Responses of immunocompetent cells to cavity preparation in rat molars: an immunohistochemical study using OX6-monoclonal antibody

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.

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.

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

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

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

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

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

EZH2 regulates dental pulp inflammation by direct effect on inflammatory factors

OBJECTIVE

Pulpitis is a multi-factorial disease that could be caused by complex interactions between genetics, epigenetics and environmental factors. We aimed to evaluate the role of Enhancer of Zeste Homolog 2 (EZH2) in the inflammatory response of human dental pulp cells (HDPCs) and dental pulp tissues.

METHODS

The expressions of inflammatory cytokines in HDPCs treated by EZH2 complex or EZH2 siRNA with or without rhTNF-α were examined by quantitative real-time polymerase chain reaction (q-PCR). The levels of secreted inflammatory cytokines including IL-6, IL-8, IL-15, CCL2 and CXCL12 in culture supernatants were measured by Luminex assay. In rat pulpitis model, the effects of EZH2 on dental pulp tissues were verified by histology. We invested the mechanisms of the effect of EZH2 on the inflammatory factors by ChIP assay.

RESULTS

EZH2 down-regulation inhibited the expression of inflammatory factors, including IL-6, IL-8, IL-15, CCL2 and CXCL12 in HDPCs. EZH2 complex promoted the expression and secretion of these inflammatory factors in HDPCs, while EZH2 silencing could attenuate the promotion of inflammatory factors that were induced by rhTNF-α. In pulpitis models of rats, EZH2 down-regulation inhibited the inflammatory process of dental pulp while EZH2 complex showed no significant facilitation of pulpal inflammation. In addition, EZH2 could bind on the promoters of IL-6, IL-8 and CCL2, but not IL-15 and CXCL12, to affect the transcription of these proinflammatory cytokines.

CONCLUSIONS

In HDPCs, EZH2 could induce inflammation, while EZH2 down-regulation could attenuate the inflammatory responses. EZH2 plays an important role in this inflammatory process of dental pulp.

Heterogeneity and Developmental Connections between Cell Types Inhabiting Teeth

Every tissue is composed of multiple cell types that are developmentally, evolutionary and functionally integrated into the unit we call an organ. Teeth, our organs for biting and mastication, are complex and made of many different cell types connected or disconnected in terms of their ontogeny. In general, epithelial and mesenchymal compartments represent the major framework of tooth formation. Thus, they give rise to the two most important matrix–producing populations: ameloblasts generating enamel and odontoblasts producing dentin. However, the real picture is far from this quite simplified view. Diverse pulp cells, the immune system, the vascular system, the innervation and cells organizing the dental follicle all interact, and jointly participate in transforming lifeless matrix into a functional organ that can sense and protect itself. Here we outline the heterogeneity of cell types that inhabit the tooth, and also provide a life history of the major populations. The mouse model system has been indispensable not only for the studies of cell lineages and heterogeneity, but also for the investigation of dental stem cells and tooth patterning during development. Finally, we briefly discuss the evolutionary aspects of cell type diversity and dental tissue integration.

Innate immune response of the dental pulp in healthy and carious human teeth

Antigen-presenting cells are capable of participating in the stimulation of T cells by antigen presentation. Antigen-presenting cells are considered essential for the induction and expansion of the immune reaction, because their interaction with antigen is the first step in immune induction. We have studied the distribution of class II-expressing cells in developing, healthy and carious human teeth to clarify when human pulp acquires an immunologic defense potential. Antigen-expressing cells were identified immunohistochemically with HLA-DR monoclonal antibodies (for dendritic cells) and CD68 monoclonal antibodies (for macrophages). In the pulp of unerupted developing teeth, HLA-DR-positive cells were distributed mainly in and around the odontoblast layer. A few CD68 positive cells were located more coronary around the blood vessels. In erupted teeth, HLA-DR-positive cells were located, for the most part just beneath the odontoblast layer. CD68 positive cells were also located coronary mainly around the blood vessels. Superficial caries lesions caused an aggregation of HLA-DR-positive cells and macrophages in the dental pulp corresponding to the lesion. Our results showed that human teeth are already equipped with an immunological defense potential prior to eruption. In the initial stage of caries infection, an immunoresponse mediated by class-II-expressing cells is initiated in human dental pulp. Keywords: human dental pulp, developing tooth, dental caries, dendritic cells, macrophages, immunohistochemistry

ASH1L Suppresses Matrix Metalloproteinase through Mitogen-activated Protein Kinase Signaling Pathway in Pulpitis

INTRODUCTION

Pulpitis is an inflammation of dental pulp produced by a response to external stimuli. The response entails substantial cellular and molecular activities. Both genetic and epigenetic regulators contribute to the occurrence of pulpitis. However, the epigenetic mechanisms are still poorly understood. In this research, we studied the role of the absent, small, or homeotic-like (ASH1L) gene in the process of pulpitis.

