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PubMed2003

Pulp biology: progress during the past 25 years.

During the past 25 years there has been a rapid expansion in our knowledge of the dentine and pulp complex. This paper provides representative examples of important advances that researchers have made in this field. Topics to be considered include: differentiation of odontoblasts, dentine matrix proteins, extent of odontoblast processes, pulpal stem cells, apoptosis, interstitial fluid pressure in normal and inflamed pulps, class II antigen-presenting cells of the pulp, cytokines, antibodies, pulpal calcifications, tertiary dentine and pulpal inflammation associated with bacterial contamination of exposed dentine beneath restorations.

Antigen-Presenting Cells↗
PubMed2004

Immunolocalization of Alk8 during replacement tooth development in zebrafish.

The novel type I transforming growth factor-beta (TGF-beta) family member receptor Alk8 was previously identified in a degenerate RT-PCR screen for zebrafish type I and II TGF-beta family member receptors. Functional analyses revealed that Alk8 acts through Bmp signaling pathways in early embryonic dorsoventral patterning, in neural crest cell specification, and in patterning and differentiation of neural crest cell-derived pharyngeal arch cartilages. In addition, Alk8 forms active signaling complexes with TGF-beta1 and the TGF-beta RII receptor, suggesting that Alk8 mediates cross talk between Bmp and TGF-beta subfamily members. In this study, immunohistochemical analysis was performed on zebrafish aged 2 days postfertilization to 1 year, revealing immunolocalization of Alk8 to tissues of the tooth-bearing ceratobranchial 5 (cb5) arch including dental epithelial and mesenchymal tooth tissues of developing primary and replacement teeth, mucous-producing crypt epithelium, keratinized bite plate, and developing taste buds. These results suggest roles for Alk8 in patterning tooth-bearing pharyngeal epithelium, in the initiation of tooth development, in odontoblast and ameloblast differentiation, and in osteoblast maturation. The ability for zebrafish to continuously form teeth throughout their lives allows for the comparison of Alk8 expression in both primary and replacement tooth development, revealing identical Alk8 expression profiles. This study advances our current understanding of the functions of Alk8, particularly with respect to primary and replacement tooth formation, reveals additional roles for Alk8 in dental epithelial patterning and in odontoblast, ameloblast and osteoblast differentiation, and demonstrates the utility of the zebrafish as a model for primary and replacement tooth development.

Activin Receptors, Type I↗
PubMed2005

Differential regulation of dentin matrix protein 1 expression during odontogenesis.

Dentin matrix protein 1 (DMP1) is highly expressed in mineralized tooth and bone. Both in vitro and in vivo data show that DMP1 is critical for mineralization and tooth morphogenesis (growth and development). In this study, we studied Dmp1 gene regulation. The in vitro transient transfection assay identified two important DNA fragments, the 2.4- and 9.6-kb promoter regions. We next generated and analyzed transgenic mice bearing the beta-galactosidase (lacZ) reporter gene driven by the 2.4- or 9.6-kb promoter with the complete 4-kb intron 1. The 9.6-kb Dmp1-lacZ mice conferred a DMP1 expression pattern in odontoblasts identical to that in the endogenous Dmp1 gene. This is reflected by lacZ expression in Dmp1-lacZ knock-in mice during all stages of odontogenesis. In contrast, the 2.4-kb Dmp1-lacZ mice display activity in odontoblast cells only at the early stage of odontogenesis. Thus, we propose that different transcription factors regulate early or later cis-regulatory domains of the Dmp1 promoter, which gives rise to the unique spatial and temporal expression pattern of Dmp1 gene at different stages of tooth development.

Animals↗
PubMed2001

Immunohistochemical evidence for ATP receptors in human dental pulp.

Evidence is accumulating which supports a role for ATP in the initiation of pain by acting on P2X receptors, in particular P2X3, expressed on nociceptive afferent nerve terminals. To investigate whether this receptor plays a role in dental pain, we studied the presence and distribution of P2X3 receptors in human dental pulp, and their co-localization with other neural markers. Pulps were removed from extracted third molars and immunohistochemically stained with an antibody against P2X3 receptors. P2X3 immunoreactive (-ir) nerve fibers were detected in the main body of the pulp, in the sub-odontoblastic plexus of Raschkow, and within the odontoblastic area. Co-localization of the P2X3-ir neurons with neurofilament protein (NF) showed that the majority of the fibers were positive for both NF and P2X3. Double labeling with isolectin B4 (IB4) showed that all P2X3-ir neurons also bind IB4. We conclude that P2X3 receptors are present on both myelinated and unmyelinated nerve fibers in human dental pulp and may play a role in dental pain mechanisms.

