Determinaciones de algunas propiedades termofísicas del esmalte y la dentina / Determination of some termophysical of dental enamel and dentin

La prevención de caries mediante la aplicación de métodos físicos, entre ellos la radiación láser, requiere de una caracterización detallada de las propiedades de los tejidos dentarios duros. Algunas propiedades importantes son las termofísicas, dentro de las cuales la densidad y el calor específico han sido determinados en el presente trabajo. Estos valores obtenidos pueden servir no sólo para las investigaciones en relación con el láser sino también para otras líneas relativas a tejidos duros del diente

Chondrocyte-like colony formation of mesenchymal cells by dentin extracts in agarose gel culture.

In this study, the effects of guanidine extracts from demineralized bovine dentin matrix on rat mesenchymal cells were investigated by use of an agarose gel culture. The dentin extracts were divided into water-soluble and -insoluble fractions. Rat mesenchymal cells obtained from the cultivation of skeletal muscle tissue and embedded in agarose gel were treated with these two fractions. After three weeks of cultivation, the treated cells formed colonies that were stained metachromatically with toluidine blue in a dose-dependent manner. The activity necessary to form chondrocyte-like colonies by the water-insoluble fraction was significantly higher than that by the water-soluble fraction. Each chromatographic fraction of the water-insoluble part of dentin extracts on tandem Sephacryl S-200 High-resolution columns was also investigated. Chondrocyte-like colony-forming activity was concentrated in a single fraction. However, the electrophoretic pattern of this fraction revealed that there were still some bands of molecular weight between 18 and 30 kDa. According to the Western blot analysis of this fraction, there was a band corresponding to purified transforming growth factor beta (TGF-beta) under the non-reducing condition. After reduction, this band disappeared and we found a band corresponding to a component of 13 kDa as well as TGF-beta. These findings suggest that TGF-beta is present not only in bone but also in the dentin matrix.

Wavelength-independent microradiography: a method for non-destructive quantification of enamel and dentin mineral concentrations using polychromatic x-rays.

Wavelength-independent Microradiography (WIM), described in this paper, used polychromatic, high-energy (less than or equal to 60 kV) x-rays for determination of mineral concentrations in tooth material non-destructively. This was done with the aid of a reference step-wedge made of 94% aluminum, 6% zinc. The mass attenuation coefficient of this material has a wavelength-independent ratio to the mass attenuation coefficients of enamel and dentin. With this method, mineral concentrations of enamel and dentin samples, with a thickness up to 500 microns, were determined at 20- and at 60-kV tube voltage. The samples were demineralized for 72 and 144 h and measured again. Comparison of the data showed that mineral quantification was within 1.5%, independent of the x-rays used. Finally, these mineral concentrations--obtained from the Wavelength-independent Microradiography--were compared with measurements of the same samples by Longitudinal Microradiography. A correlation of 0.99 was found for enamel and one of 0.96 for dentin.

Quantitation of growth factors IGF-I, SGF/IGF-II, and TGF-beta in human dentin.

Human bone matrix is known to contain a battery of polypeptide growth factors. Since dentin is a mineralized tissue similar to bone in composition and perhaps in formation, human dentin was assayed for the presence of similar growth factors. Root dentin proteins were extracted by demineralization in 4 M guanidine hydrochloride (Gu) and 30 mM Tris (pH 7.4) containing 20% EDTA and proteinase inhibitors. Gu-EDTA extracts were desalted and used for the following assays: (1) bone cell proliferation in chick calvarial cell mitogenic assay using the incorporation of [3H]thymidine into TCA-insoluble material; (2) osteocalcin by radioimmunoassay (RIA); (3) insulin-like growth factor I (IGF-I) by RIA; (4) skeletal growth factor/insulinlike growth factor II (SGF/IGF-II) by radioreceptor assay; and (5) transforming growth factor beta (TGF-beta) by bioassay. Gu-EDTA extracts stimulated bone cell proliferation. At 10 micrograms/ml, dentin proteins increased the incorporation of [3H]thymidine by calvarial cells to 320% of that by BSA-treated control cells. Consistent with the presence of mitogenic activity, growth factors were found in dentin in the following concentrations (ng/micrograms Gu-EDTA protein): (1) IGF-I, 0.06; (2) SGF/IGF-II, 0.52; and (3) TGF-beta, 0.017. All three growth factors were present in concentrations lower than that found in human bone. Osteocalcin was detected at a concentration of 3.0 mg/g Gu-EDTA protein, also much lower than that in bone.

