Self-assembly of and charge transfer at N-docosyl-N′-methyl viologen on electrode surfaces

Self-assembled molecular films were formed on the electrode surfaces of glassy carbon (GC), platinum (Pt), gold, silver and indium–tin oxide in aqueous electrolyte solutions of N-docosyl-N′-methyl viologen (C₂₂VC₁). The temperature dependence of voltammetric responses showed a higher stability with higher surface coverage and with a Pt than a GC surface. Charge transfer reactions of the solution redox species of Ru(NH₃)₆³⁺ and Fe(CN)₆^4? at the irreversibly self-assembled C₂₂VC₁ ∣ GC interface were found to take place by an interplay of direct penetration of solution species through the self-assembled molecular layer of C₂₂VC₁ and of cross reaction between solution and surface bound redox agents.     

Longevity of cast gold inlays and partial crowns – a retrospective study at a dental school clinic

From 1963 to 1993, 890 patients were treated with 3518 cast gold restorations by students and postgraduate dentists. The longevity of these restorations was studied retrospectively using the patient files. Longevity was calculated using the method described by Kaplan and Meier. After the observation period, 111 (3.2%) of the examined restorations were not in place anymore. The most frequent reasons for failure were caries (33.7%), lack of retention (32.7%), endodontic treatment (29.6%), insufficient marginal adaptation (3.1%) and extraction (1%). The cumulative survival rate and a 95% interval of confidence was calculated for all restorations and for each of the locations and surfaces included in the trial. The 10-year survival rate for occlusal inlays was, 76.1% (12.1) for MO inlays 88.3% (4.2), for DO inlays 83.4% (4.6), for MOD inlays 87.5% (2.4), for partial crowns 86.1% (3.3) and 85.7% (1.7) for all restorations. Based on the statistical method used, the cast gold restorations demonstrated satisfactory longevity results. Received: 6 October 1998 / Accepted: 28 April 1999     

‘In-situ’ observation of halide ion adsorption on a gold electrode using synchrotron far infrared spectroscopy

The adsorption of chloride and bromide ions on a gold electrode in the double layer region in 0.5 M perchloric acid solution was observed ‘in-situ’ for the first time using the technique of synchrotron far infrared reflectance spectroscopy (SFIRS). The Au–Cl surface vibrational frequency was measured to be about 263 cm^?1 in chloride concentrations from 0.005 to 0.05 M. The Au–Br stretching mode was observed at 182 cm^?1. The SFIRS technique is a promising tool for the investigation of interfacial electrochemical structures and processes with monolayer sensitivity.     

Electrochemical behaviour of N-aminopyridinium,and the viologens N,N′-diamino-4,4′-bipyridilium and N,N′-bis(4-aminophenyl)-4,4′-bipyridilium in aqueous acid:: towards the formation of polymer hybrids of pyridine and aniline

A new polymer has been prepared by anodic polymerisation of N,N′-diamino-4,4′-bipyridilium as the tetrafluoroborate salt in aqueous acidic at a gold electrode. The polymer was electroactive and conductive, with $\text{D}$ for the inserting counter ion being 8.0×10^?10 cm^?2 s^?1 during reduction and 4.8×10^?10 cm^?2 s^?1 during oxidation. The polymer was not electrochromic, being blue–black at all impressed potentials. Yields of polymer were poor, being particularly so at low pH (0<pH<1). The best pH for electrodeposition was about 2.0. N,N′-diamino-4,4′-bipyridilium was not electroactive at negative potentials. Conversely, N-aminopyridinium yields a blue water-soluble radical on reduction, and electron transfer to N,N′-bis(4-aminophenyl)-4,4′-bipyridilium as the dichloride salt—which has a particularly stable radical cation—yields a thin film of red–black radical-cation salt. Neither of these two latter species are electroactive at positive potentials.     

Electrochemical detection of silver ions and the study of metal–polymer interactions on a polybenzidine film electrode

Silver ions (Ag(I)) were preconcentrated efficiently at open circuit from aqueous silver nitrate solution into polybenzidine (poly-Bz) film electrodes. The poly-Bz films were electrodeposited by means of cyclic voltammetry from benzidine (Bz) in acidic aqueous solutions. It was found that preconcentration of Ag(I) ions into the film is highly dependent on the pH, being more favored at neutral pH, that is, when the nitrogen in imine–amine groups in the polymer chain are not protonated. Under these conditions the Ag(I) ions do not compete with the H⁺ ions for the same site within the film. A simple diffusion model is assumed to explain the incorporation of Ag(I) ion into the poly-Bz electrodes. The distribution of the Ag(I) ion between the solution and film was established and a probable analytical application given.     

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.     

Galvanic coupling of steel and gold alloy lingual brackets with orthodontic wires: Is corrosion a concern?

