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

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.

X-ray crystallography of incisor enamel from red kangaroo.

X-ray powder diffraction of red kangaroo (Macropus rufus) dental enamel, with a relative density greater than 2.60, showed a longer a-axis length of the apatite unit cell, a = 9.462 A, a shorter c-axis length, c = 6.877 A, and a smaller crystallite size, ca. 185 A, than those of human dental enamel. The a-axis of red kangaroo dental enamel was one of the longest among the values reported previously, whereas the c-axis was one of the shortest. The crystallite size was almost equal to that of dentin crystallites. It is suggested that the chemical composition of the dental enamel apatite of the red kangaroo is markedly substituted, resulting in lattice distortion.

Effects of fluoride on matrix proteins and their properties in rat secretory enamel.

This publication concerns the selective adsorption of rat enamel proteins onto hydroxyapatite, their solubility in aqueous solutions, and the effect that systemic fluoride has on these properties. The enamel proteins used as adsorbates were extracted in 0.5 mol/L acetic acid from the secretory enamel of the upper and lower incisors of SD rats (females, 200-220 g body weight). Equilibration of the proteins with hydroxyapatite was performed in two solutions: (i) 50 mmol/L acetate buffer at pH 6.0 and 0 degrees C, and (ii) 50 mmol/L Tris buffer containing 4 mol/L guanidine at pH 7.4 and room temperature. Enamel was dissected from animals, which were given either de-ionized water (control group) or water containing 25, 50, 75, or 100 ppm fluoride as NaF for four weeks. From these enamel samples, the proteins were extracted in sequence with 160 mmol/L NaCl and 3 mmol/L phosphate (pH 7.3), 50 mmol/L carbonate buffer (pH 10.8), and finally, with 0.5 mol/L acetic acid for dissolution of the enamel mineral. The F, Ca, and P contents of the various enamel samples were determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Optical quantification of caries-like lesions in vitro by use of a fluorescent dye.

An experimental method was developed for measurement of the fluorescence intensity of a dye that was introduced into caries-like lesions in vitro. A distinct pattern of change of fluorescence intensity with time appeared, displaying a plateau value and a peak value for each measurement. Both plateau and peak values showed a linear correlation with calcium loss, as measured with longitudinal microradiography. The correlation coefficients were r = 0.87 for plateau values and r = 0.89 for peak values. The difference in scattering by dry and wet caries lesions was also measured with the same equipment, which showed a linear correlation with calcium loss of r = -0.53.

Prevention of enamel demineralization adjacent to glass ionomer filling materials.

In order to study the release of fluoride and prevention of enamel demineralization by different filling materials, standardized cavities were prepared in 80 extracted human molars. The cavities were filled as follows: 1. Fuji II F; 2. Ketac-Fil; 3. Ketac-Silver; 4. Silar. Twenty molars were used as controls (no filling). Enamel slabs with the fillings were subjected to 9 days of demineralization (30 min daily) and remineralization (artificial saliva, replaced daily). Fluoride release in the saliva was determined on days 1, 3, 5, and 9. Enamel fluoride content adjacent to the cavities was determined initially and after the de-remineralization using the acid etch technique. On day 1, the largest amount of fluoride in the saliva was released by Fuji, but on day 9 the largest amount was released by Ketac-Fil. Ketac-Silver released significantly less fluoride than Fuji and Ketac-Fil. The average initial fluoride content of enamel was 2200 ppm. After the test period, fluoride contents adjusted for biopsy depth were 1822, 1690, 1693, 1337, and 888 ppm in groups 1-5, respectively. The amounts of phosphorus dissolved by the second acid etch were 28.9 (SE 2.6), 30.2 (2.0), 34.4 (2.8), 44.1 (2.7), and 42.2 (2.4) micrograms, respectively. Softening of surface enamel during the test period was clearly reduced in teeth filled with Fuji and Ketac-Fil. The results show that glass ionomer materials release considerable amounts of fluoride and prevent demineralization of the adjacent enamel in vitro. Fuji and Ketac-Fil seem to be more effective than Ketac-Silver.

Thermal decomposition of developing enamel.

The decomposition of forming, maturing, and mature enamel was studied between room temperature and 1,000 degrees C by powder X-ray diffraction and infrared absorption methods. In mature dental enamel, carbonate decomposition proceeds relatively fast until 500 degrees C and at a slower rate beyond it. In forming and maturing enamel, decomposition is faster and is completed around 800 degrees C. The formation of beta-Ca3(PO4)2 is observed in dental enamel at 500 degrees C. At 1,000 degrees C, the apatite phase in forming and maturing enamel transforms almost completely to beta-Ca3(PO4)2, whereas in mature enamel, even at 1,000 degrees C, only partial decomposition occurs. Infrared results show the appearance in dental enamel of (1) A-type carbonate at room temperature and in the 500-900 degrees C range, in addition to the commonly observed B-type carbonate, and (2) intermediate CO2 molecules during carbonate decomposition (200-500 degrees C).

