Pulpal status of hypomineralized permanent molars

PURPOSE

Young patients with hypomineralized teeth frequently complain of symptoms suggestive of dentin hypersensitivity. It has been proposed that these symptoms may be exacerbated by an underlying pulpal inflammation. The purpose of the study was to determine the pulpal status of hypomineralized teeth.

METHODS

The experimental material comprised 25 sound and 19 hypomineralized permanent first molars obtained from children requiring dental extractions under general anesthesia. Pulp sections were processed for indirect immunofluorescence using combinations of: (1) protein gene product 9.5; (2) leukocyte common antigen; and (3) Ulex europaeus I lectin. Image analysis was then used to determine the percentage area of staining of each label.

RESULTS

Innervation density was significantly greater in the pulp horn and subodontoblastic region of hypomineralized teeth than in sound teeth. Immune cells were most abundant within pulps of hypomineralized teeth exhibiting enamel loss. Vascularity was found to be similar for both hypomineralized and sound teeth, but was significantly greater in hypersensitive hypomineralized samples.

CONCLUSION

This study provides biological evidence that inflammatory changes may be present within the pulpal tissue of these teeth.

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.

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.

Immunolocalization of CXC�chemokine and recruitment of polymorphonuclear leukocytes in the rat molar periodontal tissue after topical application of lipopolysaccharide

This study investigated the recruitment of polymorphonuclear leukocytes (PMNs) and the immunolocalization of CXC chemokines, including macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant-2 (CINC-2) in rat periodontal tissue after topical application of lipopolysaccharide (LPS; 5 mg/ml) from Escherichia coli into the rat molar gingival sulcus. In normal periodontal tissues, a small number of MIP-2- and CINC-2-positive cells were seen in junctional epithelium (JE), especially in its coronal half. After topical application of LPS, a prominent increase of MIP-2- and CINC-2-positive JE cells was observed. Almost all JE cells strongly expressed them at day 1 and day 2, and then the number of chemokine-positive cells returned to normal at day 7. Corresponding to these chemokine expressions, LPS application induced a significant increase in the number of PMNs in the sub-JE area from 1 h to 2 days and a significant increase in JE area from 3 h to 5 days, indicating a dynamic flow of PMNs from the sub-JE area into JE. These findings indicated that JE cells produced MIP-2 and CINC-2 in response to LPS stimulation and suggested that MIP-2 and CINC-2 may be responsible for PMN migration toward the periodontal pathogen and may play an important role in the initiation of inflammation and subsequent periodontal tissue destruction.

Immunohistochemical localisation of extracellular matrix proteins in the periodontium during cementogenesis in the rat molar

OBJECTIVE

The development of the periodontium involves the coordinated expression of numerous extracellular matrix (ECM) macromolecules and their receptors (integrins). The aim of this study was to determine the expression of selected hard and soft tissue matrix molecules and the integrin alpha5beta1 in the periodontal tissues, during cementogenesis in the rat molar.

METHODS

Using immunohistochemical methods, the distribution of the extracellular matrix proteins, fibronectin, tenascin, and bone sialoprotein (BSP), as well as the integrin subunits alpha5 and beta1 were studied in rats aged 3, 5 and 8 weeks.

RESULTS

Fibronectin was widely distributed in the gingival epithelium, gingival connective tissue and in the periodontal ligament. Tenascin expression was less marked compared with fibronectin, but was more distinctly associated with cells and peri-cellular areas of the epithelial-connective tissue interface, the gingiva and within the periodontal ligament. The fibronectin-receptor alpha5beta1 integrins were expressed by epithelial cells, periodontal ligament cells and gingival fibroblasts. A notable finding was the increased staining intensity of fibronectin, tenascin and alpha5beta1 integrin in all 5-week old molar sections in the periodontal ligament matrix and cells, apical to the cemento-enamel junction (CEJ) along the alveolar crest (AC) ridge height. Bone sialoprotein was distinctly associated with the hard tissues of the periodontium as acellular cementum and alveolar bone matrix expressed bone sialoprotein throughout all sections, in all age groups.

