Identification of dentin phosphophoryn localization by histochemical stainings

The rachitic tooth: Refining the use of interglobular dentine in diagnosing vitamin D deficiency

PURPOSE

This study provides guidelines on how IGD can be differentiated from other microstructures that naturally occur in dentine. Interglobular dentine (IGD) has recently been linked to disruption in vitamin D, calcium, and phosphorous pathways offering a valuable method to investigate vitamin D deficiency in archaeological individuals, but not all dentine defects are IGD.

METHODS

A detailed review of dental literature and dental histology cases gathered from known living and archaeological individuals were incorporated into interpretations.

RESULTS

Investigation of tooth dentine revealed that there can be instances where IGD is not linked to vitamin D deficiency. Information on how to differentiate different forms of defects in dentine were identified.

CONCLUSIONS

We conclude that caution is required when evaluating low-grade IGD, as it may be misidentified.

CONTRIBUTION TO KNOWLEDGE

Information reviewed and assimilated contributes to refining the role of IGD to act as a biological marker, particularly in less severe cases of vitamin D deficiency through provision of clear guidance.

LIMITATIONS OF THIS STUDY

Information from earlier experimental work is limited and until recently understanding of vitamin D and deficiency of this pro-hormone was restricted.

SUGGESTIONS FOR FURTHER RESEARCH

Further data could be gathered from living individuals with known biological/medical information.

Hydrogen Peroxide Might Bleach Natural Dentin by Oxidizing Phosphoprotein

Recent studies suggested that bleaching agents may whiten teeth by oxidizing the fluorescent materials, which are the proteins located in the organic-inorganic interface. Therefore, we postulated that fluorescence of dentin came from dentin phosphoprotein (DPP) and that bleaching agents might bleach dentin by oxidizing DPP. Fifty-six specimens were randomly divided into 4 groups and exposed to distilled water, hydrogen peroxide (HP), ethylenediamine tetraacetic acid disodium salt (EDTA), and acetic acid for 24 h. After measuring the organic and inorganic components, fluorescence, and color characteristics of dentin before and after exposure, we found that when DPP was removed from dentin by EDTA, fluorescent intensity declined proportionally with the reduction in Raman relative intensity, and dentin was whitened considerably, with an Δ E value 6 times higher than that of the distilled water group. On the contrary, due to the incapability of acetic acid to dissolve DPP during decalcification, fluorescent intensity values and tooth color remained nearly unchanged after exposure to acetic acid. Dentin exposed to neutral HP showed no obvious morphologic and organic/inorganic component changes except for the destruction of DPP. Similarly, dramatically decreased fluorescent intensity and lightened color were found in the HP group. Moreover, DPP solution of the HP group exhibited decreased ultraviolet absorbance, especially between 250 and 300 nm, which arose from aromatic amino acids. The results indicated that DPP was responsible for the fluorescent properties of dentin and that HP might bleach dentin by the oxidization of aromatic amino acids in DPP. These findings are of great significance in promoting our further understanding of the mechanism of tooth bleaching and the fluorescent property of normal dentin.

Formation and characterization of hypermineralized zone beneath dentine lesion body induced by topical fluoride in-vitro

OBJECTIVE

This in-vitro study aimed to evaluate and characterize the hypermineralized zone (Hyper-zone) formed beneath the remineralized dentine lesion body by transverse microradiography (TMR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS).

DESIGN

Demineralized bovine dentine specimens were treated with fluoride solutions (APF, NaF) and remineralized for 2-4 weeks. Then thin sections were prepared to characterize the Hyper-zone by TMR, EDS. Fractured specimen surfaces were observed by SEM.

RESULTS

TMR analysis revealed a higher mineral density at Hyper-zone than that of sound dentine (48vol%) ranging from 50 up to 61vol% and the thickness ranging from 197 to 344μm for 4-week specimens, while specimens without fluoride treatment did not show Hyper-zone. SEM pictures at Hyper-zone showed no evident crystal-like deposits in dentinal tubules and no notable difference when compared to that in sound dentine. EDS analysis demonstrated higher concentrations of Ca and P at Hyper-zone than those in sound dentine, which corresponded to the TMR profile, while the magnesium (Mg) concentration was low at this zone.

