Components Of Dentin Research Articles

Effect of a chemo-mechanical caries removal system (CarisolvTM) on dentin topography of non-carious dentin

The purpose of the present study was to examine the morphology of healthy dentin surfaces after treatment with CarisolvTM followed by conditioning with phosphoric acid and EDTA, since surface morphology may be of interest for dentin bonding. Another purpose was to evaluate the effect of treatment with CarisolvTM on healthy non-carious dentin surfaces with exposed collagen fibers. Scanning electron microscopy was utilized to carry out a detailed morphological examination of the dentin surfaces with regard to presence or absence of both smear layer and collagen fibers. Twelve premolars extracted for orthodontic reasons from young adults were used. The two etchants appeared to have produced two distinctly different surfaces. Etching with phosphoric acid following CarisolvTM treatment resulted in a porous dentin surface, while EDTA etching without prior CarisolvTM treatment appeared to have uncovered an intact collagen network. In contrast, the surfaces treated with CarisolvTM prior to EDTA etching displayed smooth intertubular surfaces with only occasional fibers. Apparently, the ability of EDTA to expose collagen in the dentin surface is counteracted or inhibited by the CarisolvTM treatment. Furthermore, it cannot be excluded that the CarisolvTM treatment in itself may have dissolved collagen fibers. Since most bonding systems claim bonding to the collagenous component of dentin, the question arises which of the etched surfaces is preferable and to what degree the collagenous component contributes to bonding strength. Further studies are thus needed to evaluate the micromechanical retention of a restoration to the different surfaces described in the present study.

The surface modification of tooth dentine with a Free Electron Laser (FEL)

Free Electron Laser (FEL) with the wide wavelength tunability has been developed and used for various applications. The FEL gives high efficiency for the photo-induced ablation when the laser is tuned to an absorption maximum of the target. The FEL was tuned to 9.4 μm, which is an absorption maximum of phosphoric acid ion, a known major component of dentine. The FEL pulse length was several ps. The average output power was varied from 5 to 20 mW by filters. The change of irradiated dentine surface was analyzed by mass spectroscopy and Energy Dispersive X-ray (EDX) spectroscopy. Positive ions which correspond to Na +, CO 3 + and many phosphoric acid ions were measured. It was found that atomic ratio of P/Ca had reduced from 0.65–0.60. The atomic ratio of P/Ca, however had not changed with irradiation by Er:YAG laser (2.9 μm), or CO 2 laser (10.6 μm). These results indicate the selective ablation of phosphoric acid ion by the 9.4 mm FEL irradiation.

Invasion of dentinal tubules by oral streptococci is associated with collagen recognition mediated by the antigen I/II family of polypeptides.

Cell surface proteins SspA and SspB in Streptococcus gordonii and SpaP in Streptococcus mutans are members of the antigen I/II family of polypeptides produced by oral streptococci. These proteins are adhesins and mediate species-specific binding of cells to a variety of host and bacterial receptors. Here we show that antigen I/II polypeptides are involved in the attachment of oral streptococci to collagen and that they also determine the ability of these bacteria to invade human root dentinal tubules. Wild-type S. gordonii DL1 (Challis) cells showed heavy invasion of tubules to a depth of approximately 200 microm, whereas the abilities of cells of isogenic mutant strains OB220 (sspA) and OB219 (sspA sspB) to invade were 50 and >90% reduced, respectively. Likewise, wild-type S. mutans NG8 cells invaded dentinal tubules, whereas cells of isogenic mutant strain 834 (spaP) did not. The invasive abilities of strains OB220 and OB219 were restored by heterologous expression of S. mutans SpaP polypeptide in these strains. The extents of tubule invasion by various wild-type and mutant strains correlated with their levels of adhesion to type I collagen, a major component of dentin. Furthermore, S. gordonii DL1 cells exhibited a growth response to collagen by forming long chains. This was not shown by ssp mutants but was restored by the expression of SpaP in these cells. The production of SspA polypeptide by S. gordonii DL1, but not production of SspB polypeptide by strain OB220 (sspA), was enhanced in the presence of collagen. These results are the first to demonstrate that antigen I/II family polypeptides bind collagen and mediate a morphological growth response of streptococci to collagen. These antigen I/II polypeptide activities are critical for intratubular growth of streptococci and thus for establishment of endodontic infections.

