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PubMed2002

Expression of amelin and trauma-induced dentin formation.

According to recent studies, amelin (ameloblastin, sheathlin) is expressed in young odontoblasts at the initiation of dentin formation during odontogenesis. The purpose of the present investigation was to study whether amelin is also expressed at the onset of trauma-induced reparative dentin formation. The mandibular developing first molars of 5-day-old rats were surgically taken out, and their pulp tissue briefly separated from the inner dentin surface and immediately repositioned. Then the teeth were re-implanted in their alveoli. At 0, 2, 4, 6, 8, 12 or 14 days after surgery, the animals were sacrificed and the experimental teeth evaluated by histology and immunohistochemistry for amelin. At 2, 4, 6 and 8 days after surgery, the detached and traumatized odontoblasts in the experimental teeth exhibited increasing signs of degeneration and loss of intracellular structures. At days 6 and 8 after surgery, immunohistochemistry revealed a strong staining for amelin in the traumatized odontoblastic layer. Twelve and 14 days after replantation, only necrotic cell remnants of the traumatized odontoblasts were discernible. At this stage, no amelin could be detected by immunostaining. A wide zone of an unorganized mineralized tissue surrounded the odontoblastic cell remnants. On the pulpal side of the unorganized tissue, a new, highly organized tubular reparative dentin layer was observed, bordered by columnar odontoblast-like cells abutting on newly formed predentin. The results indicate that the initiation of trauma-induced reparative dentin formation mimics that of primary dentin formation and that amelin seems to be involved in both processes, possibly as a signaling molecule.

Animals↗
PubMed1992

Short-term dentinogenic response of dog dental pulp tissue after its induction by demineralized or native dentine, or predentine.

The events initiating the expression of odontoblastic potential by pulpal ectomesenchymal cells were investigated by exposing the pulp to demineralized, native and unmineralized autogenous dentine. The pulp responses to implants were histologically evaluated 3, 7 and 10 days postoperatively, while the surface structure of the newly mineralized matrices was examined 12 and 28 days after implantation. Differentiation of odontoblast-like cells in close proximity to the implanted matrix was consistently demonstrated after exposure to predentine. Scattered columnal cells undergoing polarization, characterized ultrastructurally by the orientation of their rough endoplasmic reticulum, were also found in direct contact with the demineralized dentine. However, in response to demineralized implants, groups of differentiated odontoblast-like cells were clearly seen only in association with a zone of matrix secreted in a polar, predentine-like pattern, indicating an asynchronous inductive influence of this type of implant on pulp cells. Further, the response of pulp cells to native dentine was characterized by the elaboration of a two-layered matrix (a fibrous and a polarly deposited matrix) before initiation of secondary dentinogenesis. Scanning electron microscopy of the newly deposited matrices revealed differences between the indirect matrix synthesis, observed in short-term response to implants of demineralized or native dentine, and the specific, dentinogenic function of the odontoblast-like cells. These observations indicate that the dentine-induced dentinogenesis is initiated by two mechanisms--direct induction of odontoblast-like cells as well as indirect matrix synthesis, which further controls cell polarization. Immobilization of the cells on implanted matrix seems to be the critical requirement for direct expression of the odontoblastic phenotype.

Animals↗
PubMed1995

Spatial distribution of enamel proteins and fibronectin at early stages of rat incisor tooth formation.

