Immunocompetent cells in the pulp of human deciduous teeth

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.

Advances in the Study of the Mechanisms of Physiological Root Resorption in Deciduous Teeth

Physiological root resorption of deciduous teeth is a complex physiological process that is essential for the normal replacement of deciduous teeth and permanent teeth in clinical practice, but its importance is often overlooked due to the presence of permanent teeth. This physiological process includes not only the resorption of hard tissues of deciduous teeth, such as dentin and cementum, but also the elimination of soft tissues, such as pulp and periodontal ligament (PDL). However, the mechanisms of physiological root resorption are not yet clear. In this article, the advances of research on the mechanisms related to physiological root resorption will be reviewed in two main aspects: hard tissues and soft tissues of deciduous teeth, specifically in relation to the effects of inflammatory microenvironment and mechanical stress on the resorption of hard tissues, the repair of hard tissues, and the elimination and the histological events of soft tissues.

A Bioinformatics Systems Biology Analysis of the Current Oral Proteomic Biomarkers and Implications for Diagnosis and Treatment of External Root Resorption

External root resorption (ERR) is a silent destructive phenomenon detrimental to dental health. ERR may have multiple etiologies such as infection, inflammation, traumatic injuries, pressure, mechanical stimulations, neoplastic conditions, systemic disorders, or idiopathic causes. Often, if undiagnosed and untreated, ERR can lead to the loss of the tooth or multiple teeth. Traditionally, clinicians have relied on radiographs and cone beam computed tomography (CBCT) images for the diagnosis of ERR; however, these techniques are not often precise or definitive and may require exposure of patients to more ionizing radiation than necessary. To overcome these shortcomings, there is an immense need to develop non-invasive approaches such as biomarker screening methods for rapid and precise diagnosis for ERR. In this review, we performed a literature survey for potential salivary or gingival crevicular fluid (GCF) proteomic biomarkers associated with ERR and analyzed the potential pathways leading to ERR. To the best of our knowledge, this is the first proteomics biomarker survey that connects ERR to body biofluids which represents a novel approach to diagnose and even monitor treatment progress for ERR.

Effect of tumor necrosis factor α on ability of SHED to promote osteoclastogenesis during physiological root resorption

Physiological root resorption of deciduous teeth is a normal phenomenon, however, the potential mechanisms underlying this process remain unclear. This study aimed to investigate ability of stem cells from human exfoliated deciduous teeth (SHED) on promoting the osteoclastic differentiation of osteoclast precursors and clarify mechanisms underlying this process in vitro. SHED and dental pulp stem cells (DPSCs) were obtained from deciduous teeth and healthy permanent teeth. An indirect co-culture system of SHED or DPSCs were used. The osteoclast precursor peripheral blood mononuclear cells (PBMCs) were established. Ability of SHED and DPSCs in promoting osteoclastogenesis was determined using triiodothyronine receptor auxiliary protein (TRAP) staining, real-time real-time PCR (RT-PCR) and western blotting. The effect of inflammation on the pro-osteoclastogenesis ability of SHED was determined using enzyme linked immunosorbent assay (ELISA), RT-PCR and western blotting. The function of the nuclear factor-κB (NF-κB) pathway in promoting the osteoclastogenesis ability of SHED was determined using RT-PCR and western blotting. SHED exhibited an increased ability to promote osteoclastic differentiation. Expression of tumor necrosis factor-α (TNF-α) was significantly higher in SHED than in DPSCs. Expression of cathepsin K (CTSK), TRAP, and receptor-activator of nuclear-factor-κ B ligand (RANKL), RANKL/osteoprotegerin (OPG) ratio, and expression of cytoplasmic phosphorylated inhibitor of NF-κB α (p-IκBα) and nuclear p65 were markedly up-regulated in SHED post the TNF-α treatment but decreased following NF-κB inhibition. In conclusion, inflammatory cytokine TNF-α appeared to activate NF-κB pathway to up-regulate expression of NF-κB, enhancing ability of SHED in promoting osteoclastogenesis via regulating RANKL/OPG expression.

