Effect Of Fluoride Concentration Research Articles

Corrosion behavior of Ti-Nb-Ni foil as bipolar plates substrate in simulated PEMFC solution: Effects of fluoride concentration and temperature

In this work, corrosion behavior of Ti-Nb-Ni foil in 0.5 M H2SO4 solution containing different fluoride concentrations at various temperatures was investigated by electrochemical measurements, X-ray photoelectron spectroscopy and scanning electron microscopy. Corrosion resistance of specimens degraded with temperature and fluoride concentration increasing judged by more negative open circuit potential, larger corrosion current density as well as reducing polarization resistance. The critical fluoride concentrations were in the range of 100 ∼ 200 ppm for 20℃ and 50 ∼ 100 ppm for 40℃ to 80℃, above which passive film was destroyed causing contact between substrate and solution. While in the cases of fluoride concentrations lower than critical value, passivation of foil was retained. Furthermore, a nickel-rich layer was found via X-ray photoelectron spectroscopy analyses and thickness of the layer descended with fluoride concentration and temperature increasing. Interfacial contact resistance of the foils after being potentiostatically polarized at 0.6 V for 6 h at 80℃ were lower than 10 mΩ·cm−2, meeting the requirement of Department of Energy (DOE) and interfacial contact resistance increased by different degrees with fluoride concentrations.

Oxidation behavior of SiC layer of TRISO particles with the presence of NaF

In the present work, the oxidation behavior of the SiC layer of TRISO particles in NaF salt at concentrations of 0.2–2 % and at temperatures ranging between 800 and 1400 °C was studied. The results showed that the oxidation rate was accelerated with the increase in temperature and fluoride concentration, while the effect of fluoride concentration on oxidation rate was much greater than that of the temperature. This could be due to the reaction of fluoride with SiC/SiO2 and the dissolution of silicon oxide by the alkaline silicate formed during the oxidation process, which accelerated the diffusion of oxygen.

