Odontoblasts: Specialized hard-tissue-forming cells in the dentin-pulp complex

Enhancing Dental Pulp Stem Cell Proliferation and Odontogenic Differentiation with Protein Phosphatase 1-Disrupting Peptide: An In Vitro Study

The reparative and regenerative capabilities of dental pulp stem cells (DPSCs) are crucial for responding to pulp injuries, with protein phosphatase 1 (PP1) playing a significant role in regulating cellular functions pertinent to tissue healing. Accordingly, this study aimed to explore the effects of a novel cell-penetrating peptide Modified Sperm Stop 1-MSS1, that disrupts PP1, on the proliferation and odontogenic differentiation of DPSCs. Employing MSS1 as a bioportide, DPSCs were cultured and characterized for metabolic activity, cell proliferation, and cell morphology alongside the odontogenic differentiation through gene expression and alkaline phosphatase (ALP) activity analysis. MSS1 exposure induced early DPSC proliferation, upregulated genes related to odontogenic differentiation, and increased ALP activity. Markers associated with early differentiation events were induced at early culture time points and those associated with matrix mineralization were upregulated at mid-culture stages. This investigation is the first to document the potential of a PP1-disrupting bioportide in modulating DPSC functionality, suggesting a promising avenue for enhancing dental tissue regeneration and repair.

Mild heat stress promotes the differentiation of odontoblast-like MDPC-23 cells via yes-associated protein

PURPOSE

Dentin hypersensitivity (DH) is a prevalent condition, but long-term effective treatments are scarce. Differentiation of odontoblast-like cells is promising for inducing tertiary dentinogenesis and ensuring sustained therapeutic efficacy against DH. This study examined the effects and mechanism of action of mild heat stress (MHS) on the differentiation of odontoblast-like MDPC-23 cells.

METHODS

We used a heating device to accurately control the temperature and duration, mimicking the thermal microenvironment of odontoblast-like cells. Using this device, the effects of MHS on cell viability and differentiation were examined. Cell viability was assessed using the MTT assay. The expression and nucleoplasmic ratio of the yes-associated protein (YAP) were examined by western blotting and immunofluorescence. The gene expression levels of heat shock proteins (HSPs) and dentin matrix protein-1 (DMP1) were measured using qPCR. Dentin sialophosphoprotein (DSPP) expression was evaluated using immunofluorescence and immunoblotting. Verteporfin was used to inhibit YAP activity.

RESULTS

Mild heat stress (MHS) enhanced the odontoblast differentiation of MDPC-23 cells while maintaining cell viability. MHS also increased YAP activity, as well as the levels of HSP25 mRNA, HSP70 mRNA, HSP90α mRNA, DMP1 mRNA, and DSPP protein. However, after YAP inhibition, both cell viability and the levels of HSP90α mRNA, DMP1 mRNA, and DSPP protein were reduced.

CONCLUSION

YAP plays a crucial role in maintaining cell viability and promoting odontoblast differentiation of MDPC-23 cells under MHS. Consequently, MHS is a potential therapeutic strategy for DH, and boosting YAP activity could be beneficial for maintaining cell viability and promoting odontoblast differentiation.

Vertebrate mineralized tissues: A modular structural analysis

Vertebrate mineralized tissues, present in bones, teeth and scales, have complex 3D hierarchical structures. As more of these tissues are characterized in 3D using mainly FIB SEM at a resolution that reveals the mineralized collagen fibrils and their organization into collagen fibril bundles, highly complex and diverse structures are being revealed. In this perspective we propose an approach to analyzing these tissues based on the presence of modular structures: material textures, pore shapes and sizes, as well as extents of mineralization. This modular approach is complimentary to the widely used hierarchical approach for describing these mineralized tissues. We present a series of case studies that show how some of the same structural modules can be found in different mineralized tissues, including in bone, dentin and scales. The organizations in 3D of the various structural modules in different tissues may differ. This approach facilitates the framing of basic questions such as: are the spatial relations between modular structures the same or similar in different mineralized tissues? Do tissues with similar sets of modules carry out similar functions or can similar functions be carried out using a different set of modular structures? Do mineralized tissues with similar sets of modules have a common developmental or evolutionary pathway? STATEMENT OF SIGNIFICANCE: 3D organization studies of diverse vertebrate mineralized tissues are revealing detailed, but often confusing details about the material textures, the arrangements of pores and differences in the extent of mineralization within a tissue. The widely used hierarchical scheme for describing such organizations does not adequately provide a basis for comparing these tissues, or addressing issues such as structural components thought to be characteristic of bone, being present in dermal tissues and so on. The classification scheme we present is based on identifying structural components within a tissue that can then be systematically compared to other vertebrate mineralized tissues. We anticipate that this classification approach will provide insights into structure-function relations, as well as the evolution of these tissues.

Focused ion beam-SEM 3D study of osteodentin in the teeth of the Atlantic wolfish Anarhichas lupus

The palette of mineralized tissues in fish is wide, and this is particularly apparent in fish dentin. While the teeth of all vertebrates except fish contain a single dentinal tissue type, called orthodentin, dentin in the teeth of fish can be one of several different tissue types. The most common dentin type in fish is orthodentin. Orthodentin is characterized by several key structural features that are fundamentally different from those of bone and from those of osteodentin. Osteodentin, the second-most common dentin type in fish (based on the tiny fraction of fish species out of ∼30,000 extant fish species in which tooth structure was so far studied), is found in most Selachians (sharks and rays) as well as in several teleost species, and is structurally different from orthodentin. Here we examine the hypothesis that osteodentin is similar to anosteocytic bone tissue in terms of its micro- and nano-structure. We use Focused Ion Beam-Scanning Electron Microscopy (FIB/SEM), as well as several other high-resolution imaging techniques, to characterize the 3D architecture of the three main components of osteodentin (denteons, inter-denteonal matrix, and the transition zone between them). We show that the matrix of osteodentin, although acellular, is extremely similar to mammalian osteonal bone matrix, both in general morphology and in the three-dimensional nano-arrangement of its mineralized collagen fibrils. We also document the presence of a complex network of nano-channels, similar to such networks recently described in bone. Finally, we document the presence of strings of hyper-mineralized small 'pearls' which surround the denteonal canals, and characterize their structure.

Dental Pulp Cell Transplantation Combined with Regenerative Endodontic Procedures Promotes Dentin Matrix Formation in Mature Mouse Molars

Regenerative endodontic procedures (REPs) are promising for dental pulp tissue regeneration; however, their application in permanent teeth remains challenging. We assessed the potential combination of an REP and local dental pulp cell (DPC) transplantation in the mature molars of C57BL/6 mice with (REP + DPC group) or without (REP group) transplantation of DPCs from green fluorescent protein (GFP) transgenic mice. After 4 weeks, the regenerated tissue was evaluated by micro-computed tomography and histological analyses to detect odontoblasts, vasculogenesis, and neurogenesis. DPCs were assessed for mesenchymal and pluripotency markers. Four weeks after the REP, the molars showed no signs of periapical lesions, and both the REP and REP + DPC groups exhibited a pulp-like tissue composed of a cellular matrix with vessels surrounded by an eosin-stained acellular matrix that resembled hard tissue. However, the REP + DPC group had a broader cellular matrix and uniquely contained odontoblast-like cells co-expressing GFP. Vasculogenesis and neurogenesis were detected in both groups, with the former being more prominent in the REP + DPC group. Overall, the REP was achieved in mature mouse molars and DPC transplantation improved the outcomes by inducing the formation of odontoblast-like cells and greater vasculogenesis.

Wound-healing Processes After Pulpotomy in the Pulp Tissue of Type 1 Diabetes Mellitus Model Rats

INTRODUCTION

Patients with type 1 diabetes mellitus (DM1) tend to have delayed wound healing, even in the pulp tissue. We hypothesized that hyperglycemia affects odontoblast-like cell (OLC) differentiation and is involved in macrophage polarization. Accordingly, we evaluated dental pulp stem cell differentiation and macrophage phenotypes after pulpotomy.

