Electrochemical study of the redox dyes Nile Blue and Toluidine Blue adsorbed on graphite and zirconium phosphate modified graphite

Solid graphite electrodes were modified with the redox dyes Nile Blue (NB) and Toluidine Blue (TB), following irreversible adsorption from ethanol solution, and a droplet evaporation procedure. The shift of redox potential for both dyes to the negative direction upon adsorption on graphite was estimated from cyclic voltammetry, and from extrapolation of the dependence of E_p versus I_p to I_p=0, to vary between 60 and 110 mV. For electrodes containing a controlled amount of NB or TB, heterogeneous charge transfer rate constants of 31 and 11.6 s^?1, respectively, were estimated by extrapolation of the data to zero coverage of the electrode surface. The rate constants obtained are several times higher than those obtained for multilayer coatings with the dyes. The modification of solid graphite electrodes with zirconium phosphate (ZrP), followed by the adsorption of NB and TB was performed. For NB, two forms of the dye were found to be present, one of them presenting an usual adsorbate of NB on graphite, and another one having E_pc shifted by ca. 0.15–0.30 V to more positive potential values. The latter form is ascribed to NB, included in the ZrP host matrix, as follows by comparing its electrochemical behavior with that observed for NB, included in carbon paste containing ZrP.     

Cyclic Fatigue Resistance of Reciproc Blue and Reciproc Files in an S-shaped Canal

Introduction

This study evaluated the cyclic fatigue resistance (CFR) of Reciproc (R25 and R40; VDW, Munich, Germany) and Reciproc Blue (R25 and R40, VDW) instruments used in an artificial S-shaped canal.

Electrochemical anion doping of poly[(tetraethyldisilanylene) oligot 2,5-thienylene)] derivatives and their p-type semiconducting properties

Chemically synthesized poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] derivatives (DS/mT; m = 3 to 5) have been successfully anion-doped by electrochemical oxidation. Band-gap energies of 2.52, 2.65, 2.82 and 3.27 eV were evaluated for DS5T, DS4T, DS3T and DS2T respectively. The DS5T, DS4T and DS3T films exhibited electrical conductivities of the order of 10^?3 to 10^?4 S cm^?1 when doped with BF₄^?. The work functions of the films changed from 5.1 to ca. 5.5 eV with electrochemical anion doping. In cyclic voltammograms of the polymer films for anion doping and dedoping, an anodic peak potential and a cathodic one (E_pc.) shifted to the positive direction as the number m of thienylene units decreased. E_pcs at a sweep rate of 100 mV s^?1 were about 0.8, 0.9 and 1.0V for DS5T, DS4T and DS3T respectively. Reversible electrochemical doping and dedoping of the DS5T film were feasible when the potential was cycled between 0 and 1.2 V. At potentials more positive than 1.2 V, however, both overoxidation of the oligo(thienylene) unit and Si-Si bond cleavage took place, leading to decreases in conductivity and work function of the film.     

Torsional Fatigue Resistance of Blue-treated Reciprocating Instruments

Introduction

The aim of the present study was to evaluate the influence of blue thermal treatment on the torsional resistance behavior of M-Wire Reciproc files (VDW, Munich, Germany).

Effect of Glide Path Creating on Cyclic Fatigue Resistance of Reciproc and Reciproc Blue Nickel-titanium Files: A Laboratory Study

Introduction

The purpose of this article was to compare the cyclic fatigue resistance of Reciproc and Reciproc Blue files (VDW GmbH, Munich, Germany) that were used to prepare root canals of mandibular molar teeth with or without a glide path.

