Neutral Fluoride Solution Research Articles

Effects of Fluoride on NiTi Orthodontic Archwires: An X-ray Diffraction Study:

Objective: To explore the changes in nickel-titanium (NiTi) archwires after exposure to fluoride-containing acetic acid solutions. Materials and methods: Preformed rectangular NiTi wires were immersed in either an acidulated fluoride solution, a neutral fluoride solution or distilled water (control) for 1.5 hours at 37°C. After immersion, the unloading force values at four deflection points were measured by three-point bending test. Scanning electron microscopy and X-ray diffraction analysis were also performed to characterize the effects of the fluoride exposure on the wire. Results: Unloading force values of NiTi orthodontic wires were significantly decreased after exposure to both fluoride solutions (p < 0.001). Corrosive changes in surface topography were observed for both fluoride solutions. Wires exposed to acidic fluoride appeared as more severely affected. X-ray diffraction analysis showed no change in crystal lattice of NiTi wires in both solutions. Conclusion: The results suggest that using topical fluoride agents with NiTi wire could decrease the functional unloading mechanical properties of the wire and contribute to prolonged orthodontic treatment.

Stress and electrochemical corrosion of titanium produced by laser rapid forming

Objective: To investigate the stress corrosion and electrochemical corrosion resistance of titanium produced through laser rapid forming (LRF), and to provide a basis for their clinical application. Methods: Forged commercial pure titanium (CP-Ti) was used as control group and LRF pure titanium was used as LRF group. All samples were placed in acidic artificial saliva containing fluorine (pH=7), and loaded with a stress of 1.2 × σ(0.2) Pa (σ(0.2) represents the yield strength of material). Stress corrosion resistance of specimens that have been soaked for 30 days was analyzed by naked eye observation, X-ray diffraction analysis and scanning electron microscopy. For samples placed in artificial saliva, neutral fluoride solution (pH=7) and acidic fluoride solution (pH=3) (4 test pieces in each corrosive medium), and their electrochemical corrosion resistance was evaluated by free corrosion potential (Ecorr) measurements, corrosion current (Icorr), electrochemical impedance spectroscopy (EIS), and anodic polarization curves. Results: With the prolongation of immersion time, the corrosion products gradually increased. The stress corrosion of CP-Ti group was significantly more than that of LRF-Ti group, and the pit diameter was significantly larger than that of LRF-Ti group. The electrochemical corrosion results showed that the Ecorr (-469 mV) of LRF-Ti in artificial saliva was higher than that of CP-Ti (-555 mV), and the Ecorr (-925 mV) of LRF-Ti was higher than that of CP-Ti (-943 mV) in neutral fluoride solution. In acid fluoride solution, the Ecorr (-943 mV) of LRF-Ti was higher than that of CP-Ti (-956 mV). The Ecorr of the same metal was the highest in artificial saliva and the lowest in acid fluoride solution; the Icorr of the same metal was the lowest in artificial saliva and the highest in acid fluoride solution. Conclusions: Under the same corrosion conditions, LRF Ti demonstrated better stress and electrochemical corrosion resistance than CP-Ti.

Corrosion and Mechanical Degradation of Ni-Ti Superelastic Alloy in Neutral Fluoride Solution

The corrosion behavior and mechanical degradation of Ni-Ti superelastic alloy in neutral fluoride solution were investigated with a focus on the effect of temperature during immersion. Corrosion was accelerated by increasing the temperature, and mass loss increased with immersion time. Furthermore, Ti ions (Ni ions) preferentially dissolved in the early (later) stage of immersion. The tensile strength of the immersed specimen decreased when the mass loss was approximately 0.040-0.050 mg/mm3. The fracture mechanisms of specimens immersed in 2.0% NaF solution were active path corrosion at room temperature and presumably hydrogen embrittlement at 80 °C. For long-term (e.g., 180 days) immersions at 80 °C, hydrogen embrittlement did not occur, because the absorbed hydrogen diffused to the center of the immersed specimens, rendering the hydrogen distribution comparatively uniform. These findings suggest that the fracture mechanism of immersed specimens can change as a result of the temperature during immersion.

An in vitro assessment of the mechanical characteristics of nickel-titanium orthodontic wires in Fluoride solutions with different acidities.