METHODS

Human dental pulp cells (HDPCs) were stimulated with proinflammatory cytokine tumor necrosis factor alpha (TNF-α). Gene expression profiling was performed to assess the occurrence of epigenetic regulators. Pulp tissue from rat experimental pulpitis was subjected to immunofluorescence to detect the occurrence of ASH1L and trimethylation of lysine 4 histone 3 (H3K4me3). The presence of ASH1L in HDPCs that had been generated by TNF-α stimulation was analyzed by Western blot procedures and cellular immunofluorescence. Once detected, ASH1L was silenced through the use of specific small interfering RNA. The effects of ASH1L on the occurrence and operation of matrix metalloproteinases (MMPs) were then tested by analysis of quantitative polymerase chain reactions, Western blotting, and zymography. Chromatin immunoprecipitation was performed to detect whether ASH1L and H3K4me3 were present in the promoter regions of MMPs. We then used Western blot procedures to examine the nuclear factor kappa B and the mitogen-activated protein kinase (MAPK) responses to the silencing of ASH1L. We also examined the specific pathway involved in ASH1L regulation of the MMPs.

RESULTS

After stimulating HDPCs with TNF-α, ASH1L emerged as 1 of the most strongly induced epigenetic mediators. We found that TNF-α treatment induced the expression of ASH1L through the nuclear factor kappa B and MAPK signal pathways. ASH1L was found in both the nucleus and the cytoplasm. TNF-α treatment was particularly active in inducing the accumulation of ASH1L in cellular cytoplasm. As is also consistent with in vitro results, ASH1L was found in increased quantities in experimental dental pulpitis tissue. ASH1L knockdown markedly up-regulated the occurrence of MMP-1, MMP-2, and MMP-13. It also exercised an impact on the enzymatic activity of MMP-2 in HDPCs that had been stimulated with TNF-α. ASH1L knockdown activated the MAPK signal pathway in TNF-α-triggered HDPCs, the inhibition of which reversed the induction of MMPs.

CONCLUSIONS

Our research identifies a mechanism by which ASH1L suppresses the occurrence and operation of MMPs during pulpitis. It does this through the MAPK pathway.

Effect of adhesive system application for cavities prepared with erbium, chromium: yttrium scandium gallium garnet laser on rat dental pulp tissue

We examined the effects of adhesive systems under study applied for a laser-cut cavity using an Er,Cr:YSGG laser on rat dental pulp at 24 h and 14 days postoperatively. Group 1, laser-cut cavities were treated with a self-etching-primer and bonding agent; group 2, pretreated with a phosphoric-acid, and then treated with a self-etching-primer and bonding agent; group 3, pretreated with a phosphoric-acid and sodium-hypochlorite, and then treated with a self-etching-primer and bonding agent; and group 4, treated with an all-in-one adhesive. A flowable resin composite was used as filling material for each cavity treated with each group. A glass-ionomer-cement was used as a control. The following items were evaluated: pulp-tissue-disorganization (PTD), inflammatory-cell-infiltration (ICI), tertiary-dentin-formation (TDF), and bacterial-penetration (BP). The results were statistically analyzed using the Kruskal-Wallis test and Mann-Whitney U test. No significant differences were observed among the experimental groups for all parameters after 24 h and 14 days (P > 0.05). The majority of the specimens showed PTD with edema formation after 24 h; however, all the specimens demonstrated pulpal healing with TDF after 14 days. On the parameter of TDF, all groups showed significant differences between the two postoperative periods (P < 0.01). On the parameter of ICI, a significant difference was found between the two postoperative periods in group 4 (P < 0.05). No specimens showed BP. The pretreatment on the cavity prepared with the laser using phosphoric-acid or sodium-hypochlorite did not affect the dental pulp healing of rat tooth.

Wnt5a promotes inflammatory responses via nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in human dental pulp cells

Wnt5a has been found recently to be involved in inflammation regulation through a mechanism that remains unclear. Immunohistochemical staining of infected human dental pulp and tissue from experimental dental pulpitis in rats showed that Wnt5a levels were increased. In vitro, Wnt5a was increased 8-fold in human dental pulp cells (HDPCs) after TNF-α stimulation compared with control cells. We then investigated the role of Wnt5a in HDPCs. In the presence of TNF-α, Wnt5a further increased the production of cytokines/chemokines, whereas Wnt5a knockdown markedly reduced cytokine/ chemokine production induced by TNF-α. In addition, in HDPCs, Wnt5a efficiently induced cytokine/chemokine expression and, in particular, expression of IL-8 (14.5-fold) and CCL2 (25.5-fold), as assessed by a Luminex assay. The cytokine subsets regulated by Wnt5a overlap partially with those induced by TNF-α. However, no TNF-α and IL-1β was detected after Wnt5a treatment. We then found that Wnt5a alone and the supernatants of Wnt5a-treated HDPCs significantly increased macrophage migration, which supports a role for Wnt5a in macrophage recruitment and as an inflammatory mediator in human dental pulp inflammation. Finally, Wnt5a participates in dental pulp inflammation in a MAPK-dependent (p38-, JNK-, and ERK-dependent) and NF-κB-dependent manner. Our data suggest that Wnt5a, as an inflammatory mediator that drives the integration of cytokines and chemokines, acts downstream of TNF-α.

