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At least 109 records · Page 6Linked to original sources
PubMed1994

Heat-treatment-induced reduction in the apparent solubility of human dental enamel.

Holcomb and Young (1980) have shown a significant increase in human dental enamel (HE) structural order resulting from heat treatment in the temperature range of from 275 to 400 degrees C. Also, previous work in our laboratory had shown dramatic decreases in the initial dissolution rates (IDRs) of both carbonated apatite (CAP) heated at similar temperatures (from 300 to 500 degrees C) and HE exposed to CO2 laser irradiation for which calculated surface temperatures were in this same range. We hypothesize that thermal treatment shifts the apparent solubility distribution profile of HE toward lower apparent solubilities, paralleling the observed increased in crystal structural order and the decrease in IDRs. Powdered HE was heated in a furnace at temperatures ranging from 150 to 500 degrees C for 24 hours. The apparent solubility distributions of both heated and unheated HE powders were measured by equilibration for 24 hours in a series of partially saturated solutions simulating various amounts of HE dissolved in a pH 4.5 dissolution medium. The apparent solubility distribution for the unheated HE showed a peak at KHAP [the ion activity product based on the Ca10(PO4)6(OH)2 stoichiometry] of 10(121.0). Heat treatment shifted the apparent solubility distribution to lower solubilities. The peak KHAP values were approximately 10(124.8) at 200 degrees C; approximately 10(127.8) at 300 degrees C; and approximately 10(-129.1) from 400 to 500 degrees C. This approximately 8 orders of magnitude decrease in KHAP for HE heated at from 400 to 500 degrees C correlates with the previously observed reduction in the IDR driving force for laser-treated HE experiencing a similar surface temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Apatites↗
PubMed2002

[Characteristics of dental enamel and its resistance to caries].

Systematical research of basic texture characteristics (specific surface area, specific volume and size of micro-, meso- and macropores, porosity) of intact dental enamel of persons with various degree of resistance to caries has been performed using methods of adsorption and Hg-porosimetry. Studied objects have been shown to be small-porous (total porosity epsilon = 4-6%), roughly-dispersed (specific surface S6ET = 0.7-1.5 m2/g) materials. Regularities of changes of specific surface and porous structure in researched samples have been established. More mesoporous enamel structure has been shown to form in the series of samples varying from high level of resistance to very low level. Meanwhile intact dental enamel has the same degree of macroporosity irrespective of the level of its resistance to caries. Micropores within the samples have been established to be heterogenous and their volume to be very insignificant (2-4 x 10(-9) m3/g). Substantiation of various degree of resistance of intact dental enamel to carious process has been suggested within the framework of structurally-geometrical approach.

Adolescent↗
PubMed2003

[Study of thermal stability of intact dental enamel in subjects with different levels of caries resistance].

Thermal stability of intact dental enamel was compared by combined TH-DTH-DTA analysis in subjects with different caries resistance. Thermal stability was found to depend on the presence and degree of organic and inorganic components stability. The content of organic phase virtually was virtually the same in samples with different levels of resistance, which was confirmed by the fact that oxidative destruction of organic substances in intact dental enamel took place at the same temperatures in samples of all resistance levels.

Adolescent↗
PubMed1976

[Ultrastructure of conditioned enamel surfaces and their adhesive matrices in dental enamel sealing].

The enamel sealant Nuva Seal was tested in model tests on caries-free human molars and premolars. Under the scanning electron microscope the acid-etched enamel areas (natural and ground surfaces) and the corresponding Nuva Seal matrices were studied. In the evaluation, the surface reliefs of the objects were compared. Thus, information on flow capacity, wetting and polymerization behavior of the adhesive was obtained. Evaluation of pairs of stereo pictures of the inverse surface reliefs in the enamel/adhesive contact zone suggests that the sealant has an average measurable depth of penetration of 7 mum. Peg-shaped elevations 10-20 mum in size that can sometimes be observed in the Nuva Seal impressions are interpreted as representing enamel defects.