Rat incisor dentine contains a factor which alters the phenotypic expression and stimulates chondrogenesis in fibroblast-like cells in vitro.

A low molecular weight protein fraction isolated under dissociative conditions during the demineralization of rat incisor dentine has the ability to modulate, in culture, the expression of fibroblast-like cells explanted from neonatal rat muscle. The protein fraction enhances the incorporation of 35S-sulphate into a proteoglycan larger in weight than that produced by the uninduced cells; furthermore it induces the production of type II collagen. These changes take place in the absence of cell proliferation as measured by 3H-thymidine incorporation. The altered fibroblast-like cells form nodules and secrete an abundant extracellular matrix which stains for proteoglycan after 7-9 days in culture. These data show that the dentine matrix does contain a factor which can initiate a mitogenesis-independent alteration in the expression of the muscle-explant outgrowth cells. Those changes are consistent with a shift to a chondrogenic mode.

Validity and interpretation of blood lead levels: a study of Danish school children.

Blood lead concentrations were measured in a group of children from a group of 9- to 10-year-old school children in Aarhus, Denmark. The study group was selected as a high-level and a low-level lead group, as identified by the lead concentration in the circumpulpal dentine in deciduous teeth shed 2-3 years previously. The validity of the blood sampling technique was investigated in adult volunteers, and lead was determined by electrothermal atomic absorption. Capillary blood sampling by a finger-stick method was preferred, as the slight contamination caused by this technique was deemed acceptable. The children with the highest dentine lead levels (n = 70), had blood lead concentrations of 0.08-0.63 mumol/l and a geometric mean of 0.28 mumol/l. The children with lowest dentine levels (n = 76) had blood lead concentrations of 0.08-0.70 mumol/l and a geometric mean of 0.18 mumol/l. The blood lead concentrations were compared with interview data on behaviour, family habits, diet, parents' tobacco smoking and occupation, water lead measurements, and traffic counts. A total of 20% of the variation in blood lead was explained by parents' tobacco smoking, the child's number in the sibship, gender, and consumption of canned food at home.

[States of dentine surface and interface between dentine and coupling agent].

In order to research the states of dentine surface and dentine surface primed with coupling agent, we used microscope, transmission electron microscope (TEM) and solid fluorescence method. Observed under microscope, patterning of dentinal tubules and their poles was very explicit; through the view of interface between coupling agent adsorbed and human dentine powder by TEM, it was revealed that the coupling agent was adsorbed onto the dentine surface as if it "grew out" of the dentine surface; through examination of interface between the coupling agent adsorbed and dentine surface by fluorescence spectrum, which differed from that of the coupling agent or dentine surface, i.e., this fluorescence spectrum of interface changed obviously (red shift). This phenomenon indicated that there was a chemical reaction occurring between tooth surface and adsorbed coupling agent. Therefore we can conclude that the three examinations are necessary to provide the argument for establishment of chemical bonding mechanism between dentine and coupling agent.

The inorganic components of cementum- and enamel-related dentin in the rat incisor.

Recently, we have shown that, in rodent incisors, the crown- and root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and PO4 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and PO4 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content.

Transmission electron microscopic characterization of hypersensitive human radicular dentin.

Transmission electron microscopy (TEM) and x-ray microanalysis (XMA) were used for the study of the ultrastructure of the lumens of dentinal tubules in superficial layers of dentin specimens obtained by use of a new biopsy technique from both hypersensitive and naturally desensitized areas of exposed root surfaces, in vivo. The TEM images showed clearly that the lumens of most of the tubules were occluded with mineral crystals in naturally desensitized areas, but such lumens were empty and surrounded with peritubular and intertubular dentin in hypersensitive areas. Moreover, electron-dense structures that lined peritubular dentin were observed in the empty lumens of dentinal tubules.

Visualization of glycosaminoglycans in rat incisor predentin and dentin with cetylpyridinium chloride-glutaraldehyde as fixative.

