Fluoride retention in human enamel after a single phosphoric acid and mixed phosphoric acid/SnF2 application in vitro

Pieces of enamel were treated with either an APF solution or a 1:1 mixture of APF/SnF₂ (APF: 1.23 per cent F^?, 0.1 M H₃PO₄; and SnF₂: 2 per cent) for 4 min at 37 °C followed by 30 min washing. There was an increase of 1640 parts/10⁶ in the fluoride concentration of APF-treated enamel. Most of the fluoride was, however, washed away within 24 h to a level of 230 parts/10⁶. After 7 × 24 h the F concentration was of the same order: 280 parts/10⁶. The initial increase in fluoride concentration was lower after a mixed topical application (1120 parts/10⁶) but after 24 h the fluoride concentration was 510 parts and after 7 × 24 h 370 parts/10⁶, although statistically not significant, higher than after a single APF-treatment. The higher F concentration may be due to the formation of more firmly-bound fluoride as a fluoridated hydroxyapatite. It is more probable that the CaF₂ layer is protected by insoluble Sn compounds.     

Characterisation of a Bioactive SiO2-CaO-CaF2-Na2O Glass Used in Composites

ObjectivesTo characterise the ion release, pH changes and apatite formation of a phosphate free bioactive glass.MethodsA SiO₂-CaO-CaF₂-Na₂O glass was synthesized by a melt route with a composition close to the reactive glass in the commercial Cention N® composite. The glass was characterized after immersion in three media: Artificial Saliva pH4 (AS4) Artificial Saliva pH7 (AS7) and in a high phosphate artificial saliva at pH6.5 (AS6.5). The pH and fluoride release were measured using a pH meter and an ion selective electrode. The concentration of Ca, P, Na and Si were measured by ICP-OES. The glass powders after immersion were characterized by FTIR, X-ray powder diffraction and ¹⁹F MAS-NMR.ResultsThe glass increased the pH in all three media. Fluoride was detected in all three media but was much higher in AS 6.5. Calcium fluoride formed in AS4 with a small amount of fluorapatite at long immersion times. Fluorapatite and calcium fluoride formed in AS7, whilst in AS6.5 fluorapatite formed.The ion concentrations in solution after immersion reflected the glass composition and the immersion media with fluorapatite being favoured by higher pHs and phosphate contents in the media.SignificanceThe results demonstrated the ability of the glass to increase the pH and to form fluorapatite in phosphate containing media. This may explain the low incidence of secondary caries found in the commercial composite. Unlike the commercial composite evidence was found for the precipitation of fluorite, which will act to reduce the release of fluoride for preventing secondary caries.     

Surface properties of hydroxyapatite: I. The effect of various inorganic ions on the electrophoretic behavior.

The zeta potential of hydroxyapatite (HA) at a constant pH depends on the type of acid used. Fluoride ions increase the charge density and make the surface less prone to attack by acid or alkali. Sn2+ and Th4+ ionic complexes with fluoride ions and increase the uptake of fluoride by HA.     

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.     

Glass ionomer cements: Effect of strontium substitution on esthetics,radiopacity and fluoride release

Objective

SrO and SrF₂ are widely used to replace CaO and CaF₂ in ionomer glasses to produce radiopaque glass ionomer cements (GIC). The purpose of this study was to evaluate the effects of this substitution on release of ions from GIC as well as its effect on esthetics (translucency) and radiopacity.

Materials and methods

Cements were produced from ionomer glasses with varying content of Sr, Ca and F. The cements were stored in dilute acetic acid (pH 4.0) for up to 7 days at 37 °C. Thereafter, the cements were removed and the solution was tested for F⁻, Sr²⁺, Ca²⁺, and Al³⁺ release. Radiopacity and translucency were measured according to BS EN ISO 9917-1:2003.

Results

Ion release was linear to t^1/2 suggesting that this is a diffusion controlled mechanism rather than dissolution. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium. Radiopacity shows a strong linear correlation with Sr content. All cements were more opaque than the C_0.70 0.55 standard but less opaque than the C_0.70 0.90 standard which is the limit for the ISO requirement for acceptance.

Significance

This study shows that the replacement of calcium by strontium in a glass ionomer glass produces the expected increase in radiopacity of the cement without adverse effects on visual properties of the cement. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium.     

