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At least 163 records · Page 9Linked to original sources
PubMed1990

Effect of Nd:YAG laser irradiation on human dental enamel.

The crystallographic alterations of the hydroxyapatite under the laser irradiation were evaluated by the x-ray diffraction pattern analysis and scanning electron microscopic observation. Recrystallization may occur in fused and resolidified dental enamel by the pulsed Nd: YAG laser irradiation. Two different grades of energy densities such as 400 pulses and 800 pulses were given to the powdered enamel. The irradiation was performed at a peak power of 500W with a pulse width of 10 msec.; the average output of 10W, spot size of 3mm and two pulses were given in every second. After the 800 pulses of Nd:YAG laser irradiation to the human dental enamel the x-ray diffraction pattern demonstrated both alpha-tricalcium phosphate and hydroxyapatite peaks. With the lower level of energy at 400 pulses, no significant differences were seen in the diffraction patterns between lased and unlased enamel. In scanning electron microscopic findings, there were no significant changes between lased and unlased enamel. When the unlased and lased enamel were exposed to acid solution, unlased enamel showed a honeycomb pattern, while the lased enamel showed preferentially removed prism core material.

Crystallization↗
PubMedDate not supplied

Composition of fluoridated dental enamel studied by x-ray photoelectron spectroscopy (ESCA).

A combination of ESCA and argon-ion etching has been shown to be effective in determining the surface and subsurface composition of dental enamel. The heavy organic coating on enamel has been investigated. Beneath this coating, untreated enamel was found to have invariant phosphorus and calcuim concentrations over the region surface. The surface of enamel treated with an acid phosphate-fluoride gel was shown to be almost entirely connected to calcium fluoride. A phosphate species, noncalcium and possibly a sodium salt, was found to be present in the surface layer. At a depth lower than about 60 nm, there was a gradual increase in phosphorus concentration that approached the value for untreated enamel with increasing depth. The increasing phosphorus and decreasing fluorine concentrations were primarily caused by the increasing concentration of unreacted hydroxyapatite. These results have shown that ESCA coupled with argon-ion etching, can be used effectively to examine the surface and subsurface composition of dental enamel. The surface sensitivity, ability to strip thin layers of material, sensitivity to low atomic weight elements, and ability to differentiate between different oxidation states makes a combination of these two techniques extremely useful for dental research.

Acetates↗
PubMed2003

Irradiation of dental enamel with Q-switched lambda = 355-nm laser pulses: surface morphology, fluoride adsorption, and adhesion to composite resin.

BACKGROUND AND OBJECTIVES: Lasers can be used to modify the chemical composition of dental enamel to increase the bond strength to restorative materials and to render the mineral phase more resistant to acid dissolution. Previous studies have suggested a synergistic relationship between CO(2) laser irradiation and fluoride treatment on increased resistance to acid dissolution. In this study a near-UV laser operating with lambda = 355-nm laser pulses of 3-5 nanoseconds duration was used to modify the surface morphology of dental enamel to increase the bond strength to restorative materials and increase the uptake of topical fluoride to render the surface more resistant to acid dissolution. We hypothesize that the short UV laser pulses are primarily absorbed by protein and lipid localized between the enamel prisms resulting in removal of intact mineral effectively etching the surface without thermal modification of the mineral phase. Such modification is likely to increase the permeability of the enamel surface and the subsequent absorption of fluoride. In addition, there is an increase in surface roughness without the formation of a layer of loosely adherent, thermally modified enamel that increases the bond strength to composite restorative materials. STUDY DESIGN/MATERIALS AND METHODS: The surfaces of blocks of bovine enamel, 5 x 5 mm(2), were uniformly irradiated by 355-nm laser pulses and subsequently bonded to composite. The shear bond test was used to assess the bond strength of non-irradiated blocks (negative control), acid etched blocks (positive control), and laser irradiated blocks. The resistance to acid dissolution was evaluated using controlled surface dissolution experiments on irradiated samples, irradiated samples exposed to topical fluoride, and non-irradiated control samples with and without fluoride. RESULTS: The laser surface treatments significantly increased the shear-bond strength of enamel to composite, to a level exceeding 20 MPa which was significantly more than the non-irradiated control samples and significantly less than the acid etch. Laser irradiation alone and topical fluoride application alone did not significantly increase the resistance to acid dissolution. The laser treatment followed by topical application of fluoride significantly increased the resistance to acid dissolution to a level of over 50% versus the control samples. CONCLUSIONS: We present a novel method for increasing bond strength to restorative materials and enhancing fluoride delivery to enamel surfaces and shed some light on the underlying mechanisms of caries inhibition via laser treatment and topical application of fluoride.