Bicuspid↗
PubMed1993

[The effect of rare earth metal-containing toothpastes on dental enamel solubility in vitro].

The effect of different REE containing toothpastes has been studied on human dental enamel, in an experimental model, using diluted suspensions of toothpastes. The grade of remineralization has been characterised by the amount of dissolved phosphorus from the enamel samples. All the investigated-, REE containing toothpastes decreased the acid-solubility of dental enamel, the best results were found in the group of samarium-containing toothpastes.

Dental Enamel Solubility↗
PubMed1999

In vitro study of the Nd:YAG laser effect on human dental enamel: optical and scanning electron microscope analysis.

OBJECTIVE: The Nd:YAG laser irradiation of dental enamel was evaluated in enamel demineralization experiments in a Streptococcus mutans culture media. SUMMARY BACKGROUND DATA: Previous studies had shown that a continuous wave Nd:YAG laser at an energy of approximately 67 mJ may induce an increased acid resistance in human dental enamel when exposed to severe demineralization conditions. METHODS: Enamel windows of 3 x 4 cm in the buccal surface were irradiated with a continuous wave Nd:YAG laser at a wavelength of 1,064 microns using energy densities of from 83.75 to 187.50 J/cm2. Enamel windows of 3 x 4 cm on the lingual surface served as control (without the laser irradiation). The enamel windows were then exposed to a Streptococcus mutans culture media at a temperature of 37 degrees C for 15 and 21 days. The laser effects and demineralization were examined both by optical microscopy and scanning electron microscopy (SEM). RESULTS: A comparison between the lased and the unlased windows of enamel showed fusion and recrystalization of the enamel and increased acid-resistance in all groups irradiated with the Nd:YAG laser. On the other hand, the 3 x 4 delimited enamel surfaces from the control group (not irradiated with the Nd:YAG laser) showed 100% demineralization. CONCLUSIONS: These findings are consistent with the finding that laser irradiation of dental results in significant reduction of the effective solubility of enamel mineral.

Dental Enamel↗
PubMed1991

Structural and composition studies on the mineral of newly formed dental enamel: a chemical, x-ray diffraction, and 31P and proton nuclear magnetic resonance study.

The present report describes a study of the development and maturation of the mineral component of dental enamel. We prepared porcine enamel of different stages of maturation, from the very immature enamel of unerupted teeth, with a mineral content of 45%, to fully mature enamel, with a mineral content of approximately 99%. We fractionated the less mature enamel by density centrifugation and examined the enamel density fractions and unfractionated enamel by a variety of chemical and physical techniques, including conventional and radial distribution function x-ray diffraction analysis, conventional and Fourier transform infrared spectroscopy, 31P and 1H nuclear magnetic resonance spectroscopy, and chemical analysis. The three most immature preparations, from unerupted teeth, had mineral contents of 45, 67, and 91 and Ca/P molar ratios of 1.41, 1.44, and 1.47. Density distribution histograms of the three fractions show that the early maturation of dental enamel mineral is accompanied by an increase in tissue density, reflecting the increase in mineral content. The density distribution in each sample is relatively narrow, indicating that the maturation process occurs at a fairly homogeneous rate, with all enamel in an anatomically defined zone mineralizing to about the same extent. X-ray diffraction studies indicate that even the least mature, least mineralized of these immature samples is considerably more crystalline than the most mature bone mineral studied and that crystalline perfection of the enamel crystals crystals increases further with maturation. Both the a and c axes of the mineral unit cell expand significantly during early stages of maturation. Solid-state 31P nuclear magnetic resonance spectroscopy studies indicate that dental enamel contains a DCPD-like HPO4 component in an apatitic lattice, similar to the component previously observed in bone and some synthetic calcium phosphates. The proportion of this DCPD-like component decreases with maturation but is readily detectable even in fully mature enamel. The infrared spectroscopic studies indicate that the 3570 cm-1 band ascribed to the OH- group of the hydroxyapatite crystals is absent in the least mature enamel but can be detected and becomes progressively stronger as the enamel becomes more mature. The increase in the content of the OH- groups of the apatite crystals is concomitant with the observed increase in unit cell parameters. Similar studies on very young and very old mature bone of four different species failed to detect the presence of OH- groups.

