Electrochemical reduction of dioxygen on carbon nanotubes–dihexadecyl phosphate film electrode

The electrochemical reduction of dioxygen on the single-walled carbon nanotubes–dihexadecyl phosphate (SWNTs–DHP) film electrode has been investigated. Two well-defined dioxygen reduction peaks were observed at about ?0.39 and ?0.93 V in 0.1 M air-saturated NaOH at the SWNTs–DHP film electrode suggesting two two-electron reduction steps of dioxygen. The numbers of electron transferred and transfer coefficients in the dioxygen reduction process were calculated. The influences of some parameters on the reduction of dioxygen were examined including the concentration and amount of nanotubes, and ratio of SWNTs vs. DHP. Based on the experiment results under the conditions employed here, a possible mechanism is proposed and discussed.     

Catechin antioxidant action at various pH studied by cyclic voltammetry and PM3 semi-empirical calculations

The mechanism of catechin electro-oxidation at various pH was studied using cyclic voltammetry (CV) on the glassy carbon (GC) electrode and PM3 semi-empirical calculations. The influence of activation of the surface of the GC electrode on CV results has been discussed. Mixed adsorption–diffusion control has been observed by applying mechanistic criteria of CV to the results obtained at the activated electrode. The calculated catechin diffusion coefficient D = 2.78 × 10^?6 cm² s^?1. A linear increase of the current peak has been observed with the increase of substrate concentration up to 40 μmol dm^?3 (surface coverage Γ ～ 10^?11 mol cm^?2). In the whole investigated pH range, the dE/dpH value is very close to the anticipated Nernstian dependence of ?59 mV/pH indicating that the slope is not affected by the different sequences of e^? and H⁺ transfer. Molecular modeling results show a decrease of ≈5 kcal mol^?1 in ΔHoF (between radical and parent molecule) and a decrease of ≈6 eV in IP (of the parent molecule) when the parent molecule is changed from neutral to monoanionic form of catechin showing that both processes – hydrogen and electron abstraction are facilitated by deprotonation. Electrochemical oxidation of catechin is known to proceed as a two step one-electron oxidation of the B-ring of o-phenolic groups. Upon an increase in the pH, the mechanistic pathway of catechin electro-oxidation in both oxidation steps changes from an eH to the He process. In the reaction with a free radical, this may induce the change from hydrogen to electron donation.     

Novel magnetic nanoparticle-containing adhesive with greater dentin bond strength and antibacterial and remineralizing capabilities

Objectives

A nanoparticle-doped adhesive that can be controlled with magnetic forces was recently developed to deliver drugs to the pulp and improve adhesive penetration into dentin. However, it did not have bactericidal and remineralization abilities. The objectives of this study were to: (1) develop a magnetic nanoparticle-containing adhesive with dimethylaminohexadecyl methacrylate (DMAHDM), amorphous calcium phosphate nanoparticles (NACP) and magnetic nanoparticles (MNP); and (2) investigate the effects on dentin bond strength, calcium (Ca) and phosphate (P) ion release and anti-biofilm properties.

Electrochemical formation of Se atomic layers on Au(1 1 1) surfaces: the role of adsorbed selenate and selenite

We report an investigation of the electrodeposition of Se atomic layers on Au(1 1 1) surfaces from aqueous SeO₂ solutions. The behavior of this system is complex, and characterized by two major surface-limited reduction waves in the potential window positive of the onset of Se bulk deposition. These two waves occur at potentials negative of the known E° for the Se(IV)/Se(0) couple due to the large overpotential for Se deposition on Au surfaces, and therefore cannot be considered true underpotential deposition. On the basis of potential switching and concentration dependence experiments, the first surface wave is unambiguously assigned as arising from the two-electron reduction of an adsorbed selenate species to adsorbed selenite. In some earlier reports, this feature has been assigned as corresponding to the four-electron reduction of selenite to elemental selenium. The second major surface-limited wave corresponds to the four-electron reduction of adsorbed selenite to elemental selenium. Coulometric measurements indicate that the selenium coverage corresponds to approximately 0.41 monolayers, in good agreement with previous scanned probe microscopy investigations which indicate that Se forms a (√3×√3)R30° adlayer on Au(1 1 1) surfaces.     