METHODS

After modifying DM1 rat models by streptozotocin, 8-week-old rats' upper left first molars were pulpotomized with mineral trioxide aggregate. Meanwhile, the control group was administered saline. Immunohistochemical localization of nestin, osteopontin, α-smooth muscles (α-SMAs), and CD68 (pan-macrophage marker) was conducted 7 days after pulpotomy. The OLC differentiation stage was determined using double immunofluorescence of nestin and α-SMA. Double immunofluorescence of CD68 and iNOS was counted as M1 macrophages and CD68 and CD206 as M2 macrophages. Proliferating cell nuclear antigen and Thy-1 (CD90) were evaluated by immunofluorescence.

RESULTS

In DM1 rats, the reparative dentin bridge was not complete; however, the osteopontin-positive area did not differ significantly from that in controls. Proliferating cell nuclear antigen, indicative of cell proliferation, increased in positive cells in DM1 rats compared with controls. Double-positive cells for α-SMA and nestin indicated many immature OLCs in DM1. CD90 was positive only in controls. CD68-positive cells, especially M1 macrophages, were increased in DM1 rats, allowing the inflammatory stage to continue 7 days after pulpotomy.

CONCLUSIONS

The condition of DM1 model rats can interfere at various stages of the wound healing process, altering OLC differentiation and macrophage polarization. These findings highlight the importance of normal blood glucose concentrations during pulp wound healing.

piR-368 promotes odontoblastic differentiation of dental papilla cells via the Smad1/5 signaling pathway by targeting Smurf1

PURPOSE

The important role of non-coding RNAs in odontoblastic differentiation of dental tissue-derived stem cells has been widely demonstrated; however, whether piRNA (a subclass of non-coding RNA) involved in the course of odontoblastic differentiation is not yet available. This study aimed to investigate the expression profile of piRNA during odontogenic differentiation of mDPCs and the potential molecular mechanism in vitro.

MATERIALS AND METHODS

The primary mouse dental papilla cells (mDPCs) were isolated from the first molars of 1-day postnatal Kunming mice. Then, they were cultured in odontogenic medium for 9 days. The expression profile of piRNA was detected by Small RNA sequencing. RT-qPCR was used to verify the elevation of piR-368. The mRNA and protein levels of mineralization markers were examined by qRT-PCR and Western blot analysis. Alkaline phosphatase (ALP) activity and alizarin red S staining were conducted to assess the odontoblastic differentiation ability.

RESULTS

We validated piR-368 was significantly upregulated and interference with piR-368 markedly inhibited the odontogenic differentiation of mDPCs. In addition, the relationship between Smad1/5 signaling pathway and piR-368-induced odontoblastic differentiation has been discovered. Finally, we demonstrated Smurf1 as a target gene of piR-368 using dual-luciferase assays.

CONCLUSION

This study was the first to illustrate the participation of piRNA in odontoblastic differentiation. We proved that piR-368 promoted odontoblastic differentiation of mouse dental papilla cells via the Smad1/5 signaling pathway by targeting Smurf1.

Exosomes derived from odontogenic stem cells: Its role in the dentin-pulp complex

Odontogenic stem cells originate from cranial neural crest cells and offer unique advantages in the regeneration of dentin-pulp complex. There is increasing evidence that stem cells exert their biological functions mainly through exosome-based paracrine effects. Exosomes contain DNA, RNA, proteins, metabolites, etc., which can play a role in intercellular communication and have similar therapeutic potential to stem cells. In addition, compared with stem cells, exosomes also have the advantages of good biocompatibility, high drug carrying capacity, easy to obtain, and few side effects. Odontogenic stem cell-derived exosomes mainly affect the regeneration of the dentin-pulp complex by regulating processes such as dentintogenesis, angiogenesis, neuroprotection and immunomodulation. This review aimed to describe "cell-free therapies" based on odontogenic stem cell-derived exosomes, which aim to regenerate the dentin-pulp complex.

Expression of 20 SCPP genes during tooth and bone mineralization in Senegal bichir

The African bichir (Polypterus senegalus) is a living representative of Polypteriformes. P. senegalus possesses teeth composed of dentin covered by an enameloid cap and a layer of collar enamel on the tooth shaft, as in lepisosteids. A thin layer of enamel matrix can also be found covering the cap enameloid after its maturation and during the collar enamel formation. Teleosts fish do not possess enamel; teeth are protected by cap and collar enameloid, and inversely in sarcopterygians, where teeth are only covered by enamel, with the exception of the cap enameloid in teeth of larval urodeles. The presence of enameloid and enamel in the teeth of the same organism is an opportunity to solve the evolutionary history of the presence of enamel/enameloid in basal actinopterygians. In silico analyses of the jaw transcriptome of a juvenile bichir provided twenty SCPP transcripts. They included enamel, dentin, and bone-specific SCPPs known in sarcopterygians and several actinopterygian-specific SCPPs. The expression of these 20 genes was investigated by in situ hybridizations on jaw sections during tooth and dentary bone formation. A spatiotemporal expression patterns were established and compared with previous studies of SCPP gene expression during enamel/enameloid and bone formation. Similarities and differences were highlighted, and several SCPP transcripts were found specifically expressed during tooth or bone formation suggesting either conserved or new functions of these SCPPs.

GATA4 inhibits odontoblastic differentiation of dental pulp stem cells through targeting IGFBP3

OBJECTIVE

The odontogenic differentiation of human dental pulp stem cells (HDPSCs) is associated with reparative dentinogenesis. Transcription factor GATA binding protein 4 (GATA4) is proved to be essential for osteoblast differentiation and bone remodeling. This study clarified the function of GATA4 in HDPSCs odontoblast differentiation.

METHODS

The change in GATA4 expression during reparative dentin formation was detected by immunohistochemistry staining. The expression of GATA4 during HDPSCs odontoblastic differentiation was detected by western blot and quantitative polymerase chain reaction. The effect of GATA4 on odontoblast differentiation was investigated following overexpression lentivirus transfection. RNA sequencing, dual luciferase assay and chromatin immunoprecipitation (CHIP) were conducted to verify downstream targets of GATA4. GATA4 overexpression lentivirus and small interference RNA targeting IGFBP3 were co-transfected to investigate the regulatory mechanism of GATA4.

RESULTS

Upregulated GATA4 was observed during reparative dentin formation in vivo and the odontoblastic differentiation of HDPSCs in vitro. GATA4 overexpression suppressed the odontoblastic potential of HDPSCs, demonstrated by decreased alkaline phosphatase activity (p < 0.0001), mineralized nodules formation (p < 0.01), and odonto/osteogenic differentiation markers levels (p < 0.05). RNA sequencing revealed IGFBP3 was a potential target of GATA4. CHIP and dual luciferase assays identified GATA4 could activate IGFBP3 transcription. Additionally, IGFBP3 knockdown recovered the odontoblastic differentiation defect caused by GATA4 overexpression (p < 0.05).

CONCLUSIONS

GATA4 inhibited odontoblastic differentiation of HDPSCs via activating the transcriptional activity of IGFBP3, identifying its promising role in regulating HDPSCs odontoblast differentiation and reparative dentinogenesis.

Identification of potential key variants in mandibular premolar hypodontia through whole-exome sequencing

Determining genotype-phenotype correlations in patients with hypodontia is important for understanding disease pathogenesis, although only a few studies have elucidated it. We aimed to identify genetic variants linked to non-syndromic bilateral mandibular second premolar hypodontia in a Korean population for the first time by specifying the phenotype of hypodontia. Twenty unrelated individuals with non-syndromic bilateral mandibular second premolar hypodontia were enrolled for whole-exome sequencing. Using a tooth agenesis gene set panel consisting of 112 genes based on literature, potential candidate variants were screened through variant filtering and prioritization. We identified 13 candidate variants in 12 genes, including a stop-gain variant (c.4750C>T) in LAMA3. Through the functional enrichment analysis of the prioritized genes, several terms related to tooth development were enriched in a protein-protein interaction network of candidate genes for mandibular premolar hypodontia. The hypodontia group also had approximately 2-fold as many mutated variants in all four genes related to these key terms, which are CDH1, ITGB4, LAMA3, LAMB3, as those in the 100 healthy control group individuals. The relationship between enriched terms and pathways and mandibular premolar hypodontia was also investigated. In addition, we identified some known oligodontia variants in patients with hypodontia, strengthening the possibility of synergistic effects in other genes. This genetic investigation may be a worthwhile preliminary attempt to reveal the pathogenesis of tooth agenesis and sets a background for future studies.

