The roles of odontoblasts in dental pulp innate immunity

Immune System of Dental Pulp in Inflamed and Normal Tissue

Teeth are vulnerable to structural compromise, primarily attributed to carious lesions, in which microorganisms originating from the oral cavity deteriorate the mineralized structures of enamel and dentin, subsequently infiltrating the underlying soft connective tissue, known as the dental pulp. Nonetheless, dental pulp possesses the necessary capabilities to detect and defend against bacteria and their by-products, using a variety of intricate defense mechanisms. The pulp houses specialized cells known as odontoblasts, which encounter harmful substances produced by oral bacteria. These cells identify pathogens at an early stage and commence the immune system response. As bacteria approach the pulp, various cell types within the pulp, such as different immune cells, stem cells, fibroblasts, as well as neuronal and vascular networks, contribute a range of defense mechanisms. Therefore, the immune system is present in the healthy pulp to restrain the initial spread of pathogens, and then in the inflamed pulp, it prepares the conditions for necrosis or regeneration, so inflammatory response mechanisms play a critical role in maintaining tissue homeostasis. This review aims to consolidate the existing literature on the immune system in dental pulp, encompassing current knowledge on this topic that explains the diverse mechanisms of recognition and defense against pathogens exhibited by dental pulp cells, elucidates the mechanisms of innate and adaptive immunity in inflamed pulp, and highlights the difference between inflamed and normal pulp tissue.

TLR2 and TLR4 Polymorphisms Are Not Associated with Dental Caries in Polish Children

The aim of the present study was to analyze the association of the TLR2 (Toll-like receptor 2 gene) 2258G>A (rs5743708), TLR4 (Toll-like receptor 4 gene) 896A>G (rs4986790), and TLR4 1196C>T (rs4986791) polymorphisms with dental caries in Polish children. The participants, 261 15-year-old children, were divided into two groups: 82 cases (i.e., children with DMFT (Decayed, Missing, and Filled Teeth) index >5, having either moderate or high caries experience, assigned as the "higher" caries experience group) and 179 controls (i.e., children with DMFT ≤ 5, having either low or very low caries experience, assigned as the "lower" caries experience group). Genomic DNA was isolated from buccal swabs, and genotyping was determined by means of real-time PCR (polymerase chain reaction). There were no significant differences in the genotype or allele distributions in all tested SNPs (single nucleotide polymorphisms) between children with "higher" caries experience and those with "lower" caries experience. TLR4 haplotype frequencies did not differ significantly between cases and controls. In an additional analysis with another case definition applied (subjects with DMFT ≥ 1 were assigned as "cases", whereas children with DMFT = 0 were assigned as "controls"), no significant differences in the TLR2 and TLR4 genotype, allele frequencies, and TLR4 haplotype frequencies were found between the case and the control groups. The results of the present study broaden our knowledge on the potential genetic factors that might affect caries risk and suggest that TLR2 rs5743708 and TLR4 rs4986790 and rs4986791 SNPs are not associated with dental caries susceptibility in Polish children.

Mitochondrial homeostasis in odontoblast: Physiology, pathogenesis and targeting strategies

Caries and pulpitis remain a major global disease burden and affect the quality of life of patients. Odontoblasts are key players in the progression of caries and pulpitis, not only secreting and mineralizing to form dentin, but also acting as a wall of defense to initiate immune defenses. Mitochondrion is an information processor for numerous cellular activities, and dysregulation of mitochondrion homeostasis not only affects cellular metabolism but also triggers a wide range of diseases. Elucidating mitochondrial homeostasis in odontoblasts can help deepen scholars' understanding of odontoblast-associated diseases. Articles on mitochondrial homeostasis in odontoblasts were evaluated for information pertinent to include in this narrative review. This narrative review focused on understanding the complex interplay between mitochondrial homeostasis in odontoblasts under physiological and pathological conditions. Furthermore, mitochondria-centered therapeutic strategies (including mitochondrial base editing, targeting platforms, and mitochondrial transplantation) were emphasized by resolving key genes that regulate mitochondrial function. Mitochondria are involved in odontoblast differentiation and function, and act as mitochondrial danger-associated molecular patterns (mtDAMPs) to mediate odontoblast pathological progression. Novel mitochondria-centered therapeutic strategies are particularly attractive as emerging therapeutic approaches for the maintenance of mitochondrial homeostasis. It is expected to probe key events of odontoblast differentiation and advance the clinical resolution of dentin formation and mineralization disorders and odontoblast-related diseases.

Dentin Mechanobiology: Bridging the Gap between Architecture and Function

It is remarkable how teeth maintain their healthy condition under exceptionally high levels of mechanical loading. This suggests the presence of inherent mechanical adaptation mechanisms within their structure to counter constant stress. Dentin, situated between enamel and pulp, plays a crucial role in mechanically supporting tooth function. Its intermediate stiffness and viscoelastic properties, attributed to its mineralized, nanofibrous extracellular matrix, provide flexibility, strength, and rigidity, enabling it to withstand mechanical loading without fracturing. Moreover, dentin's unique architectural features, such as odontoblast processes within dentinal tubules and spatial compartmentalization between odontoblasts in dentin and sensory neurons in pulp, contribute to a distinctive sensory perception of external stimuli while acting as a defensive barrier for the dentin-pulp complex. Since dentin's architecture governs its functions in nociception and repair in response to mechanical stimuli, understanding dentin mechanobiology is crucial for developing treatments for pain management in dentin-associated diseases and dentin-pulp regeneration. This review discusses how dentin's physical features regulate mechano-sensing, focusing on mechano-sensitive ion channels. Additionally, we explore advanced in vitro platforms that mimic dentin's physical features, providing deeper insights into fundamental mechanobiological phenomena and laying the groundwork for effective mechano-therapeutic strategies for dentinal diseases.

Inducing cyclooxygenase-2 expression, prostaglandin E2 and prostaglandin F2α production of human dental pulp cells by activation of toll-like receptor-3, mitogen-activated protein kinase kinase/extracellular signal-regulated kinase and p38 signaling

Background/purpose

Bacterial infection was the major etiology for pulpal/root canal infection. This study aimed to investigate the activation of toll-like receptor-3 (TLR) on cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) and PGF2α production of human dental pulp cells (HDPCs) and associated signaling.

Materials and methods

HDPCs were exposed to different concentrations of Poly (I:C) (a TLR3 activator). Cell viability was determined by 3- (4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay and alkaline phosphatase (ALP) activity was evaluated by ALP staining. Activation of extracellular signal-regulated kinase (ERK) and p38 by Poly (I:C) was determined by immunofluorescent staining. The COX-2 protein expression was analyzed by Western blot. PGE2 and PGF2α production was measured by enzyme-linked immunosorbent assay. The mRNA expression was studied by real-time polymerase-chain reaction. Moreover, HDPCs were exposed to Poly(I:C) with/without U0126 or SB203580 treatment and analysis of COX-2 expression and prostanoid production were conducted.