The Potentiometric determination of fluoride in various brands of toothpaste

The potentiometric analysis of the fluoride content (as F-ion) in toothpaste suspension with an ion-selective fluoride electrode is simple, reliable and inexpensive. Very low fluoride ion concentrations (up to 10–5 mol / l) can be determined with a fluoride-selective electrode, whereby the ionic strength of a solution is regulated and the concentration of hydroxide ions and interfering metal ions is controlled. The influence of the pH value and the complex ions of metals can be successfully regulated by the Total ionic strength adjustment buffer (TISAB) solution and by maintaining the pH value in the range from 5.00 to 8.00. The fluoride concentrations of 34 different toothpaste samples of different brands are determined using an ion-selective electrode. The highest value is 1285.85 ppm from Germany (Blend a. Med) and the lowest value is 18.15 ppm from Indonesia (Formula junior). Most of the low values are from Asian countries between (18.15-514.84) ppm, which are less than 600 ppm and this concentration is insufficient for Iraqi prescriptions and World Health Organization (WHO) specifications, the highest Values are between (940.66-1285.85) ppm, from Japan, USA and Germany References Abramowitz, A. (1967) ‘Principles, current practice, and applications of potentiometers based on Poggendorff’s second method’, Review of Scientific Instruments, 38(7), pp. 898–904. doi: 10.1063/1.1720918. Barmes, D. E. (1996) ‘Fluorides and oral health’, Community Dental Health, pp. 3–4. Bereczki, R. et al. (2006) ‘How to assess the limits of ion-selective electrodes: Method for the determination of the ultimate span, response range, and selectivity coefficients of neutral carrier-based cation selective electrodes’, Analytical Chemistry, 78(3), pp. 942–950. doi: 10.1021/ac050614s. Bralić, M. et al. (2001) ‘Fluoride electrode with LaF3-membrane and simple disjoining solid-state internal contact’, Talanta, 55(3), pp. 581–586. doi: 10.1016/S0039-9140(01)00448-9. Chakraborty, M., Pandey, M. and Pandey, P. (2017) ‘Spectrophotometric method vs ion selective electrode for field determination of fluoride in water and complex samples’, Reserch Journal of Chemical Sciences, 7(5)(5), pp. 31–37. Available at: http://www.isca.in/rjcs/Archives/v7/i5/5.ISCA-RJCS-2017-022.pdf. Gao, W., Xie, X. and Bakker, E. (2020) ‘Direct Potentiometric Sensing of Anion Concentration (Not Activity)’, ACS Sensors, 5(2), pp. 313–318. doi: 10.1021/acssensors.9b02523. J, U. (2019) ‘a Review on Effect of Fluoride Concentration in Drinking Water.’, International Journal of Advanced Research, 7(3), pp. 475–478. doi: 10.21474/ijar01/8659. Jasielec, J. (no date) Modelling of potentiometric ion sensors. Julie, L. (1967) ‘A Universal Potentiometer’, IEEE Trans Instr. Meas., IM(3), pp. 187–191. Lennon, M. A. et al. (2004) ‘Rolling Revision of the WHO Guidelines for Drinking-Water Quality’, World Health Organization, (September), pp. 105–116. Available at: http://www.who.int/water_sanitation_health/dwq/chemicals/en/nitratesfull.pdf. Light, T. S. and Cappuccino, C. C. (1975) ‘Determination of fluoride in toothpaste using an lon-selective electrode.’, Journal of chemical education, 52(4), pp. 247–250. doi: 10.1021/ed052p247. Michalski, R. and Mathews, B. (2006) ‘Simultaneous determination of fluoride and monofluorophosphate in toothpastes by supressed ion chromatography’, Central European Journal of Chemistry, 4(4), pp. 798–807. doi: 10.2478/s11532-006-0042-0. Midgley, D. (1987) ‘Limits of detection of ion-selective electrodes: Theory and practice’, Transactions of the Institute of Measurement & Control, 9(1), pp. 25–36. doi: 10.1177/014233128700900105. Radić, J. et al. (2020) ‘Development of the New Fluoride Ion-Selective Electrode Modified with FexOy Nanoparticles’, Molecules (Basel, Switzerland), 25(21). doi: 10.3390/molecules25215213. Seguí Femenias, Y. et al. (2016) ‘Ag/AgCl ion-selective electrodes in neutral and alkaline environments containing interfering ions’, Materials and Structures/Materiaux et Constructions, pp. 2637–2651. doi: 10.1617/s11527-015-0673-8. TOKALIOGLU, Š., KARTAL, S. and SAHIN, U. (2004) ‘Determination of Fluoride in Various Samples and’, Turk J Chem, 28(2), pp. 203–211. Tzimou-Tsitouridou, R., Kabasakalis, B. and Alexiades, C. A. (1985) ‘A new TISAB with Aluminon for fluoride determination in water with ion-selective electrode’, Microchemical Journal, 32(3), pp. 373–382. doi: 10.1016/0026-265X(85)90104-3. Yildiz, Y. et al. (2018) ‘Analytical Chemistry : An Indian Journal Potentiometric Determination of % Fluoride Ion Content ( w / v ) in Toothpastes by Ion Selective Electrode’, 18(August), pp. 0–8. Zohoori, F. V. et al. (2015) ‘Effect of exercise on fluoride metabolism in adult humans: A pilot study’, Scientific Reports, 5, pp. 1–9. doi: 10.1038/srep16905.

Effect of Fluoride Concentration in Drinking Water on Dental Fluorosis in Southwest Saudi Arabia.

This study was intended to evaluate the fluoride concentration in drinking water and its effect on dental fluorosis in Southwest Saudi Arabia. Water samples were gathered rom wells, filtration plants and commercial brands (bottled water) in distinct urban and rural areas of Asir region of the Kingdom of Saudi Arabia (KSA). Overall, 63 water samples were collected from 12 locations and 9 brands of bottled water. ExStik® FL700Fluoridemeter was used in the analysis of water samples for fluoride levels. The total number of screened patients for dental fluorosis, aged between 9 and 50 years, was 1150; among them, 609 were males and 541 were females. Dean’s index criteria were used to examine the patients for dental fluorosis. The results revealed that fluoride levels varied between 0.03 and 3.8 ppm. People who drank well water displayed increased fluoride levels (>0.81 ppm). The prevalence of dental fluorosis was established to be 20.43% among the total number of examined patients. The findings of this study show very mild to moderate dental fluorosis prevail among the patients who consume well water in the Asir region.

