Biological behavior of human dental pulp cells in response to carious stimuli analyzed by PCNA immunostaining and AgNOR staining

Plithotaxis, a collective cell migration, regulates the sliding of proliferating pulp cells located in the apical niche

Using the proliferating cell nuclear antigen (PCNA) immunostaining, we previously identified, after pulp exposure, three zones of proliferating cells in the rat molar pulp. Zones I and II were in the crown near the pulp. Zone III was near the apex revealing a recruitment of mitotic cells at distance from the lesion. To gain further insight into the spatio-temporal evolution of proliferating pulp cells of zone III, we performed a longitudinal study of PCNA staining in rat molar mesial root at 3, 8, and 15 d after pulp exposure associated to implantation of unloaded or amelogenin loaded agarose beads. At day 3 after implantation, PCNA-positive cells were located in the central part of the radicular pulp. At day 8, PCNA-labeled cells were aligned in the lateral part of the pulp beneath the odontoblast/sub-odontoblast layer. At day 15, PCNA labeling became undetectable in the root and was located in the coronal pulp. These results suggest that after pulp exposure, PCNA-positive cells may migrate from the central part of the radicular pulp to the sub-odontoblast cell layer and then from the apical root to the crown. Electron microscopy and immunostaining analysis showed that pulpal cells were linked by desmosome-like and gap-junctions. Extracellular matrix was composed of thin collagen fibrils associated with glycosaminoglycans favoring cell mobility. These data suggest that the syncytium-like structure formed by pulp radicular cells may be a pre-request for plithotaxis, a collective cell migration process. This emergent mechanism may govern pulp healing and regeneration after dental lesion.

Expression of insulin-like growth factor-1 and proliferating cell nuclear antigen in human pulp cells of teeth with complete and incomplete root development

AIM

To quantify the expression of insulin-like growth factor-1 (IGF-1) and proliferating cell nuclear antigen (PCNA) in human pulp cells of teeth with complete or incomplete root development, to support the specific role of IGF-1 in cell proliferation during tooth development and pulp reparative processes.

METHODOLOGY

Twenty six pulp samples were obtained from freshly extracted human third molars, equally divided in two groups according to root development stage (complete or incomplete root development). All samples were processed and immunostained to determine the expression of IGF-1 and PCNA in pulp cells. Sections were observed with a light microscope at 80x and morphometric analyses were performed to calculate the area of PCNA and IGF-1 immunostaining using digital image software. Mann-Whitney's test was used to determine statistically significant differences between groups (P < 0.05) for each peptide and the co-expression of both.

RESULTS

Expression of IGF-1 and PCNA was observed in all human pulp samples with a statistically significant higher expression in cells of pulps having complete root development (P = 0.0009).

CONCLUSION

Insulin-like growth factor-1 and PCNA are expressed in human pulp cells, with a significant greater expression in pulp cells of teeth having complete root development.

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.

PCNA-expression of cementoblasts and fibroblasts on the root surface after extraoral rinsing for decontamination

Periodontal cells capable of proliferation were studied immunohistochemically on extracted human teeth after 2-min irrigation with saline or ozonized water and marking of Proliferating Cell Nuclear Antigen (PCNA). All specimens expressed PCNA. The labelling index (LI), i.e. the number of positive cells compared to the total number of cells, was 6.6% after irrigation with saline and 7.8% after irrigation with ozone. There was no difference in number and distribution of PCNA-positive cells from the coronal to the apical thirds of the roots. Irrigation with ozonized water showed higher labelling indices in comparison with saline, but this could not be statistically substantiated (P = 0.24). Ozonized water, not being isotonic, had no negative effect on periodontal cells remaining on the tooth surface after irrigation for 2 min.

Histological investigation of physiologically resorbing primary teeth using Ag-NOR staining method

OBJECTIVE

The aim of this study was to investigate pulpal tissue of primary teeth in early and late stages of physiological resorption by means of silver-binding nucleolar organizer region (Ag-NOR) staining.

STUDY DESIGN

Ten primary teeth in early, ten in the late stage of resorption and five sound premolar teeth pulps as the control group were investigated by means of silver-binding nucleolar organizer region (Ag-NOR) staining.

RESULTS

The mean number of Ag-NOR's per nucleus increased with the continuing of the resorption process. The difference in the mean number of Ag-NORs was statistically significant both in the early and late stage of resorption compared with controls (P > 0.001). In the early stage of resorption calcific plates in the apical part of the pulps were observed. Odontoclasts, as well as inflammatory cells, were observed in the late stages of resorption.

CONCLUSIONS

The increase in the mean number of Ag-NORs per nucleus with the progression of the resorption process in primary teeth suggests that metabolic cell activity in the early stages of resorption is enhanced and increased with the continuing of the process, thus showing the importance of the pulp tissue in the resorption process.

bcl-2, p53, and MIB-1 in human adult dental pulp

Little is known about the renewal of some groups of cells in dental pulp, and the occurrence and significance of physiological cell death in dental pulp is not yet understood. The possibility of odontoblast disappearance by apoptosis has been proposed, and the presence of apoptotic cells in the rat and human odontoblastic and subodontoblastic layers has been recently described. bcl-2 and p53 are proteins involved in the apoptotic pathway, whereas MIB-1 is a proliferating cell marker. The aim of our study was an immunohistochemical evaluation of bcl-2, p53, and MIB-1 in healthy normal pulps of young human subjects. With bcl-2 immunostaining, some positive cells were found in the odontoblastic and subodontoblastic layers, whereas with MIB-1, only a few stromal cells were positive, and all odontoblasts were consistently negative. No cells were positive to p53. The bcl-2 immunoreactivity of the cells of the odontoblastic and subodontoblastic layers could help to explain the presence of apoptotic cells found in these regions.