CONCLUSIONS

Demineralized dentine lesions exposed to fluoride and remineralization treatments exhibited Hyper-zone beneath the lesion body, in which the mineral density was higher than that of sound dentine. Possible mechanism for the formation of Hyper-zone was discussed by assuming removal of mineral regulators such as Mg and other organic substances from sound dentine during de-/remineralization processes.

Biological markers for evaluation of root resorption

BACKGROUND

External apical root resorption is a pathologic consequence of orthodontic tooth movement. Cementum and dentin are removed from the root surface while active force is present.

OBJECTIVE

The aim of this study was to identify and quantify extracellular matrix proteins, dentin matrix protein 1 (DMP1), dentin phosphophoryn (PP), and dentin sialoprotein (DSP) in the gingival crevicular fluid (GCF) of subjects undergoing orthodontic treatment.

METHODS

Subjects with mild (less than 2mm) and severe (more than 2mm) root resorption during orthodontic treatment were identified by radiographs. A control group of subjects with neither signs of root loss nor undergoing orthodontic treatment was also identified. GCF was collected from the upper incisors by using filter paper strips (Periopaper). The absorbed GCF was eluted and the proteins were separated by SDS-PAGE analysis and stained. Western blot and ELISA were also performed. One-way ANOVA and Scheffé test were used for statistical analysis.

RESULTS

SDS-PAGE analysis identified proteins at 77, 66, 55, 50 and 26kDa. Immunoblotting did not show any differential expression pattern between control and study groups. ELISA results revealed a significant difference in the concentrations of DMP1, PP and DSP between control and root resorption groups. Concentration of PP and DSP in severe root resorption group was also statistically higher than in mild root resorption group.

CONCLUSION

DSP and PP could be suitable biological markers for monitoring root resorption during orthodontic treatment, since a significant difference in the level of these dentin specific proteins is detected in all groups.

Dentin sialophosphoprotein knockout mouse teeth display widened predentin zone and develop defective dentin mineralization similar to human dentinogenesis imperfecta type III

Dentin sialophosphoprotein (Dspp) is mainly expressed in teeth by the odontoblasts and preameloblasts. The Dspp mRNA is translated into a single protein, Dspp, and cleaved into two peptides, dentin sialoprotein and dentin phosphoprotein, that are localized within the dentin matrix. Recently, mutations in this gene were identified in human dentinogenesis imperfecta II (Online Mendelian Inheritance in Man (OMIM) accession number 125490) and in dentin dysplasia II (OMIM accession number 125420) syndromes. Herein, we report the generation of Dspp-null mice that develop tooth defects similar to human dentinogenesis imperfecta III with enlarged pulp chambers, increased width of predentin zone, hypomineralization, and pulp exposure. Electron microscopy revealed an irregular mineralization front and a lack of calcospherites coalescence in the dentin. Interestingly, the levels of biglycan and decorin, small leucine-rich proteoglycans, were increased in the widened predentin zone and in void spaces among the calcospherites in the dentin of null teeth. These enhanced levels correlate well with the defective regions in mineralization and further indicate that these molecules may adversely affect the dentin mineralization process by interfering with coalescence of calcospherites. Overall, our results identify a crucial role for Dspp in orchestrating the events essential during dentin mineralization, including potential regulation of proteoglycan levels.

A transmission electron microscope study using vitrified ice sections of predentin: structural changes in the dentin collagenous matrix prior to mineralization

The assembly of the collagenous organic matrix prior to mineralization is a key step in the formation of bones and teeth. This process was studied in the predentin of continuously forming rat incisors, using unstained vitrified ice sections examined in the transmission electron microscope. Progressing from the odontoblast surface to the mineralization front, the collagen fibrils thicken to ultimately form a dense network, and their repeat D-spacings and banding patterns vary. Using immunolocalization, the most abundant noncollagenous protein in dentin, phosphophoryn, was mapped to the boundaries between the gap and overlap zones along the fibrils nearest the mineralization front. It thus appears that the premineralized collagen matrix undergoes dynamic changes in its structure. These may be mediated by the addition and interaction with the highly anionic noncollagenous proteins associated with collagen. These changes presumably create a collagenous framework that is able to mineralize.

In vivo study of the pulp reaction to Fuji IX, a glass ionomer cement

OBJECTIVE

Our aims were to investigate the pulp biocompatibility of Fuji IX, a glass ionomer cement (GIC) used as a restorative material in cavities prepared in rat's upper molars, and to assess the value of this in vivo model for testing dental biomaterials.