Effect of Fluoride Concentration and pH on Corrosion Behavior of Ti–15Mo in Artificial Saliva

Corrosion behavior of Ti–15Mo alloy in artificial saliva containing variation in pH (7.2, 3.5) and varying concentrations of fluoride ions (2500, 5000 and 10,000 ppm) was evaluated using potentiodynamic polarization, electrochemical impedance spectroscopy studies to ascertain its suitability for dental implant applications. The study reveals that there is a strong dependence of the corrosion resistance of Ti–15Mo alloy on the concentration of fluoride ions in the electrolyte medium. Surface morphological characterization was carried out using SEM–EDAX to investigate the corrosion resistance in artificial saliva containing sodium fluoride at various pH conditions, and it was found that the surface roughness of the specimens was highly increased at pH 3.5. In spite of the active dissolution, the Ti–15Mo alloy exhibits passivity at anodic potentials at all concentrations of the fluoride ions studied. The results suggest that Ti–15Mo alloy can be a suitable alternative for dental implant applications.

Effect of Fluoride Concentration on Niobium Anodic Dissolution

Anodic behaviour of niobium in HF was investigated using potentiodynamic polarization technique. The effect of concentration was studied by varying the nominal HF concentration and few experiments were carried out by adding H2SO4 and KF to HF solutions, to determine the effect of various species on Nb dissolution. In the potentiodynamic polarization curves, distinct active and passive regions were seen at all the concentrations studied. A kinetic model involving a chemical and an electrochemical dissolution step in parallel was proposed to model the observed results. The model captures all the major characteristics of the polarization curves. HF2 - is identified as the contributing species for the chemical dissolution and remaining HF as the contributing species for the electrochemical dissolution.

Effect of Fluoride Concentration on Niobium Anodic Dissolution

Niobium is one of the valve metals [1] and, when exposed to air or water, it readily forms a chemically inert and mechanically strong oxide layer [2]. Nb is used as a popular alloying element in carbon and steel industry [3] due to its high corrosion resistance. Nb is also used for fabricating super conducting radio frequency cavities [2] used in particle accelerators which demand very smooth surfaces. The passive layer on Nb is stable in most aqueous media. However, it can be attacked by hydrofluoric acid [4, 5] or strong alkali [6]. Nb anodic dissolution in HF shows clear active and passive regions, followed by an increase and a large current plateau signifying transpassive dissolution [5]. The polarization and EIS data of Nb in warm alkali and acidic fluoride media was analyzed in the framework of surface charge approach combined with interfacial reactions [4]. The species that are reported to be formed in aqueous HF solutions are HF, H+, F-, HF2 - and H2F3 - [7] and the dissociation of HF involves the following reactions. HF ↔ H+ + F-, HF + F-↔ HF2 -, along with HF + HF2 - ↔ H2F3 - The corresponding equilibrium constants are respectively, 6.84 × 10-4, 5 and 0.58 [7]. In this study, we present the experimental results of anodic dissolution of Nb in different concentrations of HF and propose a kinetic model to match the observed results. All the experiments were carried out using Nb rotating disc electrode (RDE) in a standard three-electrode cell with Ag/AgCl (3.5 M KCl) as reference and Pt wire as counter electrode. HF concentration was changed between 50 mM and 1000 mM. In order to reduce the solution resistance effects, a supporting electrolyte (1 M Na2SO4) was used. The electrode rotational speed was maintained at 900 rpm. Before each experiment, the electrode was mechanically polished with 400, 800 and 1200 grade emery paper followed by ultra-sonication in ethanol and DI water. Potentiodynamic polarization data were acquired by sweeping the potential from open circuit potential (OCP) to 1 V above OCP, at 2 mV/s scan rate. Figure 1A shows the typical anodic behaviour of Nb measured as described above in different concentrations of HF used. The peak current values shift towards right with increase in HF concentration. The potential at which the peak occurs also shifts to more anodic values at higher HF concentration. The concentration of all the constituent species increases with increase in nominal HF concentration [8]. Therefore, few experiments were carried out adding H2SO4and KF to aqueous HF solutions to isolate the effect of different species on the dissolution (Fig 1B). Reaction mechanism analysis was employed to understand the dissolution mechanism of Nb in HF. A four step mechanism involving two dissolution steps, chemical and electrochemical was proposed to explain the results. The model captures all the major characteristics of the polarization curves.

