The inhibitory effects of silver diamine fluorides on cysteine cathepsins

Aim

The expression of cysteine cathepsins in human carious dentine suggests that this enzyme contributes to the collagen degradation in caries progress. This study investigated whether silver diamine fluoride (SDF) inhibited the activity of cysteine cathepsins.

Methods

Three commercial SDF solutions with concentrations at 38%, 30% and 12% were studied. Two fluoride solutions with the same fluoride ion (F^-) concentrations as the 38% and 12% SDF solutions, and 2 silver solutions with the same silver ion (Ag⁺) concentrations as the 38% and 12% SDF solutions were prepared. Five samples of each experimental solution were used to study their inhibitory effect on two cathepsins (B and K) using cathepsin assay kits. Positive control contained assay buffer and cathepsins dilution was used to calculate the percentage inhibition (difference between the mean readings of the test solution and control solution divided by that of the control group).

Results

The percentage inhibition of 38%, 30% and 12% SDF on cathepsin B were 92.0%, 91.5% and 90.3%, respectively (p < 0.001); on cathepsin K were 80.6%, 78.5% and 77.9%, respectively (p < 0.001). Ag⁺ exhibited the inhibitory effect against both cathepsin B and K with or without the presence of F^- (p < 0.01). The solutions containing Ag⁺ have significantly higher inhibitory effect than the solutions containing F^- only (p < 0.01).

Conclusion

According to this study, SDF solution at all 3 tested concentrations significantly inhibited the activity of cathepsin B and K.     

Effect of experimental mouthrinses containing the combination of NaF and TiF4 on enamel erosive wear in vitro

Objective

This study analysed the anti-erosive effect of experimental solutions containing TiF₄ and NaF.

Methods

Bovine enamel samples (n = 15) were treated with: (1) commercial solution with SnCl₂/NaF (Erosion Protection^®); (2) experimental solution with 0.0815% TiF₄; (3) 0.105% NaF; (4) 0.042% NaF + 0.049% TiF₄; (5) 0.063% NaF + 0.036% TiF₄ or (6) control. The samples were submitted to pH cycles and daily fluoride applications for seven days. The enamel wear was measured using a contact profilometer and analysed by ANOVA (p < 0.05).

Results

The best anti-erosive effect was found for experimental solution with 0.0815% TiF₄ (99% reduction in enamel wear), followed by SnCl₂/NaF (78%) and 0.049% TiF₄ + 0.042% NaF solution (41%).

Conclusions

The experimental solution containing a specific combination of TiF₄ + NaF has the ability to partially reduce enamel erosion.     

Six-month evaluation of adhesives interface created by a hydrophobic adhesive to acid-etched ethanol-wet bonded dentine with simplified dehydration protocols

Objectives

To evaluate the efficacy of simplified dehydration protocols, in the absence of tubular occlusion, on bond strength and interfacial nanoleakage of a hydrophobic experimental adhesive blend to acid-etched, ethanol-dehydrated dentine immediately and after 6 months.

Methods

Molars were randomly assigned to 6 treatment groups (n = 5). Under pulpal pressure simulation, dentine crowns were acid-etched with 35% H₃PO₄ and rinsed with water. Adper Scotchbond Multi-Purpose was used for the control group. The remaining groups had their dentine surface dehydrated with ethanol solutions: group 1 = 50%, 70%, 80%, 95% and 3 × 100%, 30 s for each application; group 2 the same ethanol sequence with 15 s for each solution; groups 3, 4 and 5 used 100% ethanol only, applied in seven, three or one 30 s step, respectively. After dehydration, a primer (50% BisGMA + TEGDMA, 50% ethanol) was used, followed by the neat comonomer adhesive application. Resin composite build-ups were then prepared using an incremental technique. Specimens were stored for 24 h, sectioned into beams and stressed to failure after 24 h or after 6 months of artificial ageing. Interfacial silver leakage evaluation was performed for both storage periods (n = 5 per subgroup).

