Electrochemical study of self-assembled monolayers of a β-cyclodextrin methyl sulfide covalently linked to anthraquinone

Self-assembled monolayers of a β-cyclodextrin with methyl sulfides on the primary sites of the molecule and mono-functionalized with anthraquinone on a secondary site have been formed on gold electrodes. The surface coverages obtained by electrochemistry are consistent with values reported previously or calculated for similar non-electroactive β-CD derivatives. The electron transfer rate constants vary markedly with pH, increasing rapidly between pH 7 and 9 to values of approximately 700–900 s^?1. These values are faster than reported previously for thiol derivatives of anthraquinone dispersed in an alkylthiol SAM matrix. Near pH 6, slow electron transfer is observed with a splitting into individual one-electron steps. Lowering the pH further results in very sluggish kinetics and indistinguishable peaks. Inclusion of naphthalene into the β-CD cavity appears to affect the anodic rate constant, and a small potential shift occurs. The efficient electron transfer of the anthraquinone spaced from the gold surface by a β-CD unit suggests promise for use of such molecules as ‘immobilized artificial enzymes’.     

Adhesion durability of dual-cure resin cements and acid–base resistant zone formation on human dentin

ObjectivesBond durability and resistance to acid-base challenge of dentin with dual-cure resin cement have been rarely investigated. The purpose of this study was to evaluate dentin bond strength and observe the adhesive-dentin interface after acid-base challenge using three different dual-cure resin cements.MethodsThirty dentin surfaces from caries-free human premolars were ground and bonded with one of three dual-cure resin cements: PANAVIA V5 (V5), ESTECEM II (E II) and Rely X Ultimate (RXU) and thermocycled for 0, 5,000 and 10,000 cycles. A microtensile bond strength (μTBS) test was undertaken and the interface of the bonded specimens after acid-base challenge was examined by SEM.ResultsThe μTBS of V5 exhibited a stable bond strength despite thermal cycling while the bond of EII and RXU after 10,000 cycles dropped significantly among all thermal cycle periods (p<0.05). An acid-base resistant zone (ABRZ) was observed in all groups, however, the morphology of the bonded interface differed among the tested cements.ConclusionBonding durability to dentin and ABRZ morphologies differed among the cements evaluated. PANAVIA V5 cement system with tooth primer provided the most reliable bond strength and was best able to resist the acid–base challenge.     

A monomer–dimer equilibrium in self-assembled monolayers of N-ethyl-N′-octadecylviologen on the electrode surface. The influence of water content and hexafluorophosphate ion

This paper describes the dimerization of self-assembled monolayers (SAMs) of N-ethyl-N′-octadecylviologen (1) on GC and Au electrode surfaces in the presence of 0.1 M NH₄PF₆ aqueous solutions. The ‘wet’ and ‘dry’ SAMs of 1 showed multiple redox peaks for the first reduction of 1 in the presence of NH₄PF₆, in contrast to the case of other supporting electrolytes (typically KCl, NaNO₃, Na₂SO₄ and NaClO₄) where both wet and dry SAMs of 1 exhibited a single redox wave for the first reduction. The dry SAM showed a well defined reduction peak at ?0.57 V along with a shoulder reduction peak at ?0.50 V and two oxidation peaks at ?0.50 and ?0.42 V. On the contrary, the wet SAM gave a very sharp reduction peak at ?0.50 V and a small shoulder peak at ?0.57 V in addition to two oxidation peaks like those observed for the dry SAM. The reduction peak of ?0.50 V was ascribed to the reduction of strongly hydrated dications of 1, while the reduction peak at more negative potential (?0.57 V) was attributed to the reduction of the dehydrated dications of 1. The two oxidation peaks at ?0.50 and ?0.42 V were ascribable to the oxidation of the usual radical cation monomer and the radical cation dimer, respectively. In the case of the wet SAM, upon continuous potential cycling, the sharp reduction peak of ?0.50 V clearly decreased, whereas the more negative reduction peak of ?0.57 V was highly stable. In this case, in the oxidation process, the monomer peak of ?0.50 V increased, while the dimer peak of ?0.42 V decreased. Thus it is reasonably assumed that in the wet SAM, initially the radical cations of 1 feel an aqueous environment in the monolayer where the dimerization is highly favored and at subsequent potential cycles, due to the entry of hydrophobic anions of PF₆^? into the monolayer, the pre-existent water molecules are expelled from the monolayer and under this circumstance the radical cations of 1 may feel the environment very similar to non-aqueous media where the dimerization is totally suppressed. The adsorption tendency of 1 on the electrode surface was also studied using the SAMs prepared by dissolving 1 in water+ethanol mixtures of different ratios. The appearance of multiple peaks was found to depend significantly on the alkyl chain length of asymmetric viologen. The inclusion/expulsion of solvents and anions into/from the SAM during the redox reaction were studied by the electrochemical quartz crystal microbalance (EQCM). It was found that in the presence of SO₄^2? ions ca. 17 water molecules per one SO₄^2? ion were transported to the SAM of 1 during the oxidation, whereas ca. five water molecules were transported in the presence of PF₆^? ions.     