Animals↗
PubMed2006

The effect of copper on demineralization of dental enamel.

Previous studies have concluded that copper might inhibit enamel demineralization in vitro. Our aim was to assess the effect of copper (Cu2+), with and without amine fluoride, on human dental enamel under cariogenic challenge in situ. In a double-blind randomized four-leg crossover trial, 14 individuals wore a removable appliance containing 2 enamel slabs, 1 containing an artificial caries lesion. During each leg, the appliance was exposed twice daily to one of the test solutions: 1.25 mM CuSO4, amine fluoride (250 ppm F), copper and amine fluoride combined, or a placebo (water). A cariogenic challenge was provided in all cases by 5 daily exposures to 10% sucrose. Slabs were assessed before and after 21 days' exposure by Knoop microhardness and transverse microradiography. Significantly less demineralization was observed with Cu2+ and fluoride in combination than with fluoride treatment alone (p < 0.05), whereas copper alone had no significant protective effect.

Adult↗
PubMed2004

Distribution and structure of dental enamel in incisors of Tabby mice.

OBJECTIVE: In Tabby mice, the Ta (EDA) gene is mutated. The resulting syndrome is homologous to hypohidrotic ectodermal dysplasia in humans. The Tabby phenotype is characterized by developmental defects of ectodermally derived structures. The teeth show aberrations in number, size and morphology. Dental enamel is a product of specialized epithelial cells, the ameloblasts. It was the aim of the present study to investigate the dental enamel phenotype in Tabby incisors, with emphasis on its distribution and structure. DESIGN: The incisors from five female Tabby and three female wild-type mice were sectioned and ground transversely, etched for 45s with 0.1% nitric acid, sputter-coated with gold-palladium, and observed in SEM. RESULTS: All measured dimensions were more variable in Tabby mice, as was the outline of the enamel-dentin junction. Maxillary incisors were wider in Tabby mice, while mandibular incisors were wider in wild-type mice. No significant difference in enamel thickness was observed. The enamel on the mesial aspect tended to extend further lingually in Tabby incisors in both jaws. On the lateral aspect, this tendency was only significant in mandibular incisors. The enamel-dentin junction often lacked the mesial concavity. Instances of hypoplastic enamel were observed. The complex mouse enamel structure was generally well preserved in Tabby mice, only few instances of aberrant structure were observed. CONCLUSIONS: It is suggested that the reciprocal expression pattern of Ta and Edar (the Ta ligand receptor gene) in outer and inner enamel epithelium, respectively, may influence the position of the enamel-cementum junction.

Animals↗
PubMed1996

Structural changes in fluorosed dental enamel of red deer (Cervus elaphus L.) from a region with severe environmental pollution by fluorides.

A macroscopic, microradiographic and scanning electron microscope study was performed on the structure of fluorosed dental enamel in red deer from a fluoride polluted region (North Bohemia, Czech Republic). As was revealed by analysis of mandibular bone fluoride content, the rate of skeletal fluoride accumulation in the fluorotic deer was about 6 times that in controls taken from a region not exposed to excessive fluoride deposition. In all fluorosed mandibles, the 1st molar was consistently less fluorotic than the other permanent teeth. This was related to the fact that crown formation in the M1 takes place prenatally and during the lactation period. Fluorosed teeth exhibited opaque and posteruptively stained enamel, reduction or loss of enamel ridges, moderately to grossly increased wear and, in more severe cases, also enamel surface lesions of partly posteruptive, partly developmental origin. Microradiographically, fluorosed enamel was characterised by subsurface hypomineralisation, interpreted as a result of fluoride interference with the process of enamel maturation. In addition, an accentuation of the incremental pattern due to the occurrence of alternating bands with highly varying mineral content was observed in severely fluorosed teeth, denoting fluoride disturbance during the secretory stage of amelogenesis. A corresponding enhancement of the incremental pattern was also seen in the dentine. The enamel along the more pronounced hypoplasias consisted of stacked, thin layers of crystals arranged in parallel, indicating that the ameloblasts in these locations had lost the distal (prism-forming) portions of their Tomes processes. The findings of the present study indicate that red deer are highly sensitive bioindicators of environmental pollution by fluorides.