Enamel proteins are secreted very early during amelogenesis, that is prior to mantle dentine formation, raising the possibility that they may participate in epithelial-mesenchymal interactions taking place during tooth development. These first enamel proteins associate with elements of the basement membrane interposed between the differentiating ameloblasts and odontoblasts. Fibronectin, a component of the basement membrane, is redistributed and accumulates along the apical portion of odontoblasts during their terminal differentiation. In order to determine whether any correlation exists between the redistribution of fibronectin and the secretion of the first enamel proteins, the spatial distribution of these two extracellular matrix proteins was examined during the presecretory stage of amelogenesis. Male Wistar rats were perfused with a formaldehyde-based fixative, and undemineralized and EDTA demineralized incisors were dehydrated in methanol and embedded in Lowicryl K4M resin. Ultrathin tissue sections were then processed for post-embedding, colloidal-gold immunocytochemistry with antibodies to enamel proteins, fibronectin or type III collagen. In the region of ameloblasts facing pulp, labelling for fibronectin was weak and mostly associated with the lamina fibroreticularis of the basement membrane separating differentiating ameloblasts and odontoblasts. As the mantle predentine formed the immunoreaction for fibronectin increased, particularly in the region of the basement membrane. Enamel proteins were also immunodetected in association with the lamina fibroreticularis and gradually accumulated as patches within mantle dentine and at its interface with ameloblasts. Von Korff collagen bundles, present between odontoblasts and in dentine, were immunolabelled for fibronectin and for type III collagen. Patches of granular material, immunoreactive for fibronectin and/or enamel proteins, were found along the odontoblastic processes and cell bodies. Although no evidence was obtained indicating a precise colocalization of fibronectin and enamel proteins, the results confirm that these two proteins can be found within similar extracellular compartments during mantle predentine-dentine formation. These data suggest that enamel proteins, by themselves or synergistically with other proteins, may play a part in the differentiation and/or formative events taking place at the ameloblast-odontoblast interface during the early stages of tooth development.

Ameloblasts↗
PubMed2004

Immunohistochemical evidence for proteolipid protein and nestin expression in the late bell stage of developing rodent teeth.

In this study, the expression of proteolipid protein (PLP) and nestin is studied in the late bell stage of developing rodent teeth in neonatal rats. By using immunohistochemistry, it was shown that odontoblasts, ameloblasts and the stratum intermedium are positive for PLP in regions of active matrix deposition. Reactivity for nestin could be detected in the odontoblasts, stratum intermedium and in some of the apical processes of the ameloblasts. The fact that mutations in the PLP gene can cause disturbances in tooth form, number and eruption taken together with the presence of PLP reactivity in odontoblasts and ameloblasts of healthy animals, suggests a crucial role for PLP in developing teeth because of its structural supportive characteristics. These results also imply the possible use of PLP antibody as a new marker for, respectively, dentin and enamel-secreting odontoblasts and ameloblasts. PLP and nestin expression could point to a possible similarity in function between the oligodendrocyte and the odontoblast, both derived from the neural crest. To compare with the situation in human tissue, PLP and nestin expression were preliminarily tested on human dental pulp. The odontoblasts were positive for both PLP and nestin.

Ameloblasts↗
PubMed2004

Bono1: a gene associated with regions of deposition of bone and dentine.

We have examined the mRNA expression pattern of the murine expressed sequence tag (EST) clone in embryonic and early postnatal mice. Expression was strongly and specifically localised to developing bones and odontoblasts in teeth, therefore we have named this gene Bono1 (Bone and odontoblasts). Bono1, which has human, rat and chicken orthologues designated as FKSG28 was expressed in most ossification regions of the head including calvarial bones, skull and jaws. Expression was localised to osteoblasts derived from both intramembraneous and endochondral ossification processes. Comparative analysis of the expression of Bono1 in the mandible with Bone sialoprotein (BSP), a marker of advanced osteoblastogenesis, revealed that Bono1 expression starts later in the osteoblast cell lineage than BSP. In the tooth, Bono1 was localised in secretory odontoblasts. This expression was complementary to BSP, which was only present in early pre-odontoblasts. In secretory odontoblasts, Bono1 was shown to be co-expressed with Dentin sialophosphoprotein (DSPP). In summary, Bono1 was expressed in functional osteoblasts and odontoblasts and was associated with regions of matrix mineralization.

Animals↗
PubMed2002

Analysis of incisor pulp cell populations in Wistar rats of different ages.