Immunohistochemical study of the inflammatory response of the dental pulp

Defense reactions of the dental pulp involve a variety of biological reactions, in which the immune system plays a very important role. The class II major histocompatibility complex (MHC) molecule expressing cells, termed dendritic cells and lymphocytes in human dental pulp are highly sensitive to exogenous antigenic stimuli. Their drastic changes in number and localization are induced by dental caries. This study investigated the responses of the immune system in two different clinical conditions: shallow and deep cavities. Cells were identified immunohistochemically by using the following monoclonal antibodies: HLA-DR, CD45RO and CD20. Initial pulpal response was characterized by a localized accumulation of HLA-DR antibody-positive cells in the pulp tissue beneath the dentinal tubules communicating with the caries lesion. In the pulp of progressed caries, a large number of HLA-DR-positive cells was observed with a marked increase of other kinds of immunocompetent cells. This might indicate the occurrence of antigen presentation locally in the pulp tissue, which is very important for the immune response. Results obtained in this study demonstrated that dental pulps respond to the progression of the carious lesion and cellular and humoral immune responses occur in the pulp tissue.

In situ proliferation and differentiation of macrophages in dental pulp

The presence of macrophages in dental pulp is well known. However, whether these macrophages proliferate and differentiate in the dental pulp in situ, or whether they constantly migrate from the blood stream into the dental pulp remains unknown. We have examined and compared the development of dental pulp macrophages in an organ culture system with in vivo tooth organs to clarify the developmental mechanism of these macrophages. The first mandibular molar tooth organs from ICR mice aged between 16 days of gestation (E16) to 5 days postnatally were used for in vivo experiments. Those from E16 were cultured for up to 14 days with or without 10% fetal bovine serum. Dental pulp tissues were analyzed with immunohistochemistry to detect the macrophages and with reverse transcription and the polymerase chain reaction (RT-PCR) for the detection of factors related to macrophage development. The growth curves for the in vivo and in vitro cultured cells revealed similar numbers of F4/80-positive macrophages in the dental pulp. RT-PCR analysis indicated the constant expression of myeloid colony-stimulating factor (M-CSF) in both in-vivo- and in-vitro-cultured dental pulp tissues. Anti-M-CSF antibodies significantly inhibited the increase in the number of macrophages in the dental pulp. These results suggest that (1) most of the dental pulp macrophages proliferate and differentiate in the dental pulp without a supply of precursor cells from the blood stream, (2) M-CSF might be a candidate molecule for dental pulp macrophage development, and (3) serum factors might not directly affect the development of macrophages.

Inflammatory and immunological aspects of dental pulp repair

The repair of dental pulp by direct capping with calcium hydroxide or by implantation of bioactive extracellular matrix (ECM) molecules implies a cascade of four steps: a moderate inflammation, the commitment of adult reserve stem cells, their proliferation and terminal differentiation. The link between the initial inflammation and cell commitment is not yet well established but appears as a potential key factor in the reparative process. Either the release of cytokines due to inflammatory events activates resident stem (progenitor) cells, or inflammatory cells or pulp fibroblasts undergo a phenotypic conversion into osteoblast/odontoblast-like progenitors implicated in reparative dentin formation. Activation of antigen-presenting dendritic cells by mild inflammatory processes may also promote osteoblast/odontoblast-like differentiation and expression of ECM molecules implicated in mineralization. Recognition of bacteria by specific odontoblast and fibroblast membrane receptors triggers an inflammatory and immune response within the pulp tissue that would also modulate the repair process.

Innate Immune Responses of the Dental Pulp to Caries

Various cells and inflammatory mediators are involved in the initial pulpal responses to caries. This review focuses on the cellular, neuronal, and vascular components of pulpal innate responses to caries. Discussion will include dentinal fluid, odontoblasts, neuropeptides, and neurogenic inflammation, which are not classic immune components but actively participate in the inflammatory response as the caries progress pulpally. Summaries of innate immune cells as well as their cytokines and chemokines in healthy and reversible pulpitis tissues are presented.

Differential regulation of immune responses by odontoblasts

Odontoblasts (OBs) are cells lining the inner surface of the tooth. Their potential role in host defenses within the tooth is suggested by their production of antimicrobial beta-defensins, but their role needs confirmation. The present study sought to define the roles of human OBs in microbial recognition and innate host responses. Toll-like receptor 2 (TLR2) and TLR4, as well as CCR6, were immunolocalized in human OBs and their dentinal processes in situ. To examine OB function we used organotypic tooth crown cultures to maintain human OBs within their dentin scaffold. Cells in the OB layer of cultured and non-cultured crown preparations expressed mRNA for several markers of innate immunity including chemokine CCL20, chemokine receptor CCR6, TLR2, TLR4 and the OB marker dentin sialophosphoprotein (DSPP). Expression of human beta-defensin 1 (hBD1), hBD2, hBD3, interleukin-8 (IL-8), and CCL20 increased with time in culture. Tooth crown odontoblast (TcOB) cultures were stimulated with agonist that was specific for TLR2 (Pam3CSK4) or TLR4 [Escherichia coli lipopolysaccharide (LPS)]. Nuclear factor-kappaB assays confirmed the TLR2 activity of Pam3CSK4 and the TLR4 activity of LPS. LPS up-regulated IL-1beta, tumor necrosis factor-alpha (TNF-alpha), CCL20, hBD2, IL-8, TLR2 and TLR4; however, Pam3CSK4 down-regulated these mRNAs. IL-1beta, TNF-alpha, CCL20 were also up-regulated from six-fold to 30-fold in TcOB preparations from decayed teeth. Our results show for the first time that OBs express microbial pattern recognition receptors in situ, thus allowing differential responses to gram-positive and gram-negative bacteria, and suggest that pro-inflammatory cytokines and innate immune responses in decayed teeth may result from TLR4 signaling.