Liquid junction potential between electrolyte solutions in different solvents: further study on the component related to ion solvation

The liquid junction potential (LJP) between electrolyte solutions in different solvents was studied by paying attention to the component related to ion solvation (component (b)). The actual variation in component (b) was obtained as the variation in corrected emfs (E_corrected) of a cell and compared with the theoretical values (E_j(b)_calc). New data for the E_corrected ? E_j(b)_calc relation were obtained using amphiprotic ethylene glycol (EG) and formamide (FA) as solvent on one side of the junctions. The E_corrected ? E_j(b)_calc relations at miscible FA/ and EG/organic solvent junctions were nearly linear with average slopes of 0.32 and 0.33, respectively, in contrast to 0.46 for H₂O/organic solvents, 0.26 for MeOH/aprotic solvents, and ～0 between two aprotic solvents. On the other hand, for partially miscible FA/ and EG/nitrobenze (NB), the slopes were 0.70 and 0.84, respectively, approaching unity with the decrease in miscibility. Some factors that may influence component (b) were pointed out and were discussed in detail by considering the phenomena at the junctions. Additional data that support the method to estimate the actual values of component (b) by (slope) × E_j(b)_calc were obtained. By appropriate corrections for component (b), the component due to solvent–solvent interactions was shown to be electrolyte-independent also at the junctions containing EG, FA and N-methylformamide on one side.     

Effect of pH on the catalytic electrooxidation of NADH using different two-electron mediators immobilised on zirconium phosphate

A detailed study is reported on the electrocatalytic oxidation of β-nicotinamide adenine dinucleotide at three different carbon paste electrodes modified with redox mediators commonly used in bioelectrochemistry, viz. Meldola blue, methylene green and riboflavin, adsorbed on zirconium phosphate. Cyclic voltammetric investigations of these chemically modified electrodes performed in aqueous tris buffer solutions at different pHs allowed us to conclude that the immobilised redox species presented very stable redox properties, with midpoint potentials (E_m, ?125, ?40, and ?140 mV versus SCE for Meldola blue, methylene green and riboflavin, respectively) virtually independent of the pH of the contacting solution. The second-order rate constant for electrocatalytic oxidation of NADH as well as its pH dependence (from 6 to 8) were evaluated from rotating disk electrode (RDE) experiments, using the Koutecky–Levich approach.     

Mechanical behaviour of prosthodontic CAD/CAM polymer composites aged in three food-simulating liquids

ObjectivesThis study investigated the effect of ageing in three food-simulating liquids (FSLs) on mechanical properties of three prosthodontic CAD/CAM polymer composites intended for construction of implant-supported frameworks.MethodsMaterials investigated were: (i) a carbon fibre-reinforced composite (CarboCAD 3D dream frame; CC), (ii) a glass fibre-reinforced composite (TRINIA; TR), and (iii) a reinforced PEEK (DentoKeep; PK). Filler contents and microstructural arrangements were determined by thermo-gravimetry and tomography (µ-CT), respectively. Flexural properties (FS and E_f) were measured by 3-point bending (3PB) of 1 mm and 2 mm thick beam specimens. Fracture toughness (K_IC) was measured by single-edge-notched-bending (SENB). All measurements were made at baseline (dry) and after 1-day and 7-day storage at 37 ℃ in either water, 70 % ethanol/water (70 % E/W) or methyl ethyl ketone (MEK). Failed specimens were examined microscopically. Statistical analyses included four-way ANOVA, two-way ANOVA and multiple Tukey comparison tests (α = 0.05). Multiple independent t-tests were performed regarding thickness effects on FS and E_f (α = 0.05).ResultsAt baseline, the mechanical properties increased in the sequence: PK < TR < CC (p < 0.001). FS ranged from 192.9 to 501.5 MPa; E_f from 4.2 to 18.1 GPa; and K_{IC f}rom 4.9–12.4 MPa.m^0.5. Fibre-reinforced composites (CC and TR) were significantly stronger than PK. However, all properties of CC and TR reduced after 1 d storage in 70 % E/W and MEK with FS ranging from 58.6 to 408 MPa; E_f from 1 to 15.4 GPa; K_IC from 6.87 to 10.17 MPa.m^0.5. Greater reductions occurred after 7 d storage. MEK was more detrimental than 70 % E/W and water on fibre-reinforced composites.SignificanceMechanical properties of each CAD/CAM composite were strongly dependent upon media and ageing. Although the mechanical properties of PK were initially inferior, it was relatively stable in all FSLs. All three materials exhibited sufficient mechanical properties at 1 mm thickness, but thicker specimens were more tolerant to ageing.     