Schwann Cell Responses and Plasticity in Different Dental Pulp Scenarios

Mammalian teeth have evolved as dentin units that enclose a complex system of sensory innervation to protect and preserve their structure and function. In human dental pulp (DP), mechanosensory and nociceptive fibers form a dense meshwork of nerve endings at the coronal dentin-pulp interface, which arise from myelinated and non-myelinated axons of the Raschkow plexus (RP). Schwann cells (SCs) play a crucial role in the support, maintenance and regeneration after injury of these fibers. We have recently characterized two SC phenotypes hierarchically organized within the coronal and radicular DP in human teeth. Myelinating and non-myelinating SCs (nmSCs) display a high degree of plasticity associated with nociceptive C-fiber sprouting and axonal degeneration in response to DP injuries from dentin caries or physiological root resorption (PRR). By comparative immunolabeling, confocal and electron microscopy, we have characterized short-term adaptive responses of SC phenotypes to nerve injuries, and long-term changes related to aging. An increase of SCs characterizes the early responses to caries progression in association with axonal sprouting in affected DP domains. Moreover, during PRR, the formation of bands of Büngner is observed as part of SC repair tracks functions. On the other hand, myelinated axon density is significantly reduced with tooth age, as part of a gradual decrease in DP defense and repair capacities. The remarkable plasticity and capacity of SCs to preserve DP innervation in different dental scenarios constitutes a fundamental aspect to improve clinical treatments. This review article discusses the central role of myelinating and non-mSCs in long-term tooth preservation and homeostasis.

Cytotoxic and biological effects of bulk fill composites on rat cortical neuron cells

The aim of this study was to investigate potential cellular responses and biological effects of new generation dental composites on cortical neuron cells in two different exposure times. The study group included five different bulk-fill flow able composites; Surefil SDR Flow, X-tra Base Flow, Venus Bulk Flow, Filtek Bulk Flow and Tetric-Evo Flow. They were filled in Teflon molds (Height: 4 mm, Width: 6 mm) and irradiated for 20 s. Cortical neuron cells were inoculated into 24-well plates. After 80% of the wells were coated, the 3 µm membrane was inserted and dental filling materials were added. The experiment was continued for 24 and 72 h. Cell viability measured by MTT assay test, total antioxidant and total oxidant status were examined using real assay diagnostic kits. The patterns of cell death (apoptosis) were analyzed using annexin V-FITC staining with flow cytometry. Β-defensins were quantitatively assessed by RT-PCR. IL-6, IL-8 and IL-10 cytokines were measured from the supernatants. All composites significantly affected analyses parameters during the exposure durations. Our data provide evidence that all dental materials tested are cytotoxic in acute phase and these effects are induced cellular death after different exposure periods. Significant cytotoxicity was detected in TE, XB, SS, FBF and VBF groups at 24 and 72 h, respectively.

Dental Pulp Defence and Repair Mechanisms in Dental Caries

Dental caries is a chronic infectious disease resulting from the penetration of oral bacteria into the enamel and dentin. Microorganisms subsequently trigger inflammatory responses in the dental pulp. These events can lead to pulp healing if the infection is not too severe following the removal of diseased enamel and dentin tissues and clinical restoration of the tooth. However, chronic inflammation often persists in the pulp despite treatment, inducing permanent loss of normal tissue and reducing innate repair capacities. For complete tooth healing the formation of a reactionary/reparative dentin barrier to distance and protect the pulp from infectious agents and restorative materials is required. Clinical and in vitro experimental data clearly indicate that dentin barrier formation only occurs when pulp inflammation and infection are minimised, thus enabling reestablishment of tissue homeostasis and health. Therefore, promoting the resolution of pulp inflammation may provide a valuable therapeutic opportunity to ensure the sustainability of dental treatments. This paper focusses on key cellular and molecular mechanisms involved in pulp responses to bacteria and in the pulpal transition between caries-induced inflammation and dentinogenic-based repair. We report, using selected examples, different strategies potentially used by odontoblasts and specialized immune cells to combat dentin-invading bacteria in vivo.

