Enamel dissolution as a function of solution degree of saturation with respect to hydroxyapatite: a nanoindentation study

The objective of this study was to investigate human enamel dissolution as a function of degree of saturation (DS) of the surrounding solution with respect to hydroxyapatite. Nanoindentation was used to compare changes in enamel nanomechanical properties due to dissolution by two solutions. Citric acid solution (DS=0.000, pH 3.30) and citric acid solution containing calcium (299 mg/l) and phosphate (54.0 mg/l) (DS=0.032, pH 3.30) were compared with a control mineral water (DS=0.673, pH 7.48). Exposure times were 0, 120, 300, 600, 900, and 1200 s. Compared to untreated enamel, there was a statistically significant change in enamel hardness after 120 s exposure to both citric acid solutions, and in elastic modulus after 300 s exposure. The rate of change of both variables decreased with exposure time. This suggests that dissolution rate is diffusion-limited under these conditions, in agreement with previous studies. There was no statistically significant difference between the hardness or elastic modulus of enamel exposed to the two citric acid solutions at any time. This may be due to a change in solution composition during contact with the enamel.     

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.     

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。     

Determination of fluoride in zinc concentrates, processing products and solutions with an ion-specific electrode

Determination of fluoride in hydrometallurgical zinc-plant processing products and solutions with a fluoride-ion electrode is described. Various types of buffers were tested, to find a suitable common buffer for use in analysis of all types of substances generated at the zinc plant. The method involves decomposition of samples either by fusion with sodium hydroxide or by leaching with perchloric acid to bring fluoride into solution. The fluoride concentration is measured directly with a fluoride-specific electrode. In standard addition tests 100% recovery was obtained when a citric acid/sodium nitrate buffer was used. Validation tests gave satisfactory results.     

碱熔-蒸馏-滴定法测定萤石中的氟化钙含量

采用碱熔-蒸馏-滴定法测萤石中氟含量,计算得到氟化钙含量.萤石试样首先用碳酸钠碱熔消解,然后经硫酸-水蒸气蒸馏分离氟,以茜素磺酸钠作指示剂,用硝酸钍溶液滴定测出其中氟含量,并计算得到氟化钙含量.利用X射线衍射光谱(X RD)法验证了萤石中氟的存在形式,并通过实验确定了碳酸钠使用量、硫酸溶液加入量、蒸馏温度和蒸馏时间等的...     

Adsorption of SDS and PEG on calcium fluoride studied by sum frequency generation vibrational spectroscopy

The adsorption of sodium dodecyl sulfate (SDS) from aqueous solution onto a calcium fluoride substrate (CaF(2)), in the presence of polyethylene glycol (PEG) of different molecular weights, has been investigated using the interface specific nonlinear optical technique of sum frequency generation (SFG) vibrational spectroscopy. Spectra of adsorbed SDS (in the C-H stretching region) were recorded at the surface of a CaF(2) prism in contact with SDS solutions at concentrations up to the cmc (8 mM) of the pure surfactant and in contact with binary solutions containing SDS and PEG with molecular weights from 400 to 12 000. In contrast with SFG spectra from the same combinations of surfactant and polymer on a hydrophobic surface, there was no evidence of spectra arising from the actual polymer adsorbed on CaF(2) at any polymer molecular weight either in the absence or presence of surfactant. However, there was indirect evidence for the presence of adsorbed polymer from changes in the SDS SFG spectra in the presence of polymer compared with spectra when the polymer was absent. The SFG spectra of SDS at 0.8 mM were closely similar to each other at all polymer molecular weights and different from the spectra in the absence of the polymer. The spectral differences between the polymer present and polymer absent was much smaller when the solution concentration of surfactant was 8 mM.     

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.     