Effect of ascorbic acid deficiency on primary and reparative dentinogenesis in non-ascorbate-synthesizing ods rats

Ascorbic acid is essential to the biosynthesis of collagen, the major organic matrix component of dentine. The ODS rat is a mutant strain of Wistar rat characterized by hereditary lack of l-gulono-gamma-lactone oxidase and thus is unable to synthesize ascorbic acid. ODS rats were given an ascorbic acid-free diet to investigate how ascorbic acid deficiency affects dentine formation in vivo. Histomorphometric analysis on their growing molars and incisors showed a significant reduction in both size and mineral apposition rate of dentine, as revealed by contact microradiography and fluorescent time-marking, respectively. A similar reduction in bone formation was simultaneously demonstrated in the mandible, confirming the previously reported osteopathic effects of ascorbic acid deficiency. When pulp inflammation was induced in lower first molars by making unsealed pulp exposures, specimens from control animals showed continuous deposition of an osteodentine-like tissue in the radicular pulp chamber; this type of mineralized tissue formation was greatly reduced in ascorbic acid-deprived animals. These results indicate that ascorbic acid deficiency hampers dentine formation under both physiological and pathological conditions of the dentine/pulp complex. ODS rats could be useful in investigating in vivo effects of ascorbic acid deficiency on the formation of dentine and other dental mineralized tissues.

Current concepts on adhesion to dentin.

This review examines fundamental concepts in bonding to dentin. Emphasis is placed on the structure and permeability characteristics of dentin and how they may influence its interaction with adhesive resin. Several new techniques to examine the interfaces between resin and dentin are reviewed along with some of their limitations. The advantages and disadvantages of acid etchants/conditioners vs. self-etching conditioners/primers are discussed. The problems of matching the surface tension of resin-bonding systems to the surface energy of the substrate are reviewed in terms of wetting the various components of dentin. The problems associated with matching the permeability of intertubular dentin to the diffusibility of bonding reagents are explored. Speculation is advanced on how to ensure polymerization and wetting of dentinal collagen. Theoretical problems associated with dentin bonding and with bond testing are reviewed to encourage future research in this rapidly developing area.

Human genes for dental anomalies.

The development of the tooth at gene level is beginning to be understood. This paper reviews current knowledge and the advances in research on human genes whose defect leads to dental anomalies. Amelogenesis imperfecta (AI) is a diverse group of hereditary disorders characterized by a variety of developmental enamel defects including hypoplasia and hypomineralization, some of which have been revealed to be associated with defective amelogenin genes. The human amelogenin genes on X and Y chromosomes have been cloned and investigated extensively. Although autosomally inherited forms of AI are more common than the X-linked forms, most studies on the genes causing AI have been performed on the genes of X-linked forms. Recently, the gene for the human tuftelin protein (an enamelin) has been cloned as a candidate gene for the autosomal forms of AI with another gene on chromosome 4 involved in some families. Dentinogenesis imperfecta (DI) may be associated with osteogenesis imperfecta (OI), which is an autosomal dominant bone disease. Most patients with OI have mutations in either the COLIA1 or COLIA2 genes, which encode the alpha 1(I) or alpha 2(I) subunits of type I collagen, the major organic component of bone and dentin. Gene defects causing isolated DI have not been identified. Recently, it was demonstrated that a missense mutation of MSXI, a human homeobox gene, causes autosomal dominant agenesis of second premolars and third molars. Data indicating an important function for MSXI, the mouse counterpart of the human MSXI gene, in mouse tooth development have been accumulating since 1991. Knockout mice lacking this gene exhibited multiple craniofacial anomalies including complete tooth agenesis. X-linked anhidrotic ectodermal dysplasia (EDA), characterized by abnormal hair, teeth, and sweat glands, was demonstrated to be caused by a mutation in a novel transmembrane protein gene that is expressed in epithelial cells and in other adult and fetal tissues. The predicted EDA protein may belong to a novel class of proteins with a role in epithelial-mesenchymal signaling. Several mutations have been reported in genes causing hypophosphatasia, which is characterized by defective mineralization of the skeletal and dental structures.