Adenosine Triphosphate↗
PubMed2001

Growth-hormone-stimulated dentinogenesis in Lewis dwarf rat molars.

In dentinogenesis, certain growth factors, matrix proteoglycans, and proteins are directly or indirectly dependent on growth hormone. The hypothesis that growth hormone up-regulates the expression of enzymes, sialoproteins, and other extracellular matrix proteins implicated in the formation and mineralization of tooth and bone matrices was tested by the treatment of Lewis dwarf rats with growth hormone over 5 days. The molar teeth were processed for immunohistochemical demonstration of bone-alkaline phosphatase, bone morphogenetic proteins-2 and -4, osteocalcin, osteopontin, bone sialoprotein, and E11 protein. Odontoblasts responded to growth hormone by more cells expressing bone morphogenetic protein, alkaline phosphatase, osteocalcin, and osteopontin. No changes were found in bone sialoprotein or E11 protein expression. Thus, growth hormone may stimulate odontoblasts to express several growth factors and matrix proteins associated with dentin matrix biosynthesis in mature rat molars.

Alkaline Phosphatase↗
PubMed1979

Cellular mechanics of dentinal bridge repair using 3H-thymidine.

Cellular reorganization in the pulp following mechanical pulp exposure involves three steps: First, lysis and macrophage resolution of the clot form; second, there is an invasion of the clot area by fibroblasts and endothelial cells, i.e., formation of granulation tissue; third, an organization and differentiation of these cells into functional odontoblasts occurs as early as 9 days after exposure. Autoradiographic results showed an increased DNA synthesis in the fibroblast and endothelial cell populations which coincided with a histologically-observed increase in those populations. A relative increase in fibroblastic activity, as compared to endothelial cell activity, suggested that fibroblasts may be the cells that replace odontoblasts.

Animals↗
PubMed1985

The dentin-predentin complex and its permeability: anatomical overview.

This paper provides an anatomical overview of the dentin-predentin complex and its permeability. An unique anatomical feature of this complex is the presence of dentinal tubules which extend peripherally from the odontoblast-predentin junction throughout the thickness of the tissue. The permeability of dentin is a consequence of the presence of these tubules. Thus, this review concentrates on the anatomy of dentinal tubules and, in particular, on those studies which in the last decade have increased our knowledge of this anatomy. The structure, size, and number of dentinal tubules and the relationship of these features to the permeability of the tissue are discussed. This is followed by a description of the contents of dentinal tubules, with particular emphasis being paid to the literature concerning the extent of the odontoblast process.

Animals↗
PubMed1985

Dentin-predentin complex and its permeability: pathology and treatment overview.

This review paper focuses attention on tissue changes which may take place in dentin and on localized alterations in tissue formation in the predentin area. A number of reaction patterns has been described in dentin affecting both the inorganic and organic components. Dentinal tubules may become partly or completely obturated by growth of the peritubular dentin. Precipitation of mineral salts within the tubules, which may be a reprecipitation of minerals from adjacent demineralized dentin, represents a fundamentally different mode of obturation of dentinal tubules. Initially, demineralization selectively affects the peritubular dentin. If dentin is exposed to the oral environment, the surface layer may become hypermineralized. The surface layer of dentin, exposed by grinding, becomes covered by a smear layer. Displacement of the contents of the tubules or of the odontoblasts is a characteristic change in the organic components. Odontoblast destruction or degeneration will lead to a lack of, or reduced, predentin formation. Changes in the protein components which lead to alterations in dentin permeability have also been reported. The structure of the interface between dentin and localized formations of irregular secondary dentin varies considerably. If there is no tubular communication between primary and secondary dentin, the interface will act as an impermeable barrier. Changes in dentin, including irregular secondary dentin formation, affect the permeability of the tissue. Such changes are clinically important for the outcome of all types of restorative work performed on vital teeth.

Adult↗
PubMed1985

Appearance of dentin gamma-carboxyglutamic acid-containing proteins in developing rat molars in vitro.