Animals↗
PubMed1995

Influence of fluoride applications on some physicochemical surface properties of synthetic hydroxyapatite and human dental enamel and its consequences for protein adsorption.

Synthetic hydroxyapatite and human dental enamel (polished and non-polished) were subjected to various fluoride applications, i.e., using solutions of sodium fluoride (NaF), acidulated phosphate fluoride (APF), and stannous fluoride (SnF2). Treatment with APF has a strong influence on the morphology of the apatite. All fluorides, in particular SnF2, make the enamel surfaces more hydrophobic. NaF and APF applications slightly alter the electrokinetic potentials of the surfaces, but SnF2 renders them much more negatively charged. The adsorption of the proteins lysozyme and alpha-lactalbumin on these surfaces can be explained in terms of electrostatic and hydrophobic interactions between the proteins and the sorbent surfaces.

Acidulated Phosphate Fluoride↗
PubMed1986

Some aspects of artificial caries lesion formation of human dental enamel in vitro.

Investigations of artificial carious lesion formation of human dental enamel showed great variability in caries susceptibility. Human specimens were demineralized in acid buffers with Ca and phosphate ions, undersaturated with respect to hydroxyapatite. Under nearly all conditions the results varied from no lesion formations to etching. This may be due to properties of the surface layer such as fluoride content and permeability.

Decalcification Technique↗
PubMed1989

Solubility, unit cell dimensions and crystallinity of fluoridated human dental enamel.

The aim was to describe the dimensions of the fluorhydroxyapatite unit cell and the solubility of fluorhydroxyapatite as a function of the fluoride concentration in the apatitic lattice. Various amounts of powdered human dental enamel were suspended in a pH 4.5 acetate buffer containing fluoride. The suspensions were equilibrated for 365 days at 20 degrees C. After equilibration the fluoride concentration in the apatite varied from 0.003 to 0.89 (mole fraction). X-ray diffraction showed that the length of the alpha-axis decreased with increasing fluoride concentration, whilst a broadening of the (300) reflection indicated the presence of mixtures of various fluorhydroxyapatites. The solubility of the apatite after the long equilibration decreased slightly with increasing fluoride concentration in the solid. In a few samples the fluoride concentration in the aqueous phase was still discernible, indicating that even after 365 days, equilibrium had not been attained. In these samples the amount of dissolved apatite was extraordinarily low.

Apatites↗
PubMed1995

Molecular mechanisms of dental enamel formation.

Tooth enamel is a unique mineralized tissue in that it is acellular, is more highly mineralized, and is comprised of individual crystallites that are larger and more oriented than other mineralized tissues. Dental enamel forms by matrix-mediated biomineralization. Enamel crystallites precipitate from a supersaturated solution within a well-delineated biological compartment. Mature enamel crystallites are comprised of non-stoichiometric carbonated calcium hydroxyapatite. The earliest crystallites appear suddenly at the dentino-enamel junction (DEJ) as rapidly growing thin ribbons. The shape and growth patterns of these crystallites can be interpreted as evidence for a precursor phase of octacalcium phosphate (OCP). An OCP crystal displays on its (100) face a surface that may act as a template for hydroxyapatite (OHAp) precipitation. Octacalcium phosphate is less stable than hydroxyapatite and can hydrolyze to OHAp. During this process, one unit cell of octacalcium phosphate is converted into two unit cells of hydroxyapatite. During the precipitation of the mineral phase, the degree of saturation of the enamel fluid is regulated. Proteins in the enamel matrix may buffer calcium and hydrogen ion concentrations as a strategy to preclude the precipitation of competing calcium phosphate solid phases. Tuftelin is an acidic enamel protein that concentrates at the DEJ and may participate in the nucleation of enamel crystals. Other enamel proteins may regulate crystal habit by binding to specific faces of the mineral and inhibiting growth. Structural analyses of recombinant amelogenin are consistent with a functional role in establishing and maintaining the spacing between enamel crystallites.

Amelogenesis↗