Comparison of apical leakage shown by four different dyes with two evaluating methods

A study was conducted in vitro to assess and compare the extent of apical leakage of four dyes by two commonly-used evaluation methods. For the study, 120 single-rooted extracted teeth were prepared by the step-back technique and obturated by lateral condensation with gutta-percha and Roth 801 sealer. After randomly allocating the roots into six groups, they were immediately immersed in dye for 72 h, using vacuum for 30 min at 40°C. Teeth were immersed in Eosin, Methylene Blue, Black India Ink and Procion Brilliant Blue and cross-sectioned in 0.7 mm thick slices. Those immersed in Black India Ink and Procion Brilliant Blue were also evaluated by the clearing process. Dye penetration was assessed using a stereomicroscope. A statistically significant greater dye penetration was measured in the cross-sectioned group compared to the clearing group using the same dyes (Black India Ink, P = 0.020, Procion Brilliant Blue, P = 0.040). In the cross-section groups, no statistical significant difference was observed in the amount of leakage comparing the four dyes. No statistically significant difference was found in the leakage pattern of Procion Brilliant Blue and Black India Ink using the clearing technique ( P = 0.797). The evaluating method (cross-sections versus clearing) rather than the dye properties was the main difference between results. More research is needed to standardize dye leakage studies.     

Micro–computed Tomographic Assessment of the Residual Filling Volume,Apical Transportation,and Crack Formation after Retreatment with Reciproc and Reciproc Blue Systems in Curved Root Canals

IntroductionThe purpose of the present study was to evaluate the remaining root canal filling material, apical transportation, and crack formation after retreatment with M-Wire Reciproc (VDW GmbH, Munich, Germany) and Reciproc Blue (VDW GmbH) systems in curved root canals.MethodsTwenty-six mandibular first and second molars with mesial roots that had 2 separate canals with angles between 20° and 40° were selected for this study. The root canals were prepared with M-Wire Reciproc size 25 instruments (VDW GmbH), and they were filled with gutta-percha and AH Plus sealer (Dentsply Sirona, Tulsa, OK). The samples were randomly divided into 2 groups (n = 13 each) according to the retreatment system used: an M-Wire Reciproc group and a Reciproc Blue group. The canals were retreated up to instrument size 25 and then to size 40 in both groups. After the retreatment procedures, the residual filling material volume, apical transportation, and crack formation were assessed using micro–computed tomographic imaging.ResultsThere were no significant differences between the groups in the amount of residual filling material (P > .05). The apical canal transportation values were significantly higher in the M-Wire Reciproc group than in the Reciproc Blue group at 1 mm. No significant differences were observed between the groups at any of the other levels with regard to apical transportation (P > .05) The new uncompleted and completed cracks were observed in both groups. There were no statistically significant differences between the groups in terms of crack and fracture formation (P > .05).ConclusionsThe Reciproc Blue system is as effective as the M-Wire Reciproc system in terms of the retreatment of the curved mesial roots of mandibular molars. However, the formation of new uncompleted and completed cracks was found during the retreatment procedures.     

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase immobilized on active carbon

For the first time horseradish peroxidase (HRP) immobilized on the surface of active carbon powder modified at the surface of a glassy carbon electrode has been shown to undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E^0′, is ?0.363 V in phosphate buffer solution (pH 6.8) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 50–700 mV/s. The dependence of E^0′ on the pH of the buffer solution indicated that the conversion of HRP–Fe(III)/HRP–Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized HRP retained its bioelectrocatalytic activity to the reduction of H₂O₂. Furthermore, the HRP adsorbed on the surface of the active carbon powder can be stored at 4 °C for several months without any loss of the enzyme activity. The method presented for immobilizing HRP can be easily extended to immobilize and obtain the direct electrochemistry of other enzymes.     