Results

Poly (I:C) showed little effect on ALP activity, but decreased viability of HDPCs. It stimulated COX-2 mRNA and protein expression. Poly (I:C) induced PGE2 and PGF2α production of HDPCs. Poly (I:C) activated p-ERK, and p-p38 protein expression. Treatment by U0126 (a mitogen-activated protein kinase kinase (MEK)/ERK inhibitor) and SB203580 (a p38 inhibitor) attenuated Poly (I:C)-induced COX-2 mRNA and protein expression as well as PGE2 and PGF2α production.

Conclusion

TLR3 activation is involved in the infection and inflammatory responses of pulp tissues, via MEK/ERK, and p38 signaling to mediate COX-2 expression as well as PGE2 and PGF2α production, contributing to the pathogenesis and progression of pulpal/periapical diseases.

Morphometric parameters of dental pulp in immature teeth in a sheep model after mechanical pulp exposure and restoration with reinforced zinc oxide-eugenol

Background

The aim of the study was to investigate the morphometric parameters of dental pulp in open apices immature teeth in a sheep model after mechanical pulp exposure and restoration with reinforced zinc oxide-eugenol.

Materials and Methods

In this experimental study, a total of 12 immature mandibular central incisors from six adult male sheep, weighing 30-40 kg and with the age of 1 year old with Merino race were examined. After anesthesia, the pulps of the teeth in the case group were mechanically exposed and then were restored with reinforced zinc oxide-eugenol and amalgam. In the control group, the teeth remained intact. The animals were sacrificed at intervals of 2, 4, 6, and 8 weeks (E2, E4, E6, and E8) in the case and 2 and 8 weeks (C2 and C8) in the control groups. Then, their teeth were removed with the surrounding supporting tissues and alveolar bones. Tissue processing and staining were done, and the sections were examined under a light microscope. The Kruskal-Wallis and Mann-Whitney U tests were used to analyze the data and compare the changes between the two groups. P < 0.05 was considered statistically significant.

Results

In response to mechanical exposure, reparative or tertiary dentin was formed, and its thickness increased during the time of the study. The thickness of the odontoblastic layer in the E4 group was the highest amount. The pulp chamber diameter in the C2 group was significantly larger than the other groups, and the diameter of the apical foramen in the E8 was decreased significantly compared to the controls (P < 0.05).

Conclusion

In response to mechanical exposure and restoration with reinforced zinc oxide-eugenol, some morphometric parameters of the dental pulp changed significantly in the sheep model compared to the controls.

Piezo Mediates the Mechanosensation and Injury-Repair of Pulpo-Dentinal Complex

OBJECTIVES

The aim of this research was to investigate the functions of Piezo channels in dentin defect, including mechanical signalling and odontoblast responses.

METHODS

Rat dentin-defect models were constructed, and spatiotemporal expression of Piezo proteins was detected in the pulpo-dentinal complex. Real-time polymerase chain reaction (rtPCR) was used to investigate the functional expression pattern of Piezo channels in odontoblasts. Moreover, RNA interference technology was employed to uncover the underlying mechanisms of the Piezo-driven inflammatory response and repair under fluid shear stress (FSS) conditions in vitro.

RESULTS

Piezo1 and Piezo2 were found to be widely expressed in the odontoblast layer and dental pulp in the rat dentin-defect model during the end stage of reparative dentin formation. The expression levels of the Piezo1 and Piezo2 genes in MDPC-23 cells were high in the initial stage under FSS loading and then decreased over time. Moreover, the expression trends of inflammatory, odontogenic, and mineralisation genes were generally contrary to those of Piezo1 and Piezo2 over time. After silencing of Piezo1/Piezo2, FSS stimulation resulted in significantly higher expression of inflammatory, odontogenesis, and mineralisation genes in MDPC-23 cells. Finally, the expression of genes involved in the integrin β1/ERK1 and Wnt5b/β-catenin signalling pathways was changed in response to RNA silencing of Piezo1 and Piezo2.

CONCLUSIONS

Piezo1 and Piezo2 may be involved in regulating the expression of inflammatory and odontogenic genes in odontoblasts stimulated by FSS.

Antibacterial and Immunomodulatory Properties of Stem Cells from Human Exfoliated Deciduous Teeth: An In Vitro Study

Stem cells from human exfoliated deciduous teeth (SHED) provide an important autologous source for stem cell-based regenerative therapies with their easy acquisition and multipotency. However, the understanding of their antibacterial and immunomodulatory properties is limited. This in vitro research aims to determine whether SHED inhibits the growth of Streptococcus mutans (S. mutans) and Enterococcus faecalis (E. faecalis), as well as whether or not it has immunomodulatory effects by measuring interleukins (ILs)-2 and -6 levels. SHEDs were derived from the pulp of deciduous teeth that had undergone up to two-thirds of their roots' resorption. Isolated SHEDs were characterized on their morphological features, viability, assessment of surface markers, and in vitro induction into osteocytes and adipocytes. SHED was tested for its antibacterial efficacy against S. mutans and E. faecalis using a colony-forming units (CFU) assay. Lastly, we checked the cytokine levels by enzyme-linked immune sorbent assay (ELISA) for assessing the immunomodulatory properties of SHED. The results showed that the established SHED had fibroblastic morphology with higher viability. The ability to differentiate into osteocytes and adipocytes, as well as the expression of stem cell-specific markers, demonstrated their potential and flexibility under in vitro settings. SHED demonstrated antibacterial characteristics by significantly (p < 0.05) lowering S. mutans CFU, whereas E. faecalis CFU was either unaffected by or just slightly affected by the cells. SHED also helped keep inflammatory indicators, including IL-2 and IL-6, at stable levels when compared to the control. The results indicate that SHED may aid in preventing or reducing an infection due to its antibacterial activity and may provide immunomodulatory activities by controlling the production of cytokines.

How to cite this article

Tyagi A, Shetty J, Shetty S, et al. Antibacterial and Immunomodulatory Properties of Stem Cells from Human Exfoliated Deciduous Teeth: An In Vitro Study. Int J Clin Pediatr Dent 2023;16(S-3):S240-S246.

