Composition Profiles of Dental Enamel Studied by X-Ray Photoelectron Spectroscopy (ESCA)

Abstract

The surfaces of both normal and fluoride treated human dental enamel were examined with x-ray photoelectron spectroscopy (ESCA). Using argon-ion etching to remove thin layers of enamel, subsurface layers were also analyzed. The resulting composition-depth profile showed that stannous fluoride produced a subsurface layer containing both tin and fluoride whereas fluorine was absent from the surface layer. Acid fluoride treatments, however, converted the surface to calcium fluoride which steadily decreased in concentration with depth.     

表面官能团作用下的牙釉质原位再矿化研究

采用酸蚀后的牙釉质作为早期龋缺损模型,在缺损牙釉质表面修饰-SO3-功能基团,分别在人工唾液和含氟人工唾液中进行原位再矿化的研究。利用X-射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、能谱仪(EDS)、选区电子衍射(SAED)研究原位再矿化晶体的组成和结构。结果表明,在人工唾液和含氟人工唾液中,表面修饰的官能团均可有效促进牙釉质再矿化。在含氟人工唾液中生成了沿c轴取向生长的具有较大长径比的棒状氟羟基磷灰石(FHA),这种FHA晶体具有类牙釉质的成分和结构,对修复早期龋有重要的意义。     

Synchrotron X-ray diffraction characterization of healthy and fluorotic human dental enamel

With the introduction of fluoride as the main anticaries agent used in preventive dentistry, and perhaps an increase in fluoride in our food chain, dental fluorosis has become an increasing world-wide problem. Visible signs of fluorosis begin to become obvious on the enamel surface as opacities, implying some porosity in the tissue. The mechanisms that conduct the formation of fluorotic enamel are unknown, but should involve modifications in the basic physical-chemistry reactions of demineralization and remineralisation of the enamel of the teeth, which is the same reaction of formation of the enamel's hydroxyapatite (HAp) in the maturation phase. The increase of the amount of fluoride inside of the apatite will result in gradual increase of the lattice parameters. The aim of this work is to characterize the healthy and fluorotic enamel in human tooth using Synchrotron X-ray diffraction. All the scattering profile measurements were carried out at the X-ray diffraction beamline (XRD1) at the Brazilian Synchrotron Light Laboratory—LNLS, Campinas, Brazil. X-ray diffraction experiments were performed both in powder samples and polished surfaces. The powder samples were analyzed to obtain the characterization of a typical healthy enamel pattern. The polished surfaces were analyzed in specific areas that have been identified as fluorotic ones. X-ray diffraction data were obtained for all samples and these data were compared with the control samples and also with the literature data.     

用XPS和SEM研究氟化物对牙釉质早期脱矿和再矿化的影响

用光电子能谱和扫描电镜分析体外人牙釉质片经含不同浓度氟化物的脱矿液和再矿化液处理后釉质化学成分和形态学变化。结果发现，脱矿液中单独加入低浓度氟化物不能有效抑钙和磷溶解，在有外源性钙和磷存在时，才能获得再矿化而抑制钙和磷溶解，脱矿环境中有高浓度氟，通过局部沉积氟化钙而抑制酸与牙的反应，氟促进再矿化主要表现在加速钙的沉积，同时本身参以形成氟磷灰石，提高了牙齿的耐酸能力。     

Depth profiles of fluoride interactions in hyperfine subsurface layers of dental enamel

Summary Information on chemical reactions of fluoride in topmost surface layers of dental enamel was obtained — in vitro — by analytical techniques with hyperfine depth resolution: electron spectroscopy combined with ion etching for depth profiling the chemical composition of surface layers and interference microscopy for measuring the depth of etching steps. From slightly acidic media, which are typical for some topical fluoride applications, the ion is taken up after apatite degradation in the form of calcium fluoride. Layers mixed of unreacted apatite and of calcium fluoride are formed. There is evidence that the calcium fluoride rich layer with less than 1 m thickness, may contribute to the observed cariostatic effectiveness of fluorides. Only less attention has been paid till now to this effect.

