Self-assembly of mono- and bidentate oligoarylene thiols onto polycrystalline Au

Four thiolated oligoarylene molecules (i) 4-methoxy-terphenyl-4″-methanethiol (MTM), (ii) 4-methoxy-terphenyl-3″,5″-dimethanethiol (MTD), (iii) 4-nitro-terphenyl-4″-methanethiol (NTM), and (iv) 4-nitro-terphenyl-3″,5″-dimethanethiol (NTD) were synthesized and self-assembled as monolayers (SAMs) on polycrystalline Au electrodes of organic field-effect transistors (OFETs). SAMs were characterized by contact angle and AC/DC electrochemical measurements, whereas atomic force microscopy was used for imaging the pentacene films grown on the coated electrodes. The electrical properties of functionalized OFETs, the electrochemical SAMs features and the morphology of pentacene films were correlated to the molecular organization of the thiolated oligoarylenes on Au, as calculated by means of the density functional theory. This multi-methodological approach allows us to associate the systematic replacement of the SAM anchoring head group (viz. methanethiol and dimethanethiol) and/or terminal tail group (viz. nitro-, -NO2, and methoxy, -OCH3) with the change of the electrical features. The dimethanethiol head group endows SAMs with higher resistive features along with higher surface tensions compared with methanethiol. Furthermore, the different number of thiolated heads affects the kinetics of Au passivation as well as the pentacene morphology. On the other hand, the nitro group confers further distinctive properties, such as the positive shift of both threshold and critical voltages of OFETs with respect to the methoxy one. The latter experimental evidence arise from its electron-withdrawing capability, which has been verified by both DFT calculations and DC electrochemical measurements.

An experimental model of biofilm detachment in liquid fluidized bed biological reactors

Dimensional analysis was applied for the description of biofilm detachment in liquid fluidized bed biological reactors. This technique allowed the identification of the significant parameters influencing detachment mechanisms and suggested suitable experiments for the characterization of involved phenomena. The influence of the significant variables was established on a lab-scale reactor and an empirical model was proposed to correlate experimental results. The detachment rate was strongly dependent on liquid velocity, while the influence of other parameters, such as solid hold-up and liquid shear stress, was found to be less important.

Probing charge transport in oxidatively damaged DNA sequences under the influence of structural fluctuations

We present a detailed study of the charge transport characteristics of double-stranded DNA oligomers including the oxidative damage 7,8-dihydro-8-oxoguanine (8-oxoG). The problem is treated by a hybrid methodology combining classical molecular dynamics simulations and semiempirical electronic structure calculations to formulate a coarse-grained charge transport model. The influence of solvent- and DNA-mediated structural fluctuations is encoded in the obtained time series of the electronic charge transfer parameters. Within the Landauer approach to charge transport, we perform a detailed analysis of the conductance and current time series obtained by sampling the electronic structure along the molecular dynamics trajectory, and find that the inclusion of 8-oxoG damages into the DNA sequence can induce a change in the electrical response of the system. However, solvent-induced fluctuations tend to mask the effect, so that a detection of such sequence modifications via electrical transport measurements in a liquid environment seems to be difficult to achieve.

Fibre-reinforced composite crowns luted to implant abutments via electroformed primary copings: an in vitro retention study

AIM

The aim of this study was to investigate the retention values and mode of failure of metal crowns and fibre-reinforced composite crowns.

METHODS

Seventy-five implants and the corresponding abutments were used. After the galvanic copings were fabricated, the specimens were distributed into three groups: in group A traditional metal crowns were realized, whereas in groups B and C fibre-reinforced composite crowns were made. In group B the same resin based cement used in group A was employed for luting the fibre-reinforced composite crowns to the galvanic copings, while in group C a dedicated self-adhesive composite cement was used. All galvanic coping/crown assemblies were cemented onto abutments with Panavia 21 cement. Specimens were subjected to a pull-out test; median retentive values and standard deviations were calculated.