Pulp cell function and viability is important for maintaining tooth vitality throughout life. However, the effects of ageing on pulpal cell populations and pulp tissue remodelling are still unclear. The aim here was to quantify age-related cell-density changes in the pulp of rat incisor teeth, using histomorphometric analysis and ANOVA. Mandibular (n=35) and maxillary (n=34) incisors were carefully extracted from 20 Wistar rats aged between 1 and 18 months, fixed and processed for light microscopy. Cell counts were performed in mature and immature regions at both labial and lingual aspects of all teeth. Odontoblast and subodontoblast cell densities were reported per mm of pulp-dentine border and core fibroblast density per mm2 pulp tissue. Irrespective of age, odontoblast and subodontoblast densities were lower in the immature than the mature regions of both maxillary and mandibular incisors (P<0.001). However, in both regions odontoblast and subodontoblast densities decreased significantly with increasing age (P<0.0001). The age-related reduction in odontoblasts was significantly greater in mature than immature regions (P<0.02) but not influenced by other variables. In contrast, the age-related reduction in subodontoblasts was significantly different between mandibular and maxillary teeth (P=0.012) but not influenced by site. Unlike odontoblasts and subodontoblasts, core fibroblasts showed small but significant increases with increasing age (P<0.0001). These age-related reductions in the density of odontoblasts and subodontoblasts may partly explain the slower rate of secondary dentine secretion and decreased pulp repair activity associated with ageing.

Aging↗
PubMed2003

The influence of fluoride on the cellular morphology and synthetic activity of the rat dentine-pulp complex in vitro.

Exposure to high fluoride concentrations in the immediate environment of the tissue is recognized to result in the post-translational modification of non-collagenous dentine extracellular matrix (ECM) components, potentially altering dentine mineralization. However, less is known about the effects of fluoride exposure on the morphology or metabolism of the cells associated with the dentine-pulp complex. This study examined the effects of fluoride exposure at defined concentrations on the cellular morphology and ECM synthetic activities of odontoblasts and pulpal fibroblasts by the culture of tooth sections from male Wistar rat incisors in Trowel-type cultures for up to 14 days, in the presence and absence of 6mM sodium fluoride. Histomorphometric analysis of the dentine-pulp complex of sodium fluoride-exposed tooth sections demonstrated no obvious gross morphological differences with respect to the odontoblasts and pulpal fibroblasts throughout the 14-day culture period, in comparison with unexposed tooth sections. No significant differences in odontoblast and pulpal fibroblast cell numbers were determined in the absence and presence of fluoride. Image analysis examination of odontoblast cytoplasmic:nuclear (C/N) ratios also showed no significant differences in fluoride-exposed and unexposed tooth sections, although reductions in the C/N ratios of pulpal fibroblasts were evident in fluoride-exposed sections at days 10 and 14. No significant differences in predentine width were observed in fluoride-exposed and unexposed tooth sections over the 14-day culture period. Autoradiography following [3H]proline incorporation into the dentine-pulp complex demonstrated inhibition of collagen synthesis, particularly by the odontoblasts in tooth sections exposed to 6mM sodium fluoride. These findings, in association with those from previous studies, imply that dentine ECM alterations may contribute to the altered mineralization of dentine during fluorosis, rather than secretory-related changes in odontoblast morphology.

Animals↗
PubMed2002

Investigation of osteocalcin, osteonectin, and dentin sialophosphoprotein in developing human teeth.