Results

Group 1 showed higher bond strengths at 24 h or after 6 months of ageing (45.6 ± 5.9^a/43.1 ± 3.2^a MPa) and lower silver impregnation. Bond strength results were statistically similar to control group (41.2 ± 3.3^ab/38.3 ± 4.0^ab MPa), group 2 (40.0 ± 3.1^ab/38.6 ± 3.2^ab MPa), and group 3 at 24 h (35.5 ± 4.3^ab MPa). Groups 4 (34.6 ± 5.7^bc/25.9 ± 4.1^c MPa) and 5 (24.7 ± 4.9^c/18.2 ± 4.2^c MPa) resulted in lower bond strengths, extensive interfacial nanoleakage and more prominent reductions (up to 25%) in bond strengths after 6 months of ageing.

Conclusions

Simplified dehydration protocols using one or three 100% ethanol applications should be avoided for the ethanol-wet bonding technique in the absence of tubular occlusion, as they showed decreased bond strength, more severe nanoleakage and reduced bond stability over time.     

A qualitative and quantitative investigation into the effect of fluoride formulations on enamel erosion and erosion-abrasion in vitro

Objectives

To investigate the effect of a single application of highly concentrated SnF₂ and NaF solutions and a NaF/CaF₂ varnish on human enamel subjected to hydrochloric acid erosion and tooth brush abrasion.

Methods

Forty enamel samples were prepared from human third molars and NaF (9500 ppm, pH 8.0), SnF₂ (9500 ppm, pH 2.6) solutions; Bifluorid10^® varnish (42,500 ppm, NaF 5%, CaF₂ 5%) and deionized water (control) was applied to the enamel. Following this three, six and nine cycles of erosion [1 cycle = erosion (0.01 M HCl, pH 2.2, 2 min) + artificial saliva (1 h, pH 7.0)] and erosion-abrasion [1 cycle = erosion (0.01 M HCl, pH 2.2, 2 min) + artificial saliva (1 h, pH 7.0) + abrasion (120 linear strokes in artificial saliva from Tepe medium soft brushes 200 g loading)] were carried out. The fluoride treated enamel was analysed using Knoop microhardness, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

Results

For erosion alone, there was significantly less microhardness reduction in the Bifluorid10^® group after three and six cycles of erosion (P < 0.05), however no other groups showed statistically different hardness (P > 0.05). The EDS analysis showed that only the Bifluorid10^® group had any detectable fluorine following erosion and erosion-abrasion (0.1 wt.% and 0.2 wt.% fluorine respectively). The surface fluorine was found to have been removed after erosion and erosion-abrasion for all other surface treatments. Although precipitates were observed after application of the surface treatments, following erosion-abrasion, no visible surface effects from any fluoride preparation remained.

Conclusions

Enamel surface precipitates from application NaF, SnF₂ solutions appear to not be able to provide protection against gastric erosion and tooth brush abrasion. The NaF/CaF₂ varnish provided limited protection against erosion but the role for such varnishes in gastric erosion and tooth brush abrasion remains uncertain.     

Ionic liquid salt bridge based on N-alkyl-N-methylpyrrolidinium bis(pentafluoroethanesulfonyl)amide for low ionic strength aqueous solutions

The phase-boundary potential between the moderately hydrophobic ionic liquid and a low ionic strength aqueous solution is demonstrated to be stable and constant with the standard deviation of 0.4 mV down to 20 μmol kg⁻¹ HBr, LiBr, and KBr solutions, for three ionic liquids that consist of either N-methyl-N-octylpyrrolidinium, N-heptyl-N-methylpyrrolidinium, or N-hexyl-N-methylpyrrolidinium and a common anion species, bis(pentafluoroethanesulfonyl)amide. This stability is promising for accurate measurements of pH of low ionic strength samples and reliable estimates of single ion activities in general. The phase-boundary potential deviates from the value determined by the partition of the ionic liquid in further dilute aqueous solutions. The magnitude of the deviation ranges from 3 to 11 mV at 5 μmol kg⁻¹ MBr (M is H⁺, Li⁺, or K⁺). The solubility of these ionic liquids in water is 0.2 mmol dm⁻³ at most at 25 °C, which is another advantage of ionic liquid salt bridge in electroanalytical chemistry.     

Sorption of water, ethanol or ethanol/water solutions by light-cured dental dimethacrylate resins

Objectives

This work is concerned with the study of the sorption and desorption process of water, ethanol or ethanol/water solution 50% (v/v) or 75% (v/v) by the dental resins prepared by light curing of Bis-GMA, Bis-EMA, UDMA, TEGDMA or D₃MA.