Objectives:The aim of this research was to assess galvanic behavior of lingual orthodontic brackets coupled with representative types of orthodontic wires.Materials and Methods:Three types of lingual brackets: Incognito (INC), In-Ovation L (IOV), and STb (STB) were combined with a stainless steel (SS) and a nickel-titanium (NiTi) orthodontic archwire. All materials were initially investigated by scanning electron microscopy / x-ray energy dispersive spectroscopy (SEM/EDX) while wires were also tested by x-ray diffraction spectroscopy (XRD). All bracket-wire combinations were immersed in acidic 0.1M NaCl 0.1M lactic acid and neutral NaF 0.3% (wt) electrolyte, and the potential differences were continuously recorded for 48 hours.Results:The SEM/EDX analysis revealed that INC is a single-unit bracket made of a high gold (Au) alloy while IOV and STB are two-piece appliances in which the base and wing are made of SS alloys. The SS wire demonstrated austenite and martensite iron phase, while NiTi wire illustrated an intense austenite crystallographic structure with limited martensite. All bracket wire combinations showed potential differences below the threshold of galvanic corrosion (200 mV) except for INC and STB coupled with NiTi wire in NaF media.Conclusions:The electrochemical results indicate that all brackets tested demonstrated galvanic compatibility with SS wire, but fluoride treatment should be used cautiously with NiTi wires coupled with Au and SS brackets.     

The Development of a Regional Cleft Lip and Palate Database—A Preliminary Report

Abstract

The development of a regional cleft lip and palate database since its inception in 1988 is described. The method of data collection is outlined together with difficulties found and improvements it is hoped to achieve—both in the method of data collection and, ultimately, in the standard of care provided.     

The controversial issue of centric relation: a historical and current dental perspective?

Human mandible is related to the anatomic skull in several positions among these; centric relation is a significant spatial position. It contributes not only as a reference position to build optimal occlusion in artificial dentition, but is also related to sound periodontal health and stomatognatic function. The purpose of this article is to critically discuss the historical and current definitions of centric relation, the different methods used for recording the same and its clinical implication in the restorative dental practice.     

Application of Danckwerts’ expression to first-order EC′ reactions. Transient currents at inlaid and recessed microdisc electrodes

A general relationship, arising from Danckwerts’ expression (P.V. Danckwerts, Trans. Faraday Soc. 47 (1951) 1014), allows the computation of the transient limiting current in a system with a homogeneous first-order reaction regenerating the electroactive species (an EC′ mechanism), with diffusion and convection, from the limiting currents at the same electrode when there is no homogeneous reaction. For the method to apply the boundary conditions and hydrodynamic regime must be time independent. A simple procedure (which could serve as an alternative to convolution or semi-integral methods) to determine the kinetic parameter from limiting currents obtained in an electrode of arbitrary geometry and size is suggested. An estimation of the time needed to approach steady-state is provided. Diffusion-limited transient currents at the inlaid and recessed microdisc electrode with first-order homogeneous kinetics are studied in detail, checking approximate analytical expressions and simulation data arising from the Finite Element Method. If diffusion is the only transport phenomenon, all currents tend to the planar (cottrellian) behaviour when t tends to 0, regardless of the kinetic constant or the shape of the electrode.     

Jaw fractures diagnosed and treated at Malmö University Hospital: a comparison of three decades

The aim was to report the distribution, frequency and aetiology of jaw fractures in patients treated at the University Hospital, Malmö, 1993–2003 and to compare two previous studies from 1952–1962 and 1975–1985. In 1993–2003, 461 patients, 137 women (mean age 42 years; range 15–82) and 324 men (mean age 28 years; range 17–59) were diagnosed and treated. Women were significantly older than men (P < 0.001). The most frequent cause of jaw fractures was falls in women (45%). In men, interpersonal violence (46%) was most common followed by road traffic accidents (RTAs) (24%) mostly involving bicycles (14%). The frequency of falls in women and men was significantly different (P < 0.001) as was the difference between violence in men and women (P < 0.001). The proportion of fractures caused by RTAs was significantly higher in 1952–1962 than in 1993–2003 (P < 0.001). There was a significant increase in the proportion of fractures caused by violence between the two studies (P = 0.007). In 1993–2003 the proportion of fractures in women due to falls was significantly higher than in 1952–1962 (P = 0.006). Violence has replaced RTAs as the main cause for jaw fractures in men; for women falling is the commonest cause.     

The impact of malocclusions on oral health-related quality of life in children—a systematic review and meta-analysis

Introduction

A limited amount of systematic literature reviews on the association between malocclusions and oral health-related quality of life (OHRQOL) summarize inconclusive results. Therefore, we conduct a systematic review and meta-analysis on the association of malocclusions with OHRQOL in children.