CONCLUSIONS

In conclusion, this study has demonstrated the selective distribution of several hard and soft tissue matrix molecules during periodontogenesis. The results highlight the complex nature of interactions of various proteins and molecules during development. The interactions between these molecules and their specific roles in development and regeneration await further investigation.

Possible role of immunocompetent cells and the expression of heat shock protein-25 in the process of pulpal regeneration after tooth injury in rat molars

Recent studies have established that heat shock proteins (HSPs) potentially play a role in immunosurveillance. The purpose of the present study was to clarify the relationship between the chronological changes of immunocompetent cells and the expression of HSP-25 in the process of pulpal regeneration after tooth injury in rat molars by immunocytochemistry for HSP-25 and class II major histocompatibility complex (MHC) antigen. In untreated control teeth, intense HSP-25 immunoreactivity was found in the cell bodies of odontoblasts. Both cavity preparation and tooth replantation caused the degeneration of the odontoblast layer to result in the loss of HSP-25 immunoreactions in the suffered dental pulp at the early stages after tooth injury. Numerous class II MHC-positive cells appeared along the pulp-dentin border and extended their cell processes into the dentinal tubules at 12-24 h after cavity preparation and 3 days after tooth replantation. Newly differentiated odontoblast-like cells with HSP-25 immunoreactivity were arranged at the pulp-dentin border and the class II MHC-positive cells retreated towards the subodontoblastic layer by post-operative days 3-5 after tooth injury. Thus, the common cellular events occur during pulpal regeneration following two different experimental injuries. These findings indicate that the time course of changes in the expression of HSP-25 immunoreactivity reflects the degeneration/regeneration process of odontoblasts and that the temporal appearance of the class II MHC-positive cells at the pulp-dentin border suggests their participation in odontoblast differentiation as well as in initial defence reactions during the pulpal regeneration process.

Responses of immunocompetent cells in the dental pulp to replantation during the regeneration process in rat molars

Responses of immunocompetent cells to tooth replantation during the regeneration process of the dental pulp in rat molars were investigated by immunocytochemistry using antibodies to class II major histocompatibility complex (MHC) molecules (OX6 antibody), monocyte/macrophage lineage cells (ED1 antibody) and protein gene product 9.5 (PGP 9.5), as well as by histochemical reaction for periodic acid-Schiff (PAS). Tooth replantation caused an increase in both the number of OX6- and ED1-positive cells and their immunointensity in the replanted pulp, but almost all PGP 9.5-immunoreactive nerves diminished in the initial stages. By postoperative day 3, many OX6- and ED -immunopositive cells had accumulated along the pulp-dentin border to extend their cytoplasmic processes into the dentinal tubules in successful cases. Once reparative dentin formation had begun after postoperative day 7, OX6- and ED1-immmunopositive cells became scattered in the odontoblast layer, while reinnervation was found in the coronal pulp. The temporal appearance of these immunocompetent cells at the pulp-dentin border suggests their participation in odontoblast differentiation as well as in initial defense reactions during the pulpal regeneration process. On postoperative day 14, the replanted pulp showed three regeneration patterns: (1) reparative dentin, (2) bone-like tissue formation, and (3) an intermediate form between these. In all cases, PAS-reactive cells such as polymorphonuclear leukocytes (PML) and mesenchymal cells occurred in the pulp space. However, the prolonged stagnation of inflammatory cells was also discernible in the latter two cases. Thus, the findings on PAS reaction suggest that the migration of the dental follicle-derived cells into the pulp space and the subsequent total death of the proper pulpal cells are decisive factors for eliciting bone-like tissue formation in the replanted pulp.