Aging↗
PubMed1998

A secondary ion mass spectroscopic study of the elemental composition pattern in rat incisor dental enamel during different stages of ameloblast differentiation.

In most earlier studies on the elemental composition pattern of dental enamel, a picture is presented which describes a limited region. In this study, estimates of the incorporation of some critical elements into enamel were correlated with the differentiation stages of the ameloblasts through out the whole tooth. Elemental analyses of rat incisor dental enamel during the secretory, transitional and maturation phases were performed using two different modes of secondary ion mass spectrometry (SIMS). The results were presented as ion images and three-dimensional spatial resolution graphs. In the elemental images of 23Na, 26CN, 35Cl and 39K, counts were detected during the secretory and maturation phases of amelogenesis. Variations were interpreted as resulting from secretion of elements during the secretory phase and resorption during the maturation phase. In line scans the ion yield from enamel during different stages of differentiation of the ameloblasts was analysed. The elements investigated were 12C, 19F, 23Na, 31P, 39K and 77CaCl. As seen in the images, most elements exhibited a higher ion yield during the earlier stages of secretion, and lower yields during the maturation-phase resorption. Cl, together with P, increased during the phases of maturation. In the most apical portions of the teeth, corresponding to a presecretory phase, an inverse pattern was seen for most of the elements. If the surface yield was high at the onset of the secretory phase, the presecretory yields were lower, and vice versa.

Amelogenesis↗
PubMed1990

A possible mechanism of acquired acid resistance of human dental enamel by laser irradiation.

A possible mechanism of acquired acid resistance of lased enamel was proposed on the basis of the investigations of optical properties, compositional and structural changes and permeability of lased and unlased human dental enamel. Lased enamel showed a high positive birefringence, suggesting the formation of 'microspaces' in enamel. No new products were found, though a decrease of lattice strain and a slight a-axis contraction were recognized in lased enamel compared with unlased enamel. The contents of water, carbonate and organic substances were reduced in lased enamel. Gradual changes of birefringence were observed in lased enamel during treatment with acid solutions, and this change was attributed to mineralization of the microspaces. The ions released by an acid decalcification would be trapped in the microspaces in lased enamel, whereas such ions diffuse to the surrounding solution in unlased enamel.

Acids↗
PubMedDate not supplied

Study of physiopathological phenomena in dental enamel by neutron activation analysis.

An epithermal neutron activation method is used to determine the concentration of mineral elements in human dental enamel. A large number (252) of samples from ancient and modern origins are analyzed. The analytical results are mathematically processed using a statistical multivariant method. This allows to differentiate deciduous from permanent teeth and decayed from sound enamel. It is also possible to distinguish the teeth coming from two different necropoles. The origin and the localization of determined elements in the mineralized part, or in the aqueous-organic part, of enamel is suggested. Their role, as witnessed in the physiopathological phenomena of dental enamel, is discussed.

Bone Density↗
PubMed1986

Measurement of the permeability of dental enamel and its variation with depth using an electrochemical method.

To investigate the permeability of the dental enamel of erupted and unerupted human pre-molars and its variation with depth, we determined the resistivity of successive 100-micron-thick layers. The electrical resistance of halved tooth crowns at zero Hertz, which according to Scholberg et al. (1982, 1984) is inversely related to the permeability, was measured before and after removal of successive enamel layers from the outer surface toward the dentino-enamel junction (D.E.J.). The resistivity of the successive enamel layers increased from the D.E.J. toward the outer surface in approximately the same way in erupted as well as in unerupted pre-molars, except within the outermost layer of 100 to 200 microns thickness. The resistivity of this layer in erupted pre-molars was considerably higher than that in unerupted pre-molars, which may be due to post-eruptive mineralization.