Measurements of the diffusion coefficient of NaF in human dental plaque in vitro

Using a new technique, the diffusion coefficient, D, of NaF in plaque at 37 °C was measured by monitoring its clearance from a thin layer of plaque. D, for both the sodium and the fluoride ions, was 4.2 × 10⁻⁶cm²s^-t1, which is about one quarter of the diffusion coefficient of NaF in water at 37 °C. No significant change in D was found over the physiological pH range of plaque. It is concluded that fluoride diffuses rapidly in plaque, with a halving-time , of 6.7s for a 100 μm layer of plaque. This suggests that a thorough cleaning and polishing of the teeth may not be essential before topical application of fluoride.     

Remineralising fluorine containing bioactive glass composites

ObjectivesThe objective was to investigate the mechanical properties, fluoride release and apatite formation of resin based dental composites based on a fluoride containing Bioactive Glass (BG) with and without a silylating agent.MethodsA SiO₂–P₂O₅–CaO–SrO–Na₂O–CaF₂ BG was synthesized by the melt quench route. This glass and a commercially available inert glass (IG) were incorporated into a light cured BisGMA-TEGMA resin. The composite resins were then evaluated in terms of their ability to form apatite by Fourier Transform Infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM) following immersion in artificial saliva at pH 4 (AS4) and pH 7 (AS7). The experiments were performed with and without silylation of the BG. The compressive strength and flexural strength were determined after 1, 28 and 84 days of immersion in the AS4 and AS7 immersion media.ResultsThe FTIR spectra of the BG composites exhibited split bands at approximately 560 and 600 cm^?1 corresponding to a apatite formation in the surface or on the surface under all immersion conditions. SEM showed the presence of a reacted layer of glass particles in the composite surface and the presence of a surface layer of apatite in AS7.The compressive strength and flexural strength were significantly higher for the silylated BG composites. The strengths of both silylated and non silylated BG composites and IG composites decreased upon immersion.SignificanceBG composites exhibit reduced strengths upon immersion but still exhibit strengths comparable to existing composites after 84 days of immersion.     

The inhibition of acid production in human saliva by monofluorophosphate.

Sodium monofluorophosphate (MFP) and NaF were compared for their ability to inhibit acid production in human saliva-glucose mixtures. Whole stimulated saliva was incubated at 37 °C with 2.5 per cent glucose in the presence of NaF (1.05 mmol/l) or MFP (initially 1.05 mmol/1 or neither (controls). Because MFP was gradually decomposed, releasing fluoride, further incubations were included in which increments of NaF were added to reproduce this increasing fluoride concentration. Acid production in the MFP incubations was less than in the controls and greater than in those containing equimolar NaF, but almost the same as in those in which added fluoride reproduced the release from MFP. This showed that the inhibition of acid production in the MFP incubations was due to the fluoride released and that the PO₃F^2? ion itself had little or no effect. The hydrolysis of MFP by salivary enzymes was greater at pH 7 than at pH 4. A direct effect on plaque microorganisms by MFP is an unlikely explanation for the cariostatic properties of MFP toothpastes.     

Effect of fluoride on carbon dioxide and acid formation in salivary sediment mixtures incubated with glucose

The effect of fluoride on the acid and CO₂ formed from glucose by the bacteria in salivary sediment was investigated.Fluoride inhibited the formation by salivary sediment of both lactic and acids other than lactic. The inhibition was greater with higher levels of fluoride and was favoured by an acidic pH. Fluoride (20 ppm) stimulated the formation of CO₂ from glucose at acidic pH values but 4.4 ppm or less had little or no effect on its reaction even at acidic pH. The CO₂ released from glucose stimulated by fluoride arose exclusively from glucose-carbons 3 and 4.The results were consistent with the conclusion that inhibition of glucose uptake is a preliminary step in fluoride inhibition of bacterial glycolysis in salivary sediment.     

The breakdown of glucose, xylitol and other sugar alcohols by human dental plaque bacteria.

The aerobic and anaerobic incubation of plaque bacteria in media consisting of saliva supernatant containing ribitol, arabinitol, sorbitol and mannitol produced a fall in pH whereas incubations and serial transfer in saliva-xylitol media did not lead to any significant change. Addition of 100 mM xylitol did not affect pH fall during incubation with 100 mM sucrose, nor did 5–100 mM xylitol alter the rate of plaque glycolysis in 25 mM glucose solutions when measured as the release of ³H₂O from [5-³H]-glucose at pH 5.0 and 7.5. Plaque carbohydrate catabolism, when measured as the evolution of ¹⁴CO₂ from [U-¹⁴C]-glucose and -xylitol in 25 and 250 mM sugar solutions, respectively, at pH 7.5, showed that carbon dioxide release from xylitol was 7–27 per cent of that released from glucose. However, the anaerobic oxidation of glucose to carbon dioxide only represented 4 per cent of the total glucose utilised by glycolysis in 250 mM glucose solutions and demonstrates the minor role of oxidation in plaque sugar breakdown. Xylitol had no inhibitory effect on plaque sugar metabolism but was itself oxidised, although at a slower rate than was glucose; this metabolic inertness probably contributes to its relative non-cariogenicity.     