Effect of intermittent long-lasting electrical tooth stimulation on pulpal blood flow and immunocompetent cells: a hemodynamic and immunohistochemical study in young rat molars

Release of sensory neuropeptides after stimulation of afferent nerve fibers has previously been shown to induce vasodilation and increased vascular permeability in the dental pulp, a condition recognized as neurogenic inflammation. In the present study a possible role for the sensory neuropeptides in transendothelial migration of immunocompetent cells was investigated. The dental pulp is an isolated tissue densely innervated with sensory fibers containing neuropeptides, and following electrical stimulation of the crown, the effect on pulpal blood flow and immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal blood flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation promptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar nerve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43+, CD4+, CD11+, and I-A antigen-expressing cells was performed, and the effect of stimulation on calcitonin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-immunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin-biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in the first molar pulp, whereas nerve fibers in the gingiva and neighboring teeth were unaffected. A significant increase in the number of CD43+ cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P < 0.01) and unstimulated control (P < 0.05) first molars. For I-A antigen-expressing cells a significant increase (P < 0.05) was found between the innervated stimulated and unstimulated control, but not between the innervated and denervated stimulated first molars. Hence, from the present experiment it is concluded that the pulpal nerves participate in and facilitate transendothelial migration of CD43+ cells during acute neurogenic inflammation.

Immunohistochemical demonstration of prostaglandins in various tissues of the rat

To demonstrate the tissue localization of prostaglandin (PG) E2, PGF2 alpha and 6-keto-PGF1 alpha (a stable metabolite of PGI2) various tissues, including decalcified periodontal tissue of 7-week-old male Wistar strain rats, were immunohistochemically examined using a streptavidin-biotin complex method. Besides tissue macrophages and endothelial cells in various tissues, hepatocytes, renal tubular cells, and parietal and chief cells in the gastric mucosa showed a positive reaction for the various PGs examined. PGs were demonstrated in the cytoplasm or in association with the cell membrane. We generally observed no difference between the localization patterns of PGE2-, PGF2 alpha-, and 6-keto-PGF1 alpha-positive cells in these tissues. However, in the periodontal ligament and alveolar bone, 6-keto-PGF1 alpha was localized in the cytoplasm of osteocytes, osteoblasts, cementocytes, and cementoblasts, while no reaction for PGE2 or PGF2 alpha was revealed in these cells. We demonstrated the immunohistochemical localization of PGs in various rat tissues including decalcified periodontal tissue and discuss the important roles of PGs in the modulation of their normal functions in these tissues.

Recruitment of immunocompetent cells after dentinal injuries in innervated and denervated young rat molars: an immunohistochemical study

The dental pulp represents a peripheral end-organ deprived of a collateral nerve supply. After inferior alveolar nerve (IAN) axotomy, rat molar pulp is denervated over a period of at least 6 days. Therefore, rat molar pulp was used as an experimental model to study the effect of sensory nerve fibers on influx of immunocompetent cells after dentinal injury. In the present study we performed a quantitative analysis of CD43+, CD4+, CD11b+, and I-A antigen-expressing cells subjacent to dentinal cavities in denervated and innervated first mandibular molars. For visualization of nerve fibers, antibodies to protein gene product (PGP) 9.5, the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), and the sympathetic neuropeptide Y (NPY) were used. Immunohistochemistry was performed by the avidin-biotin-peroxidase method. In the innervated teeth, a correlation between increased sensory nerve density and influx of immunocompetent cells was found. Compared to the contralateral innervated molars, a significant reduction in recruitment of immunocompetent cells was found in the denervated pulp tissue subjacent to the dentinal cavities. The rat molar represents a unique model to illustrate the influence of sensory nerves and neuropeptides on inflammation and recruitment of immunocompetent cells.