METHOD

Half-moon class V-like cavities were drilled on the mesial aspect of 26 rat upper first molars. Half of the experimental rats whose molars were restored with the GIC were killed after 8days and the second half after 30days. They were compared with two control groups, also submitted to cavity preparation, but with cavities left unfilled. Again, half of the control rats were killed at 8 days and the second half after 30days. Following intracardiac perfusion with the fixative solution, the specimens were processed to histologic procedures.

RESULTS

After 8 days, in both groups a few inflammatory cells were observed. The odontoblastic layer was disrupted and dilated blood vessels were seen in the pulp area related to the cut tubules. The experimental group displayed a moderate inflammatory reaction whereas only a slight reaction was detected in the control group. In few teeth, bacteria were visualized in dentine tubules beneath the GIC restoration. Such colonies were not observed in unfilled molars.After 30days, in both groups, the pulp tissue recovered and displayed a normal appearance. Disruptions of the odontoblast layer were not visible anymore. Bacteria penetration into dentine tubules was reduced compared with the 8-day situation. A thick layer of reparative osteodentine was formed. However no difference in thickness was detected between the experimental and control groups, supporting that the formation of reparative dentine is not impaired. Irregular mineralizations including calcospherites were induced by the GIC.

CONCLUSIONS

This study demonstrates that, despite small alterations in the mineralization processes, the GIC Fuji IX has a good biocompatibility and does not induce any harmful effect on pulp cells.

Peritubular dentin formation: crystal organization and the macromolecular constituents in human teeth

Peritubular dentin (PTD) is a relatively dense mineralized tissue that surrounds the tubules of coronal tooth dentin. It is composed mainly of crystals of carbonated apatite together with a small amount of collagen. Its mode of formation has been investigated by studying the relatively dense particles isolated from a powdered preparation. Electron microscopic examination of the PTD particles, including 3-dimensional image reconstruction and electron diffraction, shows that the organization of the crystals of PTD is very similar to that of the adjacent intertubular dentin (ITD). The latter contains relatively large amounts of collagen and the carbonated apatite crystals are closely associated with the collagen matrix. The proteins present in the PTD particles are soluble after decalcification and stain with Stains All. The principal protein has higher molecular weight and a quite different amino acid composition than the phosphophoryns of the intertubular dentin. The interface between the PTD and the ITD shows structural continuity. These data show how two distinct carbonated apatite-based mineralized tissues can be organized and formed contiguously within the same organ by utilizing different sets of matrix proteins.

Effects of inositol hexasulphate, a casein kinase inhibitor, on dentine phosphorylated proteins in organ culture of mouse tooth germs

To study the effects of impaired protein phosphorylation on dentine formation and mineralization, inositol hexasulphate, an intracellular type I and type II casein kinase inhibitor, was used in an in vitro organotypic culture system. Mandibular first molar tooth germs were dissected from 18-day-old mouse embryos and cultured for 11 days with and without inositol hexasulphate at different concentrations. At 0.04-0.08 mM inhibitor, cellular alterations were not detected. Dentine displayed the characteristic purple-blue colour when Stains all, a specific stain for extracellular phosphoproteins, was used. At 0.1 mM, dentine failed to stain and mineralization did not occur, as seen from the von Kossa method. The presence of numerous lysosome-like vesicles inside cells indicated that the experiment was at the limits of cytotoxicity; higher concentrations induced severe cellular alterations. Therefore, quantitative radioautography was carried out on germs treated or not with the inhibitor at 0.1 mM. [33P]-phosphate incorporation showed that grain density in inhibited germs compared with that in control germs was about double in odontoblasts and half in the predentine/dentine compartment. In the presence of inositol hexasulphate the incorporation of [3H]serine into odontoblast cell bodies was unchanged between 2 and 24 h while in predentine/dentine, grain density was higher between 1 and 4 h, and reduced at 24 h. Both with [33P]phosphate and [3H]serine, labelling was seen throughout the porous dentine formed in vitro and not as a band located at the predentine/dentine junction, as is the case in vivo. With [3H]proline, in the presence of the inhibitor, a small reduction of grain density occurred in cell bodies, no significant difference was seen between 1 and 4 h in predentine/dentine, and more silver grains were present after 24 h both in cells and in the matrix. The radioautographic data support the view that the inhibitor interacts mostly with post-transductional phosphorylation and does not alter significantly other cell synthetic pathways and functions. Finally, the experiments presented here confirm that phophorylated proteins have a key role in dentine mineralization.