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。     

Preparation of durable superhydrophobic surface by sol–gel method with water glass and citric acid

Durable superhydrophobic surface on cotton fabrics has been successfully prepared by sol–gel method. Cellulose fabric was first coated with silica sol prepared with water glass and citric acid as the acidic catalyst. The silica coated fabric was then padded with hydrolyzed hexadecyltrimethoxysilane afterwards obtaining low surface energy. Water contact angle and hydrostatic pressure were used to characterize superhydrophobicity and washing durability. Scanning electron microscopy was used to characterize the surface morphology changes after certain washing times. All results showed good durable hydrophobicity on cellulose fabrics. In addition, the influence of citric acid and sodium hypophosphite (NaH₂PO₂) on the durability of hydrophobicity was also investigated. The durability of treated cotton improved with the increase of concentration of citric acid in the presence of NaH₂PO₂. It could be concluded that citric acid acted as multi-functional heterogeneous grafting chemicals to improve washing durability of hydrophobicity by forming the ester bonds between cotton fabric and silica sol and improved the durability of hydrophobicity.     

Reactions of dental enamel with superficially applied fluorides: electron spectroscopic investigations

Electron spectroscopy combined with argon ion etching was applied for studying reactions of fluoride with dental enamel. Using this assembly to alternately record the spectra and etch the surface, depth profiles of topmost surface enamel can be obtained. The hyperfine depth resolution of the technique provided new information on the distribution of fluoride and its reaction products in the outermost layers of dental enamel.     

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.     

Micropore to macropore structure-designed silicas with regulated condensation of silicic acid nanoparticles

A new preparation method for porous silica particles was developed using activated silica sols which are called nano-silica solutions in this paper. Several kinds of organic and inorganic acids are employed to neutralize diluted sodium silicate solutions to form the nano-silica solutions: formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, dl-malic acid, citric acid, and tricarballylic acid as carboxylic acids, and sulfuric acid and hydrochloric acid as inorganic acids. The effect of salts in the nano-silica solution is also studied. The products were investigated using a field emission scanning electron microscope, an X-ray diffractometer, the nitrogen adsorption technique, and a mercury porosimeter. Microporous silicas were produced when carboxylic acids were applied; the formation of micropores was influenced by the pH of the nano-silica solutions and molecular sizes of the carboxylic acids. Addition of a salt in a citric acid solution increased the mesopore volume. Macropores were formed when inorganic acids including salts were applied; the salt nanoparticles which were crystallized in silica spheres acted as templates. The anion types and salt concentrations in the nano-silica solutions affected the aggregation condition of silica nanoparticles, following the Schulze-Hardy rule.     

Peptidomic analysis of human acquired enamel pellicle

Human acquired enamel pellicle is the result of a selective interaction of salivary proteins and peptides with the tooth surface. In the present work, the characterization of the peptides as well as the type of interactions established with the enamel surface was performed. Peptides from in vivo bovine enamel implants in the human oral cavity were sequentially extracted using guanidine and trifluoroacetic acid solutions and the fractions obtained were analysed by LC-MS and LC-MS/MS. Based on the LC-MS data, six phosphorylated peptides were identified in an intact form, strongly adsorbed to the enamel surface. Data from the LC-MS/MS analyses allowed us to identified 30 fragment peptides non-covalently bonded to enamel [basic proline-rich proteins, histatins (1 and 3) and acidic proline-rich protein classes]. The tandem mass spectrometry experiments showed the existence of a pattern of amide bond cleavage for the different identified peptide classes suggesting a selective proteolytic activity. For histatins, a predominance of cleavage at Arg, Lys and His residues was observed, while for basic proline-rich proteins, cleavage at Arg and Pro residues prevailed. In the case of acidic proline-rich proteins, a clearly predominance of cleavage of the Gln-Gly amide bond was evident.     