Using cetylpyridinium chloride (CPC) in glutaraldehyde as fixative, we observed sinuous fiber-like structures 300-500 nm long and 7-14 nm thick in the spaces between the collagen fibers of rat incisor predentin. Small granules and fibrils were also detected. Electron-dense vesicles were seen inside the odontoblast processes. The plasma membrane was irregularly stained with material that adhered to its surface. In demineralized dentin, needle-like structures were seen at the periphery of globular structures which were not stained. Staining the sections with Alcian blue did not greatly improve the visualization of CPC-precipitated glycosaminoglycans. The specificity of staining was assessed on serial sections by selective dissociation of glycosaminoglycan aggregates with 2 M calcium chloride and their digestion by bovine testicular hyaluronidase. The glycosaminoglycans were probably combined with lipids, because treatment of the sections with a chloroform/methanol mixture removed the CPC-induced precipitates from both predentin and dentin.

Dentin dysplasia type II: absence of type III collagen in dentin.

A three-generation family with dentin dysplasia (DD) Type II is presented. Affected family members share common radiologic features with clinically varied expression of tooth discoloration and occlusal wear. Both the primary and the permanent dentition appear to be affected. No generalized connective tissue involvement is found. The mode of inheritance is autosomal dominant. Histologically, the findings are consistent with DD Type II. In indirect immunofluorescence, the irregular radicular dentin of an affected permanent tooth failed to stain with specific antibodies against Type III collagen and the N-terminal propeptide of Type III procollagen.

[Comparison of organic dentin matrix composition between bovine permanent and deciduous teeth].

Minor differences in chemical composition of permanent and deciduous teeth have been suggested, however, clear data on the difference in organic composition have not yet been established. In the present study, organic dentin matrix components of bovine permanent and deciduous teeth were investigated. Bovine permanent and deciduous dentin were obtained from respective incisors and divided into crown and root. They were crushed into powder and extracted with 4M guanidine-HCl (G-extract), and then with 0.5 M EDTA, 4M guanidine-HCl (E-extract). E-extracts from permanent crown and root dentin and also deciduous crown and root dentin were separately applied to DEAE-cellulose column and each peak was examined precisely by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). A quantitative difference in organic matrix composition was recognized between permanent and deciduous dentin. Furthermore, a non-collagenous protein fraction, which existed in permanent teeth but not in deciduous ones, was discovered. This protein was purified as a single band in SDS-PAGE, which demonstrated an apparent molecular weight of approximately 30 Kd. Its amino acid composition was analyzed and the nature of this protein was discussed.

[The effect of pulp extirpation on the function of the hard dental tissues]. / Vliianie depul'pirovaniia na sostoianie tverdykh tkanei zuba.

The authors analyze the results of clinical and experimental studies of the status of hard dental tissues before and after pulp removal. The findings evidence that Ca and P levels reduce and O2 and oxide levels increase in the hard tissues of pulpless teeth, this probably resulting in changed color and friability of pulpless teeth. These data may be useful in dental surgery when forming carious cavities in pulpless teeth and in orthodontics to make pulp insertions with due consideration for the friability of pulpless teeth.

In vivo fluoride uptake in enamel and dentin from fluoride-containing materials.

The ability of fluoride-containing materials to deposit fluoride into the cavity walls could be a measure of their anticariogenic properties. Great penetration depths of fluoride were found in all groups in this study, with deeper penetration in dentin compared to enamel.

Learning disabilities in children: significance of low-level lead-exposure and confounding factors.

The hypothesis that low-level lead absorption is a risk factor for learning disabilities in school children was examined in the municipality of Aarhus, Denmark. During 1982-1983, a total of 1,302 children in the first grade (54% of the eligible population) delivered shed deciduous teeth. The lead concentration in the circumpulpal dentin was used as an indicator of the cumulated lead absorption, and 200 cases (high-lead) and controls (low-lead) were selected, and matched for socioeconomic group and gender. The parents were interviewed regarding the child's development and past medical history. Possible confounders were identified and controlled for in a logistic multivariate model. The influence of lead absorption became statistically significant only after exclusion of the children with proven medical risk factors, thereby the adjusted odds ratio in the weighted analysis was changed from 2.2 to 4.3. Thus, in a Scandinavian low-level lead-polluted area, lead absorption appears to be a risk factor for learning disabilities.