RESULTS

All samples in the group A showed separation at the abutment-galvanic cap interface. All samples in the group B showed decementation at galvanic cap-crown interface. In 13 samples of the group C the decementation occurred at the abutment-galvanic cap interface and in 12 samples of this group the decementation occurred at the galvanic cap-crown interface. The mean retention value was 659.1 N±162.9 for group A, 304.7 N±101.4 for B and 635.4 N±155.9 for C. Differences between groups A/B and B/C are statistically significant (t-student test, P<0.01), while is not statistically different between groups A/C.

CONCLUSION

When a self-adhesive composite cement is used, fibre-reinforced composite single crowns and conventional metal crowns show similar retentive performance.

In vitro retentive strength of metal superstructures cemented to solid abutments

AIM

The aim of this study was to evaluate the effect of sandblasting on the retentive strength of metal single crowns luted with a resin cement to Straumann implant/abutment assemblies.

METHODS

Fifty 4.1 mm-wide Straumann solid screw implants were mounted in self-polymerizing soft resin. Standard 5.5 mm-high, 8 degree tapered solid abutments were placed on each implant and torqued to 35 Ncm. Fifty metal castings were made using prefabricated burn-out caps. Each implant/abutment assembly and its corresponding metal casting was numbered and they were divided into two groups of 25. In the test group, the external surface of the abutments and the cavosurface of the corresponding metal casting were sandblasted. In the control group, neither the implant abutment nor the metal casting underwent sandblasting. Each metal casting was cemented onto its respective implant/abutment assembly using Panavia 21 (Kuraray Europe GmbH, Dusseldorf, Ger-many) resin cement. Specimens were then subjected to a pull-out test using a universal Instron testing machine. The load required to dislodge each crown was recorded and mean values were calculated for each group. Retention values were analyzed using the ANOVA test.

RESULTS

The test group showed a higher mean retention value (83.78 kgf+/-19.61) than the control group (44.03 kgf+/-9.45) and the difference was statistically significant.

CONCLUSION

Within the limitations of this in vitro study, the results suggest that sandblasting treatment significantly increases mechanical retention of crowns cemented using a resin cement. It is at the clinician's discretion to evaluate whether additional retention is desired in cementing an implant-supported fixed partial denture.

First-principles density-functional theory calculations of electron-transfer rates in azurin dimers

We have conceived and implemented a new method to calculate transfer integrals between molecular sites, which exploits few quantities derived from density-functional theory electronic structure computations and does not require the knowledge of the exact transition state coordinate. The method uses a complete multielectron scheme, thus including electronic relaxation effects. Moreover, it makes no use of empirical parameters. The computed electronic couplings can then be combined with estimates of the reorganization energy to evaluate electron-transfer rates that are measured in kinetic experiments: the latter are the basis to interpret electron-transfer mechanisms. We have applied our approach to the study of the electron self-exchange reaction of azurin, an electron-transfer protein belonging to the family of cupredoxins. The transfer integral estimates provided by the proposed method have been compared with those resulting from other computational techniques, from empirical models, and with available experimental data.

Retention of nativelike conformation by proteins embedded in high external electric fields

In this Communication, we show that proteins embedded in high external electric fields are capable of retaining a nativelike fold pattern. We have tested the metalloprotein azurin, immobilized onto SiO2 substrates in air with proper electrode configuration, by applying static fields up to 10(6)-10(7) Vm. The effects on the conformational properties of protein molecules have been determined by means of intrinsic fluorescence measurements. Experimental results indicate that no significant field-induced conformational alteration occurs. Such results are also discussed and supported by theoretical predictions of the inner protein fields.

Hydrogen-induced surface metallization of beta-SiC(100)-(3x2) revisited by density functional theory calculations

Recent experiments on the silicon terminated (3 x 2)-SiC(100) surface indicated an unexpected metallic character upon hydrogen adsorption. This effect was attributed to the bonding of hydrogen to a row of Si atoms and to the stabilization of a neighboring dangling bond row. Here, on the basis of density-functional calculations, we show that multiple-layer adsorption of H at the reconstructed surface is compatible with a different geometry: in addition to saturating the topmost Si dangling bonds, H atoms are adsorbed at rather unusual sites, i.e., stable bridge positions above third-layer Si dimers. The results thus suggest an alternative interpretation for the electronic structure of the metallic surface.