Intercellular mitochondrial transfer alleviates pyroptosis in dental pulp damage

Mitochondrial transfer is emerging as a promising therapeutic strategy for tissue repair, but whether it protects against pulpitis remains unclear. Here, we show that hyperactivated nucleotide-binding domain and leucine-rich repeat protein3 (NLRP3) inflammasomes with pyroptotic cell death was present in pulpitis tissues, especially in the odontoblast layer, and mitochondrial oxidative stress (OS) was involved in driving this NLRP3 inflammasome-induced pathology. Using bone marrow mesenchymal stem cells (BMSCs) as mitochondrial donor cells, we demonstrated that BMSCs could donate their mitochondria to odontoblasts via tunnelling nanotubes (TNTs) and, thus, reduce mitochondrial OS and the consequent NLRP3 inflammasome-induced pyroptosis in odontoblasts. These protective effects of BMSCs were mostly blocked by inhibitors of the mitochondrial function or TNT formation. In terms of the mechanism of action, TNF-α secreted from pyroptotic odontoblasts activates NF-κB signalling in BMSCs via the paracrine pathway, thereby promoting the TNT formation in BMSCs and enhancing mitochondrial transfer efficiency. Inhibitions of NF-κB signalling and TNF-α secretion in BMSCs suppressed their mitochondrial donation capacity and TNT formation. Collectively, these findings demonstrated that TNT-mediated mitochondrial transfer is a potential protective mechanism of BMSCs under stress conditions, suggesting a new therapeutic strategy of mitochondrial transfer for dental pulp repair.

Hereditary dentin defects with systemic diseases

OBJECTIVE

This review aimed to summarize recent progress on syndromic dentin defects, promoting a better understanding of systemic diseases with dentin malformations, the molecules involved, and related mechanisms.

SUBJECTS AND METHODS

References on genetic diseases with dentin malformations were obtained from various sources, including PubMed, OMIM, NCBI, and other websites. The clinical phenotypes and genetic backgrounds of these diseases were then summarized, analyzed, and compared.

RESULTS

Over 10 systemic diseases, including osteogenesis imperfecta, hypophosphatemic rickets, vitamin D-dependent rickets, familial tumoral calcinosis, Ehlers-Danlos syndrome, Schimke immuno-osseous dysplasia, hypophosphatasia, Elsahy-Waters syndrome, Singleton-Merten syndrome, odontochondrodysplasia, and microcephalic osteodysplastic primordial dwarfism type II were examined. Most of these are bone disorders, and their pathogenic genes may regulate both dentin and bone development, involving extracellular matrix, cell differentiation, and metabolism of calcium, phosphorus, and vitamin D. The phenotypes of these syndromic dentin defects various with the involved genes, part of them are similar to dentinogenesis imperfecta or dentin dysplasia, while others only present one or two types of dentin abnormalities such as discoloration, irregular enlarged or obliterated pulp and canal, or root malformation.

CONCLUSION

Some specific dentin defects associated with systemic diseases may serve as important phenotypes for dentists to diagnose. Furthermore, mechanistic studies on syndromic dentin defects may provide valuable insights into isolated dentin defects and general dentin development or mineralization.

Dopamine is involved in reparative dentin formation through odontoblastic differentiation of dental pulp stem cells

Conventional direct pulp-capping materials induce pulp cells to secrete various biomolecules in pulp tissues that promote reparative dentin formation through induction of odontoblastic differentiation of dental pulp stem cells (DPSCs). However, these biomolecules sometimes induce bone-like dentin with poor sealing properties. Therefore, exploration of biomolecules that allow tight sealing by tubular reparative dentin is required. We recently reported that dopamine (DA) is involved in dentinogenesis. Hence, we investigated the effect of DA on odontoblastic differentiation of DPSCs and reparative dentin formation. Both tyrosine hydroxylase (TH), a DA synthetase, and DA were expressed in odontoblast-like cells in vivo. In vitro, their expression was increased during odontoblastic differentiation of DPSCs. Furthermore, TH-overexpressing DPSCs had promoted odontoblastic differentiation and DA production. Moreover, DA stimulation promoted their differentiation and induced tubular reparative dentin. These results suggest that DA produced by TH is involved in odontoblastic differentiation of DPSCs and has an inductive capacity for reparative dentin formation similar to primary dentin. This study may lead to the development of therapy to preserve vital pulp tissues.

The Role of Cellular Metabolism in Maintaining the Function of the Dentine-Pulp Complex: A Narrative Review

The cellular metabolic processes ensure the physiological integrity of the dentine-pulp complex. Odontoblasts and odontoblast-like cells are responsible for the defence mechanisms in the form of tertiary dentine formation. In turn, the main defence reaction of the pulp is the development of inflammation, during which the metabolic and signalling pathways of the cells are significantly altered. The selected dental procedures, such as orthodontic treatment, resin infiltration, resin restorations or dental bleaching, can impact the cellular metabolism in the dental pulp. Among systemic metabolic diseases, diabetes mellitus causes the most consequences for the cellular metabolism of the dentine-pulp complex. Similarly, ageing processes present a proven effect on the metabolic functioning of the odontoblasts and the pulp cells. In the literature, several potential metabolic mediators demonstrating anti-inflammatory properties on inflamed dental pulp are mentioned. Moreover, the pulp stem cells exhibit the regenerative potential essential for maintaining the function of the dentine-pulp complex.

Incidence and influential factors in pulp necrosis and periapical pathosis following indirect restorations: a systematic review and meta-analysis

BACKGROUND

Restoring vital teeth with indirect restorations may threaten dental pulp integrity. However, the incidence of and influential factors on pulp necrosis and periapical pathosis in such teeth are still unknown. Therefore, this systematic review and meta-analysis aimed to investigate the incidence of and influential factors on pulp necrosis and periapical pathosis of vital teeth following indirect restorations.

METHODS

The search was conducted in five databases, using MEDLINE via PubMed, Web of Science, EMBASE, CINAHL, and Cochrane Library. Eligible clinical trials and cohort studies were included. The risk of bias was assessed using Joanna Briggs Institute's critical appraisal tool and Newcastle-Ottawa Scale. The overall incidences of pulp necrosis and periapical pathosis following indirect restorations were calculated using a random effects model. Subgroup meta-analyses were also performed to determine the potential influencing factors for pulp necrosis and periapical pathosis. The certainty of the evidence was assessed using the GRADE tool.

RESULTS

A total of 5,814 studies were identified, of which 37 were included in the meta-analysis. The overall incidences of pulp necrosis and periapical pathosis following indirect restorations were determined to be 5.02% and 3.63%, respectively. All studies were assessed as having a moderate-low risk of bias. The incidence of pulp necrosis following indirect restorations increased when the pulp status was objectively assessed (thermal/electrical testing). The presence of pre-operative caries or restorations, treatment of anterior teeth, temporization for more than two weeks, and cementation with eugenol-free temporary cement, all increased this incidence. Final impression with polyether and permanent cementation with glass ionomer cement both increased the incidence of pulp necrosis. Longer follow-up periods (> 10 years) and treatment provided by undergraduate students or general practitioners were also factors that increased this incidence. On the other hand, the incidence of periapical pathosis increased when teeth were restored with fixed partial dentures, the bone level was < 35%, and the follow-up was > 10 years. The certainty of the evidence overall was assessed as low.

CONCLUSIONS

Although the incidences of pulp necrosis and periapical pathosis following indirect restorations remain low, many factors affect these incidences that should thus be considered when planning indirect restorations on vital teeth.

DATABASE REGISTRATION

PROSPERO (CRD42020218378).