Raman spectra of human dentin mineral

Human dentin mineral has been investigated by using micro-Raman spectroscopy. Fluorescence and thermal problems were largely avoided by preparing dentin samples by grinding and ultrasonic agitation in acetone. The Raman spectral features were consistent with those of impure hydroxyapatite containing CO, and HPO₄. While spectral differences between enamel and dentin were clearly observable as changes in the bandwidth of the PO₄³ v^?1 band and the intensities of the OH^? CO₃^2- and HPO₄²bands, the technique could not detect spectral differences between coronal and root dentin. NaOCl, NaF and APF–gel treatments caused measurable changes in intensities of the bands due to CO² and HPO₄^?2; the results were found to be useful for band assignments. After NaOCl treatment, the Raman bands, presumably due to amide and HPO₄^?2, were lost, but the band intensity of the CO₃^?2 v, bands increased by 35–60%. This increase coincided with the appearance of a new broad band (250–300 cm^?1). The same treatment on enamel caused no increase in the CO₃² V, band intensity. This NaOCl–induced carbonate could be removed within 20 h in a 1000 ppm NaF solution. These findings indicate that the carbonate ions induced by the NaOCl treatment are presumably in or on the mineral surface. After 3 min of APF–gel treatment on NaOCl–pretreated dentin, the intensities of the hydroxyapatite phosphate bands dropped by approximately 20%, and newly formed CaF₂ and HPO₄ bands became observable.     

Distribution and forms of iodine in human oral cavity

Neither iodinated proteins nor iodinated. low-molecular weight compounds (e.g. iodinated tyrosine derivatives) could be detected in concentrated human salivary supernatant by using the Ce(SO₄)₂-method either directly or after thin-layer chromatography. Salivary sediment contained free 1^? ions, loosely bound iodine (released with saline) and strongly bound iodine (released with sonication, detergent and acid hydrolysis). A positive correlation between salivary and crevicuiar excretion of l^? from plasma was observed. Thiocyanate ions, which competitively inhibit peroxidase-catalysed oxidation and iodination reactions and which are abundant in human saliva, possibly prevent the coupling of l^? to protein in vivo although some human salivary proteins are very susceptible to iodination in vitro.     

Effect of pH and temperature on carbon-supported manganese oxide oxygen reduction electrocatalysts

Manganese oxides nanoparticles were chemically deposited on a high area (ca. 300 m² g⁻¹) carbon black substrate to act as electrocatalysts for oxygen reduction. The morphology and chemistry of the carbon-supported MnO_x nanoparticles was characterised by Transmission Electron Microscopy), X-ray Diffraction, and chemical analysis. The oxygen reduction reaction (ORR) catalytic activity was studied in the 7–10 pH range using a rotating disk electrode (RDE). High activity towards oxygen reduction and very good stability in neutral and slightly basic solution were obtained. At low current densities, at 25 °C, MnO_x/C displayed a reaction order with respect to OH⁻ ions of −0.5 and Tafel slopes of −0.153 and −0.167 V dec⁻¹ at pH 7 and 10 respectively; showing that the ORR mechanism on MnO_x/C is unchanged in the 7–10 pH range. From the data, we propose that the first electrochemical step of the 4-electron ORR mechanism, in the 7–10 pH range, is the quasi equilibrium proton insertion process in MnO₂ yielding MnOOH (insoluble in neutral or slightly basic solution). The ORR activity of the MnO_x/C materials increased with increasing temperatures from 5 to 40 °C. The 2-electron pathway of oxygen reduction, yielding hydrogen peroxides as intermediates, may however be favoured over the 4-electron O₂ reduction at higher temperatures.     