Voltammetric determination of stability constants of iron(III)–glycine complexes in water solution

Determination of the stability constants of dissolved iron(III)–glycine system in water solution (I = 0.6 mol L^?1 in NaClO₄ at 25 ± 1 °C) using differential pulse cathodic voltammetry (DPCV) was performed on a static mercury drop electrode (SMDE). Iron(III) concentration of 2.5 × 10^?5 mol L^?1 and the pH range from 9.05 to 6.36 ensured the formation of enough concentration of iron(III)–glycine higher coordination complexes (1:2 and 1:3) to be measured by the applied method. The concentrations of total glycine varied from 0.1 to 0.5 mol L^?1. Cyclic voltammetry (CV) measurements were used to investigate reversibility of the iron(III)–glycine complexes which showed one-electron reversible character. The stability constants of iron(III) [Fe(Gly)₂]⁺ and Fe(Gly)₃ complexes, which had not been reported in the literature so far, were found to be log β₂ = 16.83 ± 0.47 and log β₃ = 18.64 ± 0.70, respectively. The model that best fitted the data gave two iron(II)–glycine stability constants for [FeGly]⁺ log K₁ = 3.69 ± 0.19 and for Fe(Gly)₂ log β₂ = 5.08 ± 0.60. According to the constants found, chemical distribution of iron(III) in glycine water solution, as a function of pH, was calculated and proposed.     

The influence of SiO2 and SiO2–TiO2 intermediate coatings on bond strength of titanium and Ti6Al4V alloy to dental porcelain

ObjectivesThe purpose of this study was to evaluate the bond strength of commercially pure CPTi and Ti6Al4V alloy with SiO₂ and SiO₂–TiO₂ intermediate coatings to Triceram low-fusing dental porcelain.MethodsThe multilayered systems were characterized from the standpoint of microstructure analysis (SEM), the mode of failure, the nature of bonding and the influence of intermediate coatings on the improvement of bond strength. The SiO₂ and SiO₂–TiO₂ intermediate coatings were applied on the substrate materials by the sol–gel dipping technique. The metal–ceramic bond strength was investigated according to ISO 9693 standards using the three-point flexure bond test.ResultsStatistically significant higher bond strength of the metal–porcelain for Ti6A14V alloy (28.24 MPa), Ti6Al4V/SiO₂ (32.17 MPa) and Ti6Al4V/SiO₂–TiO₂ (36.09 MPa) was noted in comparison to CPTi (23.04 MPa), CPTi/SiO₂ (27.98 MPa) and CPTi/SiO₂–TiO₂ (28.84 MPa), respectively. The nature of metal-intermediate coating–porcelain bonding was both mechanical and chemical. The failure in all systems was cohesive and adhesive, mainly adhesive.SignificanceThe application of SiO₂ and SiO₂–TiO₂ intermediate coatings, produced by the sol–gel method, to both CPTi and Ti6Al4V alloy significantly improves the bond strength of metal–porcelain systems in comparison to the metal substrate only after sandblasting, and may have clinical use.     

Electroreduction of halogenated fumaric esters: a combined electrochemical and computational investigation

Diethyl fumarate and related halogenated derivatives have been studied by cyclic voltammetry and electrolysis, on mercury and glassy carbon electrodes, in DMF + 0.1 mol L^?1 TBAP and in acetonitrile + water (3:4) with 0.1 mol L^?1 NaCl or 0.1 mol L^?1 TEAP. For compounds with two reducible functionalities, the electron-deficient olefin and the C–X group, the grade of substitution on the halogenated carbon causes differences on the site involved in the first electron transfer thus determining the chemical reactivity. Enediester compounds with –CH₂– groups insulating the gem-trihalide groups (–CX₃, X=Br and Cl) suffer reduction, and the C–X cleavage is the reaction of choice. The reaction pathway also depends on the nature of the electrode and significant positive potentials shifts for compounds with a gem-tribromide group are evident in the cyclic voltammogram on a mercury electrode, in relation to results on a glassy carbon electrode. The formation of easily reduced organomercurials is the main reason for this intense positive shift in the first electron transfer. On a vitreous carbon electrode, factors directly related to the strength of the C–X bond play a determinant role. Concerning electrolysis, the gem-tribromo derivative furnishes H₂CCBr₂ and ethyl hydrogenfumarate, through hydrolysis produced by initial cleavage of the C–Br. For the other polyfunctional compounds (–CHX₂, –CH₂X), the olefin is reduced first to yield dimers and/or hydrogenated products depending upon the reaction conditions. Quantum chemical calculations performed on the anion radical of these compounds yield spin densities located on the –CBr₃/–CCl₃ group and on the enediester group for the –CCl₂/–CBr₂, –CH₂Br/–CH₂Cl derived compounds. Upon geometry optimisation, the C–Br bond in compounds containing –CBr₃ groups are longer, suggesting that this bond can easily be cleaved, yielding organomercurial compounds, in the case of the use of a mercury electrode or leading to bond cleavage, for inert electrodes. For the other substituents, the optimisation basically does not affect the geometry of the radical anion compared to the neutral substrate. These results have been confirmed by the calculated dissociation energy of the C–Br bond, which for the –CBr₃ group is approximately 100 kJ mol^?1 as against 240 kJ mol^?1 for the same bond in the –CH₂Br group. The coherence between the experimental and calculated data reinforces the usefulness of these computational tools in rationalising the reactivity of electrogenerated species as well as in predicting the electrochemical reaction outcome.     

Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties

ObjectivesSecondary caries and restoration fracture are the two main challenges facing tooth cavity restorations. The objective of this study was to develop a composite using tetracalcium phosphate (TTCP) fillers and whiskers to be stress-bearing, and to be “smart” to increase the calcium (Ca) and phosphate (PO₄) ion release at cariogenic pH.MethodsTTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97 μm. Whiskers fused with nano-sized silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0 to 75%. Ca and PO₄ ion releases were measured vs. time at pH of 7.4, 6, and 4. Composite mechanical properties were measured via three-point flexure before and after immersion in solutions at the three pH.ResultsTTCP composite without whiskers had flexural strength similar to a resin-modified glass ionomer (Vitremer) and previous Ca–PO₄ composites. With whiskers, the TTCP composite had a flexural strength (mean ± S.D.; n = 5) of (116 ± 9) MPa, similar to (112 ± 14) MPa of a stress-bearing, non-releasing hybrid composite (TPH) (p > 0.1). The Ca release was (1.22 ± 0.16) mmol/L at pH of 4, higher than (0.54 ± 0.09) at pH of 6, and (0.22 ± 0.06) at pH of 7.4 (p < 0.05). PO₄ release was also dramatically increased at acidic pH. After immersion, the TTCP–whisker composite matched the strength of TPH at all three pH (p > 0.1); both TTCP–whisker composite and TPH had strengths about threefold that of a releasing control.SignificanceThe new TTCP–whisker composite was “smart” and increased the Ca and PO₄ release dramatically when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit caries. Its strength was two- to threefold higher than previously known Ca–PO₄ composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.     

Effect of honey in preventing gingivitis and dental caries in patients undergoing orthodontic treatment

ObjectivesThis study was conducted to investigate the following: (1) the effects of chewing honey on plaque formation in orthodontic patients, (2) the effect of chewing honey on dental plaque bacterial counts, (3) determine if honey possesses antibacterial effects on bacteria recovered from plaques.MethodsFemale orthodontic patients (n = 20, 12–18 years of age) participated in this randomized controlled study. The effects of honey were compared to treatment with either 10% sucrose or 10% sorbitol that served as positive and negative controls, respectively. The pH of plaque was measured using a digital pH meter prior to baseline and at 2, 5, 10, 20, and 30 min after chewing honey or rinsing with control solutions and the numbers of Streptococcus mutans, Lactobacilli, and Prophymonas gingivalis in respective plaques were determined. The antibacterial activity of honey was tested against commonly used antibiotics using the disk diffusion method.ResultsSignificant differences in pH were observed in the honey and sucrose groups compared to the pH observed in the sorbitol group (p ? 0.001). The maximum pH drop occurred at 5 min in both the honey and sucrose groups; however the pH in the honey group rapidly recovered 10–20 min after exposure and did not drop below the critical decalcification pH of 5.5. On the other hand, the pH following sucrose exposure fell <5.5 and was associated with a 30 min recovery time. The pH observed for the sorbitol group did not change over time. Bacterial counts were significantly reduced in the honey group compared to the other treatment groups (p ? 0.001) and honey significantly inhibited the growth of all studied strains compared to inhibition observed with antibiotics (p ? 0.001).ConclusionsHoney can be used as an alternative to traditional remedies for the prevention of dental caries and gingivitis following orthodontic treatment.     

Should adhesive debonding be simulated for intra-radicular post stress analyses?