The effects of 4-Phenylbutyric acid on ER stress during mouse tooth development

Introduction: During tooth development, proper protein folding and trafficking are significant processes as newly synthesized proteins proceed to form designated tissues. Endoplasmic reticulum (ER) stress occurs inevitably in tooth development as unfolded and misfolded proteins accumulate in ER. 4-Phenylbutyric acid (4PBA) is a FDA approved drug and known as a chemical chaperone which alleviates the ER stress. Recently, several studies showed that 4PBA performs therapeutic effects in some genetic diseases due to misfolding of proteins, metabolic related-diseases and apoptosis due to ER stress. However, the roles of 4PBA during odontogenesis are not elucidated. This study revealed the effects of 4PBA during molar development in mice. Methods: We employed in vitro organ cultivation and renal transplantation methods which would mimic the permanent tooth development in an infant period of human. The in vitro cultivated tooth germs and renal calcified teeth were examined by histology and immunohistochemical analysis. Results and Discussion: Our results revealed that treatment of 4PBA altered expression patterns of enamel knot related signaling molecules, and consequently affected cellular secretion and patterned formation of dental hard tissues including dentin and enamel during tooth morphogenesis. The alteration of ER stress by 4PBA treatment during organogenesis would suggest that proper ER stress is important for pattern formation during tooth development and morphogenesis, and 4PBA as a chemical chaperone would be one of the candidate molecules for dental and hard tissue regeneration.

Dentin regeneration based on tooth tissue engineering: A review

Missing or damaged teeth due to caries, genetic disorders, oral cancer, or infection may contribute to physical and mental impairment that reduces the quality of life. Despite major progress in dental tissue repair and those replacing missing teeth with prostheses, clinical treatments are not yet entirely satisfactory, as they do not regenerate tissues with natural teeth features. Therefore, much of the focus has centered on tissue engineering (TE) based on dental stem/progenitor cells to create bioengineered dental tissues. Many in vitro and in vivo studies have shown the use of cells in regenerating sections of a tooth or a whole tooth. Tooth tissue engineering (TTE), as a promising method for dental tissue regeneration, can form durable biological substitutes for soft and mineralized dental tissues. The cell-based TE approach, which directly seeds cells and bioactive components onto the biodegradable scaffolds, is currently the most potential method. Three essential components of this strategy are cells, scaffolds, and growth factors (GFs). This study investigates dentin regeneration after an injury such as caries using TE and stem/progenitor cell-based strategies. We begin by discussing about the biological structure of a dentin and dentinogenesis. The engineering of teeth requires knowledge of the processes that underlie the growth of an organ or tissue. Then, the three fundamental requirements for dentin regeneration, namely cell sources, GFs, and scaffolds are covered in the current study, which may ultimately lead to new insights in this field.

Multiple growth factors accommodated degradable submicron calcium sulfate hemihydrate/porous hydroxyapatite for dentin-pulp regeneration

Vital pulp therapy (VPT) has gained significant consideration by utilizing the natural healing capacity of the inflamed pulp in healing process. However, the protective pulp capping materials that facilitate this healing process are still under investigation for the successful promotion of dentin-pulp regeneration. Herein, we developed a bioactive and biodegradable pulp capping material (denoted as sCSHA-GFs) by synthesizing inorganic submicron calcium sulfate hemihydrate (sCS)/porous hydroxyapatite (HA) loaded with growth factors (GFs) such as transforming growth factor-beta 1 (TGF-β1), fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF). Physiochemical characteristics of submicron CSHA-GFs (sCSHA-GFs) cement were determined. Human dental pulp stem cells (hDPSCs) were used for analyzing their biocompatibility and bioactivity for dentin mineralization. To evaluate the efficacy of sCSHA-GFs, we compared it with a commercial material, mineral trioxide aggregate (MTA), the reference standard used clinically on pulp capping. Our results showed that sCSHA-GFs cement presented good biodegradability with dissolution properties for sustained release of calcium (Ca²⁺) ions and GFs, and facilitated attachment, proliferation, differentiation and migration of hDPSCs. In addition, sCSHA-GFs cement was found to be more effective than MTA at prolonged incubation time in inducing the mRNA expression levels of odontoblastic differentiation markers, dentin sialophosphoprotein (DSPP) and dentin matrix protein (DMP-1), leading to increased mineralization (with calcium deposits) along with increased alkaline phosphatase (ALP) expressions, evident from Alizarin Red S and ALP staining assays. Our findings suggest that sCSHA-GFs cement may act as a suitable material in VPT for dentin-pulp regeneration.

2-hydroxyethyl methacrylate-derived reactive oxygen species stimulate ATP release via TRPA1 in human dental pulp cells

Extracellular ATP (adenosine triphosphate) and transient receptor potential ankyrin 1 (TRPA1) channels are involved in calcium signaling in odontoblasts and dental pain. The resin monomer 2-hydroxyethyl methacrylate (HEMA), used in dental restorative procedures, is related to apoptotic cell death via oxidative stress. Although the TRPA1 channel is highly sensitive to reactive oxygen species (ROS), the effect of HEMA-induced ROS on ATP release to the extracellular space and the TRPA1 channel has not been clarified in human dental pulp. In this study, we investigated the extracellular ATP signaling and TRPA1 activation by HEMA-derived ROS in immortalized human dental pulp cells (hDPSC-K4DT). Among the ROS-sensitive TRP channels, TRPA1 expression was highest in undifferentiated hDPSC-K4DT cells, and its expression levels were further enhanced by osteogenic differentiation. In differentiated hDPSC-K4DT cells, 30 mM HEMA increased intracellular ROS production and ATP release, although 3 mM HEMA had no effect. Pretreatment with the free radical scavenger PBN (N-tert-butyl-α-phenylnitrone) or TRPA1 antagonist HC-030031 suppressed HEMA-induced responses. These results suggest that ROS production induced by a higher dose of HEMA activates the TRPA1 channel in human dental pulp cells, leading to ATP release. These findings may contribute to the understanding of the molecular and cellular pathogenesis of tertiary dentin formation and pain in response to dental biomaterials.

Lead inhibits the odontogenic differentiation potential of dental pulp stem cells by affecting WNT1/β-catenin signaling and related miRNAs expression

Lead (Pb) is ubiquitous in environment that accumulates in teeth and calcified tissues from where it releases gradually with aging and adversely affects dental health. This study aimed to determine the effect of Pb exposure on odontogenic differentiation potential of isolated human dental pulp stem cells and investigate the possible underlying epigenetic factors. In the absence of Pb exposure, stem cells displayed significant odontogenic markers including elevated Alkaline Phosphatase (ALP) activity, Alizarin red staining intensity, and increased expression of odontogenic DMP1 and DSPP genes. Exposure to 60 μM Pb resulted in reduced ALP activity and calcium deposition. Also, diminished expression of RUNX2, DMP1, and DSPP, as well as Wnt signaling mediators including WNT1, and β-catenin were detected. The expression of Wnt signaling related microRNAs, miRNA-139-5p and miRNA-142-3p, on the other hand, were shown to have a significant increase. We concluded that Pb could adversely affect the odontogenic differentiation potential of dental pulp stem cell. The underlying mechanism might related to Pb-induced epigenetic dysregulation of WNT1/β-catenin pathway-related miRNAs leading to down-regulation of Wnt/β-catenin related odontogenic genes and eventually impaired odontogenic differentiation process.

Enamel Matrix Derivative Enhances the Odontoblastic Differentiation of Dental Pulp Stem Cells via Activating MAPK Signaling Pathways

The odontoblastic differentiation of dental pulp stem cells (DPSCs) contributes to pulp-dentin regeneration. Enamel matrix derivative (EMD) is considered to be a critical epithelial signal to induce cell differentiation during odontogenesis and has been widely applied to clinical periodontal tissue regeneration. The purpose of this study was to explore the effect of EMD on DPSCs proliferation and odontoblastic differentiation, as well as the underlying mechanisms. We conducted in vitro and in vivo researches to get a comprehensive understanding of EMD. In vitro phase: cell proliferation was assessed by a cell counting kit-8 (CCK-8) assay; then, alkaline phosphatase (ALP) activity and staining, alizarin red staining, real-time RT-PCR, and western blot analysis were conducted to determine the odontoblastic potential and involvement of MAPK signaling pathways. In vivo phase: after ensuring the biocompatibility of VitroGel 3D-RGD via scanning electron microscopy (SEM), the hydrogel mixture was subcutaneously injected into nude mice followed by histological and immunohistochemical analyses. The results revealed that EMD did not interfere with DPSCs proliferation but promoted the odontoblastic differentiation of DPSCs in vitro and in vivo. Furthermore, blocking the MAPK pathways suppressed the EMD-enhanced differentiation of DPSCs. Finally, VitroGel 3D-RGD could well support the proliferation, differentiation, and regeneration of DPSCs. Overall, this study demonstrates that EMD enhances the odontoblastic differentiation of DPSCs through triggering MAPK signaling pathways. The findings provide a new insight into the mechanism by which EMD affects DPSCs differentiation and proposes EMD as a promising candidate for future stem cell therapy in endodontics.