Electrochemistry of Langmuir–Blodgett and self-organized monolayers of an azocrown ether,both pure and mixed with a phospholipid

The electrochemical behavior of monolayers of an azocrown ether (L16), both pure and mixed with dioleoylphosphatidylcholine (DOPC) was investigated using a mercury electrode. The monolayers formed at the air ∣ water interface were transferred onto the electrode using the Langmuir–Blodgett approach. The reversibility of the electrode processes depends on the surface pressure during the transfer of the monolayer. The reduction mechanism of the azo to the hydrazo group was studied in acidic medium by cyclic voltammetry and potential-step chronocoulometry. The dependence of the faradaic charge due to azo group reduction at constant pH upon scan rate (for voltammetry) or upon electrolysis time (for chronocoulometry) was examined on the basis of a general kinetic approach. The same approach was used to interpret the dependence of the faradaic charge upon pH at constant scan rate or electrolysis time. The reduction of the azo to the hydrazo group takes place via the reversible uptake of one electron, followed by the rate determining protonation of the resulting radical anion. When L16 is in the form of a pure monolayer its electroreduction is accompanied by a 2D phase transition involving the passage from a liquid-like to a solid-like structure. No such phase transition is observed in mixed L16–DOPC monolayers. At intermediate compositions of this mixture, strong attractive interactions between L16 and DOPC molecules decrease the mean area per molecule with respect to the ideal behavior at the air ∣ water interface, and prevent complete electroreduction of the L16 molecules in the monolayer.     

Current–voltage curves of a composite bipolar membrane in organic acid–water solutions

The current–voltage curves of a composite bipolar membrane (CBM) were measured experimentally for the various mole fractions of formic acid+water, acetic acid+water and propionic acid+water mixed solution systems. The experimental results showed that a CBM has the characteristics of a bipolar membrane. The current–voltage characteristics were analyzed using Mafé’s and Ram??rez’s ion transport theory by applying the chemical reaction model in the intermediate region, and the theoretical calculations could well explain the experimental results. The increase in the mole fraction of the organic acid causes the increase of the ion concentration in the solution, and this effect enhances the water splitting. On the other hand, the increase in the mole fraction of the organic acid causes the decrease of the water concentration in the space charge region of the membrane also, and the effect lessens the water splitting. Based on the above two effects, it could be expected that with an increase in the mole fraction of the organic acid, the maximum local effective value of a CBM resistance decreases firstly, and then increases when the mole fraction of water becomes rather low. The results that we found in our experiments correspond to the above discussion.     

Acoustic emission analysis of the effect of simulated pulpal pressure and cavity type on the tooth–composite interfacial de-bonding