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Tiefenprofile von Fluorid-Wechselwirkungen in hyperfeinen Oberflächenschichten von Zahnschmelz

Zusammenfassung Hinweise auf chemische Reaktionen von Fluorid in äußersten Schichten von Zahnschmelz wurden in vitro durch analytische Techniken mit hyperfeiner Tiefenauflösung erhalten: Elektronenspektroskopie in Verbindung mit lonenätzen zur Erstellung von Tiefenprofilen der chemischen Zusammensetzung und Interferenzmikroskopie zur Messung von Ätzstufen. Analytische Verfahren mit hyperfeiner Tiefenauflösung liefern zusätzliche Daten zum Verständnis von Fluorid-Wechselwirkungen mit Oberflächenschmelz. Aus schwach saueren Medien, wie sie für einige lokale Applikationen typisch sind, wird Fluorid nach Schmelzzersetzung als Calciumfluorid aufgenommen. Gemischte Schichten aus unreagiertem Apatit und aus Calciumfluorid werden gebildet. Die Calciumfluorid-reiche Schicht, mit weniger als 1 um Dicke, scheint zur kariostatischen Wirksamkeit der Fluoride beizutragen. Dieser Tatsache wurde bisher nur wenig Aufmerksamkeit geschenkt.

     

Determination of fluorine by PIGE analysis on bovine tooth enamel treated with bamboo salt SMFP toothpaste and fluoride mouth rinsing solution

The purpose of this study was to evaluate the effectiveness of a toothpaste containing bamboo salt on fluorine uptake in bovine enamel and to compare the efficiency of fluorine uptake between sodium monofluorophosphate (SMFP) toothpaste and sodium fluoride (NaF) mouthrinsing solution using proton induced -ray emission analysis. 30 bovine tooth enamel specimens were prepared and assigned to 5 groups as follows: (a) specimens without any treatment, (b) specimens which were treated with a toothpaste containing dicalcium phosphate dihydrate (DCPD) only, (c) specimens which were treated with a toothpaste containing DCPD and SMFP, (d) specimens which were treated with a toothpaste containing DCPD, SMFP and 2% bamboo salt, (e) specimens which were treated with 0.05% NaF mouthrinsing solution. After 5 and 10 hours of treatment, fluorine concentration was measured at the depth of 263, 625, 2530 nm from the surface of the specimens. The surface concentration of fluorine was markedly increased using SMFP dentifrice. Bamboo salt did not encourage the uptake of fluorine into the enamel surface. NaF mouthrinsing solution showed a considerably higher uptake of fluoride in the intact enamel surface than the SMFP dentifrices.     

Proton microprobe determination of fluorine depth distributions and surface multielement characterization in dental enamel

Particle induced X-ray emission analysis (PIXE) and nuclear reaction analysis have been applied to multielemental analysis of human dental enamel in a proton microprobe. The PIXE technique was excercised for the characterization of multielemental lateral distributions on and just below the sample surface. For the assessment of depth distributions of fluorine the resonant nuclear reaction¹⁹F(p,aλ)¹⁶O was used. The combination of two analytical techniques comprising both atomic and nuclear interactions in a microprobe was applied to enamel samples of different origins. One sample constituted a healthy enamel and the other one enamel from a restored tooth. The microprobe in the combined mode was demonstrated to permit the establishment of lateral, concentration gradients of elements heavier than phosphorus with a resolution of 15 μm in enamel and simultaneously of depth distributions of fluorine better than 0.7 μm. The detection limits approached, 10–25 ppm for most of the elements considered. Supported by the Swedish Natural Science Research Council     

Artificial Caries Lesion Characteristics after Secondary Demineralization with Theobromine-Containing Protocol