NK and NKT cells in the rat dental pulp tissues

OBJECTIVE

The objective of this study was to elucidate the presence of natural killer (NK) and natural killer T (NKT) cells in rat dental pulp.

STUDY DESIGN

Male Wistar rats (n = 10) were used. The presence of NK and NKT cells in the coronal and root pulps of the lower first molars was detected immunohistochemically.

RESULTS

Infiltration of NK and NKT cells into the normal pulp was observed, and most of these cells were located in the coronal pulp rather than in the root pulp. The population of NKT cells in the pulp was only small compared to the population of NK cells.

CONCLUSION

NK and NKT cells are present in normal pulp, indicating an important role for the innate immune system in the pulp tissues.

Pulpal responses to cavity preparation in aged rat molars

The dentin-pulp complex is capable of repair after tooth injuries including dental procedures. However, few data are available concerning aged changes in pulpal reactions to such injuries. The present study aimed to clarify the capability of defense in aged pulp by investigating the responses of odontoblasts and cells positive for class II major histocompatibility complex (MHC) to cavity preparation in aged rat molars (300-360 days) and by comparing the results with those in young adult rats (100 days). In untreated control teeth, immunoreactivity for intense heat-shock protein (HSP)-25 and nestin was found in odontoblasts, whereas class-II-MHC-positive cells were densely distributed in the periphery of the pulp. Cavity preparation caused two types of pulpal reactions based on the different extent of damage in the aged rats. In the case of severe damage, destruction of the odontoblast layer was conspicuous at the affected site. By 12 h after cavity preparation, numerous class-II-MHC-positive cells appeared along the pulp-dentin border but subsequently disappeared together with HSP-25-immunopositive cells, and finally newly differentiated odontoblast-like cells took the place of the degenerated odontoblasts and acquired immunoreactivity for HSP-25 and nestin by postoperative day 3. In the case of mild damage, no remarkable changes occurred in odontoblasts after operation, and some survived through the experimental stages. These findings indicate that aged pulp tissue still possesses a defense capacity, and that a variety of reactions can occur depending on the difference in the status of dentinal tubules and/or odontoblast processes in individuals.

Immunocompetent cells in the pulp of human deciduous teeth

This immunohistological study sought to determine how the distribution and density of various immunocompetent cells change in the pulp of human deciduous teeth during the process of physiological root resorption. Forty-three extracted deciduous teeth at various stages of resorption were subjected to immunoperoxidase staining with the use of antibodies directed to HLA-DR, CD68, factor XIIIa and lymphocyte subsets. In intact deciduous teeth (group 0), all types of cells examined, except for CD20+ B lymphocytes, were detected. In teeth in which resorption was less than 1/3 of the root length (group 1), all types of cells showed a statistically significant increase compared with group 0 (P<0.05; Mann-Whitney's U-test). HLA-DR+, CD68+, and factor XIIIa+ cells with a dendritic profile kept their distribution in the periphery of the pulp, and oval and round, newly recruited macrophages accumulated in the central portion of the pulp and near the resorption sites. In teeth where resorption was 1/2 to 2/3 (group 2), all the cell types increased further. Aggregations of HLA-DR+, CD68+, and factor XIIIa+ cells were frequently seen in the central portion of the pulp, and T and B lymphocytes occasionally formed some clusters. Comparisons with group 1 revealed that the density of these cells, except for CD20+ cells, showed significant increases (P<0.05; Mann-Whitney's U-test). These results provided evidence showing that immunocompetent cells of deciduous tooth pulp increase with the progress of physiological root resorption, suggesting that immunocompetency of deciduous teeth is altered by this process.

Class II antigen-presenting dendritic cell and nerve fiber responses to cavities, caries, or caries treatment in human teeth

Major histocompatibility complex (MHC) class II molecule-expressing cells are distributed in human dental pulp, and have been shown to accumulate beneath caries lesions. The responses of these cells and nerve fibers were analyzed under 5 different clinical conditions: shallow and deep experimental cavities, active and slow untreated caries, and treated caries. Under deep cavities, class II molecule-expressing dendritic cells displaced the injured odontoblasts during a period of one month, while such a response was not observed in shallow cavities and untreated or treated carious teeth. The class II molecules seen in the neural elements under active caries were no longer detectable in treated carious teeth. However, six months after treatment, clusters consisting of dendritic cells, T-lymphocytes, and nerve fibers still remained locally in the subodontoblastic area. These results indicate that dental pulps respond differently to cavity preparation and restoration between normal and caries conditions, and that immunoresponses persist for many months, even after caries treatment.