Methods

A thin resin disc is placed in a bath of time to obtain the sorption curve m_t = f(t). Then the liquid is desorbed until a constant mass for the disc is reached and the desorption curve is recorded. These experimental curves help in the determination of the sorbed/desorbed liquid amount at equilibrium, the percentage of the extracted mass of unreacted monomer known as “solubility”, and the sorption/desorption diffusion coefficient which expresses correspondingly the rate of the liquid sorption/desorption.

Results

The highest liquid uptake by dental resins was 13.3 wt% ethanol for Bis-GMA-resin, 12.0 wt% ethanol for UDMA-resin, 10.10 wt% ethanol/water solution for TEGDMA-resin, 7.34 wt% ethanol for D₃MA-resin and 6.61 wt% ethanol for Bis-EMA-resin. The diffusion coefficient for all resins was higher in water than in ethanol/water solution or ethanol. Bis-GMA-resin showed the highest diffusion coefficient (11.01 × 10⁻⁸ cm² s⁻¹) followed by Bis-EMA-resin (7.43 × 10⁻⁸ cm² s⁻¹), UDMA-resin (6.88 × 10⁻⁸ cm² s⁻¹), D₃MA-resin (6.22 × 10⁻⁸ cm² s⁻¹) and finally by TEGDMA-resin (1.52 × 10⁻⁸ cm² s⁻¹).

Significance

All studied dental resins, except TEGDMA-resin, absorbed higher amount of pure ethanol than water or ethanol water solution. TEGDMA-resin absorbed higher amount of ethanol/water solution (50/50 or 75/25 (v/v)) than water or ethanol. For all studied dental resins the diffusion coefficient was higher in water than in ethanol/water solution or ethanol.     

Efficacy of the stannous ion and a biopolymer in toothpastes on enamel erosion/abrasion

Objectives

Sn²⁺ has promising erosion-inhibiting properties in solutions, but little is known about respective effects in toothpastes. In addition, biopolymers might have protecting potential. Aim of this study was to investigate the effects of Sn²⁺ in toothpastes and of a biopolymer (chitosan) added to a Sn²⁺ formulation on erosion/abrasion.

Methods

Enamel samples were subjected to cyclic erosion procedures (10 days; 0.50% citric acid, pH 2.5; 6× 2 min/day), and brushing (2× 15 s/day, load 200 g) during immersion in slurries (2 min). The toothpastes were NaF formulations (NaF/1, NaF/2, NaF/3) and Sn²⁺ formulations (NaF/SnCl₂, AmF/SnF₂, AmF/NaF/SnCl₂) and AmF/NaF/SnCl₂ + 0.5% chitosan.Declared concentrations of active ingredients in toothpastes were 1400–1450 μg/g F⁻ and 3280–3500 μg/g Sn²⁺. Negative controls were erosion only and placebo, positive control was a SnF₂ gel. Tissue loss was quantified profilometrically, Sn on enamel surfaces was measured by energy dispersive X-ray spectroscopy.

Results

Loss values (μm) for erosion only and placebo were 14.4 ± 4.5 and 20.2 ± 3.8, respectively, and 4.6 ± 1.9 for the positive control (p ≤ 0.001 each compared to erosion only). The other loss values were: NaF/1 16.5 ± 3.0, NaF/2 14.0 ± 2.7, NaF/3 12.6 ± 3.9, NaF/SnCl₂ 14.7 ± 5.1, AmF/SnF₂ 13.5 ± 4.8, AmF/NaF/SnCl₂ 12.4 ± 4.2, AmF/NaF/SnCl₂ + chitosan 6.6 ± 3.5 (except NaF/1 all p ≤ 0.01 compared to placebo). AmF/NaF/SnCl₂/chitosan was more effective than all other toothpastes (p ≤ 0.01 each). Sn on the enamel surface ranged between 1.3 ± 0.3 and 2.8 ± 0.04 wt.% with no obvious relationship with efficacy.

Conclusions

The NaF and Sn²⁺ toothpastes without chitosan exhibited similar anti-erosion and abrasion-prevention effects. The experimental Sn²⁺ formulation with chitosan revealed promising results similar to those of the positive control.

Clinical significance

NaF toothpastes offer a degree of protection against erosion/abrasion, which is likely sufficient for most subjects with average acid exposures. For patients with initial erosive lesions, however, more effective toothpaste is desirable. The combination of Sn²⁺ and a biopolymer appears promising in this context.     