Biofilm sensitivity of seven Streptococcus mutans strains to different fluoride levels

ABSTRACTThe effect of fluoride concentrations in dental products could be different depending on the Streptococcus mutans strain. The aim of this study was to investigate the effect of different fluoride concentrations corresponding to dental products on biofilm formation and metabolic activity of S. mutans strains. Seven S. mutans strains (UA159, A32-2, NG8, 10449, UA130, LM7, and OMZ175) were inoculated into 96-well microtiter plates and were tested with various concentrations of sodium fluoride (0.0, 1.0, 1.56, 3.13, 6.25, 12.5, 25, 50, 100, 125, 175, 225, 275, 625, 1,250, 2,250, and 5,500 ppm) for inhibition of biofilm formation and bacterial metabolic activity by recording absorbance values followed by scanning electron microscope (SEM) images. Data were analyzed by one-way analysis of variance and Tukey’s tests (α = 5%). Significantly more (p≤0.05) biofilm mass in the presence of fluoride was produced by A32-2 and NG8. UA130, LM7, and OMZ175 were more sensitive to increased fluoride and demonstrated few bacterial cells and extracellular polysaccharide (EPS) production at 100 ppm in SEM images. All strains were unable to produce significant biofilm at concentrations >225 ppm. Patients with tolerantS. mutans strains would potentially benefit less from the inherent antibacterial effect of fluoride.

Effect of Fluoride Concentration in Drinking Water on Intelligence Quotient of 12-14-Year-Old Children in Mathura District: A Cross-Sectional Study.

Aims:The aim was to assess and correlate the influence of the concentration of fluoride in ingested water on the intelligence quotient (IQ) of 12–14-year-old youngsters in Mathura district.Materials and Methods:A total of 219 children were selected, 75 from low F area, 75 medium F area, and 69 from high F area. The concentration of fluoride in the routinely ingested water was estimated using “Ion Selective Electrode method”; then, Raven's Test was utilized to estimate the IQ of the study participants. Independent t-test, Tukey's post hoc, Chi-square an analysis of variance tests were used to associate the mean and proportion IQ scores in high-, medium-, and low-fluoride regions along with inter-group significant differences (P ≤ 0.05).Results:The comparison of IQ score showed that 35 (46.7%) participants from the high fluoride and 10 (13.3%) participants from the medium-fluoride areas had below average IQ. Further, it was noted that the lowest mean marks were obtained by the children in the high-fluoride region (13.9467) followed by those in medium (18.9467) and uppermost in least noted fluoride area (38.6087). However, gender-based intergroup comparison did not produce a significant relation with fluoride (P ≥ 0.05).Conclusion:Concentration of Fluoride in the ingested water was significantly associated with the IQ of children. It has also coined the proportional variability in mental output in accordance to the ingested fluoride level. As two sides of a coin, fluoride cannot be utterly blamed for a lower intelligence in a population; it puts forward a fact that intelligence is a multifactorial variable with a strategic role played by genetics and nutrition to develop cognitive and psychosomatic activities in an individual.

Effect of Fluoride Concentration on Reduction of Enamel Demineralization According to the Cariogenic Challenge.

Fluoride present in toothpaste at 1,100 µg/g is considered effective on caries control. However, under high cariogenic challenge due to increasing sugar exposure, higher fluoride concentration (5,000 µg/g) could be necessary to compensate the unbalance on caries process. This was tested in a pH-cycling regimen, which evaluated the effect of fluoride concentration relative to toothpaste on reduction of enamel demineralization under conditions of two levels of cariogenic challenge. Enamel slabs (n=20) were subjected to two pH-cycling regimens, simulating 8x and 16x/day sugar exposure and were treated with solutions containing: 0 (no fluoride), 275 or 1,250 µg F/mL, resulting in 6 treatment groups: 4-h/0-F; 8-h/0-F; 4-h/275-F; 8-h/275-F; 4-h/1,250-F and 8-h/1,250-F. The 275 and 1,250 µg F/mL concentrations simulate mouth salivary dilution when 1,100 and 5,000 µg/g toothpastes are used. Enamel demineralization was assessed by surface (%SHL) and cross-sectional hardness. Fluoride taken up by enamel was also evaluated. Data were analyzed by ANOVA one-way and Tukey's test. The treatment with 1,250 µg F/mL significantly reduced %SHL compared with 275 µg F/mL (p<0.05), irrespective the level of cariogenic challenge (4-h/1,250-F vs. 4-h/275-F and 8-h/1,250-F vs 8-h/275-F comparisons, respectively). These data were supported by fluoride concentration found in enamel. These findings suggest that higher fluoride concentrations could partly compensate the greater caries risk under higher cariogenic challenge due to increasing sugar exposure.

