New immunological approaches to studying the odontoblast

Morphological Study and Analysis of Microhardness and Permeability of the Furcation of Maxillary Premolars

The morphology, microhardness and dentin permeability of the furcation region of maxillary premolars were evaluated. Ten premolars were cut lengthwise and the furcation region was delimited. In one group (n=10) microhardness was measured in the buccal, central and palatal regions, in the outer middle and inner layers of the furcation, and in the buccal and palatal regions adjacent to the furcation. Knoop hardness was tested with 10 g load for 15 s. Data were analyzed statistically by ANOVA and Tukey-Kramer test (a=0.05). In the other group (n=10) confocal microscopy was used to study dentin morphology. Other 10 specimens were instrumented with ProTaper and immersed in 10% copper sulfate for analysis of permeability under light microscopy. About microhardness, there was no significant difference (p>0.05) among the buccal (39.9±3.1), central (39.5±4.4) and palatal (39.7±5.0) regions of the furcation, or between these regions and the adjacent buccal (39.1±5.8) and palatal (39.7±5.8) regions (p>0.05). The inner layer (42.3±3.7) had significantly higher microhardness (p<0.05) than the outer layer (37.1±3.9). There was a tendency of calcification of the dentinal tubules from the outer towards the inner layer. The percentage of stained area was 12.45±2.0%, restricted to the outer layer. The buccal, central and palatal regions of the furcation as well as the buccal and palatal adjacent regions had similar microhardness values. In conclusion, the inner dentin layer is harder than the outer dentin layer. The dentinal tubules are sinuous and intertwine towards the middle layer. Dye penetration is restricted to the outer layer.

The extent of odontoblast processes in the dentin is distinct between cusp and cervical regions during development and aging

The question of whether odontoblast processes extend to the dentinal surface has been widely debated in previous studies. In this study odontoblast processes were investigated in the developing and aging dentin of rats and monkeys (Japanese macaques). For this purpose, F-actin of microfilaments and cellular membranes were stained with phalloidin and DiI, respectively. This dual staining demonstrated that positive signals for odontoblast processes were present in the dentinal surface in both the cusp and cervical regions of the dentin at 2 weeks of age. The tips of doubly positive processes were detectable in the dentinal surface in the cusp region even at 100 weeks of age, whereas in the cervical region they were retracted from the dentinal surface towards the pulp during the period of 3-6 weeks of age. During these stages, phalloidin-positive signals showing retracted odontoblast processes in the cervical region were closely associated with the interglobular dentin that was stained with sWGA-lectin. After 6 weeks of age, no association was observed between the processes and the interglobular dentin, since they were retracted approximately to the inner third portion of the dentinal tubules. This staining pattern can be detected until 100 weeks of age. Moreover, different distribution patterns of odontoblast processes between the two dentinal regions were also confirmed in dentin of monkey teeth. These results suggest that the existence of the regional differences in the extent of the odontoblast processes in the dentin, i.e., the persistence of the processes in the dentinal surface in the cusp region and their retraction from the dentinal surface in the cervical region.

Ultrastructure of human dentine 40 years ago--progress and perspectives

In the 1959 premier issue of the Archives of Oral Biology, the first TEM observations were presented of sections of undecalcified human mature dentine produced with diamond knives. The odontoblast process was clearly shown to be a cytoplasmic extension of the odontoblast. The peritubular dentine appeared to be more calcified than the intertubular dentine and contained hydroxyapatite as demonstrated by selective area electron diffraction. In the 40 years which followed, significant progress was made in TEM methodology, including improvements in fixation and embedding, development of ultrastructural cytochemistry and immunocytochemistry, and the use of electron microscope autoradiography. Additionally, we saw the advent of SEM and HRTEM. Thus, better knowledge was gained of (1) the odontoblast and its process and the lamina limitans, (2) the dentinal nerve fibrils and (3) the HRTEM aspects of dentine. Interestingly, to the present day, diamond knives have continued to serve as the best tool for preparing thin sections of non-decalcified mature hard tissue for TEM and HRTEM, not only for dentine but also for bone, enamel and cementum.

Cytoskeleton of the mesenchymal cells of the rat dental papilla and dental pulp

This study describes the immunolocalization of actin, cytokeratins and vimentin during differentiation of the dental papilla in the rat. Incisors and first molars were sectioned from mandibles of Wistar rats from embryonic day (E)-14 to (E)-21 and weeks 1, 2, 3, 12 and 104 after birth, fixed in 90% alcohol, decalcified in EDTA, infiltrated with 5% sucrose, frozen in dry ice, and cryosectioned at 10 microns. The sections were immunolabelled using indirect immunofluorescence with a panel of monoclonal antibodies and FITC-phalloidin for F-actin localization. F-actin was present in follicular mesenchyme and odontoblast processes. Vimentin labelled dental papilla fibroblasts, differentiating, functional (secretory) and aged odontoblasts. Vimentin was uniformly localized in the cytoplasm of pre-odontoblasts but was redistributed to the apical pole of these cells during polarization. Of the cytokeratins, only cytokeratin 19 was found in differentiating odontoblasts. It was not present in dental papilla fibroblasts, functional or aged odontoblasts. These results suggest that actin and the redistribution of vimentin may be involved in odontoblast differentiation and odontoblast process formation/support and that these events may be preceded by the expression of cytokeratin 19.