Dentin permeability reduction by a sequential application of calcium and fluoride–phosphate solutions

Objective

A sequential topical application of calcium and fluoride–phosphate solutions was reported to occlude open dentin tubules, mainly with fluoroapatite precipitates by a rapid ionic reaction, and to be effective at treating dentin hypersensitivity. However, its ability to reduce dentin permeability (Lp) is unknown. The aim of this in vitro study was to evaluate the effect of this treatment on Lp.

Methods

Nine extracted human third molars were sectioned transversely to obtain 0.5 mm-thick discs, which were then etched and rinsed. Aqueous solutions of 5% (w/w) disodium phosphate containing 0.3% (w/w) sodium fluoride (A) and 10% (w/w) calcium chloride (B) were prepared. The sequential application of the A&B solutions was repeated three times on each disc, which was then rinsed with distilled water. The Lp of the discs was measured before and after the application using a modified Pashley's fluid flow measuring system. The differences in the Lp values between the conditions before and after the solution applications were analysed using a generalized estimating equation method and paired t-test. Scanning Electron Microscopy (SEM) was used to observe the dentin surfaces.

Results

All nine discs consistently indicated reduced Lp following the application of the A&B solutions. There was a significant decrease in the mean Lp [μL/(cm² s cm H₂O)] from baseline (−0.27 ± 0.25, p = 0.011). Overall, an average decrease of 34% Lp occurred after the application of the A&B solutions. SEM observation indicated that the reaction products covered the entire dentin disc surface.

Conclusion

The application of the A&B solutions was effective at reducing the Lp of the dentin discs.     

Adsorptive stripping voltammetric determination of vanadium(V) witch chloranilic acid using cyclic renewable mercury film silver based electrode

The cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of vanadium(V) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) with presence of chloranilic acid as a ligand is presented. The calibration graph obtained for V(V) is linear from 0.25 nM (12.7 ng L⁻¹) to 150 nM (7.6 μg L⁻¹) for a preconcentration time of 20 s, with correlation coefficient of 0.9992. For a Hg(Ag)FE with a surface area of 6.6 mm² the detection limit for a preconcentration time of 90 s is as low as 0.5 ng L⁻¹. The repeatability of the method at a concentration level of the analyte as low as 1.3 μg L⁻¹, expressed as RSD is 2.1% (n = 5). The proposed method was successfully applied and validated by studying the certified reference materials TMRAIN-95, SPS-SW1, SPS-SW2 and simultaneously recovery of V(V) from spiked water samples.     

Antifungal activity of dental resins containing amphotericin B-conjugated nanoparticles

Objectives

To evaluate the antifungal activity, biocompatibility and mechanical properties of dental resins containing silica nanoparticles functionalized with amphotericin B (SNP-DexOxAmB) against five species of Candida.

Methods

Dental resin composites (Spectrum, Dentsply DeTrey, GmbH, Germany) having 2% (w/w) of SNP-DexOxAmB (SNPs of 5 and 80 nm, denoted as SNP5 and SNP80) were aged for 10, 20 and 30 days at 37 °C, in phosphate buffer saline buffer pH 7.4 (PBS). At different time, the antifungal activity was evaluated by a direct contact assay against 1 × 10⁴ cells of Candida. The biocompatibility of the resins was tested against human fibroblasts, endothelial cells and red blood cells.

Results

Dental resins containing SNP5-DexOxAmB have high (1 × 10⁴ cells killed in 5 h by ∼70 mg of dental resin composite containing 2% (w/w) of SNP-DexOxAmB) and durable (for at least 1 month) antifungal activity against five strains of Candida. The incorporation of the nanoparticles (NPs) had no significant change in the mechanical properties of the resin, specifically the flexural strength and modulus. Our results further show that the antifungal activity is mainly mediated by direct contact and not by leaching of NPs from the resin. Resins incorporating SNP5-DexOxAmB have longer-term antifungal activity than SNP80-DexOxAmB. The antimicrobial activity of resins with SNP5-DexOxAmB persists after 4 cycles of re-use and it is superior to the activity obtained for dental resins containing silver NPs. In addition, dental resins incorporating SNP5-DexOxAmB are non-cytotoxic against human skin fibroblasts and human umbilical vein endothelial cells, and non-hemolytic against human red blood cells.