An in vitro model of mineralization was devised in order to study the developmental appearance of dentin gamma-carboxyglutamic acid-containing proteins (DGPs) in relation to the onset of mineralization. Maxillary third molars from 11-day-old rats were cultured with or without fetal calf serum (FCS) as modified from Navia et al. (1984). Molars were incubated without radiolabel, or with either 45CaCl2 (5 microCi/ml) for 24 hr at various stages of a ten-day culture period or [3H]-leucine (10 microCi/ml) for 24 hr at the eighth day of culture. Molars were lyophilized and extracted with 10% formic acid overnight at 4 degrees C. DGPs in extracts were detected by immunologic and chromatographic techniques; DGPs in molar sections were detected by immunolocalization using indirect immunofluorescence. Molar development was evaluated histologically using the Von Kossa staining technique. Molars cultured with FCS showed histologic evidence for mineralized dentin and enamel and a significant increase in 45Ca uptake after the sixth day in vitro. Eleven-day-old molars in vivo and molars cultured without FCS showed no evidence of the presence of mineralized tissues. [3H]-Leucine-labeled DGPs were isolated and identified by affinity and reversed-phase high-performance liquid chromatography and by gel electrophoresis from both mineralized and unmineralized molars. DGP antigens were localized immunohistochemically using rabbit anti-rat antibodies raised against a highly purified DGP preparation. In the unmineralized molar, antigenicity was seen in odontoblasts but not in predentin matrix, preodontoblasts, or in any other cell type. Antigens in the mineralized molar were localized to odontoblasts and dentin.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Carboxyglutamic Acid↗
PubMed1986

The effect of dentinal stimulation on pulp nerve function and pulp morphology in the dog.

The effect of dentinal stimulation on pulpal nerve responses and pulp morphology has been studied in the dog. Canine tooth (n = 25) dentin was stimulated by drilling, probing, and air-blasting for from two to five hours. Acid-etching was used to open dentinal tubules. All test teeth showed disruption of the odontoblast layer and its separation from the predentin; also, dislocation of odontoblast nuclei into dentinal tubules was found in most cases. Single-fiber (n = 14, conduction velocity = 24.3 +/- 7.4 (SD) m/s) recordings of the responses of canine tooth pulpal nerves to dentinal stimulation were made in ten of the stimulated teeth. No changes in the sensitivity of the nerves to dentinal stimulation could be detected. It is concluded that pulpal nerve function and morphological changes of the pulp are not clearly correlated. The condition of the dentin surface seems to be the important factor.

Acid Etching, Dental↗
PubMed1988

Histochemical demonstration of carbonic anhydrase activity in the odontogenic cells of the rat incisor.

Aldehyde-fixed, EDTA-demineralized frozen sections of the rat maxillary incisor were histochemically stained for carbonic anhydrase activity, by use of Hansson's method. Intense staining was observed in the odontoblasts, all types of epithelial cells of enamel organ in the maturation zone, cementoblasts, and the cells of the lingual dental sac. Less intense but consistent staining was observed in all types of epithelial cells of odontogenic origin directly facing the pulp and pulp cells adjacent to the odontoblast cell layer in the apical part of the pulp, and was considered due to the carbonic anhydrase-catalyzed reaction. Staining of these cells was completely inhibited by heat pretreatment (120 degrees C, 30 min), 10(-6) mol/L acetazolamide in the incubation medium, incubation by continuous immersion under the liquid surface, and omission of the substrate, NaHCO3. The dentin also exhibited heavy staining which was inhibited by the heat pre-treatment. However, this dentinal staining resisted the inhibition by 10(-3) mol/L acetazolamide and was not inhibited by incubation by continuous immersion or incubation without the substrate NaHCO3. The dentinal staining was thus judged to have been due to non-enzymatic cobalt precipitation.

Animals↗
PubMed1995

Evidence that high-sucrose diet reduces dentin formation and disturbs mineralization in rat molars.

In addition to its caries-promoting effect, a high-sucrose diet reduces the apposition of mineralized dentin in young rats. This study was undertaken to test whether it has a similar effect on the width of the as-yet-uncalcified matrix, predentin. Female Wistar rats were weaned at the age of 3 weeks and fed for 7 weeks with either a high-sucrose diet, a non-cariogenic raw potato starch diet, or a non-cariogenic commercial powdered rat food (for reference). The sucrose diet induced the greatest number of caries lesions. Dentin formation was smaller and the predentin zone wider in rats fed a sucrose diet when compared with rats fed the reference diet. In rats fed a starch diet, dentin formation was smaller than in rats fed a reference diet, but no alterations in the areas of caries lesions or predentin width were observed. Widening of the predentin zone in rats fed a high-sucrose diet may reflect changes in odontoblast function, such as reduced matrix synthesis and possibly disturbed mineralization. Dentinal caries progression may thus be modulated by odontoblast function, not as much by matrix formation but rather by mineralization.

Analysis of Variance↗
PubMed1996

Induced hypoxia in rat pulp and periapex demonstrated by 3H-misonidazole retention.