Dentin Phosphoprotein and Dentin Sialoprotein Are Cleavage Products Expressed from a Single Transcript Coded by a Gene on Human Chromosome 4: DENTIN PHOSPHOPROTEIN DNA SEQUENCE DETERMINATION

Dentin is the major mineralized extracellular matrix of the tooth. The organic components of dentin consist of type I collagen (90%) with 10% noncollagenous proteins, which are also components of bone. Two dentin proteins, dentin sialoprotein and dentin phosphoprotein, have been shown to be tooth-specific being expressed mostly by odontoblast cells. In this study, we screened a mouse molar tooth library for dentin sialoprotein and dentin phosphoprotein cDNA clones. Analysis of the clones resulted in characterization of a 4420-nucleotide cDNA that contained a 940-amino acid open reading frame. The signal peptide and NH2-terminal sequence was 75% homologous to the cDNA sequence of rat dentin sialoprotein. The continued open reading frame, however, contained a RGD sequence followed by a region of repeated aspartic acid and serine residues. This portion of the protein codes for amino acid sequence consistent with that of dentin phosphoprotein. The noncoding region contains three potential polyadenylation signals, two of which were shown to be utilized. Northern blot analysis indicated the presence of two major transcripts of 4.4 and 2.2 kilobases in odontoblasts. Chromosomal mapping localized the gene to human chromosome 4. These data suggest that the previously identified dentin extracellular matrix proteins, dentin sialoprotein and dentin phosphoprotein, are expressed as a single cDNA transcript coding for a protein that is specifically cleaved into two smaller polypeptides with unique physical-chemical characteristics. Therefore, we propose that the gene be named dentin sialophosphoprotein. The location of the human dentin sialophosphoprotein gene on chromosome 4 suggests that this gene may be a strong candidate gene for the genetic disease dentinogenesis imperfecta type II.

ボンディングシステムの歯質に対する接着強さ : 組成の異なる 2 種類のボンディングシステムの組み合わせによる影響

Many kinds of dentin bonding systems have recently been introduced, which are reported to have significantly improved bond strengths to dentin. To enhance the dentin adhesion, the adhesion process of these dentin bonding systems include various processes such as, 1) acid etching of enamel to create a mechanical retention, 2) dentin conditioning to fully or partially remove the smear layer, 3) pretreating of dentin surfaces with primers, 4) application of a bonding agent before resin filling. All the components of these dentin bonding systems are designed in different mechanism to enhance the bonding strength, and careful observance of all the manufacturers' directions is also recommended. The effect of each component of dentin bonding systems on the tooth bonding has so far been unclear in detail. In this report, two different kinds of dentin bonding systems, Clearfil Liner Bond System (CLB) and Scotchbond Multi-Purpose (SMP), were used in various combinations to smearlayer-covered-dentin and polished-enamel surfaces of freshly extracted caries-free human molars and incisors to investigate the effects of the conditioners, primers and bonding agents on the tooth bonding. The conditioners, primers and bonding agents of the two dentin bonding systems were used in various combinations. The specimens were stored in room temperature for 48 hr, before tensile bond testing with cross-head speed of 2mm/min. The results were analyzed using ANOVA (p<0.05). The scanning electron microscope (SEM) was also used to observe the conditioner and/or primer treated dentin surfaces and the fracture surface after tensile bond test. The bonding aspect of bonding agent and synthetic hydroxyapatite (HAP) with SEM were also performed by using the method described by Hsiao et al. (1987). In the cases of smear-layer-covered-dentin surfaces, the tensile bond strengths of the original combination of LBS show a higher bond strength than any other combination. There were no statistically significant differences in the combination use of different conditioners or dentin primers. The tensile bond strength shows a significant decrease in the case of dentin surfaces without dentin conditioning. SEM micrographs showed an opening tubule appearance in the condition and/or primer treated dentin surfaces. Cohesive failures of dentin were observed in the case of dentin surface treated with conditioner. The adhesion failures of bonding were noted in the specimens without conditioner treating. In the cases of polished-enamel surfaces, the tensile bond strengths of both the original combination and non-primer treatment of LBS and SMP show a higher bond strength than any other combination. The tensile bond strength shows a significant decrease in the case of enamel surfaces without conditioning, especially SMP. SEM micrographs showed an etched appearance in the condition and/or primer treated enamel surfaces. Cohesive failures of enamel were observed in the case of dentin surface treated with conditioner. The adhesion failures of bonding were noted in the specimens without conditioner treating. The dentin primer pretreated hydroxyapatite showed an enhanced bonding capacity with bonding agent, especially in case of those primers and bonding agents containing adhering substances. The results indicate that acidic conditioners are necessary for high bond strength with either system and that MP can substitute KP and vice versa. Using manufacturers' directions, LBS gave higher dentin tensile bond strength than did SMP. Acidic conditioners are necessary for dentin bonding system and an adhesive-containing bonding agent might contribute to a higher bond strength.