Objectives:The aim was to evaluate the in vitro effects of fluoride solutions with different acidities on load-deflection characteristics of nickel-titanium (NiTi) orthodontic wires.Materials and Methods:In this study, which lasted 30 days, 36 (3 cm long, 0.016 × 0.022 inches, SENT 1622, G & H wire Company, Greenwood, Indiana, USA) NiTi wires, were divided into three experimental groups of 12 each. Two groups were subjected to 0.05 topical fluoride mouthwash with different acidities (G1, pH 4; G2, pH 6.6) for 90 s, twice a day, and kept in normal saline after that. The third group (G3, the control group) was kept in normal saline only. Load and unload forces were measured with three bracket bending test in a universal testing machine (Testometric Co, Rochdale, UK). Loading and unloading plateaus and hysteresis were also recorded. Data were then analyzed using analysis of variance and honestly significant difference Tukey at P < 0.05.Results:During the loading phase, there was a significant difference between deflections (P < 0.001); but there was no interaction effect (P = 0.191) and no significant difference among three groups (P = 0.268). In the unloading phase, there was a significant difference between deflections (P < 0.001) and an interaction effect was also observed (P = 0.008). Further, significant differences noted among three groups (P = 0.037). Only in the unloading phase, at deflections of 2.2 through 0.2 mm, significant differences between the mean force values of the G1 and G3 groups were observed (P = 0.037).Conclusion:Based on this in-vitro study, compared to neutral fluoride solution, daily mouthwash with a fluoride solution with more acidic pH of 4 affected the NiTi wires load-deflection characteristics during the unloading phase. This finding may have clinical implications and can be further validated by in-vivo studies.

Effect of co-existing ions during the preparation of alumina by electrolysis with aluminum soluble electrodes: Structure and defluoridation activity of electro-synthesized adsorbents

The electrochemical dissolution of aluminum was carried out to prepare hydrated aluminas which were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), chemical titrations and defluoridation activities. Aluminas were obtained at controlled pH depending upon the counter cations of the electrolyte. A boehmite AlOOH phase was isolated mainly in ammonium solution, while aluminas synthesized in the other media contained a mixture of phases, usually both boehmite and bayerite γ-Al(OH)3. All the boehmite phases contained nano-crystallites of less than 3nm. Batch defluoridation experiments revealed a second influence of the original electrolyte. Aluminas were very effective in defluoridation with abatement rates of 99.5%, 98.5% and 97.3% from neutral fluoride solution at 10mgL−1 when they were prepared in solution of (NH4)2SO4, (NH4)HCO2 and NH4Cl, respectively. The maximum fluoride capacities were 46.94; 10.25 and 12.18mg g−1 for aluminas prepared in solution of (NH4)2SO4; (NH4)HCO2 and NH4Cl, respectively. The amount of dissolved Al was found to be less than 0.19mgL−1 at neutral pH. These results show that a defluoridation with electro-synthesized aluminas would be more efficient and safe than a direct electrocoagulation.

Fracture and corrosion behaviors of Ni–Ti superelastic alloy under sustained tensile loading in neutral fluoride solution containing hydrogen peroxide

The fracture and corrosion behaviors of Ni–Ti superelastic alloy have been investigated by carrying out sustained tensile-loading tests in neutral 2% NaF aqueous solutions containing various H2O2 concentrations. The times to fracture in solutions with 0.001M, 0.01M and 1M H2O2 are shorter than that in a solution without H2O2. In the solution with 0.1M H2O2, however, the time to fracture becomes long and the fractographic features are markedly changed. On the basis of the polarization behavior, corrosion is enhanced with increasing H2O2 concentration. Under an applied stress above the critical stress for the stress-induced martensite transformation, the fluctuations of corrosion potential and corrosion current density become larger than those without the applied stress. The present results suggest that the fracture and corrosion behaviors of the alloy in neutral fluoride solutions are sensitively affected by the H2O2 concentration, but the relationship between fracture and corrosion does not always straightforwardly correspond to the H2O2 concentration.

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

Electrochemical etching of NiTi alloy in a pH 6 fluoride solution is proposed as a convenient alternative to chemical etching in oxidizing HF media. Anodization produces protons at the electrode surface, and local acidification increases the concentration of HF that efficiently dissolves the surface oxides, promoting a sustained dissolution current that decreases with increasing mass-transfer rate. The voltammetric pattern includes a "pseudoplateau" at low potentials, in which only a metal dissolution takes place, and a steady current increase at higher potentials due to the onset of oxygen evolution. The treatment produces a semilustrous rough surface, showing a structure of shallow microscopic cavities in SEM images. EIS spectra recorded in the pseudoplateau region are similar to those observed during anodic polarization of Ti in HF and their analysis indicates formation of a thin barrier film of thickness increasing linearly with potential.