Pulpal regeneration after cavity preparation, with special reference to close spatio-relationships between odontoblasts and immunocompetent cells

The regeneration process of the odontoblast cell layer incident to tooth injury, especially its relationship with immunocompetent cells in pulp healing, has not been fully understood. The purpose of the present study was to clarify this relationship between odontoblasts and immunocompetent cells in the process of pulp regeneration following cavity preparation in rat molars by immunocytochemistry for heat shock protein (Hsp) 25 as well as class II major histocompatibility complex (MHC) molecules. In untreated control teeth, intense Hsp 25-immunoreactivity was found in the cell bodies of odontoblasts and their processes within the predentin, whereas class II MHC-positive cells were predominantly located beneath the odontoblast cell layer. Cavity preparation caused the destruction of the odontoblast layer to form an edematous lesion and the shift of class II MHC-positive cells with the injured odontoblasts toward the pulp core at the affected site. Some damaged odontoblasts without apparent cytoplasmic processes, round in profile, retained the immunoreactivity for Hsp25, suggesting the survival of a part of the odontoblasts against artificial external stimuli. Twelve hours after cavity preparation, numerous class II MHC-positive cells appeared along the pulp-dentin border and extended their processes deep into the exposed dentinal tubules. By postoperative 72 hours, newly differentiated odontoblasts with Hsp 25-immunoreactivity were arranged at the pulp-dentin border, but the class II MHC-positive cells moved from the pulp-dentin border to the subodontoblastic layer. These findings indicate that the time course of changes in the expression of Hsp 25-immunoreactivity reflects the regeneration process of odontoblasts. The functional roles of Hsp 25-positive odontoblasts and immunocompetent cells such as class II MHC-positive cells in the process of pulp regeneration after cavity preparation are discussed in conjunction with our previous experimental data.

Age-related changes in the immunoreactivity of the monocyte/macrophage system in rat molar pulp after cavity preparation

OBJECTIVE

Our objective was to compare the response of the monocyte/macrophage system of dental pulp to cavity preparation in aged rats (12 and 18 months old) with that seen in young adult rats (3 and 6 months old).

STUDY DESIGN

Cavities were prepared on the upper first molars, and the lower first molars served as intact controls. Specimens were collected at 1 day after cavity preparation, and cryostat sections were made.

RESULTS

Accumulation of OX6+ antigen-presenting cells along the pulp-dentin border and a marked increase in cell size ED2+ resident macrophages were noted in both young adult and aged rats after cavity preparation. In both cases, the number of ED1+ cells increased significantly after cavity preparation because of infiltrating monocytes.

CONCLUSION

These findings suggest that the pulpal defense reaction of the monocyte/macrophage system to cavity preparation in aged rats does not differ markedly from that in young adult rats.

Immunohistochemical study on pulpal response in rat molars after cavity preparation by Er:YAG laser

While Er:YAG laser systems are in extensive use for caries removal and cavity preparation, the effects of such treatment on pulp tissue remain unclear. This study evaluates these systems using immunohistochemical methods and compares the results with information gained from treatment using conventional burs. Cervical cavities were prepared in the upper first molars of rats, using either an Er:YAG laser or a conventional tungsten-carbide bur. At intervals of 5 min, 6 h, 12 h, 1 d, 3 d and 7 d after cavity preparation, the teeth were processed for immunohistochemical analyses of tissue non-specific alkaline phosphatase, OX6-positive major histocompatibility complex class II antigen-expressing cells and PGP 9.5-immunoreactive nerve fibers. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Tissue non-specific alkaline phosphatase was observed mainly in the subodontoblastic layer under the cavity lesion, from 5 min, in both groups. The immunoreactivity was more pronounced in the laser group, but by 7 d no significant differences were recognizable. At 12 h, TUNEL-positive cells were detected around the odontoblastic layer in both groups. From 3 d to 7 d, a limited number of positive cells were still visible in the group that underwent standard treatment. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5-immunoreactive nerve fibers were also noted. From 12 h to 1 d, OX6-positive cells accumulated along the pulp-dentin border, extending their processes into the dentinal tubules. Numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer at 7 d. These results demonstrated that there was no appreciable difference in the manner in which pulp tissue responded to treatment with either Er:YAG laser or a conventional drill. This would seem to indicate the usefulness of the Er:YAG laser system in the removal of caries and cavity preparation.