Adolescent↗
PubMed2002

Effects of fluoride on rat dental enamel matrix proteinases.

Enamel fluorosis is characterised by increased porosity and a delay in the removal of enamel matrix proteins as the enamel matures. Amelogenin is the primary matrix protein in secretory-stage dental enamel. As enamel matures, amelogenins are hydrolysed by a number of enamel proteinases, including matrix metalloproteinase-20 (MMP-20 or enamelysin) and serine proteinase. Here, the effect of ingested fluoride on the relative activity of proteinases in the enamel matrix and the specific effect of fluoride on MMP-20 activity were examined. Proteinase activity relative to total enamel matrix protein was measured by fluorescence assay of enamel matrix dissected from rats given 0, 50, or 100 parts per 10(6) fluoride in their drinking water. To determine the specific effect of fluoride on the activity of MMP-20, the hydrolysis of a full-length recombinant human amelogenin by recombinant MMP-20 (rMMP-20) in the presence of 0, 2, 5, 10 or 100 microM fluoride was compared by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis (PAGE). In addition, a fluorescent peptide assay was developed to quantify enzyme activity against the tyrosine-rich amelogenin peptide cleavage site. In the late maturation stage, total proteinase activity per unit protein was lower in the fluoride-exposed rats than in the control rats. This in vivo finding indicates that fluoride ingestion can alter the relative amount of active proteinase in mature enamel. Hydrolysis of amelogenin at neutral pH by rMMP-20 was reduced in the presence of 100 microM F. In the peptide assay, rMMP-20 activity was significantly reduced by concentrations of fluoride as low as 2 microM at pH 6, with no significant effect at pH 7.2. These in vitro assays show that micromolar concentrations of fluoride can alter metalloproteinase activity, particularly when the pH is reduced to 6.0. These studies suggest that the effects of fluoride on enamel matrix proteinase secretion or activity could be involved in the aetiology of fluorosis in enamel and other mineralising tissues.

Amelogenin↗
PubMed2001

Residual heat deposition in dental enamel during IR laser ablation at 2.79, 2.94, 9.6, and 10.6 microm.

BACKGROUND AND OBJECTIVE: The principal factor limiting the rate of laser ablation of dental hard tissue is the risk of excessive heat accumulation in the tooth. Excessive heat deposition or accumulation may result in unacceptable damage to the pulp. The objective of this study was to measure the residual heat deposition during the laser ablation of dental enamel at those IR laser wavelengths well suited for the removal of dental caries. Optimal laser ablation systems minimize the residual heat deposition in the tooth by efficiently transferring the deposited laser energy to kinetic and internal energy of ejected tissue components. STUDY DESIGN/MATERIALS AND METHODS: The residual heat deposition in dental enamel was measured at laser wavelengths of 2.79, 2.94, 9.6, and 10.6 microm and pulse widths of 150 nsec -150 microsec using bovine block "calorimeters." Water droplets were applied to the surface before ablation with 150 microsec Er:YAG laser pulses to determine the influence of an optically thick water layer on reducing heat deposition. RESULTS: The residual heat was at a minimum for fluences well above the ablation threshold where measured values ranged from 25-70% depending on pulse duration and wavelength for the systems investigated. The lowest values of the residual heat were measured for short (< 20 micros) CO(2) laser pulses at 9.6 microm and for Q-switched erbium laser pulses at 2.79 and 2.94 microm. Droplets of water applied to the surface before ablation significantly reduced the residual heat deposition during ablation with 150 microsec Er:YAG laser pulses. CONCLUSIONS: Residual heat deposition can be markedly reduced by using CO(2) laser pulses of less than 20 microsec duration and shorter Q-switched Er:YAG and Er:YSGG laser pulses for enamel ablation.

Animals↗