Developing artificial caries lesions with varying characteristics is needed to adequately study caries process in vitro. The objective of this study was to investigate artificial caries lesion characteristics after secondary demineralization protocol containing theobromine and fluoride. Sixty bovine enamel slabs (4 × 3 mm) were demineralized using a Carbopol-containing protocol for 6 days. A baseline area (2 × 3 mm) was protected with acid-resistant nail varnish, after which specimens were exposed for 24 h to a secondary demineralization protocol containing acetic acid plus one of four fluoride/theobromine combinations (n = 15): theobromine (50 or 200 ppm) and fluoride (0 or 1 ppm). Specimens were sectioned and analyzed using transverse microradiography for changes in mineral content, lesion depth, and surface layer mineralization. Data was analyzed using paired t-test and analysis of variance followed by Bonferroni test at 0.05 significance level. After secondary demineralization, fluoride-containing groups had significantly deeper lesions (p = 0.002 and 0.014) compared to the group with 0 ppm fluoride and 50 ppm theobromine. Mineral content and lesion depth were significantly different compared to baseline for all groups. Theobromine did not show an added effect on mineral uptake. Theobromine-containing groups exhibited particularly deep lesions with a more uniform mineral profile in the presence of fluoride.     

New insights into structural alteration of enamel apatite induced by citric acid and sodium fluoride solutions

Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found.     

Relationship between microhardness and fluorine contents on tooth enamel determined by PIGE analysis

The remineralization effect of fluoride has been measured by surface microhardness on tooth enamel. The purpose of this study was to investigate the relationship between microhardness and fluorine concentration on tooth enamel. Twelve sound bovine enamel specimens were prepared and immersed in 0.05% NaF solution for 1, 3, 6, 24 and 36 hours, respectively. The concentration of fluorine in specimens were measured by PIGE analysis and surface microhardness of each specimen was measured by surface microhardness tester. Fluorine concentration was increased by immersing time. There was no change in microhardness of each specimen by fluorine content. The results of this study suggest that there was no relationship between the fluorine concentration and surface microhardness in sound tooth enamel. PIGE analysis can be used effectively to assess the remineralization effect of fluorine content in tooth enamel.     

An in vitro investigation of human enamel wear by restorative dental materials

A radiometric method was applied to assess enamel wear by another enameland by restorative materials. The radioactive enamel was submitted to wearin a machine which allows sliding motion of an antagonistic surface in contactwith the radioactive enamel. The enamel wear was evaluated by measuring thebeta-activity of ³²P transferred to water from this irradiatedtooth. Results obtained indicated that dental porcelains cause pronouncedenamel wear when compared with that provoked by another natural enamel orby resin materials. Resin materials caused less enamel wear than another naturalenamel. Vickers microhardness data obtained for antagonistic materials showeda correlation with the wear caused to the enamel.     

Microscopic and electron spectroscopic characterization of dental enamel surfaces

 The effects of surface pretreatment on the topography and composition of dental enamel surfaces of extracted bovine teeth have been investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Surface pretreatment with a solution of benzoic acid in acetone does not change the topography of the surface; it leads to enrichment of calcium and, to a lesser extent, phosphorus at the enamel surface. The higher adhesion strength reported between enamel surfaces pretreated with benzoic acid in acetone and glass ionomer cement might be explained in terms of a greater number of chemical bonding sites due to the enrichment of calcium and phosphorus at the surface. Received: 6 November 1998 Accepted in revised form: 3 December 1998     

Enhanced penetration of fluoride particles into bovine enamel by combining dielectrophoresis with AC electroosmosis

Fluoride deposition into the pores of enamel is necessary at high concentrations to reduce enamel demineralization and with a high degree of penetration to account for loss by ingestion. Current diffusion and electrochemical methods are inadequate for effectively transporting fluoride greater than 20 μm into enamel. The study explores the coupling of dielectrophoresis (DEP) and AC electroosmosis (ACEO) to selectively concentrate fluoride particles from fluoride gel excipients and enhance their penetration into enamel. By measuring the frequency response of approximately 10‐μm‐sized sodium fluoride particles in an aqueous gel media, appropriate frequencies for positive DEP, negative DEP, and ACEO are identified. An assembly composed of two cross‐planar interdigitated electrode (IDE) arrays with open slots is driven successively by fields at appropriate frequencies to drive fluoride particles through the slots of the IDE and into the enamel pores using a combination of DEP and ACEO methods. Fluoride uptake and penetration of 1.23% acidulated phosphate fluoride gel into bovine tooth enamel at various depths is measured using wavelength dispersive spectrometry to compare deposition by diffusion, DEP, and DEP plus ACEO. Fluoride levels in all DEP groups were significantly higher than diffusion groups at depths 10 and 20 μm. The highest fluoride concentrations at 10, 20, 50, and 100 μm depths occur under deposition conditions combining DEP with ACEO. Fluoride levels at 50 μm were equivalent to long‐term prophylactic exposure. These methods may potentially benefit populations at high risk for development of caries and periodontal disease, including underserved children and disparate groups.     