Cellular hypoxia may be a useful indication of tissue distress in the dental pulp that could be used to investigate the early stages of pulpal responses. Tritiated misonidazole (3H-MISO) is a marker which preferentially labels cells with decreased oxygen tension (hypoxia). The experiments reported here were carried out to determine whether this agent could distinguish between hypoxic and normoxic pulp and periapical tissues. Rats were injected intra-peritoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic, hypoxic, and control groups. Normoxic animals were maintained at ambient pressure. We induced hypoxia by maintaining animals in a hypobaric chamber at 0.5 atm for 24 hrs. 3H-MISO retention was assessed by quantitative analysis of tissue autoradiographs. 3H-MISO retention rates in normoxic animals showed little variation except for increased retention in mature ameloblasts and immature odontoblasts in the continually erupting incisor. In both incisor and molar pulps, hypobaric hypoxia significantly increased 3H-MISO retention when compared with normoxic controls. Hypobaric hypoxia also resulted in intense 3H-MISO retention in cellular cementum, periodontal ligament, osteocytes, and, occasionally, in molar pulp horn odontoblasts. This study demonstrated that, with standard autoradiographic techniques, 3H-MISO can label induced hypoxic disturbances in the pulp and surrounding periodontium.

Ameloblasts↗
PubMed1998

Bone morphogenetic protein-7 (osteogenic protein-1, OP-1) and tooth development.

Bone morphogenetic proteins (BMPs) form a family of growth factors originally isolated from extracellular bone matrix that are capable of inducing bone formation ectopically. We studied the expression, tissue localization, and function of BMP-7 (OP-1) during tooth development in rodents. Patterns of BMP-7 gene expression and peptide distribution indicated that BMP-7 was present in dental epithelium during the dental lamina, bud, and cap stages. During the bell stage, BMP-7 mRNA expression and protein distribution shifted from dental epithelium toward the dental mesenchyme. With advancing differentiation of odontoblasts, BMP-7 protein staining in the dental papilla became restricted to the layer of fully functional odontoblasts in the process of depositing (pre)dentin. Secretory-stage ameloblasts exhibited weak immunostaining for BMP-7. A restricted pattern of staining in ameloblasts became apparent in post-secretory stages of amelogenesis. Also, cells of the forming periodontal ligament were immunopositive. Histological analysis of tooth development in neonatal BMP-7-deficient mice did not reveal obvious changes compared with wild-type mice. We conclude that, in developing dental tissues, BMP-7 has distribution and expression patterns similar to those of other BMP members but is not an essential growth factor for tooth development, possibly because of functional redundancy with other BMP members or related growth factors.

Ameloblasts↗
PubMed2001

Enamel matrix derivative promotes reparative processes in the dental pulp.

During odontogenesis, amelogenins from the preameloblasts are translocated to differentiating odontoblasts in the dental papilla, suggesting that amelogenins may be associated with odontoblast changes during development. In the present study, we have explored the effects of enamel matrix derivative (EMD) on the healing of a pulpal wound. Coronal pulp tissue of permanent maxillary premolars of miniature swine were exposed through buccal class V cavities. The exposed pulp was capped with EMD. The contralateral teeth served as controls and were capped with a calcium hydroxide paste (Dycal). The cavities were sealed with glass-ionomer cement. After 2 and 4 weeks, the histology of the teeth was analyzed. In the EMD-treated teeth, large amounts of newly formed dentin-like hard tissue with associated formative cells outlined the pulpal wound separating the cavity area from the remaining pulp tissue. Inflammatory cells were present in the wound area but not subjacent to the newly formed hard tissue. Morphometric analysis showed that the amount of hard tissue formed in EMD-treated teeth was more than twice that of the calcium-hydroxide-treated control teeth (p < 0.001), suggesting that EMD is capable of promoting reparative processes in the wounded pulp more strongly than is calcium hydroxide.

Animals↗
PubMed2001

Sex- and age-related differences in primary and secondary dentin formation.

Clinical studies carried out on dentin thickness in adults, as well as experimental studies carried out on ovariectomized animals, indicate that odontoblast activity, like that of osteoblastic cells, differs in the two sexes. To examine the evidence for differences in odontoblast activity before puberty, we have measured dentin thickness and other crown dimensions from bitewing radiographs of the lower first molars in 240 children aged 4-16 years. The radiographs were obtained from pedodontic clinics throughout Israel. Only teeth without caries or fillings were used, and the study population had minimal attrition. The results showed that dentin thickness, measured on the roof of the pulp chamber, was significantly greater in boys than in girls at all ages, and that the differences increased during puberty. The differences remained highly significant even when standardized for crown size. They demonstrate that dimorphism in dentin thickness is present even in the earliest stages of odontogenesis and increase with puberty.

Adolescent↗
PubMed2001

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.

Dental Caries↗