柠檬酸改性Hβ分子筛上的苯与丙烯烷基化反应

研究了柠檬酸改性对Hβ分子筛上苯与丙烯烷基化反应性能的影响。通过比较分析改性前后催化剂寿命、二异丙苯选择性及其异构体组成分布等的变化。结果表明，二异丙苯的选择性及各异构体的分布与催化剂的酸密度和酸强度有关；较高酸密度和酸强度有利于烷基转移反应的进行，但却加快了催化剂的失活。柠檬酸改性处理可调节Hβ分子筛的酸密度和酸强度，改善苯烷基化的催化反应性能。经0.50mol/L的柠檬酸处理后，Hβ催化剂的寿命比原来延长30%，正丙苯的质量分数减少90%。     

EDTA络合滴定法测定选铁尾矿中CaF2含量

采用EDTA络合滴定法测定选铁尾矿中的氟化钙含量。选用稀乙酸浸取试样中的碳酸钙,分离过滤氟化钙,用锆-二甲酚橙褪色分光光度法测定浸取液中的氟含量,折算为在稀乙酸中微溶的氟化钙的量;同时沉淀部分用氯化铝溶液在沸水浴中溶解浸取氟化钙,以三乙醇胺掩蔽干扰离子,在KOH介质中,以钙指示剂为指示剂,用EDTA标准滴定溶液测定沉淀中氟化钙的量,两者之和为试样中氟化钙的含量。用此法对试样进行11次平行测定,相对标准偏差（RSD）小于1.0%。在选铁尾矿试样中加入萤石标准物质进行加标回收实验,加标回收率在99%-102%。方法流程短,操作简单。精密度和加标回收率均能满足要求。     

Adsorption and self-assembly of octyl hydroxamic acid at a fluorite surface as revealed by sum-frequency vibrational spectroscopy

In the study described here, the surface structure of a self-assembly octyl hydroxamic acid at a calcium fluoride (CaF(2)) surface is evaluated using sum-frequency vibrational spectroscopy (SFVS). Of particular significance are the results that show octyl hydroxamic acid adsorbs at the fluorite surface from octanol solution and has more ordering and molecular conformation than the octyl hydroxamic acid adsorbed from solution. At the fluorite/0.1 M octyl hydroxamic acid octanol solution interface a bilayer-like structure consisting of an octyl hydroxamic acid layer in contact with fluorite and a tilted alcohol layer was observed by SFVS. The alcohol molecules are oriented with respect to the hydroxamic acid monolayer with the OH groups directed towards the bulk alcohol phase and the terminal CH(3) group oriented to face the alkyl chains of the hydroxamic acid monolayer.     

Formation constants beta(2) of calcium and magnesium fluorides at 25 degrees C

Until now, scientific work on the reactions of the complexation in water of fluoride ions with calcium or magnesium ions considered only soluble order 1 complexes (CaF(+) and MgF(+)). The precipitation of the compounds CaF(2) and MgF(2) did not take into account the preliminary formation in solution of these order 2 complexes (CaF(2)(0) and MgF(2)(0)). We therefore studied their formation using a direct potentiometric method in the F(-) ion-selective electrode at 25 degrees C. This experiment, together with a computerized thermodynamic study, allowed us to determine the values of formation constants at ionic strength equal to zero: log beta (CaF (2)(0))=5.7 and log beta (CaF (2)(0))=3.2 , as well as limiting solubilities: S(CaF(2))=10(-4.8) and S(MgF(2))=10(-5) mol l(-1). Then, some examples were studied showing the necessity to take into account the formation constant of CaF(2): the supersaturation of solutions, the validity of results from the fluoride selective electrode, the difference between released fluoride in distilled water and in artificial saliva in restorative dentistry, the fluoride concentration in hard waters and its health consequences.     

Simple baths for the deposition of nickel oxides

In the present investigation new baths have been adopted for the anodic deposition of different nickel oxides. The deposition of the different oxides was carried out from their metal salt solutions in the presence of a complexing agent. The following oxides were obtained: NiO₂ from nickel chloride in the presence of ammonium chloride and sodium fluoride; Ni₂O₃ from nickel sulphate in the presence of ammonium chloride and citric acid; Ni₃O₄ from nickel chloride in the presence of sodium hydroxide, formaldehyde and potassium chloride, and finally NiO from nickel chloride in the presence of sodium carbonate, sodium chloride and ethanol.     

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.