Elemental depth profiling of fluoridated hydroxyapatite: saving your dentition by the skin of your teeth?

Structural and chemical changes that arise from fluoridation of hydroxyapatite (Ca(5)(PO(4))(3)OH or "HAp"), as representing the synthetic counterpart of tooth enamel, are investigated by X-ray photoelectron spectroscopy (XPS). Elemental depth profiles with a depth resolution on the nanometer scale were determined to reveal the effect of fluoridation in neutral (pH = 6.2) and acidic agents (pH = 4.2). With respect to the chemical composition and the crystal structure, XPS depth profiling reveals different effects of the two treatments. In both cases, however, the fluoridation affects the surface only on the nanometer scale, which is in contrast to recent literature with respect to XPS analysis on dental fluoridation, where depth profiles of F extending to several micrometers were reported. In addition to the elemental depth profiles, as published in various other studies, we also present quantitative depth profiles of the compounds CaF(2), Ca(OH)(2), and fluorapatite (FAp) that were recently proposed by a three-layer model concerning the fluoridation of HAp in an acidic agent. The analysis of our experimental data exactly reproduces the structural order of this model, however, on a scale that differs by nearly 2 orders of magnitude from previous predictions. The results also reveal that the amount of Ca(OH)(2) and FAp is small compared to that of CaF(2). Therefore, it has to be asked whether such narrow Ca(OH)(2) and FAp layers really can act as protective layers for the enamel.     

Dielectrophoresis: a model to transport drugs directly into teeth

The article describes an innovative delivery system based on the principles of dielectrophoresis to transport drugs directly into site-specific intraoral targets. The hypothesis that a drug can be driven into tooth enamel during the application of an applied electrical potential difference was tested by the authors in in vitro studies comparing dielectrophoresis to diffusion to transport carbamide peroxide and fluoride. The studies showed that these agents can be transported directly into teeth using an alternating current (AC) electric field more effectively than diffusion. It was found that a 20-min bleaching treatment on human teeth with dielectrophoresis increased carbamide peroxide absorption by 104% and, on average, improved the change in shade guide unit 14 times from 0.6 SGU to 9 SGU. After applying a 1.23% acidulated phosphate fluoride gel to bovine incisors for 20 min by dielectrophoresis or diffusion, analysis with wavelength dispersive spectrometry determined that dielectrophoresis doubled fluoride uptake in the superficial layers compared to diffusion, and drove the fluoride significantly deeper into enamel with an uptake 600% higher than diffusion at 50 μm depth. Finally, dielectrophoresis promises to be a viable model that can potentially be used clinically to deliver other targeted drugs of variable molecular weight and structure.     

The adsorption of fluoride containing polyelectrolytes on hydroxyapatite

In this study the preparation of three polyvinylpyridinium fluorides with different hexadecyl group contents is described. Their adsorption on hydroxyapatite (the main constituent of dental enamel) was studied as a function of time and concentration. It was found that increasing hexadecyl group content resulted in lower amounts of adsorbed polymer. The adsorption of the polyelectrolytes is accompanied with the uptake of fluoride by hydroxyapatite at a higher rate and with greater amounts. Phosphate ions present in aqueous suspensions of hydroxyapatite were responsible for this phenomenon. Desorption experiments showed that the adsorption of these macromolecules was irreversible in water. Excess calcium resulted to some extent in desorption.     