High resolution scanning electron microscopy of the subplasmalemmal cytoskeleton in human odontoblasts

The subplasmalemmal cytoskeleton in human odontoblasts was studied by high resolution scanning electron microscopy. The odontoblast layer was isolated and exposed to formaldehyde, glutaraldehyde, and OsO4 for some specimens, while the membraneous structures and soluble proteins in the dental tissue were removed by Zenker's solution and 1% OsO4 for other specimens, without further fixation of the remaining components. The cytoskeletal elements comprised a dense network of interlacing filaments of different diameters in the cell body. Most cytoskeletal elements were parallel to the axis of the cell processes situated inside the dentinal tubules. The appearance and orientation of the investigated subplasmalemmal cytoskeletal elements was unaffected by the choice of method. Both methods confirm the presence of a subplasmalemmal cytoskeleton in human odontoblasts.

Dentin formation in so-called "fibro-osteo-cemental" lesions of the jaw: histologic, electron microscopic, and immunohistochemical investigations

Two cases of the so-called fibro-osteo-cemental lesions of the jaws, containing unusual deposits of hard tissue, are described. There were peculiar spheroid calcifications or larger masses forming small cavities with a radial arrangement and discontinuous blasts extending with axonlike cell processes toward an acellular core. For further definition, electron microscopic and immunohistologic studies were done. The most conspicuous features were abundant intracytoplasmic vimentin filaments in the blasts, tight junctions, matrix vesicle formation, a globular accretion pattern, and so-called matrix maturation. These findings militate against an osseous or cementous nature of this hard tissue. Rather, both the light and electron microscopic findings are highly compatible with the assumption that the blasts are odontoblasts and that an immature type of dentin is formed. In addition to fibroblasts, osteoblasts, and cementoblasts, apparently also a further descendant of the ectomesenchyme--the odontoblasts with dentin formation--may participate in the so-called fibro-osteo-cemental lesions.

Gap junctions between odontoblasts revealed by transjunctional flux of fluorescent tracers

Cell communication between odontoblasts was investigated with the use of fluorescent-dye tracers; Lucifer Yellow CH (molecular weight = 457.3), and dextran-Lucifer Yellow CH (average molecular weight = 10,000). Dyes were injected into cell bodies of individual odontoblasts via an intracellular microelectrode or into a group of cells through their processes, and passage to adjacent cells was examined with a fluorescence microscope. Lucifer Yellow CH appeared to diffuse very easily among odontoblasts, while dextran-Lucifer Yellow remained within the injected cell or cells. This efficient migration of Lucifer Yellow CH can be considered a functional manifestation of gap junctions between odontoblasts.

Localization of actin during differentiation of the ameloblast, its related epithelial cells and odontoblasts in the rat incisor using NBD-phallacidin

Using NBD-phallacidin, which specifically binds to F-actin, we investigated changes in the localization of actin during the differentiation of ameloblasts, related epithelial cells and odontoblasts in rat incisors. In cryosections treated with NBD-phallacidin, intense fluorescence was observed in undifferentiated epithelial cells in the apical loop and at the proximal extremity of undifferentiated inner enamel epithelial cells. During differentiation, the distal extremity began to exhibit strong fluorescence. In cross-sections of secretory ameloblasts, the fluorescence took the form of polygons of uniform intensity at the proximal end, and of rectangles of non-uniform intensity at the distal end. At the distal end, the fluorescence was more intense at right angles to the long axis of the incisor. At the distal end, this pattern was established just before the appearance of the enamel layer. These patterns were maintained during the secretory stage of ameloblasts. The location, pattern and time of appearance of these sites were identical to those of the terminal webs in ameloblasts. NBD-phallacidin weakly labelled the peripheral cytoplasm of the cell body of ameloblasts, and also labelled Tomes' process. The cells forming the stratum intermedium were mainly labelled at their periphery (i.e. forming larger polygons), while the overlying epithelial cells exhibited labelling throughout their cytoplasm. Except for the terminal webs, the cell bodies of odontoblasts were weakly labelled throughout the period of differentiation. Young odontoblasts secreting predentin were first labelled on the terminal web, with the fluorescence becoming gradually more intense as the thickness of the dentin increased.(ABSTRACT TRUNCATED AT 250 WORDS)

An immunocytochemical study of the human odontoblast process using antibodies against tubulin, actin, and vimentin

An immunofluorescence technique was applied at the light microscope level to human third molar coronal dentin in order to localize the intracellular components tubulin, vimentin, and actin. Third molars were split immediately upon extraction, and immersed in periodate-lysine-paraformaldehyde fixative. The crowns were demineralized, dehydrated, and wax-embedded, and 6-micron sections were prepared. The sections were post-fixed in -20 degrees C acetone, and then incubated with monoclonal mouse anti-tubulin, anti-vimentin, or anti-actin antibodies, followed by fluorescein-conjugated sheep anti-mouse immunoglobulins. Intratubular immunofluorescence labeling for tubulin and vimentin was very similar in pattern and intensity and extended to the dentino-enamel junction. In contrast, the actin labeling appeared less intense and more punctate, and was located primarily in the pulpal half of the crown, although some labeling was detectable up to the dentino-enamel junction. The presence of tubulin-, vimentin-, and actin-containing structures extending to the dentino-enamel junction supports the hypothesis that the odontoblast process does extend to the dentino-enamel junction in the human, and is in agreement with earlier studies of rat molars.