Evaluation of the influence of serum and salivary fluoride levels on periodontal disease status in endemic fluorosis patients

Background: The major determinant of the prevalence and severity of dental fluorosis has been shown to be the concentration fluoride in the water consumed, but limited studies are available evaluating the effects of fluoride concentration on periodontal disease status. Aims: The aim of this study is to estimate the levels of fluoride in saliva, serum and in ground water of the villages where the subjects hail from and to correlate the levels of fluoride in serum and saliva to the periodontal disease severity. Materials and Methods: A total number of 120 subjects selected for the study are divided into two groups. Group A (test group) consisted of dental subjects diagnosed with dental fluorosis and periodontitis. Group B (control group) consisted of 20 non-fluorosed subjects. Assesment of fluoride in saliva and serum has been done by ion selective electrode method. The periodontal status was measured using the community periodontal index and clinical attachment level? Scores and were compared between the groups. Statistical Analysis Used: Correlation of altered fluoride levels in serum and saliva to the periodontal disease severity was done using the Pearson correlation coefficient and one-way analysis of variance was used for inter group comparison. Results and Conclusions: No correlation was found between salivary and fluoride levels and the periodontal disease severity. However, mean salivary fluoride levels were found to significantly influence the dental fluorosis severity.

The effects of fluoride and aluminum ions on ferrous-iron oxidation and copper sulfide bioleaching with Sulfobacillus thermosulfidooxidans

Microorganisms that grow at high temperatures can improve Fe(II) bio-oxidation and thereby its technological applications, such as bioleaching and H2S removal. Conversely, elements present in industrial growth media, such as fluoride, can inhibit bacterial growth and iron bio-oxidation. In this work, the influence of fluoride on the kinetics of ferrous-iron bio-oxidation with Sulfobacillus thermosulfidooxidans was investigated. The effects of fluoride concentrations (0–0.5mmolL−1) on both iron oxidation and bacterial growth rates were assessed. In addition, the effect of the addition of aluminum, which was intended to complex free fluoride and reduce the concentration of HF through the formation of aluminum–fluoride complexes, was also investigated. The results show that 0.5mmolL−1 NaF completely inhibited bacterial growth within 60h. Nevertheless, fluoride toxicity to S. thermosulfidooxidans was minimized by control of the aluminum–fluoride ratio in the system because, at a 2:1 aluminum–fluoride molar ratio, bacterial growth was similar to that observed in the absence of fluoride ions. Despite a slower bacterial growth rate, fluoride concentrations less than the inhibitory concentration increased the Fe(II) oxidation rate. Successful copper bioleaching (80–100%) from fluoride-containing sulfide ores (1% total fluoride) was demonstrated in the presence of aluminum.

Effect of fluoride concentration in pH 4.3 and pH 7.0 supersaturated solutions on the crystal growth of hydroxyapatite

Objectives: Present study was undertaken to investigate the crystal growth onto synthetic hydroxyapatite (HA) seeds in pH 4.3 and pH 7.0 supersaturated solutions with different fluoride concentrations. Materials and Methods: 8 groups of pH 4.3 and 7.0 calcium phosphate supersaturated solutions were prepared with different fluoride concentrations (0, 1, 2 and 4 ppm). Calcium phosphate precipitates yield crystal growth onto the HA seed surface while solutions flow. For evaluation of crystallizing process, the changes of , , concentrations of the inlet and outlet solutions were determined. The recovered solid samples were weighed to assess the amount of minerals precipitated, and finally determined their composition to deduce characteristics of crystals. Results: During the seeded crystal growth, there were significantly more consumption of , , in pH 4.3 solutions than pH 7.0 (p , , consumption in experimental solutions, weight increment of HA seed, and fluoride ratio in crystallized samples were increased. There were significant differences among the groups (p