Determination of some trace elements in human tooth enamel

Determination of seven elements (Cu, Fe, Mg, Mn, Pb, Sr and Zn) in whole enamel and surface layers of extracted non-carious human teeth by FAAS, ETA AAS, ICP-AES and ICP-MS (Pb) is demonstrated. Techniques are described for obtaining whole enamel and its acid dissolution. Fifty microm width enamel layers from outer enamel surface to a 200 microm depth were successively etched in 1 mL of 3 M HClO4 for 3 min dissolution periods. Enamel samples were analyzed for populations under and over 20 years of age and enamel from Bronze Age teeth. Concentrations of microelements in the whole enamel and in the first surface layer (50 microm depth) were compared. With exception of Sr and Mg, all elements show significantly higher concentrations in the first layer than in whole enamel and higher concentration in teeth of individuals over 20 years, which demonstrate the cumulative effect of these elements. The Cu, Fe, Mn, Pb and Zn concentrations in four layers of erupted and non-erupted teeth decreased while Mg and Sr concentrations increased toward enamel-dentine junction. The concentrations of most elements were almost constant as they approached the 150 microm layer. This concentration gradient may result from interaction between saliva and teeth and supports the hypothesis that the surface de- and re-mineralization process is effective at most to 150 microm from the enamel surface.     

Energy absorption build-up factors in teeth

Geometric progression fitting method has been used to compute energy absorption build-up factor of teeth [enamel outer surface, enamel middle, enamel dentin junction towards enamel, enamel dentin junction towards dentin, dentin middle and dentin inner surface] for wide energy range (0.015?C15?MeV) up to the penetration depth of 40 mean free path. The dependence of energy absorption build-up factor on incident photon energy, penetration depth, electron density and effective atomic number has also been studied. The energy absorption build-up factors increases with the penetration depth and electron density of teeth. So that the degree of violation of Lambert?CBeer (I?=?I ₀e^???t ) law is less for least penetration depth and electron density. The energy absorption build-up factors for different regions of teeth are not same hence the energy absorbed by the different regions of teeth is not uniform which depends on the composition of the medium. The relative dose of gamma in different regions of teeth is also estimated. Dosimetric implication of energy absorption build-up factor in teeth has also been discussed. The estimated absorption build up factors in different regions of teeth may be useful in the electron spin resonance dosimetry.     

Apparent solubility distributions of hydroxyapatite and enamel apatite

Samples of human dental enamel and hydroxyapatite were equilibrated at 5 mg/40 ml for 9 days at 37 degrees C with acetate buffers adjusted to a range of saturations with respect to hydroxyapatite. Sigmoidal apparent solubility distributions, in which the fraction dissolved was plotted against--log(ion activity product for hydroxyapatite) (pIHA), were constructed. About 10% of the hydroxyapatite and 14% of the enamel was very soluble, dissolving even at pIHA 55. The apparent solubility distributions for both solids were invariant with pH (4.5, 5.0, 5.5), within experimental error, showing that solubility was controlled by a phase with the stoichiometry of hydroxyapatite, probably in the form of a surface layer or complex on the crystals, in agreement with other studies on carbonate-apatites and bone mineral. The pIHA at 50% dissolution was employed as an average value. The pIHA (50%) values for pooled data (58.76 for enamel and 60.17 for hydroxyapatite) were lower than the respective pIHA previously measured by conventional equilibration techniques. However, the average pIHA measured for enamel was higher than that obtained by the same technique in another study, possibly because of differences in specimen preparation and equilibration time. The possible implications of the findings for understanding the process of dental caries are discussed.     

Effects of Cerium and Combination of Fluoride and Cerium on the Hydrolysis of Hydroxyapatite and Calcium Hydrogen Phosphate

Researches have indicated that fluoride aided in decreasing the solubility of enamel of teeth and preventing caries through converting hydroxyapatite (HAP) to less dissoluble fluoroapatite (FAP). However, The toxicity of fluoride is not negligible. Recent studies^[1] suggested that rare-earth elements (for instance,lanthanum, cerium, etc.) might play an important role in enamel demineralization reduction. However, the effect of these rare-earth elements on the solubility of HAP and calcium hydrogen phosphate (CaHPO₄·2H₂O, DCPD),which are the major inorganic compositions in enamel, remains unclear. The purpose of this paper was to investigate the characteristics of the hydrolysis of DCPD and HAP under 37℃ when hydrolyzed (a) in solutions containing cerium alone, and (b) in solutions containing fluoride followed by solutions containing cerium, respectively.