ObjectiveThe aim of this study was to evaluate the influence of in vitro pulpal pressure and cavity type on the tooth–composite bonding interface by means of acoustic emission (AE) analysis.MethodsClasses I and II cavities on extracted third molars were prepared and assigned to four groups of seven teeth each: (1) direct composite restoration without simulated pulpal pressure (SPP) in class I cavity, (2) direct composite restoration with SPP in class I cavity, (3) direct composite restoration without SPP in class II cavity, (4) direct composite restoration with SPP in class II cavity. The teeth were restored with Filtek Z250 composite and Adper Scotchbond Multi-Purpose adhesive system (3M ESPE, St. Paul, MN, USA). AE events were recorded for 2000 s during light-curing. Groups 2 and 4 were subjected to 20 cm H₂O hydrostatic pressure throughout the procedures. The data were analyzed with two-way ANOVA. After the AE test, teeth were sectioned longitudinally in mesio-distal direction, the tooth–composite interface was examined using SEM.ResultsSPP in Groups 2 (4.57 ± 1.40) and 4 (3.43 ± 1.13) yielded significantly higher AE events number than those of Groups 1 (3.43 ± 1.51) and 3 (1.71 ± 0.95) where the SPP was not applied (p < 0.05). The number of AE events of class I cavity in Groups 1 and 2 were significantly higher than those of class II cavity in Groups 3 and 4 (p < 0.05). SEM examination showed that all groups had intact enamel–composite interface, while micro-gaps were observed at the dentin–composite interface, mainly at the pulpal floor of the cavity. The class I cavities with SPP in Group 2 showed wider gaps more frequently than class II cavities without SPP in Group 3.SignificanceThe SPP and class I cavity with high C-factor triggered more AE events, confirming its negative impact on the bonding interface.     

Studying the binding of Cd2+ by ω-mercaptoalkanoic acid self assembled monolayers by cyclic voltammetry and scanning electrochemical microscopy (SECM)

Cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) have been used for studying the binding of protons and cadmium(II) ions by 8-mercaptooctanoic acid monolayer that was assembled on an Au surface. Binding of the cations by the monolayer affected the kinetics of electron transfer to negatively charged species, i.e., ${\mathrm{IrCl}}_6^{3-}$, in the solution. Increasing the pH of the solution causes the CV of ${\mathrm{IrCl}}_6^{3-}$ to become less reversible and the feedback current of the SECM to decrease as the distance between the microelectrode and the surface decreases. On the other hand, addition of Cd²⁺ to the solution at pH 6.8 increases the CV reversibility and the feedback current of the SECM as a result of neutralizing the negative charge of the monolayer by the metallic ions. A model based on the Frumkin correction was used to account for these findings and for extracting the heterogeneous association constant of Cd²⁺ by the monolayer.     

Chemical analysis of in vivo–irradiated dentine of head and neck cancer patients by ATR-FTIR and Raman spectroscopy

Objectives

To evaluate the effect of in vivo radiotherapy on the chemical properties of human dentine by Fourier-transform infrared spectroscopy (FTIR) and Raman analysis.

Materials and methods

Chemical composition was evaluated comparing control and irradiated group (n = 8). Irradiated teeth were obtained from radiotherapy patients subjected to fractionated X-ray radiation of 1.8 Gy daily totaling 72 Gy. The teeth were sectioned according to the type of dentine (crown or root dentine), obtaining 3-mm dentine cervical slices. The analyzed parameters by FTIR and Raman spectroscopies were mineral/matrix ratio (M:M), carbonate/mineral ratio (C:M), amide I/amide III ratio, and amide I/CH₂ ratio. Raman also calculated the phosphate and carbonate crystallinity.

Results

FTIR revealed that M:M had a decrease in both factors (p = 0.008; p = 0.043, respectively) and root dentine showed a lower C:M in the irradiated group (p = 0.003). Raman revealed a higher phosphate crystallinity and a lower carbonate crystallinity in crown dentine of irradiated group (p = 0.021; p = 0.039). For amide I/amide III, the irradiated showed a lower ratio when compared to the control group (FTIR p = 0.002; Raman p = 0.017). For amide I/CH₂, the root dentine showed a higher ratio than the crown dentine in both methods (p < 0.001).

Conclusions

Radiotherapy altered the chemical composition of human dentine. The exchange of phosphate-carbonate ions in the hydroxyapatite and higher concentration of organic components was found after radiotherapy.

Clinical relevance

The increased risk of radiation-related caries in patients undergoing head and neck radiotherapy is due not only to salivary, dietary, and microbiological changes but also to changes in tooth chemical composition.