An analysis of paramagnetic centers in irradiated dentin using electron spin resonance.

The ESR spectra produced in irradiated dentin have been studied over a range of incident radiation energies from 50 kVp to 25 MVp. The behavior of the dentin ESR signal strength is similar to that of enamel as a function of the energy of the incident radiation. The magnitude of the dentin ESR signals are, however, up to 10 times smaller than the signals of dental enamel for a given radiation energy. The possible contributions of radiation interaction coefficients, chemical structure, and crystallite size to the differences in ESR spectra are discussed.

Immunohistochemical localization of glycosaminoglycans and proteoglycans in predentin and dentin of rat incisors.

We examined immunocytochemically the type and distribution of glycosaminoglycans and proteoglycans (PG) in predentin and dentin demineralized with EDTA after aldehyde fixation of rat incisors using (a) four monoclonal antibodies (1-B-5,9-A-2,3-B-3, and 5-D-4) which recognize epitopes in unsulfated chondroitin (C0-S), chondroitin 4-sulfate (C4-S), chondroitin 6-sulfate (C6-S), and keratan sulfate (KS) associated with the PG, and (b) monoclonal (5-D-5) and polyclonal antibodies specific for the core protein of large and small dermatan sulfate (DS) PG. Light microscope immunoperoxidase staining after pre-treatment of tissue sections with chondroitinase ABC localized the majority of stainable PG (C4-S, KS, DSPG, C0-S, and C6-S) in predentin and, to a lesser extent (C4-S and small DSPG), in the dentin matrix. The former site demonstrated relatively homogeneous PG distribution, whereas the latter site revealed that strong staining of C4-S and small DSPG was confined mostly to dentinal tubules surrounding odontoblastic processes, with only weak staining in the rest of the dentin matrix. These results indicate that there is not only a definite difference between PG of predentin and dentin but also a selective decrease in the concentration or alteration of these macromolecules during dentinogenesis and mineralization.

Purification of rabbit bone morphogenetic protein derived from bone, dentin, and wound tissue after tooth extraction.

Bone morphogenetic protein (BMP) was extracted from bone matrix, dentin matrix, and wound tissue after tooth extraction in rabbits, and purified. These purified fractions were shown to be homogeneous by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE), and induced new bone in situ in 3 weeks when implanted into the calf muscles of Wistar rats. The dentin matrix-derived BMP was different from the other two types in molecular weight and the properties revealed in the process of purification. However, each tissue-derived BMP was shown to induce new bone growth in a bioassay of xenogenic implantation. For this reason, BMP is thought to have subunits with certain commonalities in different tissue.

Chemical and crystallographic events in the caries process.

The chemical and crystallographic events associated with the caries process can be described based on the results from the following studies: (a) effects of carbonate, magnesium, fluoride, and strontium on the physico-chemical properties--lattice parameters, crystallinity (crystal size and strain); dissolution properties of synthetic apatites; (b) factors influencing the in vitro formation and transformation of DCPD, OCP, AP (Ca-deficient apatites), FAP, beta-TCMP (Mg-substituted), and CaF2; and (c) studies on properties (crystallinity, composition, chemical, and thermal stabilities) of enamel, dentin, and bone. The dissolution of CO3-rich/Mg-rich/F-poor dental apatite crystals and re-precipitation of CO3-poor/Mg-poor/F-rich apatite in the presence of F- ions in solution contribute to a more acid-resistant surface layer of the caries lesion. Fluoride promotes the formation of less Ca-deficient and more stable apatite crystals. The presence of Ca, P, and F in solution inhibits dissolution of apatite more than does the presence of F alone. Low levels of F in solution promote the formation of (F, OH)-apatite, even under very acid conditions; an increase in F levels causes the formation of CaF2 at the expense of DCPD or apatite, especially in acid conditions. F in apatite and/or in solution suppresses extensive dissolution of dental apatite and enhances the formation of (F, OH)-apatite crystals which are more resistant against acid-dissolution than are F-free apatite crystals.