First-principles theory of correlated transport through nanojunctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short-range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.

Ab initio simulations of homoepitaxial SiC growth

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the beta-SiC(111)-(sqrt[3]xsqrt[3]) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.

Epithelial odontogenic ghost cell tumour of the mandibular gingiva

The epithelial odontogenic ghost cell tumour (EOGCT) is considered as a solid 'neoplastic' variant of the calcifying odontogenic cyst and is an uncommon lesion for which various names have been proposed over the years. We describe here an extraosseous case occurring on the edentulous mandibular gingiva in the right bicuspid area of a 70-year-old woman. The lesion was a painless nodule that appeared clinically as a hyperplastic mass, which was considered to be of reactive nature. Radiographic examination showed a localised resorption of the underlying mandibular bone. The tumour was excised; there was no recurrence at a 2-year follow-up examination.

Terminal settling velocity and bed-expansion characteristics of biofilm-coated particles

Fluid dynamic behavior of biofilm-coated particles in ambient water has been investigated. New experimental results are presented and compared with published data. From experimental measurements of the single particle terminal settling velocity the corresponding drag coefficient was found to be larger (by a factor of 1.6) than that for a smooth, rigid sphere at the same Reynolds number. A new simple correlation describing this finding is suggested. For multiparticle systems the Richardson-Zaki equation, derived empirically for rigid particles, provided a satisfactory description of biological beds. Of the two numerical parameters characterizing the expansion law, i. e. the slope n and the extrapolation to voidage equal one ui, the first was found to be similar to that suggested by Richardson and Zaki (1954), whereas ui gave results smaller than the single-particle terminal settling velocity, in contrast with the mentioned work but in agreement with more recently published behavior.

Gingival and mandibular bone necrosis caused by a paraformaldehyde-containing paste

A paraformaldehyde preparation (Toxavit) was applied to an inflamed and symptomatic pulp of the mandibular right first molar (tooth #46), in a 30-year-old woman. Leakage from the product was responsible for marked necrosis of the gingiva and the alveolar cortical bone, which resulted in loss of the tooth.

Ectopic third molar in the maxillary sinus. Case report

Ectopic eruption of teeth can occur in a wide variety of sites. These include the mandibular condyle, coronoid process, palate, nasal cavity and maxillary sinus. While this process is unusual, the detection of a third molar in the maxillary antrum is extremely rare. A case is presented of ectopic eruption of a third molar in the left maxillary sinus of a 35-year-old caucasian male giving rise to local morbidity.

Submandibular sialolithiasis with concurrent sialoadenitis in a child

Sialolithiasis is a relatively common condition in adults, but it is rarely observed in children. We report a case in a 7-year-old child with a sialolith in the anterior right Wharton's duct resulting in a submandibular sialoadenitis. Under local anesthesia the calculus was removed by means of a sialodochotomy. Post-operative recovery was uneventful and follow-up examinations showed recovery of the function of the affected gland.

Comparative immunohistochemical analysis between jaw myxoma and mesenchymal cells of tooth germ

The histogenesis of jaw myxoma is still debated. According to some authors it arises from the primitive mesenchymal components of developing teeth. In this study, we have studied the expression of S-100 protein and vimentin in dental follicle, dental papilla and periodontal ligament cells using monoclonal and polyclonal antibodies. Myxoma of the jaw expresses vimentin and S-100 protein. On the contrary, as compared to jaw myxoma, the normal developmental structures were immunonegative for S-100 protein but stained for vimentin. These results could indicate a difference in the derivation other than tooth mesenchyma.