     

Effect of post-curing light exposure time on the physico–mechanical properties and cytotoxicity of 3D-printed denture base material

ObjectiveThis study investigated the effect of post curing light exposure time on the physico-mechanical properties and cytotoxicity of a 3D-printed PMMA-based denture material in comparison to a conventional heat-cured alternative as a control.Methods3D-printed specimens were fabricated followed by post-curing for 0, 5, 10 or 20 min at 200 W and light wavelength range of 390–540 nm. Heat-cured specimens were fabricated using a standard protocol. Specimens were placed in artificial saliva at 37 ℃ for 48 h (immediate groups) and 6 months (aged group), then evaluated flexural strength/modulus, fracture toughness, microhardness, and degree of conversion. Water sorption and solubility was assessed after 28 days. Flexural strength, flexural modulus, and fracture toughness were tested through three-point bending tests, while the surface hardness was tested using Vickers’s test. Fractured specimens were viewed by scanning electron microscope (SEM). Cytotoxicity in term of cell viability was evaluated using human oral fibroblasts.ResultsFlexural strength/modulus, fracture toughness and surface hardness significantly improved with the increase in light curing time up to 20 min. The same pattern of improvement was found with degree of conversion, water sorption, solubility, and cell viability. There was no significant difference (p < 0.01) between heat-cured material and 3D specimens post-cured for 20 min in term of flexural strength/modulus, surface hardness, and degree of conversion at the two-storage time points.SignificanceGenerally, the physico-mechanical properties of the 3D-printed denture base material improve as post curing time increases up to 20 min which exhibited comparable performance as the conventional heat-cured control.     

Ion release and physical properties of CPP–ACP modified GIC in acid solutions

A new glass-ionomer cement (GIC) (Fuji VII? EP) includes 3% (w/w) casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) to enhance ion release.ObjectivesTo assess this new GIC compared with a GIC without CPP–ACP (Fuji VII?) with respect to ion release, changes in surface hardness and in mass under a variety of acidic and neutral conditions.MethodsEighty blocks of Fuji VII? (F7) and Fuji VII? EP (F7EP) were subjected to three acidic solutions (lactic and citric acids pH 5.0, hydrochloric acid pH 2.0) and water (pH 6.9) over a three-day period. Ion release, surface hardness and weight measurements were carried out every 24 h.ResultsHigher calcium ion release from F7EP was observed under all acidic conditions. Increased inorganic phosphate ion release was observed for F7EP in hydrochloric and citric acids. Fluoride ion release was similar between F7 and F7EP under all conditions but was significantly higher in acids compared with water. After three days there was no significant difference in surface hardness (p > 0.05) between the two materials under all conditions except hydrochloric acid. Minimal change in mass was observed for F7 and F7EP in water, lactic and hydrochloric acids, however citric acid caused significantly more mass loss compared with water (p < 0.001).ConclusionIncorporation of 3% (w/w) CPP–ACP into F7 enhanced calcium and phosphate ion release, with no significant change in fluoride ion release and no adverse effects on surface hardness or change in mass.Clinical significance statementGICs have the potential to release fluoride ions particularly under acidic conditions associated with dental caries and erosion. A new GIC containing CPP–ACP and fluoride releases not only fluoride ions but also calcium and phosphate ions under acidic conditions which should help to inhibit demineralisation associated with caries and erosion.     

Formation of a nickel hydroxide monolayer on Au through a self-assembled monolayer of 5,5′-dithiobis(2-nitrobenzoic acid): voltammetric,SERS and XPS investigations of the modified electrodes

The formation of self-assembled monolayers (SAM) of 5,5′-dithiobis (2-nitrobenzoic acid), DNBA on gold has enabled further derivatization of the electrode surface with functional moieties anchored to the surface bound molecules. A SAM of DNBA was formed on the Au surface. Nickel ions tethered to the SAM-covered Au surface, were subsequently derivatized electrochemically to yield nickel hydroxide overlayers, thereby showing the possibility of preparing ultra-thin films of metal oxides through solution chemistry. The nickel hydroxide surface coverage obtained on bare and SAM-covered electrodes was estimated from voltammetric peaks and it varied from one monolayer to about 300 monolayers. The formation of a monolayer of nickel hydroxide has been achieved for the first time by electrochemical modification. Further, the modified electrodes were subjected to SERS and XPS studies to understand their surface characteristics. Modified electrodes provide a catalytic pathway involving nickel hydroxide for the electro-oxidation of glucose in alkaline solutions.     