Adhesion to mineralized tissue: Bonding to human dentin

We consider the conditions and demonstrable reactions which promote chemical bonding to human dentin. The desirability of developing durable adhesion to dentin is used as background for a discussion of feasible reactions to the dentin components, for possible use in new formulations. This is followed by a discussion of the demonstrable reactions found in the literature, as well as our own surface-sensitive IR work on the reaction between dentin protein and 2-hydroxyethyl methacrylate, an ingredient found in proprietary tissue replacement formulations.

The chemistry of enamel development.

The central problems of enamel biochemistry are the mechanisms concerned with initiation and development of the mineral crystals, together with their architectural arrangement within the tissue. These processes are mediated by the extracellular matrix as well as the composition of the mineral itself. Initial mineral deposition occurs at the dentine surface, nucleated either by dentinal components or early enamel matrix, possibly non-amelogenin molecules. The early crystals are small in size and rich in magnesium and carbonate resulting in relatively poor crystallinity. This is in spite of the fact that fluoride is high at this stage. Crystal development includes a reduction in magnesium, carbonate and fluoride as crystals increase in length following the retreating ameloblasts from the dentine. The matrix acquires increasing concentrations of amelogenin and albumin. Prismatic structure begins to develop together with some growth of crystals in width and thickness. Degradation of amelogenin and non-amelogenin molecules generates a series of specific molecular fragments possibly concerned with modulating crystal growth and morphology and the creation of prismatic and interprismatic structures. Towards the end of secretion, matrix, now almost completely degraded, is replaced by fluid followed by massive crystal growth during maturation. Degradation of albumin also occurs at this stage, probably as a result of comprehensive destruction of molecules which might impair crystal growth. Selective acquisition of magnesium and fluoride at this stage may reflect the hydrated state of the tissue as well as cell changes. Fluid is displaced as crystals grow and the enamel acquires concentrations of mineral characteristic of mature tissue.

Specific and charge interactions mediate collagen recognition by oral lactobacilli.

The mechanisms by which oral lactobacilli, one of the three major genera of cariogenic bacteria, attach to tooth surfaces are unknown. We hypothesize that recognition of collagen, the major component of dentin, may be a mechanism which localizes these bacteria to exposed root surfaces as well as to carious lesions which have penetrated the dentin. We found that the majority of oral Lactobacillus spp. strains recognize and bind collagen type I. Binding of 125I-labeled collagen type I to two strains of L. casei rhamnosus has been characterized in some detail. These strains were previously characterized with respect to their attachment to dentin (Switalski and Butcher, 1994). The process of 125I-collagen binding was mediated via specific as well as charge interactions. The putative adhesin-mediated (specific) interaction involved a limited number of bacterial surface components (2 x 10(3)/cell). Under conditions conducive for non-specific interactions (low ionic strength), the binding was higher by an order of magnitude. Collagen binding strains were found to adhere to collagen-coated surfaces, while strains unable to bind collagen adhered to a much lesser extent. Adherence of bacteria to collagen-coated surfaces could be competitively inhibited with collagen. These interactions may target collagen-binding strains of lactobacilli to dentin collagen in the oral cavity and thus play a role in the pathogenesis of root surface and/or coronal caries. Interference with this collagen-mediated attachment of lactobacilli may provide effective means of caries control, particularly in view of the fact that other oral acidogenic microbiota also interact with collagen.