A comparative study of the transition between predentin and dentin, using various preparative procedures in the rat

The appearance of the junction between predentin and dentin of rat incisors was investigated after chemical fixation (aldehyde), physical fixation (high pressure freezing and freeze substitution) and by histochemistry. Physical fixation revealed a 1-2 micron wide intermediary zone, in which only the collagen fibers were mineralized. In dentin, which looked denser and more homogeneous, both collagen fibers and intercollagenous spaces were mineralized. The intermediary layer could not been seen after aldehyde fixation. When cationic dyes were used during fixation in order to retain proteoglycans, a 0.5-5 micron border zone located at the junction between predentin and dentin was densely stained on the dentin side, whereas in dentin only the interglobular network displayed electron density. The periodic acid-thiocarbohydrazide-silver proteinate reaction, visualizing glycoproteins, and the phosphotungstic acid/chromic acid mixture, which reveals glycoproteins and phosphorylated proteins, produced extensive staining of the transitional zone located at the dentin edge, whereas staining was weaker in dentin. These morphological and histochemical investigations support the existence of an intermediary zone in which mineralization occurs. This transitional zone between predentin and dentin has specific properties; therefore we propose it be termed metadentin.

Pulpo-dentinal complex revisited

OBJECTIVES AND METHODS

The value of the concept of a pulpo-dentinal complex was assessed on human teeth treated according to the ISO test on biological evaluation. The teeth were extracted after 1 or 3 months and examined histologically. Biochemical and biological data available from the dental literature were also re-examined.

RESULTS

During the early development of the tooth, pulp and dentine establish close links and form an undivided organ. However, examination of the tissues at later stages of development casts doubt on the validity of such a concept. Major differences are reviewed in this report between the cells (odontoblasts and heterogeneous pulpal cells) and extracellular matrix (collagens, non-collagenic proteins and phospholipids) located either in the odontoblast-dentine area or in the pulp. It seems also that clear-cut differences are detected during inflammatory and repair processes.

CONCLUSION

It is concluded that, although the existence of a dentino-pulpal reaction cannot be denied, the concept of a pulpo-dentinal complex is an oversimplification and should be revisited. This may have implications in the evaluation of restorative treatments and in the design of a tissue repair strategy.

An immunocytochemical study of the routes of secretion of collagen and phosphophoryn from odontoblasts into dentin

Polyclonal antibodies to rat incisor phosphophoryns and to the amino-telopeptide of the alpha1 (I)-chain of type I collagen were used to follow the pathways of movement of collagen I (COL1) and phosphophoryns (PP) from synthesis in the odontoblast to secretion into the mineralized dentin. The antibodies were detected at the transmission electron microscopic level by their reaction with Protein A-colloidal gold conjugates. Special care was given in specimen preparation to retention of maximal antigenicity during fixation while maintaining cellular and extracellular ultrastructure at the mineralization front (MF) in nondemineralized sections. Intracellularly, COL1 and PP were detected within the endoplasmic reticulum (ER), the Golgi (G) and secretory granules (SG). However, as determined by double-immunolabeling with different size gold particles the COL1 and PP were not found together within the same ER, G or SG compartments. PP was localized within the tubular ER, round-shaped transitional vesicles, the Golgi and in narrow asymmetric SG. These asymmetric SG were found in abundance in the odontoblastic process. PP secretion from these vesicles was near the MF at the predentin-dentin boundary. COL1 was localized within rosette form ER compartments, the Golgi and in large, distinctive SG. COL1 was deposited at the cell-predentin boundary. No COL1 SG were seen within the odontoblastic process near the MF. In the region of the MF, prior to mineralization, the PP was localized along the surfaces of the COL1 fibrils of the predentin. The mineral phase etched surfaces revealed both COL1- and abundant mineral-associated PP. These data support the hypotheses that, in dentin, the interaction between COL1 and PP may initiate crystal nucleation and that additional interactions between PP and the growing crystals may modulate the crystal growth pattern and crystal size.