Human odontoblasts contain S-100 protein-like immunoreactivity

S-100 protein is a group of three closely related isoforms (S-100ao, S-100a, and S-100b). This protein was first described as unique to the nervous system but it has also been identified subsequently in a variety of cell types of neuroectodermal (i.e., melanocytes, glial cells) and non-neuroectodermal origin (i.e., Langerhans cells, adipocytes, chondrocytes). In the present investigation the presence of S-100 protein was studied in human odontoblasts using a specific polyclonal antibody directed against S-100 protein in immunoperoxidase labelling experiments. The S-100 protein was detected in the cytoplasm of odontoblasts. This result suggests that S-100 protein can play a role in odontoblast functions.

[Myxoma of the jaws]

A review of the literature and two observations made by the Authors regarding maxillary myxoma allow a closer analysis to be made of this rare benign tumour which is, however, often recurrent in young adults. Maxillary myxoma is identified by the appearance of a non-inflammatory and often painless swelling which, in radiological terms, appears to have a zone of multilocular and sometimes unilocular osteolysis. In histological terms, this globular whitish-greyish gelatine-like tumour is made up of an abundant stroma which encloses star-shaped or fusiform cells and rare collagen fibres. Treatment should be conservative where possible since radical surgery does not preclude recurrence; follow-up should be regular and long in order to ensure an early diagnosis of recividation. Although it is considered an odontogenic tumour, the odontogenic nature of maxillary myxoma has not been undisputably ascertained. The term maxillary myxoma is therefore preferable to that of odontogenic myxoma.

Analysis of pH variation of various calcium hydroxide compounds in vitro

Among the reasons for the use of calcium hydroxide products, there is their alkalinity. Variations in the alkalinity of six commonly used calcium hydroxide compounds were studied in vitro at different time intervals. All these compounds rendered the saline solution strongly alkaline. Dycal, Life, Nucap and Reocap, had a weaker effect as compared with Contrasil and to Pulpdent paste. Such differences in the pH values were accompanied by differences in calcium loss, as revealed by scanning electron microscopy. Differences in the alkaline pH values and calcium losses among these calcium hydroxide compounds may account for their different clinical effectiveness in vivo.

[Focal epithelial hyperplasia]

Five cases of "focal epithelial hyperplasia" (FEH) of the oral mucosa observed in Switzerland are reported. The patients were of Turkish and North African extraction. The lesions of FEH were multiple, painless, located at various sites of the oral mucosa including the tongue in the form of either soft papules or hard nodules. Evidence of a human papilloma virus origin was ascertained. Among the 1067 cases reported in the literature and reviewed for this study, this condition has been described to occur among American Indians, Eskimos and North African, also in Israeli and European cases the disorder was often reported in individuals of Turkish or North African extraction.

[Psychogenic oral paresthesia]

Psychogenic oral paresthesia represent a proteiform condition, more and more frequent. The failure to recognize it can lead to unjustified investigations or/and procedures. These manifestations are secondary to a psychic problem which varies in severity. In most cases, the establishment of a trust relationship, explanations to the patient and eventually a psychotherapy are sufficient to eliminate the symptoms. In severe cases, a psychotherapy or a psychiatric treatment are almost always necessary.

[Lichen planus. Clinical diagnosis, epidemiology and pathogenesis]

Lichen planus is a common mucocutaneous disease of unknown etiology which was initially described a century ago. The specific etiology remains unclear. A number of relationships between lichen planus and other conditions have been noted. The lesions occur most commonly on the buccal mucosa. Gingival involvement occurs in approximately 10% of reported cases. The appearance of lichen planus is extremely variable which leads to confusion with other clinically similar disease entities.

Felodipine-induced gingival hyperplasia: a clinical and histologic study

This paper reports, for the first time, gingival hyperplasia in a patient treated with felodipine, a drug which belongs to the group of calcium ion antagonists. The observed gingival overgrowth was most significant in the area of interdental papillae of the anterior region of the mouth. The described hyperplastic tissue was characterized by a firm and pale appearance, with a normally stippled pattern. Histopathologically, a conspicuous increase of fibrous connective tissue, as well as an inflammatory infiltrate and hyperplasia of the overlying epithelium were observed. Consequently, the present observation adds another drug to the list of substances capable to induce gingival hyperplasia.