Biochemical investigations in rodents have shown that numerous mineralized matrix proteins share expression in bone, dentin, and cementum. Little information is available regarding the expression pattern of these proteins in human tissues, particularly during tooth formation. The aim of this study was to identify the expression pattern of the two major noncollagenous proteins of bone and dentin, osteocalcin (OC) and osteonectin (ON), in comparison to the dentin-specific protein, dentin sialophosphoprotein (DSPP). Mandibles from fetuses (5-26 weeks), neonate autopsies, forming teeth from 10-12-year-old patients, third molars extracted for orthodontic reasons, and bone tumors were collected with approval from the National Ethics Committee. Human OC, ON, and DSPP mRNAs were detected by reverse transcription-polymerase chain reaction (RT-PCR) in fetal mandibles (5-11 weeks) and in primary cell cultures of dental pulp. In addition, OC, ON, and DSPP proteins were localized in forming human mineralized tissues using immunohistochemistry. In vivo, DSPP expression was associated with tooth terminal epithelial-mesenchymal interaction events, amelogenesis and dentinogenesis. Transient DSPP expression was seen in the presecretory ameloblasts with continuous expression in the odontoblasts. In contrast, both osteoblasts and odontoblasts showed a temporal gap between OC and ON expression in early development. ON was expressed in the initial stages of cytodifferentiation, whereas OC was expressed only during the later stages, especially in the teeth. At the maturation stage of enamel formation, both proteins were detected in odontoblasts and their processes within the extracellular matrix. In contrast to bone, OC was not localized extracellularly within the collagen-rich dentin matrix (predentin or intertubular dentin), but was found in the mature enamel. ON was present mostly in the nonmineralized predentin. These results demonstrate for the first time that both OC and ON are produced by human odontoblasts and determine the expression pattern of DSPP in human teeth, and suggest that OC and ON move inside the canalicule via odontoblast cell processes becoming localized to specific extracellular compartments during dentin and enamel formation. These distinct extracellular patterns may be related to the nature of DSPP, OC, and ON interactions with other matrix-specific macromolecules (i.e., amelogenin, dentin matrix protein-1) and/or to the polarized organization of odontoblast secretion as compared with osteoblasts.

Adult↗
PubMed1995

Characterization of cellular responses involved in reparative dentinogenesis in rat molars.

During primary dentin formation, differentiating primary odontoblasts secrete an organic matrix, consisting principally of type I collagen and non-collagenous proteins, that is capable of mineralizing at its distal front. In contrast to ameloblasts that form enamel and undergo programmed cell death, primary odontoblasts remain metabolically active in a functional tooth. When dentin is exposed to caries or by operative procedures, and when exposed dentinal tubules are treated with therapeutic dental materials, the original population of odontoblasts is often injured and destroyed. The characteristics of the replacement pool of cells that form reparative dentin and the biologic mechanisms that modulate the formation of this matrix are poorly understood. Based on the hypothesis that events governing primary dentinogenesis are reiterated during dentin repair, the present study was designed to test whether cells that form reparative dentin are odontoblast-like. Cervical cavities were prepared in rat first molars to generate reparative dentin, and animals were killed at various time intervals. In situ hybridization with gene-specific riboprobes for collagen types I and III was used to study de novo synthesis by cells at the injured dentin-pulp interface. Polyclonal antibodies raised against dentin sialoprotein (DSP), a dentin-specific protein that marks the odontoblast phenotype, were used in immunohistochemical experiments. Data from our temporal and spatial analyses indicated that cells forming reparative dentin synthesize type I but not type III collagen and are immunopositive for DSP. Our results suggest that cells that form reparative dentin are odontoblast-like.

Animals↗
PubMed1996

Immunolocalization of fibronectin during reparative dentinogenesis in human teeth after pulp capping with calcium hydroxide.

Exposed dental pulp is known to possess the ability to form a hard-tissue barrier (dentin bridge). The exact mechanisms by which pulp cells differentiate into odontoblasts in this process are unknown. Fibronectin has been demonstrated to play a crucial role in odontoblast differentiation during tooth development. This study tested the hypothesis that fibronectin is involved in the initial stages of replacement odontoblast differentiation and reparative dentin formation. We observed its immunohistochemical localization during dentin bridge formation in human teeth, after pulp was capped with calcium hydroxide [Ca(OH)2]. One day after the capping, precipitation of crystalline structures was observed at the TEM level in association with cell debris at the interface between the superficial necrotic zone and underlying pulp tissue. This layer of dystrophic calcification showed positive reaction for fibronectin, and pulp cells appeared to be closely associated with this layer, seven to ten days post-operatively. At 14 days, an alignment of cells, some of which were elongated and odontoblast-like, was observed adjacent to the fibronectin-positive irregular matrix. Between the cells, corkscrew fiber-like fluorescence was visible. At 28 days, the irregular fibrous matrix was followed by the formation of tubular dentin-like matrix lined with odontoblast-like cells. Therefore, it would seem that fibronectin associated with the initially formed calcified layer might play a mediating role in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis, after pulp was capped with Ca(OH)2.