Development of a monoclonal antibody against dentin phosphophoryn: a tool to study odontoblastic activity

The role played by phosphophoryn, one of the major noncollagenous proteins of dentin extracellular matrix, in the mineralization process has not been fully characterized. The purpose of our work was to produce monoclonal antibodies (MAbs) against dentin phosphophoryn and to test their reactivity with primary culture of odontoblasts. Dentin phosphophoryn (DPP) was extracted after the mechanical dissociation of teeth and dialyzed against guanidine and EDTA solutions followed by CaC1(2) precipitation. These extracts were characterized by SDS-PAGE and staining with Coomassie blue and Stains-All. After immunization of mice with these extracts, we produced MAb 7G4, which reacted with dentin phosphophoryn as revealed by Western blot. MAb 7G4 reactivity was tested against a primary culture of pig odontoblasts, revealing filaments specifically stained by the anti-DPP antibody. This antibody will be of great interest to study the mineralization process and dental pulp reaction after capping with various calcium phosphate materials.

Characterization of a system of mineralized-tissue formation by rat dental pulp cells in culture

Pulp tissue was obtained from maxillary incisors of young adult male Wistar rats, minced and digested with 0.5% trypsin and 0.02% EGTA at 37 degrees C for 30 min. Dissociated cells were cultured with or without 10 nM dexamethasone using Eagle's minimal essential medium supplemented with 10% fetal bovine serum and 50 micrograms/ml ascorbic acid. Confluent cells were subcultured at 7 days and the medium further supplemented with beta-glycerophosphate (beta-GP). Dexamethasone in primary culture and/or secondary culture enhanced the formation of mineralized tissue while > 5 mM beta-GP was necessary for mineralization to occur. Biochemical analysis of the radiolabelled medium revealed that these cells produced type I, type I trimer and type III collagens. Analysis of [32PO4]-labelled medium, using DEAE-Sephacel ion-exchange chromatography and sodium dodecylsulphate-polyacrylamide gel electrophoresis, showed that these cells produced phosphophoryn-like protein. These results indicate that some of the rat dental pulp cells in culture express an odontoblast-like phenotype.

Immunohistochemical detection of an enamel protein-related epitope in rat bone at an early stage of osteogenesis

Monoclonal antibody MI315 was produced against hamster tooth germ homogenate by in vitro immunization. It was found that MI315 reacted with enamel matrix, ameloblasts, and bone matrix at an early stage of osteogenesis. Decalcified tissues of rat femurs and mandibles were examined with MI315 using indirect immunofluorescence. In endochondral ossification of femurs, immunoreactivity was found in bone extracellular matrix (ECM) deposited on the surface of the cartilage core of primary spongiosa, but not in the cartilage core itself. In intramembranous ossification of 0-day-old rat mandibles, intense immunofluorescence was detected in bone ECM and a few young osteocytes, but not in osteoblasts. Immunoreactivity in bone ECM of 2-day-old rats decreased and almost disappeared from bone ECM of 4-day-old rats. Although in nondecalcified sections of 0-day-old rats, negligible immunofluorescence was detected in bone ECM which showed positive staining in decalcified tissues, the immunostaining appeared after decalcification using ethylenediaminetetraacetic acid (EDTA). These results indicate that a substance(s), which had a common epitope with an enamel-derived protein(s), existed in immature bone ECM of both endochondral and intramembranous ossification, and that it might be masked by bone mineral. Monoclonal antibody MI315 is a useful tool to investigate the time- and position-specific changes in osteogenesis and amelogenesis.

Effects of fixation and demineralization on the retention of bone phosphoprotein and other matrix components as evaluated by biochemical analyses and quantitative immunocytochemistry