Axonal Degeneration in Dental Pulp Precedes Human Primary Teeth Exfoliation

The dental pulp in human primary teeth is densely innervated by a plethora of nerve endings at the coronal pulp-dentin interface. This study analyzed how the physiological root resorption (PRR) process affects dental pulp innervation before exfoliation of primary teeth. Forty-four primary canine teeth, classified into 3 defined PRR stages (early, middle, and advanced) were fixed and demineralized. Longitudinal cryosections of each tooth were stained for immunohistochemical and quantitative analysis of dental pulp nerve fibers and associated components with confocal and electron microscopy. During PRR, axonal degeneration was prominent and progressive in a Wallerian-like scheme, comprising nerve fiber bundles and nerve endings within the coronal and root pulp. Neurofilament fragmentation increased significantly during PRR progression and was accompanied by myelin degradation and a progressive loss of myelinated axons. Myelin sheath degradation involved activation of autophagic activity by Schwann cells to remove myelin debris. These cells expressed a sequence of responses comprising dedifferentiation, proliferative activity, GAP-43 overexpression, and Büngner band formation. During the advanced PRR stage, increased immune cell recruitment within the dental pulp and major histocompatibility complex (MHC) class II upregulation by Schwann cells characterized an inflammatory condition associated with the denervation process in preexfoliative primary teeth. The ensuing loss of dental pulp axons is likely to be responsible for the progressive reduction of sensory function of the dental pulp during preexfoliative stages.

Phenotypic analysis of immunocompetent cells in healthy human dental pulp

INTRODUCTION

Like other tissues in the body, the human dental pulp is equipped with a network of immune cells that can be mobilized against pathogens when they invade the tooth. Very little data, mostly obtained with classic histologic methods, have reported their quantities and relative percentages. The objective of this study was to characterize and precisely quantify immunocompetent cells in healthy human dental pulp by using fluorescence-activated cell sorting, together with identifying specific cell subsets in the leukocyte (CD45(+)) cells.

METHODS

Healthy human third molars were collected from 42 young patients. Dental pulps were separated from the hard tissues and prepared for flow cytometry or immunostaining analyses.

RESULTS

CD45(+) cells represented 0.94% ± 0.65% of cells obtained from the enzymatic digestion of whole dental pulps (n = 34). CD16(+)CD14(+) granulocytes/neutrophils (50.01% ± 9.08%, n = 7) were found to represent the major subpopulation in CD45(+) cells followed by CD3(+) T lymphocytes (32.58% ± 11%, n = 17), CD14(+) monocytes (8.93% ± 5.8%, n = 7), and HLA-DR(high) Lin1(-) dendritic cells (4.51% ± 1.12%, n = 7). Minor subpopulations included CD3(-)CD56(+) natural killer cells (2.63% ± 1.15%, n = 7) and CD19(+) B lymphocytes (1.65% ± 0.89%, n = 17). We further identified cells harboring a phenotype compatible with Foxp3/CD25-expressing regulatory T lymphocytes (CD45(+)CD3(+)CD4(+)CD127(low)). Fluorescence-activated cell sorting analysis and confocal microscopy also revealed expression of HO-1 in HLA-DR(+) cells.

CONCLUSIONS

For the first time, this study identifies and precisely quantifies the relative proportion of immunocompetent cells potentially involved in tissue homeostasis of healthy human dental pulp.

Pulpal status of human primary molars with coexisting caries and physiological root resorption

AIM

This study sought to investigate the effect of caries, in association with physiological root resorption, on the pulpal status of human primary molars.

DESIGN

Fifty-three mandibular primary molars were obtained from children requiring extractions under general anaesthesia. Following extraction, teeth were split longitudinally and placed in Zamboni's fixative. Teeth were categorised according to i) the depth of caries (less than or greater than halfway through dentine thickness) and ii) the degree of physiological root resorption (<33%, 34-66% or >67% of the root length). Ten-micrometre pulp sections were subject to indirect immunofluorescence using a combination of PGP 9.5 (a general neuronal marker), CD45 (a general neuronal marker), and Ulex europaeus agglutinin I (a marker of vascular endothelium). Image analysis was used to determine the percentage area of staining (PAS) for innervation and immune cells.

RESULTS

Marked differences were seen between different samples, but there were no significant differences in mean PAS for PGP 9.5 or CD45 according to the degree of caries or extent of physiological root resorption (two-way anova, P > 0.05).

CONCLUSION

Findings suggest that even if primary molars are undergoing exfoliation, they show comparable caries-induced changes to teeth without physiological root resorption, thus retaining potential for healing and repair.