Methods

Relevant studies were identified in Pubmed, Embase, Cochrane, Google Scholar and other databases. All studies with data on malocclusions or orthodontic treatment need and OHRQOL in children were included. Methodological quality of the studies was assessed with the Newcastle-Ottawa Scale (NOS). Random effects models were used to estimate summary effect measures for the association between malocclusion and OHRQOL in a continuous and a categorical data analysis. Tests for heterogeneity, publication bias and sensitivity of results were performed.

Results

In total, 40 cross-sectional studies were included in the meta-analyses. Summary measures of the continuous data show that OHRQOL was significantly lowered in children with malocclusions (standardized mean difference (95 % CI]?=?0.29 (0.19–0.38)). The summary odds ratio for having an impact on OHRQOL was 1.74 times higher in children with malocclusion than in children without malocclusions. Heterogeneity among studies was partly explained by malocclusion assessment, age of the children and country of study conduction.

Conclusion

Our results provide evidence for a clear inverse association of malocclusion with OHRQOL. We also showed that the strength of the association differed depending on the age of the children and their cultural environment.

Clinical relevance

Dentists benefit from understanding the patient differences regarding the impact of malocclusions.

     

Dental status of women in a 24-year longitudinal and cross-sectional study. Results from a population study of women in G?teborg.

The aim of the study was to describe dental health status among middle-aged and elderly women over a 24-year period. Because of the design of the study it was possible to make both longitudinal and cross-sectional comparisons. The study started in 1968-69 with a combined medical and dental examination of women aged between 38 and 60 years. New dental examinations of these same women were performed in 1980-81 and again in 1992-93, and included new cohorts of 38-year-old women on both occasions. In the cross-sectional perspective, it was shown that the number of edentate individuals decreased significantly during the 24-year period. Among dentate women, the number of remaining teeth and restored teeth increased significantly cross-sectionally. However, the youngest age group, women of 38 years, showed a lower number of restored teeth in the latest study (in 1992-93). There was also a lower number of crowns, root-fillings, and pontics in the latest study for the youngest age group. The two older age groups studied cross-sectionally showed similar numbers in all studies. In the longitudinal study, there was a decrease with time in incidence of edentulism. Among the dentate women in the longitudinal study the number of restored teeth related to those remaining was high (range 76-90%) and did not change much between the studies in the different age groups. There was a clear tendency during the 24-year period in all age groups for more teeth to be restored with crowns rather than different fillings. In conclusion, this population study, with a follow-up of 24 years, shows that dental status improved in that fewer individuals lost all their teeth and younger age groups have more remaining teeth and fewer restorations than previously.     

The immunohistochemical profile of basal cell nevus syndrome–associated and sporadic odontogenic keratocysts: a systematic review and meta-analysis

Clinical Oral Investigations - To provide a systematic review of the literature on studies comparing the immunoprofile of nevoid basal cell carcinoma syndrome (BCNS)–associated and sporadic...     

The association of tooth loss with all-cause and circulatory mortality. Is there a benefit of replaced teeth? A systematic review and meta-analysis

We systematically reviewed whether the number of teeth is related to all-cause or circulatory mortality and whether replaced teeth are protective against all-cause or circulatory mortality. The search was based on the PubMed database. All cohort studies published in peer-reviewed journals were selected. Studies on periodontal disease and mortality were excluded if they did not provide information on the number of teeth. Risk estimates from studies with appropriate exposure definition, confounder adjustment and sample size were included in a meta-analysis. Three high-quality studies found a relationship between the number of teeth and circulatory mortality, whereas a moderate study did not. Two out of four moderate- to high-quality studies reported a relationship between the number of teeth and all-cause mortality. No study has investigated whether replaced teeth are protective against mortality. Therefore, denture use was taken as proxy. The methodological quality of studies on denture use and mortality was generally low to moderate. The findings of two moderate studies indicated an effect of prosthodontic replacements on all-cause mortality, which was supported in bias analysis. It is open whether competing risks of cause-specific death other than circulatory mortality reduce an effect of the number of teeth on all-cause mortality. An effect of denture use on circulatory mortality remains to be established, as well as whether the number of replaced teeth affects mortality. Specifying the role of potential pathways by which tooth loss-related mortality is mediated will possibly increase the value of dental treatment for general health.     

The Brånemark Novum protocol: description of the treatment procedure and a clinical pilot study of 11 cases

The Br?nemark Novum system is a new procedure for the one-day reconstruction of periodontally hopeless or edentulous mandibles. It consists of a series of four drill templates and eight drill guides to precisely position three implants that are completely level and parallel to one another. A prefabricated lower bar is attached to the implants. A prefabricated upper bar attaches precisely to the lower bar. The restorative clinician takes a bite registration at a previously established vertical dimension of occlusion. The case is waxed up and tried in the same day and delivered after processing. The procedure is described in detail, and 11 cases are reviewed.