Aqueous tissue processing and demineralization procedures may adversely affect the inorganic mineral phase of a calcified sample and, where mineral and organic constituents interact, may consequently also indirectly alter organic matrix ultrastructure and distribution. In the present work, the effects of demineralization have been investigated on the retention in chicken bone of two phosphoamino acids, O-phosphoserine and O-phosphothreonine, found in bone phosphoproteins proposed to be important in vertebrate mineralization and, more specifically, on the retention and distribution of a 66 kD bone phosphoprotein (66 kD BPP, osteopontin) also implicated in the calcification process. In tibiae fixed initially with 1% glutaraldehyde and then demineralized in 0.5 N HCl, 0.5 N acetic acid, or 0.1 M EDTA (all containing 1% glutaraldehyde), amino acid analyses and quantitative immunocytochemistry revealed that the phosphoamino acid content and the distribution of the 66 kD BPP were essentially the same as in fixed undemineralized controls. However, demineralization slightly altered the ultrastructural appearance of immunolabeled, electron-dense patches of organic material in the bone matrix. In unfixed bone demineralized with any of these acids, there was a substantial loss of phosphoamino acids and the 66 kD BPP from the bone matrix. The relative ability of these acids to extract phosphoproteins from unfixed bone was found to decrease in the order EDTA greater than HCl greater than acetic acid. These results emphasize the differential effects on structural components of various demineralization and extraction procedures for biochemical and immunocytochemical studies of biologic tissues. Furthermore, they demonstrate that initial fixation with glutaraldehyde retains phosphoproteins in bone, with or without demineralization, while being adequate for immunocytochemical localization of certain bone matrix proteins and that an understanding of the action of specimen preparation on organic constituents (as well as inorganic components) is essential for accurately describing ultrastructural matrix-mineral relationships.

Domain structure and sequence distribution in dentin phosphophoryn

Phosphophoryn (PP) is a protein unique to the mineralized matrix of dentin. It also has a unique composition, with aspartic acid and phosphoserine comprising greater than 85% of all amino acid residues. Because of this unique composition and high content of phosphoserine, it has been difficult to apply direct peptide sequencing procedures effectively. However, to understand its function, and to prepare suitable probes for screening cDNA libraries, some sequence distribution information is required. To this end, using bovine (b) and rat incisor (ri) PPs, partial mild acid hydrolysis has been used to cleave at the aspartic acid residues and generate free amino acids and small peptides. The nature of the released amino acids and peptides has been determined. Peptides have also been generated by limited digestion with trypsin. Some of the peptides have been purified by h.p.l.c. techniques and sequenced. About 90% of the bPP and riPP were resistant to trypsin, and the large resistant fragment was sharply depleted of the non-aspartic acid and non-phosphoserine [(P)Ser] residues. All peptides isolated were acidic, but the remaining residues (other than aspartic acid and serine) appeared to be collected in regions flanking the trypsin-resistant core. These data show directly the presence of regions [Asp]n, [(P)Ser]m and [Asp-(P)Ser-Asp]k as prominent sequence features. A domain structure model is proposed.

Metalloproteinases in the mineralized compartments of porcine dentine as detected by substrate-gel electrophoresis

Several gelatinolytic activities were detected in the 4M guanidine HCl-soluble fraction extracted from demineralized porcine dentine matrix. These matrix proteinases were active in the range of pH 6-9, and the activities were enhanced by calcium ions. The enzymes also degraded some of the non-collagenous proteins coexisting in the extract. The results indicate that the changes in the composition of non-collagenous proteins during the development of dentine are related to proteolytic enzyme activity.

Immunohistochemical localization of alpha 2HS glycoprotein in dentin

Monoclonal antibody against bovine serum alpha 2HS glycoprotein was raised in mice and the localization of this glycoprotein in bovine and human teeth was examined by immunohistochemical techniques on undemineralized ground sections after surface etching with dilute HCl. Positive reactions were found in both bovine and human peritubular dentin, whereas virtually negative staining was detected in the intertubular dentin. When the ground section was examined without surface etching, no reaction was found in any area of mineralized dentin. These results suggest that alpha 2HS glycoprotein is present mainly in the peritubular dentin associated with the mineral phase. The presence of this component in dentin may not be due simply to nonspecific binding to calcium phosphate crystals.