Wound healing following demineralization of resected root ends in periradicular surgery

The objective of this study was to determine the effect of demineralization of resected root ends on the temporal and qualitative healing of the dentoalveolar (apical attachment apparatus) and alveolar (osseous) tissues in the excisional wound site created during periradicular surgery. Root end resections to orthograde gutta-percha obturations were performed on the mandibular premolars of six mongrel dogs. Twenty-four experimental root ends were demineralized by citric acid burnishing of the resected surfaces. The remaining 24 standard treatment root ends were not demineralized. Microscopic evaluations at postsurgical intervals from 4 to 45 days revealed that the demineralized root ends were associated with more rapid and complete healing than the nondemineralized root ends. It is proposed that demineralization enhances cementogenesis, the key to dentoalveolar healing, by removing the smear layer barrier and exposing the organic component (collagen fibrils) of resected cementum and dentin.

Auger electron spectroscopy of dentin: elemental quantification and the effects of electron and ion bombardment

Auger electron spectroscopy was used in this investigation to quantify the elemental composition of various dentin surfaces. The surfaces included the “smeared layer,” produced by abrasion, as well as surfaces prepared by fracturing in vacuum and in air. Quantification was aided by spectra obtained from standard samples of the two main components of dentin, hydroxyapatite, and collagen. Experimental conditions were found whereby the samples could be analyzed without conductive coatings. Ion sputter etch rates were measured for dentin, hydroxyapatite, and collagen. Under the conditions used here, it was observed that collagen etched at a rate approximately five times greater than hydroxyapatite. Auger spectra of the sputtered surfaces indicated significant ion beam-induced sample changes in collagen and dentin; no significant changes were found with hydroxyapatite. The results of this investigation demonstrate that Auger electron spectroscopy can be used to characterize dentinal surfaces and that ion sputtering can cause changes in the surface composition of dentin.

Dentine microstructure in hypoplastic deciduous teeth by collagenase etching

A new method is described for studying the microstructure of dentine by treating a polished surface with collagenase. The removal of collagen in this way allows high-resolution observation of the mineral component of dentine, and in this paper scanning electron micrographs are presented of dentine surfaces from , ‘normal’ teeth and caries-free hypoplastic teeth. In both cases, dentine is shown to consist of small rounded units ∼ 10–20 mn across which coalesce to form spheroids ∼ 100 nm in diameter which themselves aggregate to form a continuous mineral phase. The main difference between normal and hypoplastic teeth is that the inter-tubular dentine of the latter displays many more spaces, produced by the removal of greater numbers of collagen fibres from between the spheroidal particles. Thus the presence of less mineral would suggest that the carious process, once generated in such a tooth, may advance more rapidly than in normal teeth. The appearance of spheroids composed of smaller building units provides further evidence in support of the theory that calcification of dentine occurs at least in part by the apposition of mineral on the surface of calcospherites.

Effect of bleaching agents on inorganic components of human dentin and cementum

The effect of bleaching agents on the inorganic composition of human dentin and cementum was examined. Intact teeth were crushed, pulverized, and separated to dentin and cementum powders. The pulverized tissues were exposed to treatments with 30% H2O2, 3% H2O2, 2% sodium perborate in 30% H2O2, 2% sodium perborate in 3% H2O2, and 2% sodium perborate in bidistilled water for periods of 15 min and 1, 24, and 72 h. The degree of dissolution and the percentage of inorganic material for both dentin and cementum were measured. Thirty percent H2O2 and 2% sodium perborate in 30% H2O2 treatments significantly increased the solubility of dentin and cementum. The degree of dissolutions and the percentage of inorganic material remaining in the undissolved dentin and cementum increased with time progression. The greatest increase occurred with 30% H2O2 and 2% sodium perborate in 30% H2O2 after 24- and 72-h treatments. It is concluded that 30% hydrogen peroxide treatment may cause alteration in the chemical structure of the dentin and cementum making them more susceptible to degradation.