Electrode reactions and accumulation of hydrogen at carbon paste electrodes in the presence of tetrachloropalladate

The electrochemical behaviour of the unmodified carbon paste electrode (CPE) in the presence of [PdCl₄]^2? in chloride solutions of different pH (in the range from 3 to 7) is studied by cyclic voltammetry (CV). During cathodic treatment or cycling, Pd(0) is deposited in situ on the electrode surface. Results obtained at negative potentials as a function of the concentrations of Pd(II) and protons in the solution are presented. It is concluded that hydrogen ions are reduced in different ways: first, the reduction at deposited Pd(0) or the simultaneous reduction of H⁺ and [PdCl₄]^2?, respectively, which occurs during the whole cathodic cycle; second, the reduction in the potential range from about ?0.5 to ?1.0 V versus SCE, where surface groups are reduced at the unmodified CPE. The second pathway is the prevailing reduction at lower pH, which occurs at the carbon surface probably via protonated chloropalladate complexes adsorbed at the electrode surface. Potentiostatic pretreatment in the voltammetric range between 0 and +0.2 V leads in solutions of pH 5 to a pronounced increase of the H⁺ reduction current caused by an increase of the sorption capacity of the electrode or by the accumulation of protons at the electrode surface. Protons could be accumulated at the electrode surface by formation of protonated chloropalladate complexes at the CPE.     

Effect of silver and fluoride ions on enamel demineralization: a quantitative study using micro-computed tomography

Background: This study aimed to investigate the effect of silver and fluoride ions on demineralization of enamel. Methods: The coronal parts of 40 extracted sound premolars were prepared into tooth blocks. An unvarnished occlusal surface window (OW) and a flat buccal/lingual surface window (FW) were created for each tooth by covering all other surfaces with an acid‐resistant varnish. These blocks were randomly allocated into four groups of 10 blocks each and immersed in respective solutions for 5 minutes: Group 1 – 2.36 M silver fluoride; Group 2 – 2.36 M potassium fluoride; Group 3 – 2.36 M silver nitrate; and Group 4 – deionized water. After 7‐day immersion in a buffered demineralization solution at pH 4.4, micro‐CT scans were taken. Results: Mean lesion depth in the FW area for tooth blocks in AgF, KF, AgNO₃ and control groups were 0 μm, 3.3 ± 10.3 μm, 156.3 ± 30.8 μm, and 173.6 ± 48.6 μm, respectively (p < 0.001). The difference in mean lesion depth between the AgNO₃ and control groups was not statistically significant (p > 0.05). Similar OW and FW lesions were observed in tooth blocks in the AgNO₃ and control groups. Conclusions: Topical application of a 2.36 M fluoride solution can inhibit demineralization of enamel while topical application of silver ions has little effect.     

Protective effect of experimental mouthrinses containing NaF and TiF4 on dentin erosive loss in vitro

Objective

This in vitro study assessed the anti-erosive effect of experimental mouthrinses containing TiF₄ and NaF on dentin erosive loss.

Material and Methods

Bovine dentin specimens were randomly allocated into the groups (n=15): 1) SnCl₂/NaF/AmF (Erosion Protection^®/GABA, pH 4.5, positive control); 2) experimental solution with 0.0815% TiF₄ (pH 2.5); 3) 0.105% NaF (pH 4.5); 4) 0.042% NaF+0.049% TiF₄ (pH 4.4); 5) 0.063% NaF+0.036% TiF₄ (pH 4.5); 6) no treatment (negative control). Each specimen was cyclically demineralized (Sprite Zero, pH 2.6, 4x90 s/day) and exposed to artificial saliva between the erosive challenges for 7 days. The treatment with the fluoride solutions was done 2x60 s/day, immediately after the first and the last erosive challenges of the day. Dentin erosive loss was measured by profilometry (μm). The data were analyzed using Kruskal Wallis/Dunn tests (p<0.05).

Results

Mouthrinses containing TiF₄ or Sn/F were able to show some protective effect against dentin erosive loss compared to negative control. The best anti-erosive effect was found for experimental solution containing 0.0815% TiF₄ (100% reduction in dentin loss), followed by 0.042% NaF+0.049% TiF⁴ (58.3%), SnCl₂/NaF/AmF (52%) and 0.063% NaF+0.036% TiF₄ (40%). NaF solution (13.3%) did not significantly differ from control.

Conclusion

The daily application of experimental mouthrinse containing TiF₄ and NaF has the ability to reduce dentin erosion, as well as Erosion Protection^® and TiF₄ alone.     