Adult↗
PubMed2001

Expression of TGF-beta receptors I and II in the human dental pulp by in situ hybridization.

Members of the TGF-beta family of growth factors are important in modulation of odontoblast secretory activity during dental tissue repair. Odontoblast expression of TGF-beta isoforms during development leads to their sequestration within the dentin matrix, from where they may be released during carious injury and participate in reparative processes. Two receptors, implicated in TGF-beta-mediated cell signaling, have been identified immunohistochemically in both odontoblasts and pulpal cells of healthy and carious human molar teeth. This study aimed to characterize the expression of the TGF-beta receptors I and II in sound and carious teeth by means of in situ hybridization, to help our understanding of the response of these cells to TGF-beta stimulation. Sound and carious human third molar teeth were routinely processed immediately following extraction, and 10-microns paraffin-embedded sections prepared. These sections were hybridized with 32P-labeled probes to TGF-beta receptors I and II, and the subsequent signal was detected by autoradiography. mRNA for both receptors I and II was mainly detected within the odontoblasts and nerve-associated cells of healthy tissues, with expression at lower levels seen within the subodontoblast and pulp core cells. The expression in odontoblasts was higher for TGF-beta receptor I than for receptor II. Expression of both receptors was more homogenous in all pulp cells within carious teeth, because of an increase of signal within the underlying pulp cell population, including blood-vessel-associated cells. We conclude that the TGF-beta receptors I and II were expressed in odontoblasts and pulp cells, and that subtle variations in the levels of their expression could be involved in the tissue response to injury.

Activin Receptors, Type I↗
PubMed2001

Alteration in the expression of heat shock protein (Hsp) 25-immunoreactivity in the dental pulp of rat molars following tooth replantation.

The regeneration process of dental pulp following tooth replantation in rat molars was investigated by immunocytochemistry for heat shock protein (Hsp) 25 and protein gene product 9.5 (PGP 9.5). In control teeth at postnatal 4 weeks, the odontoblasts showed intense Hsp 25-immunoreactivity in the coronal dental pulp, but little or no immunoreactivity in the root and floor pulp. In contrast, the Hsp 25-negative odontoblasts in the latter areas displayed immunoreactivity for PGP 9.5. Tooth replantation caused loss of Hsp 25- and PGP 9.5-immunoreactions in the dental pulp during postoperative days 1-3. At postoperative day 5, plump cells with clear nucleoli and several fine processes--presumably newly differentiated odontoblasts--at the pulp-dentin border became immunopositive for Hsp 25. These data suggest that the expression of Hsp 25- and PGP 9.5-immunoreactivity reflects the status of differentiation of the odontoblasts. Furthermore, some pulpal nerve fibers as well as the Schwann cells in the dental pulp, ordinarily negative in Hsp 25-immunoreaction, acquired their immunoreactivity by postoperative day 5, but lost it thereafter, suggesting the involvement of Hsp 25 in the regeneration of pulpal nerve fibers. In the case of bone-like tissue formation in the pulp space, on the other hand, no Hsp 25-immunoreactive odontoblasts were recognized in the pulp-dentin border. Thus, the alignment of Hsp 25-immunopositive odontoblasts along the pulp-dentin border indicates a decisive factor for inducing the reparative dentin formation after tooth replantation.

Animals↗
PubMed1991

The cellular and extracellular distribution of osteocalcin and dentin phosphoprotein in teeth of vitamin D-deficient rats.