Hypoxia Induces DPSC Differentiation versus a Neurogenic Phenotype by the Paracrine Mechanism

As previously described by several authors, dental pulp stem cells (DPSCs), when adequately stimulated, may acquire a neuronal-like phenotype acting as a favorable source of stem cells in the generation of nerves. Besides, it is known that hypoxia conditioning is capable of stimulating cell differentiation as well as survival and self-renewal, and that multiple growth factors, including Epidermal Growth factor (EGF) and basic fibroblast growth factor (bFGF), are often involved in the induction of the neuronal differentiation of progenitor cells. In this work, we investigated the role of hypoxia in the commitment of DPSCs into a neuronal phenotype. These cells were conditioned with hypoxia (O₂ 1%) for 5 and 16 days; subsequently, we analyzed the proliferation rate and morphology, and tested the cells for neural and stem markers. Moreover, we verified the possible autocrine/paracrine role of DPSCs in the induction of neural differentiation by comparing the secretome profile of the hypoxic and normoxic conditioned media (CM). Our results showed that the hypoxia-mediated DPSC differentiation was time dependent. Moreover, conditioned media (CM derived from DPSCs stimulated by hypoxia were able, in turn, to induce the neural differentiation of SH-SY5Y neuroblastoma cells and undifferentiated DPSCs. In conclusion, under the herein-mentioned conditions, hypoxia seems to favor the differentiation of DPSCs into neuron-like cells. In this way, we confirm the potential clinical utility of differentiated neuronal DPSCs, and we also suggest the even greater potential of CM-derived-hypoxic DPSCs that could more readily be used in regenerative therapies.

Demineralized Dentin Matrix for Dental and Alveolar Bone Tissues Regeneration: An Innovative Scope Review

Background:

Dentin is a permeable tubular composite and complex structure, and in weight, it is composed of 20% organic matrix, 10% water, and 70% hydroxyapatite crystalline matrix. Demineralization of dentin with gradient concentrations of ethylene diamine tetraacetic acid, 0.6 N hydrochloric acid, or 2% nitric acid removes a major part of the crystalline apatite and maintains a majority of collagen type I and non-collagenous proteins, which creates an osteoinductive scaffold containing numerous matrix elements and growth factors. Therefore, demineralized dentin should be considered as an excellent naturally-derived bioactive material to enhance dental and alveolar bone tissues regeneration.

Method:

The PubMed and Midline databases were searched in October 2021 for the relevant articles on treated dentin matrix (TDM)/demineralized dentin matrix (DDM) and their potential roles in tissue regeneration.

Results:

Several studies with different study designs evaluating the effect of TDM/DDM on dental and bone tissues regeneration were found. TDM/DDM was obtained from human or animal sources and processed in different forms (particles, liquid extract, hydrogel, and paste) and different shapes (sheets, slices, disc-shaped, root-shaped, and barrier membranes), with variable sizes measured in micrometers or millimeters, demineralized with different protocols regarding the concentration of demineralizing agents and exposure time, and then sterilized and preserved with different techniques. In the act of biomimetic acellular material, TDM/DDM was used for the regeneration of the dentin-pulp complex through direct pulp capping technique, and it was found to possess the ability to activate the odontogenic differentiation of stem cells resident in the pulp tissues and induce reparative dentin formation. TDM/DDM was also considered for alveolar ridge and maxillary sinus floor augmentations, socket preservation, furcation perforation repair, guided bone, and bioroot regenerations as well as bone and cartilage healing.

Conclusion:

To our knowledge, there are no standard procedures to adopt a specific form for a specific purpose; therefore, future studies are required to come up with a well-characterized TDM/DDM for each specific application. Likely as decellularized dermal matrix and prospectively, if the TDM/DDM is supplied in proper consistency, forms, and in different sizes with good biological properties, it can be used efficiently instead of some widely-used regenerative biomaterials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-022-00438-4.

The effect of low-level laser on the quality of dentin barrier after capping with bioceramic material: A histomorphometric analysis

The study aims to investigate the quality of dentin barriers and pulp reaction to EndoSequence Root Repair Material (ERRM) combined with low-level laser application. In eight dogs, pulps were exposed via class V, half of the samples received low-level diode laser at 870 nm. Thereafter, cavities were capped with fast-set or regular-set ERRM. The specimens were processed for histomorphological and immunohistochemical examination after 2 weeks and 2 months. Dentin bridges were observed in all samples, and 87.5% were complete. The low-level laser group had significantly more reparative dentin area than the non-lased group (p < 0.05). The dentin bridges were found to have an unprecedented tubularity of 43%-89%. Tiny dentin island formation was observed within the material particles. Initial mild-to-moderate inflammatory reactions were observed, which subsided after 2 months. RUNX2 and osteocalcin staining were evident for all samples at both time intervals. Low-level laser combined with bioactive ERRM is effective in inducing reparative dentin formation.

Application of Proteomics in Apical Periodontitis

Apical periodontitis is an inflammatory reaction of the periradicular tissues as a consequence of multispecies microbial communities organized as biofilms within the root canal system. Periradicular tissue changes at the molecular level initiate and orchestrate the inflammatory process and precede the presentation of clinical symptoms. Inflammatory mediators have been studied at either the proteomic, metabolomic, or transcriptomic levels. Analysis at the protein level is the most common approach used to identify and quantify analytes from diseased periradicular tissues during root canal treatment, since it is more representative of definitive and active periradicular inflammatory mediator than its transcript expression level. In disease, proteins expressed in an altered manner could be utilized as biomarkers. Biomarker proteins in periradicular tissues have been qualitatively and quantitatively assessed using antibodies (immunoassays and immunostaining) or mass spectrometry-based approaches. Herein, we aim to provide a comprehensive understanding of biomarker proteins identified in clinical studies investigating periradicular lesions and pulp tissue associated with apical periodontitis using proteomics. The high throughput mass spectrometry-based proteomics has the potential to improve the current methods of monitoring inflammation while distinguishing between progressive, stable, and healing lesions for the identification of new diagnostic and therapeutic targets. This method would provide more objective tools to (a) discover biomarkers related to biological processes for better clinical case selection, and (b) determine tissue response to novel therapeutic interventions for more predictable outcomes in endodontic treatment.

Angiogenesis during coronal pulp regeneration using rat dental pulp cells: Neovascularization in rat molars in vivo and proangiogenic dental pulp cell-endothelial cell interactions in vitro

Background/purpose

Angiogenesis is considered a crucial event for dental pulp regeneration. The purpose of this study was to demonstrate neovascularization during coronal pulp regeneration in rat molars using rat dental pulp cells (rDPCs) and to examine whether rDPC-endothelial cell interactions promote proangiogenic capacity in vitro.

Materials and methods

Maxillary first molars of Wistar rats (n = 42) were pulpotomized and rDPCs isolated from incisors were implanted with a porous poly (l-lactic acid) (PLLA) scaffold and hydrogel (Matrigel). After 3, 7, and 14 days, coronal pulp tissues were examined histologically and by nestin and CD146 immunohistochemistry. rDPCs and rat dermal microvascular endothelial cells (rDMECs) were cocultured for 4 days and vascular endothelial growth factor (VEGF) synthesis and angiogenic factor gene expression were determined by enzyme-linked immunosorbent assays and real-time polymerase chain reaction, respectively. Effects of cocultured medium on tube formation by rDMECs were also evaluated.

Results

Implantation of rDPC/PLLA/Matrigel induced coronal pulp regeneration with dentin bridge formation and arrangement of nestin-positive odontoblast-like cells at 14 days. PLLA/Matrigel without rDPCs did not induce pulp regeneration. CD146-positive blood vessels increased in density in the remaining pulp tissues at 3 and 7 days, and in the regenerated pulp tissue at 14 days. rDPC/DMEC coculture significantly promoted VEGF secretion and mRNA expression of nuclear factor-kappa B, angiogenic chemokine CXCL1, and chemokine receptor CXCR1. Cocultured medium significantly promoted tube formation.