Adsorption of Streptococcus mutans lipoteichoic acid to hydroxyapatite

abstract – lipoteichoic acid extracted from cells of S. mutans strain BHT exhibited a high affinity for hydroxyapatite. Phosphate ions, fluoride ions and to a lesser extent human saliva inhibited or reversed this adsorption. Extracellular lipoteichoic acid preparations obtained from the supernatant of cultures of the same bacteria exhibited similar properties. It is suggested that lipoteichoic acids could play a significant role in the colonization of teeth by Gram-positive bacteria and thereby contribute to the formation and pathogenicity of dental plaque.     

In vitro fluoride release from restorative materials in water versus artificial saliva medium (SAGF)

Objectives. An extensive number of investigations have focused in recent years on the process of fluoride release by glass–ionomer cements. In order to compare the fluoride release of two recent resin-modified glass–ionomer cements (RMGICs) and one compomer, we investigated the initial and subsequent fluoride release in distilled water and in a mineral medium with composition similar to saliva (SAGF), as well as the renewal effect of the media on the release.Method. A preliminary thermodynamic study defined conditions under which the measurements by fluoride-selective electrode potentiometry were not affected by the presence of Ca²⁺ ions in SAGF. Disk-shaped samples (5 mm×3 mm) for each material were placed in 5 ml of distilled water (n=12) or 5 ml of SAGF (n=12) and fluoride released was measured after 1, 2 and 7 days. For the investigation of medium renewal effect, RMGIC samples were dipped into distilled water for 5 days. Subsequently 12 samples of each material were placed for 7 days into water or SAGF, with or without daily renewal of the medium before fluoride-release measurements. The elements present on the surface of the RMGICs were analyzed by scanning electron microscopy.Results. RMGICs released significantly more fluoride in water than in artificial saliva. The presence of CaF₂ at the interface accounts for this phenomenon. The thickness of the CaF₂ layer depends on the speed of its initial formation and renewal of the testing medium. A pattern of CaF₂ formation was proposed.     

Application of a direct pulp capping cement containing S-PRG filler

Objectives

To evaluate new pulp capping cements containing surface pre-reacted glass ionomer (S-PRG) filler and to investigate ion release kinetics and pH shift of eluates from the cement.

Materials and methods

Molars of Wistar rats were directly pulp capped using three kinds of cement containing S-PRG filler and mineral tri-oxide aggregate (MTA) was used as a control. After 1, 2, or 4 weeks, histological evaluation was performed and differences of tertiary dentin formation were analyzed. Release of Sr²⁺, BO₃³⁻, SiO₃²⁻, Na⁺, and Al³⁺ ions was determined by inductively coupled plasma-atomic emission spectrometry, and F⁻ ion release was measured using a fluoride ion selective electrode. The pH of the eluate from each cement after mixing was measured with a pH electrode.

Results

One of S-PRG cements promoted tertiary dentin formation to the same extent as the control (p > 0.05) and it showed a tendency of less inflammatory response. This cement released more BO₃³⁻ and SiO₃²⁻, but less Sr²⁺, Na⁺, and F⁻ than other S-PRG specimens. Each cement recovered nearly neutral compared with glass ionomer cement.

Conclusions

S-PRG cement induced tertiary dentin formation based on multiple ion releases, suggesting that it is suitable as a pulp capping material.

Clinical relevance

This new material can be an alternative pulp capping agent to MTA.

     

Electrochemistry of human enamel: Selectivity to potassium in solutions containing calcium or phosphate ions

Further studies have been made at 25 ± 1 °C of the steady-state electromotive forces (emfs) developed across the enamel caps of whole teeth and synthetic hydroxyapatite membranes in concentration cells using KH₂PO₄, K₂HPO₄ and K₃PO₄ solutions at their natural pH values, and of the variation in the emf of enamel and Permutit C20 cation-exchange membranes in 0.100/0.010 M KCl concentration cells when small concentrations of calcium and phosphate are added separately (as CaCl₂ and K₂HPO₄) to both KCl solutions. Over the concentration range examined, the cationic selectivity of both enamel and HA cells with the potassium phosphate gradients was always greater than that with KCl gradients, the selectivity with K₂HPO₄ and K₃PO₄ gradients being virtually ideal. The results thus appear to substantiate the inferences drawn in previous work that (a) the mineral fraction is responsible for the observed effects and (b) that enamel is a “non-leaky” membrane. In KCl concentration cells with small calcium additions, a marked decrease in the membrane potential was observed which, by comparison with the results for the synthetic cation-exchange membrane C20, is attributed to the preferential selectivity of the enamel for Ca²⁺ ions under these conditions. With small concentrations of added phosphate, a decrease in potential was observed which could be ascribed to changes in the K⁺ ion gradient in the cells.