Activin receptor-like kinase 3: a critical modulator of development and function of mineralized tissues

Mineralized tissues, such as teeth and bones, pose significant challenges for repair due to their hardness, low permeability, and limited blood flow compared to soft tissues. Bone morphogenetic proteins (BMPs) have been identified as playing a crucial role in mineralized tissue formation and repair. However, the application of large amounts of exogenous BMPs may cause side effects such as inflammation. Therefore, it is necessary to identify a more precise molecular target downstream of the ligands. Activin receptor-like kinase 3 (ALK3), a key transmembrane receptor, serves as a vital gateway for the transmission of BMP signals, triggering cellular responses. Recent research has yielded new insights into the regulatory roles of ALK3 in mineralized tissues. Experimental knockout or mutation of ALK3 has been shown to result in skeletal dysmorphisms and failure of tooth formation, eruption, and orthodontic tooth movement. This review summarizes the roles of ALK3 in mineralized tissue regulation and elucidates how ALK3-mediated signaling influences the physiology and pathology of teeth and bones. Additionally, this review provides a reference for recommended basic research and potential future treatment strategies for the repair and regeneration of mineralized tissues.

3D Organoids for Regenerative Endodontics

Apical periodontitis is the inflammation and destruction of periradicular tissues, mediated by microbial factors originating from the infected pulp space. This bacteria-mediated inflammatory disease is known to interfere with root development in immature permanent teeth. Current research on interventions in immature teeth has been dedicated to facilitating the continuation of root development as well as regenerating the dentin-pulp complex, but the fundamental knowledge on the cellular interactions and the role of periapical mediators in apical periodontitis in immature roots that govern the disease process and post-treatment healing is limited. The limitations in 2D monolayer cell culture have a substantial role in the existing limitations of understanding cell-to-cell interactions in the pulpal and periapical tissues. Three-dimensional (3D) tissue constructs with two or more different cell populations are a better physiological representation of in vivo environment. These systems allow the high-throughput testing of multi-cell interactions and can be applied to study the interactions between stem cells and immune cells, including the role of mediators/cytokines in simulated environments. Well-designed 3D models are critical for understanding cellular functions and interactions in disease and healing processes for future therapeutic optimization in regenerative endodontics. This narrative review covers the fundamentals of (1) the disease process of apical periodontitis; (2) the influence and challenges of regeneration in immature roots; (3) the introduction of and crosstalk between mesenchymal stem cells and macrophages; (4) 3D cell culture techniques and their applications for studying cellular interactions in the pulpal and periapical tissues; (5) current investigations on cellular interactions in regenerative endodontics; and, lastly, (6) the dental-pulp organoid developed for regenerative endodontics.

Next-generation biomaterials for dental pulp tissue immunomodulation

OBJECTIVES

The current standard for treating irreversibly damaged dental pulp is root canal therapy, which involves complete removal and debridement of the pulp space and filling with an inert biomaterial. A regenerative approach to treating diseased dental pulp may allow for complete healing of the native tooth structure and enhance the long-term outcome of once-necrotic teeth. The aim of this paper is, therefore, to highlight the current state of dental pulp tissue engineering and immunomodulatory biomaterials properties, identifying exciting opportunities for their synergy in developing next-generation biomaterials-driven technologies.

METHODS

An overview of the inflammatory process focusing on immune responses of the dental pulp, followed by periapical and periodontal tissue inflammation are elaborated. Then, the most recent advances in treating infection-induced inflammatory oral diseases, focusing on biocompatible materials with immunomodulatory properties are discussed. Of note, we highlight some of the most used modifications in biomaterials' surface, or content/drug incorporation focused on immunomodulation based on an extensive literature search over the last decade.

RESULTS

We provide the readers with a critical summary of recent advances in immunomodulation related to pulpal, periapical, and periodontal diseases while bringing light to tissue engineering strategies focusing on healing and regenerating multiple tissue types.

SIGNIFICANCE

Significant advances have been made in developing biomaterials that take advantage of the host's immune system to guide a specific regenerative outcome. Biomaterials that efficiently and predictably modulate cells in the dental pulp complex hold significant clinical promise for improving standards of care compared to endodontic root canal therapy.

Development of Rat Caries-Induced Pulpitis Model for Vital Pulp Therapy

Rodent animal models for vital pulp therapy are commonly used in dental research because their tooth anatomy and cellular processes are similar to the anatomy and processes in humans. However, most studies have been conducted using uninfected sound teeth, which makes it difficult to adequately assess the inflammatory shift after vital pulp therapy. In the present study, we aimed to establish a caries-induced pulpitis model based on the conventional rat caries model and then evaluate inflammatory changes during the wound-healing process after pulp capping in a model of reversible pulpitis induced by carious infection. To establish the caries-induced pulpitis model, the pulpal inflammatory status was investigated at different stages of caries progression by immunostaining targeted to specific inflammatory biomarkers. Immunohistochemical staining revealed that both Toll-like receptor 2 and proliferating cell nuclear antigen were expressed in moderate and severe caries-stimulated pulp, indicating that an immune reaction occurred at both stages of caries progression. M2 macrophages were predominant in moderate caries-stimulated pulp, whereas M1 macrophages were predominant in the severe caries-stimulated pulp. Pulp capping in teeth with moderate caries (i.e., teeth with reversible pulpitis) led to complete tertiary dentin formation within 28 d after treatment. Impaired wound healing was observed in teeth with severe caries (i.e., teeth with irreversible pulpitis). During the wound-healing process in reversible pulpitis after pulp capping, M2 macrophages were predominant at all time points; their proliferative capacity was upregulated in the early stage of wound healing compared with healthy pulp. In conclusion, we successfully established a caries-induced pulpitis model for studies of vital pulp therapy. M2 macrophages have an important role in the early stages of the wound-healing process in reversible pulpitis.

Upregulation of transient receptor potential ankyrin 1 (TRPA1) but not transient receptor potential vanilloid 1 (TRPV1) during primary tooth carious progression

OBJECTIVE

To quantify the changes in Transient Receptor Potential Ankyrin 1 (TRPA1) and Transient Receptor Potential Vanilloid 1 (TRPV1) expression throughout the process of inflammation induced by caries.

METHODS

Forty primary teeth were obtained from children requiring dental extractions under local or general anesthesia. The teeth were grouped according to three stages reflecting the progression of dental caries: nine with intact dentin, 15 with exposed dentin (but not to the extent of the pulp), and 16 with exposed pulp. Immunofluorescence was used to validate the presence of dental pulp inflammation by demonstrating a decrease in NF-κB nuclear translocation. The expression levels of TRPA1 and TRPV1 were quantified in the pulp horn and the subodontoblastic and midcoronal regions of the pulp.

RESULTS

The percentage of cells with NF-κB nuclear translocation was highest for teeth with intact dentin and decreased progressively during the progression of caries. TRPA1 expression was lowest in intact teeth and gradually increased as caries advanced. TRPV1 expression was similar in teeth with intact dentin, exposed dentin, and exposed pulp.