Conclusion

Coronal pulp regeneration with rDPC/PLLA/Matrigel was accompanied by neovascularization. rDPC-rDMEC interactions may promote angiogenic activity represented by proangiogenic factor upregulation and tube formation in vitro.

Aberrant NF-κB activation in odontoblasts orchestrates inflammatory matrix degradation and mineral resorption

Inflammation-associated proteinase functions are key determinants of inflammatory stromal tissues deconstruction. As a specialized inflammatory pathological process, dental internal resorption (IR) includes both soft and hard tissues deconstruction within the dentin-pulp complex, which has been one of the main reasons for inflammatory tooth loss. Mechanisms of inflammatory matrix degradation and tissue resorption in IR are largely unclear. In this study, we used a combination of Cre-loxP reporter, flow cytometry, cell transplantation, and enzyme activities assay to mechanistically investigate the role of regenerative cells, odontoblasts (ODs), in inflammatory mineral resorption and matrices degradation. We report that inflamed ODs have strong capabilities of matrix degradation and tissue resorption. Traditionally, ODs are regarded as hard-tissue regenerative cells; however, our data unexpectedly present ODs as a crucial population that participates in IR-associated tissue deconstruction. Specifically, we uncovered that nuclear factor-kappa b (NF-κB) signaling orchestrated Tumor necrosis factor α (TNF-α)-induced matrix metalloproteinases (Mmps) and Cathepsin K (Ctsk) functions in ODs to enhance matrix degradation and tissue resorption. Furthermore, TNF-α increases Rankl/Opg ratio in ODs via NF-κB signaling by impairing Opg expression but increasing Rankl level, which utterly makes ODs cell line 17IIA11 (A11) become Trap⁺ and Ctsk⁺ multinucleated cells to perform resorptive actions. Blocking of NF-κB signaling significantly rescues matrix degradation and resorptive functions of inflamed ODs via repressing vital inflammatory proteinases Mmps and Ctsk. Utterly, via utilizing NF-κB specific small molecule inhibitors we satisfactorily attenuated inflammatory ODs-associated human dental IR in vivo. Our data reveal the underlying mechanisms of inflammatory matrix degradation and resorption via proteinase activities in IR-related pathological conditions.

Endogenous Mechanisms of Craniomaxillofacial Repair: Toward Novel Regenerative Therapies

In the fields of oral and craniomaxillofacial surgery, regeneration of multiple tissue types-including bone, skin, teeth, and mucosal soft tissue-is often a desired outcome. However, limited endogenous capacity for regeneration, as well as predisposition of many tissues to fibrotic healing, may prevent recovery of normal form and function for patients. Recent basic science research has advanced our understanding of molecular and cellular pathways of repair in the oral/craniofacial region and how these are influenced by local microenvironment and embryonic origin. Here, we review the current state of knowledge in oral and craniomaxillofacial tissue repair/regeneration in four key areas: bone (in the context of calvarial defects and mandibular regeneration during distraction osteogenesis); skin (in the context of cleft lip/palate surgery); oral mucosa (in the context of minimally scarring repair of mucosal injuries); and teeth (in the context of dental disease/decay). These represent four distinct healing processes and outcomes. We will discuss both divergent and conserved pathways of repair in these contexts, with an eye toward fundamental mechanisms of regeneration vs. fibrosis as well as translational research directions. Ultimately, this knowledge can be leveraged to develop new cell-based and molecular treatment strategies to encourage bone and soft tissue regeneration in oral and craniomaxillofacial surgery.

Phenotype and molecular characterizations of a family with dentinogenesis imperfecta shields type II with a novel DSPP mutation

Background

Dentinogenesis imperfecta (DGI), Shields type-II is an autosomal dominant genetic disease which severely affects the function of the patients’ teeth. The dentin sialophosphoprotein (DSPP) gene is considered to be the pathogenic gene of DGI-II. In this study, a DGI-II family with a novel DSPP mutation were collected, functional characteristics of DGI cells and clinical features were analyzed to better understand the genotype-phenotype relationship of this disease.

Methods

Clinical data were collected, whole exome sequencing (WES) was conducted, and Sanger sequencing was used to verify the mutation sites. Physical characteristics of the patient’s teeth were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The localization of green fluorescent protein (GFP)-fused wild-type (WT) dentin sialoprotein (DSP) and its variant were evaluated via an immunocytochemistry (ICC) assay. The behaviors of human dental pulp stem cells (hDPSCs) were investigated by flow cytometry, osteogenic differentiation, and quantitative real-time polymerase chain reaction (qRT-PCR).

Results

A novel heterozygous mutation c.53T > G (p. Val18Gly) in DSPP was found in this family. The SEM results showed that the participants’ teeth had reduced and irregular dentinal tubes. The EDS results showed that the Ca/P ratio of the patients’ teeth was significantly higher than that of the control group. The ICC assay showed that the mutant DSP was entrapped in the endoplasmic reticulum (ER), while the WT DSP located mainly in the Golgi apparatus. In comparison with normal cells, the patient’s cells exhibited significantly decreased mineralization ability and lower expression levels of DSPP and RUNX2.

Conclusions

The c.53T > G (p. Val18Gly) DSPP variant was shown to present with rare hypoplastic enamel defects. Functional analysis revealed that this novel variant disturbs dentinal characteristics and pulp cell behavior.

Assessment of bone marrow-derived mesenchymal stem cells capacity for odontogenic differentiation and dentin regeneration in methimazole-treated albino rats (Light microscopic Study)

BACKGROUND

Methimazole is an antithyroid drug. It has side effects on many tissues. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are promising in the field of tissue regeneration.

OBJECTIVE

To investigate the capacity of BM-MSCs on odontogenic differentiation and dentin regeneration at different time intervals in methimazole treated rats.

METHODS

Twenty-eight male albino rats were classified as: Group I: got distilled water. Group II: obtained therapeutic dosage of methimazole as pro-drug "Neo-Mercazole®". Group III: received methimazole then solitary injection of BM-MSCs at day 21. Group IV: obtained methimazole and single injection of BM-MSCs at the beginning of the experiment. Light microscope was used to examine specimens. Recently formed collagen and β-catenin-immunoreactivity area% were appraised histomorphometrically and statistically.

RESULTS

Histological examination of odontoblasts and dentin illustrated normal structure in Group I and nearly normal features in Group IV. Group II demonstrated discontinuation of odontoblastic layer and areas of different stainability in dentin. Group III showed an evidently wide layer of odontoblast-like cells and distinct dentinal tubules. Masson's trichrome results of dentin in Groups I &IV showed apparently equal areas of new and old collagen. Group II illustrated old collagen mainly. Group III explored new collagen only. β-catenin-immunoreactivity was strong in Groups I & IV, mild in Group II and moderate in Group III. Statistical results revealed that the highest mean of newly formed collagen area% was in Group III, followed by Group I, Group IV then Group II respectively. Regarding β-catenin-immunoreactivity area%, the highest mean was recorded in Group I, subsequently Group IV, next Group III then Group II.

CONCLUSIONS

Methimazole has destructive consequences. BM-MSCs have a time-based increased capacity for odontogenic differentiation and regeneration of dentin.

Effectiveness of Direct Pulp Capping Bioactive Materials in Dentin Regeneration: A Systematic Review

Background: Regenerative endodontics aims to restore normal pulp function in necrotic and infected teeth, restoring protective functions, such as innate pulp immunity, pulp repair through mineralization, and pulp sensibility. The aim of this systematic review was to assess the dentin regeneration efficacy of direct pulp capping (DPC) biomaterials. Methods: The literature published between 2005 and 2021 was searched by using PubMed, Web of Science, Science Direct, Google Scholar, and Scopus databases. Clinical controlled trials, randomized controlled trials, and animal studies investigating DPC outcomes or comparing different capping materials after pulp exposure were included in this systematic review. Three independent authors performed the searches, and information was extracted by using a structured data format. Results: A total of forty studies (21 from humans and 19 from animals) were included in this systemic review. Histological examinations showed complete/partial/incomplete dentin bridge/reparative dentin formation during the pulp healing process at different follow-up periods, using different capping materials. Conclusions: Mineral trioxide aggregate (MTA) and Biodentine can induce dentin regeneration when applied over exposed pulp. This systematic review can conclude that MTA and its variants have better efficacy in the DPC procedure for dentin regeneration.