Experimental and clinical data indicate that dentin mineralization is vitamin D-dependent. This calcium-regulating steroid controls protein synthesis, for instance that of osteocalcin in osteoblasts. This protein also elaborated by odontoblasts was used as a molecular marker for vitamin D action on odontoblasts. Since the most characteristic protein synthesized by odontoblasts is the dentin phosphoprotein which is thought to regulate hydroxyapatite growth, its cellular and extracellular distribution was also studied. Tooth formation in the molars and incisors of successive generations of vitamin D-deficient animals (-D) and in controls (+D) was compared by microadiography, toluidine blue histochemistry, and immunocytochemistry. In -D samples, the presence of dentin phosphoprotein in odontoblasts indicated that their differentiation occurred despite major morphological disturbances at the cusp tips. In contralateral teeth, osteocalcin was depleted in odontoblasts and dentin, suggesting an inhibition of protein synthesis induced by vitamin D-deficiency. In the extracellular matrix of +D animals, phosphoprotein distribution was associated with dentin, especially within actively forming calcospherites at the mineralization front. In contrast, in -D dentin, the mineralization defects corresponded to irregular absence of histochemically detectable phosphoprotein. This protein indeed appeared either absent or uniformly sparse in -D dentin by immunocytochemistry. These data suggest that vitamin D acts directly on odontogenic cells at various synthetic (osteocalcin) or secretory (phosphoprotein) levels indicating that odontoblasts are target-cells for vitamin D. Therefore, this hormone could contribute to the regulation of extracellular mineralization during dentinogenesis, via different mechanisms in the processing of matrix protein.

Animals↗
PubMed1989

The fine structure of initial mineralisation during tooth development in the gummy shark, Mustelus manazo, Elasmobranchia.

In the enameloid matrix a large number of tubular vesicles appeared around the odontoblast processes at the stage of enameloid matrix formation. The tubular vesicles were limited by unit membrane and the membrane often seemed to connect with that of the odontoblast processes. The tubular vesicles probably originated from the odontoblasts. Electron-dense granules were observed in the tubular vesicles before the appearance of crystals and then, in the stage of mineralisation, initial enameloid crystals appeared in each tubular vesicle. Parts of the odontoblast process surrounded small aggregations of tubular vesicles in the unmineralised dentine matrix. There were many multivesicular bodies and lysosomes in the odontoblasts forming the dentine. The odontoblasts probably absorb and break down the tubular vesicles after the beginning of dentinogenesis. Only in the predentine, during the enameloid maturation stage, did a few matrix vesicles appear, but no crystals were found in them. Hence, the initial mineralisation in tooth germs of the shark can be said to be different from that in teleosts.

Amelogenesis↗
PubMed1979

Inhibition of tooth germ differentiation in vitro by diazo-oxo-norleucine (DON).

Molar tooth germs from mouse embryos were studied in a Trowell-type organ culture. After 5 days of culture the odontoblasts had secreted predentine and the ameloblasts had differentiated. When cultured in the presence of 10-50 micro M diazo-oxo-norleucine (DON), which is a glutamine analogue, the differentiation of odontoblasts was inhibited, but the teeth looked otherwise healthy. When DON was added after 2 days of culture in control medium (at this time the odontoblasts in the cuspal area were already differentiated), it did not inhibit predentine secretion, ameloblast differentiation, nor enamel secretion. However, this was seen only in the cuspal area and the boundary to the undifferentiated, more cervical cells was distinct. The results support the concept that the mechanism of the differentiation of odontoblasts is different from that of the ameloblasts. We have shown earlier that a close association between the basement membrane and the mesenchymal cells is required for odontoblast differentiation. Because DON interferes with glycosaminoglycan and glycoprotein synthesis we suggest that DON inhibits odontoblast differentiation by affecting the mesenchymal cell surface and/or the basement membrane.

Ameloblasts↗
PubMed1997

Detection of sugar residues in rabbit embryo teeth with lectin-horseradish peroxidase conjugate: II. A light microscopal study.