Analysis of the hydrogen electrode reaction mechanism in thin-layer cells. 1. Theory

This work develops the equations that relate the kinetic parameters of the hydrogen electrode reaction (HER) with the current density (j) vs. potential (E) dependences of a thin-layer cell (TLC). Two operation modes of the TLC are analyzed. The first one proposes to examine the j(E) dependence of the hydrogen evolution reaction (her) on one electrode while the paired electrode oxidized the dissolved H₂ back to H⁺ under diffusion control. The second mode proposes to analyze the j(E) dependence of the hydrogen oxidation reaction (hor) on one electrode while the other generates dissolved H₂ from H⁺ under diffusion control. In both cases, as very high mass-transport rates are reached for distances in the micrometer range, the j(E) curves are sensitive to the complete set of kinetic parameters even for very large reaction rates. Possible ways to incorporate these equations in the theoretical formalisms of well-established TLC-based techniques such as scanning electrochemical microscopy are discussed.     

Performance of Reciproc Blue R25 Instruments in Shaping the Canal Space without Glide Path

Introduction

This study assessed the frequency in which Reciproc Blue R25 instruments (VDW, Munich, Germany) reached the full working length (WL) of mandibular molar canals without a glide path. The influence of the type of electric motor (ie, conventional corded or cordless) on the instrument's performance was also assessed.

In vitro comparison of mechanical properties and degree of cure of bulk fill composites

Objectives

The aim of our study was to measure and compare degree of conversion (DC) as well as micro- (indentation modulus, E; Vickers hardness, HV) and macromechanical properties (flexural strength, σ; flexural modulus, E _flexural) of two recently launched bulk fill resin-based composites (RBCs): Surefil® SDR? flow (SF) and Venus® bulk fill (VB).

Materials and methods

DC (n?=?6) was investigated by Fourier transform infrared spectroscopy (FTIR) in clinical relevant filling depths (0.1, 2, and 4 mm; 6 mm bulk, 6 mm incremental) and irradiation times (10, 20, 40 s). Micro- (n?=?6) and macromechanical (n?=?20) properties were measured by an automatic microhardness indenter and a three-point bending test device after storing the specimens in distilled water for 24 h at 37°C. Furthermore, on the 6-mm bulk samples, the depth of cure was determined. A field emission scanning electron microscope was used to assess filler size. Results were evaluated using one-way analysis of variance, Tukey’s honest significance test post hoc test, a multivariate analysis (α?=?0.05) and an independent t test. Weibull analysis was used to assess σ.

Results

VB showed, in all depth, significant higher DC (VB, 62.4–67.4 %; SF, 57.1–61.9 %), but significant lower macro- (VB, E _flexural?=?3.6 GPa; σ?=?122.7 MPa; SF, E _flexural?=?5.0 GPa; σ?=?131.8 MPa) and micromechanical properties (VB, E?=?7.3–8.8 GPa, HV?=?40.7–46.5 N/mm²; SF, E?=?10.6–12.2 GPa, HV?=?55.1–61.1 N/mm²). Both RBCs showed high reliability (VB, m?=?21.6; SF, m?=?26.7) and a depth of cure of at least 6 mm at all polymerization times. The factor “RBC” showed the strongest influence on the measured properties (η ²?=?0.35–0.80) followed by “measuring depth” (η ²?=?0.10–0.46) and “polymerization time” (η ²?=?0.03–0.12).

Conclusions

Significant differences between both RBCs were found for DC, E, σ, and E _flexural at all irradiation times and measuring depths.

Clinical relevance

Curing the RBCs in 4-mm bulks for 20 s can be recommended.     

Micro–computed Tomography Shaping Ability Assessment of the New Blue Thermal Treated Reciproc Instrument

Introduction

The present study aimed to assess canal preparation outcomes achieved by the new Reciproc Blue instrument using micro–computed tomography technology. M-Wire Reciproc was used as a reference instrument for comparison.

Electrochemically modulated liquid chromatography (EMLC) as a probe of the adsorption characteristics of monosubstituted benzenes at porous graphitic carbon

The utility of electrochemically modulated liquid chromatography (EMLC) as a probe of the adsorption characteristics of monosubstituted benzenes at porous graphitic carbon (PGC) is investigated. An analysis on the extent of the changes in retention as a function of applied potential (E_appl) is performed to develop preliminary insights into the critical interactions between these compounds and PGC. The results show that the retention, and therefore the extent of adsorption, of these compounds increases as E_appl becomes more positive. Furthermore, the dependence of the increase varies between compounds, reflecting differences in the sensitivities of the adsorption strengths to π-donor/acceptor interactions. Together, these results demonstrate the potential value of EMLC as (1) a tool for investigating fundamental issues related to the adsorption of organic compounds on electrode surfaces and (2) a separation technique for mixtures of this important class of analytes.     