Effect of HEMA on bonding to dentin

The present study investigated the effectiveness of treating dentin with 2-hydroxyethyl methacrylate (HEMA) prior to application of an adhesive resin. The adhesive resin was 5% 4-methacryloxyethyl trimellitate anhydride (4-META) in methyl methacrylate (MMA) combined with poly-MMA powder. Polymerization of this resin was initiated by tri-n-butyl borane (TBB). Bovine dentin samples were ground with 600-grit Carbimet paper discs, and demineralized with either an aqueous solution of 10% citric acid/3% ferric chloride (10-3) or an aqueous solution of 10% citric acid (10-0). Improved bond strengths were achieved with HEMA treatment of bovine dentin samples, and improvement of bond strengths was dependent upon the time period of HEMA application. Scanning electron microscope (SEM) examination revealed the formation of a transitional zone of resin-reinforced dentin, termed the “hybrid” layer, in those specimens receiving 10-3 pre-treatment. The adhesive resin impregnated the exposed collagen bundles with which it entangled to create the “hybrid”, essesntial in the attainment of high tensile bond strengths. Specimens pre-treated with 10-0 did not readily form “hybrid” layers. However, if HEMA application followed the 10-0 pre-treatment, “hybrids” were demonstrated on SEM, and bond strength increased to 13 MPa. The ferric ions in the 10-3 effectively improved the diffusivity of dentinal substrates, as did HEMA. This study indicates that HEMA applied to dentinal substrates enhances monomer diffusion and entanglement with dentinal components, and facilitates the formation of a “hybrid” layers.

Adhesion to bovine dentin--surface characterization.

X-ray photo-electron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the dentin surface, to determine the effects of different pre-conditioning procedures on the elemental composition of the dentin surface, and to investigate the interaction between dentin and a dentin bonding agent (ScotchBond) by studying the changes in the elemental composition of dentin as a result of the interaction. Scanning electron microscopy (SEM) was used to characterize sample surface morphology, which was then correlated with surface elemental composition. The results showed that: (a) the elemental composition of the smear layer was similar to that of the underlying dentin; (b) cleaning with hydrogen-peroxide did not produce any modification in the elemental composition of the dentin surface; and (c) acid-etching led to an almost complete demineralization of the dentin, leaving behind an organic-rich surface. The results suggest that bonding systems that use acid-etching as a pre-conditioning procedure should be based on agents able to interact with the organic components of dentin, since bonding agents that rely on a chelation-to-calcium reaction are unlikely to be successful. The investigation of the interaction between the bonding agent and dentin led to a postulated adhesive-bonding reaction mechanism and suggested a partially cohesive failure in the bonding agent during fracturing of a dentin-bonding-agent-bonded assembly.

11. Resorption of both inorganic and organic components of dentine and bone by osteoclasts in vitro

11. Resorption of both inorganic and organic components of dentine and bone by osteoclasts in vitro

Evidence for an inhibitor of osteoclast attachment in dentinal matrix

The ability of osteoclasts to colonize in vitro different preparations of dentin extracted with guanidinium hydrochloride (GuHCl) was studied in order to establish morphological evidence for an extractable inhibitor of osteoclast spreading within dentin. Osteoclasts were isolated from neonatal rats and seeded onto pieces of fully mineralized dentin, demineralized dentin and predentin extracted with GuHCl. Osteoclasts were also seeded onto unextracted tissues. The results were evaluated with scanning electron microscopy. Osteoclasts colonized and resorbed fully mineralized dentin, whereas clastic cells were not observed on unextracted demineralized dentin and predentin. In contrast to this, osteoclasts attached and spread on demineralized dentin and predentin extracted with GuHCl. It was concluded that the non-collagenous organic component of dentin contains an extractable inhibitor of osteoclastic attachment and spreading. It is tempting to speculate that the inhibitor may be responsible for the naturally occurring resistance of dentin to resorption.

Immunohistochemical localization of α2HS glycoprotein in dentinHS 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.