth factors were detected by growth factors array. Enzyme-linked immunosorbent assay showed that TGF-β1 was released in all irrigation groups. Compared with the group with 17% EDTA (6.92 ± 4.49 ng/mL), the groups with 1.5% NaOCl + 17% EDTA and 2.5% NaOCl + 17% EDTA had significantly higher release of TGF-β1 (69.04 ± 30.41 ng/mL and 59.26 ± 3.37 ng/mL, respectively), with a peak release at day 1. The release of bFGF was detected at a low level in all groups (0 ng/mL to 0.43 ± 0.22 ng/mL). Migration assay showed the growth factors released from root segments induced dental pulp stem cell migration.

CONCLUSIONS

The root segment model in present study simulated clinical scenario and indicated that the current irrigation protocol released a significant amount of TGF-β1 but not bFGF. The growth factors released into root canal space induced dental pulp stem cell migration.