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

Electrochemical etching of NiTi alloy in a pH 6 fluoride solution is proposed as a convenient, less dangerous procedure than traditional chemical etching in oxidizing HF media. Anodic polarization produces protons at the electrode surface, and local acidification increases the concentration of HF that efficiently dissolves the surface oxides, promoting a sustained dissolution current that decreases with increasing mass-transfer rate. The voltammetric pattern includes a “pseudoplateau” at low potentials, in which only a metal dissolution takes place, and a steady current increase at higher potentials due to the onset of oxygen evolution. The treatment produces a semilustrous rough surface, showing a structure of shallow microscopic cavities in scanning electron microscopy images. Impedance spectra recorded in the pseudoplateau region are similar to those observed during anodic polarization of Ti in HF, and their analysis indicates a formation of a thin barrier film whose thickness increases linearly with potential.

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

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Susceptibility to Hydrogen Absorption and Hydrogen Thermal Desorption of Titanium Alloys Immersed in Neutral Fluoride Solution under Applied Potential

The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37°C under various applied cathodic potentials. Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than −1.5 V, −1.9 V and −1.4 V versus a saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of −2.0 V for 24 h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride solutions, whereas the hydrogen thermal desorption behaviors of Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution, the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6Al-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys.

Effects of potential on hydrogen absorption and desorption behaviors of titanium in neutral fluoride solutions

The effects of potential on the hydrogen absorption and desorption of commercial pure titanium immersed in neutral 2.0% and 0.2% NaF solutions for 24 h have been investigated by hydrogen thermal desorption analysis. Hydrogen absorption occurs in both solutions under less noble potentials than −1.2 V versus a saturated calomel electrode. The amount of absorbed hydrogen increases with decreasing applied potential. Under the same applied potential, the amount of hydrogen absorbed in the 2.0% NaF solution is larger than that in the 0.2% NaF solution. Hydrogen thermal desorption is observed in the temperature range from 250–300 to 700 °C. For the 2.0% NaF solution, compared with the 0.2% NaF solution, the amount of hydrogen desorbed in the high temperature range is large. The hydrogen desorption behavior for neutral NaF solutions under the applied potential is not necessarily consistent with that for acidulated phosphate fluoride solutions without the applied potential reported previously.

Fracture of sustained tensile-loaded Ti–0.2% Pd alloy in acid and neutral fluoride solutions

The fracturing of Ti–0.2 mass% Pd (Ti–0.2Pd) alloy in acid and neutral fluoride solutions has been investigated by a sustained tensile-loading test. In 2.0% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solution, the time to fracture of the Ti–0.2Pd alloy is shorter than that of commercial pure titanium for the same applied stress. In 2.0 and 0.2% APF solutions, fractures are characterized by a cup-cone mode irrespective of applied stress. In 2.0 and 0.2% NaF solutions, transitions from cup-cone to shear modes of the fractures are observed with decreasing applied stress. The results of the present study suggest that the susceptibility to fracturing of the Ti–0.2Pd alloy is higher than that of commercial pure titanium.

Hydrogen absorption of titanium and nickel‐titanium alloys during long‐term immersion in neutral fluoride solution

Hydrogen absorption of biomedical titanium and Ni-Ti alloys in a neutral fluoride (2.0% NaF) solution for up to 10,000 h at 37 degrees C has been evaluated by means of hydrogen thermal desorption analysis. For alpha titanium (commercial pure titanium), the amount of absorbed hydrogen was, at most, 10-30 mass ppm, and the corrosion product and hydride formation were revealed on the surface of the specimen by X-ray diffraction analysis. Ni-Ti superelastic alloy absorbed approximately 150 mass ppm of hydrogen, which was probably sufficient to result in the pronounced degradation of the mechanical properties, although corrosion was hardly observed. In contrast, hydrogen absorption of alpha-beta titanium (Ti-6Al-4V) and beta titanium (Ti-11.3Mo-6.6Zr-4.3Sn) alloys was negligible, although general corrosion was observed. The results of the present study indicate that the susceptibility of titanium and Ni-Ti alloys to hydrogen absorption in the neutral fluoride solution is different from that in the acidic fluoride solution reported previously.

Formation of self-ordered nano-tubular structure of anodic oxide layer on titanium

Room temperature anodization of titanium foil specimens was carried out in 0.5 M phosphoric acid solution with addition of various halide ions. Addition of 0.138 M HF or NaF resulted in self-ordered nano-tubular oxide structure. Addition of bromide and chloride ions initiated only pitting and nano-pores were not observed during anodization. Acidified fluoride solution is found to be necessary to obtain ordered nano-structure as neutral fluoride solution did not form nano-pores. Instability of the oxide layer during anodization and formation of the self-ordered structure can be explained by the perturbation theory. Separation of individual nano-tubes of titanium oxide layer from the inter-connected nano-pores could be attributed to the possible repulsion forces of the cation vacancies.