Objective

Elucidate the influence of debonding on stress distribution and maximum stresses for intra-radicular restorations.

The electrochemical behavior of p-sulfonated calix[4]arene

The electrochemical behavior of p-sulfonated calix[4]arene was studied. In aqueous solution, p-sulfonated calix[4]arene can be oxidized when the potential is more than 0.7 V versus SCE. It is confirmed that the reaction is an irreversible two-electron transfer electrochemical reaction. The anodic peak potential, E_p, is affected by the acidity of the solution. E_p shifts in the negative direction when the pH increases. The electron transfer coefficient, α, is 0.65. At 25 °C, the diffusion coefficient of p-sulfonated calix[4]arene is 3.1 × 10^?5 cm² s^?1. The activation energy, E_a, for the electrochemical reaction is (18.8 ± 0.2) kJ mol^?1.     

Evaluation of interface characterization and adhesion of glass ceramics to commercially pure titanium and gold alloy after thermal- and mechanical-loading

ObjectivesThis study evaluated the effect of thermal- and mechanical-cycling on the shear bond strength of three low-fusing glassy matrix dental ceramics to commercial pure titanium (cpTi) when compared to conventional feldspathic ceramic fused to gold alloy.MethodsMetallic frameworks (diameter: 5 mm, thickness: 4 mm) (N = 96, n = 12 per group) were cast in cpTi and gold alloy, airborne particle abraded with 150 μm aluminum oxide. Low-fusing glassy matrix ceramics and a conventional feldspathic ceramic were fired onto the alloys (thickness: 4 mm). Four experimental groups were formed; Gr1 (control group): Vita Omega 900–Au–Pd alloy; Gr2: Triceram–cpTi; Gr3: Super Porcelain Ti-22–cpTi and G4: Vita Titankeramik–cpTi. While half of the specimens from each ceramic–metal combination were randomly tested without aging (water storage at 37 °C for 24 h only), the other half were first thermocycled (6000 cycles, between 5 and 55 °C, dwell time: 13 s) and then mechanically loaded (20,000 cycles under 50 N load, immersion in distilled water at 37 °C). The ceramic–alloy interfaces were loaded under shear in a universal test machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were noted and the interfaces of the representative fractured specimens from each group were examined with stereomicroscope and scanning electron microscope (SEM). In an additional study (N = 16, n = 2 per group), energy dispersive X-ray spectroscopy (EDS) analysis was performed from ceramic–alloy interfaces. Data were analyzed using ANOVA and Tukey's test.ResultsBoth ceramic–metal combinations (p < 0.001) and aging conditions (p < 0.001) significantly affected the mean bond strength values. Thermal- and mechanical-cycling decreased the bond strength (MPa) results significantly for Gr3 (33.4 ± 4.2) and Gr4 (32.1 ± 4.8) when compared to the non-aged groups (42.9 ± 8.9, 42.4 ± 5.2, respectively). Gr1 was not affected significantly from aging conditions (61.3 ± 8.4 for control, 60.7 ± 13.7 after aging) (p > 0.05). Stereomicroscope images showed exclusively adhesive failure types at the opaque ceramic–cpTi interfacial zone with no presence of ceramic on the substrate surface but with a visible dark titanium oxide layer in Groups 2–4 except Gr1 where remnants of bonder ceramic was visible. EDS analysis from the interfacial zone for cpTi–ceramic groups showed predominantly 34.5–85.1% O₂ followed by 1.1–36.7% Al and 0–36.3% Si except for Super Porcelain Ti-22 where a small quantity of Ba (1.4–8.3%), S (0.7%) and Sn (35.3%) was found. In the Au–Pd alloy–ceramic interface, 56.4–69.9% O₂ followed by 15.6–26.2% Si, 3.9–10.9% K, 2.8–6% Na, 4.4–9.6% Al and 0–0.04% Mg was observed.SignificanceAfter thermal-cycling for 6000 times and mechanical-cycling for 20,000 times, Triceram–cpTi combination presented the least decrease among other ceramic–alloy combinations when compared to the mean bond strength results with Au–Pd alloy–Vita Omega 900 combination.     