Release of organic matrix components from bovine incisor roots during in vitro lesion formation

The solubilization of organic matrix components during demineralization of powdered and intact root sections from adult bovine incisors was investigated. Root powder was demineralized with 0.1 mol/L acetic acid, pH 4.0, at 4 degrees C and 37 degrees C. Surfaces of intact root sections were subjected to 0.1 mol/L acetic acid, pH 4.0 (for production of erosive lesions), or to 0.1 mol/L lactic acid, 0.2 mmol/L methane hydroxy diphosphonate, pH 5.0 (for production of subsurface lesions at 37 degrees C). The solubilized organic material was analyzed for collagen, total noncollagenous protein (NCP), organic phosphate (Po), and proteoglycans (PGs), which were measured as chondroitin 4-sulfate (C-4-S). For root powder, a maximal release of NCPs and PGs was found only after neutralization of the extraction mixture. For both temperatures tested, the average amounts of liberated noncollagenous components (NCCs) were the same, i.e., 0.68 micrograms [NCP - Po], 0.11 microns Po, and 0.10 micrograms C-4-S per mumols released calcium. The amino acid composition of the NCP fraction revealed relatively high amounts of aspartic acid and serine. These findings indicate that the NCCs were easily liberated from the tissue, and that the NCP fraction consisted mainly of phosphoprotein. Demineralization of intact root sections resulted in average amounts of solubilized NCCs of 0.21 micrograms [NCP - Po], less than 0.01 micrograms Po, and less than 0.01 micrograms C-4-S per mumols released calcium, independent of incubation time and lesion type. The amino acid composition of all NCP fractions was virtually the same, high in glutamic acid, but lower in aspartic acid and serine when compared with the neutralized powder extracts. For both demineralization solutions, the amounts of solubilized collagen were 0.07 and 0.16 micrograms per micromol released calcium after three and 28 days of incubation, respectively. Our experiments indicate that phosphoprotein and proteoglycans may be released from root surfaces during the periods of neutral pH that follow acid demineralization.

Phosphoprotein extraction from the dentine/cementum complex of human tooth roots

Root shards were placed in dialysis tubing and demineralized to completion in either 10% disodium EDTA, pH 7.4, 0.6 M HCl, 0.1 M HCl, 0.5 M acetic or 75 mM-25 mM lactic-acetic acids. The demineralized shards were then re-extracted with 0.05 M tris-HCl, 1.0 M NaCl. DEAE chromatography revealed that the major peak of the 0.6 M CHl and EDTA extracts contained organic phosphorus, whereas much less organic phosphorus was found in the major peak of the 0.1 M HCl extract. Analysis of the re-extracts gave a pattern opposite to that obtained from the initial extractions. Measurements of protein and organic phosphorus released during extraction and re-extraction confirmed these results. Staining of SDS-PAGE gels for phosphoprotein with Stains-All resulted in a blue smear in fractions containing organic phosphorus. Thus the extraction of phosphoproteins from human tooth roots differed depending upon the demineralizing conditions. This ability to remove phosphoprotein differentially will allow further investigation of the role of phosphoprotein in mineralization and remineralization.

Changes in levels of osteonectin in bovine dentine during tooth development

Bovine incisors were classified into three developmental stages and non-collagenous proteins extracted from them. Sodium dodecyl sulphate gel electrophoresis of the extracts showed a reduction in osteonectin with the various stages. The reduction was confirmed by enzyme immunoassay using antiserum against bone osteonectin. This change is in contrast to dentine phosphoprotein, indicating functional differences between these two proteins.

A search for the osteogenic factor in dentin. Rat incisor dentin contains a factor stimulating rat muscle cells in vitro to incorporate sulfate into an altered proteoglycan

Demineralized dentin matrix has the capacity to induce bone formation via a chondrogenic pathway when implanted into muscle, in a fashion entirely analogous to bone matrix implants. In this work we have attempted to isolate, from rat incisor dentin, the matrix factor responsible for initiating osteogenesis. Rat incisor dentin was demineralized with EDTA plus 4.0 M guanidine. HCl. The proteins in the extracts were collected and, after a CaCl2 precipitation step, fractionated on Sephacryl S-200 in 6.0 M guanidine. HCl. The primary assay for activity was the incorporation of 35S-sulfate into proteoglycan in cultures of the fibroblast-like outgrowth cells from explants of neonatal rat muscle. Two Sephacryl S-200 fractions showed enhanced sulfate incorporating activity, but only one showed enhanced incorporation without a concomitant increase in cell number. In the presence of this fraction, the cell cultures produced a larger amount of a new small proteoglycan, as compared to controls, and a significant amount of a much larger proteoglycan. The active fraction had proteins in the Mr range from 8,000 to 15,000 as the major components. These data suggest that the fraction identified may contain the factors responsible for initiating the osteogenic response to dentin matrix upon its implantation in muscle in vivo.