CONCLUSION

The differences in TRPA1 and TRPV1 expression in response to caries suggest that these receptors play unique roles in the immune response during the progression of caries and that the pathophysiology of inflammation in the dental pulp varies between the early and late stages of caries.

Lipopolysaccharides and hydrogen peroxide induce contrasting pathological conditions in dental pulpal cells

AIM

To determine the effects of lipopolysaccharides (LPS), hydrogen peroxide (H₂ O₂ ), and both combined on cell proliferation/differentiation, inflammation, mitochondrial dynamics as indicated by mitochondrial fission/fusion, antioxidants as indicated by superoxide dismutase 2 (SOD2), and apoptosis of human dental pulpal cells (HDPCs).

METHODOLOGY

Pulpal tissues from eight healthy subjects (n = 8) were collected from Faculty of Dentistry, Chiang Mai University. Isolated HDPCs from healthy donors were divided into four experimental groups: vehicle, 20 μg/ml LPS, 400 μM H₂ O₂ , and the two combined. All experimental groups were investigated to assess cell proliferation, mineralization, differentiation, inflammation, mitochondrial dynamics, antioxidants, and apoptosis.

RESULTS

H₂ O₂ and combined agents decreased cell proliferation of HDPCs equally. LPS, H₂ O_2, and both combined decreased mineralization and differentiation with an increase in tumour necrosis factor-alpha (TNF-α) levels. Surprisingly, LPS and combined agents increased SOD2 expression and caused an imbalance in mitochondrial dynamics. A significant increase in apoptosis was observed in the case of H₂ O₂ and combined agents.

CONCLUSIONS

These findings suggest that LPS induced inflammation, imbalanced mitochondrial dynamics, and reduced cell differentiation without altering apoptosis and cell proliferation. However, H₂ O₂ decreased cell proliferation, and differentiation, and increased inflammation, and apoptosis without interfering with mitochondrial dynamics. Based on our findings, combining LPS and H₂ O₂ could be potentially used as the inducers in in vitro study to mimic the clinical pulpitis.

Concentrated Growth Factors Combined with Lipopolysaccharide Stimulate the In Vitro Regenerative and Osteogenic Activities of Human Dental Pulp Stem Cells by Balancing Inflammation

Aim

We investigated the long-term effects of exposure to concentrated growth factors (CGFs) on the regenerative properties of dental pulp stem cells (DPSCs) in the presence and absence of lipopolysaccharide (LPS) as a proinflammatory agent.

Methods

DPSCs were cultured with CGF at different concentrations of LPS (0.1, 1, and 10 µg/ml) for 21 days. Then, using MTT and scratch assays, the cell viability and migration were examined. Osteogenic stimulation was evaluated by alkaline phosphatase (ALP) staining and Sirius Red staining, which determined the ALP activity and collagen levels, respectively. The expression levels of osteogenic markers were quantified using the qRT-PCR method. One-way analysis of variance (ANOVA) and Tukey's HSD test were used to analyze differences between groups.

Results

Long-term treatment of DPSCs with CGFs reduced LPS-induced cell death. Moreover, CGF and LPS (1 µg/ml), either in combination or alone, improved the DPSC migratory ability and caused a significant increase in osteogenic stimulation through the upregulation of collagen levels and ALP activity. Additionally, CGFs significantly upregulated RUNX2, DSPP, OCN, and OPN mRNA levels (as osteogenic markers), while LPS (1 µg/ml) only significantly increased OCN overexpression.

Conclusion

Our findings are evidence that CGF could be a promising agent to induce dentin-pulp complex healing in long-term chronic inflammation.

Gene expression analysis of toll like receptor 2 and 4, Dectin-1, Osteopontin and inflammatory cytokines in human dental pulp ex-vivo

BACKGROUND

Toll like receptors (TLR) 2 and 4 present on innate immune cells of the dental pulp detect cariogenic bacteria. Along with bacteria, C. albicans may also be present in dental caries. The presence of C. albicans can be detected by Dectin-1 a C type Lectin receptor. Expression of Dectin-1 in human pulpits has not been reported. Similarly, cytokines are released as a consequence of dental pulp inflammation caused by cariogenic bacteria. The T helper (Th) 1 inflammatory response leads to exacerbation of inflammation and its relationship with Osteopontin (OPN) is not known in pulp inflammation.

OBJECTIVE

The aim of this study was to observe the expression of Dectin-1, TLR-2, OPN and pro-inflammatory cytokines in irreversibly inflamed human dental pulp and to observe relationship between Dectin-1/TLR-2 and OPN/Pro-inflammatory cytokines in the presence of appropriate controls.

METHODS

A total of 28 subjects diagnosed with irreversible pulpitis were included in this ex-vivo study. Fifteen samples were subjected to standard hematoxylin and Eosin (H&E) and immunohistochemistry staining. Whereas, gene expression analysis was performed on 13 samples to observe mRNA expression of pro-inflammatory cytokines; tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1 beta (ß), IL-6 Dectin-1, OPN, TLR-2 and TLR-4. SPSS version 21 was used for statistical analysis. One way analysis of variance (ANOVA), Pearson correlation and Chi-square test were used at p ≤ 0.05.

RESULTS

Gene expressions of Dectin-1, TLR-2 and TLR-4 were observed in all samples. Dectin-1 and TLR-2 expressions were significantly correlated (r = 0.5587, p = 0.0002). Similarly, OPN and TNF-α expression showed a significant correlation (r = 0.5860, p = 0001). The agreement between histologic and clinical diagnosis was 69.2% in the cases of irreversible pulpitis.

CONCLUSION

Dectin-1 was expressed by inflamed human dental pulp. Dectin-1 and TLR-2 expression pattern was suggestive of a collaborative receptor response in inflamed pulp environment. OPN and TNF-α expressions showed a positive correlation indicating a possible relationship.

Clinical, radiological, and histological correlation in diagnosis of pulpitis

BACKGROUND

To establish an endodontic diagnosis, a clinician should consider a variety of factors. Various studies have failed to demonstrate a strong correlation between histological findings with clinical and radiographic assessments. This study sought to evaluate the histopathological features of reversible and irreversible pulpitis diseases and their correlation with clinical diagnosis in extracted human molar teeth.