Responses of odontoblasts to cavity preparation in rat molars as demonstrated by immunocytochemistry for heat shock protein (Hsp) 25

Responses of odontoblasts to cavity preparation in rat molars were investigated by immunocytochemistry for heat shock protein (Hsp) 25. In untreated control teeth, intense Hsp 25-immunoreactivity was found in the cell bodies of odontoblasts and their processes within the predentin. Confocal microscopy of Hsp 25-immunostained and rhodamine-labeled sections revealed that the immunoreactive odontoblasts were intensely labeled for phalloidin at the periphery of their cytoplasm and throughout their processes, but the reaction for phalloidin was limited within the inner half of the dentin. Cavity preparation caused an edematous reaction between the injured odontoblasts and predentin as well as a beaded swelling and successive destruction of the odontoblast processes. Immediately after cavity preparation, the odontoblasts beneath the edematous lesion showed an immunoreactivity for Hsp 25, which subsequently disappeared completely from the pulp-dentin border by 12 h after the operation. However, round cells without apparent cytoplasmic processes continued to be immunoreactive, suggesting the survival of a part of the odontoblasts against preparation stimuli. Numerous phalloidin-reactive but Hsp 25-immunonegative cells appeared along the pulp-dentin border and extended their processes deep into the exposed dentinal tubules, probably categorized in a lineage of immunocompetent cells. By postoperative 72 h, newly differentiated odontoblasts with Hsp 25-immunoreactivity were arranged at the pulp-dentin border. These findings indicate that the time course of changes in the expression of Hsp 25-immunoreactivity reflects the regeneration process of odontoblasts, and suggest that this protein is a useful marker substance for differentiated odontoblasts.

Changes in the pattern of horseradish peroxidase diffusion into predentin and dentin after cavity preparation in rat molars

OBJECTIVE

The purpose of this study was to examine the process of reducing dentin permeability in adult rat molars after cavity preparation with horseradish peroxidase as a tracer.

STUDY DESIGN

Class V cavities were prepared on the upper first molars of 18 rats. Horseradish peroxidase was injected into the vascular system at intervals of 3 hours and 3, 5, 7, 10, and 14 days after cavity preparation, and frozen sections were processed by the diaminobenzidine procedure.

RESULTS

Horseradish peroxidase reaction products were noted in the dentinal tubules immediately beneath the cavity up until 14 days after cavity preparation. An abrupt stoppage of reactive products caused by impermeable junctional zone formation at the interface of the primary dentin and reparative dentin was observed at 14 days after cavity preparation.

CONCLUSION

Reparative dentin formation and subsequent impermeable junctional zone formation participate in the reduction of dentin permeability after cavity preparation.

Presence or absence of tertiary dentinogenesis in relation to caries progression

Studies have shown that dental caries may or may not be associated with tertiary dentin formation in the pulp. On the basis of histological examinations of 69 clinical well-defined caries lesions, a hypothesis is proposed on the dynamics of the hard-tissue responses of the pulp to caries. In active non-cavitated lesions, the formation of tertiary dentin seems to be initiated by primary odontoblast cells that subsequently result in atubular dentin/fibrodentinogenesis, whereas, in similarly aged but more rapidly progressing cavitated enamel lesions, no tertiary dentin is laid down by primary odontoblast cells. In all old-dentin exposed lesions, a so-called closed lesion environment was defined with subjacent atubular dentin formation. As these lesions progress, a shift from a closed to a more large and open lesion environment may develop in the very old lesions, and a new tubular dentinal matrix is noted on the top of the fibrodentin, also defined as reparative dentinogenesis. In very old slowly progressing lesions, a relatively small open lesion environment is also observed, with tubular tertiary dentin resembling the primary dentin being strictly tubular. It is suggested that the absence of tertiary dentinogenesis can be expected in very rapid caries lesions, whereas a variety of tertiary dentin is observed in older dentin cavitated lesions guided by a changing external lesion environment over time.

Response of Class II molecule-expressing cells and macrophages to cavity preparation and restoration with 4-META/MMA-TBB resin

AIM

The aim was to test the hypothesis that the resin and bonding agent 4-META/MMA-TBB (4-META), has the potential to prevent transdentinal antigenic challenges.

METHODOLOGY

Class I cavity preparation and immediate restoration with 4-META were made in the maxillary right first molars of 36 six-week-old Wistar rats. Contralateral teeth with an unrestored cavity served as positive control (cavity without 4-META) group. The maxillary first molars of 12 age-matched normal rats (total 24 teeth) were also examined as negative control (intact tooth group). At 3 or 28 days after cavity preparation, the teeth were subjected to immunoperoxidase staining using OX6 (anticlass II molecules) and ED1 (antimacrophages) as primary antibodies.

RESULTS

A total of 10 teeth were not available for histological examination. In the teeth filled with 4-META at 3 days, the density of OX6+ and ED1+ cells in the coronal pulp was significantly higher than that in the intact tooth group. At 28 days, formation of sound reparative dentine was noted and the density of the immunocompetent cells was comparable to the intact teeth. In the teeth without 4-META at 3 days, pulpal abscess was observed in 14 out of 16 and the density of OX6+ and ED1+ cells was significantly increased (P < 0.001, paired t-test) compared with the 4-META group. Partial pulp necrosis had developed in the teeth without 4-META at 28 days.

CONCLUSIONS

Restoration with 4-META significantly reduced transdentinal antigenic challenges. This property may have special implications for 4-META's capacity to protect the dentine/pulp complex.