Effect of sonic-activated resin composites on the repair of aged substrates: an in vitro investigation

Objectives

This study aimed to evaluate whether sonic-activated resin-based composites (RBCs) used as repair materials might improve the repair bond strength of aged RBC substrates.

Materials and methods

Five RBCs were repaired by themselves and by all other materials. The repair was applied with and without sonic activation, resulting in 50 material application technique combinations (n?=?15) and 750 specimens. The cohesive strength of the five materials was used as control (n?=?15). Substrates were aged for 8 weeks in distilled water at 37 °C, roughened, cleaned with phosphoric acid, and repaired by using a silane primer and an adhesive as intermediate agents. The repair bond strength was assessed in a shear test. The modulus of elasticity (E) of the five RBCs was additionally evaluated in a three-point bending test.

Results

Results were compared using one- and multiple-way analyses of variance and Tukey’s honestly significant difference post hoc test (α?=?0.05), partial eta-square statistics, Pearson’s correlation, and Weibull’s analysis. No significant effect of sonic activation on the repair material was found in any material combination. The repair strength was 35.4–90.9 % of the cohesive strength of the original composites. E varied between 4.1 GPa (CLEARFIL MAJESTY Esthetic) and 9.7 GPa (CLEARFIL MAJESTY Posterior). The strongest influence on the shear bond strength was performed by E _repair (η ² _P?=?0.167), whereas the effect of E _substrate was significant but low (η ² _P?=?0.098). None of these parameters influenced the reliability of the repaired specimens (the Weibull parameter, m). The fracture pattern was mainly cohesive (93.3 %) in the control group and predominantly adhesive (89.2 %) in the repaired specimens.

Conclusions

Except for the material with the highest modulus of elasticity used as a substrate material, it was not detrimental to combine different RBCs in terms of repair.

Clinical relevance

If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity.     

Adsorption of human serum albumin on electrochemical titanium dioxide electrodes: Protein–oxide surface interaction effects studied by electrochemical techniques

The adsorption of Human Serum Albumin (HSA) on a semiconductor TiO₂ electrochemical oxide was investigated using Cyclic Voltammetry (CV), Capacity–Potential curves (C–E) and time-resolved techniques as a function of electrode potential and protein concentration. The presence of HSA adsorbed on the electrode surface modifies the voltamperometric behavior of the hydrogen evolution reaction (her) and also produces a major modification in the diffusional layer thickness of the H⁺ ions. The adsorbed amounts of HSA were analyzed throughout different adsorption isotherms. The experimental data were modeled with a modified Langmuir type isotherm, considering a weak chemisorption on a surface with heterogeneity in site-energy distribution with some degree of attractive lateral interactions between the adsorbed protein molecules. The effect of the adsorption potential (E_ads) was investigated polarizing the electrode at −0.70, −0.50 and −0.08 V vs. SCE. The capacity response obtained from the different impedance experiments was determined by the space charge region in the semiconductor. It was possible to correlate processes produced by the protein adsorption on the surface (occurring in the electrolyte side of the interface) with changes in the semiconductor properties of the TiO₂ (in the oxide side of the interface). The adsorption of HSA produces an increase in donor concentration (N_D) of the semiconductor and a shift of the E_fb to more negative values. These effects are more pronounced with an increase in the protein concentration. The relative change in N_D is lower and the change in E_fb is higher when the adsorption occurs at less negative applied potentials. Adsorption kinetics and thermodynamic parameters were calculated for a wide protein concentration range.     

Effect of brand and shade of resin cements on the final color of lithium disilicate ceramic

Statement of problem

Resin cements are available in various shades from different manufacturers. However, there is no standard for the optical properties of these cements, which may result in differences in the color of translucent ceramic restorations.