MATERIALS AND METHODS

In this experimental ex vivo study, 75 molars with caries and three intact molars were used. According to the radiographic findings and clinical criteria and the need for root canal therapy, samples were categorized as having normal/reversible pulpitis and irreversible pulpitis. Immediately after extraction, an exposure was made at 2 mm below the cementoenamel junction. Formalin-fixed specimens were decalcified, sectioned and stained with hematoxylin and eosin for histological examinations using light microscopy. Variables including the type and severity of the inflammation, hyperemia, necrosis, fibrosis and the existence of an odontoblastic layer and dentin bridge were evaluated. The Fisher's exact test and the Chi-squared test were used for statistical analysis. P <0.05 was considered as significant.

RESULTS

Acute inflammation, hyperemia and pulp exposure were significantly more common among subjects with irreversible pulpitis (P < 0/005). However, fibrosis was significantly higher in the reversible group (P < 0/005). There were no statistically significant differences between the groups regarding the other variables.

CONCLUSION

Some discrepancies between clinical, radiographic and histological findings were observed in our experimental study. Indeed, effective clinical practice requires consideration of all discrepancies found.

Hematopoietic progenitor cells specifically induce a unique immune response in dental pulp under conditions of systemic inflammation

Teeth are exposed to various stimuli, including bacterial, thermal, and physical stimuli. Therefore, immune cells present in the normal dental pulp and the immune response to these stimuli have been studied. However, the relationship between systemic inflammation, such as that induced by viral infection, and changes occurring in dental pulp is not well known. This study aimed to investigate the immunological and hematological responses to systemic inflammation in dental pulp. Poly(I:C), a toll-like receptor 3 agonist, was injected into mice every two days to simulate a systemic inflammatory state in which type I interferon (IFN–I) was produced. The untreated normal state was defined as a steady state, and the states of acute and chronic inflammation were defined according to the period of administration. Changes in the abundance and dynamics of hematopoietic and immune cells in dental pulp, bone marrow and peripheral blood were quantitatively investigated in the steady state and under conditions of inflammation induced by IFN-l. We found that dental pulp in the steady state contained only a few hematopoietic cells, but a greater variety of immune cells than previously reported. B cells were also found in the steady state. An increase in multipotent progenitor cell levels was observed in the dental pulp during both acute and chronic inflammation. The increased multipotent progenitor cells in the dental pulp during acute inflammation tended to differentiate into the myeloid lineage. On the other hand, there was an influx of B cells into the dental pulp during chronic inflammation. These results revealed that a unique immune response is induced in the dental pulp by systemic inflammation, which would lead to a significant change in the perspective of dentists on the utility of dental pulp in the management of systemic diseases.

Upregulation of Toll-like Receptor 2 in Dental Primary Afferents Following Pulp Injury

Pulpitis (toothache) is a painful inflammation of the dental pulp and is a prevalent problem throughout the world. This pulpal inflammation occurs in the cells inside the dental pulp, which have host defense mechanisms to combat oral microorganisms invading the pulp space of exposed teeth. This innate immunity has been well studied, with a focus on Toll-like receptors (TLRs). The function of TLR4, activated by Gram-negative bacteria, has been demonstrated in trigeminal ganglion (TG) neurons for dental pain. Although Gram-positive bacteria predominate in the teeth of patients with caries and pulpitis, the role of TLR2, which is activated by Gram-positive bacteria, is poorly understood in dental primary afferent (DPA) neurons that densely innervate the dental pulp. Using Fura-2 based Ca²⁺ imaging, we observed reproducible intracellular Ca²⁺ responses induced by Pam₃CSK₄ and Pam₂CSK₄ (TLR2-specific agonists) in TG neurons of adult wild-type (WT) mice. The response was completely abolished in TLR2 knock-out (KO) mice. Single-cell RT-PCR detected Tlr2 mRNA in DPA neurons labeled with fluorescent retrograde tracers from the upper molars. Using the mouse pulpitis model, real-time RT-PCR revealed that Tlr2 and inflammatory-related molecules were upregulated in injured TG, compared to non-injured TG, from WT mice, but not from TLR2 KO mice. TLR2 protein expression was also upregulated in injured DPA neurons, and the change was corresponded with a significant increase in calcitonin gene-related peptide (CGRP) expression. Our results provide a better molecular understanding of pulpitis by revealing the potential contribution of TLR2 to pulpal inflammatory pain.

Wnt Signalling in Regenerative Dentistry

Teeth are complex structures where a soft dental pulp tissue is enriched with nerves, vasculature and connective tissue and encased by the cushioning effect of dentin and the protection of a hard enamel in the crown and cementum in the root. Injuries such as trauma or caries can jeopardise these layers of protection and result in pulp exposure, inflammation and infection. Provision of most suitable materials for tooth repair upon injury has been the motivation of dentistry for many decades. Wnt signalling, an evolutionarily conserved pathway, plays key roles during pre- and post-natal development of many organs including the tooth. Mutations in the components of this pathway gives rise to various types of developmental tooth anomalies. Wnt signalling is also fundamental in the response of odontoblasts to injury and repair processes. The complexity of tooth structure has resulted in diverse studies looking at specific compartments or cell types of this organ. This review looks at the current advances in the field of tooth development and regeneration. The objective of the present review is to provide an updated vision on dental biomaterials research, focusing on their biological properties and interactions to act as evidence for their potential use in vital pulp treatment procedures. We discuss the outstanding questions and future directions to make this knowledge more translatable to the clinics.

The Role of microRNAs in Pulp Inflammation

The dental pulp can be affected by thermal, physical, chemical, and bacterial phenomena that stimulate the inflammatory response. The pulp tissue produces an immunological, cellular, and vascular reaction in an attempt to defend itself and resolve the affected tissue. The expression of different microRNAs during pulp inflammation has been previously documented. MicroRNAs (miRNAs) are endogenous small molecules involved in the transcription of genes that regulate the immune system and the inflammatory response. They are present in cellular and physiological functions, as well as in the pathogenesis of human diseases, becoming potential biomarkers for diagnosis, prognosis, monitoring, and safety. Previous studies have evidenced the different roles played by miRNAs in proinflammatory, anti-inflammatory, and immunological phenomena in the dental pulp, highlighting specific key functions of pulp pathology. This systematized review aims to provide an understanding of the role of the different microRNAs detected in the pulp and their effects on the expression of the different target genes that are involved during pulp inflammation.