Significance

The incorporation of SNP5-DexOxAmB in dental resins resulted in a non-cytotoxic composite with high and durable antifungal activity.     

Speciation of Fe in Fe-modified zeolite catalysts

Fe-modified zeolites (ferrierite and MFI) were prepared by four impregnation methods followed by calcination and tested as catalysts in oxidative dehydrogenation of ethane by nitrous oxide at 350 °C. The Fe cationic and Fe oxidic species were identified by combination of UV–Vis spectroscopy and voltammetry. Monomeric or dimeric Fe ions have only UV absorption bands and some of them evolve voltammetrically identifiable [Fe(OH)_x]^(3−x)+ ions in contact with acetic acid-sodium acetate buffer. Fe oxide nanoclusters characterised by UV band at about 28,000 cm⁻¹ are not detected by voltammetry under chosen conditions because they are situated inside the zeolite channels. Amorphous, nanocrystalline, and crystalline Fe(III) oxides were distinguished sensitively by their specific voltammetric reduction peaks at potentials −0.1 to −0.8 V/SCE in acetate buffer (pH 4.7) and by phase-specific electron pair transitions responsible for Vis absorption band centred at 17,500–21,000 cm⁻¹. The proposed method to differentiation between these ferric oxides is novel in materials analysis and solid state speciation. The monomeric and dimeric ferric ions are active in oxidative dehydrogenation of ethane to ethene with selectivity about 40–60% under used conditions, while Fe oxide nanoclusters are too active and over-oxidise ethane and/or ethene to C, CO and CO₂. Oppositely to general expectations, ferric oxides are indifferent in the catalytic reaction and do not decrease reaction selectivity.     

Oxygen reduction reaction selectivity of RuxSey in formic acid solutions

Carbon-supported and non-supported cluster-like Ru_xSe_y were synthesized in aqueous media. The structure and morphology were analyzed by XRD and TEM, respectively. Particles dispersed uniformly on the support with an averaged size of 2.1 nm were obtained. The oxygen reduction reaction (ORR) in presence of HCOOH was investigated by means of rotating disk electrode at 25 °C on Ru_xSe_y nanoclusters. The kinetics of HCOOH oxidation for non-supported and carbon-supported Ru_xSe_y catalysts was analyzed. A reaction order of 1/1.4 and 1/1.6 was determined for Ru_xSe_y and Ru_xSe_y/C, respectively. This reaction order indicates that the reaction mechanism is similar to Pt/C. The chalcogenide catalyst showed a high tolerance and selectivity towards the ORR in electrolytes containing up to 0.1 M HCOOH. At the highest formic acid concentration (5 M) the potential, at e.g. current density of 0.2 mA cm⁻², shifts to negative for non-supported and carbon-supported Ru_xSe_y by 0.24 V and 0.28 V, respectively. The results reported in this work are the basis for overcoming the negative impact of fuel cross-over in microfluidic formic acid fuel cells that currently use Pt as cathode catalyst.     

Development of amperometric arsine gas sensor using gold-modified diamond electrodes

Amperometric gas sensor of arsine was developed using gold-modified diamond electrodes as the working electrodes. The detection method was conducted in high concentration of H₂SO₄. The reaction was declared based on two oxidation steps, involving oxidation of As³⁻ to As⁰ at mild potential in strong acid, followed by electrochemical oxidation of As⁰ to As³⁺ at gold-based electrodes. Linear calibration curve was observed in the concentration range of 5–50 ppb (r² = 0.985) with detection limit of ∼4.43 ppb (S/N = 3). Current decreasing of measurement was found ∼5.5% for 5 measurements. However, better stability was observed after the 5th measurement, indicated that the sensor could be applied for long time measurement. Investigation to several possible interference gasses, i.e. SO₂, H₂S, NO, NO₂, CO, O₃ and H₂ indicated no significant interference of the gas to arsine measurements.     

A 2-year in vitro evaluation of a chlorhexidine-containing acid on the durability of resin-dentin interfaces

Objective

This study evaluated the effect of 2% chlorhexidine-containing acid (Ac/CHX) and 2% chlorhexidine digluconate solution (CHX) on immediate (IM) and 2-year (2Y) resin-dentin bond strength (BS) and silver nitrate uptake (SNU) for two simplified etch-and-rinse adhesives.