The cellular distribution and changes of sugar residues during tooth development in embryos of the rabbit Oryctolagus cuniculus were investigated by using horseradish peroxidase-conjugated lectins (lectin-HRP). The lectins SBA, ECA, and LTA show no binding to any region of the dental cap and bell stages, whereas BS-1 and UEA-1 bind to dental cells at both stages. Appropriate control studies confirmed the specificity of the binding of the lectins. At cap stage, the lectins BS-1 and UEA-1 show moderate binding to the (pre)-ameloblast and (pre)-odontoblast cells. These results suggest that the acetylgalactosamine and alpha-L-fucose residues present in (pre)-ameloblasts and (pre)-odontoblasts, respectively, are common to determined but relatively undifferentiated cells capable of forming matrices of hard tissues. Since the odontoblast and ameloblast express dentin and enamel, respectively, it can be speculated that the abundance of these residues in these cells might be associated with the maintenance of the capacity of the cells to produce such matrices. At the bell stage, the odontoblasts display considerable amounts of alpha-L-fucose, whereas alpha-L-fucose is poorly localized in ameloblasts. However, ameloblasts contain significant quantities of N-acetylgalactosamine, whereas only a diffuse positivity for this carbohydrate is apparent in odontoblasts. The marked changes of the glycosylation pattern of these glycoconjugates might indicate that they play a role during the cell-to-cell interaction and might also be involved in the odontoblastic and ameloblastic functional activity. Such a possibility is entirely speculative until specific in vitro experiments are conducted.

Animals↗
PubMed1983

Autoradiographic location of sensory nerve endings in dentin of monkey teeth.

We have used the autoradiographic method to locate trigeminal nerve endings in monkey teeth. The nerve endings were labeled in two adult female Macaca fascicularis by 20 hours of axonal transport of radioactive protein (3H-L-proline). We found a few labeled axons in contralateral mandibular central incisors and one mandibular canine. In ipsilateral teeth, numerous myelinated and unmyelinated axons were labeled; they formed a few terminal branches in the roots but primarily branched in the crown to form the peripheral plexus of Raschkow and to terminate as free endings in the odontoblast layer, predentin, and as far as 120 micrometers into dentinal tubules. Electron microscopic autoradiography showed that the radioactive axonally transported protein was confined to sensory axons and endings; odontoblasts and dentin matrix were not significantly labeled. Labeled free nerve endings were closely apposed to odontoblasts in dentin but did not form distinctive junctions with them. Nerve endings were most numerous in the regular tubular dentin of the crown adjacent to the tip of the pulp horn, occurring in at least half of the dentinal tubules there. Reparative dentin was poorly innervated, even near the tip of the crown, and it had a different tubular structure and adjacent pulpal structure from the innervated dentin. Radicular dentin was not innervated in most areas but did contain a few labeled axons where the predentin was wide and the odontoblasts were columnar, as at the buccal and lingual poles of some roots. Our results show tha dentinal sensory nerve endings in primate teeth can be profuse, sparse, or absent depending on the location and structure of dentin and its adjacent pulp. When dentin was innervated, the tubules were straight and contained odontoblast processes, the predentin was wide, the odontoblast cell bodies were relatively columnar, and there was an adjacent cell-free zone and pulpal nerve plexus.

Animals↗
PubMed1991

Immunohistochemical demonstration of amelogenin penetration toward the dental pulp in the early stages of ameloblast development in rat molar tooth germs.

In order to examine the synthesis and secretion of enamel protein by ameloblasts in their early stages of development, immunohistochemical localization was carried out at light and electron microscopic levels using a monoclonal antibody produced in a preliminary experiment. Materials used were tooth germs of mandibular first molars of rats at 0-5 days after birth. Immunoblot analysis after two-dimensional electrophoresis revealed that antigen molecules recognized by the monoclonal antibody were amelogenins of 26-28 kDa (pI, 6.6-7.0). An immunohistochemical examination using this monoclonal antibody demonstrated that the presecretory ameloblasts in their early stages of differentiation both synthesized amelogenin and secreted through a classical merocrine secretory pathway. In some presecretory ameloblasts as well as ameloblasts we observed the distended cisternae of rough endoplasmic reticulum (rER) which demonstrated heterogenous immunolabelling. The immunolabellings were also detected in the predentin as well as the intercellular spaces of odontoblasts and dental pulp cells which indicated penetration of amelogenin from the presecretory ameloblast layer to the dental pulp. The presence of coated pits at the plasma membrane of odontoblasts in close proximity to enamel protein along with the immunolabelling of lysosomes of the odontoblasts suggests the phagocytosis of the enamel protein into the odontoblasts. These observations suggest the possibility that the penetration of enamel protein toward the dental pulp and odontoblasts plays a role in the interaction between ameloblasts and odontoblasts.

Ameloblasts↗