The Role of Dendritic Cells during Physiological and Pathological Dentinogenesis

The dental pulp is a soft connective tissue of ectomesenchymal origin that harbors distinct cell populations, capable of interacting with each other to maintain the vitality of the tooth. After tooth injuries, a sequence of complex biological events takes place in the pulpal tissue to restore its homeostasis. The pulpal response begins with establishing an inflammatory reaction that leads to the formation of a matrix of reactionary or reparative dentin, according to the nature of the exogenous stimuli. Using several in vivo designs, antigen-presenting cells, including macrophages and dendritic cells (DCs), are identified in the pulpal tissue before tertiary dentin deposition under the afflicted area. However, the precise nature of this phenomenon and its relationship to inherent pulp cells are not yet clarified. This literature review aims to discuss the role of pulpal DCs and their relationship to progenitor/stem cells, odontoblasts or odontoblast-like cells, and other immunocompetent cells during physiological and pathological dentinogenesis. The concept of “dentin-pulp immunology” is proposed for understanding the crosstalk among these cell types after tooth injuries, and the possibility of immune-based therapies is introduced to accelerate pulpal healing after exogenous stimuli.

Fibroblasts Control Macrophage Differentiation during Pulp Inflammation

INTRODUCTION

During pulp inflammation, recruited macrophages can differentiate into 2 phenotypes: proinflammatory M1 and anti-inflammatory M2. Pulp fibroblasts have previously been shown to regulate pulp inflammation via cytokine and growth factor secretion. We hypothesized that upon carious injury, pulp fibroblasts interact with macrophages and modulate their differentiation.

METHODS

Cultures of pulp fibroblasts were physically injured and incubated with lipoteichoic acid (LTA) to mimic the pulp environment underlying a carious lesion. Physical injuries without LTA were performed on cultured fibroblasts to simulate the surrounding pulp tissue. Fibroblast supernatants were collected and added to undifferentiated macrophages to study their differentiation into M1 or M2 phenotypes by investigating cytokine secretion profiles and phagocytosis capacity. Histologic staining and immunofluorescence were performed on healthy and carious human tooth sections to localize the 2 macrophage phenotypes.

RESULTS

LTA-stimulated fibroblasts induced macrophage differentiation into the M1 phenotype with a significant increase both in tumor necrosis factor alpha secretion and phagocytosis capacity. By contrast, injured fibroblasts without LTA led to M2 differentiation with a significant increase in interleukin 10 secretion and low phagocytosis capacity. In carious teeth, M1 macrophages were detected mainly in the pulp zone underlying caries, whereas M2 macrophages were detected in the peripheral inflammatory zone.

CONCLUSIONS

Fibroblasts induced macrophage differentiation to proinflammatory M1 with high bacteria phagocytosis capacity to control infection at the carious front. Fibroblasts located at the periphery of the inflammatory zone induced macrophage differentiation to anti-inflammatory M2. The fine balance between the 2 phenotypes may represent a prerequisite for initiating the healing process.

Immunomodulatory Expression of Cathelicidins Peptides in Pulp Inflammation and Regeneration: An Update

The role of inflammatory mediators in dental pulp is unique. The local environment of pulp responds to any changes in the physiology that are highly fundamental, like odontoblast cell differentiation and other secretory activity. The aim of this review is to assess the role of cathelicidins based on their capacity to heal wounds, their immunomodulatory potential, and their ability to stimulate cytokine production and stimulate immune-inflammatory response in pulp and periapex. Accessible electronic databases were searched to find studies reporting the role of cathelicidins in pulpal inflammation and regeneration published between September 2010 and September 2020. The search was performed using the following databases: Medline, Scopus, Web of Science, SciELO and PubMed. The electronic search was performed using the combination of keywords "cathelicidins" and "dental pulp inflammation". On the basis of previous studies, it can be inferred that LL-37 plays an important role in odontoblastic cell differentiation and stimulation of antimicrobial peptides. Furthermore, based on these outcomes, it can be concluded that LL-37 plays an important role in reparative dentin formation and provides signaling for defense by activating the innate immune system.

The Genetic and Epigenetic Mechanisms Involved in Irreversible Pulp Neural Inflammation

Aim

To identify the critical genetic and epigenetic biomarkers by constructing the long noncoding RNA- (lncRNA-) related competing endogenous RNA (ceRNA) network involved in irreversible pulp neural inflammation (pulpitis).

Materials and Methods

The public datasets regarding irreversible pulpitis were downloaded from the gene expression omnibus (GEO) database. The differential expression analysis was performed to identify the differentially expressed genes (DEGs) and DElncRNAs. Functional enrichment analysis was performed to explore the biological processes and signaling pathways enriched by DEGs. By performing a weighted gene coexpression network analysis (WGCNA), the significant gene modules in each dataset were identified. Most importantly, DElncRNA-DEmRNA regulatory network and DElncRNA-associated ceRNA network were constructed. A transcription factor- (TF-) DEmRNA network was built to identify the critical TFs involved in pulpitis.

Result

Two datasets (GSE92681 and GSE77459) were selected for analysis. DEGs involved in pulpitis were significantly enriched in seven signaling pathways (i.e., NOD-like receptor (NLR), Toll-like receptor (TLR), NF-kappa B, tumor necrosis factor (TNF), cell adhesion molecules (CAMs), chemokine, and cytokine-cytokine receptor interaction pathways). The ceRNA regulatory relationships were established consisting of three genes (i.e., LCP1, EZH2, and NR4A1), five miRNAs (i.e., miR-340-5p, miR-4731-5p, miR-27a-3p, miR-34a-5p, and miR-766-5p), and three lncRNAs (i.e., XIST, MIR155HG, and LINC00630). Six transcription factors (i.e., GATA2, ETS1, FOXP3, STAT1, FOS, and JUN) were identified to play pivotal roles in pulpitis.

Conclusion

This paper demonstrates the genetic and epigenetic mechanisms of irreversible pulpitis by revealing the ceRNA network. The biomarkers identified could provide research direction for the application of genetically modified stem cells in endodontic regeneration.

Protective effect of quercetin on alteration of antioxidant genes expression and histological changes in the dental pulp of the streptozotocin-diabetic rats

OBJECTIVE

We aimed to assess the effect of quercetin as one of the most common polyphenols with anti-inflammatory and antioxidant properties on expression levels of catalase (CAT), superoxide dismutase 1 (SOD1), and glutathione peroxidase 1 (GPX1), involved in the detoxification of reactive oxygen species (ROS), and histology of dental pulp in streptozotocin-diabetic rats.

DESIGN

Type 1 diabetes mellitus (T1DM) was induced by intraperitoneal injection of streptozotocin in adult male Wistar rats. Animals (n = 24) were equally distributed into control, diabetes, and diabetes treated with quercetin groups. Rats were gavaged daily with quercetin (25 mg/kg) for forty days. To measure the mRNA levels of antioxidant genes, quantitate real-time PCR was applied. The oxidative stress parameters such as total antioxidant capacity (TAC) and histopathological assessments were performed.