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.

[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.

Properties of phosphorylated 32 kd nonamelogenin proteins isolated from porcine secretory enamel.

Enamel proteins were isolated from specific locations of permanent porcine incisors at various developmental stages, namely, the outer (young) and inner (old) secretory, and maturing (chalk-like in appearance) enamel. The selective adsorption of these matrix proteins onto hydroxyapatite (HA) crystals was investigated in the presence of dissociative agents. The results showed that the proteins with the highest adsorption affinity were present at the highest concentration in the vicinity of the ameloblasts, i.e., in the outer enamel layer; a substantial reduction of these proteins was observed in the older (inner) secretory enamel and in the tissue in the maturing stage. An interesting finding was that a group of proteins having molecular masses of 32 kd present only in the inner secretory enamel, adsorbed strongly onto the HA crystals and were potent inhibitors of HA crystal growth. This 32 kd group contains phosphorylated glycoproteins; they are rich in Pro, Glu, Gly, and Asp and the N-terminal sequence was LXQVPGRIPPGYGRPPTP-, having no resemblance to the reported sequences of amelogenins. It was also found that the 32 kd moieties remained only as trace constituents in the maturing enamel, suggesting that most of them were removed as soluble constituents in the tissue fluid or further degraded by enzymatic activity during the late secretory stage. The results obtained support the view that amelogenetic mineralization is regulated by the presence of various organic matter and, importantly, that their efficacy as inhibitors of mineralization may be modulated through their degradation.

Evaluating residence patterns among prehistoric populations: clues from dental enamel composition.

We determined enamel composition (Ca, P, Mg, Cu, Mn, Se, Zn, Al, Sr, Pb) for the mandibular canines of 94 individuals from 4 prehistoric Arikara cemetery populations, collecting the compositional data using scanning electron microscopy energy dispersive x-ray analysis. We examined each of the four samples independently and then pooled them for a group comparison using correspondence analysis. The results indicate significant intrapopulational dispersal, particularly when viewed by age and sex subgroups. When all sites are included for correspondence analysis, a distinctive pattern of adult male dispersal compared to the more tightly clustered adult female and subadult subsample is apparent. We hypothesize that the observed pattern of dispersal indicates local geographic and possible dietary differences among the groups. Furthermore, we hypothesize that the observed differences between males, and females and subadults for each site are the result of a residence pattern of out-migration for males.

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.

Fluoride analysis in nanoliter- and microliter-size fluid samples.

A variety of techniques is described for measuring fluoride in volumes of from 0.005 to 5 microL, including: (1) micropipette procedures for transference and dilution of samples, (2) construction of miniature and micro fluoride-selective electrodes, and (3) methods for adapting standard electrodes for micro- and semi-micro volumes. These described techniques have a number of advantages, including speed of analysis, high accuracy, and adaptability to many types of fluid samples. Recent studies involving use of these procedures include the analysis of fluoride in: (1) plaque fluid samples from single sites before and after topical fluoride administration, (2) tooth mineral samples recovered by acid-etch or microdrill biopsy of enamel, and (3) fluid recovered from the interior of the tooth during simulation of the caries process.

Influence of fluoride on in vitro remineralization of artificial subsurface lesions determined with a sandwich technique.

Remineralization experiments of bovine enamel with subsurface lesions were carried out with the use of a sandwich technique. The remineralizing solutions contained no or 2 ppm fluoride added to the solution. The amount of remineralization was determined after remineralization periods up to 324 by means of quantitative microradiography. After 84 h the group with fluoride showed significantly (p less than 0.05) less remineralization than the nonfluoride group. This inhibition of fluoride on the remineralization may be explained by the inhibiting effect that fluoride at certain concentrations has on the crystal growth of apatites.

[The development of initial enamel caries--a phenomenon of interfacial reactions]. / Die Entwicklung der initialen Schmelzkaries--ein Phänomen von Grenzflächenreaktionen.

The investigation deals with earliest chemical changes in outermost enamel surfaces during initial caries development. After in vitro demineralization of enamel samples in acidulated hydroxyethylcellulose solution (pH = 5.1) for periods between 1 and 288 h the Ca/P molar ratios were determined in depths of 0.04 micron using the Rutherford Backscattering spectroscopy. The measured Ca/P ratios oscillate around the initial value. This behaviour is interpreted as a combined de/remineralization process.

Fluoride and mineral redeposition in outermost layers of bovine enamel during surface softening.

Mineral and fluoride concentration changes in the outermost layers of bovine enamel (depth less than 1 micron) were measured after demineralization in unbuffered hydroxyethylcellulose gels of pH = 5.4 with an intrinsic fluoride concentration of about 0.02 ppm. A combination of two nuclear analytical techniques, Rutherford backscattering spectrometry (RBS) and proton-induced gamma ray emission spectrometry (PIGE) was applied to determine the Ca/P molar ratios and F depth profiles, respectively. When compared to deeper layers, a reduced loss of mineral content is observed for the depth range of about 0-0.1 micron corresponding well with a F concentration increase from about 500 to about 5,000 ppm in the same range. These findings are interpreted as a fluoride-induced partial remineralization of the superficial surface layer during an overall demineralization process.