Genome-wide distribution of 5hmC in the dental pulp of mouse molars and incisors

The dental pulp is critical for the production of odontoblasts to create reparative dentin. In recent years dental pulp has become a promising source of mesenchymal stem cells that are capable of differentiating into multiple cell types. To elucidate the transcriptional control mechanisms specifying the early phases of odontoblast differentiation, we analyzed the DNA demethylation pattern associated with 5-hydroxymethylcytosine (5hmC) in the primary murine dental pulp. 5hmC plays an important role in chromatin accessibility and transcriptional control by modeling a dynamic equilibrium between DNA methylation and demethylation. Our research revealed 5hmC enrichment along genes and non-coding regulatory regions associated with specific developmental pathways in the genome of mouse incisor and molar dental pulp. Although the overall distribution of 5hmC is similar, the intensity and location of the 5hmC peaks significantly differs between the incisor and molar pulp genome, indicating cell type-specific epigenetic variations. Our study suggests that the differential DNA demethylation pattern could account for the distinct regulatory mechanisms underlying the tooth-specific ontogenetic programs.

Pediatric Endodontic Treatment of Adolescent Patients

This article is intended to familiarize clinicians with several pulp therapy modalities and new materials that are currently available for immature young pulp in the adolescent population. Objectives and considerations for immature young permanent teeth as well as the healing potential of the young pulp tissue after treatment of the inflammatory process are discussed. The article emphasizes that the future holds great possibilities for the regeneration of dental pulp in adolescent patients.

Expression of nitric oxide synthases in rat odontoblasts and the role of nitric oxide in odontoblastic differentiation of rat dental papilla cells

As precursor cells of odontoblasts, dental papilla cells (DPCs) form the dentin-pulp complex during tooth development. Nitric oxide (NO) regulates the functions of multiple cells and organ tissues, including stem cell differentiation and bone formation. In this paper, we explored the involvement of NO in odontoblastic differentiation. We verified the expression of NO synthase (NOS) in rat odontoblasts by nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining and immunohistochemistry in vivo. The expression of all three NOS isoforms in rat DPCs was confirmed by quantitative reverse-transcription polymerase chain reaction (qRT-PCR), immunofluorescence, and western blotting in vitro. The expression of neuronal NOS and endothelial NOS was upregulated during the odontoblastic differentiation of DPCs. Inhibition of NOS function by NOS inhibitor l-N^G -monomethyl arginine (L-NMMA) resulted in reduced formation of mineralized nodules and expression of dentin sialophosphoprotein (DSPP) and dentin matrix protein (DMP1) during DPC differentiation. The NO donor S-nitroso-N-acetylpenicillamine (SNAP, 0.1, 1, 10, and 100 μM) promoted the viability of DPCs. Extracellular matrix mineralization and odontogenic markers expression were elevated by SNAP at low concentrations (0.1, 1, and 10 μM) and suppressed at high concentration (100 μM). Blocking the generation of cyclic guanosine monophosphate (cGMP) with 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ) abolished the positive influence of SNAP on the odontoblastic differentiation of DPCs. These findings demonstrate that NO regulates the odontoblastic differentiation of DPCs, thereby influencing dentin formation and tooth development.

Cell Differentiation and Replication during Postnatal Development of the Murine First Molar

Simple Summary

Teeth are necessary to prepare food for swallowing. The process of teeth development before and after birth may be studied in normal mice and also by reproducing diseases or genetic conditions. However, mice teeth are different from human teeth, since mice have only permanent teeth. Moreover, their incisors continue to grow for the whole lifespan. Hence, it is important to know how the mouse teeth develop. We studied the development of the first molar in mice from birth to weaning and showed that dividing cells are located in a different part of the developing tooth according to age.

Abstract

Various signaling molecular pathways are involved in odontogenesis to promote cellular replication and differentiation. Tooth formation is controlled mainly by epithelial–mesenchymal interactions. The aim of this work was to investigate how cellular replication and differentiation ensue during the formation of the murine first molar in postnatal ages until eruption, focusing on morphogenesis, odontoblast differentiation and cellular replication. Wild-type CD1 mice were examined from birth to weaning. Morphogenesis and interaction between developing epithelial and mesenchymal tissues were evaluated in hematoxylin–eosin and Gomori trichome stained sections. Immunohistochemistry for nestin, which mediates the differentiation of odontoblasts, especially their polarization and elongation, showed that this intermediate filament was apparent already at postnatal day P1 in the apical region of odontoblasts and progressed apically from cusp tips, while it was not present in epithelial tissues. The expression of nuclear antigen Ki-67 highlighted dividing cells in both epithelial and mesenchymal tissues at P1, while one week later they were restricted to the cementoenamel junction, guiding root elongation. The link between odontoblast maturation and cellular replication in the different tooth tissues is essential to understand the development of tooth shape and dimension, to outline mechanisms of tooth morphogenesis and possibly eruption.

Advanced imaging of dentin microstructure

This study aimed to demonstrate the feasibility of using optical coherence tomography (OCT) for locating the sectioning site of a specimen before characterizing the ultrastructural features of dentin surfaces as well as the inner wall of the dentinal tubules (DT) using a field emission scanning electron microscope (FESEM). Eight sound human molar teeth were extracted, examined via cross-polarization optical coherence tomography (CP-OCT), embedded, and hemisectioned using a low-speed diamond sawing machine. Next, each sectioned surface was further trimmed, polished, and examined under a confocal laser scanning microscope (CLSM) to locate the target area on the superficial dentin. Subsequently, each section was gold-coated and examined using FESEM. Backscattered reflection from the dentin layer was less than that from the enamel under CP-OCT. Distinct reflections from certain enamel and dentin microstructures were observed before sectioning the specimens. Areas with enamel cracks and dentin defects were identified and avoided during sectioning. At the micron level, the CLSM images exhibited a homogenous distribution of the DT orifices. Low magnification FESEM images showed intertubular dentin as a loosely condensed globular layer with shallow grooves in between, whereas peritubular dentin exhibited more organized condensation of apatite crystals surrounding the DT orifices. High magnification of the DT revealed a cross-linking layer of mineralized collagen network extending in the peri-intratubular lumen, with scattered globules of matrix vesicles. CP-OCT enabled the realization of rapid initial scanning and image acquisition with high contrast at the micron scale before profound insights into dentin ultrastructures at the nano scale were provided by FESEM. The variations in structural densities of the dental tissues significantly affected the image contrast and helped identify underlying structures.

Current Concepts of Dentinal Hypersensitivity

INTRODUCTION

Although many clinical studies have reported on the prevalence of dental pain, far fewer studies have focused on the mechanisms of dental pain. This is an important gap because increased understanding of dental pain mechanisms may lead to improved diagnostic tests or therapeutic interventions. The aim of this study was to comprehensively review the literature on the mechanisms of dentinal sensitivity.

METHODS

PubMed and Ovid were searched for articles that addressed dentinal pain and or pulpal sensitivity. Because of the breadth of research ranging from cellular/molecular studies to clinical trials, a narrative review on the mechanisms of dentinal sensitivity was constructed based on the literature.

RESULTS

Five various mechanisms for dentinal sensitivity have been proposed: (1) the classic hydrodynamic theory, (2) direct innervation of dentinal tubules, (3) neuroplasticity and sensitization of nociceptors, (4) odontoblasts serving as sensory receptors, and (5) algoneurons.

CONCLUSIONS

These theories are not mutually exclusive, and it is possible that several of them contribute to dentinal sensitivity. Moreover, pulpal responses to tissue injury may alter the relative contribution of these mechanisms. For example, pulpal inflammation may lead to neuronal sprouting and peripheral sensitization. Knowledge of these mechanisms may prompt the development of therapeutic drugs that aim to disrupt these mechanisms, leading to more effective treatments for pulpal pain.

Dental-Derived Mesenchymal Stem Cells: State of the Art

Mesenchymal stem cells (MSCs) could be identified in mammalian teeth. Currently, dental-derived MSCs (DMSCs) has become a collective term for all the MSCs isolated from dental pulp, periodontal ligament, dental follicle, apical papilla, and even gingiva. These DMSCs possess similar multipotent potential as bone marrow-derived MSCs, including differentiation into cells that have the characteristics of odontoblasts, cementoblasts, osteoblasts, chondrocytes, myocytes, epithelial cells, neural cells, hepatocytes, and adipocytes. Besides, DMSCs also have powerful immunomodulatory functions, which enable them to orchestrate the surrounding immune microenvironment. These properties enable DMSCs to have a promising approach in injury repair, tissue regeneration, and treatment of various diseases. This review outlines the most recent advances in DMSCs' functions and applications and enlightens how these advances are paving the path for DMSC-based therapies.