Dental injury models: experimental tools for understanding neuroinflammatory interactions and polymodal nociceptor functions

Recent research has shown that peripheral mechanisms of pain are much more complex than previously thought, and they differ for acutely injured normal tissues compared with chronic inflammation or neuropathic (nerve injury) pain. The purpose of the present review is to describe uses of dental injury models as experimental tools for understanding the normal functions of polymodal nociceptive nerves in healthy tissues, their neuroinflammatory interactions, and their roles in healing. A brief review of normal dental innervation and its interactions with healthy pulp tissue will be presented first, as a framework for understanding the changes that occur after injury. Then, the different types of dental injury that allow gradation of the extent of tissue damage will be described, along with the degree and duration of inflammation, the types of reactions in the trigeminal ganglion and brainstem, and the type of healing. The dental injury models have some unique features compared with neuroinflammation paradigms that affect other peripheral tissues such as skin, viscera, and joints. Peripheral inflammation models can all be contrasted to nerve injury studies that produce a different kind of neuroplasticity and neuropathic pain. Each of these models provides different insights about the normal and pathologic functions of peripheral nerve fibers and their effects on tissue homeostasis, inflammation, and wound healing. The physical confinement of dental pulp and its innervation within the tooth, the high incidence of polymodal A-delta and C-fibers in pulp and dentin, and the somatotopic organization of the trigeminal ganglion provide some special advantages for experimental design when dental injury models are used for the study of neuroinflammatory interactions.

Co-increase of nerve fibers and HLA-DR- and/or factor-XIIIa-expressing dendritic cells in dentinal caries-affected regions of the human dental pulp: an immunohistochemical study

Neuro-immune interaction has been suggested to play some modulatory role in the immunodefense of the dentin/pulp complex. In this study, we performed a simultaneous immunohistochemical observation of neural elements and pulpal dendritic cells (PDCs) on human carious teeth, to obtain morphological evidence for neuro-immune interaction in response to dentinal tubule-derived carious stimuli. Human third molars bearing a pulp-exposure-free caries lesion were studied. Immunoperoxidase staining was performed with anti-HLA-DR, anti-coagulation factor XIIIa, and anti-CD14 as PDC markers, and anti-low-affinity nerve growth factor receptor (NGFR), anti-protein gene products 9.5, and anti-calcitonin gene-related peptide as nerve markers. The carious teeth usually exhibited localized accumulation of both PDCs and nerve fibers immunoreactive to each marker, in the para-odontoblastic region corresponding to the pulpal end of carious dentinal tubules. Semi-quantitative digital densitometry revealed that pixel numbers corresponding to factor-XIIIa- and NGFR-immunoreactivity were significantly higher in the carious regions than those in the non-carious regions of the same teeth as well as those in the corresponding regions of intact teeth. Classification of specimens with respect to caries depth showed that the co-increase was most apparent in teeth with superficial caries. The increase of PDCs was less pronounced in carious teeth with reparative dentin. These findings suggest that both pulpal nerves and PDCs respond promptly and actively to dentinal tubule-derived carious stimuli. The synchronized accumulation of the two structures suggests an increased opportunity for neuro-immune interaction that may be of significance in the modulation of pathological processes in the dental pulp.

Responses of macrophage-associated antigen-expressing cells in the dental pulp of rat molars to experimental tooth replantation

Bacterial infection of the dental pulp is a major hindrance to successful pulp regeneration after tooth replantation. This study examined how macrophages and class II molecule-expressing cells of the pulp respond to tooth replantation, on the hypothesis that they contribute to the defence and repair of the traumatized pulp. Upper right first molars of 5-week-old male Wistar rats were replanted immediately after extraction; contralateral untreated teeth served as controls. Pulpal cells expressing macrophage-associated antigens were immunohistochemically demonstrated at 0 h (immediately after the replantation) to 84 days postoperatively using antirat monoclonal antibodies OX6 (anti-class II molecules), ED1 (pan-macrophage antibody, reactive also with dendritic cells) and ED2 (anti-resident macrophages). Between 3 and 7 days postoperatively, ED1+ and OX6+ cells, but not ED2+ cells, were concentrated in areas of degeneration formed in the coronal pulp, and frequently showed a marked accumulation along the pulp-dentine border of the cuspal area. Confocal laser scanning microscopy revealed that some of the OX6+ cells with a dendritic profile extended several cytoplasmic processes into the dentinal tubules communicating with the enamel-free area at the tip of the cusp. From 14-84 days, approx. two-thirds of specimens exhibited pulp-tissue regeneration with increasing formation of reparative dentine. Following the formation of sound reparative dentine, cells positive to each antibody were distributed more centrally in the pulp than in the controls, and thus did not show any accumulation along the pulp-dentine border. However, in the other specimens where a bone-like hard tissue had formed in the pulp chamber, many ED1+ and OX6+ cells were still concentrated in the remaining pulp tissue and showed a marked accumulation along the pulp dentine border. Few ED2+ cells were observed in these specimens. These findings suggest that, following tooth replantation, exudative macrophages are actively engaged in eliminating dentinal tubule-derived infectious stimuli and that class II molecule-expressing cells, most probably containing dendritic cells, are positioned strategically at the outermost portion of the injured pulp to monitor incoming antigens. The intensity of the pulpal defence reaction may be dependent on the status of hard-tissue formation, which influences the amount of incoming antigens.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