Effect of a strontium complex on fluoride uptake by artificial caries lesions and sound enamel in vitro.

The effect of a strontium-polyacrylate complex on fluoride uptake by bovine enamel was determined. A salivary pellicle was formed on sound enamel and enamel with artificially formed caries lesions. Ten specimens of each were treated with solutions containing (A) 225 ppm F, (B) 225 ppm F plus Sr complex, (C) 200 ppm F, 0.1 M phosphate, pH 4.5 or (D) placebo for 1 h and then washed 24 h to remove labile fluoride. Analysis of ten thin layers of enamel showed that, on both enamel types, solution (C) deposited the largest amount of fluoride. The strontium complex decreased fluoride deposition, particularly in the outermost layer.

Comparison of lead levels in human permanent teeth from Strasbourg, Mexico City, and rural zones of Alsace.

A comparative study of the mean lead concentrations in enamel and dentin of human premolars and permanent molars was conducted by means of a systematic sampling procedure with energy-dispersive x-ray fluorescence analysis. In a first series of analyses, no significant statistical differences in mean lead concentrations at various levels of enamel and dentin were noted between young patients of Strasbourg and those of small villages of Alsace, nor between elderly patients living in these two locations, despite the fact that motor traffic was significantly lower in the rural zones. However, in both locations, a significantly higher concentration of lead was observed in enamel and dentin in relation to age. In a second series of analyses, the mean lead concentrations of both dental hard tissues of premolars and permanent molars of young individuals from Strasbourg, rural Alsace, and Mexico City were compared. Significantly higher mean lead concentrations were found in enamel and dentin samples from Mexico City. This was most evident for inner coronal dentin (5.7 and 6.1 times greater than in teeth of Strasbourg and rural zones of Alsace, respectively) and for pulpal root dentin (6.9 and 8.9 times greater than in teeth of Strasbourg and rural zones of Alsace). It is proposed that the higher lead concentrations are related to the higher lead content of motor gasoline and to more intense traffic conditions. The dental hard tissues appear to be of value for the study of environmental lead pollution.

Biochemical characterization of stable high molecular-weight aggregates of amelogenins formed during porcine enamel development.

Analysis of the enamel matrix during porcine tooth formation has revealed a number of high molecular-weight (Mr) enamel proteins (greater than 30 kDa), which are related to the major amelogenins (20-26 kDa). To examine the nature of these proteins, amelogenins were extracted and separated by conventional gel filtration and reverse phase HPLC. Many of the proteins in the high Mr fraction reacted with a polyclonal antibody, affinity-purified against a mixture of 20-26 kDa amelogenins. Another antibody, affinity-purified against a fraction containing the LRAP, reacted with amelogenins 30-36 kDa in size but not with amelogenins 40 kDa or larger, indicating that the high Mr amelogenins were a heterogeneous group of enamel proteins. Analysis of amino acid composition and N-terminal amino acid sequence, as well as PASGE of electrophoretically eluted proteins, indicated that the high Mr amelogenins were aggregates of various major amelogenins. Three amelogenin aggregates (43, 40 and 32 kDa) isolated by electrophoretic elution were less stable at 100 degrees C in SDS-containing buffer than at 60 degrees C. In contrast to the major amelogenins, which are found in constant proportions throughout enamel development, the high Mr amelogenins appeared to increase in maturing enamel relative to the total matrix protein. Thus, at least in the pig high Mr amelogenins appear to be naturally occurring, stable aggregates of major amelogenins. It is proposed that amelogenin aggregation occurs as a consequence of the diminishing spaces between growing crystals in maturing enamel.

[The use of an improved method of comparative dispersion of birefringence for research on dental enamel mineralization]. / Primenenie usovershenstvovannogo metoda sravnitel'noi dispersii dvuprelomleniia dlia issledovanii mineralizatsii émali zubov.

A number of modifications were made in the double refraction comparative dispersion techniques, permitting a quantitative analysis of apatites. These modifications are related to some features of monochromator employment, to the method of the compensator graduation, and to the mathematical processing of the measurement results, and they have essentially simplified the original technique and made it more reliable. The study has revealed that applications of 3% remodent solution followed by coating the teeth with 3% remodent-containing cyanacrylate lacquer increase calcium content in the enamel by 1.03-1.28%. Treatment with fluoride lacquer results in a lesser rise of Ca content, and single applications of 3% remodent solution are conducive to but a negligible increase of Ca content in the enamel surface layer only within the first day after exposure. Combined application of remineralization means increased phosphorus content in the enamel surface layer as well.