Susceptibility to delayed fracture of alpha–beta titanium alloy in fluoride solutions

The susceptibility to delayed fracture of the alpha–beta titanium alloy Ti–6Al–4V has been investigated in acidic and neutral fluoride solutions at room temperature. The time to fracture decreased with increasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions at pH 5.0. The time to fracture in the 2.0% APF solution was shorter than that in the 0.2% APF solution, although at an applied stress higher than 1000 MPa, the times to fracture were almost the same in both the solutions. For immersion in the 0.2% APF solution, when the applied stress was lower than 700 MPa, delayed fracture did not occur within 1000 h. The fracture surface of specimens immersed in the 2.0% APF solution exhibited brittleness associated with hydrogen absorption, while that in the 0.2% APF solution was ductile and characterized macroscopically as having a cup–cone morphology. The amounts of hydrogen absorbed in 2.0% and 0.2% APF solutions for 24 h were approximately 200 and 30 mass ppm, respectively. As the immersion time increased, the amount of hydrogen absorbed in the 2.0% APF solution increased, whereas that in the 0.2% APF solution hardly increased. In neutral 2.0% and 0.2% NaF solutions, the delayed fracture did not occur within 1000 h, although general corrosion was observed. These results indicate that the susceptibility to delayed fracture of alpha–beta titanium alloy, compared with those of the alpha titanium and beta titanium alloy reported previously, is low in acidic and neutral fluoride solutions.

Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions.

Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride.

Fracture associated with hydrogen absorption of sustained tensile-loaded titanium in acid and neutral fluoride solutions.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600 degrees C. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties.

Calcium Fluoride Formation on Sound Enamel Using Fluoride Solutions with and without Lactate

The formation of calcium (Ca) fluoride (CaF2) on bovine enamel blocks during clinically relevant treatment times using neutral fluoride (F) solutions (0.26 mol/l F) with and without 0.1 mol/l lactate was investigated. Uncoated and pellicle-coated blocks were evaluated for alkali-soluble (1 mol/l KOH, three consecutive 24-hour treatments) Ca, PO4, and F after treatment by the F solutions for 0, 5, 15, 30, and 60 min. There was an overall time-related increase in F recovery, while Ca tended to remain at baseline levels. Less F was recovered from the pellicle-coated blocks. The addition of lactate to the F treatment solution did not result in an overall increase in alkali-soluble F recovery, but did result in the formation of cuboidal shaped crystals which closely approached the morphology of pure CaF2. A 1:2 stoichiometric ratio Ca:2F (mol:mol) was not established based on chemical analyses. The ultrastructural and elemental composition of surface deposits on the samples, as determined using scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy, established the presence of CaF2 after 24-hour F treatments; however, it was not possible to directly demonstrate the formation of CaF2 after clinically relevant treatment times.

The effect of time of exposure on fluoride uptake by human enamel from acidulated fluoride solutions in vitro.

Fluoride uptake on and in enamel during topical application of acidulated solutions was studied. The variables were different time intervals and different pH levels of the treatment solutions. The experiment was carried out with human enamel exposed to 2% NaF solutions, pH 3.5 and 5.5, for 30 sec, 60 sec, 5 min, and 60 min. The amounts of fluoride formed on (as calcium fluoride) and in (as fluorapatite) enamel were determined by chemical assessments, and scanning electron microscopy provided the visualization of the deposits on the surface. It could be demonstrated that the two pH levels caused deposition of large amounts of calcium fluoride and that almost twice as much was deposited at pH 3.5 as at 5.5. The amount of deposit increased rapidly with time of exposure in both situations compared with similar experiments with neutral fluoride solutions. Firmly bound fluoride was incorporated in the enamel only during the 60-min incubation.

Polarography in neutral fluoride solution with particular reference to lead

The polarographic behaviour of 35 ions in 1 M ammonium fluoride solution adjusted to pH 7 has been investigated. In this base electrolyte lead is reduced reversibly and, except for considerably larger amounts of copper, bismuth, cadmium, antimony(III) and iron(III), the only ions interfering with the d.c. polarographic determination of lead are vanadium(V), thallium(I), tellurium(IV), uranium-(VI) and tin(II). By arranging for vanadium, tellurium and tin to be in the +4, +6 and +4 oxidation states, respectively, interference from these elements could be eliminated and a selective polarographic method for lead is available.