Root resorption of primary molars without successor teeth. An experimental study in the beagle dog

Tooth agenesis is a common craniofacial congenital malformation in humans, but little is known about the mechanisms of root resorption in this condition. The purpose of this study was to investigate the mechanisms of root resorption in primary molars without successors. An animal model without permanent tooth germs was established by surgery in beagles. The times of onset of primary molar root resorption, with and without successors, were compared. The distribution of immune cells, odontoclasts, and their activating factors were determined by histochemistry and immunohistochemistry. Root resorption of primary mandibular molars without successors began later than physiological resorption. In primary molars without permanent germs, odontoclasts and immune cells were present mainly in the apical pulp at the start of root resorption, whereas in control teeth receptor activator of nuclear factor-κB ligand (RANKL)-positive cells were found mainly in the region of the periodontal ligament. CD14(+) and CD3(+) cells were found in both the pulp and the periodontal ligament region. These results suggest that the dental pulp of primary molars, as well as immune cells, may play an important role in root resorption in primary molars without permanent tooth germs.

Pulpal status of human primary teeth with physiological root resorption

OBJECTIVE

The overall aim of this study was to determine whether any changes occur in the pulpal structure of human primary teeth in association with physiological root resorption.

METHODS

The experimental material comprised 64 sound primary molars, obtained from children requiring routine dental extractions under general anaesthesia. Pulp sections were processed for indirect immunofluorescence using combinations of: (i) protein gene product 9.5 (a general neuronal marker); (ii) leucocyte common antigen CD45 (a general immune cell marker); and (iii) Ulex europaeus I lectin (a marker of vascular endothelium). Image analysis was then used to determine the percentage area of staining for each label within both the pulp horn and mid-coronal region. Following measurement of the greatest degree of root resorption in each sample, teeth were subdivided into three groups: those with physiological resorption involving less than one-third, one-third to two-thirds, and more than two-thirds of their root length.

RESULTS

Wide variation was evident between different tooth samples with some resorbed teeth showing marked changes in pulpal histology. Decreased innervation density, increased immune cell accumulation, and increased vascularity were evident in some teeth with advanced root resorption. Analysis of pooled data, however, did not reveal any significant differences in mean percentage area of staining for any of these variables according to the three root resorption subgroups (P > 0.05, analysis of variance on transformed data).

CONCLUSIONS

This investigation has revealed some changes in pulpal status of human primary teeth with physiological root resorption. These were not, however, as profound as one may have anticipated. It is therefore speculated that teeth could retain the potential for sensation, healing, and repair until advanced stages of root resorption.

Physiologic root resorption in primary teeth: molecular and histological events

Root resorption is a physiologic event for the primary teeth. It is still unclear whether odontoclasts, the cells which resorb the dental hard tissue, are different from the osteoclasts, the cells that resorb bone. Root resorption seems to be initiated and regulated by the stellate reticulum and the dental follicle of the underlying permanent tooth via the secretion of stimulatory molecules, i.e. cytokines and transcription factors. The primary root resorption process is regulated in a manner similar to bone remodeling, involving the same receptor ligand system known as RANK/RANKL (receptor activator of nuclear factor-kappa B/ RANK Ligand). Primary teeth without a permanent successor eventually exfoliate as well, but our current understanding on the underlying mechanism is slim. The literature is also vague on how resorption of the pulp and periodontal ligament of the primary teeth occurs. Knowledge on the mechanisms involved in the physiologic root resorption process may enable us to delay or even inhibit exfoliation of primary teeth in those cases that the permanent successor teeth are not present and thus preservation of the primary teeth is desirable.

A flow cytometric analysis of the biodefensive response of deciduous tooth pulp to carious stimuli during physiological root resorption

The present study observed biodefensive responses of deciduous tooth pulp to advancing caries lesions and analysed the role of physiological root resorption on pulpal defense potential. For this purpose, immunocompetent cell content of deciduous tooth pulp was examined using flow cytometry. A total of 49 deciduous incisor and molar teeth at various stages of physiological root resorption (carious or non-carious) to be extracted for clinical reasons were used in this study. Teeth were classified according to carious lesion depth and root resorption stage. CD3+ lymphocytes were observed to be most prevalent in the pulp and to show remarkable increase along with increase in carious lesion depth. Numbers of CD8+ lymphocytes also increased significantly as carious lesions approached the pulp. However, increase in the number of CD3+ and CD8+ cells did not significantly alter CD4+/CD8+ ratios. The study also found that while B-lymphocytes increased significantly in association with root resorption, there were no significant differences in B/CD3+ lymphocyte ratios. Thus, there was no evidence of irreversible pulpal pathosis in any groups. It can be concluded that pulp maintains its healing and defense capacity against advancing carious lesion and progressive root resorption in deciduous teeth.