RESULTS

A significant increase in the relative quantification mRNA levels of SOD1, CAT, GPX1 was detected in diabetic rat dental pulp. Besides, persistent hyperglycemia led to the enhancement of TAC level and degeneration of connective tissue of the dental pulp. Interestingly, quercetin normalized the expression mRNA levels of CAT, SOD1, GPX1 to near the normal level. Moreover, quercetin treatment normalized TAC levels.

CONCLUSIONS

Because of the crucial role of antioxidants in diabetic complications, the findings of the current study presented a molecular basis for the protective effect of quercetin on dental pulp in diabetic conditions.

Long noncoding RNA MEG3 expressed in human dental pulp regulates LPS-Induced inflammation and odontogenic differentiation in pulpitis

Pulpitis refers to inflammation of the inner pulp by invading microbes, and tissue repair occurs due to odontogenic differentiation of human dental pulp cells (hDPCs) with multidifferentiation potential. Long noncoding RNAs (lncRNAs) can modulate numerous pathological and biological processes; however, the role of lncRNAs in the inflammation and regeneration of the dentin-pulp complex in pulpitis is unclear. Here, we performed high-throughput sequencing to identify differentially expressed lncRNAs between human normal and inflamed pulp and concluded that lncMEG3 (lncRNA maternally expressed gene 3, MEG3) was significantly upregulated in both inflamed pulp and LPS-treated hDPCs. MEG3 expression in the pulp tissue was detected using the RNAscope® technique. RNA pulldown assays identified the MEG3-interacting proteins and the potential mechanisms. With MEG3 knockdown, we investigated the role of MEG3 in the secretion of inflammatory cytokines in LPS-treated hDPCs and odontogenic differentiation of hDPCs. MEG3 downregulation inhibited the secretion of TNF-α, IL-1β and IL-6 in LPS-treated hDPCs, and the p38/MAPK signaling pathway may be related to this effect. MEG3 knockdown promoted odontogenic differentiation of hDPCs by regulating the Wnt/β-catenin signaling pathway. Our study suggested that MEG3 has a negative effect on inflammation and regeneration of the dentin-pulp complex in pulpitis.

Effects of melatonin in wound healing of dental pulp and periodontium: Evidence from in vitro, in vivo and clinical studies

INTRODUCTION

Database research has revealed that melatonin has beneficial effects in pulpal and periodontal regeneration. Several studies reported protective effects of melatonin against inflammation in several organs including the heart, brain, and teeth. In addition to inflammation reduction, melatonin has been involved in tissue regeneration and wound healing. The aim of this review is to summarize the evidence from in vitro, in vivo and clinical studies on the effects of melatonin in wound healing of dental pulp and periodontium. This review gives a thorough summary of the possible role of melatonin in wound healing of dental pulp and periodontium in connection with anti-inflammatory and antioxidant effects, cell proliferation, and cell differentiation. Any contradictory evidence is also assessed.

METHODS

The PubMed database was searched for all research articles published before April 2020 with the search terms "melatonin" and "dental pulp". Articles with the search terms "melatonin", "periodontal disease" and "bone" published before October 2019 were also included. Non-English articles were excluded.

RESULTS

Melatonin has been shown to reduce inflammation, inhibit cell proliferation and regulate differentiation of pulp cells. Melatonin increased odontoblast activities, resulting in the differentiation in the dental pulp. However, melatonin did not initiate differentiation in undifferentiated pulp cells but seemed to have beneficial effects in periodontitis by promoting periodontium's wound healing.

CONCLUSION

Those findings suggest that melatonin could have beneficial effects on pulpal and periodontal cells under inflammatory conditions. However, discrepancies remain between in vitro and in vivo findings regarding the effect of melatonin on dental pulp and periodontium.

Responses of oral-microflora-exposed dental pulp to capping with a triple antibiotic paste or calcium hydroxide cement in mouse molars

Introduction

Responses of oral-microflora-exposed dental pulp to a triple antibiotic paste (TAP), a mixture of ciprofloxacin, metronidazole, and minocycline in ointment with macrogol and propylene glycol, remain to be fully clarified at the cellular level. This study aimed to elucidate responses of oral-microflora-exposed dental pulp to capping with TAP in mouse molars.

Methods

A cavity was prepared on the first molars of 6-week-old mice to expose the dental pulp for 24 h. The exposed pulp was capped with TAP (TAP group) or calcium hydroxide cement (CH group), in addition to the combination of macrogol (M) and propylene glycol (P) (MP, control group), followed by a glass ionomer cement filling. The samples were collected at intervals of 1, 2, and 3 weeks, and immunohistochemistry for nestin and Ki-67 and deoxyuride-5′-triphosphate biotin nick end labeling (TUNEL) assay were performed in addition to quantitative real-time polymerase chain reaction (qRT-PCR) analyses.

Results

The highest occurrence rate of pulp necrosis was found in the control group followed by the CH group at Weeks 2 and 3, whereas the highest occurrence rate of healed areas in the dental pulp was observed in the TAP group at each time point. Tertiary dentin formation was first observed in the dental pulp of the TAP group at Week 2. In contrast, bone-like and/or fibrous tissues were frequently observed in the CH group. qRT-PCR analyses clarified that TAP activated the stem and dendritic cells at Weeks 1 and 2, respectively.

Conclusions

The use of TAP as a pulp-capping agent improved the healing process of oral-microflora-exposed dental pulp in mouse molars.

•

We established a mouse model to evaluate the pulpal responses to capping materials.

•

TAP induced odontoblast-like cell differentiation faster than calcium hydroxide.

•

Tertiary dentin was predominantly seen at the exposure site in the TAP group.

•

TAC-P tends to activate dental pulp stem cells earlier than calcium hydroxide.

•

TAP favored the repair process of the oral-microflora-exposed pulpal tissue.

Natural Antimicrobials in the Dental Pulp

INTRODUCTION

Like many tissues, the dental pulp is equipped with innate and adaptive immune responses, designed to defend against infection and limit its spread. The pulp's innate immune response includes the synthesis and release of antimicrobial peptides by several dental pulp cell types. These naturally-occurring antimicrobial peptides have broad spectrum activity against bacteria, fungi and viruses. There is a resurgence of interest in the bioactivities of naturally-occurring antimicrobial peptides, largely driven by the need to develop alternatives to antibiotics.

METHODS

This narrative review focused on the general properties of antimicrobial peptides, providing an overview of their sources and actions within the dental pulp.

RESULTS

We summarized the relevance of antimicrobial peptides in defending the dental pulp, highlighting the potential for many of these antimicrobials to be modified or mimicked for prospective therapeutic use.

CONCLUSION

Antimicrobial peptides and novel peptide-based therapeutics are particularly attractive as emerging treatments for polymicrobial infections, such as endodontic infections, because of their broad activity against a range of pathogens.