Methods

Forty-two caries-free extracted molars had a flat dentin surface exposed. In the control groups (groups 1), the surfaces were acid etched with conventional phosphoric acid and the adhesives Prime&Bond NT (PB) or Adper Single Bond 2 (SB) was applied after rinsing, drying and rewetting with water. In groups 2, Ac/CHX groups the adhesives were applied in a similar manner; however a 2% CHX-containing acid was previously applied. In groups 3, the adhesives were applied according to the control group; however the rewetting procedure was performed with an aqueous solution of 2% CHX for 60 s. Composite build-ups were constructed incrementally and microtensile specimens (0.8 mm²) were prepared for microtensile bond strength testing in the IM or 2Y periods at 0.5 mm/min. For SNU, 2 bonded sticks from each tooth were coated with nail varnish, placed in the silver nitrate, polished down with SiC papers and analysed by EDX-SEM. The data from each adhesive was submitted to a two-way repeated measures ANOVA and Tukey's test (α = 0.05).

Results

After 2Y, significant reductions of BS were observed for both adhesives in the control group (p < 0.05). In Ac/CHX or CHX groups the BS remained stable for both systems. SNU was more evident in the control than in the experimental groups (p < 0.05) both in IM and 2Y periods. The use of CHX in an aqueous solution or associated with the acid conditioner was effective to reduce the degradation of dentin bonds over a 2-year period.

Significance

The addition of CHX digluconate in the acidic conditioner may be an excellent tool to increase the long-term stability of collagens fibrils within the hybrid layer against host-derived metalloproteinases without the need for additional steps for the bonding protocol.     

Investigation of polarographic interference between Se(IV) and Cr(VI), its elimination and application to Gerede river water

Trace chromium(VI) determination plays an important role since it is carcinogenic agent and toxic pollutant. For this purpose a direct method is developed using differential pulse polarography, DPP. When selenite was added into solutions of some ions such as copper(II), lead(II), cadmium(II), zinc(II), and chromium(VI) their DP polarographic peak decreased. This kind of interference will cause large errors in the determinations, its elimination is very important. The interference between selenite and Cr(VI) ions could be eliminated in B-R (Britton-Robbinson) buffer at pH 8.5. In this work the effect of components present in buffer has been investigated and it was found that phosphate and borate eliminated the formation of Cr–Se intermetallic compound formation. While it was possible to determine 1 × 10⁻⁵ M Cr(VI) in the presence of 100 times more selenite as (1.0 ± 0.1) × 10⁻⁵ M, in borate medium, it was possible to determine (1.0 ± 0.05) × 10⁻⁵ M in phosphate medium. In the presence of selenite detection limit (S/N = 3) was 9.0 × 10⁻⁸ M Cr(VI) by using either phosphate or borate This method was applied to Gerede river water, after oxidation all Cr(III) present into Cr(VI).     

Determination of trace vanadium(V) by adsorptive anodic stripping voltammetry on an acetylene black paste electrode in the presence of alizarin violet

A sensitive and simplified voltammetric method is developed for the determination of trace amounts of vanadium(V) by adsorptive anodic stripping voltammetry using an acetylene black (AB) paste electrode. The method is based on the preconcentration of the V(V)–alizarin violet (AV) complex at open circuit while stirring the solution for 90 s in 0.15 mol dm⁻³ hexamethylenetetraamine–hydrochloric acid buffer (pH 4.4), the adsorbed complex is then oxidized, producing a response with a peak potential of 564 mV when scanning linearly from 0 to 1000 mV. For voltammetric determination of V(V), the parameters influencing the peak current have been optimized. Under the selected conditions, the peak current and concentration of V(V) accorded with linear relationship in the range of 8.0 × 10⁻¹⁰ mol dm⁻³–1.0 × 10⁻⁷ mol dm⁻³ (c_AV = 2.0 × 10⁻⁶ mol dm⁻³) and 1.0 × 10⁻⁷ mol dm⁻³–8.0 × 10⁻⁶ mol dm⁻³ (c_AV = 2.0 × 10⁻⁵ mol dm⁻³), the detection limit (three times signal to noise) was estimated to be 6.0 × 10⁻¹⁰ mol dm⁻³ for 90 s accumulation. The relative standard deviation (RSD) is 1.9% and 2.3% for V(V) concentrations of 1.0 × 10⁻⁷ mol dm⁻³ and 1.0 × 10⁻⁸ mol dm⁻³ respectively. Finally, this proposed method was successfully applied to the determination of V(V) in natural water samples.     