XPS and electrochemical studies of ferrocene derivatives anchored on n- and p-Si(1 0 0) by Si–O or Si–C bonds

High-coverage functionalization of H-terminated n- and p-Si(1 0 0) with vinylferrocene (VFC) and ferrocenecarboxaldehyde (FCA) has been obtained by wet chemistry methods, via the formation of a covalent bond between silicon atoms and the carbon (VFC) or the oxygen (FCA) termination of the molecules. The resulting functionalized electrodes have been analyzed by XPS, before and after cyclic voltammetry and capacitance–voltage measurements in an electrochemical cell. The very high quality of the hybrid species Si–CH₂–CH₂–C₅H₄–Fe²⁺–C₅H₅, resulting from VFC, has been certified by the negligible presence of silicon oxide and ferrocenium ions, and by the correct carbon/iron atomic ratio, accounting for the molecular species. The hybrid produced from FCA, Si–O–CH₂–C₅H₄–Fe²⁺–C₅H₅, presents a higher amount of silica, carbon and ferrocenium, as a consequence of the higher temperature of the functionalization procedure and of the higher reactivity of FCA. The use of two closely similar redox molecules has allowed to compare the behaviour of the Si–C–Y vs. Si–O–Y bond (Y being the redox moiety), with respect to their electrochemical reactivity in an organic solution. Both hybrids behave similarly on n- and p-Si substrates, in terms of redox potentials, stability to more than 1000 voltammetric cycles, linearity of the current intensity with the scan rate. The vinyl derivative, however, showed a faster and more reversible electron transfer kinetics than the carboxaldehyde derivative and an enhanced stability to long-term electrochemical experiments. VFC/p-Si is the first reported ferrocene derivative anchored to monocrystalline silicon via a C–Si bond. It is also the only large-area hybrid capacitor, to date, to be frequency-independent up to several hundred Hz, having a redox capacitance of 10^?4 F cm^?2, the highest reported so far for a monolayer on a Si(1 0 0) face.     

Electrogenerated chemiluminescence. 75. Electrochemistry and ECL of 9,10-bis(2-naphthyl)anthracene

The spectroscopy, electrochemistry, and electrogenerated chemiluminescence (ECL) of 9,10-bis(2-naphthyl)anthracene (BNA) was investigated. BNA shows high fluorescence quantum yields (φ=0.86). Strong, intense ECL was observed on the surface of a Pt electrode in benzene + acetonitrile (1:1) while pulsing between the potentials for the first oxidization and reduction of BNA. The peak of ECL light emission was at 430 nm with an ECL efficiency about 90% of that of 9,10-diphenylanthracene (DPA). Cyclic voltammograms (CVs) of BNA show nernstian one-electron oxidations and reductions to the radical ions attributed to electron transfers to the anthracene core. The first reduction is followed by a second irreversible one-electron step and then two, closely spaced nernstian one-electron reductions assigned to electron transfer to the naphthalene moieties. The reduction CV was digitally simulated to establish the reduction mechanism.     

Optimization of the etch-and-rinse technique: New perspectives to improve resin–dentin bonding and hybrid layer integrity by reducing residual water using dimethyl sulfoxide pretreatments

Objective

To determine whether bonding effectiveness and hybrid layer integrity on acid-etched dehydrated dentin would be comparable to the conventional wet-bonding technique through new dentin biomodification approaches using dimethyl sulfoxide (DMSO).

Influence of thermo-mechanical cycling on porcelain bonding to cobalt–chromium and titanium dental alloys fabricated by casting,milling, and selective laser melting

Purpose

The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co–Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM).

Spectral and electrochemical studies of axial ligand binding reactions of carbonylruthenium(II) meso-tetramesitylporphyrin

The spectral and electrochemical properties of carbonylruthenium(II) meso-tetramesitylporphyrin, Ru(CO)(TMP) in the presence of imidazole, N-methylimidazole and hydroxide anion as axial ligands were investigated. Spectrophotometric titration of Ru(CO)(TMP) of the nitrogeneous bases caused the absorption spectrum to shift to longer wavelengths. Larger shifts in wavelength were observed in the titration using tetrabutylammonium hydroxide. The formation constants for these ligands coordinated to the ruthenium center were calculated. The effect of axial ligand ligation caused the decrease of vibrational frequency of CO as detected from FT-IR spectroscopy. The CO stretching frequency (ν_CO) of Ru(CO)TMP in CH₂Cl₂ is 1940 cm^?1, which is lowered to 1936 and 1913 cm^?1 upon coordination of nitrogenous bases and hydroxide anion, respectively. Cyclic voltammetry of Ru(CO)(TMP) in CH₂Cl₂ showed an irreversible reduction wave at ?1.63 V and two reversible oxidations at E_1/2 = 0.78 and 1.27 V vs. Ag|AgCl, respectively. Addition of imidazole and hydroxide into Ru(CO)(TMP) solution caused shifts in the redox potential and accordingly, the binding constants of the ligands to the one- and two-electron oxidized ruthenium porphyrins were estimated and compared. Spectroelectrochemical methods were used to characterize the above electron-transfer reactions.     