Segregated localization of immunocompetent cells and osteoclasts in the periodontal ligament of the rat molar

The spatial distribution of dendritic cells, macrophages, and their respective precursor cells in the periodontal ligament of rat molars was examined by means of ACPase enzyme histochemistry and immunohistochemistry. Intense reactions for ACPase were localized in both the multinucleated-and mononucleated cells of the periodontal ligament located exclusively in the portions of physiological bone resorption due to the physiological migration of the molar teeth. Immunohistochemical staining with OX6-monoclonal antibody that recognizes antigen-presenting cells such as dendritic cells and macrophages revealed the localization of immunopositive cells predominantly in the portions of the periodontal ligament that showed only trace reactions for ACPase. On the other hand, a large number of ED1-immunopositive cells, comprising a broad spectrum of cells of monocyte origin including dendritic cells and osteoclasts, displayed an almost even distribution throughout the periodontal ligament. Our current study is the first to show clear-cut in vivo morphological evidence that the cells of the bone-resorbing, osteoclastic cell lineage and those of the non-bone resorbing, macrophagic and/or dendritic cell lineages are exclusively localized in roughly the distal and proximal regions of the periodontal ligament of rat molars, respectively. An advantage is proposed for the use of the rat molar periodontal ligament as an in vivo model system for pursuing differentiation pathways of cells of the monocyte lineage, particularly of the osteoclastic cells.

Chondroitin sulfates in developing mouse tooth germs. An immunohistochemical study with monoclonal antibodies against chondroitin-4 and chondroitin-6 sulfates

The role of glycosaminoglycans and proteoglycans during ontogenesis is not known. The developing tooth offers a potentially important model for studies of structure-function relationships. In this study, we have analysed the temproal and spatial expression of chondroitins of differing sulfation patterns in embryonic molars and incisors. For this purpose, we have used monoclonal antibodies (Mabs) specific for unsulfated, 4-sulfated, and 6-sulfated forms of chondroitin in conjunction with indirect immunofluorescence or immunoperoxidase labeling. Unsulfated chondroitin was not detected in embryonic teeth. Chondroitin 4- and chondroitin 6-sulfates were present in the stellate reticulum but otherwise they were confined to the dental mesenchyme. The 3B3 and MC21C-epitope, which are markers of 6-sulfated chondroitin, were uniformly distributed in the dental mesenchyme during the bud stage; they disappeared from the dental papilla of the cusps and of the anterior region of the incisor as development proceeded. These epitopes were absent from the basement membrane and from the predentin. In the odontoblastic cell lineage, the 3B3 and MC21C-epitopes were detected only between preodontoblasts at an early stage of differentiation. The monoclonal antibody 2B6 served as a probe to localize chondroitin 4-sulfate. This glycosaminoglycan was detected as early as the dental lamina stage but its expression was restricted to the basement membrane of the teeth until the late bell stage. After the onset of cusp formation, strong staining was also observed over the occlusal region of the dental papilla while the cervical region of the dental papilla remained 2B6-negative. Incisors at the bell stage exhibited a decreasing gradient of immunostaining by 2B6 from their anterior region to their posterior end. The extracellular matrix surrounding preodontoblasts reacted with 2B6 and the predentin, produced by the odontoblasts, was also intensely labeled with this antibody. Comparison between immunostaining with 3B3 and 2B6, on consecutive sections revealed a mutually exclusive pattern of distribution of the corresponding epitopes during odontogenesis. Furthermore, in the continuously growing incisor, a striking positive correlation was found between the immunostaining patterns produced by 3B3 and MC21C and the mitotic indices along the anterior-posterior axis of the tooth. Hence, sulfation of chondroitin seems developmentally regulated. We postulate that changes in the sulfation pattern of chondroitin might play a role in ontogenesis by locally altering the functional properties of the extracellular matrix.

IgE in postsecretory ameloblasts suggesting a hypersensitivity reaction at tooth eruption

The clinical symptoms associated with the eruption of primary teeth resemble a mild hypersensitivity reaction. Light microscopic examination showed that IgE accumulated in postsecretory ameloblasts. The formation of IgE was elicited by enamel matrix proteins, which are chemotactic for mast cells.