Ancient dental pulp: Masterpiece tissue for paleomicrobiology

Introduction

Dental pulp with special structure has become a good reference sample in paleomicrobiology‐related blood‐borne diseases, many pathogens were detected by different methods based on the diagnosis of nucleic acids and proteins.

Objectives

This review aims to propose the preparation process from ancient teeth collection to organic molecule extraction of dental pulp and summary, analyze the methods that have been applied to detect septicemic pathogens through ancient dental pulps during the past 20 years following the first detection of an ancient microbe.

Methods

The papers used in this review with two main objectives were obtained from PubMed and Google scholar with combining keywords: “ancient,” “dental pulp,” “teeth,” “anatomy,” “structure,” “collection,” “preservation,” “selection,” “photography,” “radiography,” “contamination,” “decontamination,” “DNA,” “protein,” “extraction,” “bone,” “paleomicrobiology,” “bacteria,” “virus,” “pathogen,” “molecular biology,” “proteomics,” “PCR,” “MALDI‐TOF,” “LC/MS,” “ELISA,” “immunology,” “immunochromatography,” “genome,” “microbiome,” “metagenomics.”

Results

The analysis of ancient dental pulp should have a careful preparation process with many different steps to give highly accurate results, each step complies with the rules in archaeology and paleomicrobiology. After the collection of organic molecules from dental pulp, they were investigated for pathogen identification based on the analysis of DNA and protein. Actually, DNA approach takes a principal role in diagnosis while the protein approach is more and more used. A total of seven techniques was used and ten bacteria (Yersinia pestis, Bartonella quintana, Salmonella enterica serovar Typhi, Salmonella enterica serovar Paratyphi C, Mycobacterium leprae, Mycobacterium tuberculosis, Rickettsia prowazeki, Staphylococcus aureus, Borrelia recurrentis, Bartonella henselae) and one virus (Anelloviridae) were identified. Y. pestis had the most published in quantity and all methods were investigated for this pathogen, S. aureus and B. recurrentis were identified by three different methods and others only by one. The combining methods interestingly increase the positive rate with ELISA, PCR and iPCR in Yersinia pestis diagnosis. Twenty‐seven ancient genomes of Y. pestis and one ancient genome of B. recurrentis were reconstructed. Comparing to the ancient bone, ancient teeth showed more advantage in septicemic diagnosis. Beside pathogen identification, ancient pulp help to distinguish species.

Conclusions

Dental pulp with specific tissue is a suitable sample for detection of the blood infection in the past through DNA and protein identification with the correct preparation process, furthermore, it helps to more understand the pathogens of historic diseases and epidemics.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Odontoblastic Exosomes Attenuate Apoptosis in Neighboring Cells

Each odontoblast is tightly linked to other odontoblasts. They form a line of defense and are capable of withstanding external stimuli, particularly the inflammation caused by caries. Thus, we investigated exosomes derived from odontoblasts as an intercellular mechanism by which inflamed odontoblasts are protected from apoptosis. CD63, an exosome marker, was expressed at high levels in caries-affected regions of the dental pulp. We conducted an ex vivo experiment by applying different concentrations of lipopolysaccharide (LPS) to the odontoblast-like cells (mineralization was induced in stem cells derived from the apical papilla). Odontoblast-like cells treated with a high concentration of LPS (20 µg/mL LPS, severely affected) exhibited an accelerated release of exosomes, which attenuated the LPS-induced cell apoptosis of odontoblast-like cells treated with a low concentration of LPS (1 µg/mL LPS, mildly affected). Next, we blocked exosome uptake with chlorpromazine, and the rescue effect vanished. Based on our findings, severely inflamed odontoblasts attenuate the apoptosis of mildly inflamed neighboring cells through an exosome-mediated intercellular signaling pathway.

3D cellular visualization of intact mouse tooth using optical clearing without decalcification

Dental pulp is composed of nerves, blood vessels, and various types of cells and surrounded by a thick and hard enamel-dentin matrix. Due to its importance in the maintenance of tooth vitality, there have been intensive efforts to analyze the complex cellular-level organization of the dental pulp in teeth. Although conventional histologic analysis has provided microscopic images of the dental pulp, 3-dimensional (3D) cellular-level visualization of the whole dental pulp in an intact tooth has remained a technically challenging task. This is mainly due to the inevitable disruption and loss of microscopic structural features during the process of mechanical sectioning required for the preparation of the tooth sample for histological observation. To accomplish 3D microscopic observation of thick intact tissue, various optical clearing techniques have been developed mostly for soft tissue, and their application for hard tissues such as bone and teeth has only recently started to be investigated. In this work, we established a simple and rapid optical clearing technique for intact mouse teeth without the time-consuming process of decalcification. We achieved 3D cellular-level visualization of the microvasculature and various immune cell distributions in the whole dental pulp of mouse teeth under normal and pathologic conditions. This technique could be used to enable diverse research methods on tooth development and regeneration by providing 3D visualization of various pulpal cells in intact mouse teeth.

Angiogenic effect of platelet-rich concentrates on dental pulp stem cells in inflamed microenvironment

OBJECTIVE

In this study, we aimed to determine the suitable concentrations of human platelet lysate (HPL) and platelet-rich plasma (PRP) for maintaining the in vitro proliferative and angiogenic potential of inflamed dental pulp stem cells.

MATERIALS AND METHODS

Lipopolysaccharide (LPS)-induced inflamed dental pulp-derived stem cells (iDPSCs) were treated with different concentrations of HPL and PRP (10% and 20%) followed by determination of viability using Alamar Blue assay. Expression of angiogenesis-, adhesion-, and inflammation-regulating genes was also analyzed using RT-qPCR array. Furthermore, expression of growth factors at protein level in the cell culture microenvironment was measured using multiplex assay.

RESULTS

Viability of iDPSCs was significantly (p < 0.05) higher in 20% HPL-supplemented media compared to iDPSCs. Expression of 10 out of 12 selected angiogenic genes, four out of seven adhesion molecules, and seven out of nine cytokine-producing genes were significantly (p < 0.05) higher in cells maintained in 20% HPL-supplemented media compared to that in FBS-supplemented media. Furthermore, expression of all the selected growth factors was significantly higher (p < 0.05) in the supernatants from 20% HPL media at 12 and 24 h post-incubation.

CONCLUSION

This study suggests that 20% HPL could be optimum to stimulate angiogenesis-related factors in iDPSCs while maintaining their viability.

CLINICAL RELEVANCE

This data may suggest the potential use of 20% HPL for expanding DPSCs scheduled for clinical trials for regenerative therapies including dental pulp regeneration.