Detection of free radicals formed by in vitro metabolism of fluoride using EPR spectroscopy

In many parts of the globe, where water contains large amount of fluoride, fluorosis is a serious public health problem. It is accompanied by many changes, not only in the bones, but practically in all organs of the body. Since it was discovered that oxidation stress, together with the peroxidation of lipids which accompanies it, results in many diseases, research has been carried out on this aspect of fluorosis. The findings, however, are incomplete and divergent. The aim of our study was to determine the presence of free radicals in hepatocytes exposed to fluoride in concentrations which do not lead to changes in the concentrations of calcium and magnesium ions.Free radical properties of hepatocytes incubated with fluoride were studied by an X-band electron paramagnetic resonance (EPR) spectroscopy. Hepatocytes are paramagnetic and broad unsymmetrical EPR spectra were obtained for them. Oxygen free radicals with g-factor of 2.0032 exist in hepatocytes. The effect of fluoride concentration and the time of incubation on free radicals amount in cells were examined. The amount of free radicals in hepatocytes increases with the increase of fluoride concentration for all the incubation times (10, 30, and 60min). The amount of free radicals in hepatocytes decreases with the increase of time of incubation for all the used fluoride concentrations (0.002, 0.082, and 0.164mmol/l). EPR spectra of the studied cells are homogeneously broadened. Continuous microwave saturation of EPR lines indicates that slow spin–lattice relaxation processes exist in the studied cells. Strong dipolar interactions responsible for the broadening (ΔBpp: 1.45–1.87mT) of the EPR spectra exist in the hepatocytes.

Effects of anodization parameters on the formation of titania nanotubes in ethylene glycol

The effects of fluoride concentration, anodization temperature, and anodization applied potential difference on the formation and dimensions of the titania nanotubes in ethylene glycol/water systems were investigated. It was found that fluoride concentration and anodization temperature were the two critical parameters for controlling the nanotube formation whilst anodization applied potential difference mainly contributes to tuning the dimension of the nanotubes. Electrolytes containing a low fluoride concentration are beneficial for initiating nanotube formation, whilst a higher anodization temperature is helpful to the rapid growth of the nanotubes. It is shown that the current–time curve obtained during the anodization can be used as an effective tool to predict the morphology of titania nanotubes. A model based on the competition between electrochemical oxidation of the titanium and chemical dissolution by fluoride ions is developed to explain the experimental observations.

Electrochemical stability and surface analysis in evaluation fluoride effect on new bioalloy Ti7Al3V2Mo2Fe used in dentistry

The aim of this study is focused on the effect of fluoride concentration on the corrosion behavior of Ti7Al3V2Mo2Fe alloys uncoated/coated in artificial saliva. Ti7Al3V2Mo2Fe alloys were covered by chemical methods with hydroxyapatite to enhance the osteointegration of implants materials. The stability of Ti7Al3V2Mo2Fe alloys uncoated/coated in artificial saliva with/without fluoride ions was studied by electrochemical techniques (open circuit potential, cyclic voltammetry, and linear polarization). On the covered samples, dissolution test in simulated body fluids and wettability test were performed. Investigations regarding the sample surface modifications were made by atomic force microscopy and Fourier transform infrared spectroscopy. The results show that the corrosion resistance of Ti7Al3V2Mo2Fe in solution containing fluoride decreases in comparison with that in a solution not containing fluoride. Significant changes appear at a concentration larger than 0.05 M. The coating has a positive effect on corrosion resistance of metallic substrate in the fluoride presence acting as a semi-mechanical barrier.

Effects of Fluoride Concentration on Developmental Defects Enamel in Endemic fluoride area of Nalgonda District Andhra Pradesh

Effects of Fluoride Concentration on Developmental Defects Enamel in Endemic fluoride area of Nalgonda District Andhra Pradesh

The effects of the fluoride concentration of acidulated buffer solutions on dentine remineralization