In vitro release of elastase from human blood and gingival crevicular neutrophils

Peripheral PMNs were collected from blood, and crevicular PMNs separated by filtration from gingival washings in 13 patients, aged 22-75 y, who had varying degrees of gingivitis and periodontitis. After pre-incubation with cytochalasin B, the same number of crevicular and peripheral cells were incubated either in PBS (with Ca2+ and Mg2+) (spontaneous release) or in the same buffer containing increasing concentrations of FMLP (stimulated release); elastase activity was measured in the supernatant by a fluorometric technique. There was a higher spontaneous release of enzyme from crevicular than from peripheral neutrophils. The average elastase activity in the supernatant of 1 x 10(4) crevicular cells was more than five times higher than that obtained from the same number of peripheral cells. However, stimulated crevicular PMNs liberated smaller amounts of enzyme than did stimulated peripheral PMNs. These results suggest that crevicular PMNs are already releasing elastase, and are consistent with the possibility that lysosomal enzymes contribute to tissue damage during gingivitis and periodontitis.

[Amalgam fillings and T-lymphocyte changes]

Dental amalgam and nickel alloys have been considered quite safe. Previous authors reported the effect of dental amalgam and nickel alloys on human T-lymphocytes modifications after amalgam dental fillings, into dose-dependence of any modifications and into possible temporary. Eight patients were subjected to dental care with amalgam dental fillings. Drawings of blood were executed at start, fifteen days after late fillings and two months later. The results about modifications of T-lymphocytes were not univocal. We believe, at now, that temporary modifications of the immunity seem to be related to a cytotoxic mechanism.

[Intramandibular inclusions of salivary gland tissue]

Salivary gland tissue inclusions in the mandible appear as well delimited radiolucency areas, asymptomatic, usually located in the mandibular angle and sometimes in the premolar canine and symphysis regions. The examination of 8,500 radiographs has demonstrated an incidence of one radiolucent area at the mandibular angle every 500 radiographs. Our result is slightly inferior to the mean reported in the literature. Seven cases were examined. Six of them have been treated surgically and histologically. At exploration a defect in the lingual cortical plate was found. The cavities were filled by salivary gland tissue. The contents of the cavities were attached via the lingual cortical defect to the near salivary gland. The cause of such radiolucency situated in the mandibular angle seems to be an altered resorption and apposition process of the bone triggered by a modification of the salivary glands elasticity; on the contrary, the salivary inclusions in the symphysis region is referred to as embryonic origin. In the literature different terms are used often in relation with a pathogenetical hypothesis; in this paper we suggest rather a description terminology such as intramandibular salivary tissue.

Synthesis of alpha 2-macroglobulin in human gingiva: a study of the concentration of macroglobulin and albumin in gingival fluid and serum

Albumin and alpha 2-macroglobulin were analysed in gingival fluid collected by filter paper strips from 6 volunteers before, during and after 10 days of dental plaque accumulation. The two proteins were also determined in samples of venous blood at the beginning of abstention from tooth brushing and 10 days later. A nephelometric technique was used for the analysis of albumin, but alpha 2-macroglobulin was determined by ELISA. The plaque and gingival indices, as well as the flow of gingival fluid, increased significantly during the period of plaque accumulation and then returned to baseline values. The concentrations of the two proteins in blood remained within normal limits. In gingival fluid, however, the concentration of albumin increased about two-fold at the peak of inflammation, while that of alpha 2-macroglobulin increased as much as 6 times. The enhanced passage of alpha 2-macroglobulin into the gingival sulcus in comparison to the entirely plasma-derived albumin was consistent with the concept that the greater excretion of globulin during inflammation must be due to an increased local synthesis.