A probable common disturbance in the early stage of odontoblast differentiation in Dentinogenesis imperfecta type I and type II

Deciduous teeth from 7 patients with dentinogenesis imperfecta (DI) Type I and Type II were examined by conventional microscopy. A defective layer was found which runs parallel with the dentinal surface in the outer portion of dentin in teeth of both types. Dentinal tubules were interrupted in the vicinity of this layer. When the ground sections were examined after being stained by the phosphophoryn staining method, the DI Type I dentin was found to contain phosphophoryn at the same low level as the DI Type II dentin, suggesting similar deficiency in phosphophoryn concentration. These results suggest that both types of DI have a common primary disturbance in the early stage of odontoblast differentiation.

Difference in noncollagenous matrix composition between crown and root dentin of bovine incisor

A comparative study of the organic matrix in crown dentin and root dentin of the bovine incisor has been performed utilizing biochemical analyses and histochemical stainings. Root dentin contained only half the amount of dentin phosphophoryn present in crown dentin. Composition of noncollagenous matrix other than phosphophoryn was also suggested to be different between crown and root dentin. These data indicate that odontoblasts forming root dentin may secrete a noncollagenous matrix having a composition different from that of crown dentin, and that crown and root dentin may be separate in nature. The distinct compositions of noncollagenous matrix may reflect the difference in the mineralization process between crown and root dentin.

Induction and inhibition of hydroxyapatite formation by rat dentine phosphoprotein in vitro

Highly phosphorylated rat incisor phosphoprotein (PP-H) was purified and covalently attached to agarose beads. The beads were incubated for 24 h in solutions having an ionic strength of 0.165, a molar Ca/P ratio of 1.67, and a pH of 7.4. The calcium-phosphate concentration products [( Ca][P]) in the stable incubation solutions ranged from 1.0 to 1.8 mM2, from which no spontaneous precipitation occurred. In a timed series mineral formation was monitored by SEM and X-ray diffraction. The inhibitory capacity of PP-H, free solution, was also studied. The first mineral appeared after 10 min at a [Ca][P] product as low as 1.2 mM2; X-ray diffraction showed that the mineral was (hydroxy)apatite. Thus small amounts of PP-H attached to a surface are capable of inducing mineral formation in vitro at comparatively low supersaturation, whereas PP-H is a mineral inhibitor when free in solution.

Increase of dentin phosphophoryn with dentin formation

Dentin phosphophoryn was quantified on bovine and rabbit dentin at three developmental stages. Phosphophoryn was extracted from teeth with 0.6M HCl, and quantified as optical density on DEAE-cellulose chromatogram or as phosphoserine content. Bovine phosphophoryn showed progressive increase with formation of dentin. Matrix-associated phosphophoryn was also quantified as phosphoserine content in insoluble dentin residue which was extracted with 6 M urea after decalcification. This fraction increased with formation of dentin both in bovine and rabbit dentin. Phosphophoryn is thought to be related to the later stage of dentin formation.

Effects of dentin phosphophoryn on precipitation of calcium phosphate in gel in vitro

In vitro precipitation of calcium phosphate was carried out using a one-dimensional double diffusion system in agar gel. Bovine dentin phosphophoryn enhanced the sharpness of the precipitation bands, although it reduced the total amount of the precipitates. Dephosphorylated phosphophoryn had no effect on the pattern of precipitates. Therefore, phosphophoryn is thought to raise the local density of nucleation in spite of its inhibitory activity on apatite formation.

Histological distribution of phosphophoryn in normal and pathological human dentins

Dentin phosphophoryn is a highly phosphorylated protein which has a hydrophilic character but is not soluble in dilute acetic acid. A histochemical method was developed for staining this protein with Stains-all in situ utilizing those chemical properties. We have succeeded in detecting the presence of this protein in circumpulpal orthodentin of human permanent and deciduous teeth, but not in mantle dentin, secondary dentin and reparative dentin. Phosphophoryn staining was also absent in the dentin of dentinogenesis imperfecta (DI) Type II, a genetic disorder of dentin formation. From these results, it is suggested that phosphophoryn is synthesized and secreted only by physiologically-differentiated odontoblasts and that the mineralization processes of mantle, secondary, reparative and DI dentins may be different from that of circumpulpal orthodentin.