상아질의 재광화에 적당한 불소농도에 대하여는 서로 다른 주장이 존재하므로 불소가 병소 내 무기질의 분포와 수산화인회석 결정성장에 미치는 영향을 분석하기 위하여 이 연구를 시행하였다. 치아절편을 유산완충 탈회용액에 넣어 인공 치아우식을 형성한 후, 재광화 효과를 관찰하기 위해 불소농도가 각각 1, 2, 4 ppm인 유산완충 재광화용액에서 7일간 유지시켰다. 우식 진행과 재광화 양상을 관찰하기 위하여 탈회 2일, 재광화 7일 등 총 9일간 편광현미경으로 관찰하였으며 수산화인회석결정의 변화를 관찰하기 위하여서는 정상상아질, 탈회 2일군, 재광화 7일군의 파절시편을 주사전자현미경으로 관찰하여 다음과 같은 결과를 얻었다. 1. 모든 군에서 병소상부의 무기질침착과 병소하부의 무기질소실이 동시에 일어났다. 2. 불소농도가 증가하면 우식 병소의 무기질침착이 증가하였다. 3. 수산화인회석결정이 커졌다. 본실험의 결과에 의하면, 상아질의 우식과 재광화과정이 단순히 탈회 또는 재광화만이 독립적으로 일어나는 과정이 아니고 이 두 과정이 동시에 일어나는 동력학적인 과정이다. 또한 불소농도의 증가와 함께 재광화 양상도 증가하였고, 이러한 재광화는 유기기질망 주위의 수산화인회석결정을 중심으로 진행되었다. 【The aim of this vitro-study is to evaluate the effects of fluoride on remineralization of artificial dentine caries. 10 sound permanent premolars, which were extracted for orthodontic reason within 1 week. were used for this study. Artificial dentine caries was created by using a partially saturated buffer solution for 2 days with grounded thin specimens and fractured whole-body specimens. Remineralization solutions with three different fluoride concentration (1 ppm. 2 ppm and 4 ppm) were used on demineralized-specimens for 7 days. Polarizing microscope and scanning electron microscope were used for the evaluation of the mineral distribution profile and morphology of crystallites of hydroxyapatite. The results were as follows: 1. When treated with the fluoride solutions, the demineralized dentine specimens showed remineralization of the upper part and demineralization of the lower part of the lesion body simultaneously. 2. As the concentration of fluoride increased, the mineral precipitation in the caries dentine increased. The mineral precipitation mainly occurred in the surface layer in 1 and 2 ppm- specimens and in the whole lesion body in 4 ppm -specimens. 3. When treated with the fluoride solution, the hydroxyapatite crystals grew. This crystal growth was even observed in the lower part of the lesion body which had shown the loss of mineral.】

Intra-Oral Fluoride Retention 3 Minutes after Fluoride Mouthrinsing in 4- to 5-Year-Old Children: Effects of Fluoride Concentration and Rinsing Time

This study was undertaken to explore the site-specific retention rate and the possibility of shortening fluoride (F) mouthrinsing time of kindergarten children. Fluoride retention after 10-, 20- and 30-second mouthrinsing was determined in 43 kindergarten children aged 4–5 years. Tooth surfaces were sampled by a paper point method. Fluoride concentrations in the salivary film on tooth surfaces increased from primary molars to primary incisors in the maxilla and decreased from primary molars to primary incisors in the mandible. The fluoride solution reached the primary molars even after a 10-second rinse, but F concentrations were higher after 20 s than after 10 s and significantly higher after 30 s than after 10 s. No significant difference was observed between 20 and 30 s. The average total F retained in the mouth was 0.13 mg after 20 s and 0.17 mg after 30 s. It was concluded that 30-second mouthrinsing, which is used extensively in Japanese kindergartens, can be shortened to 20 s.

Two distinct fracture modes of copper alloys in fluoride environments

The susceptibility of aluminum brass and aluminum bronze to stress corrosion cracking (SCC) was evaluated in fluoride environments by means of the slow strain rate technique. The effects of fluoride concentration and applied electrochemical potential on the SCC susceptibility were investigated. The SCC mechanism of aluminum brass was found to be dependent upon the de-alloying phenomenon while that of aluminum bronze on the film-rupture mechanism occurring within a certain range of applied electrochemical potentials. For aluminum brass, both the stress ratio and the time-to-fracture ratio were closely related to the logarithmic concentration of F − ions. The fracture modes were ductile dimpled tearing fracture for the aluminum brass at the corrosion potential while intergranular for the aluminum bronze at various anodic potentials. The micro-galvanic effects of the constituent elements were used to estimate the anodic equilibrium potentials of the two alloys.