An in vitro model of human dental pulp repair

Pulp tissue responds to dentin injury by laying down reactionary dentin secreted by existing odontoblasts or reparative dentin elaborated by odontoblast-like cells that differentiated from precursor cells in the absence of inner dental epithelium and basement membrane. Furthermore, growth factors or active dentin matrix components are fundamental signals involved in odontoblast differentiation. In vitro, dental pulp cells cultured under various conditions are able to express typical markers of differentiation, but no culture system can re-create pulp response to dentin drilling. This paper reports the behavior of thick slices from human teeth drilled immediately after extraction and cultured from 3 days to 1 month. Results show that the damaged pulp beneath the cavity is able to develop, in vitro, some typical aspects correlated to tissue healing, evidenced by cell proliferation (BrdU-positive cells), neovascularization (positive with antitype-IV collagen antibodies), and the presence of functional (3H proline-positive) cuboidal cells close to the injured area. After 30 days of culture, elongated spindle-shaped cells can be seen aligned along the edges of the relevant dentin walls, whereas sound functional odontoblasts are well-preserved beneath healthy areas. This tissue recovery leads us to believe that such a culture model will be a useful system for testing factors regulating pulp repair.

Dendritic cells: a novel cellular component of the rat incisor enamel organ appearing in the late stages of enamel maturation

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using OX6, ED1, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The OX6 immunopositive cells (MHC cells) were located exclusively in the enamel maturation zone. MHC cells increased in number in the incisal direction and occasionally extended cytoplasmic processes deep into the ameloblast layer. Migration of MHC cells in the ameloblast layer were also encountered. MHC cells lacked phagolysosomes and could be distinguished from typical macrophages. ED2 immunopositive cells were not seen in the enamel organ. ED1 positive cells displayed identical localization to MHC cells except that some appeared in the transitional zone. MHC cells could not be seen in the enamel organ of rat molar tooth germs. Our data confirmed the presence of a large population of "dendritic" immunocompetent cells in the enamel organ of rat incisors and characterized the ultrastructural features of these cells. Biological significance of the immunocompetent cells in the enamel organ during amelogenesis needs to be clarified.

Immunohistochemical localization of HLA-DR-positive cells in unerupted and erupted normal and carious human teeth

Class II major histocompatibility complex (MHC) antigen-expressing cells are generally associated with the early phase of the immune response. We have studied the distribution of class II-expressing cells in developing, normal, and carious human teeth to clarify when human pulp acquires an immunologic defense potential and how this reacts to dental caries. Antigen-expressing cells were identified immunohistochemically by means of HLA-DR monoclonal antibody. In the pulp of unerupted developing teeth, numerous HLA-DR-positive cells were distributed mainly in and around the odontoblast layer. In erupted teeth, HLA-DR-positive cells were located, for the most part, just beneath the odontoblast layer, with slender cytoplasmic processes extending into the layer. Superficial caries lesions caused an aggregation of HLA-DR-positive cells in dental pulp corresponding to the lesion. In teeth with deeper caries lesions, this aggregation of cells expanded to include the odontoblast layer. Also noted were HLA-DR-positive cells lying along the pulp-dentin border, with cytoplasmic processes projecting deep into the dentinal tubules, where they co-localized with odontoblast processes. These findings suggest that: (1) human dental pulp is equipped with immunologic defense potential prior to eruption; (2) in the initial stage of caries infection, an immunoresponse mediated by class-II-expressing cells is initiated in human dental pulp; and (3) HLA-DR-positive cells trespass deep into dentinal tubules as the caries lesion advances.

Nuclear DNA fragmentation during postnatal tooth development of mouse and hamster and during dentin repair in the rat

The TUNEL (transferase-mediated, dUTP-biotin nick end labeling) method for in situ labeling of DNA strands was utilized to localize DNA fragmentation in cells involved in tooth formation in the neonatal mouse and hamster. Positive reactions for the presence of DNA fragments were obtained in some epithelial cells of the cervical loop region of incisors, late secretory, transitional and early maturation stage ameloblasts, stratum intermedium cells and in shortened ameloblasts just before eruption. Also, cells of the periodontal ligament of the continuously erupting incisors stained positive shortly before eruption. Odontoblasts were negative but became strongly positive during the formation of physiological osteodentin at the tip of developing incisors. Osteodentin matrix and the surfaces of unerupted enamel and cementum just prior to eruption stained for DNA fragments as well. DNA fragmentation could be elicited in odontoblasts and underlying pulpal tissues of mature erupted molars after mechanical injury to the odontoblast processes during cavity preparation. We conclude that, in rodents, DNA fragmentation and cell death are biological processes which take place in a variety of cells involved in formation of teeth. The TUNEL staining technique is a simple but powerful tool to examine the fate of cells and tissues undergoing either programmed cell death (apoptosis) or fragmentation of nuclear DNA induced by external factors leading to pathological changes.