The electrochemistry and thin-layer luminescence spectroelectrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode

We report on the first direct electrochemistry and fluorescence spectroelectrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode. The value of n determined in spectropotentiostatic experiments at 1.87×10^?6 mol l^?1 of rhodamine 6G in 0.20 mol l^?1 KCl solution is 1.15, and the experimental value obtained for E⁰′ is ?0.787 V versus Ag ∣ AgCl ∣ KCl_sat, which agrees very well with the value (E⁰′=?0.791 V) obtained using cyclic voltammetry at a modified gold electrode. The values of the diffusion coefficients D_O and D_R for the oxidized and reduced forms of rhodamine 6G calculated from results of potential step and in situ fluorescence measurement experiments are 4.0×10^?6 cm² s^?1 and 4.2×10^?6 cm² s^?1, respectively. Cyclic voltammograms of rhodamine 6G show that the peak current I_p is proportional to the square root of the potential scan rate v^1/2, the ratio of the reduction to the oxidation peak height is about unity, and the separation of both reduction and reoxidation peak potentials ΔE_P is essentially constant at 135 mV at low scan rates. These results indicate that electrochemistry of rhodamine 6G at a 4,4′-bipyridine-modified gold electrode is a quasi-reversible one-electron electrode process.     

New surgical instrument for the treatment of condylar fractures: the digitised condylar retractor

Reduction is one of the most difficult steps in condylar fracture surgery, and a key factor governing the postoperative outcome. In this study we evaluated quantitatively the effects of a digitised condylar retractor on the duration and rate of reduction. In a prospective, randomised, controlled clinical trial, 48 patients with unilateral condylar fractures who were listed for surgical treatment were randomised to an experimental and a control group (n = 24 in each). The experimental group was treated with a digitised condylar retractor, and the control group with traditional surgical instruments only. The primary outcome variables were duration and rate of reduction. The continuity correction chi squared test and independent samples t test were used for statistical analyses. The results showed that the mean reduction time was 21.3 minutes in the experimental group and 42.4 minutes in the control group (p = 2.48*10⁻⁸, <0.001). The reduction rate was 21/24 in the experimental group and 17/24 in the control group (p = 0.16). The results indicated that the mean duration of reduction was significantly shorter, and the reduction rate was higher, in the experimental group than among controls. In conclusion, the digitised condylar retractor can assist surgeons to improve efficiency and accuracy in the reduction of condylar fractures, so it merits promotion as an aid to their surgical treatment.     

Nanoleakage,ultramorphological characteristics,and microtensile bond strengths of a new low-shrinkage composite to dentin after artificial aging

ObjectivesTo study the microtensile bond strengths and nanoleakage of low-shrinkage composite to dentin. The null hypotheses tested were (1) aging does not affect the bonding of low-shrinkage composite; (2) there is no difference in microtensile bond strengths and nanoleakage using different bonding strategies.Methods32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15 s with phosphoric acid + LS System Adhesive (LSpa); Adper Single Bond Plus (SB, 3M ESPE); SB + LS Bond (SBLS). Occlusal dentin was exposed and restored with Filtek LS (3M ESPE). The samples were tested after 24 h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8 ± 0.2 mm² and fractured at a crosshead speed of 1 mm/min. The data were submitted to ANOVA/Duncan's post hoc test, at p < 0.05. Five slabs from each group were selected and immersed in 50 wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal–Wallis at p < 0.05.ResultsNo statistically significant difference was found among the experimental groups for the factor dentin treatment (p = 0.165) and aging (p = 0.091). All experimental groups exhibit some degree of nanoleakage. There was no adhesion of Filtek LS applied directly over dentin surfaces treated with SB.SignificanceThe new low-shrinkage resin composite showed compatibility only with its dedicated adhesive. Pre-etching did not improve the bond strengths to low-shrinkage resin composite. Some degree of nanoleakage was evident in all groups.