Immediate Dentin Sealing: A Literature Review

Purpose

The immediate application of a dentin-bonding agent after tooth preparation and before impression-taking (immediate dentin sealing [IDS]) has been suggested to provide several advantages concerning bacterial microleakage, hypersensitivity, and bonding quality. We reviewed the literature and clarified certain aspects related to each step of IDS application.

Materials and Methods

The search strategy comprised an electronic research in MEDLINE, Cochrane, Ovid and Scopus for studies published from January 1990 to December 2020 regarding the IDS technique and including both in vitro and clinical studies.

Results

After exclusion of irrelevant or duplicate articles, 88 articles focusing on aspects of the IDS technique were assessed. IDS seems to be advantageous with regard to bond strength, gap formation, bacterial microleakage, and dentin hypersensitivity. However, issues arising from interaction with impression materials, the provisional phase, and conditioning methods before cementation require further investigation.

Conclusion

There are no documented reasons preventing clinicians applying IDS in their everyday practice. On the contrary, the presented technique seems to be beneficial in certain aspects regarding indirect restorations.

Role of Cell Death in Cellular Processes During Odontogenesis

The development of a tooth germ in a precise size, shape, and position in the jaw, involves meticulous regulation of cell proliferation and cell death. Apoptosis, as the most common type of programmed cell death during embryonic development, plays a number of key roles during odontogenesis, ranging from the budding of the oral epithelium during tooth initiation, to later tooth germ morphogenesis and removal of enamel knot signaling center. Here, we summarize recent knowledge about the distribution and function of apoptotic cells during odontogenesis in several vertebrate lineages, with a special focus on amniotes (mammals and reptiles). We discuss the regulatory roles that apoptosis plays on various cellular processes during odontogenesis. We also review apoptosis-associated molecular signaling during tooth development, including its relationship with the autophagic pathway. Lastly, we cover apoptotic pathway disruption, and alterations in apoptotic cell distribution in transgenic mouse models. These studies foster a deeper understanding how apoptotic cells affect cellular processes during normal odontogenesis, and how they contribute to dental disorders, which could lead to new avenues of treatment in the future.

The role of biomineralization in disorders of skeletal development and tooth formation

The major mineralized tissues are bone and teeth, which share several mechanisms governing their development and mineralization. This crossover includes the hormones that regulate circulating calcium and phosphate concentrations, and the genes that regulate the differentiation and transdifferentiation of cells. In developing endochondral bone and in developing teeth, parathyroid hormone-related protein (PTHrP) acts in chondrocytes to delay terminal differentiation, thereby increasing the pool of precursor cells. Chondrocytes and (in specific circumstances) pre-odontoblasts can also transdifferentiate into osteoblasts. Moreover, bone and teeth share outcomes when affected by systemic disorders of mineral homeostasis or of the extracellular matrix, and by adverse effects of treatments such as bisphosphonates and fluoride. Unlike bone, teeth have more permanent effects from systemic disorders because they are not remodelled after they are formed. This Review discusses the normal processes of bone and tooth development, followed by disorders that have effects on both bone and teeth, versus disorders that have effects in one without affecting the other. The takeaway message is that bone specialists should know when to screen for dental disorders, just as dental specialists should recognize when a tooth disorder should raise suspicions about a possible underlying bone disorder.

Mitochondrial DNA leakage induces odontoblast inflammation via the cGAS-STING pathway

Background

Mitochondrial DNA (mtDNA) is a vital driver of inflammation when it leaks from damaged mitochondria into the cytosol. mtDNA stress may contribute to cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway activation in infectious diseases. Odontoblasts are the first cells challenged by cariogenic bacteria and involved in maintenance of the pulp immune and inflammatory responses to dentine-invading pathogens. In this study, we investigated that mtDNA as an important inflammatory driver participated in defending against bacterial invasion via cGAS-STING pathway in odontoblasts.

Methods

The normal tissues, caries tissues and pulpitis tissues were measured by western blotting and immunohistochemical staining. Pulpitis model was built in vitro to evaluated the effect of the cGAS-STING pathway in odontoblast-like cell line (mDPC6T) under inflammation. Western blot and real-time PCR were performed to detect the expression of cGAS-STING pathway and pro-inflammatory cytokines. The mitochondrial function was evaluated reactive oxygen species (ROS) generated by mitochondria using MitoSOX Red dye staining. Cytosolic DNA was assessed by immunofluorescent staining and real-time PCR in mDPC6T cells after LPS stimulation. Furthermore, mDPC6T cells were treated with ethidium bromide (EtBr) to deplete mtDNA or transfected with isolated mtDNA. The expression of cGAS-STING pathway and pro-inflammatory cytokines were measured.

Results

The high expression of cGAS and STING in caries and pulpitis tissues in patients, which was associated with inflammatory progression. The cGAS-STING pathway was activated in inflamed mDPC6T. STING knockdown inhibited the nuclear import of p65 and IRF3 and restricted the secretion of the inflammatory cytokines CXCL10 and IL-6 induced by LPS. LPS caused mitochondrial damage in mDPC6T, which promoted mtDNA leakage into the cytosol. Depletion of mtDNA inhibited the cGAS-STING pathway and nuclear translocation of p65 and IRF3. Moreover, repletion of mtDNA rescued the inflammatory response, which was inhibited by STING knockdown.

Conclusion

Our study systematically identified a novel mechanism of LPS-induced odontoblast inflammation, which involved mtDNA leakage from damaged mitochondria into the cytosol stimulating the cGAS-STING pathway and the inflammatory cytokines IL-6 and CXCL10 secretion. The mtDNA-cGAS-STING axis could be a potent therapeutic target to prevent severe bacterial inflammation in pulpitis.

Hard Dental Tissues Regeneration-Approaches and Challenges

With the development of the modern concept of tissue engineering approach and the discovery of the potential of stem cells in dentistry, the regeneration of hard dental tissues has become a reality and a priority of modern dentistry. The present review reports the recent advances on stem-cell based regeneration strategies for hard dental tissues and analyze the feasibility of stem cells and of growth factors in scaffolds-based or scaffold-free approaches in inducing the regeneration of either the whole tooth or only of its component structures.

A Cross-Sectional Cohort Study of the Effects of FGF23 Deficiency and Hyperphosphatemia on Dental Structures in Hyperphosphatemic Familial Tumoral Calcinosis

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder caused by mutations in FGF23, GALNT3, KLOTHO, or FGF23 autoantibodies. Prominent features include high blood phosphate and calcific masses, usually adjacent to large joints. Dental defects have been reported, but not systematically described. Seventeen patients with HFTC followed at the National Institutes of Health underwent detailed clinical, biochemical, molecular, and dental analyses. Studies of teeth included intraoral photos and radiographs, high-resolution μCT, histology, and scanning electron microscopy (SEM). A scoring system was developed to assess the severity of tooth phenotype. Pulp calcification was found in 13 of 14 evaluable patients. Short roots and midroot bulges with apical thinning were present in 12 of 13 patients. Premolars were most severely affected. μCT analyses of five HFTC teeth revealed that pulp density increased sevenfold, whereas the pulp volume decreased sevenfold in permanent HFTC teeth compared with age- and tooth-matched control teeth. Histology revealed loss of the polarized odontoblast cell layer and an obliterated pulp cavity that was filled with calcified material. The SEM showed altered pulp and cementum structures, without differences in enamel or dentin structures, when compared with control teeth. This study defines the spectrum and confirms the high penetrance of dental features in HFTC. The phenotypes appear to be independent of genetic/molecular etiology, suggesting hyperphosphatemia or FGF23 deficiency may be the pathomechanistic driver, with prominent effects on root and pulp structures, consistent with a role of phosphate and/or FGF23 in tooth development. Given the early appearance and high penetrance, cognizance of HFTC-related features may allow for earlier diagnosis and treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.