The role of functional monomers in bonding to enamel: Acid–base resistant zone and bonding performance

Objectives

To investigate the effects of two functional monomers on caries-inhibition potential and bond strength of two-step self-etching adhesive systems to enamel.

Methods

Clearfil SE Bond and similar experimental formulations different in the functional monomer were used. Four combinations of primer and bonding agents were evaluated: (1) Clearfil SE Bond which contains MDP in both primer and bonding (M–M); (2) Clearfil SE Bond primer and Phenyl-P in bonding (M–P); (3) Phenyl-P in primer and Clearfil SE Bond bonding (P–M); (4) Phenyl-P in primer and bonding (P–P). Ground buccal enamel surfaces of human sound premolars were treated with one of the systems and the bonded interface was exposed to an artificial demineralising solution (pH 4.5) for 4.5 h, and then 5% NaOCl with ultrasonication for 30 min. After argon-ion etching, the interfacial ultrastructure was observed using SEM. Micro-shear bond strength to enamel was measured for all groups and results were analysed using one-way ANOVA and Turkey's HSD, while failure modes were analysed by chi-square test.

Results

An acid–base resistant zone (ABRZ) was found with all adhesive systems containing MDP either in primer or bond; however, ultramorphology and crystallite arrangement in the ABRZ were different among groups. P–P was the only group devoid of this protective zone. Micro-shear bond strength in M–M was significantly higher than those in M–P, P–M and P–P, while the latter three were not different from each other. Failure modes were significantly different (p < 0.05).

Conclusions

Functional monomers in two-step self-etching systems influence both the bonding performance and the formation of ABRZ on enamel.     

Metallurgical and interfacial characterization of PFM Co–Cr dental alloys fabricated via casting,milling or selective laser melting

Objectives

Bulk and interfacial characterization of porcelain fused to metal (PFM) Co–Cr dental alloys fabricated via conventional casting, milling and selective laser melting.

Methods

Three groups of metallic specimens made of PFM Co–Cr dental alloys were prepared using casting (CST), milling (MIL) and selective laser sintering (SLM). The porosity of the groups was evaluated using X-ray scans. The microstructures of the specimens were evaluated via SEM examination, EDX and XRD analysis. Vickers hardness testing was utilized to measure the hardness of the specimens. Interfacial characterization was conducted on the porcelain-covered specimens from each group to test the elemental distribution with and without the application of INmetalbond. The elemental distribution of the probed elements was assessed using EDX line profile analysis. Hardness results were statistically analyzed using one-way ANOVA and Holm–Sidak's method (α = 0.05).

Results

X-ray radiography revealed the presence of porosity only in the CST group. Different microstructures were identified among the groups. Together with the γ phase matrix, a second phase, believed to be the Co₃Mo phase, was also observed by SEM and subsequent XRD analysis. Cr₇C₃ and Cr₂₃C₆ carbides were also identified via XRD analysis in the CST and MIL groups. The hardness values were 320 ± 12 HV, 297 ± 5 HV and 371 ± 10 HV, and statistically significant differences were evident among the groups.

Significance

The microstructure and hardness of PFM Co–Cr dental alloys are dependent on the manufacturing technique employed. Given the differences in microstructural and hardness properties among the tested groups, further differences in their clinical behavior are anticipated.     

Quantification of monomer elution and carbon–carbon double bonds in dental adhesive systems using HPLC and micro-Raman spectroscopy

Objectives

To quantify monomer elution from different adhesive systems using reverse-phase high-performance liquid chromatography (HPLC) and correlate this elution with the ratio of carbon–carbon double bonds from monomer to polymer (RDB) obtained using micro-Raman spectroscopy.

Methods

Thirty dentine discs were cut from 30 human, intact, third molars and randomly allocated to five groups according to the adhesive applied: total-etch, Excite (Ivoclar Vivadent), two-bottle self-etch, Clearfil SE (Kuraray), one-bottle self-etch, Clearfil 3S (Kuraray), ormocer-based, Admira (Voco) and Filtek Silorane adhesive system (FS) (3M ESPE). Monomer elution was studied 1 h, 6 h, 24 h, 96 h and 7 days after immersion in 75% ethanol/water. The RDB was calculated immediately after light-curing and thereafter at 24 h and 7 days. The data were statistically analysed using one-way ANOVA and Pearson's correlation coefficient (p < 0.05).