Adsorption of tetraethylammonium ions on Cd(0 0 0 1) single crystal plane from solutions in ethanol

The adsorption of tetraethylammonium (TEA⁺) ions on the basal (0 0 0 1) plane of the cadmium single crystal from solutions in ethanol has been investigated by impedance measurement method. The experimental data were obtained in 0.02 M mixed-electrolyte solutions and the calculations performed with electrode potential as the independent electrical variable. The Gibbs energy of adsorption of TEA⁺ ions has been calculated using the simple virial adsorption isotherm and it was found that the adsorption of TEA⁺ cations is weaker than the adsorption of halide anions. The electrosorption valency evaluated has a nearly constant value in the potential region studied. It was concluded that the formed effective surface dipole is significantly screened by the solvent molecules and the metal electron gas. Comparing the adsorption characteristics with the parameters obtained for bismuth single crystal electrodes, it was found that the Gibbs adsorption energy on uncharged electrode surface is close for these metals. The results obtained indicate that only weak interaction between TEA⁺ ions and cadmium surface takes place and there is no remarkable partial charge transfer from the adsorbed ions to the Cd(0 0 0 1) surface atoms.     

Effect of sodium,amine and stannous fluoride at the same concentration and different pH on in vitro erosion

Objective

This study aimed to compare the effects 0.5% and 1% sodium, amine and stannous fluoride at different pH on enamel erosion in vitro.

Methods

Bovine enamel samples were submitted to a cyclic de- and remineralisation for 3 days. Each day, the samples were exposed for 120 min to pooled human saliva and subsequently treated with one of the fluoride solutions for 3 min: amine fluoride (AmF, 0.5% and 1% F⁻), sodium fluoride (NaF, 0.5% and 1% F⁻), each at pH 3.9 and 7.0, and stannous fluoride (SnF₂, 0.5% and 1% F⁻), at pH: 3.9. Additionally, two groups were treated with fluoride-free placebo solutions (pH: 3.9 and 7.0) and one group served as control (no fluoridation). Ten specimens each group were inserted in a so-called artificial mouth and eroded six times daily with hydrochloric acid (pH 2.6) for 90 s each intermitted by exposure to artificial saliva (1 h). After 3 days, enamel loss was analyzed profilometrically and evaluated statistically by ANOVA.

Results

Only the acidic 0.5% and 1% SnF₂ and 1% AmF solutions were able to reduce erosive enamel loss significantly, while all other solutions and placebos did not differ significantly from the control. Between the acidic SnF₂ and the 1% AmF solutions no significant differences could be detected.

Conclusion

At the same concentrations, acidic SnF₂ and AmF may be more effective than NaF to protect enamel against erosion.     

Effect of acidic fluoride treatments on early enamel erosion lesions—A comparison of calcium and profilometric analyses

Objective

The protective effect of fluoride solutions against acidic challenge on enamel was tested in vitro using calcium- and profilometer analyses.

Methods

HF-, SnF₂-, TiF₄- and NaF solutions (0.1 M F⁻, with a pH of 2.0, 2.9, 1.5, 7.3, respectively) and H₂O were tested on a total of 60 enamel specimens divided into 10 groups. Prior to and after F-treatment five groups were exposed for 1 min to 0.01 M citric acid, and the other five groups for 10 min to 0.1 M citric acid. Enamel specimens were measured by profilometry at baseline and before and after each acidic challenge. [Ca] in the collected citric acid samples was measured by atom absorption spectroscopy (AAS). ΔCa and Δ surface height were calculated for each specimen and the data were analysed using one-way ANOVA, Tukeys test and Pearson r correlation.

Results

AAS showed that the acidic F-treatments significantly reduced enamel dissolution for both the 1 min and 10 min acidic challenge. Profilometry showed no significant differences between the F-solutions for the 1 min groups. Significant differences could be seen between the fluorides for the 10 min groups and there was a large correlation between the profilometric and AAS results. In conclusion, all fluoride solutions reduced enamel dissolution when specimens were exposed to citric acid.

Conclusions

The profilometer was not sensitive enough to measure the effects of the different fluorides against a low acidic challenge. AAS was able to show these differences and for the 10 min acidic challenge there was a good correlation between the results from the two methods.