Results

More than 90% of the whole elution occurred during the first 1 h, except for BisGMA in FS, with the highest absolute amount from Clearfil SE and the highest wt% from Admira. Initial RDB was in the ascending order FS < Admira < Excite < Clearfil SE < Clearfil 3S. In all groups, the RDB was significantly higher after 24 h and 7 days than immediately after light-curing (p < 0.05). Negative correlation was found only for the elution of HEMA and the RDB of Clearfil 3S.

Conclusions

Different adhesive systems showed different monomer elution kinetics. In all systems, the RDB increased after monomer elution. Overall, no direct correlation exists between the RDB of adhesives and the elution of unreacted monomers.     

Morphometry of the cranial base and the cranial–cervical–mandibular system in young patients with type II,division 1 malocclusion,using tomographic cone beam

Aims:

Traditionally, diagnosis and treatment planning of structural and three-dimensional anomalies have been performed using two-dimensional X-rays. Cone beam computed tomography (CBCT), the technology utilized in this study, allows creation of specialized images from the craniofacial region that provide more precise and reliable results. The growth of the cranial base, position and size of the cervical system, and the hyoid bone has an influence upon the morphogenesis and the growth of the maxillofacial complex. The data obtained through this current study offer a better understanding of the origin and manifestation of malocclusions, and will, therefore, offer a better therapeutic approach. The objective of the current study is to describe the measurements of the cranial base and the cranial–cervical–mandibular system in young patients with type II, division 1 malocclusion, using CBCT.

Methodology:

Twenty-four CBCT images were obtained for young patients with type II, division 1 malocclusion. The i-CAT Vision (Imaging Sciences International, Hatfield, PA, USA) was used to view the images. Linear and angular measurements were obtained in the mid-sagittal plane. Univariate and bivariate analyses, as well as a multivariate analysis of principal components, were conducted.

Results:

The only metric with a statistically significant difference regarding gender was S–N major in the male participants. The metrics SNA–SNB and SNPg are positively related and inversely proportional to the angles BA–S–N and PO–P McGregor. The inclination of the upper incisor showed an inverse relationship with the angles SNA–SNB and SNpg. The craniovertebral angle was diminished in the entire sample, and the variable that vertically relates the hyoid was independent of the other variables.

Conclusions:

After evaluating 24 images of young patients with type II, division 1 malocclusion using helical spiral CBCT, it was concluded that relationships exist between the cranial base structures, the structures that determine the sagittal position of the maxilla, mandible and chin, and the cervical vertebrae complex and hyoid bone.     

Periodontal disease as a risk factor for adverse pregnancy outcomes: a systematic review and meta-analysis of case–control studies

Periodontal disease is a highly prevalent group of illnesses of microbial etiology, whose consequence is a severe breakdown of tooth-supporting structures. A link between periodontal infection and several systemic conditions, among which adverse pregnancy outcomes, has been suggested in the recent years. The aim of this review based on case?Ccontrol studies was to evaluate if periodontal disease could be considered as a risk factor for preterm birth, low birth-weight and preterm low birth-weight. An electronic search (via Pubmed) was performed for case?Ccontrol studies investigating the relationship between periodontal disease and adverse pregnancy outcomes. From the initially retrieved 417 articles, 17 case?Ccontrol studies, accounting for a total of 10,148 patients, were included in the review and in the meta-analysis. The estimated odds ratio was 1.78 (CI 95%: 1.58, 2.01) for preterm birth, 1.82 (CI 95%: 1.51, 1.20) for low birth-weight and 3.00 (CI 95%: 1.93, 4.68) for preterm low birth-weight. Despite the results of the analysis of pooled data suggested a link between periodontal diseases and adverse pregnancy outcomes, the presence of important confounders, whose effect could not be addressed, prevents a validation of the meta-analysis outcomes. Further more accurate investigations based on individual data analysis could give a better insight into the topic of the present review.